MythBusters Episode 97: Airplane on a Conveyor Belt
Air Date: January 30, 2008
An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.
busted
First some small-scale tests were performed with a model airplane on a treadmill and the plane was able to take off. For the large-scale test, the MythBusters used a 400 pound ultralight aircraft with a 2000 foot tarp under it. The tarp was pulled backwards to simulate a moving runway. The ultralight pilot had no trouble taking off. This is because the thrust of the airplane engines acts on the air, not on the ground.
A cockroach can survive a nuclear blast.
busted
The MythBusters irradiated cockroaches and several other bugs. The cockroaches all eventually died, and they died sooner than some of the other bugs. Nonetheless, cockroaches would survive longer than humans.
If you freeze a can of shaving cream, cut it open, and then put the foam in a car, it will heat and expand to fill the car.
busted
This myth was first tested with one can of shaving cream; there was little effect. Even with 50 cans of opened shaving cream in the car, the foam did not significantly expand. Lastly, the MythBusters tried putting a large quantity of polyurethane foam in the car, and it expanded to completely fill the car.
Newer: Episode 98: James Bond Special 2
Older: Episode 96: Lead Balloon
flawed test. The original hypothises was that the plane would not be moving over the ground. That was not the case in this test. Plane was moving before it took off and creating air over the wings which is what it takes for a plane to create lift. That light sport plane used in the experiment has a big engine for its weight and does not need much air flowing over the wings in order for it to fly. Myth is definetyley not busted that was the worst put together experiment I ever saw. Do it right myth guys and read up on basic aerodynamics so you know what should happen for a plane to fly.
January 30, 2008 at 10:17 PMYou obviously did the plane on the treadmill wrong because a plane will only take off when air passes over the wings and the plane isn’t meant to move froward at all
January 30, 2008 at 10:18 PMJamie, Adam,
January 30, 2008 at 10:20 PMYou blew it big time. I am a pilot and I can tell you that the myth about the airplane conveyor belt is supposed to be confirmed. If you would have used an actual conveyor belt and the AIRPLANE’S wheels were allowed to free spin, then the airplane would not have been able to move when power for takeoff was reached. Your myth conveyor belt still allowed the wheels to contact a non-moving surface through the tarpoline. A non-moving plane(with no headwind either) like your pilot told you, will not have air moving over the wings, therefore would not be able to produce lift. Your “mythical” conveyor belt was just that, mythical. It did not act as a real conveyor belt. A real conveyor, would not have allowed any friction with the tires and surface. Your tarpoline did allow friction with the ground, and therefor forward motion for the plane to fly.
I agree, if the wheels were spinning at takeoff (rotation) speed but the aircraft had no forward movement, no air would have been flowing over/under the wings (airfoil) so, no lift would have been created.
January 30, 2008 at 10:27 PMhttp://www.straightdope.com/columns/060203.html
It takes off. Physics says so. Everybody go home.
January 30, 2008 at 10:27 PMDean, the plane did fly
You other guys, it makes no difference if the conveyor belt would be pulled at the same time the plane accelerated because the plane did still move forward and if they are to be moving at the same speed like they did in the myth, then the plane would have taken off like it did.
January 30, 2008 at 10:29 PMBTW, what was the make and model of the ultralight airplane, anyone??
January 30, 2008 at 10:30 PMWhy would the airplane have no forward movement?
January 30, 2008 at 10:30 PMA true conveyor belt would keep the plane stationary in the same sense that full breaks would (the only difference being spinning wheels). Aircraft go to full power in take off configuration all the time and don’t take off. Smaller aircraft with high thrust to weight ratios may take off in the same sense that a helicopter would but that is not in the spirit of the myth.
January 30, 2008 at 10:38 PMit flew get over it
January 30, 2008 at 10:39 PMI agree with the first 4 posts. They failed to control the one critical variable in this experiment.
January 30, 2008 at 10:39 PMDean,
Are you saying the plane only needed a total of 1 or so ft of ground through the tarp to take off? Then it should have stayed still most of the time and gain forward speed only when touching the ground through the holes. Which did not happen.
The conveyor belt made no difference at all to the plane’s forward speed, and it took off normally.
January 30, 2008 at 10:42 PMLOL Like they said it has nothing to do with the wheels… They need to use the highspeed camera and you will see that the wheel speed was actually faster than 25mph. read some other sites. No pilot here and I can see the logic in it taking off. NEWTON’s LAW Read it.
January 30, 2008 at 10:43 PMsome people need idiot tags…
January 30, 2008 at 10:45 PMon a treadmill, a person has no “forward motion” because the surface is moving. If you placed a plane on a treadmill, AND THE WHEELS WERE ABLE TO SPIN AT THE SAME SPEED AS THE TREADMILL, the airplane would not be able to move forward. Then without the forward motion, no air motion over the wing, therefore, no lift. Do we all agree, the purpose of a tradmill is for the object to stay in place and the surface move, then if a plane were on a treadmill, and the running at takeoff speed, the wheels are moving at liftoff speed, NOT THE PLANE. As for power to move the plane from a more powerful engine, the engine is producing all of its power to get to takeoff speed. There is no excess power.
January 30, 2008 at 10:46 PMPlease remember that an airplane is not a car. A car moving forward on a treadmill would need to move faster forward than the treadmill is pushing it back. Since the thrust of the airplane pushes on air the wheels of the airplane would just spin faster.
January 30, 2008 at 10:46 PMWhere is the idiot tags? Planes use thrust to move, not wheels. the wheels just act like bearings and spin faster.
Newtons law.
January 30, 2008 at 10:49 PMYou guys in the “failed” test camp need to think about it a while longer. Your intuition is incorrect…and I don’t care if you’re a pilot or not. Sure the test wasn’t perfect, but they proved that the plane moved forward with no ill effect from the treadmill. Like Jamie and Adam said in the episode…”People cannot wrap their brains around the fact that airplanes are propelled by the props and not their wheels.” (or something to that effect.)
Think about it. The test was not flawed. You’re making yourselves look like idiots.
January 30, 2008 at 10:51 PMTarp ≠ Conveyor Belt so Mythbusters = FAIL
January 30, 2008 at 10:52 PMDean, your logic is completely flawed. Grats on failing physics 101.
January 30, 2008 at 10:53 PMAll those who say it should not fly, I really hope your not serious.
Simple physics.
Why would the wheels hold it back? They are basicly bearings. Not powered like a vehicle. All the engine thrust has to do something, think it can not over come a bit of friction caused by the wheels???
January 30, 2008 at 10:55 PMADINSX, My plane takes off at 55 miles per hour. If it were at that speed, the engine will be producing all of its power. On a treadmill at 55 miles per hour, my tires will be going 55 miles per hour, NOT MY WINGS, no movement of the wings, no lift!!!! Jedi pimp is right. The tarpoline was not a true treadmill.
January 30, 2008 at 10:59 PMAlright, here’s a little lesson for those of you who think that airplanes are cars: THEY’RE NOT! Airplanes DO NOT create forward motion by interacting with the ground! The wheels on the landing gear are there to reduce friction with the ground to negligible levels in order to allow the plane to roll forward when the engine is running. There is no drive system in the landing gear. The only thing that will stop a plane from moving forward is a headwind that overpowers the thrust of the engines, but then again it would still take off due to air flowing over the wings.
Again, airplanes interact with the AIR, not the ground, in order to fly. By the reasoning of those who support this myth, an amphibious plane wouldn’t be able to take off if it was working against a current.
Apply this theory in reverse: if a car is facing a 50 mph headwind and the driver stomps the gas, the car will still move forward because it is driven from the ground. If a fan boat is sailing forward at 20 mph into a 20 mph current, it might lose a tiny bit of speed but will still sail forward because it is being driven by the AIR.
There was nothing wrong with the experiment, it accurately replicated the conditions of the myth. No matter how fast the conveyor moves, the plane will still fly because it’s power is generated by pushing against the air.
BUSTED!
January 30, 2008 at 11:07 PMi agree with most of these posts… i just saw the episode and immediately said it was flawed. like most of you have said, as soon as i saw it, the plane was moving forward. As a pilot, and engineering student, it is obvious that if the plane wasn’t moving forward, then no air would pass over the wing meaning no lift. That is the point of an air foil, to create lift using Bernoulli’s principle, which requires air to flow over the wing. Their “conveyor belt” was a definite flaw. If the myth is that the plane is not moving due to a conveyor belt, then no flight… period, no matter what speeds the conveyor belt is, or the speed of the tires. if the plane is not moving, than it’s not gonna take off.
January 30, 2008 at 11:09 PMDean, if you are a pilot, you need to have your license revoked. I hope you don’t fly passenger jets.
January 30, 2008 at 11:10 PM“Gilsham:
You obviously did the plane on the treadmill wrong because a plane will only take off when air passes over the wings and the plane isn’t meant to move froward at all”
wrong sir, if there is 0 friction on the ground and the only amount of friction is the plain pulling on the air the plain can then move forward based on the pulling of air (small though it may be) being greater then the 0 friction of the wheels.
January 30, 2008 at 11:10 PM** hey moose… its “plane” not a flat field of grass
January 30, 2008 at 11:13 PMJust watched Mythbusters re plane on a conveyor belt. Even my wife agrees that this was the worst-defined myth we have ever witnessed.
Take a plane on a conveyor belt. The belt is moving at takeoff speed. The airplane faces the opposite direction. Was the myth
1) That the plane can not take off even if it reaches takeoff airspeed (false)
2) That the plane can not take off because it can not reach takeoff airspeed (false)
3) That the plane will not take off if it matches the ground speed of the conveyor belt relative to the conveyor belt, but with the opposite direction. (true)
This was never clearly stated in the myth, but it seems obvious that the myth tested was #2. This is equivalent to asking if you can take off with a tailwind equal to normal takeoff airspeed. The answer would be “it depends on whether the airplane can reach takeoff air speed within the runway available, but generally ‘yes’”. I suppose one good test would be to have a string tied to the tail of the model plane preventing it from running off the treadmill, but still free to lift. This way it could rev it’s engine far beyond normal takeoff to really push the myth. One could even test it at various treadmill speeds, even far beyond normal takeoff speed.
Far below your usual standards, guys.
January 30, 2008 at 11:14 PMGuys, the point is NOT that a plane not moving forward will take off – it can’t.
The point is this – a treadmill can not stop a plane moving forward! Think about it.
January 30, 2008 at 11:15 PMLOL you guys are serious…. LOOK UP NEWTON’s LAW… What is gonna keep the fuselage from moving? The wheel bearings? LOL
January 30, 2008 at 11:16 PMagreed scott.
January 30, 2008 at 11:16 PMBUT…
if the myth is about whether or not the plane can take off… sure it can, just as long as it can get moving forward so that it can get air to flow over the wings… if the myth is about the airplane not moving forward, then it will not be able to take off
January 30, 2008 at 11:17 PMMax, the entire premise of the myth is that a conveyor belt CAN prevent the forward motion of a plane, which it in fact CAN’T. No matter how fast the ground (tread) moves, the force of rolling friction produced by the wheels is negligible compared to the force of the planes propeller. VERY negligible. The plane WILL move forwards, and air WILL flow over the wing, and no need to throw Bernoulli’s principle out there just to make yourself sound smart.
January 30, 2008 at 11:18 PMI should have mentioned that I thought the myth being tested was 3. The good test would be the string on the model….and here I dinged them for lack of clarity….wait a minute: they have a TV show! Editors! Producers! It should be a polished and shining example of clarity!
January 30, 2008 at 11:18 PMhydrophilia, the entire myth came from this: http://i130.photobucket.com/albums/p267/ADINSX3/plane.jpg image. It was made up as a joke on the internet. Nobody ever thought it would actually be tested. But the joke spread, and eventually reached the mythbusters. It isn’t the mythbusters fault the internet hate machine poorly defined the myth.
January 30, 2008 at 11:21 PMADINSX, i’ll agree with you, but i feel that it was unclear as to what they actually meant. and the Bernoulli statement had its purpose because thats how an aircraft takes off… but if its just to see if the airplane will move forward… then it will, i’ll agree with that. i believe that it was just unclear as to what they were actually trying to prove
January 30, 2008 at 11:22 PMand to add on, now that i know that the idea is if a plane will move forward or not… take a plane mid flight… part of the requirements of getting a private pilots license is to practice slow flight. This means that the airspeed is around 40knots and the groundspeed (depending on wind) is almost zero, and to get out of it you give the airplane full power and the airplane will accelerate to a higher speed. Thus, meaning that the affect of tires on the ground has nothing to do with whether or not an airplane can accelerate
January 30, 2008 at 11:28 PMto think about it and understand it is really simple, it is just a question to mess with your mind… But the part that some can not wrap there head around it is the funny part.
January 30, 2008 at 11:42 PMEven the way they word the question was meant to mess with your head.
Nothing says that the plane cant move.
theres zero debate about what this myth was. you losers are just butthurt you were wrong. how could this have been about a plane taking off thats not moving when it WILL move? everyone kept talking about how it wont work because theres no wind over the wings. HOW WOULDNT THERE BE ANY WIND WHEN THE TREADMILL CANT HOLD IT BACK? the only logical myth about this was can a treadmill hold a plane in place. the clear answer is no, it cannot.
January 30, 2008 at 11:49 PMLET ME CLARIFY. A PLANE’S ENGINE AT FULL THROTTLE FOR TAKEOFF WILL PRODUCE ENOUGH POWER TO REACH, SAY 129 MPH. IF IT WAS ON A TREADMILL, AND ALLOWED TO ACCELERATE PAST ITS TAKEOFF SPEED OF 55 MPH, IT WILL THEN TAKEOFF. THEREFORE, IF THE TREADMILL WERE GOING LESS THEN 129 MPH. THEN TAKEOFF WOULD BE POSSIBLE. IF THE TREADMILL WERE MORE THAN 129 MPH, THEN THE PLANE (DISCOUNTING AXEL/TIRE FRICTION) WOULD NOT MOVE.
January 30, 2008 at 11:51 PMmax, don’t try to hide the fact you were wrong. saying that you thought it was something different is stupid. “if its just to see if the airplane will move forward… then it will, I’ll agree with that”. what the hell did you think the myth was then? the only other way to interpret it was if a treadmill could keep up with the planes speed. IT CANT. any other way of reading into the myth requires the plane to not move, and it will move. so how can you change things around now?
January 30, 2008 at 11:53 PMpiledriver.. youre an idiot. the speed of the treadmill/wheels are not any part of the equation of it taking off.
January 30, 2008 at 11:55 PMBOB ARE YOU KIDDING ME. THE ANSWWER IS, AS LONG AS THE AIR MOVING OVER THE WINGS IS GREAT ENOUGH TO PRODUCE LIFT, THE PLANE FLIES. YOUR QUESTION, IF I HAVE FULL THROTTLE AND AM PRODUCING POWER FOR 129 MPH. THE TREADMILL IS GOING 129 MILES PER HOUR, HOW FAST IS THE AIRPLANE WING MOVING?
January 31, 2008 at 12:04 AMpiledriver.. if the plane is going 129 miles an hour, youve already taken off so it wouldnt matter what speed the treadmill is going. the wheels are not pushing the plane, why are you talking like they do?
January 31, 2008 at 12:07 AMmyth has nothing to do with the wheels. That is why the question throws people off. Like they said everyone that says no, is stuck on the part with the wheels, or speed.
January 31, 2008 at 12:11 AMi find this so laughable that people STILL dont get it. like this piledriver guy. you are talking like the plane is a car. that the forward speed is wheel speed. sorry, the foward speed in a plane is AIR speed. full throttle in a plane is going to be moving the plane through the AIR. nothing to do with the wheels.
January 31, 2008 at 12:11 AMsome of you are so stupid and just
January 31, 2008 at 12:15 AMdoant comprehend physics. good test mythbusters, these people that disagree simply dont understand that the wheels of a plane do not provide power and that they free spin. It does not matter that its not a treadmill, it would still yield the same result.
A PLANE CAN OVERPOWER A TREADMILL. BUT IF A PLANE WERE ONLY ABLE TO GET THE WHEELS TO SPIN AT 129 MPH WHILE ALL WHEELS WERE ON THE GROUND. WOULDN’T THE PLANE STAY STILL ON A TRADMILL GOING 129 MPH.?
January 31, 2008 at 12:16 AM“A PLANE CAN OVERPOWER A TREADMILL. BUT IF A PLANE WERE ONLY ABLE TO GET THE WHEELS TO SPIN AT 129 MPH WHILE ALL WHEELS WERE ON THE GROUND. WOULDN’T THE PLANE STAY STILL ON A TRADMILL GOING 129 MPH.?”
NO.
The plane would be moving forward at an airspeed of 126mph and the wheels would be spinning at 252mph.
Duh.
January 31, 2008 at 12:18 AMSorry, 129 and 258.
January 31, 2008 at 12:18 AMeven on a treadmill a plane will be able to fly.
January 31, 2008 at 12:25 AMWhen I heard of this myth I was told there is no friction between the wheels and the run-way .. ie. this experiment cannot be replicated ..
January 31, 2008 at 12:36 AMThe wheels of a plane are not powered. The prop provides the thrust. The prop will always overcome the speed of the conveyor no matter how fast the conveyor is moving. The plane will fly. The tarp was not a real conveyor, but that does not matter.
January 31, 2008 at 12:38 AMwould be nice to know if the ultralight used the same distance to take off as it normally uses.
January 31, 2008 at 12:40 AMI believe that the only way in which wheels enter the equation is that they rob some (albeit a very small) amount of energy from the plane in order to accelerate the wheels. Newton says that in order for a body to accelerate, it must be acted on by a force, in this case, the force comes from the tires friction with the ground which must be enough to overcome any friction in the bearing as well as overcoming the inertia of the tire. This force is sooooooo small when compared to the reaction force produced by the propeller/jet that, given good bearings, would not be noticeable.
January 31, 2008 at 12:41 AMyea, as long as the wheels can handle spinning at those speeds.
Say the wheels/bearings are rated to 300Mph, then in theory the plane may not take off if the treadmill is traveling at 161mph and the thrust is enough to produce 129mph then if the wheels fall off the plane probably won’t take off, but in real world it probably would anyway.
so the question is what is the speed rating of the airoplanes tyres/bearings?…
in all cases the tredmill is irrelevant, unless it is spinning at a higher speed than the speed rating of the tyres minus the thrust speed rating of the plane…
*/end conversation/* back to my normal interweb pages…
January 31, 2008 at 12:45 AMA plane will be able to fly off a tradmill/conveyor, as long as it could reach it’s takeoff speed. There is nothing to prevent it from doing so, except the length of the treadmill/conveyor.
January 31, 2008 at 12:47 AMThe plane will TAKE OFF. But there’s no guarantee of it FLYING. Once it reaches a speed fast enough to overcome friction of the conveyor belt the engine has to be powerful enough to generate lift against air rather than the ground. If the plane were in a vacuum (no air) it would not fly. That’s my stab at it any way.
January 31, 2008 at 12:50 AMIf the treadmill is moving back 129 mph and the plane produces enough power for 129 mph the plane will still move forward. The tires will spin at 258 mph. I think your caps lock is on.
January 31, 2008 at 12:51 AMnot a problem, planes are designed with engines powerful enough to generate lift against air.
January 31, 2008 at 12:54 AMthe physics are behind the busted myth, a planes flight has nothing to do with wheels on the ground but about air over wings. The plane is connected to the air via the propeller, not the ground via the wheels, the ground-wheel interface is simply a convenient one, flight has nothing to do with the wheel/ground connection, the ground/wheel and air/propeller interfaces are two different frames of reference. It scares me to know that pilots don’t know this.
January 31, 2008 at 12:59 AMI THINK THE ULTRALIGHT WAS A RANS S-6S COYOTE II.
January 31, 2008 at 1:00 AMthey should have done other tests with the conveyor moving 2x, and even 5x the speed of the plane backwards. because it would have been EXACTLY the same result.
January 31, 2008 at 1:02 AMI’m here to represent a discussion coming from a foreign forum with about 16 thousand views and 1 thousand posts…and everybody is saying that the test was totally invalid and with no proven scientific results. Jamie and Adam, you blew it.
January 31, 2008 at 1:02 AMThe plane was clearly moving faster than the belt! Not same speed as they mentioned at the start of the myth. Myth not busted!
January 31, 2008 at 1:04 AMTHE PLANE WILL LIFT. I THINK WE ARE ALL HAVING A PROBLEM WITH WHETHER THE PLANE CAN GET MOVING FORWARD TO TAKOFF SPEED ON A TREADMILL. IT WILL
January 31, 2008 at 1:05 AMAs it has been said many times: The wheels don’t matter.
On a normal runway: when a plane is going 100mph (again air), then its wheels are turning at 100mph (against ground).
On a conveyor belt turning at 100mph: when a plane is moving at 100mph (against air), then its wheels are moving at 200mph (against ground/conveyor).
On a conveyor belt moving 200mph: when a plane is moving 100mph (against air), then its wheels are moving at 300mph (against ground/conveyor)
The conveyor can move as fast as it wants, because the plane is moving against the air. The only hope for the ground is friction. To test that, just make the wheels so they don’t turn. Will the plane still take off? I guess it depends on the plane. But it would be impossible for a conveyor belt to produce that kind of friction on moving wheels.
January 31, 2008 at 1:06 AMSeveral problems with the test that was shown on TV.
First, it was stated that the plane was to have forward motion EQUAL to the reverse motion of the conveyor belt. This was NOT the case on TV… because the plane moved FORWARD (thus not equal).
Second, the planes used were so light that the engine (propeller) provided enough lift to get the aircraft to lift off without (much) needed lift by the forward motion of the plane.
January 31, 2008 at 1:07 AMIgnorance in the face of facts. A plane was shown taking off from a gigantic conveyor belt, and STILL there are idiots saying it wouldn’t take off? Amazing. I’m going to start using this as an engineering interview question to see who can think clearly, and who can’t.
January 31, 2008 at 1:08 AMFor everyone who things that the plane won’t take off. TAKE A COLLEGE PHYSICS COURSE. READ A BOOK. You people are idiots. Though the mybusters explained it like a 3 year old, they are still right.
January 31, 2008 at 1:08 AMian, you have a lot of really stupid people on your forum.
January 31, 2008 at 1:08 AMDAVID T, SPEED DIFFERENCE NOT AN ISSUE. THE PLANE WILL ALWAYS BE ABLE TO MOVE FORWARD FASTER THAN THE BELT. MYTH BUSTED. MYTH: A TREADMILL/CONVEYOR CAN PREVENT A PLANE FROM TAKING OFF. BUSTED
January 31, 2008 at 1:08 AMthe planes flight is a connection between the wings and the air, not the ground, the connection to the air is the propeller or a jet engine, the ground/wheel connection is irrelevant beyond stabilizing the air wing connection, two different frames of reference are at play here.
January 31, 2008 at 1:09 AMFor everyone who things that the plane will not take off. TAKE A COLLEGE PHYSICS COURSE. READ A BOOK. You guys are just idiots. For the pilots out there, my only suggestion to you, learn how your fly really flies, or, learn how your airplane engine works.
January 31, 2008 at 1:10 AMHere’s another way to take the wheels out of the equation: suspend the plane from a crane. If the wheels aren’t moving will it still take off? Of course. The only way to stop a plane from taking off (without altering the plane) is to remove the air.
January 31, 2008 at 1:12 AMjack, you know, they should have started the truck first. altho that may have ripped the tarp. the truck could have even gotten up to speed before the plane even started. and the truck could have continued to go faster and faster until it was going the vehicles full speed and the plane STILL would have taken off effortlessly. the only problem with the episode is that they should have OVERDONE it so they could rub everyones noses in it that the plane has NO problems at ALL taking off
January 31, 2008 at 1:13 AMALLEN C. THAT WOULD BE A GREAT IDEA FOR A LARGE CONTROL LINE MODEL
January 31, 2008 at 1:16 AMAllen C. THAT IS EXACTLY THE POINT HERE. THE CONVEYOR CAN NOT STOP THE PLANE FROM MOVING FORWARD TO LIFTOFF SPEED.
January 31, 2008 at 1:17 AMMy thought of the general public of people. STUPID. For the people who know the plane will take off, good job, you guys are fairly intelligent. For the rest of the people who think the plane won’t take off, read a science book.
January 31, 2008 at 1:19 AMI know. I was just trying to restate the point from a different perspective. It appears some people don’t get it.
January 31, 2008 at 1:20 AMlift is created by a pressure differential over the wing, thrust provides the sufficient speed to acquire the pressure differential over the wing, but the speed factor is the wing through air, not over ground
this is similar to:
put a winch on a car sitting on a treadmill with a cable and connect the cable to some stable point off the treadmill, wind up the winch with the treadmill running, the car will move forward relative to the cable winch fixed connection, nothing to do with the ground.
the plane connects to the air via the thrust source, it has nothing to do with what the ground does with the wheels because the ground is not interfacing with air flow over the wings, that interface is relegated to the plane/thrust/air connection
January 31, 2008 at 1:21 AMFOR ALL YOU SAYING THE WINGS NEED TO MOVE, THEY WILL. THE PLANE WILL NEVER BE ABLE TO SIT STILL ON THE TREADMILL. IT WILL BE MOVED FORWARD BY THE PROPELLOR. JUST BECAUSE IT IS ON A TREADMILL, THE PLANES TIRES ARE NOT GOING TO JUST SPIN IN PLACE.
January 31, 2008 at 1:25 AMthe plane is not connected to the runway for flight, it does not matter what the ground does, it matters what the air-plane wing connection does, that connection is via a thrust source propeller or jet, if the energy source moves the plane wing through the air adequately, lift occurs, it has nothing to do with what the ground does
January 31, 2008 at 1:28 AMTHE NAY-SAYERS ARE ASSUMING THAT THE TREADMILL WILL PREVENT THE PLANE FROM MOVING…JAKE I THINK YOU ANNALOGY ABOUT THE WINCH CLINCHES IT. THE PROPELLOR PUTS THRUST IN THE EQUATION THAT OVERCOMES THE TREADMILL.
January 31, 2008 at 1:32 AMwatcher – its because people drive cars, and they think that forward motion is always a function of contact with the ground, flight is about connection with air, and a plane interfaces with the air for lift, not the ground, there is a reason planes take off and land into the wind
January 31, 2008 at 1:35 AMwhats scary about this is that people here claiming to be pilots don’t know why their planes fly, no wonder they need unions to stay employed
January 31, 2008 at 1:38 AMSo… the naysayers are saying, in essence, that a plane that does not move cannot take-off… Yes, in that, you are correct. If something does not move, it cannot take off. That, sherlock, is very observant. However, the concept is that a conveyor cannot keep a plane still. It’s force of motion is caused by the prop/engine – not by the wheels.
January 31, 2008 at 1:40 AMGIVEN THE ABILITY TO MAINTAIN CONTROL, OR ENOUGH SPACE. A PLANE CAN EVEN ACCELERATE AND TAKE OFF FROM ICE. THAT SHOULD PROVE THE NEED FOR GROUND/TREADMILL TO WHEEL FRICTION IS NOT NEEDED
January 31, 2008 at 1:40 AMWE OF COURSE KNOW HOW OUR PLANES FLY. THEY JUST DON’T UNDERSTAND THAT THE PLANE
January 31, 2008 at 1:46 AMW I L L N O T B E A B L E T O S I T
S T I L L O N A T R E A D M I L L.
fightagainstidocy – exactly correct, a plane does not need to move against the ground to gain lift, it needs to move against the air, the ground/wheel connection and the plane/air connection are two different interfaces, and the air and ground are not the same interface, the plane can interface with the air without the ground being involved at all, the plane doesn’t care what the ground does.
January 31, 2008 at 1:46 AMHOW IS THAT FOR THE REST OF YOU? IS THIS CLASS FINISHED??????
January 31, 2008 at 1:48 AMHey, I’m cool with the naysayers. If they believe what they’ve been saying here, then oh boy! – I got some subprime mortgage loans they might be interested in…
January 31, 2008 at 1:49 AMif you take an airplane, say a light private craft, sit it on the ground, wheels and ground motionless, and blow air over the plane fast enough will it lift?
January 31, 2008 at 1:51 AMI’M GOOD WITH THAT!!!! I THOUGHT THE TREADMILL WOULD P R E V E N T MY PLANE FROM FORWARD MOTION. IT WON’T. JAMIE, ADAM, I APPOLOGIZE FOR MY IGNORANCE. MYTH BUSTED.
January 31, 2008 at 1:52 AMIf you stand on a treadmill wearing roller skates while holding on to a rope you will remain stationary. Start pulling on the rope and you move. Pulling = engine thrust, and thus air will pass over the wings and produce lift. Its pretty simple. A harder problem for me to solve is how to kill people through the internet, which after reading some of these comments sounds highly attractive.
January 31, 2008 at 1:53 AMJAKE, IT HAPPENED TO A PLANE NEXT TO MINE. A GUST OF WIND GAVE IT ENOUGH LIFT TO GO STRAIGHT UP LIKE AN ELEVATOR AND SLAM DOWN RIGHT NEXT TO MINE.
January 31, 2008 at 1:55 AMDean, perhaps we both realize the conceptual quandary with this particular scenario. The realities of relative motion and frames of reference in which they occur require more than passing impulive thought. I’m hoping to convey here that flight lift in terms of airplanes is a simple function of air over wings (airfoils), specifically designed to account for thrust and wing area and such, and has nothing to do with the dang ground. The thrust source, wing/airplane and air are completely independent of the ground. As you know, apparently from experience, regardless of what the ground is doing, the air/plane relationship continues even to the planes detriment.
January 31, 2008 at 2:10 AMi love the first four posts
truly idiots.
January 31, 2008 at 2:15 AMDifferent interpretations of the myth + people who are too busy throwing a little fit to properly explain their point= board full of morons
January 31, 2008 at 2:17 AMI WONDER WHAT THE OUTCOME WOULD BE IF THE PLANE WAS GIVEN ONLY ENOUGH RPM TO PRODUCE LIFT OFF SPEED. AND THE TREADMILL WAS GOING JUST OVER THAT. WOULD THE PLANE ACCELERATE FOR TAKEOFF!!!
January 31, 2008 at 2:21 AMteedub, I dunno about idiots, the plane scenario presents a false delima that plays on intuitive concepts of motion and we people have built in responses based on those perceptions that may not be really actually true. Ever been sitting at a traffic light in your car and felt like you were moving backward or forward but weren’t but the car next to you was? Its the same thing with a plane, our perception is that it must move relative to the ground to gain flight, but in reality, the plane can fly without the ground at all, the ground is just a stable and really convenient place for the plane to interact with air. The plane and the air can play together no matter what the ground does.
January 31, 2008 at 2:26 AMB T W. THE PLANE ABOVE WAS AN R. C. MODEL.
January 31, 2008 at 2:26 AMhere is a thought:
you attach Plane A to Plane B. Plane A takes off from the ground and flies in the air with Plane B attached, then releases by some mechanical means Plane B to go it alone, does Plane B need the ground in any way to fly? The answer is no, Plane B needs only air over wing in sufficient quantity to maintain lift, remember, gliders have large wing areas to maintain and maximize lift without mechanical thrust.
January 31, 2008 at 2:37 AMJAKE, I KNOW HOW PLANES FLY. I OWN ONE. IT IS JUST HARD FOR ME TO SEE THE PLANE’S ABILITY TO GET TO THAT SPEED ON A TREADMILL. IGUESS THE SAME AS IT DOES ON ICE.
January 31, 2008 at 2:44 AM..lets not call people idiots just because they dont understand a concept. No argument can be resolved by calling people names.
The conveyor belt/tarp can not prevent the plane from moving forward because the propeller pulls the plane through the air, just like when its flying. It doesn’t drive on the ground like a car. It does not drive itself up to speed; it pulls itself through the air using the propeller until there is enough wind speed to give the plane lift. Adam and Jamie did a great job explaining that. Without the necessary friction at the wheels, the belt can not prevent the plane from taking off. I know it seems like a complex problem, but once you break the idea that a plane is like a car, it will make sense.
January 31, 2008 at 2:46 AMI’ve used this example and had some luck: If you were wearing roller-skates on a treadmill and you are preventing yourself from moving backward by grabbing the rail, physically holding yourself in place while the wheels on the skates spin with the treadmill, do you think you can pull yourself toward the front of the treadmill? It’s the same principle. The treadmill can’t prevent you from pulling forward because there isn’t enough friction between you and the treadmill. The rail would be the air that the plane is using to pull forward; the wheels are the skates; try thinking about that the next time you’re on a treadmill, it will click.
I don’t know if that helps, but awesome if it does. Good luck.
yes Dean? – I’ve muddled my way through twenty years around and about the physics and practicalities of this scenario
January 31, 2008 at 2:53 AMAs a dedicated mythbusters fan who loves your show, I’m here to tell you that your airplane on the conveyor belt is busted. Here’s why: To get an airplane to fly depends on aerodynamic forces produced by airflow over the wing. If there is no airflow, there will be no lift produced and the airplane will not get airborne. If there is no wind then the plane must move relative to the surface of the earth in order to produce airflow over the wing and thereby lift. This is the propeller’s job, to get the airplane moving relative to the surface of the earth. In your experiment the plane was moving relative to the surface of the earth and thus producing airflow over the wing and enough lift to get it airborne. If the experiment had been true, with the belt and the plane “moving” at the same speed, then the plane would not move relative to the earth and no airflow would be produced over the wing.
January 31, 2008 at 2:54 AMThe problem was that your belt was not fully supporting the airplane. The weight of the plane was transferred through the belt to the earth’s surface. This achieved sufficient friction with the earth to allow the airplane to accelerate relative to the belt and the earth. Your dedicated viewer,
Chip Lancaster, MS Aeronautical Engineering
37 years of pilot experience, San Diego, CA
Dean – clearly you understand the difference between ground speed and air speed, you must to factor time and fuel, etc. In the scenario presented, all that matters is air speed, air speed is attained via the connection between the planes motor and the air, not the plane and the ground, you obviously understand that a plane can lift with no ground speed whatsoever.
January 31, 2008 at 2:58 AMIT’S NOT THE AIR THAT WILL PULL THE PLANE FORWARD. IT IS THE PROPELLOR. I THINK THAT THEORETICALLY IT WOULD BE POSSIBLE FOR A TREADMILL TO PREVENT A PLANE FROM FLYING. IF THE TREADMILL WERE GOING FASTER THAN THE FASTEST SPEED ATTAINABLE BY THE PROPELLOR/ENGINE (WHICH IT CAN NOT), OR THE ENGINE WAS ONLY GENERATING ENOUGH THRUST TO MAINTAIN POSITION AT TAKEOFF POWER (LIKE YOUR ROLLER SKATES)THE WHEELS WILL NOT BE ABLE TO GET ENOUGH FRICTION FROM THE TREADMILL AND WILL THEREFORE NOT GET ANY RESISTANCE TO ALLOW FORWARD MOTION IN REFERENCE TO THE TREADMILL. THE PLANE WILL NOT MOVE FORWARD. IT IS ONLY THE THRUST THAT EXISTS OVER AND ABOVE THAT NEEDED FOR TAKEOFF THAT ALLOWS THE PLANE TO MAKE UP FOR THE TREADMILL SPEED.
January 31, 2008 at 3:01 AMON A ROLLING SURFACE (TREADMILL), THE WHEELS NEED TO BE ABLE TO MOVE FASTER THAN THE TREADMILL INORDER TO MOVE FORWARD. IT IS THE PROP THAT ALLOWS THIS EXTRA SPEED. IT IS THE PROPELLOR WHICH PULLS THE PLANE, LIKE THE ARMS PULLING ON THE RAILS. WHAT I AM SAYING IS, THE ONLY REASON THE PLANE FLIES IS BECAUSE IT IS ABLE TO MOVE FASTER THAN THE SURFACE. AND ABLE THEREFORE TO GET WIND FLOWING OVER THE WINGS.
January 31, 2008 at 3:07 AMDean:
YOU ARE TOO LOUD
you are also incorrect, you fail sorry, the plane takes off, wheels have no point in the equation when props pull air, ive never seen a propeller that works on tarmac
January 31, 2008 at 3:12 AMIf the wheels were frictionless, the conveyor could be moving 1000 m/s backwards and the plane would sit still with no force applied. Since the friction force would be the only thing pulling the plane back and it is equal to 0, the acceleration (0=ma) would be 0. Since some friction does exist, there is a small force pulling the plane backwards that is relatively easy for the engine to overcome. As it overcomes the force, the plane accelerates forward, generating the lift it needs to take off. The only way to ground a plane using a conveyor belt would be to increase the friction in the wheels (by applying brakes for example).
January 31, 2008 at 3:13 AMBoth experiments done on this seemed to be greatly flawed. The first, with regards to the radio controlled plane on the treadmill test, it was flawed in that a treadmil is NOT a conveyor. Treadmills are always angled up slightly, so that the front is higher than the back. This increases resistance to the runner on the treadmill, which mimics an uphill climb and works more muscle groups than a flat land trek, making for a better workout. In this instance though, the upward tilt, however slight it is, reduces the treadmills influence on the plane. If it were a level surface like an actual runway or conveyor, then the takeoff surface would be supporting the weight of the plane entirely, thus enacting its full influence on it. At the upward angle, this is not the case, and therefor the equation inherent in the properties of the question becomes imbalanced. It is the fact that the conveyors surface is supposed to be bearing the entire weight of the plane in full, as solid level ground would, that allows for the negating properties of the backwards motion to have a full effect on the planes motion. With regards to the large scale experiment, the tarpon is not taking the place of the ground as a freely suspended conveyor surface would be, thus the stationary ground beneath the tarpon is still supporting the weight of the plane in full, rather than the actual tarpon itself, thus negating the conditions of the question altogether.
All talk of wheel friction is utterly pointless, in that the frictional energy loss on the wheel is caused by both sided equally, the plane and the conveyor, and should thus be divided in half and subtracted equally from both sides of the equation. You can remove the wheels entirely and will still get the same results either way, albeit with more force needed to achieve it.
This is not an endorsement for the plane doing one or the other, merely a simple statement as to the initial holes in the mythbusters experiments and arguments.
However, I will state that if the question is tested as it is postulated, using a freely suspended level conveyor surface( not an angled treadmill), the results might very well be different.
January 31, 2008 at 3:14 AMTHOUGHT OF IT ANOTHER WAY. YOU PUT A PLANE DOWN ON A TREADMILL, IT MOVES IN THE DIRECTION OF THE BELT. ADD THRUST, AND IT CAN STAY STILL. YOU HAVE THE TREADMILL GOING 55 MPH, TAKEOFF SPEED, AND THE PLANE WAS PRODUCING ONLY ENOUGH POWER TO PRODUCE LIFTOFF SPEED, YES OR NO, CAN THE PLANE ACCELERATE ENOUGH TO FLY?
January 31, 2008 at 3:20 AMYou give me a bad name Dean. 11:53 on Mythbusters tape with no commercials. Treadmill @ 11 MPH, Plane @ 11 MPH. It moves forward.
January 31, 2008 at 3:27 AMISN’T IT THE EXTRA THRUST, AVAILABLE FROM THE PROP, WHICH ALLOWS THE PLANE TO ACCELERATE FASTER THAN THE BELT? AFTER ALL, IF THE PLANE DOES NOT ACCELERATE FASTER THAN THE BELT IT DOES NOT MOVE.
January 31, 2008 at 3:27 AMA PLANE IS NOT A CAR. I’M ROLLING IN MY GRAVE RIGHT NOW.
January 31, 2008 at 3:29 AMSORRY DEAN, HOW DO THEY KNOW THE PLANE WAS NOT PRODUCING M O R E THAN ENOUGH THRUST TO FLY AT 11 MPH. THEY DID NOT VERIFY THE POWER SETTING REQUIRED FOR TAKEOFF. BESIDES THE POWER TO WEIGHT RATIO OF THOSE PARK FLYERS IS USUALLY VERY HIGH.
January 31, 2008 at 3:31 AMI GUARANTEE YOU. IF YOU HAD A PLANE WITH NO MORE EXTRA POWER THAN THAT CAPABLE OF PRODUCING LIFTOFF SPEED, AND YOU HAD A TREADMILL GOING LIFTOFF SPEED, THE PLANE W I L L N O T LIFT OFF. IT IS THE EXTRA POWER THAT GETS THE PLANE TO MOVE FASTER THAN THE TREADMILL THEREFORE MOVING THE PLANE FORWARD, THEREFORE GETTING WIND MOVING OVER THE WING AND THEREFORE LIFTING OFF.
January 31, 2008 at 3:38 AMI really thought you guys had a brighter audience, the plane will lift off, just as it did in the experiment. Even if the wheels are on a treadmill moving the same speed, faster or slower than the wheels.
The plane isn’t dependent on the speed of the wheels to move forward, the lift generated by the engines make the effects of a treadmill device negligible.
January 31, 2008 at 4:08 AMhttp://www.youtube.com/watch?v=4owlyCOzDiE
January 31, 2008 at 4:15 AMMAK, even a frictionless wheel would pull back on the plane. Friction or no, the wheel is making contact with the axl mount, and thus transferring the energy. Friction isnt what produces pull on the plane via the wheel, its the surface connection. Friction results from said connection, causing a loss of energy, but you can also have connection of two surfaces without friction being produced. If the wheel were mounted with a mag-lev set up in which no contact was made between it and the plane, then yes, the wheel would spin and the plane would remain stationary. However, since that is not the case and the two are indeed making surface contact by their very nature, the conveyor will enact influence on the plane, effectively pulling it backwards from a standstill position if no forward thrust is applied. If the conveyor surface is supporting the planes weight in full, it will move the plane, even with a mythical “frictionless” wheel. However, frictionless wheels are completely a thing of fiction. The laws of physics dictate that the interaction of the wheel with its mount will always produce some friction because of the nature of how they interact.
But forget wheels. This is essentially a math problem, an equation of vector forces opposing one another. The net forward thrust of the planes engine( applied thrust minus loss to air cushonning factored in), in correlation with gravity, produces a combined forward and downward force on the plane, while the conveyor meanwhile offers up a backwards and upward resistance combined vector force, as opposed to just the upward resistance offered up by still ground that cancels out gravity. The question is then, does that combined force of the conveyor, which is equal to that of the plane in conjunction with gravity, transfer in full to completely cancel out the force of the engine and weight of the plane? If Forward+Gravity=Backward+Upward resitence, then do both sides act on the same point, thus canceling each other out. If that is the case, then the plane will not move. If however, they act parallel to each other but not entirely opposite, then the plane will overcome the conveyor without much effort. Ultimately, the wheels only act to reduce surface contact and thus energy loss to friction. They are not necessary to the overall equation either way, they simply reduce the need for greater forward and backwards vector values being applied.
January 31, 2008 at 4:23 AMDean, You truely are an idiot. You need to listen to these people and shutup. Your not proving any point, because you are wrong. Its common sense dude, get real.
January 31, 2008 at 4:26 AMThe real question here is not how fast the planes wheels are “moving”, but how fast the air is going past the planes wings.
I would have preferred a smoke machine be put in front of the plane next time, as to see the actual air flow.
January 31, 2008 at 4:43 AMHEY YOU GUYS!
Here’s the deal:
All of you who think the Mythbusters experiment was wrong, stop posting your whiny crap here, get up away from your computers, go outside and set up and document a full-scale experiment which *proves* them wrong, then come back here and show your results and working, just like they did.
Until you can do that, your opinion doesn’t mean anything, so can you please STFU.
January 31, 2008 at 5:01 AMI may as well throw in my thoughts too.
Unless the atmosphere is somehow attached to the belt as well, the props or whatever are still creating thrust against a non moving surface.. the surrounding air. This obviously creates forward motion relative to the air and irrespective to the ground. Forward motion with respect to the air will then create lift. This means that the movement of the belt only acts on the wheels to make them spin faster than they normally would during takeoff.
Fun Discussion
January 31, 2008 at 6:53 AMmistake one: using a plane with thrust mechanism in front of the lift mechanism. of course this will generate lift since it’s directly blowing wind over the wings. this is not in accordance with the way I believe the myth to be stated.
mistake two: limiting the treadmill to the plane’s normal takeoff speed. the treadmill in the real myth is supposed to travel as fast as it has to (achieving infinite speed if necessary) to cause enough rolling friction to prevent the plane from moving forward relative to the ground.
they busted a myth, but it wasn’t the one i’m familar with.
January 31, 2008 at 7:38 AMyou know they didn’t understand the myth when they said
January 31, 2008 at 7:42 AM“we need a longer treadmill!”
I’d say this myth is quite definitively busted. Hydrophilia said in his first post that just definition #2 was tested. Actually, I think #3 was too, although it probably wasn’t intended. During the first test with the model plane, the propeller was off and Adam was holding up the tail so that it wouldn’t roll off the treadmill. It was stationary with the treadmill running in the opposite direction. It didn’t take off. Once that propeller started though, the plane moved forward. I’m sure this will revisited, but they should maybe concentrate on the treadill takeoff speed and distance relative to a normal takeoff (I imagine it will be about the same though). Also, the string tied to the plane idea was decent. Either that or slap a couple of wings on that model car they used.
January 31, 2008 at 8:13 AMIt’s not that difficult to grasp, guys.
Lets outline a simple analogy. Say you placed a skateboard on a treadmill. You stand on the skateboard, then start the treadmill. The freewheeling skateboard will counteract the backwards motion of the treadmill, thereby rendering you motionless. While in this state, you pull on a rope anchored to a wall in front of you, you will then begin to move forward.
The rope, in this case, provides overall forward momentum (the backwards momentum is rendered null by the freewheeling skateboard). The skateboard is the plane in this case, whille the rope is the planes engine.
Some people seem to be getting caught on the assumption that the planes engines somehow drive the wheels of the plane. This is not the case. The plane pulls itself through the air, in effect pushing itself off from the air behind it.
If the engines DID in fact drive the wheels, you would have whats called a ‘rolling road’, the devices used to test cars while keeping them stationary.
The plane takes off. Get over it.
January 31, 2008 at 8:39 AMRANDOM INTERNET GUY, GOOD SUGGESTION, BUT WAY AHEAD OF YOU. ORDERED AN EXTRA LARGE STAIRMASTER 10,000,000. (OVER NIGHT DELIVERY OF COURSE). CAME LAST NIGHT. PUT MY PLANE ON IT, A CHEROKEE, AND STARTED IT UP. STARTED THE BELT AND KEPT THE PLANE STATIONARY ON THE BELT USING THROTTLE SETTING. ADDED MORE THROTTLE THUS ADDING MORE PULLING FORCE FROM THE PROPELLOR, (IT WAS ACTING ON THE AIR NOT GROUND) TIRES SPUN FASTER THEN THE BELT, AIRPLANE ACCELLERATED TO TAKEOFF SPEED, PLANE DEPARTED BELT AS IT IS ALWAYS IS SUPPOSED TO. THANK YOU STAIRMASTER 10,000,000. AND THANK YOU MYTHBUSTERS FOR THE VERY INFORMATIVE NIGHT.
January 31, 2008 at 8:51 AMI can somewhat understand non pilots having a difficult time wrapping their minds around this problem, it is a brain tease question after all. What’s truly mind boggling is that there are actual pilots on this thread who just don’t get it either. Very disturbing.
January 31, 2008 at 9:08 AMI guess I should add, myth busted, of course the plane flys.
January 31, 2008 at 9:12 AMPILOTS DEAL WITH THE WIND PASSING THEIR WINGS. WE DON’T HAVE TO KNOW ABOUT WHY THE WHEELS FOLLOW. THEY JUST DO!!!!!!!
January 31, 2008 at 9:21 AMPeople are morons. Even when the results are right in front of them, they refuse to believe it.
Again, does an amphibious plane have any trouble taking off against a current?
Does a fan boat have any trouble sailing against a current?
No. The thrust they use to create firward motion is provided by the engine and propeller, which uses AIR, not water.
A normal plane’s engines, be they turbofans, jets, or props, use AIR to create thrust. The motion of a plane is relative to the air around it, hence the term AIR SPEED.
Wrap your brain around this: In WWII, a couple of pilots were trying to fly in a westerly direction across Europe at a speed of about 300 mph. They accidentally got into the jet stream, which was moving east at about 400 mph. The result? After 2 hours of flight, they were 200 miles EAST of where they took off. They had flown backwards because the jet stream overpowered the thrust of their engines.
January 31, 2008 at 9:32 AMQuote:
Dean:
Jamie, Adam,
You blew it big time. I am a pilot and I can tell you that the myth about the airplane conveyor belt is supposed to be confirmed…
Wow,
Maybe the FAA should require a basic high school physics course in order to get your pilot’s license. As a pilot, I would hope that you can grasp Newton’s basic laws and apply them to the concept of action-reaction as it relates to thrust in an aircraft.
I’m amazed that this is even being discussed.
January 31, 2008 at 9:36 AMAll you poor non believers. I think the reason you don’t get this is because you are thinking to hard. If the thrust is coming from the props than the props are pushing the air, not the ground (treadmill) the treadmill will have no effect on the plane moving forward. Slow down your fast judgement and think about it. The plane will go forward and create AIRSPEED. You can test this any way you want but the plane will fly.
January 31, 2008 at 9:50 AMthe airplane needs no relative motion with respect to the ground to lift off, it needs relative motion with respect to the air, the thrust source, in this case a propeller provides the interaction with the air that moves air over the wings.
A propeller does not blow wind over the wings and create lift.
Do they let anyone have a pilots license today?
January 31, 2008 at 9:54 AMI agree, the test was flawed.
The prop on a plane doesn’t provide enough moving air to create lift, it simply creates enough force to move the plane forward, allowing the wings to act on the air around them. Everybody seems to think the prop is blowing enough air over the wings to create lift, which simply isn’t the case. It couldn’t possibly move enough air to do that. So, in the end, a plane flies based on it’s relative speed to the GROUND (or the stationary air around it). The plane took off at 25 mph because that’s the speed relative to the ground that’s necessary for the wings to have enough air to act on to create enough lift. The prop speed doesn’t change from the time it starts to move until it lifts off, so obviously the wings aren’t using the air from the prop to create lift. This “myth” is testing just that… If a plane isn’t moving relative to the ground (the conveyer spinning backwards at the same rate as plane is moving forward), but the prop is spinning at full speed, will it take off? So if you chain a plane to a wall, and get the prop spinning at full speed, will it lift off the ground? That would’ve been the most accurate way to test this. And the answer is an obvious no.
January 31, 2008 at 9:57 AMLISTEN, I GET IT ALREADY. LET’S JUST SAY THAT A BIG TRUCK HIT ME LAST NIGHT, AND I FINALLY SEE THE LIGHT. LEAVE ME OUT OF THIS, I HAVE BECOME A TRUE BELIEVER.
January 31, 2008 at 10:07 AMI have to post again after reading more of the comments in this and other websites that have this topic. I will now satisfy non believers. I will now place motors on the wheels of the plane and remove the propellers (or jet engines) now the plane has the same popwer plant as a car. Now as the motors on the wheels move the plane forward, the treadmill moves at the same speed backwards, the plane is stationary and does not fly. Are you happy now?
January 31, 2008 at 10:10 AMI feel sorry for Jamie and Adam, seeing the intelligence level of their audience.
So many people here claiming to be pilots or engineers, who don’t understand the difference between powered wheels and an airscrew.
As so many others have explained, the wheels on a plane are not powered and they are NOT used for accelerating the plane to take-off speeds. They are purely for supporting the plane while it’s on the ground.
Think about it this way. Put a bicycle on a treadmill and stand beside the treadmill (not on it). Hold the bicycle upright and turn the treadmill on. The treadmill will tend to move the bicycle backwards, but put one hand behind the seat to prevent that from happening. The bicycle’s wheels (and pedals) will spin backwards and the bicycle will remain stationary. You’ll find that it doesn’t take much effort at all to keep the bicycle in place, because the wheels are rolling on the treadmill, not sliding on it. Rolling friction is MUCH less than sliding friction. Remove the bicycle chain and it will take even less effort to hold the bicycle steady, because now no effort is being wasted on turning the chain and pedals.
This is exactly the situation with an airplane. The wheels are unpowered and rotate freely.
Now push the bicycle forward with your hand. You will find that you can easily move it forward with very little effort. If you push the bicycle forward at 10 mph while the treadmill is rotating backwards at 20 mph, the bicycle wheels are actually spinning forward at 30 mph, but that takes very little effort since the wheels have ball bearings and are designed to have very low rolling resistance.
The propeller is just like your hand pushing the bike. It’s a means of forward propulsion that DOES NOT RELY on transmitting power through the wheels. Sure, it may have to spin a bit faster or you may have to increase the pitch to maintain the same forward speed when on a treadmill versus on an ordinary runway. But it can still move forward, so long as the force applied in the forward direction is greater than the rolling resistance of the wheels at some given speed of treadmill. For well designed wheels with ball bearings and low rolling resistance, this second force is tiny, compared to the power of the propeller. Therefore, the plane will easily be able to move forward, and once it moves forward, the wings can produce their lift for take-off.
January 31, 2008 at 10:11 AMYou have a barn that goes east/west.
January 31, 2008 at 10:13 AMA rooster lays an egg on the roof, which way does the egg roll?
Answer “roosters don’t lay eggs”, not “well if you surgically altered the rooster…”.
You have a plane on a conveyor belt, etc.
Answer “conveyor belts don’t stop planes from moving forward”, not “well the question says the plane stays still”. And the question doesn’t even explicitly state that.
The experiment was flawed. If “moving the runway” would cause a plane to take off then we wouldn’t need catapults to throw jets off of aircraft carriers. The catapult causes enough volume of air to move over the wings to generate lift. Moving the ground underneath the jet will not generate any volume movement of air over the wings.
If “moving the runway” underneath the plane is enough to get the plane to take off then use an ultra-light and DON’T turn on the engine. This experiment only proves that the wheels are capable of turning 50mph. Because the plane still had to achieve forward motion in three-dimensional space to get air to move over the wings to generate lift. Moving the wheels does not generate lift. This just proves that the plane can move forward at 50MPH.
January 31, 2008 at 10:23 AMImagine a plane on a conveyor belt/treadmill but held by cables anchored off the treadmill so that it cannot move.
January 31, 2008 at 10:25 AMStart the treadmill. How much force is necessary to hold the plane in place?
Just the amount necessary to overcome the friction in the wheels. Not a lot assuming that the wheel bearings are any good. Let’s get the treadmill up to a constant speed of say 100Kph.
Now spin up the engines to the point where the force from the engines can overcome the friction in the wheels. Won’t take a lot. the engines will be easily able to hold the plans position at low power.
Now throttle up the engines and the plane will begin to move forward despite the fact that the wheels are spinning furiously.
The forward movement will cause airflow over the wings and hence lift.
Oh yeah – forgot to let go the cables : )
January 31, 2008 at 10:26 AMI only read about 1/4 of this therad, but its seems that people aren’t understanding that there is no restrictive force through the axle to the airframe (if that makes sense). No, I didn’t see the show.
The amphibous example in the thread should be a give away, but here are a few more:
1) How about an airplane on erm, permenantly lubricated skids on the conveyor belt?
2) You are holding a toy airplane on a conveyor belt by the front end (propeller). Turn the belt on, the wheels freely rotate. Pull the plane forward from the prop (the source of thrust), and even the slightest tug will make it go forward as the wheels still spin freely. Great, now substitute a real plane, and voila.
3) Try #2 with a good old fashoned pinewood derby racer to figure out that the wheels rotate freely.
The only real question to this experiemnt that I saw was whether or not the wheels or belt would hold up.
January 31, 2008 at 10:36 AMThe main problem here is that they didn’t test the myth as understood by most naysayers.
The myth should have been posited as “Can an fixed-wing aircraft with zero ground-speed produce enough lift to become airborne?” This could have been tested by tethering the aircraft to the runway, with a quick-release that let go of the aircraft once there was no weight on the wheels.
It seems to me (though should be tested) that the type of aircraft would make a difference in this case. An airscrew that thrusts or draws air over the wings may be able to generate enough lift. A jet or ducted-fan probably wouldn’t (with the exception of downward-directed thrust and power:weight > 1:1, ala Harrier).
January 31, 2008 at 10:49 AMI agree along the lines of BobP. If no forward movement is needed, as I and others believe it is air moving over the wings that creates lift, then take the wheels off the plane and try this. The wheels moving clearing has nothing to do with take-off everyone on both sides agrees. But the idea of a windless environment, with the ability to match backward and forward speed such that the plane never gets wind over the wings is the issue. If the pure propeller thrust lifts the plane then no wheels are needed. But I believe the thrust is to push against air, moving the wings (and plane) forward, thus causing air to rush over the wings, the faster speed air over the top creates a low pressure zone. From the comments (I missed this epsisode) it sounds like wind was present, the plane had a low wind speed required for lift, and traction was available through the tarp to the stationary ground. Hey, 171 other people commented, so why not! :-)
January 31, 2008 at 11:01 AMIf you launch a rocket vertically, and it has wings (air-foils, not stabilizers) it will generate lift and climb. The only difference between the rocket and the plane is that the plane uses wheels to hold it off the ground as it rolls down the runway. If a planes take-off AIR SPEED is equal to 55 MPH ground speed, and the conveyor belt is moving at 55 MPH in the opposite direction, then the wheels will be spinning at 110 MPH and the plane will move forward and achive lift-off. I agree I would have liked to have seena more conventional air-craft used in the test, but the outcome is valid.
January 31, 2008 at 11:13 AMI like stupid people, they make me laugh.
Oh, and the myth is not ‘if the plane doesnt move will it take off’, it is ‘can the rolling of the treadmill/conveyor/magic carpet stop the plane moving forwards’ – which as has been said so many times here – NO! The plane doesnt move from the wheels rolling round, it moves because the props (or jets – yes jets would behave the same) provide the forward thrust to accelerate the plane, and nothing you do to the wheels would stop this from happening because the wheels don’t drive the plane.
I think next time I have to fly I might ask the pilot what the answer is. If he says the plane won’t fly, I’m getting off that plane and asking to be changed to the next flight.
January 31, 2008 at 11:16 AMa bunch of high school students are laughing their heads off at all of the naysayers right now. you people obviously skiped high school basic physics class. Idiots!
January 31, 2008 at 11:23 AMBobP said:
[The main problem here is that they didn’t test the myth as understood by most naysayers.
The myth should have been posited as “Can an fixed-wing aircraft with zero ground-speed produce enough lift to become airborne?”]
I don’t see why this would even deserve a “myth” status. Basic physics says that a plane develops lift because of air moving past its wings in a certain direction and at a certain speed. Obviously, the status of any myth that claims otherwise is “Busted” before you even begin.
You can weasle your way around it by changing the type of aircraft (one that doesn’t use wings for takeoff), by moving the air instead of the plane (like in a wind tunnel), etc. But in that case you’re not testing the myth either, you’re testing something else.
The myth as tested was perfectly good, I just don’t know why people have a hard time understanding it.
Fact: you need relative movement between the wing and the air around it to get lift.
Fact: unless you’re in a wind tunnel or in the middle of a hurricane, you gotta move the plane because the air won’t move for you.
Question: can you move a plane at sufficient speed on a treadmill for it to take off?
Simple Answer: why the heck not? Just throw more power at it. Replace the plane with a car. Can a car go 50 mph forward while on a treadmill that’s going 50 mph backwards? Sure! Just floor the accelerator pedal. The car’s speedometer will show 100 mph, the wheels will be spinning at 100 mph, but the car will only be moving 50 mph forward, because the treadmill is simultaneously spinning 50 mph backwards. It’s the same principle as an actual human on a treadmill. Can you run faster than the treadmill is moving, so you hit the support at the front? Sure you can. A human can, a car can, so can a plane.
More Nuanced Answer: Yeah, humans and cars and planes can maintain a forward speed against a treadmill, but it’s easiest for a plane to do so. That’s because humans and cars “push back” against the ground to move forward, but planes don’t. A plane can afford to have wheels which are unpowered, not connected to an engine or anything else that increases the mass and inertia of the system. They are free rotating wheels, and all the have to do to counter the effects of the treadmill is to freely rotate at some extra speed equivalent to the speed of the treadmill. With modern ball bearings and light-weight aircraft alloys, this takes very little energy.
January 31, 2008 at 11:27 AMThe only effect the treadmill should have on the planes ability to take off is some minor resistance due to friction of the wheel bearings, and almost all modern aircraft are capable of producing more thrust than required for take-off.
January 31, 2008 at 11:39 AMThe problem here is in the definition of the myth.
Most of us thing the CORRECT myth to test is the one where the airplane remains motionless (no forward movement) relative to the surrounding air. In the case of THAT ‘myth’ I’ve been a pilot for 17 years and if the airplane does not move forward AT ALL relative to the air around the wings (the ground and wheels are not relevant) then there will not be sufficent airflow over the wings and it cannot fly. (The prop is to move the plane forward, not to blow air over the wings.) For those of you that fly if you are on the ficticious treadmill and the plane is indeed stationary relative to the air then you airspeed will read zero … no air flow over the wings, no “wind” in the pitot tube, you gauge will read zero. We all know that means you cannot fly … most light singles stall when the airspeed over the wings (or in the pitot tube) is less than about 55. Zero relative airspeed = no fly.
(Picture your plane with FULL BRAKES and FULL THRUST. No forward movement, same the treadmill. You are not going to “float up in the air”. The prop at full thrust is not helping you fly if it’s not pulling you forward through the air creating airflow over the wings.)
If the myth is “can the engine overpower the treadmill so the plane can still move forward despite the treadmill” then of course it will fly. The plane is moving forward, creating air over the wings, and it will fly. That’s a silly test and is the one they conducted. (Set a treadmill at 6 MPH and any runner can run forward off the front end.)
Test myth 1.
January 31, 2008 at 11:39 AMFor those that don’t belive the Myth is busted “AS TESTED”, I direct you to the work of Simon Stevinus.
January 31, 2008 at 11:44 AMThe plane engine only needs to exert a small amount of force to over come the conveyor belt. The only way the plane would not take off is if the pilot and the conveyor operator were working together to keep the plane stationary. As soon as the pilot decides he wants to take off… He will be able to regardless of what the conveyor operator does.
The force (of the engines on the plane) required to keep the plane stationary is the same at a conveyor speed of 200mph as it is at 10mph.
When the pilot powers up the engines the plane will move forward. Yes… even if the conveyor is moving at 200mph.
Please see the following for a more in-depth explanation.
http://www.airplaneonatreadmill.com/
January 31, 2008 at 11:55 AMIrresponsible program makers… shockingly bad experiment
January 31, 2008 at 12:06 PMTo those who think the myth is whether the plane with zero ground speed flies…
DUH!!!!
Of course it wont fly – its not even worth mentioning because its just too feckin dumb to consider a myth.
The myth is whether the conveyor belt has any effect on the speed of a plane – THAT is the point of the myth and the answer is no because the wheels aren’t anything to do with how fast the plane moves.
Its a simple myth based on perception of wheels & motion – nothing to do with the speed of the airplane (which obviously wont fly if it doesnt move)
January 31, 2008 at 12:24 PMPS: Maybe some of the ‘pilots’ are getting confused because the point of wheels not being part of the motion is so obvious to them they wouldnt consider that bit to be the myth…
January 31, 2008 at 12:25 PMThere are some real retarded people out there. Mostly all of them have posted on this comment site!!!
The playe will fly morons!!!
January 31, 2008 at 12:29 PMAlso, these people that say they have been pilots for X amount of years, need to be forced to give their aircraft away and licenses revoked!!!
I just cant believe the IQ of most of the postings on here…..
January 31, 2008 at 12:31 PMSo, if Night Rider were approaching his trailer truck while he was moving, say, 60 MPH and the trailer were in front of him moving at 50 MPH. What, then, would be Night Rider’s final speed after entering the trailer?
January 31, 2008 at 12:34 PMAircraft airspeed 0, treadmill groundspeed 0, wheel rotational speed 0. Aircraft airspeed 25, treadmill groundspeed 25 (in opposite direction), wheel rotational speed 50. Aircraft airspeed 50, treadmill groundspeed 50 (in opposite direction), wheel rotational speed 100. The key thing to remember, “takeoff speed” is determined by the airspeed indicator in the aircraft not treadmill groundspeed. So in order to for the treadmill to move the aircraft will have to move through the air to generate an “airspeed”. No aircraft movement, no treadmill movement.
January 31, 2008 at 12:38 PMI think everyone who believes (still) that the plane would not take off should assemble in one area. We could photograph all of you for the biggest idiot poster in the world.
No punishment or admonishing needed. These people are going to hurt themselves more than anyone else could.
January 31, 2008 at 12:41 PMSimple supposition on this myth: The plane on the treadmill to be held from going forward! A cable w load cell from the rear holding it in place. Support the plane fron a crane with a load cell carrying the full weight of the plane with the wheels riding just on the treadmill. Start the plane’s motor and treadmill reving up to the power setting that is usually required for takeoff+. Does crane cell weight go down & does the plane lift?
January 31, 2008 at 12:43 PMPicture a skateboard on a treadmill. You are standing in front of the treadmill with a rope attached to the skateboard. Start the treadmill and hold the rope so the skateboard remains stationary. So far the only force you are applying is to overcome friction. If you start pulling the rope, the skateboard will move forward. If you yank the rope really hard, stand back and avoid being hit by the “flying” skateboard which is moving through the air just as fast as you pulled it. An airplane’s propeller or jet works just like pulling the rope–it pulls, or pushes, the plane through the air. The amount of thrust used to overcome the friction would be minimal (even though I am weak and scrawny, I can push my 7000lb truck on level ground when it is in neutral).
January 31, 2008 at 12:45 PMffs. if the plane was sitting on the treadmill, with the engines off, and the treadmill started, are you saying the plane would sit in the same spot?, no, it would move backwards, no matter how frictionless the wheels are. when the plane engine is started, it will at most be able to keep it self in the same spot, if the treadmill is moving fast enough, the plane cannot take off.
January 31, 2008 at 12:51 PMGuys- ‘real pilots’,
January 31, 2008 at 12:59 PMDon’t bash the Mythbusters, as you are the real fools. It is evident by your posts that you just don’t have a real explanation of what is happening here. The conveyor should move in the oposite direction of the plane at the same speed. THERE IT IS! They should both MOVE. NOTHING says that the plane is STATIONARY!
Anon–Yes, the plane would move backwards in your setup (why is the engine off?). You would need to add forward thrust from the propeller to overcome friction–it wouldn’t take that much force. In my skateboard analogy, how much force would you need to apply to overcome the friction. Spin the treadmill as fast as you want, it still won’t take much force. The propeller, or jet, will still have ample force to push or pull against the air with sufficient force to achieve the speed necessary for takeoff.
January 31, 2008 at 1:06 PMRE – SW. im going to have to change my posted opinion slightly , you would need a ridiculously fast treadmill to keep the plane from taking off, if the speeds are equal, the planes engines would be able to overcome the reverse friction easily. fun discussion tho
January 31, 2008 at 1:10 PMThe only mistake the Mythbustersmake is not fully explaining why this is clearly busted.
January 31, 2008 at 1:21 PMA. The power from the engine is NOT connected to the wheels.
B. The conveyor does NOT affect the air above it.
C. The wheels provide nearly zero resistance to forward movement whether on ground or on the belt.
D. The only real difference between taking off from the ground or the belt is that the wheels are going faster.
E. The treadmill could easily be going twice as fast as the plane requires and the result would be the same.
F. The power from the prop is easily overcoming the friction the wheels provide to rolling resistance.
First, many people either A) Have not read the myth and/or B) Don’t understand what they’ve read. For those like this who don’t even understand what is being argued, there is no way to reach common consensus when we are not even discussing the same thing.
However, when I try and guess WHY some people still doubt that the plane will move forward and eventually reach take off speed and thus take off… I think I have figured out the mistake they must be making?
Those doubters believe that if the forces acting against the plane; the conveyor/treadmill in a backward direction, and the propeller/jets in a forward direction are “equal” the plane will stand still. Their mistake is that BECAUSE THE WHEELS CAN TURN, the conveyor/treadmill can ***NOT*** “pull backward” on the plane when the propellor/jets are “pulling forward”.
WHEN THE FORCES BATTLE, THE WHEELS JUST SPIN AND THE PROPELLER/JETS ALWAYS WINS WHICH MEANS PLANE ***DOES*** MOVE FORWARD ALMOST AS NORMAL AND TAKES OFF!!! [/shouting]
January 31, 2008 at 1:41 PMMYTH BUSTED, I’M DONE AND NOW ITS TIME TO GO FLYING AND SEE HOW TO FLY AN NDB APPROACH BEFORE THE FAA TAKES THEM ALL AWAY.
January 31, 2008 at 1:49 PMBY THE WAY, I’M NOT A REAL PILOT, HOWEVER I DID SPEND LAST NIGHT AT THE HOIDAY INN EXPRESS. GOT U ALL>>>>>>>>>
January 31, 2008 at 1:57 PMIt’s an AIR plane, not a car. Dependence on the wheels for propulsion would result in a LOT of problems once the aircraft left the ground. Actually even interaction with air is unnecessary for propulsion. The Bell X-1, the X-15s and Spaceship One derived propulsion by expelling hot gases from rocket engines.
The principle is that a force WILL propel masses in opposite directions at velocities inversely proportional to their mass. With cars and people the force acts through friction with the ground. Since the planet is so overwhelmingly more massive than the vehicle or person the planet’s velocity change is unmeasurably small, but STILL present. Fixed wing airplanes utilize a force between their engines and either the air or exhaust gases for propulsion. As long as the wheel brakes are released the runway (conveyor belt, tarp or aircraft carrier deck) will only produce a negligible amount of friction.
And there was absolutely NO friction between the aircraft wheels and the runway through the tarp! Truck wheels to runway, tarp to runway, but NOT between aircraft wheels and runway.
January 31, 2008 at 2:00 PMok… for those of you concerned with relative speed to treadmill it will be DOUBLE take off speed at takeoff, relative to the SOLID GROUND it will be TAKEOFF SPEED. The ONLY force acting against the thrust of the engines is from wheel friction, K(coefficient of friction on airplane wheels) is something on the order of .001(for every 1000N exerted forward, 1N would be exerted backwards)so even the massive amount of force exerted by an airplane engine wouldn’t yield a considerable drag force.
January 31, 2008 at 2:19 PMDear Adam and Jamie,
I must say I was quiet disappointed with your last show.
Your experiment regarding the airplane taking off on the conveyor belt was completely flawed. According to the original myth the plane should stay still and the conveyor belt should be accelerated at the same speed as the plane moves forward. The plane should therefore stay still.
In your testing, we can clearly see that the plane moves forward. This enables airflow under the wings and therefore provides an uplift force on the wings and allows the plane to fly.
In my opinion, you should really re-visit this myth and somehow manage to match the speed of the plane and the speed of the conveyor belt, which can be pretty hard in practice.
January 31, 2008 at 2:24 PMAleks:
The conveyor speed is irrelevant to the experiment. That conveyor ONLY changes the speed the wheels FREELY rotate. The wheels have NO connection with what it takes to get airborn except to allow the plane to roll. This myth is busted no matter how you revisit it.
January 31, 2008 at 2:29 PMThe myth is not whether a plane with zero airspeed can take off, it whether a moving conveyor belt is capable of holding a plane to zero airspeed.
It is impossible to actually build a conveyor belt capable of preventing forward motion in an airplane.
With the conveyor belt moving, there is a very, *very* small amount of friction added to the wheels of the plane which the engine thrust must overcome. It is *theoretically* possible to have a conveyor belt that can move fast enough to make this added friction so high the engine thrust would not be able to overcome it. In the real world, however, such a fast conveyor belt would be impossible to build, and would probably cause the wheel axle to break.
Jamie and Adam should have repeated the full-scale experiment at higher belt speeds, as suggested by, uh, someone smart above. (The results would be the same: the plane takes off.)
January 31, 2008 at 2:30 PM“Please don’t reproduce:
Its pretty simple. A harder problem for me to solve is how to kill people through the internet”
LOL!!! My co-workers are wondering what I’m laughing about. I AM NOT GOING TO TRY TO EXPLAIN IT TO THEM!!!
January 31, 2008 at 2:39 PMFor the people who still believe that the airplane won’t move forward, I have another question. I apologize in advance if this hurts you. (it might)
If your riding in a train traveling at 50mph and you jump up into the air, will you go flying backwards towards the rear of the train?
January 31, 2008 at 2:42 PMThought Experiment: a 100 ton plane is flying East at 100 mph, wheels spinning FORWARD at 100 mph one inch above a 1 mile long X 100 foot wide conveyor belt rotating West at 100 mph. The plane touches down, what happens?
No fly guys: by your definition, the plane will CEASE FORWARD MOVEMENT!!! THINK ABOUT THAT!!!!
Of course, what happens is the plane will land normally, with the wheels initially stopping on touchdown and gradually spinning up to 100 mph.
(neglecting the tiny amount of wheel friction)as the plane rolls to a normal stop.
Case CLOSED!!
Forgot to be specific on my hypo: at touchdown
the pilot cuts power and applies no braking.
Of course, the plane CANNOT just cease all
forward motion, it simply rolls to a normal
stop.
There IS an upper limit to the speed of this
thought experiment and we all know what it is.
But, I postulate, what if everything occurs at
the speed of DARKNESS, which is -c, where E
still equals mass times the velocity of (-c)
squared?
Prove this.
Show all work.
Begin now.
Thank you.
January 31, 2008 at 2:52 PMThere seems to be a major disconnect here between force and velocity, which of course is the basis of the myth. The myth I’ve always heard is “If a plane moves forward at speed, v, and the conveyor moves at speed ‘-v’, does the plane take off?”. The answer is, who cares about the velocity of the conveyor? Newton tells you to look at forces.
There is a forward force coming from the engines of the plane. There is a backward force coming from air resistance as the plane accelerates. And there is a backward force on the wheels of the plane. This force is dependent on whether or not the wheels of the plane are slipping and the relative velocity of the wheels to the conveyor. If the wheels don’t slip, and we ignore friction in the bearings, then you just have a constant static friction force, independent of conveyor velocity, opposing the engines. If the wheels slip, then the frictional force is some function of the relative velocity of the wheels to the conveyor. In principle, you could ramp the conveyor’s speed up so high that this force would completely oppose the plane’s thrust, but it’s pretty apparent that that won’t happen by simply matching the conveyor’s speed to the plane’s speed.
January 31, 2008 at 2:55 PMDaveM
You were doing so well, but … Your analogy with the car is precisely wrong, and is also precisely why some people have so much trouble with this. Plane wheels are free-spinning (if they weren’t they’d get ripped to shreds on the runway). Car wheels are driven (if they weren’t the car wouldn’t go anywhere).
The plane does not have to work harder to any significant extent to cope with the treadmill because the only backward force the treadmill can exert is via contact with the free-spinning wheels. It’s an awful lot easier to get a wheel to spin faster than it is to drag a plane backwards when it’s engines are at full thrust, so the treadmill just makes the wheels spin faster and has a negligible effect on the plane itself.
A car engine would have to work a lot harder to maintain a given speed if the conveyor is moving backwards but a plane engine does not. If your plane can only just manage to reach takeoff speed under normal circumstances, it will still take off from the conveyor.
January 31, 2008 at 2:57 PMI should add to my post one or two back that the forces in opposition to the thrust are in no way large enough to limit forward acceleration of the plane, unless, like I said, you run the conveyor at literally ludicrous speeds.
January 31, 2008 at 3:13 PMMy previous explanation was, in part, in error. The wind and aero part was correct. The wheel part wasn’t. As Jamie pointed out, the wheels aren’t being driven, so friction between them and the belt or the earth does not matter. They just allow the plane to roll, in fact, in a frictionless experiment they would allow the plane to remain stationary as the belt moved beneath it. The plane is in the air mass, so the propeller is able to accelerate it regardless of the moving belt beneath the plane, as long as the wheels aren’t blocked. If the propeller can accelerate the plane to the point where it achieves sufficient speed with respect to the surface of the earth and thus sufficient airflow over the wing, then the airplane will fly, regardless of how fast the belt is moving.
January 31, 2008 at 3:18 PMWow, there are some really stupid people out there who still believe that a conveyor belt moving backwards could stop a plane from accelerating. Sure if the plane used it’s wheels to gain speed it would never take off but that is what the big propeller on the front is for. I’m especially stunned to see actual pilot who can not figure this out. That this was ever questioned just makes me shake my head in wonder.
January 31, 2008 at 3:37 PMThe question is not “Will a stationary plane take off?” The question is “Will a plane on a conveyor belt, moving at the same speed as the plane in the opposite direction, take off?”
Imagine you’re holding a roller skate and you’re standing in front of a moving treadmill. You put the roller skate on the treadmill and move it forward with your hand. Magically the roller skate will move forward. Now replace the skate with a plane and your hand with the force of the propeller. The plane moves forward and takes off.
January 31, 2008 at 3:38 PMThe question proposed is only true because the plane is forced into the measuring in terms GROUND SPEED VELOCITY. However, planes measure WIND SPEED VELOCITY. The plane WILL take off if this is measured with both variables being ground speed velocity. However, if the conveyor belt adjusts itself to match the WIND SPEED VELOCITY (!!!assuming calculations to like terms!!!) of the plane, the plane gains no forward motion, therefore, will not gain the wind force it takes to push the plane up.
January 31, 2008 at 3:58 PMFlight is a result of air speed not ground speed. Anyone who has flown a Piper Cub in a heavy enough headwind and flown backwards knows that. This experiment was stupid because all the plane did was overcome the rolling resistance of the belt and thus had enough air speed to fly. If the belt was capable of keeping the airplane a 0 knots ground speed it would not have flown. It can’t do this because the plane is driven by the prop and there is no “connection” to the belt. You stay in place on a running treadmill because the moving belt is your method of traction and acceleration. Hook a prop to your back and you’ll suddenly shoot forward.
January 31, 2008 at 4:05 PMTry to think of it this way; say you have an infinitely long conveyor belt, more than wide enough for a plane to sit on, going backwards at the takeoff speed for a plane.
The plane sits in the middle, stationary, and the pilot stands beside it. They don’t have to worry about falling off because the belt doesn’t end.
The pilot gets in the plane, and looks at everything moving through the window. The conveyor belt seems stationary, with the rest of the view moving towards the horizon in front of them.
The pilot starts the engine, and the plane creeps forward, the rest of the world still moving towards the horizon quickly.
The plane moves forward faster and faster as the pilot increases speed, the wheels spinning twice as fast as they usually do, but the engine going the same takeoff speed.
The plane takes off, assuming the wheels are oiled well enough to not pop off of the landing struts going twice as fast as they usually do.
January 31, 2008 at 4:22 PMOh good god.
OK, first off you need to recognize that the original question was very poorly worded and there are two ways to read it, one is slightly different than the literal wording yet the other is absurdly impossible.
The way most people would read it is that if the plane starts with 1 mph groundspeed (not conveyor speed), the conveyor moves backwards at 1 mph. Or airspeed, almost the same thing. Let’s assume there’s no wind and they ARE the same thing. That situation is possible to create and this question has an answer.
But that’s not exactly the way the myth was worded. The myth said “the conveyor moves backwards at the wheel speed”. What?? If I’m moving forward at 1 mph and wirelessly hook the treadmill up to a speedometer tied to the wheel’s turning rate, first the treadmill jumps to 1 mph backwards to match my speedometer. Well, I’m moving along at 1mph and the tread’s moving backwards at 1 mph so my speedometer reads 2 mph and the treadmill must be accelerating backwards at 2 mph… essentially it is impossible to literally meet the condition that “tread speed matches wheel speed”. If you were moving forward at even 1 foot per second the treadmill would have to be going infinitely fast, the speed of sound or speed of light doesn’t meet that condition! Not only is it impossible to actually build one, it is theoretically impossible to have an instantaneous infinite-speed device.
So given that the second interpretation creates impossible and essentially meaningless conditions, and the original question never got into “the treadmill can move infinitely fast and the bearings and tires can take any speed without exploding”, I don’t think this was ever the intent of the question and people are reading too much into it and going off on a tangent unrelated to the original question.
January 31, 2008 at 4:25 PMWell the results speak for themselves and in the spirit of the myth that was tested you can’t really dispute it. One thing that intrigues me is what happens if you accelerate the conveyor to a speed greater than the planes take off speed. Will this speed just increase until the planes wheels fall off trying to overcome the backwards momentum of the conveyor in order to reach the 25mph need to lift off? 25mph backwards + 25mph forwards means that the faster that conveyor moves in the opposite direction the faster those wheels have to be spinning to get it off the ground correct? Not saying this will keep it from flying but to see what would happen could be interesting.
January 31, 2008 at 4:57 PMYour previous post was, in TOTAL, completely in error. Nice resume, but my high schooler (in his first physics class now) knew the answer to this one off the top of his head. Being able to steer a plane doesn’t automatically give you commone sense.
January 31, 2008 at 5:10 PMThis is simple.
Replace “wheels” with “blades”
Replace “conveyor” with “moving block of ice”
Can the plane take off?
Of course it bloody can.
I really am horrified at the number of naysayers persisting in the face of such overwhelming evidence. It’s truly scary.
January 31, 2008 at 5:11 PMAleks (and anyone else who would like to repeat the experiment with the treadmill moving exactly as fast as the plane moves forward while stationary).
Go to an airport. Look at the planes parked at the gates. There’s your experiment. The plane can’t move forward if it is stationary, brainiac. Therefore, the treadmill never has to go backwards. Therefore you may as well leave out the treadmill. Take some aspirin. The headache will hurt.
January 31, 2008 at 5:21 PMIT MATTERS NOT, ITS GONNA TAKE OFF. I PROCLAIM THIS.
January 31, 2008 at 5:34 PMQuestion. If you tie the tail of any plane to a pole, fire that mother up and pull back on the stick… Will it fly???
January 31, 2008 at 6:03 PMI agree with early posts…this was the WORST experiment Adam & Jamie have ever put together. I generally give them high marks for doing things “scientifically”…not this time. There was some really bad science on that show last night.
And the correct answer is “No. The plane will not take off if it’s velocity is equal (but opposite) to the treadmill’s velocity.”
January 31, 2008 at 6:15 PMThis is the biggest case of internet spackerdom in the entire history of nerds talking crap on t’internet!
OF COURSE IT WILL TAKE OFF YOU GRADE A RETARDS!!!
January 31, 2008 at 6:30 PMIf the object is to see if the plane will fly with no forward motion, why not take the wheels off and ramp up the engine and see what happens. The treadmill is supposed to keep the plane stationary so that the forward motion caused by the propellars pull is matched by the reverse motion of the treadmill on the wheels. If you take the wheels off would the plane take off? It doesn’t matter how hard you push the engine with no forward motion I don’t believe you are going to receive the airflow under the wings. Maybe I misunderstood the myth but i thought the original suggestion was to have the plane stay in a stationary position to see if the engines thrust could pull enough air under the wings to allow for lift the treadmill was used to keep the wheels from assisting with forward motion. Would that not be the same as taking the wheels off the plane?
January 31, 2008 at 6:31 PMAlmost everyone first thinks. The plane doesn’t move forward therefore does not take off.
Then most people eventually say, “Hey, the conveyor can’t stop the plane from moving forward. The question tricked me.”
My question to the “no” people is, why don’t you join the majority and realize the conveyor can’t stop the plane.
January 31, 2008 at 7:06 PMSorry aviators, MythBusters got it right and yes, I studied aerodynamics – Bernoulli’s principle, etc.
A treadmill, simulated or otherwise, will *never* be able to “cancel” out the forward thrust of an aircraft prop/turbine/fan by going in the opposite direction no matter what the opposite speed – the aircraft just moves forward as usual but spins it’s wheels twice as fast. The prop/turbine/fan doesn’t care how fast the wheels are spinning as it creates the forward thrust needed to get airflowing over the wings.
January 31, 2008 at 7:07 PMIt’s simple. People don’t understand that wheels are meant only to reduce friction between the belly of the plane and the ground. Think of them as bearings. When a plane’s engine is throttled up, the blades of the prop pushes air rearward and the air exerts a forward pressure on the plane. This deals with Newton’s 3rd law. The low friction created by the wheels allows the plane to “push” its way through the air.
January 31, 2008 at 7:08 PMHere’s a good example…
Think of a toy car with very low friction wheels, and a conveyor belt. You hold the car on the belt with the end of your finger, and wind the belt up so it spins at lets say 20mph. Now does anybody think you will need to apply a forward force with your finger hard enough to generate 20mph of thrust? That would be like pushing thrusting your whole arm and really pushing against the little toy car. Does that sound realistic? No it doesn’t and you won’t need to. You’ll be able to just touch the car and it won’t move an inch. No matter how fast you spin the belt, you will still only need to maintain a tiny touch on the car (as there is a small amount of friction on the wheels to overcome).
Now what if you wanted to push the toy car forward? You’ll only need to gently start pushing it forward and it will move very very easily.
EXACTLY the same principle except the car is the plane and your finger is the engines.
If you don’t believe it go try – I challenge anybody to NOT be able to hold a toy car on a relatively frictionless treadmill with just their little finger. It would require hardly any force to push it forward, and you could EASILY accelerate it off the end of the conveyor with little effort – certainly not 50+mph worth.
January 31, 2008 at 7:28 PMHey smart one; why don’t you try WATCHING THE WHOLE YOUTUBE? ZOMG!!!!! It explains why frictional losses through wheels are negligible. The guy holds steady throttle while increasing speed to three times previous speed and the plane still stays in one spot. Adding minimal throttle let it overtake the treadmill.
THIS PROVES YOUR POINT AND EVERYBODY ELSE’S.
FREE SPINNING WHEELS? DO YOU UNDERSTAND THEM?
January 31, 2008 at 7:37 PMWow there are still people and pilots saying this is not possible…..
How sad. Busted this in highschool. If I was a pilot no way in hell would I say or admit that the plane would not fly. I dont care how many years as a pilot you have you will not prove this wrong. The plane will take off.
The question itself was designed to throw people off and confuse. That is where the naysayers are getting hung up first, second it thinking the wheels have something to do with it……
January 31, 2008 at 8:12 PMThis explains it well also:
“The plane is not magically levitating while standing still. It is moving forwards as usual, and ignoring what the ground underneath it is doing. Which is the entire point of having a plane, really.”
Now if the treadmill was going at CRAZY high speed eventually the plane may look down and say “wow thats actually a lot of friction, I’m going to struggle here.”
But really, lets say the treadmill was going twice as fast as the plane’s normal take off speed. It would just get down that treadmill about 1% slower than normal due to (very low) friction.
…and then take off over the heads of some very stupid people.
January 31, 2008 at 8:24 PMFlawed test. Imagine doing this in your car on a treadmill moving 100 miles per hour. You accelerate to match the speed & show 100 mph on your speedometer. Now stick your head out the window. Feel any air movement? NO… Its the AIR over the WINGS that creates lift needed to fly. The speed of the tires makes no difference.
Bob Walden
January 31, 2008 at 8:44 PMUSAF Test Pilot, Class 84B
Edwards AFB, CA
OK… Maybe we’re talking apples and oranges here. My initial impression was that (like a stationary treadmill) that the airplane remains stationary RELATIVE to the air around it while the treadmill moves rapidly underneath. In this case, NO, the airplane will not fly. However… if the treadmill is LONG enough & the airplane is allowed to accelerate RELATIVE to the air around it, YES it will take off… at its normal AIRspeed in the same AIR distance it normally uses. The speed of the conveyor belt/tires isn’t relevant at all.
The confusion here is correctly stating the motion constraints of the treadmill problem: Is it a STATIONARY treadmill problem, or am I allowed to OUTRUN the speed of the treadmill? Both sides are arguing using different assumptions. It makes big difference.
Bob Walden
January 31, 2008 at 9:05 PMUSAF Test Pilot, Class 84B
Edwards AFB, CA
Idiots still cannot overcome the hurdle of thinking a plane is a car. A car is what these idiots see everyday. Gas pedal on car, car moves forward, car moves.
A plane’s wheels does absolutely nothing except provide support to make the aircraft stay upright, and the brakes.
I can probably hold a plane stationary while standing on a platform even if the treadmill is going 300mph.
The thrust is what makes the plane move, and it’s acting against upon the surrounding air, get over the wheels planes don’t need wheels to provide forward motion. It’s not a car.
Waldo, are you really a USAF Test Pilot? Please stop flying aeroplanes, for the sake of everybody elses safety.
January 31, 2008 at 9:09 PMMr. test pilot, what generates the force to proper the airplane, the wheels or the prop/jet engine?
January 31, 2008 at 9:09 PMLook guys, if the plane needs to move 60mph to takeoff, and the treadmill is going 100mph, the plane only needs a slight amount of throttle to stay in place — just enough to overcome the friction of the undercarriage (i.e. wheels, bearings, axle, etc.). If only that amount of thrust is applied, the plane stays in place relative to the ground, produces no lift and it won’t fly.
But that thrust is only a small amount of what the plane actually produces. When full thrust is applied, the plane begins to move forward in relation to the ground. When it reaches 60mph relative to the ground, it lifts off.
NO ONE is saying that a plane that is stationary relative to the ground can take off. The key is that the treadmill doesn’t have the ability to make the plane stay stationary, and so, as the boys showed, it takes off.
January 31, 2008 at 9:23 PMEveryone, I am a physicist. Trust me when I say the plane can take off. You could have the treadmill going twice as fast the plane will still take off. Unless the breaks are on the wheels don’t apply any force to the plane.
January 31, 2008 at 9:41 PMwell you misspelled brakes. lol
but I agree.
January 31, 2008 at 10:04 PMI know it is hard to see, but do the naysayers even understand that what they are “arguing” is that a plane that is motionless cannot take off? Yeah… a plane that doesn’t move can’t take off. But, the conveyor belt, no matter how much you try to imagine it, cannot keep the plane still. And the naysayers keep saying, “But what if they adjusted the experiment so the plane can’t move?” In other words, the naysayers are basically asking, “what if you just turned off the engine or chained the plane to the conveyor belt? Can it take off then?”
February 1, 2008 at 12:04 AMthe treadmill is completely irrelevant, the treadmill only interfaces with the plane wheels, the plane’s wheels and whatever goes on down there has nothing to do with if the plane flies. The plane is connected to the AIR via the PROPELLER and the GROUND has nothing to do with the event. The GROUND and AIR are two different frames of reference as far as the plane is concerned. Nothing has to be overpowered, no propeller blows air over wings to create lift, what a planes wheels do on the ground, if the ground is moving or not, has nothing to do with what the planes wings and propeller do in the air. The ground does not dictate the air/wing interface, the propeller, or thrust source, does.
February 1, 2008 at 1:13 AMJeff:
Look guys, if the plane needs to move 60mph to takeoff, and the treadmill is going 100mph, the plane only needs a slight amount of throttle to stay in place — just enough to overcome the friction of the undercarriage (i.e. wheels, bearings, axle, etc.). If only that amount of thrust is applied, the plane stays in place relative to the ground, produces no lift and it won’t fly.
But that thrust is only a small amount of what the plane actually produces. When full thrust is applied, the plane begins to move forward in relation to the ground. When it reaches 60mph relative to the ground, it lifts off.
NO ONE is saying that a plane that is stationary relative to the ground can take off. The key is that the treadmill doesn’t have the ability to make the plane stay stationary, and so, as the boys showed, it takes off.
all that is completely false. a plane does not need any motion relative to the ground to fly and a stationary plane relative to the ground will lift if sufficient air is provided over the wings by some means. Perhaps a few discussions with some plane owners in Florida after hurricane something will clear that up. An airplane, prop driven is an airfoil concern, there are two, the prop and the wings, both of which connect with air, not the ground, not the wheels.
February 1, 2008 at 1:27 AMI thought the whole point to the experiment was to have it so that the velocity of the treadmill going backwards and velocity of the plane going forward were to equal, so in the end the plane would not be moving forward relative to it’s starting position and effectively stationary. So how does a plane, that is already using all it’s engine thrust to keep up with the treadmill (unable to increase its acceleration and therefore travelling at constant velocity), still at its starting position and unable to gain distance or forward motion get enough air to lift the plane?
Picture this. If you run on a treadmill that is set at it’s maximum speed, and you are running fast enough to match it’s speed, do you feel the air against you? If you could take it further, and used a bicycle on the treadmill, both going as hard as possible, but relative to the ground, you are stationary. Do you feel the air against you then? Of course not.
Of course, it would take a pretty special treadmill to be able to match a plane’s velocity, so i don’t think it’s even possible to test this.
February 1, 2008 at 1:57 AMYou thought the whole point of the experiment was to set it up so the plane is not moving at all? Hell, you can stare at a plane that isn’t moving at all in any airplane hanger.
February 1, 2008 at 2:51 AMThe confusion here is in the defining of the situation. We need to define velocities relative to specific objects (e.g. the ground – inertial, the conveyor belt, and the plane).
First of all, planes measure velocity using a Pitot tube or some variation. This results in the AIR SPEED being measured, as opposed to the GROUND SPEED. So if the pilot sees that he is going 25 mph, this is relative to the air.
So in the Mythbusters’ version, the conveyor belt was moving at 25 mph (relative to the ground, of course). So they determined to have the pilot match this, and go 25 mph in the opposite direction. This was not 25 mph relative to the ground, but relative to the air. It seems that the conveyor belt probably doesn’t “move” much air with it (the boundary layer could be calculated, but it probably wouldn’t reach the height of the wings of the plane). Therefore, in order for the plane to reach a 25 mph AIR SPEED, it must be moving 50 mph relative to the CONVEYOR BELT and 25 mph relative to the GROUND.
So, if it is moving at 25 mph relative to the ground (or air, in this case), it is at its take-off speed, and will take-off.
BUT, if I understand the spirit of this myth, a different situation would need to be looked at. What if the conveyor belt was, as in the last example, moving 25 mph relative to the GROUND, and the plane was moving the opposite direction 25 mph relative to the CONVEYOR BELT? This means that the plane has 0 velocity relative to the GROUND. And, as we’ve established, the conveyor belt doesn’t “pull” much air with it. So the plane’s pilot is reading approximately 0 AIR SPEED (depending on the location of the pitot tube, since the props would be moving some air… but a significant amount of air shouldn’t be moving over the wings). Since the wings need moving air to generate lift (L = Coefficientoflift*0.5*density*velocity^2*span), the plane will not take off.
I don’t know which situation is being debated here, but it seems many people are mixing them up. I watched the episode, and I wasn’t satisfied that they didn’t attempt the second scenario (although it seems they may have missed the concept), since I think that is the true spirit of this myth.
February 1, 2008 at 3:25 AMSorry, I forgot to name myself, so now replies can be directed to me if you want.
This is my comment from above: _________________________________________
The confusion here is in the defining of the situation. We need to define velocities relative to specific objects (e.g. the ground – inertial, the conveyor belt, and the plane).
First of all, planes measure velocity using a Pitot tube or some variation. This results in the AIR SPEED being measured, as opposed to the GROUND SPEED. So if the pilot sees that he is going 25 mph, this is relative to the air.
So in the Mythbusters’ version, the conveyor belt was moving at 25 mph (relative to the ground, of course). So they determined to have the pilot match this, and go 25 mph in the opposite direction. This was not 25 mph relative to the ground, but relative to the air. It seems that the conveyor belt probably doesn’t “move” much air with it (the boundary layer could be calculated, but it probably wouldn’t reach the height of the wings of the plane). Therefore, in order for the plane to reach a 25 mph AIR SPEED, it must be moving 50 mph relative to the CONVEYOR BELT and 25 mph relative to the GROUND.
So, if it is moving at 25 mph relative to the ground (or air, in this case), it is at its take-off speed, and will take-off.
BUT, if I understand the spirit of this myth, a different situation would need to be looked at. What if the conveyor belt was, as in the last example, moving 25 mph relative to the GROUND, and the plane was moving the opposite direction 25 mph relative to the CONVEYOR BELT? This means that the plane has 0 velocity relative to the GROUND. And, as we’ve established, the conveyor belt doesn’t “pull” much air with it. So the plane’s pilot is reading approximately 0 AIR SPEED (depending on the location of the pitot tube, since the props would be moving some air… but a significant amount of air shouldn’t be moving over the wings). Since the wings need moving air to generate lift (L = Coefficientoflift*0.5*density*velocity^2*span), the plane will not take off.
I don’t know which situation is being debated here, but it seems many people are mixing them up. I watched the episode, and I wasn’t satisfied that they didn’t attempt the second scenario (although it seems they may have missed the concept), since I think that is the true spirit of this myth.
February 1, 2008 at 4:53 AMgood god men! grow a brain! a treadmill/conveyor belt whatever cannot hold a plane stationary! it will always move! that is the whole point of the puzzle/riddle
February 1, 2008 at 6:16 AMHow do planes take off from aircraft carriers ?
February 1, 2008 at 7:46 AMWOW, with the stupidity of some people it really is quite impressive the human race ever made it out of the swamps!
There is only one question that needs to be considered. Can a conveyor belt prevent forward movement of a freewheeling vehicle. The answer in its basic form is NO. As Hugo says there is NOTHING that the conveyor can do to prevent the forward momentum of the aircraft, as the thrust the aircraft produces acts on the air around it, not the belt.
The only net effect of the conveyor is it slightly increases the friction in the wheels, as the wheels will have twice the angular velocity at take off speed than from a normal runway.
It’s nothing more than a test to see if you can visualise the difference between a driven wheel and a freewheeler.
February 1, 2008 at 7:52 AM“What if the conveyor belt was, as in the last example, moving 25 mph relative to the GROUND, and the plane was moving the opposite direction 25 mph relative to the CONVEYOR BELT? This means that the plane has 0 velocity relative to the GROUND.”
Yes, but this would happen with very very little or no power applied to the plane, as just the wheels spinning would be enough to create that opposite velocity relative to the conveyor. Of course it wouldn’t take off because the engines would be barely switched on. Your second test is the same as sticking an aircraft on a runway with the engines turned off and testing if it will fly. Shockingly enough it won’t – hardly needs mythbusters to test that one.
February 1, 2008 at 8:02 AMI cant believe that there are people trying to argue that the plane would not take off. Partucularly the person who’s name implies they are a science teacher. For the love of your country, please stop teaching.
February 1, 2008 at 8:22 AMAs for the “test pilot” comparing a car with a plane in relation to this. Seriously, you wouldn’t fly drunk. So stop posting when drunk.
Fizzycyst, in answer to your question,
“How do planes take off from aircraft carriers ?”
With a steam catapult, plus the speed of the ship is less than that of the plane.
Also, planes generally take off in the same direction of travel as the aircraft carrier so it’s not quite the same thing.
A plane will always be able to take off from a conveyor belt though, and I assume you support that theory.
Anyone who says the plane won’t take off is a spasticated mongoloid!
February 1, 2008 at 9:48 AMI think the problem stems from the model of the experiment. the plane simply needs to be moving forward relative to the air to create the pressure difference needed to overcome gravity. so you can take off from a conveyor belt but it would be exactly the same length as a runway.
February 1, 2008 at 10:05 AMI’m not sure how the speedometer of a plane works and i think this is where the confusion is in this particular model.
Why does a plane need a runway then? Why not chain the plane from the rear and see if it can lift?
February 1, 2008 at 10:30 AMexcellent idea billy bob putting it that way makes it pretty obvious what would happen too but i might try it next time i’m down my granddads hes got a few model airplanes.
February 1, 2008 at 10:33 AMThis “experiment” wouldn’t pass the standards of a High School Physics class!
February 1, 2008 at 10:35 AMBilly Bob…”Why does a plane need a runway then? Why not chain the plane from the rear and see if it can lift?”
What’s that got to do with anything? It’s not suggested that the conveyor could be any shorter than a normal runway, of course a plane cant take off if you chain it so it cant move! The entire point is that the conveyor cannot stop the aircraft moving forward.
What am I doing?! This is worse than trying to explain algebra to a 3 year old.
February 1, 2008 at 10:39 AM“Roger:
Billy Bob…”Why does a plane need a runway then? Why not chain the plane from the rear and see if it can lift?”
What’s that got to do with anything? It’s not suggested that the conveyor could be any shorter than a normal runway, of course a plane cant take off if you chain it so it cant move! The entire point is that the conveyor cannot stop the aircraft moving forward.
What am I doing?! This is worse than trying to explain algebra to a 3 year old.”
I think you are missing the point as the principle of the conveyour is for the plane to remain physically stationary, if that is not the point, then what is the point?… If all it takes is air over wings, use long chains to hold a physically stationary position and let the props create the needed lift over the wings, Einstein…
February 1, 2008 at 10:50 AM“I think you are missing the point as the principle of the conveyour is for the plane to remain physically stationary, if that is not the point, then what is the point?… If all it takes is air over wings, use long chains to hold a physically stationary position and let the props create the needed lift over the wings, Einstein…”
Everyone knows an aircraft held stationary can’t take off, if that were the intention of the question you would be correct, it would be UTTERLY pointless. Your proposition would only apply to a particular type of aircraft, i.e. propped forward of wing. Yes their are aircraft that can take off purely from propwash over the wings but again that is limiting the answer to a particular aircraft.
The real point is extremely simple – does an aircraft’s thrust act through the wheels, or on the air. That’s all the question is asking. Yes, it’s remarkably simple. No their is no point to it – other than to catch people out who can’t grasp the simple concept that as the thrust acts on the air surrounding it, and the wheels are freewheeling, the conveyor belt CANNOT influence the position of the aircraft relative to the ground. That is it.
February 1, 2008 at 11:04 AMI think it’s worth noting for everybody here (as it often comes up in this discussion) that kinetic friction does not change significantly for different velocities. So no matter how fast the wheels turn, there’s no difference in the frictional force acting against them. Unless they go so fast that the bearings weld or something. But come on. That’s just silly.
February 1, 2008 at 12:12 PMWhoever said that the engine creates thrust to lift the wings is wrong. The engine creates thrust to pull the airplane, then the velocity of the MOVING air under/over the wings creates the lift, NOT THE THRUST. This myth can’t be applied to all aircraft and be accurate either. What about aircraft that have their engines mounted on the bottom of the wings, or the aft part of the fuselage… they aren’t going to create any lift under the wings. Their thrust is projected behind the wings. I don’t believe if I was standing at the wing tip of a 737 or a Learjet or even a little 172 while the wheels were on a conveyor belt, and me standing on solid ground with their engines full throttle… wheels turning… but that wingtip staying in my relative position that it would take off. BULL. Picture it in your head…. if you see an airplane taking off… put down the crack pipe.
February 1, 2008 at 12:33 PMi don’t think me or billy bob were suggesting the plane would take off of course its silly but it would end this shorter runway myth once and for all.
What the myth busters proved was the entire concept is pretty stupid as a conveyor belt makes no or little difference to a plane anyway. chaining a plane would would end the last myth that a plane can take off stationary relative to the air.
February 1, 2008 at 12:39 PMso just once more then Christ… what exactly is stopping the aircraft moving forward to gain airflow over the wings? In your “picture” have you also attached chains to it to prevent it simply powering along the conveyor? Or have you possibly just made the basic mistake of thinking too much about airflow over surfaces and not considered that there is no way a moving surface can act on an axle via a free-wheeling wheel?
February 1, 2008 at 12:46 PMSteve – what shorter runway myth? There is no shorter runway myth, just a runway that can move in the opposite direction to the aircraft. The fact that the conveyor makes little or no difference IS the point of the question FFS!
February 1, 2008 at 12:48 PMIm sorry I did’nt know I also needed to tell you that the conveyer belt was spinning beneath the wheels. I figured if I said the airplane was sitting on a converyer you would assume it was going to be there to counter act the airplane from moving foward. I’ll explain things on a lower level for you next time.
February 1, 2008 at 1:10 PMRoger- Is that why they have long runways? So they can get the wheels to spin really fast? Free spinning wheels don’t mean as much as you think it does.
February 1, 2008 at 1:18 PMRoger- Look up a picture of a Learjet and tell me if you think it will takeoff under the conditions I explained earlier.
February 1, 2008 at 1:20 PMYes or NO
Thanks Christ, appreciate you taking the time to explain that. Could you use your infinite wisdom just a tad further to explain how the spinning belt manages to apply force against a free-wheeling axle to prevent it moving forwards?
(let me give you a clue – any answer that doesn’t include “oh yeah, it cant, I didn’t think of that” is incorrect)
If you need proof of this, place a toy car (one with wheels that can spin freely) onto a piece of paper, and push the car forward with your finger – now pull the paper in the opposite direction. If I’m wrong, you’ll not be able to push the car forwards, or you’ll break your finger. (clue: you wont break your finger)
February 1, 2008 at 1:21 PMand to your additional comment – I can’t tell if a lear jet can take off, simply because you’re original comment makes no sense. The aircraft wouldn’t stay stationary compared to the ground, because there is nothing to prevent it moving – once more, the conveyor CANNOT PREVENT THE AIRCRAFT MOVING.
Free wheel is EVERYTHING. A surface cannot prevent an axle moving forward if it’s only method of contact is via a free-wheel.
February 1, 2008 at 1:24 PMRoger- It all just clicked. I was wrong, I admit it. The free spinning wheels is everything. The only difference is the wheels are going to be spinning twice as fast than if it was taking off on a runway.
February 1, 2008 at 1:50 PMAs a pilot I’m surprised at the crazy comments here. First, the wheels always spin free unless you hold the brakes so they did not do anything to restrict the wheels. Second, I think they did a good job of explaining that the speed of the wheels has *NOTHING* to do with a plane taking off. Now, I guess if you tied the plane to a treadmill it would be a different story but that’s not the myth.
February 1, 2008 at 1:57 PM-Robert (I’m going flying today)
:-) Yep, you got it!
Takes a man to admit that – good on you.
February 1, 2008 at 1:58 PMNoFlys, this is the myth: “An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
It is not even remotely implied that the plane remains stationary.
February 1, 2008 at 1:59 PMIf you want to reduce or extend the amount of runway a plane uses you don’t move the runway under the wheels, you change the wind. A plane takes more distance to take off with a tailwind and less with a headwind. That is why we always take off into the wind when the wind is more than about 6 knots. Forget the surface the plane is on, its all about the air.
February 1, 2008 at 2:02 PM“the conveyor CANNOT PREVENT THE AIRCRAFT MOVING”
That’s not quite true. There is some frictional force. So at some very low level of thrust, the plane would remain stationary. Mythbusters should have show the plane 1) moving backward (ie, before it started thrusting), 2) in a steady state (ie, forward thrust = frictional force) and 3) moving forward. And shown the different thrust levels to see how negligible the frictional force truly is.
February 1, 2008 at 2:03 PMBTW: It should be noted that the pilot they “hired” is an ultralight pilot and therefor likely not an FAA certified pilot who has gone through formal pilot training. In addition, if they did pay him to fly he would require a commercial pilot’s certifiate and a commercial medical if he wants to stay out of trouble with the FAA. Avoiding the FAA is what those ultralight guys are trying to do by keeping their planes light.
February 1, 2008 at 2:03 PM“That’s not quite true. There is some frictional force. So at some very low level of thrust, the plane would remain stationary. Mythbusters should have show the plane 1) moving backward (ie, before it started thrusting), 2) in a steady state (ie, forward thrust = frictional force) and 3) moving forward. And shown the different thrust levels to see how negligible the frictional force truly is.”
Indeed – I didn’t want to confuse matters though as it is so negligible.
February 1, 2008 at 2:34 PMI didn’t read all the posts but I agree with Roger and pwb – MythBusters should have shown more. I get the physics involved. My main objection is how the term ’speed’ is used. I think they confused the issue because it isn’t clear what the reference point of the plane’s speed is. It would have been better to set up the myth with something like, “Given an engine thrust that lifts a plane into the air on a runway, how much additional thrust is needed to lift the plane if the plane is on a conveyor belt moving in a backwards direction?”
Many people, in my opinion, interpret the phrase “forward speed equal to backward speed” to mean a state in which the plane remain stationary in reference to someone standing next to, not on, the belt. So it confuses the point of this myth (that the propeller pull is independent of the belt’s speed) and people think something is wrong with the test if the plane moves forward.
February 1, 2008 at 3:44 PMEverybody who thinks it won’t take off! I thought that too, then it all clicked about an hour ago. Take a toy car, tie a string to the front of it, then take it to a grocery store and put on their belt you put your grocerys on. Then hold on to the string and let the wheels start rolling the pull the string and the car will come to you, the wheels just spin faster. The propellor is the string for the airplane and the only thing that changes is the damb wheels are gonna spinning faster and little bit more friction on the bearings. That conveyer belt will not stop that plane from going forward. Just think if the plane was sitting on the conveyer belt with its breaks off, and in one split second the conveyer belt started spinning a 500MPH… do you think the plane is gonna plummet backward at 500MPH instantly. No, those wheels are going to start spinning instantly. Im not saying it will stay in the exact spot with out any thrust. Like I said the the Thrust of the propellor will pull it and the only thing it needs to over come is the friction of the wheel bearings.
February 1, 2008 at 3:49 PMYou know, if people can’t understand the question then they certainly can’t get the correct answer…!!!
February 1, 2008 at 4:50 PMVery poor test and no comparison. The original question was about a JET a/c and a conveyor belt moving in the OPPOSITE DIRECTION OF THE WHEELS AND AT THE SAME SPEED as the wheels were turning.
That completely changes the dynamic.
First: to have the conveyor belt move at the same speed as the wheels, the conveyor belt has to have a motor or the belt speed will be slightly less than the wheel speed. That means pure thrust will eventually overtake the neutralizing effect of the conveyor belt. Pulling a tarp under an A/C is absolutely ridiculous. Second: the difference between a jet and a prop A/C is the relative airflow over the wings while sitting on the ground (or a conveyor belt). A prop may still be able to take off because it does create some relative airflow over the wings, but a jet in afterburner creates NO airflow over the wings while sitting on the ground until it MOVES the plane down the runway, and in doing that it causes wheel rotation. A turning wheel on a hard surface indicates that whatever the wheels are attached to is moving.
So the plane sits on a moving belt that perfectly matches the planes wheels and the belt is moving in the opposite direction as the planes wheels. Does the plane move forward? No. Is lift created? No. Why? Because the friction/resistance necessary between the wheels and the belt isn’t there!! The reverse action of the belt to the wheels neutralizes forward movement. Free spinning wheels don’t make a difference; they still have to move the A/C forward. If they can’t do that…the plane can’t create lift.
Okay, what about thrust? Thrust is a force that creates movement by acting against another object or force. In this case the weight of the A/C is that object(including the engine component). However, that force (or thrust) is neutralized when the point at which it is supposed to begin to move an object forward (in this case)cannot provide resistance. This is, of course, relative to a gravity based environment. The conveyor belt is negating the effect of thrust by providing an opposite force to the thrust.
With the wheels bearing the weight of the A/C and those wheels sitting on a matching speed conveyor belt resistance is marginalized.
No lift. No flight.
Do some more homework, gang.
I’m also a pilot. Those of you claiming to be pilots and still insisting that the plane shouldn’t be able to take off, need to go back to school. You would only be right if the wheels were responsible for accelerating the plane to flying speed. About the only scenario I can think of where the plane wouldn’t take off would be using Molt Taylor’s Aerocar with the wheel power engaged instead of the propellor.
February 1, 2008 at 4:57 PMIf you want the plane not to take off, you don’t use a conveyor, you use brakes.
February 1, 2008 at 7:00 PMAn airplane or jet sits on a treadmill that is causing the wheels to rotate in a forward direction at the aircraft’s takeoff speed. The pilot will have to apply approximately 20% power (just a guess, exact value is not important) to stay stationary in relation to the ground. There is no forward airspeed, no air friction, no drag other than a small amount of friction at wheel bearings. The plane does NOT fly. The pilot advances the power from 20% to 100% and the plane starts to move forward eventualy reaching takeoff speed and DOES fly.
February 1, 2008 at 7:40 PMFull power, minus power required to keep plane stationary, equals remaining power usable for flight.
Do not tell me that it would take 100% power just to remain stationary on a treadmill. This number would be more like 3% in reality.
this scenario presents two physical relationships
the plane to the ground
the plane to the air
the plane is connected to the air via a rope that is off the conveyor belt, this connection is called the prop in this case, the prop winds up the rope air moves over the wings, lift occurs
the ground relationship is ancillary, the plane does not need to move relative to the ground, its connected to the air via a prop/rope, it does not need the ground at all really, but the ground is a convenient platform to engage the relationship between the plane and the rope/propeller
i’m a little shocked at some of these responses, I guess I assumed that people interested in mythbusters acually had some sort of science education, now I think many of them just wish they had, this dilemma is very rudamentary from a physics perspective and the test is very unnecessary.
February 1, 2008 at 10:46 PMI am stunned.
I must admit that at the beginning of the show when posed with the myth, I hastily concluded that the plane would “sit still” on the conveyor in relation to the ground. BUT I WAS WRONG. And anyone who thinks that is wrong.
Did you guys who think the plane would not take off even see the show? Did you see the car on the treadmill? A car has wheels that are connected directly to the engine via the axel and driveshaft. The wheels of a car can only spin as fast as the engine does.
The wheels of a plane are free spinning. If you accelerate the treadmill backwards at the same time as powering up the plane, the plane will simply move forward as normal. The only difference is that the tires will be moving twice as fast on the treadmill than if they were on the tarmack.
The treadmill has no impact on the propeller’s ability to create thrust.
February 1, 2008 at 11:38 PMThink of the following:
How about landing on a conveyor belt?
If you are landing at say, 50MPH, and the conveyor was gowing the opposite direction to your plane, what would happen to the planes wheels as they touched down?
Would the plane stop violently and immediately?
Of course not! At the moment of impact, the tires would accelerate, with a little cloud of smoke, to 100MPH. The plane would continue moving forward because it has momentum. It would only slow down by powering down its engine and applying the brakes.
Get it??
February 1, 2008 at 11:44 PMFor those of you who think that the treadmill exerts the same force on the plane as if it were chained to a pole, you are truly morons.
February 1, 2008 at 11:48 PMThere are 2 questions that people here are getting confused:
1. Can an airplane take off if it doesn’t move?
2. Can a conveyor belt keep an airplane from moving?
Answers for the “will not take-off” group:
1. NO
2. YES
Answers for the “will take-off” group:
1. NO
2. NO
Since we all agree that a stationary airplane can not take off, let’s get rid of that question.
So, can a conveyor belt keep an airplane from moving forward?
First, let’s get the car idea out of our head. If a car is on a conveyor belt and the belt starts to move backwards at 50mph, then the car will move backwards at 50mph. [Let's assume all speeds are relative to a bystander.] That is true if the car is in Park or has the brakes applied. What if the car is in neutral? It will still move backwards, but at a slower speed. The backward motion will be produced by the friction of the wheel bearings. Since an airplane doesn’t have motors attached to the wheels, it will act similar to a car is that respect. So, can a car move forward in neutral? No, not on flat ground or a backward moving conveyor belt. An airplane is a car in neutral, but with something extra. It has propellors or jet engines, which I’ll just group together as engines. Since we all agree that the airplane will not fly if it doesn’t move, let’s assume this scenario is taking place:
An airplane is sitting still on a conveyor belt that is moving backwards at 50mph.
The airplane’s wheels are also spinning at 50mph, since it isn’t moving. BUT, the engines are not using the same amount of power as they would to push the airplane at 50mph! Why not? They only need to overcome the friction of the wheels. Remember, the plane’s wheels are in neutral. Ok, now let’s say the engines start producing more power. Will the airplane then move forward? Of course. If it is producing enough to keep it still, then produces more, it has to move forward.
Now here’s the catch: the “will not take-off” group will say, “make the conveyor move faster backwards to counteract the extra power of the engines”.
Ok, you can try. But remember, the only force the engines have to overcome is friction. Increasing a small amount will not make a difference. The engines are not pushing against the conveyor belt. They will still be able to overcome friction and move the airplane forward fast enough to make it takeoff.
February 2, 2008 at 12:41 AMDavid said “a conveyor belt moving in the OPPOSITE DIRECTION OF THE WHEELS AND AT THE SAME SPEED as the wheels were turning.”
the question has only ever said that when people have changed it to justify their belief that the plane can’t take off. There is however a major problem with that version of the question – it is an unobtainable paradox. The wheels can never turn, the conveyor can never move, because to do so would require forward movement of the plane – Either nothing moves (in which case the conveyor cannot match the speed of the wheel, terms of statement broken) or the plane moves forward – in which case the conveyor cannot match the speed of the wheel as to achieve forward momentum the speed of the wheel will be twice the speed of the conveyor – terms of the statement broken.
February 2, 2008 at 5:48 AMTherefore the terms of the statement cannot be met in the first place (hence why it was never stated that way)
I really saw the myth as, if wheel speed matches treadmill speed, so that the plane remains motionless, will the plane take off, and the obvious answer is no. In the show, the airplane had to reach the same distance with or without the belt to take off.
It really shows how they didn’t go about showing the concept they were trying to explain. Either way seems really obvious to me, though. How can that interest people? I enjoyed the lead balloon more.
February 2, 2008 at 5:55 AMFor all of the people who thing this is flawed, lets get some things straight.
All of you people saying that the airplane would not move if the conveyer built is going in the opposite direction can’t even see that what they are saying is flawed. If the airplane is not moving, how the hell can the conveyer belt be moving backwards? The problem states that the conveyer belt matches the forward speed of the AIRPLANE but in the opposite direction. So if you saying that the Airplane won’t move becuase of that, then that means the conveyer built is not moving, becuase in order for the conveyer built to move, the plane has to be moving.
You also can’t have a plane just sitting there with its wheels just spinning on a conveyer belt, because, AGAIN, if the airplane is just sitting there spinning its wheels and NOT moving, guess what, the conveyer belt isn’t moving either!
February 3, 2008 at 3:01 AMWow, I don’t know why I used the word built twice -_-
February 3, 2008 at 3:02 AMOk – Lets keep it simple – forget friction, wheels etc.
GROUNDSPEED = Speed of wheels if plane were on the ground.
The test was only flawed because they measured the takeoff speed of the aircraft at a point where GROUNDSPEED and AIRSPEED were the same (only thing moving was the aircraft).
In order to have an accurate test they would have had to match the GROUNDSPEED of the BELT to the AIRSPEED of the PLANE the belt would have to be going a fast enough GROUNDSPEED to keep the aircraft below the 25mph AIRSPEED needed for takeoff.
Example #1
February 3, 2008 at 11:16 AMPlane needs 25mph AIRSPEED to take off.
Belt at 25mph GROUNDSPEED
PLANE has to do 50mph GROUNDSPEED to reach the 25mph AIRSPEED to take off.
If they had put a speedometer on Awheel of the plane (to measure the GROUNDSPEED) they would have seen the difference.
Example #2
Every pilot knows – given a constant aircraft AIRSPEED:
TAILWIND = greater GROUNDSPEED
HEADWIND = lower GROUNDSPEED
Intelligence has it’s limits, stupidity is boundless.
The whole conveyor belt/treadmill is a red herring, anyone who can’t see that by now is willfully blind. The various examples have clearly demonstrated this. Open your minds, or resign yourself to the confines of your narrow, earth-created-in-seven-days Beliefs.
February 3, 2008 at 3:48 PMAssuming that one believes in the physics of aerodynamics (airfoil shapes, air pressure passing over wing surfaces and lift), one should know that the experiment was flawed somehow. There should have been a bit more discussion of relative motion, I thought. Looking at the video, the plane is clearly advancing forward (pulling forward against the air). The conveyor belt is NOT keeping up. Air is passing over the wings, creating the lift.
This is why we use fans (in wind tunnels) and not conveyor belts to test aircraft. This is why aircraft carriers move at flank speed into the wind. And this is why we don’t have giant conveyor belts on aircraft carriers.
February 4, 2008 at 3:01 AMUmmmmm, has anyone seen a plane take off from water? The pontoons on the sea plane would act EXACTLY as wheels spinning on a conveyor belt. That is, they have NO effect on the planes ability to take off. The propeller on the other hand provides forward motion in the form of thrust which is relative to the air NOT the ground. The ONLY purpose for the wheels is to save the belly of the plane from getting scratched up. Thus, the plane would take off.
February 4, 2008 at 3:42 AMCorporal Punishment!!!!
That’s the whole point, you fool. Of course the plane is pulling forward!!! Correct! And yes, the conveyor is going at least as fast as the plane in the OPPOSITE direction. Did you hear what Jamie said? He said he “floored it” when the plane started to move.
This myth is more like a riddle. It is a trick on the mind! The conveyor can’t stop the plane! No matter how fast it goes, the plane will still advance forward!
February 4, 2008 at 9:23 AMI pose a counter question to those who believe the plane shouldn’t take off: If a plane is taking off normally and steers onto a conveyor belt moving at takeoff speed would the plane then stop moving? because If the wheel speed had any affect on takeoff the belt would stop the plane from moving right? WRONG it’s all about airspeed not ground speed, that’s why planes usually try to take off flying INTO the wind that way you use less of the runway and takeoff faster (slightly).
February 4, 2008 at 1:43 PMLet’s see if this helps the naysayers:
I used to love this restaurant on Cape Cod. It was right on the water. One very windy day, I saw a bird hovering in mid-air, wings spread, out over the water. It’s ground speed was zero. But it’s air speed was obvious enough to keep it flying. That’s because as far as flying is concerned, all that matters is airspeed, not ground speed. From the perspective of the bird, the wind was moving at, I don’t know, 20 knots or something.
On a conveyor, all that matters to the plane is the air speed relative to the propeller, not air speed relative to the conveyor. Just like it didn’t matter that the bird’s speed relative to the ground was zero, the plane’s speed relative to the ground doesn’t matter either.
Most assume that the plane actually needs to overcome the conveyor’s speed to move forward. But because the conveyor is not also moving all the *air* backward at its speed, the conveyor won’t hold the plane back. Just the friction at the wheels.
Does that help at all?
February 4, 2008 at 3:18 PMErn,
Your example with the hovering bird is not applicable because I highly doubt that any wind created by mother nature is enough to give a plane it’s lift or to maintain it’s flight.
However, I agree that the only thing holding the plane back is the friction of the wheels on the bearings/legs on the plane.
February 4, 2008 at 8:26 PMIn a perfect world where there was no friction, a plane on a treadmill would have no change it’s position relative to the ground because it is freewheeling. The only thing moving then would be the wheels, travelling at whatever speed the treadmill is going. In order for the plane to lift off in that situation would be as simple as turning on the engines and thrust forward. If you were to add friction back into the equation, lift off would be just as simple because the engines can easily produce enough thrust to overcome the friction.
I don’t get it. The plane is not suppose to move? Of course, if the plane doesn’t move, it won’t fly! Why won’t it move? Did you tie a rope to it to hold it in place? Why won’t it move? The conveyer goes one way, the propeller pulls the plane in the other. The plane moves.
If you don’t like the Mythbusters result, set up your own test, shoot it with your video camera, and post it on YouTube. Let us see what the “proper” setup is.
February 4, 2008 at 9:54 PMThe whole argument can be simplified into this: An airplane is different from a car!
A car propels itself forward by pushing backwards against the ground. If you put a car on a free-spinning treadmill and hold the car stationary (e.g. by attaching a big chain to the back of it), the car will push the treadmill backwards.
A plane propels itself forward by pushing backwards against the air. If you put an airplane on a treadmill and hold the plane still (again, by attaching a big chain to the back of it) and the plane starts its engines to try to move forward, it won’t — but the treadmill won’t go anywhere either. Once again: the airplane isn’t pushing backward against the ground to propel itself, it’s pushing backward against the air.
The wheels on an airplane have nothing to do with going forward. They’re only there to hold the plane up when it’s landed. They do not (in almost all instances) help propel the plane at all. That’s why when you go to the airport and get on a plane, there’s a little tractor that pushes the plane back from the gate; the whole rest of the time the plane is moving forward because it’s being pushed lightly by its engines. The whole taxiing process is forward; you never go backwards because the plane has no way to push itself backwards (although it does have brakes on the wheels that are used to slow down and stop).
The analogous situation to a car on a conveyor belt is a plane in a wind tunnel, where the wind speed matches the speed of the aircraft. The plane in the wind tunnel would generate lift and take off vertically, but it would stay horizontally stationary.
February 5, 2008 at 12:16 AMMyth (As stated to be tested) An airplane cannot take off from a RUNWAY (TREADMILL) which is moving backwards at a speed EQUAL to it’s NORMAL GROUND SPEED DURING TAKEOFF. I know I am yelling but a lot of people here just didn’t read the myth. Adam & Jamie busted the hell out of this myth as it is stated. If you think for one minute that this was flawed than please explain the flaw. What I saw was a runway(treadmill) going backwards at a speed equal to the planes normal takeoff groundspeed. Where is the flaw?
February 5, 2008 at 11:00 AMFailed: The Plane went fowerd, moved air over wings, Plane flew. No air over wing no flight.
February 5, 2008 at 11:47 AMIt’s an experiment you can do yourself with a treadmill, a skateboard, and a rope tied to the front of the treadmill.
You only have to pull a tiny tiny bit harder to move forward when the treadmill is on vs. when it’s off. Just holding the rope very lightly is enough to make you stationary (in both cases). Sudden upper body movements (like waving your arms) can propel you forward in both cases as well.
People are dumbfounded by this when I show it to them. You can see their brains short-circuit right in front of your eyes. Some friends pull really hard when the treadmill is first turned on and slam into the front of it, often leaving a bruise or falling off the skateboard. They get a really confused look on their face. Some of my friends still don’t get it and want to try it again every time they come over.
You have to really be careful to pull just a tiny tiny bit. The urge to pull hard is great. The brain simply cannot comprehend it. Like an optical illusion.
February 5, 2008 at 1:10 PMA plane can take off even if it’s not moving relative to the ground. In this case, the wheels aren’t moving at all. This is called a “glider”. A good strong headwind can get the plane airborn even when it’s parked with the propeller off. Of course, it doesn’t stay airborne for long, and the landing isn’t graceful, but every time a hurricane or strong winds are around, you always hear a story about how a parked small plane was blown off its wheels. The plane took off, flew for half a second, then crashed. But it took off.
So imagine what would happen if the propellor were on? There would be more than enough power to take off. In theory, a plane can take off into a strong headwind even if it’s rolling backwards on liftoff. (another myth to test!!)
February 5, 2008 at 1:28 PMman stop complaining about the plane and the tradmill… a treadmill cannot hold the plane…
February 5, 2008 at 1:59 PMImagine trying the same thing with a 747. If you believe its true. Harrier Jet, no problem.
February 6, 2008 at 2:24 PMI was having trouble getting my brain around this until I tried this thought experiment: Substitute ice skates for wheels and a frictionless sheet of ice for the treadmill. If Jamie pulls this frictionless sheet of ice backward relative to the plane, the plane should remain motionless because of its inertia (no outside force to accelerate it). When the propeller starts turning, it will pull the plane through the air regardless of what the treadmill is doing.
February 7, 2008 at 2:57 PM3 scenarios, depending on how you interpret the problem.
1. The plane will not take off. The test done by Mythbusters, did not work. The treadmill did not go fast enough. If it had, the wheels would have caught fire, blown out, or wobbled off. You can’t ignore the friction… with no lift the friction will be high, therefore the landing/takeoff gear will fail if the fictitious conveyor belt is fast enough to prevent any movement in relationship to the ground.
Imagine the conveyor belt made out of ice! The wheels made out of skates? Much less friction. The ice would have to move at a fantastic speed to slow the slide of the plane! The skates wouldn’t hold up… they would also wobble and fall apart.
2. If you make an assumption about frictionless wheels (as well as the infinitely fast conveyor belt), then you are allowing the plane to move forward and therefore, take off. There’s nothing to stop it.
Planes don’t take off without wind going over the wings. If allowed to move “frictionless”, over a infinitely fast conveyor belt. Sure… it will take off. Now the belt has no effect on the plane at all. Doesn’t seem to be the essence of the problem.
3. If perhaps the planes takeoff speed is 100 mph. The treadmill can go 100 mpg. The plane will still roll forward and may take off… depending on if the wheels can take the 200 mph roll. Just depends. 200 mpg is pretty fast. Most of the time, I think not.
February 7, 2008 at 3:43 PMThe worst! A seriously flawed test toward a self-fullfilling result!
February 7, 2008 at 8:54 PMWhat about the Bernoulli’s principle? What about a “push” plane where the air pushed by the propeller doesn’t move over the wing?
Planes don’t depend on the engine to blow iar over the wing – the engine moves the plane forward thus moving air over the wing!
Bad! Stop watching the show bad.
umm I’m not a expert on this but isn’t the plane moving forward (it seems to be travelling around 20MPH)? I thought the whole premise of the myth is that the forward force generated by the engine is equal to the backward force from the treadmill meaning the plane would be in a fixed position i.e. not moving or stationary. As the plane is moving forward the backward force from the treadmill (or tarpoline the in this case) is less than the forward propulsion of the plane’s engine. This means the plane is able to accelerate and is therefore able to take off (which it did). I don’t know the exact forces involved in this case but from looking at the video that’s what seemed to have happened.
February 7, 2008 at 9:48 PMtotally busted.(from trinidad)
February 8, 2008 at 10:08 AMThe way that the myth was stated makes the myth impossible from the start. Like so many people before me have said, the wheels aren’t powered by the engines, their spin comes from the treadmill. Its Newtons third law of physics. Equal and opposite actions and reactions. So if the treadmill was spinning at 100mph, the wheels of the plane would be spinning 100mph in the opposite direction, thus leaving the plane stationary. So if a another force was applied(the planes engines)then the plane(relative to the treadmill) would be moving because the wheels cancel out the treadmill’s spin. So no matter how fast the treadmill spins, the planes wheels will match that speed and it’s engines will give it speed relative to the ground or air.
February 8, 2008 at 10:28 PMOne of my pilot friends watched this episode and told me that a plane could take off. I’m an aerospace engineer and this test was valid. The point of using the treadmill is to remove friction that can be applied to the ground to provide forward motion. The same situation applies to running on ice…you stay stationary (assuming completely frictionless ice) no matter how fast you run. Now put a fan on your back. You move forward…the same way a hovercraft does. Now run…you won’t move any faster forwards. And as soon as you reach the right speed, you will take off if you have wings. What I think would make this all the more clear is if they had run the conveyer belt faster than the airplane’s speed…of course safety would be an issue since plane’s wheel’s aren’t prefectly frictionless.
February 10, 2008 at 4:44 PMFORGET ABOUT THE SPEED OF THE WHEELS !!! They have absolutely nothing to do with the question of lift. Even if an airplane had skis or pontoons, it would takeoff when (and only when) the lifting surfaces experience enough lift to overcome drag and weight. If a seaplane was attempting to takeoff on a river against the current, it would do it if the airplane could produce enough thrust to achieve enough airflow over the wings to produce enough lift to overcome weight and drag. This is true of airplanes with wheels on a treadmill, concrete, pavement, glass, rocks, sand, dolomite, a collection of lime jello or any other surface you can think of.
The whole point of the question of the treadmill scenario is point this out. The point of the treadmill question is that lift is created with respect to how the lifting surfaces are functioning in the atmosphere in its local vicinity.
L=cl*S*1/2 Rho*V2. This is the lift equation. L is lift, cl is coefficient of lift, S is Surface Area, rho is the atmospheric conditions, and the biggy is V2, which is velocity squared. In case you didn’t catch that….VELOCITY SQUARED. Velocity’s contribution to the overall production of lift is squared. It is the major contributor to the physical production of lift. The lift equation only cares about the velocity of the airflow acting upon the lifting surface. It doesn’t care about how quickly the aircraft is moving over the surface…..because it just doesn’t matter.
If we operated in a vacuum ……we could always takeoff with no ground roll if we had a headwind equal to or greater than our rotation speed. And of course, if we had a way to control that wind and summons it at the right time.
So…..if an airplane was on a treadmill that was turning in such a manner as to not allow the wings of the airplane to move forward to attain the necessary velocity to create lift……it cannot take off. The treadmill in your mythbuster did not restrict the build up of velocity to disallow the creation of lift. This mythbuster episode while entertaining falls short of recreating the spirit of the hypothesis
February 11, 2008 at 11:18 AMIf the plane moves forward at the same speed as the conveyor is moving backwards, it cannot be stationary as it is moving forwards, its airspeed and groundspeed are both 25mph, the belt and plane are passing each other. Passing objects don’t cancel out each others velocity, unless they have a head-on collision, slight friction will have little effect on passing which would in this case be only double, well within safety limits for any aircraft. The plane moves forwards as fast and as far relative to the ground before takeoff with or without the conveyor.
Artemus; If we operated in a vacuum ……we could never takeoff, a headwind, or any wind cannot exist without air, no air, no airspeed, no lift.
The plane flies. End of story.
February 11, 2008 at 8:17 PMThe disagreement comes from the fact that there are at least two different problems here and each side fails to recognize the other. The point of anger is that Mythbusters said they were testing one problem, yet actually tested the other. The first problem is where the conveyor belt moves at some speed and the plane attempts to take off. The Mythbusters tested this and of course the plane took off. However, they claimed they were testing the case where the conveyor belt would increase in speed to keep the plane stationary. In this case, the plane will not take off because of the key factor: wheel friction (think how the toy plane moved backward along the treadmill with engine off). Rotational friction in the wheel bearings is proportional to angular velocity and applies a force at the edge of the wheels opposite to the direction of motion. On an ideal conveyor belt spinning at several hundred (or thousands, whatever it takes) miles per hour, the small amount of friction normally created by the wheels would amount to enough force of drag to hold the plane still relative to the air, and it would therefore generate no lift.
TL;DR: Both camps are correct if they define their problem correctly. Mythbusters didn’t.
February 11, 2008 at 11:37 PMEven I know the plane wont take off, the wheels have absolutly nothing to do with the thrust for the plane. Wheels go just as fast as the plane ‘wants’ them to go and will only go that fast. Plane going 100= wheels going 100. when a plane is in the air and it lets the wheels down so it can land the wheels are going 0 untill it hits the ground and then will instantly go the speed that the plane is going. All wheels are there for it so it can roll, they arent attached to any sort of engine to make them move.
February 14, 2008 at 1:46 PMI love it, I really freakin love it!
To all those who say it was flawed and it won’t fly etc, stop eating paint chips!
The really neato thing is, you already freakin KNOW that they don’t have to have rolling wheels, unless you have never seen a plane land on water or snow etc..
This has to be one of the funniest misunderstandings of basic physics since Newton was born!
February 16, 2008 at 6:13 AMO.K. you freakin idiots, if the plane would not move on the conveyer belt than why the hell would you need a conveyer belt that is as long as a runway? The conveyer belt would only need to be as long as the footprint of the tires. One more time slowly and loud, T H E T R E A D M I L L W I L L N O T S T O P T H E P L A N E F R O M M O V I N G F O R W A R D.
February 17, 2008 at 9:28 PMConsider the following:
You have conveyer belt a mile long with the plane at the end (meaning the end where takeoff would occur). You apply brakes and no engine power when the conveyor starts so you start moving backwards. Lets say the conveyor moves 200 mph backwards and you let the plane get up to the speed before applying engine thrust and letting go of the brakes. Now forget about the fact that the plane would properly flip over if you were going 200 mph backward; assuming it did not and you let go of the brakes and you applied full thrust; your backward motion would slow and then become forward until you reach takeoff speed…..
February 18, 2008 at 3:39 PMStop presenting arguments without first saying which case you’re arguing for: treadmill goes at takeoff speed (busted, plane takes off) or treadmill can go infinitely fast (not tested, plane won’t take off).
February 19, 2008 at 5:23 AMAny aircraft can overcome zero ground speed even on a treadmill. In that respect I agree the aircraft will take off because of airflow over the wings. It has exceeded the zero air flow and created lift over the wings. The prop on a 400-pound aircraft is enough to create the necessary airflow for lift. However, new MYTH. If you have an airplane that cannot create airflow over the wings, will the results be different? If you have an F-4 fighter capable of MACH 1 and a tread mill also capable of MACH 1, you could have a zero ground speed equilibrium. If the aircraft cannot break the ground speed equilibrium, will it fly? Easy answer…NO. You MUST HAVE AIRFLOW OVER THE WINGS to create lift. If I can break the equilibrium and accelerate past the zero ground speed no matter what that speed is, it can take off as long as it reachs take off AIRFLOW SPEED. In a 400-pound airplane with the prop on the front this is easy. With the prop on the back, I must push past the zero ground speed to create airflow takeoff speed. All this assumes calm winds. As soon as we introduce a headwind, the aircraft has the advantage. As soon as we introduce a tailwind the aircraft is at a disadvantage and must accelerate to a higher speed to overcome the tailwind. The aircraft must move forward in the airmass, period.
February 19, 2008 at 3:06 PMPavelow – its exactly the same myth. The wheels will spin at Mach 2, the F-4 will take off. The whole point is that a treadmill CANNOT hold back a plane. Any plane. It cannot hold back anything that doesn’t propel itself using the ground, so long as the wheels are fairly frictionless.
February 23, 2008 at 5:58 AMLook, for the people below me, the forward movement that you see in a plane like that is not created by the wheels, they are created by the propeller/engine by moving the air behind them, thus, when the airplane reaches the speed that the conveyor belt is moving, the plane would still accelerate faster than the conveyor belt.
February 23, 2008 at 8:07 PMwow almost everyone seems to be forgetting the critical concept here, a plane does not taxi because of motors in the wheels, it taxis on the force of air being pushed by the motors, so if the runways is moving in the opposite direction at its normal taxi speed, the plane still takes off the wheels just spin twice as fast, in effect what happens is its taxi speed is doubled, because even though it is on the ground its speed is still based on movement through air.
February 26, 2008 at 10:06 AMHere are some questions for everyone.
February 27, 2008 at 9:33 PMTo everyone that says its the thrust that makes the plane take off…. So if you run the engine and prop at takeoff speed with no wings the plane will take off?
For you that says the wheels have nothing to do with the plane taking off….. How about I give you the wings the engine and prop but make you put on the breaks on the wheels?
For you that say its the wings….How about no engine or prop but I give you the wings and air to move over the wings will the plane take off?
maybe someone can explain this for me…
say a pontoon type plane is on a river that we can control the rate of water flow…we face the plane up stream and start the engine…
…the pilot is talking to a friend on the shore. :)
we increase the flow of water until the plane is going backwards and then speed up the plane’s engine to compensate until the plane equalizes to the river speed…
…so the pilot can stay even with his friend.
we speed up the water…and speed up the plane…keeping the plane from dropping backward in relation to the river current and the shore…
now we speed the river up until the plane’s engine is at full power and still holding the plane stationary on the river…
once the plane’s engine reaches maximum speed and if we keep increasing the river’s speed won’t the plane slowly start moving backwards even with it’s engine at full speed?
would all of this preclude the plane ever taking off?
…since the plane’s wings, the shoreline, the pilot, and his friend are all essentially stationary and the only forces at work are the plane’s engine and the river.
just an observation…I like to think about it like a boat racing against the current in front of a waterfall [oh the peril!]…only with a pontoon plane instead! :)
March 15, 2008 at 9:26 PMnow here is my guess/answer to my posted question:
the plane can speed up to maintain its position in the water so the pilot can talk to his friend but…BUT!
…the pilot will have to feather the engine throttle because the plane will try to move forward regardless of the rivers speed due to the reaction the engine has with the surrounding AIR and not just the water. The plane would only have to match the drag from the pontoons in the water…not the rivers speed.
No matter how fast the water is flowing the plane is pushing against the air…another river if you will…the only affecting factor would be the drag on the pontoons and overcoming this drag…the lesser drag of wheels on a conveyor would be even easier to overcome.
Just my two cents.
March 15, 2008 at 9:42 PManother way to look at it is if you use a person swimming in the river…
the swimmer is the plane…
the river is the conveyor belt…
and lets use a rope tied off up river to a tree as the air…
the swimmer won’t move forward if the river speed and his swimming speed are the same…
but let him grab the rope [air!] and pull himself forward thru the river and he will move against the current regardless of the river’s speed [like the plane's prop grabs the air and pulls it forward].
…and if you put the plane on a conveyor with a 500 mph headwind and the planes max airspeed was 300 mph the plane wold still take off flying but moving backwards at 200mph!
and if the plane’s max air speed was 250 mph and you put it on a conveyor going 250 mph with a head wind of 250 mph the plane would lift off and glide/float above the conveyor like it was sitting still because the wings and the prop work together to make the plane function.
kind of like a bird flying/coasting in a storm wind!
March 15, 2008 at 10:14 PMMike said above:
Mike:
Here are some questions for everyone.
To everyone that says its the thrust that makes the plane take off…. So if you run the engine and prop at takeoff speed with no wings the plane will take off?
For you that says the wheels have nothing to do with the plane taking off….. How about I give you the wings the engine and prop but make you put on the breaks on the wheels?
For you that say its the wings….How about no engine or prop but I give you the wings and air to move over the wings will the plane take off?
[1] no wings….answer=not takeoff….its no longer a plane…but the engine will still pull itself thru the AIR!
turn the engine vertical…will it try to lift itself up into the air…YES! no matter which angle the engine is at it wants to pull itself thru the AIR with the PROP!
[2] breaks[sic] on the wheels…answer=takeoff…the plane will just have to overcome the friction of dragging the locked wheels down the runway until it broke the friction and took flight.
[3] no engine/no prop with wings…answer=takeoff…no you have made a glider! when the air passes over the wings the air pressure difference on the wings surface will cause lift.
March 15, 2008 at 10:25 PMhow about a helicopter on a turntable?
March 15, 2008 at 10:41 PMAnd that’s why people are arguing over this. Many people are thinking it’s about if a plane can take off from not moving forward. They aren’t simply asking whether the conveyor belt will actually stop the plane from moving forward, which your episode proved it did not.
March 17, 2008 at 2:11 AMsomehow the ultra-light was in motion on the “treadmill” because the engines would not be able to create enough wind towards the wings to get enough lift. the airplanes need a long stretch of runway to get lift from the propellers from the air going under the wings. when you did the small scale test the plane went forward because the treadmill was going slower. if the plane lifted straight off the treadmill without moving forwards then that would be busted. wind pressure on the wings wont make it move forwards just up therefore the plane was moving too fast. try teathering a mid sized model to the ground. run the propeller on an actual treadmill and if it takes off straight up then myth busted but if it just keeps moving forwards against the ropes tieing it down myth confirmed. if you were to take the propellers off the plane and tie it down as the treadmill goes backwards the plane cant create lift with no movement the only thing that can make it lift is the propeller by which to me is impossible for a propeller spinning an average 2200 rpm to create enough backwards thrust to lift an actual plane. when i do ground runs on my companies SA226 fairchild metro 2 we put on the parking brake and run the engines full power. if that doesnt make the plane lift into the air neither will the tires spinning make it lift off the air either with no speed.
March 17, 2008 at 4:22 AMand with the water concept. if the plane is moving against the waters “matching current” the propellers may create lift at the front making the plane move up and down on the water like a kid in a small wave making it have less resistance in the water as it goes by the floats at certain points. just my thought.
March 17, 2008 at 4:34 AMYOU NEED WIND GOING UNDER YOUR WINGS TO TAKE OFF. now. think of it like this. your on roller blades on a treadmill. grabbing the sides is equivelent to that of the propellers creating forward thrust equal to that of the treadmills speed. do you feel wind?
March 17, 2008 at 4:48 AMno you feel nothing. you need that wind to create lift.
or what about this. a car spoiler. it creates downwards force to get better traction. if you run a car down a treadmill so its moving stationary there is no wind pushing down on the spoiler. same with a wing how is it going to lift a wing?
March 17, 2008 at 4:50 AMITS IMPOSSIBLE! take it from someone who fixes planes. take off the wings. it cant fly. basic physics. YOU NEED LIFT
Hi I watched your episode 97 with intrest. My interest was aroused by the fact that people in your posoition would even take the time to explore this.As some of the others commented an airplane wheels have no berring on the ability of an airplane to fly. I have 33000 hours of flight time and have taken off in all kinds of different scinarios.One was taking off with float planes from a dolly. Once the airplane and dolly reached flying speed the airplane simply lifted off from the dollies. However the closest to what you where trying to show is a simple everyday occurance for bush pilots. If you are taking off from a fast flowing river with a heavy loaded plane it is almost impossible to take off toward the current in calm wind. You must take off down stream. The speed off the current already has created a headwind to help lift the airplane enough so it can start accelerating. Bob
March 17, 2008 at 8:24 AMI read through many of the comments posted on this episode and i cant believe what i read. Even pilots with many years and hrs of experience still dont have an understanding of basic physics. The planes ability to take off has no bearing on its ground speed, only its air speed. There are so many variables in this situation i think it is beyond “mythbusters” ability to test it properly. If you were to have a plane with a take off speed of say 25 mph and you put it on a treadmill moving at 25 mph in the opposit direction of take off, you would be able to power up the plane to a point where it could over come the backwards motion of the treadmill with out taking off. This would take a realitive small amount of power. However if you power up the plane to normal “take off power” it will take off regardless of the rearward motion of the treadmill.
March 20, 2008 at 10:19 PMA point that gets missed is that wheels moving backward (due to the conveyor) are spinning in the opposite direction as they need to for the plane to move forward. They do not move twice as fast, the two forces try to move the wheels in the opposite direction. If you do not believe me, get a toy car and roll it. For the plane to move forward, it has to skid the wheels. It will be like trying to take off with the brakes locked. I think a lot of planes have enough thrust and would take off.
The limiting factor is the amount of friction which the wheels have with the conveyor versus the thrust of the engine. If the force from the engine is greater than the friction force of the wheels against the conveyor, then the plane moves forward. If it gets to takeoff velocity it takes off.
Jim
March 21, 2008 at 10:27 AMIf your hypothesis gives you a predetermined outcome, and your experiment does not match your predetermined outcome YOU ARE NOT INVOLVING YOURSELF IN SCIENCE
April 6, 2008 at 10:01 AMThe tarpaulin is completely irrelevant. The propeller is screwing into the air, pulling the plane forward. The plane wheels are unpowered and only facilitate the plane to be controllable before it’s forward velocity is sufficient to create the lift via the wings. The plane would accelerate regardless of the speed of the tarpaulin as it isn’t driving through the wheels.
April 8, 2008 at 10:52 PMThis is the funniest argument I have ever seen. two sides trying to discuss their point of view, that have little to no meaning to anything.
the problem is that there are two things in the “Myth” that have no effect on each other.
a plane taking off, well you know what airspeed and runway length you need to take off, it will as long as those things are accomplished. Whether it is on a belt or not.
Now the Belt, it is there to confuse you, it does not change anything you need to take off unless it is to short, which would be the same as not having enough runway.
I think that the mythbusters did it the way they saw it, and that a belt would have no effect on a take off.
the people that think they did it wrong think that there should have been a limit on the length of the belt, therefore not allowing the plane to get up to the correct airspeed before running off the belt, ie. not taking off.
April 9, 2008 at 6:23 PMI noticed that every one was saying -air passing OVER the wings ,Lets refrase that : air over the top creates a low pressure area , the wind passing UNDER the wings Creates the HIGH PRESSURE AREA THAT IS NEEDED FOR LIFT TO MAKE THE PLANE FLY ( RIGHT??) NOW on the (help me desk under aviation) this has been going on for awhile,I say it will fly. I have over 5000 hr in jet and prop , Still hold asmelII. JUST GIVE ME A (B-47 Jet bomber . with water alcohal and a rack full behind the aft wheel well 32 bottles ( 1000 lbs thrust per bottle ,And I will promise anyone I WILL GET AIRBORN> IF not there wont be a treadmill left because it will be melted to mush by the time i get done, I didnt get to see the show( ID LIKE TO ) There are several that think they understand the princables of flight , but as some has said ( GET OUT THE IDIOT TAGS: SIGNED BY CODE NAME GIVEN TO ME BACK IN 55 :: Flying Blue EagleIN the U.S.A.F. I flew the B-47 Jet bomber ( 6 ENGINE JET) THE C-123 , & THE c-130 H I have flow several different single and multi eng prop a/c. WILL THIS A/C FLY BACKWARDS ???:: Tell you what and if you dont believe it ,just go up and tery it ( GET up to a altu. where there is a head wind that is above your stall speed for the a/c you are in , pull back the throttle and bring the nose up to just stay above stall ,right into the head wind , watch what will happen , ) YOU WILL FLY BACKWARDS < TRY IT <YOULL LIKE IT F.B.E. April 10 08 12:46 AM
April 10, 2008 at 12:47 AMTRACKBACKS/PINGS You just said it all, you hit the nail on the head blind folded, good going ,you explained it very well I think ( BUT AIR FLOWING OVER THE TOP OF THE WINGS IS NOT WHAT GIVES THE A/C THE LIFT IN ORDER TO FLY . Back in the late 80’s or early 90’s on the race cars they re designed them so that would the pavement better and be less crashes, durning races. They copyied the princables of A/C ,Except in reverse, THE air over the top of the car was given the high pressure area and the air flow going under the car was given the LOW pressure area, Which in turn would hold the car DOWN TO THE TRACK BETTER AND BETTER CONTROL > BY BY F.B.E.
April 10, 2008 at 1:00 AMI can’t believe the argument. Wheels have nothing to do with flying, wings do. It takes sufficient forward thrust to overcome drag in order to propel a plane fast enough to build enough lift to overcome gravity in order for a plane to fly. The conveyor belt theory is an element of drag, as long as the prop can produce enough thrust and the wheels can spin fast enough, the plane will fly, however, the wheels will be spinning much faster than normal. The bearings in the wheels are there in order to reduce drag or friction, as long as they are doing their job, the plane will fly
April 14, 2008 at 1:09 PMThis same test could be done with skis and a “slip-n-slide”.
Denis
This was flawed from the start. If the conveyor belt was moving at 25mph and the planes propeller propelled itself to 25mph the plane would still move 25mph faster than the conveyor belt. The true essence of this myth is that the conveyor belt should be at a speed that would cause the plane to remain stationary. The actual speed of the conveyor belt should have been 50mph. That would have caused the plane to remain in the same spot and then it would not have taken off. (Not enough air over the wings to crate lift). (Also I would like to point out to the guy who said that the propeller created the air movement over the wings is a fool. The propeller “pulls” the plain forward creating momentum which then intern creates airflow and lift, you should really read up on this S**t)
April 16, 2008 at 4:03 PMJamie, Adam,
You perpetuate ignorance. You should be doing real science. You are not scientists, you are sophists, making money instead of making sense. I still like your show though. Anyone who thinks its OK the plane took off either never took introductory physics or doesn’t understand laminar flow.
April 16, 2008 at 9:06 PMI just watched this, and I am confused. The description of the experiment was that the plane would stay stationary in relation to the ground. But it seemed that the plane moved forward, before it took off. Isn’t forward movement in relation to the ground and the air what produces less air pressure over the curve of the wing and thus lift? I think the whole premise is wrong, because a conveyor belt is not going to prevent the plane from moving forward, because the propeller will pull the airplane forward.
April 16, 2008 at 9:13 PMIf this is true then why do we need long runways at our airports? Why not just use a bunch of big conveyor belts and save space? Especially on an aircraft carrier?
April 17, 2008 at 12:26 AMAnother thing to think about that throws another monkey wrench in the logic:
A car on a treadmill can gets its speedometer significantly higher than its regular top speed, given a sufficiently fast treadmill. This is because wind resistance is the primary reason for a car’s top speed, and the car has zero wind resistance on a treadmill.
To support this, my van went 150 mph on the chassis dyno and could have easily done more (still had more RPMs and another gear). The dyno is very much like a treadmill, the wheels turn the same speed as the surface resulting in zero net motion. Well, this is enforced by straps, but that doesn’t matter for this point.
My van in regular driving could never get anywhere near 150 mph.
In case the mph numbers seem too high, I had installed an overdrive (.67 ratio) transmission and still had the original 3.00:1 gear ratios. With the engine at 6500 rpm and 27.5 in tall tires, that is a theoretical wheel speed limit of 265.9 mph. I would wager my van could go 250 mph on a 250 mph treadmill. Might break my speedometer, though ;)
April 17, 2008 at 1:46 AMHere is my attempt to clarify the question:
If a plane takes off at speed X and if that plane normally achieves that speed at almost full power, can that plane take off from a treadmill that is going at speed X in the opposite direction?
The false reasoning: When the plane gets up to full power it will be pretty much standing still because the conveyer belt is going in the opposite direction at speed X. It will not take off because it will have zero or very little wind speed.
The true fact: In spite of the treadmill, when the pilot gives the plane full power it will still achieve speed X relative to the air because the plane is pulled through the air by the propellor. The wheels will be turning at twice the speed they normally would.
On the show they used a misleading illustration that showed a plane on a small conveyer belt (just the size of the plane). It could be said that this was just a comical illustration but it played right into the “But I though you were asking if a plane could take off it was on a treadmill and not moving relative to the surroundings” school of thought. If they wanted to test THAT they wouldn’t need the conveyor belt they would just hold the plane still with a chain and see if it would go up (of course it wouldn’t).
I collect interesting brainteasers and discuss them with people all the time. Very intelligent people can have misconceptions or fall into logic traps. It’s a shame some people can’t have a discussion without resorting to name calling.
(Several people above already explained the puzzle pretty much as I did, I’m just attempting to put it as concisely as possible)
April 17, 2008 at 2:04 AMThe tarp did not work as a conveyor belt.
The planes moved forward which resulted in flight.
If the planes were truely stationary (as the myth indicates) the planes would NOT have left the ground.
Jamie and Adam got too wrapped up into the experiment to realize that they swayed away from the real myth.
April 20, 2008 at 2:10 PMtry it agen but with straght weels!!!
April 25, 2008 at 4:54 PMWhere in the original myth, did it say you could or needed to start the plane.
May 12, 2008 at 9:36 PMI for see this myth as a non powered test, to see if the carry over air currents from the conveyor belt could lift the plane.
Can’t resist the urge to leave a comment: I agree with all who state that the plane does not care about the ground, what is needed for flight is relative motion of the wings and the air. If the engine on the ultralight was big enough to get air flowing over the wings, then of course it would fly. Try it with a jumbo jet, and I doubt you’ll get the same result since the turbines only generate air flow over the wings in very limited locations (namely close to the turbines). I.e. as far as I’m concerned the experiment was flawed and the myth is not busted. Try numerical simulations for a change; they should be able to convince you that it depends on the wing shape + engine.
May 13, 2008 at 9:04 AMAs has probably been stated here (who has time to read this many comments?), the original question(s), as far as I have seen, have never stated that the plane remain stationary. Some may have interpreted it that way, and are now misremembering the wording, but the several variations I have seen are similar to: “If a plane is on a conveyor belt, and the conveyor belt moves backwards at the same speed the plane moves forward, will the plane take off?” There are minor variations, but the question is not a paradox. It is meant as a joke, a mental trick. The plane don’t care about its wheels!
Unfortunately, to cover their asses, many have revised the question to say “If a conveyor cancels out the forward motion of a plane…” Well, that’s stupid. The conveyor would have to move at mind-numbingly high speed to slow down a plane! The plane don’t care what its wheels are doing! Some of the poor suckers embarassing themselves here really don’t get the propeller-thrust(plane) vs. wheel-thrust(car) heart of the joke, but others are retconning and argumentifying to try to save face. Oh well.
May 13, 2008 at 3:02 PMOh yeah, to repeat: the myth NEVER SAID THE PLANE REMAINED STATIONARY. That is your own misinterpretations. The original brainteaser is a trick question to make you THINK the plane remains stationary! It’s a word trick! The plane WILL move forward and it WILL take off! That’s what the Mythbusters tested, and that’s what they proved. They didn’t need to, but they did anyway!
May 13, 2008 at 3:07 PMRe: PHD In Fluid Mechanics and Pilot,
You seem like an intelligent person but you have fallen into the basic trap that is at the heart of this puzzle.
The plane doesn’t fly because of air flow caused by the propellor. It flies because of the same air flow over the wings that it always gets. It moves forward at normal speed and gets normal lift from normal airflow over the wings. The treadmill does not and can not impedede it’s forward movement. Planes move by pulling themselves through the air by the propellor not by sending power to the wheels (and certainly not by blowing air over their wings!)
Please Re-read my post a couple of posts up and also Dre’s posts and tell me what part of it you don’t understand.
May 14, 2008 at 10:04 PMThe aeroplane cannot take off standing still on a moving conveyor belt. If it accelerates, it won’t keep on the belt and the wheels of the plane will spin faster than the belt is moving backwards. In theory the plane will move backwards with the belt until it starts its engine. After that it will start moving forward – no matter how fast the belt moves. You so totally blew this one. Shame on you!
May 25, 2008 at 2:10 PMI saw this episode on dicovery last night and thought: How can this be a riddle? Isnt the soulution obvous?
1. If the airplane and conveyor belt has the same, but oposite speed the plane would have zero speed relative to the wind and it would not take of. To make the arplane keep the same speed as the conveyor belt it would need almost no engine power.
2. When engine starts it will bring the plane to takeof speed relative to wind no mater what hapens to the conveyour belt. The speed of the conveyour belt does not alter the air planes ability to alter its speed.
May 26, 2008 at 1:25 AMHells bells guys. A plane does not care at what speed the ground moves. It cares at what speed the wind over the wings moves. Planes do not use wheels to cause forward motion. it uses engine thrust through a propellor or a jet etc. Wheels are just a means to an end. Never seen so many absolute brain dead arguments. What would stuff up a planes lift off is it there is a tail wind bloing at takeoff speed. That’s why Carriers used to turn into the wind , to give added lift to the wings. Not to get the wheen turning slower. Oh yes they have catapaults, thats to get the wheels turning quicker. Idiots
May 31, 2008 at 11:35 AMThere are a lot of ignorant people in the world. The propellor provides the pull (thrust) for the plane to move forward, the wind over the wings (not from the popellor) provides the lift that makes it fly. QED
June 5, 2008 at 5:00 AMI noticed that the aircraft was moving past the pylons in a forward direction. If the speed of the conveyor and the a/c were a constant then there would have been no forward movement perceived, which makes this attempt at your experiment invalid. That being said if the experiment was, “does the propeller produce enough windspeed over the wings for that particular a/c to have the lift for takeoff,” well you still failed there too. A turbine a/c would be better for your experiment as no wind is passed over the wings by the propeller. However, I can’t imagine where you would find a conveyor that would be that fast.
June 9, 2008 at 2:20 AMI’m with ADINSX on this one: everyone’s getting hung up on the speed of the conveyor, but its speed alone doesn’t mean much. It’s Force that gets the plane moving, and it would take Force – not speed! – to prevent it from taking off. Where could that force come from? Not from the wheels, they have bearing that minimize the friction force they exert on the plane.
If the questioner assumes that the conveyor could somehow stop the plane moving forward, it betrays an ignorance of the forces involved, in the plane’s motion and in the wheels. It doesn’t work that way in the real world.
June 10, 2008 at 9:02 AMThe plane was not supposed to be moving forvard on the conveyer belt, when this happens its just like its taking off on the ground but slower. Surely the conveyer belt should have been moving at a speed with the correct amount of friction so that the plane was in one spot and the only way it would move forward was if it was in the air. I found this myth very unsatisfying when it was tested, but still, i love the show.
Luke, UK
June 10, 2008 at 11:32 AMbasically the tarp and free spinning wheels cancel each other out all that is left is the is the forward motion of the engine pushing air over the wings thus producing lift.
June 13, 2008 at 3:01 PMDAaaaaaaaaaaaaa!!!!
I’m so happy that so many people felt this episode blew it. I have never been so pissed off at an episode before. Both planes were obviously moving forward, so obviously air was passing over the wings and creating lift.
Like so many have already said, it’s impossible for the treadmill/belt/tarp to have any real impact on the plane since the wheels are free spinning. The prop pulls the plane forward and the only thing the “treadmill” does is make the wheels spin twice as fast.
Yes, there is some static friction between the wheels and axles before the wheels start moving, and some dynamic friction once they are moving, but once the forward force of the prop overcomes that friction force the wheels have no real effect and the plane can’t help but move forward if the engine is at full throttle.
June 14, 2008 at 12:52 PMBTW, it should be possible for the pilot to try and match the slight backwards force of a treadmill on the moving wheels and keep the plane stationary (wrt the ground). This would take some finely tuned adjustments and the throttle would be way back. The plane, of course, would not take off in this case.
June 14, 2008 at 1:08 PMAgreed, experiment was flawed…
…unless, the experiment is defined exactly as stated: “Can a plane take off on a conveyor traveling at the plane’s takeoff speed”. That’s a “it depends”.
More generally, flight is a balance of forces, or rather, “takeoff” is due to an imbalance of said forces. If the vertical forces are imbalanced in the upward direction, then the plane takes off. If they are imbalanced horizontally, it will move forward or backward.
The vertical forces at work here are:
- gravity
- lift over wings from ambient wind
- airflow of the prop over wing surfaces
- lift portion of the prop’s thrust (which generally is down-thrust actually)
- net effect on wings of airflow generated by the moving tarp (more on this below)
All of these also change with the plane’s pitch, i.e. angle of attack.
Horizontal forces are as follows:
- thrust
- drag
- friction
Two cases:
As a baseline case, suppose you tied the plane in place on the runway so that it couldn’t move forward but could lift off. Would the plane rise? Yes, _if_ the engine was powerful enough to blow enough air over the wings. The wheels are irrelevant. Or, it would lift is there was enough ground wind. That’s why they tie small planes down for storage.
Doing the same thing on the conveyor is not exactly the same, and the net result is likely a somewhat lower “take off speed”.
The tarp causes two other effects on the airflow:
1) The tarp generates some airflow, as it essentially drags some air with it. This is going to be immeasurable at the wing height in this situation, but within a couple inches or so of the tarp, i.e. within its boundary layer thickness, there actually will be some some airflow relative to the wings.
However, there may be a measureable effect from the tarp in that the prop’s thrust is more powerful and less turbulent because the bottom half of the flow is no longer in “ground effect” due to the moving tarp. In other words, normally the bottom of the prop wash is rolling along the ground, and the speed of the ground increases relative to the plane as it rolls down the runway. With the conveyor, the ground is already moving at a high speed relative to the plane, and the effect of that is that the flow is cleaner and faster, even though the plane isn’t actually moving with respect to the ground.
Hence, likely the power needed by the engine in the above two cases will differ and the plane will take off sooner with the conveyor.
Bottom line, I’m inclined to believe the “take off speed” is affected by the tarp.
As an aside, often in wind tunnel experiments, conveyors moving at the tunnel wind speed are used on the floor or walls of the objects being tested to negate the effect of the floor and walls which much better simulates the object flying in free space.
June 22, 2008 at 3:34 PMOne perpetual myth that really needs to be busted is the one which was repeated a couple of times on this episode; The Wright Brothers were NOT the first to achieve powered manned flight. This was achieved by Richard Pearse on Tuesday 31st March 1903 in New Zealand. This flight preceded the Wright Brothers by over eight months. Richard Pearce also invented the first ’short takeoff aircraft’ which survives to this day in the Museum of Transport & Technology in Auckland NZ.
June 23, 2008 at 5:43 AMThe question should be, Can the prop wash over the wings produce enough lift to allow the plane to lift off while no forward movement is evident? Otherwise the experiment was greatly flawed… I have the perfect setup required to test that. The treadmill can be part of it, but really has NO effect since we’re dealing with AIR MOVEMENT!
June 25, 2008 at 8:46 PMThe plane engine is used to thrust the plane forward so that there’s is air moving over its wings to create lift. If no air is moving over the wings to create lift, the plane can’t take off.
Imagine holding a small motorise plane with your hand above the ground with engine running at full speed. The plane will not fly after you release the grip because there is no air movement over the wings.
This is why aircraft carrier needs a catapult to thrust the planes forward to create enough moving air for take off. If the conveyor belt thing works, they could have just build a dyno machine with the footprint of the plane wheels.
June 27, 2008 at 4:31 AMWell, you did bust a myth, but it was your own myth. The actual myth that went around the web for months was that the conveyor belt would match the rotational speed of the wheels at any given point in time but in the opposite direction such that no forward rolling motion could occur. Then it’s posed as to whether or not the plane could take off. Since it’s not really possible for that scenario to occur, it’s a moot point.
June 27, 2008 at 7:32 PMWow. Reading these responses is quite the horror show. What has happened to simple logical thinking? Only a few of us, it seems, have any ability to visualize this properly. All HTOL aircraft fly thanks to airflow over the wings. This is a basic law of fluid dynamics. If a hypothetical conveyor belt could be constructed and operated in a manner such that it’s speed was able to exactly cancel out the forward travel of the airplane, then sufficient airflow over the wings for flight could not be attained. The airplane might be moving relative to the belt, but not to the surrounding air. A statitionary HTOL aircraft cannot achieve flight. That is why VTOL aircraft such as the Harrier were designed! If an HTOL aircraft could achieve flight just from the thrust of it’s prop, then every time a pilot did his run-up prior to takeoff there would be small aircraft bouncing all over run-up areas at airports everywhere. If anybody doubts this, then take a drive to a municipal airport and pay a private pilot $50 to allow you to sit in his plane while he runs the engine up to full with the brakes on. No forward motion + full power = lots of noise, but no flight.
June 29, 2008 at 12:03 PMYou guys are doing it wrong.
“A cockroach can survive a nuclear blast. – busted”
Irradiation like you guys did would kill it, but irradation such as from a nuclear war probably wouldnt
official us government books on the topic mention repeatedly that tests show that in the event of a nuclear war, the fy population would boom as they would not be killed by the radiation?
June 29, 2008 at 5:33 PMPeople fail to see that people do not define the myth in the same way.
If the myth is #1: that a plane will not be able to take off when on a conveyor belt, it is likely false, because it is very easy for the plane to move forward (it’s not the wheels that transmit the power).
The myth tested was #2: a conveyor belt matching an airplane normal takeoff speed (when on the ground), in reverse, would not allow the plane to take off. It is obviously false, same reason as first myth version.
Now, the #3 version of the myth is that if an airplane and conveyor belt move in opposite directions, and you adjust the airplane’s thrust so that it’s wheels tangantial speed will be equal to the conveyor belt’s speed, thereby making sure the plane’s “absolute” speed (relative to some external non-moving object) is ZERO, then the plane will not be able to takeoff.
July 3, 2008 at 5:34 PMThis version of the myth is true. Note that even if your conveyor belt moves surprisingly fast, it will takes a very small amount of energy / thrust to keep the airplane in the absolute same position, because the wheels can move almost freely. Of course the airplane can take off easily, but if you lower the thrust so much, just to the point where there is enough thrust to prevent the plane from moving backwards, then obviously the airplane will not be able to take off because relative speed of wind will be zero, therefore no lift.
End of story.
Worst myth ever.
Did not need to be tested.
People just need to be comprehensive, define things clearly, and not resort to personal attacks.
Totally unscientific analysis by so many people.
Some people do understand one version right but fail to see that others do not define the myth in the same way.
Mythbusters didn’t help much, because they only tested version 2.
Tom
The airplane myth is actually very easy to understand as you will soon realize.
First of all, the wheels of the plane on the conveyor belt have nothing to do with the plane not taking off, unless, the belt is moving in the opposite direction then the plane is and at the same speed as the plane is trying to go in the opposite direction of the belt. The propeller on a plane is only the means of propelling the airplane down the runway so it can reach the air speed necessary to take off, or through the air once it is airborne
An airplane must have significant air going over the wings to give it the lift it needs to take off. A plane just sitting on the runway with the propeller turning as fast as it can will not give a plane lift.
I watched your Myth busters show; on TV; Plane on a Conveyor Belt and I agreed with the pilot before he changed his mind about your theory.
Let me explain; first of all I saw that the plane was going faster forward then the conveyor belt was going backward. For your myth to work the airplane must go faster in a forward direction then the belt is going in the opposite direction. If you will watch the filming again you will see that the airplane is moving forward and passing the cones that you set up on the ground.
The airplane should have stayed the same distance between two cones if it was traveling forward at the same speed as the conveyor belt was going in the opposite direction.
July 4, 2008 at 1:29 AMConclusion : If the plane is going forward as fast as the conveyor belt is going backward the plane should not move from its spot in relation to the grown. Thus no air speed, no lift.
It won’t fly. Mythbusters got the idea wrong.
Stupid people with their stupid comments.
July 18, 2008 at 5:12 AMThis is so unlike you guys Adam and Jamie! In most cases you would not leave a point for debate. I also feel you blew this one big time. Both the small scale and the actual test missed the point. In the first scale test, the plane probably moved forward due to more speed. With the small remote control models I can understand it. However the second test was done on a surface which was moving relative to ground, hence creating a drag on the wings, thus giving it lift. The full scale was same. I guess you guys will have to revisit this one !
July 19, 2008 at 7:16 AMI cant believe people are so stupid and believe the turning of the aircrafts wheels have anything to do with it taking off. No airflow over wings, no lift, no takeoff, and believe me I am a pilot and know what the hell I am talking about
July 20, 2008 at 4:50 AMAir Plane on a convayour belt is the stoopides myth ever!!!! #1 it will never happen! #2 if you somthing about a plane, the end resulte could not be more obveous!
July 20, 2008 at 11:12 AMI at first thought Jamie and Adam were wrong, but I thought about it some more. Cars move forward due to the friction between the wheels and the ground. Planes are pulled/pushed through the air. The contact with the ground has no impact on the planes movement. Planes can take off on ice. Cars do not move well on ice (if there was no friction, a car would not move at all. The wheels would just spin). Since a planes movement has nothing to do with the ground, the conveyor belt does not affect the plane movement. Since the plane moves, air passes over the wings are you get lift…
July 26, 2008 at 10:18 PMPlane on Conveyor- Gross Inaccuracies
Myth is True( Not busted) Conc. Violate fluid mechanics
1. Lift is independent of wheels, engines, jets and propellors etc. It is only depenent on the lift coefficent, fluid density and relative velocity of object(wing) and fluid (air). Examples include wind tunnels (air moving past stationary wing develops lift) and airplanes landing into the wind (landing speed is decreased while relative velocity between air and wing remains same, so lift remains same). In short wing with zero relative velocity between wing and air produces 0 lift.
2. Speed was measured in different frames, truck speed was measured against pavement while plane speed was measured against air. In short if take of speed was 25 mph, speed of the truck was 25 mph, the plane would only measure 25 mph if it was moving 25 mph relative to the air i.e. 50 mph relative to the conveyor (this could be shown if speedometer was installed on plane wheel). If the plane and truck were going the same speed to an outside observer, the plane would remain stationary (i.e. radar gun would measure plane speed of 0), but it didn’t it moved away from the camera.
3. It should be noted that friction, means of propulsion have nothing to do with it. One could strap wings to a car and measure the cars velocity and corresponding lift produced by the wing. If the test on the conveyor were replicated with the car and wing rig, one would see that to achieve the same amount of lift as the first test, the car would be going twice as fast (according to the spedo) ( i.e. a person sitting in the car would not see the world around sitting still but moving by at half the speed recorded by the cars spedometer
In short the plane will ONLY take off from a conveyor when the relative velocity between the wing and air is that of the measured take off speed.
Therefore the plane will take off when its speed relative to the conveyor = takeoff speed+ truck speed. NOT the speed of the conveyor
July 26, 2008 at 10:42 PMYou guys are making this WAY to completed- forget about the propeller and the wheels for a second.
This will be the only time in my explanation that I’ll bring up the fact that air movement over and under the wings is what gives the plane lift. Here’s a explanation that proves that the plane won’t leave the ground without forward movement.
The Myth is “An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
OK, lets make this easy and break it down: Say this plane, “Plane A”, moving forward ON THE GROUND at 25 MPH before it leaves the earth (starts to fly). NOW pretend it’s possible to move the runway backwards (treadmill/conveyer belt) at the same rate equal to the forward movement that the plane is moving (25 mph on the ground). So what we’ve got is the plane moving forward the same speed the road is moving backward. Thus the plane isn’t moving forward or backward. It’s staying in one place.
Do we all agree on this part (Not talking about the flight part)? The plane isn’t moving in it’s physical location because the plane is still on the ground, while the propeller is pulling it forward, while the backward moving runway is not letting it physicaly move- There moving at the same speed in different (kinda a equal strength tug-a-war). It the same as you running on a treadmill. You’re running forward, but the ground/treadmill is moving backwards resulting in you not moving. No forward movement- that’s part of the Myth- “moving backwards at a speed equal to its normal ground speed during takeoff”. Moving the ground backward while the plane moves forward results in the plane staying the same space. -SO- the plane isn’t moving. It’s stationary. Right?
July 27, 2008 at 12:30 AMGood…
OK- (I said I would’n bring this up again…) Some might say that the stationary plane’s propeller spinning is creating some air movement over the wings that might give it lift, is true but a funny though, isn’t what make the plane get off the ground. If it where, then if a braked plane (while still on the ground) with the propeller running, say full throttle, where to left off the break, the plane would instantly fly. With no forward movement. Yup, straight up. If that where true why not put a propeller on the front of a skateboard and watch it fly. :)
Just pointing out that it’s the forward motion that keeps the wind flowing over the wings that makes the plane fly. It’s the lift created my the wings.
-Lastly- (as I said at the begining)
You guys are making this WAY to completed- forget about the propeller and the wheels for a second. Does a paper airplane need a propeller or wheels to make it fly. Them, like to tossing the paper plane into the air is only there to give it forward motion. The wings make it fly.
As long as the wheel breaks are released the velocity of the conveyor/tarp is of VERY little consequence to the plane’s ability to move forward. The same throttle setting will accelerate the plane forward at VERY nearly the same rate and the takeoff distance for that particular engine RPM would barely increase.
Matching the conveyor’s rearward speed to the plane’s real world forward velocity is pointless enough. Matching the conveyor’s speed to the rate the wheels are rolling makes no sense at all. If the whole contraption were able to keep the plane from moving forward (it can’t) the wheels wouldn’t rotate and the conveyor wouldn’t have any forward motion to match.
ALSO; since the plane’s inertia at the start of the test is relative to the stationary surroundings the plane’s inertia would counter much of the slight rearward force from the friction of the wheel bearings. Unless the plane was equipped with a variable pitch prop the pilot would probably be unable to keep the plane from moving forward without applying some pressure to the wheel brakes or completely stopping the engine.
Once a carrier’s catapult starts moving the carrier’s speed isn’t vary relevant. The point with a carrier turning into the wind for aircraft launches is that the plane already has airspeed totaling the wind speed plus the carrier’s speed when the catapult starts moving.
July 27, 2008 at 2:41 AMA stationary plane can’t take off.
The point is: it is impossible to hold a plane stationary using just a conveyor belt, no matter how fast or slow the belt is moving.
July 27, 2008 at 3:09 PMI have been a MythBusters fan since the “pop rocks” pilot episode. Someone please tell me that the MythBusters cast and crew will take on the “airplane-conveyor-belt” myth again. Although it was still a great episode, everyone knows (or should know) that the airplane should have stayed stationary during the take-off roll.
MYTH: “An airplane cannot take off from a runway which is moving backwards (like a treadmill) AT A SPEED EQUAL to its normal ground speed during takeoff.
If the conveyor belt’s speed was equal to the airplane’s normal ground speed during takeoff, the airplane should have remained stationary during the entire test. Maybe the airplane would have BRIEFLY lifted off the ground because of propwash deflected by the elevator, but the airplane would not have performed a normal takeoff.
Seriously, this episode kinda ruined the show for me. I call a do-over!
July 28, 2008 at 1:18 AMAlso… the radio controlled airplane only took off because of the wind flow under the wings created by the small airplane’s propwash, and of course, for the same reason that the ultralight took off–because it was NOT stationary as it should have been (you know, like the black car that was stationary on the treadmill?)!?!?!
July 28, 2008 at 1:24 AMD0
OVER
!!!
:)
July 28, 2008 at 1:24 AMAdam and Jamie,
Hi guys I watch your show and laugh out loud. All of you are wonderful. This may help or be more confusing on the plane – tarpaulin – treadmill problem.
Here goes. Air is a fluid and is the substance lifting the plane. The ground has nothing to do with it. A prop is only a motorized fan attached to a wing. A fan behind the plane blowing air forward over the wings at the take off speed of the plane will prevent the plane from lifting off. You can keep the plane on a treadmill or not as you wish but without the air being able to pass over the wings it can’t fly. Take the fan out of the system and the plane takes off regardless if it is on a treadmill or not. As per your instructions I HAVE NOT TRIED THIS AT HOME. EVER! Could you try it in your shop? The main problem would be keeping the plane stable as the air passes over it from behind. These things aren’t designed to be stable that way; are they?
Wait, I know you could revive the fabled B-36 with the backward mounted piston engines. No, that won’t work because they’re too visually confusing. Oh well I’m out of bourbon and patience. I believe you got it right the first time through and consider myself scientifically satisfied.
Say hello to all the others.
Thanks
Lloyd
P.S. Maybe we could do it by attaching a tiny scale to a thin line that was glued to the model aircraft. As the plane took of the scale would register the ‘amount of lift’ in pounds or ounces. I’d settle for grains if necessary. Then as the plane flew at the end of it’s tether you could turn a fan on it and if the scale / measuring device decreased in “pull” then you would have demonstrated the effect of air moving over the wings from behind. It might even fall out of the air!! You guys would be heroes!!!! Again.
July 31, 2008 at 10:25 PMEngineer has it right.
Thomas has fallen for the bait. Thomas, no matter how fast the treadmill turns it cannot hold the plane back. The plane pushes itself forward through the air at whatever speed the pilot wants to go without regard to the treadmill. A plane on a treadmill is NOT like a car on a treadmill.
So the plane moves forward through the air and achieves lift just like it normally does. It is true that a plane standing still will not take off but this plane is not standing still.
Anyone who believes the idea is that the conveyer belt must make the plane stand still has taken the bait. That is the whole trick. Of course the plane can’t take off if it is standing still.
Stopping a planes forward movement by using a treadmill is like trying to stop a rocket with a treadmill. It can’t be done.
August 3, 2008 at 9:28 PMForget the plane for a moment. Just picture a rocket with wheels on a huge treadmill. Assume the rocket is pointed forward and that it has no wings and nothing about it wants to go up. It is just aimed forward. You can even put it all under a giant roof that touches the rocket so it can’t go up the slightest and is always pushing it’s wheels on the treadmill.
Now the conveyer belt is started and the rocket is lit at the same time. What will happen?
There is no amount of speed that the treadmill can turn that will impede the rockets forward motion. This is because the rocket moves by pushing against the air not by it’s wheels.
August 3, 2008 at 9:39 PMGood job Adam and Jamie, no do-over required just because some people have an IQ smaller than their shoe-size and will NEVER get it. Ever.
The plane’s wheels turn freely with a fairly small amount of friction at the bearings.
The propeller generates forward thrust by pushing against the air (which is NOT moving relative to the plane, assuming no wind).
If the conveyor belt/MOVING tarp is going backwards at 25mph, and the engine is generating enough thrust to move the plane forward at 25mph, the plane will still move forward relative to the *AIR* it is pushing against, at 25mph. The FREEWHEELING wheels on the moving surface will be spinning as through the plane’s ground speed was 50mph.
This is why aircraft have AIRSPEED indicators, that’s what matters for getting into, and staying in, the air. Ground speed is irrelevant.
I must go lie down now. The high concentration of pure stupid in these comments is making my head spin, and I’m sure the idiots will find some other flawed reasoning to support their BUSTED theory anyway. You just can’t keep a good dumbass down. ;-)
August 6, 2008 at 3:02 PMBrian – you’re still not getting it…still falling into the easy trap that makes this myth a “myth,” though it’s really just a silly play on thought.
August 13, 2008 at 11:52 PMThe point you’re missing: if you move the treadmill backwards at speed equal to the plane’s normal ground speed during takeoff: THE PLANE WILL STILL MOVE FORWARD.
There is no way to keep the plane from moving forward using that treadmill at that speed, or even most faster speeds.
August 13, 2008 at 11:59 PMI’m NOT a pilot, and it terrifies me to think that people with a license to fly do not understand the premise of this myth.
The ground, conveyor belt, etc. has NOTHING to do with the plane moving.
The airplane moves, and certainly will fly, because it pushes against the AIR with it’s propeller, causing it to move forward. Period.
August 18, 2008 at 3:13 PMI contend that the test needs to be redone (but probably won’t). The model and the ultralight would probably take off if the landing gear was clamped to a surface until the engines were revved to max power. They could probably take off on the lift from the engine alone.
August 23, 2008 at 2:14 PMA heavier airplane, even a small Cessna, would probably not take off on the tread mill or the clamps. But proving this would be both expensive and dangerous.
Sigh!
The conveyor (tarp) isn’t going to have a significant effect on the air. At any altitude more than a few inches above the tarp the air will remain stationary relative to the external camera and the surrounding terrain.
Due to the wheel bearings, as long as the the plane’s wheel brakes are released the motion of the tarp does VERY LITTLE to impede the motion of the plane. This would apply to ANY size aircraft in size ranges from the RC model up to something that would make an Airbus 380 look like a toy.
Therefore: the engine WILL pull the airplane forward relative to the external camera, outside environment AND the AIR at very nearly the acceleration possible on a normal runway.
IT is the motion though the AIR that counts. Ground speed means NOTHING to how much lift is generated. If you were to put a powerful wind machine in front of the ultralight you could fly it like a kite. Put a row of ridiculously high speed wind machines in front of an Airbus 380 and you could fly it like a kite!
IF the tarp/conveyor was too short, the plane would just drop off the end and continue accelerating. There may be brief puffs of tire smoke as the wheel RPM drops to match the suddenly halved “ground speed”. In other words: For ANY fixed wing airplane a wind tunnel or comparable wind machines ARE the equivalents to a treadmill to a person, bike or automobile!
Most fixed wing aircraft make no use of the exhaust from their propellers or jet (includes fan jets) engines to move air across the wings. It’s the motion of the wing through the air that produces lift. The wing’s motion relative to the ground (or the tarp) is of NO consequence. If the wing is VERY close to the ground the ground may act as a barrier to the downdraft that normally occurs as a wing moves through the air, increasing the pressure under the wing and the resulting lift.
August 24, 2008 at 6:21 AMPeople are looking at this in two ways but I haven’t seen anyone unify them yet.
The first issue is air speed. This is the speed of air over the wings of the aircraft.
Let’s assume there is no wind. Now air speed is the same as ground speed.
With no air speed, a plane does not generate lift so it stays on the ground.
This is why an aircraft chocked on the ground will not take off on full throttle.
It’s also why an aircraft WILL take off even with the engine off – in strong headwinds.
And finally, this is why aircraft take off and land into wind – so that they get the largest airspeed for the smallest land speed, which allows safer landings on smaller runways.
So. air speed is needed for lift. No air speed – no lift – no takeoff.
If the myth was testing the theory that an aircraft with no air speed will still take off, then they screwed up, because the camera CLEARLY shows the aircraft moving forward over the ground and out of frame, whilst a green runway marker remains stationary on the ground and in the frame.
The aircraft was moving forwards relative to the ground and the air. It had airspeed. It was not stationary.
However, if the myth was testing the theory that an aircraft will not take off on a treadmill going backwards at takeoff speed, then they got it right.
And this is the heading at the top of the page.
Such an aircraft will gain AIR SPEED – speed relative to the air and (generally) to the ground because it’s prop is throwing air backwards, which,
as Newton explains, generates an opposite force pushing the place forward in space (not relative to the treadmill).
In this scenario, the only effect of the treadmill on the airplane is to exert a small force, due to wheel friction, backwards.
If you sit the plane on the treadmill with the engine off, then plane retreats backwards.
But only because of friction in the wheels. If those wheels wrere frictionless, then the plane would stay put, and the treadmill would roll on by underneath it.
You can imagine how, if you started the treadmill very suddenly, and the wheels were well-oiled, the plane would take quite a while to start rolling backwards.
But if the wheels were square (high friction), then it would snatch backwards very suddenly because of the far higher force imparted by the far greater friction.
But with real-world wheels, friction is a factor, and the plabe will pick up backward speed until it is sitting still on the treadmill – moving backwards at the same speed.
Negative airspeed a small negative angle of attack, a small negative lift – no takeoff.
Now start the engine and increase power gradually.
A growing force is exerted forwards, due to the air thrown backwards by the prop.
This forward force accelerates the plane forward (Newton 2) which is the same as saying that the backwards speed decreases.
Now juggle the throttle to get the plan to become staionary relative to the ground.
The engine power needed to do this has no special relationship to the power needed to takeoff – it’s determined by friction in the wheels only.
As engine power increases, the plane accellerates forward. It gains ground speed and air speed. Lift is generated.
At some point enough airspeed is gained to take off.
The engine power required is very slightly greater than it would be if the treadmill were stationary, because a small backward force dur to frictionin its wheels needs to be overcome.
So – with no wind, a stationary plane will never take off.
August 29, 2008 at 12:39 PMBut a plane’s engine does not move forward by driving its wheels, but by throwing air backwards, so it will have no trouble gaining enough airspeed to take off,
even when its on a treadmill moving backwards at airspeed.
Good job ChrisXenon. I’m pretty sure I said the same thing a few posts back but your explanation is more detailed and maybe it will convince a few.
August 29, 2008 at 6:16 PMAidensx nailed it. I was getting nearer and nearer the bottom the page and thought no one would spell out the real problem/question.
You could have that treadmill running at any speed you want, 55 mph, 100 mph, 500 mph, the plane will move down the length of the treadmill and then off the end of it (or as long a runway it needs to attain appropriate lift, as long as the wheels aren’t burned up by friction of spinning hundreds of miles per hour (if we’re being silly and setting the treadmill to 1000’s of mph), that treadmill means nothing to the airplane in terms of halting or preventing its forward progress down that runway.
sum it up, the treadmill is superfluous, the plane will still travel the same physical distance, regardless of how many ‘laps’ it runs on the treadmill.
Idk how some people think the body would lift off the ground with no air ‘cutting’ on the wings to support it… (you know what I mean).
.02 USD
August 30, 2008 at 11:05 AMI’m glad I finally found this format. The episode test surely was flawed. I read most of the comments and didn’t see anyone say anything about the ultralight pilots comment that “I gunned it!” In other words he simply applied more power to provide thrust to overcome the final speed of the treadmill. Once he did this then the speed of the treadmill was negated once thrust went past what was needed to exceed the speed of the treadmill. Gravity is a huge issue here since the plane DID have weight and the ONLY way for the plane to lift off was to cause enough forward speed to provide enough lift OFF the wheels to make the plane FLY. So, if normal takeoff speed of the plane was 25mph and the topspeed of the treadmill/conveyor belt was maxed out at 25mph by the truck pulling it in the opposite direction, once the extra “I gunned it” thrust was applied to make the wheels spin faster than the 25mph belt then OF COURSE the plane will take off..but at a thrust required for 50mph!! Horizontal thrust will NEVER overcome the force of gravity on an object unless that object has WINGS to negate the force of gravity once the extra lift is achieved to do this. Remember this! The aircraft has WEIGHT that is a constant that DOES transmit to the ground THROUGH the wheels and bearings. The relative weight of the plane gets lighter as lift is generated til it reaches zero and the plane lifts off. That cannot happen without forward speed, with the weight of the plane CONSTANTLY transferring to the ground, thru the wheels and bearings, generated by the thrust of whatever is powering the aircraft horizontally. To think that the wheels and bearings mean little or nothing is ludicrous! SOMETHING has to support the weight of the aircraft during its takeoff roll til lift exceeds the weight of the plane. The only way LIFT is going to happen is with forward speed and if the wheels don’t spin fast enough, all the while bearing the weight of the plane, then it’s not going to lift off. So, if the runway (belt in this case) goes as fast in the opposite direction as the weight bearing wheels are spinning going the other way then nothing will happen. But if the belt has a final speed as did this belt in the test and then more thrust (“I GUNNED IT”) is applied to exceed what was necessary for wheel speed to compensate to takeoff lift relative to the runway then it will take off. The problem was that the truck pulling the belt stopped accelerating once it reached the speed required for the plane to take off even though the thrust on the plane was increased to PAST (“I GUNNED IT”) a takeoff speed. Another factor I noticed was that there was no simultaneous application of speed of the belt to the thrust of the plane. The plane was able to get to takeoff (thrust)power faster than the belt was being pulled and accelerated in the opposite direction. So, by all appearances, the plane began moving sooner because the belt was simply moving or accelerating slower and had not caught up to match the speed of the wheels on the plane. Did anyone else notice this flaw? I fully realize that to do this with such primative test devices and coordinating it between truck driver and pilot would be nearly impossible but it is a huge factor here. I’m positive that if thrust of the plane and acceleration of the truck were evenly applied in opposing directions the plane would have sat still. When the pilot “gunned it” as he so stated he effectively negated the experiment by exceeding the capacity of the belts FINAL speed to match the accelerating plane. I fell a lot better now. ;)
September 2, 2008 at 3:24 AMDean: ” I am a pilot and I can tell you that the myth about the airplane conveyor belt is supposed to be confirmed.” – Remind me never to up in a plane with you flying. You complete berk.
September 4, 2008 at 3:49 PMA plane is powered by thrust, not a drive system. Also, about Bournelli’s principle… The propeller of a plane is also an airfoil. The spinning of the propeller creates a low pressure in front of it, and a high pressure behind it, generating LIFT on the planes longitudinal axis, thus moving it forward (referred to as THRUST).
The tarp below will have no effect. The wheels of the plane could be spinning BACKWARDS and the plane would still move forward, and of course, take off. The tarp / ground is not going to stop the plane from moving forwards, or really have any effect at all. Maybe more friction on the wheels, is all.
September 6, 2008 at 11:03 PMThe airplane was perfectly able to take off because the belt COULD NOT decrease the aircraft’s speed forward!
The conveyor belt accelerated JUST THE LANDING GEAR of that Thing in the opposite direction –> Wheels were turning 2 times the ordinary take-off-speed.
The Plane still took off, because it was actually STILL DRAGGED forward by the Propeller until it reached its take-of-speed and went airborne!
Most likely this would also happen even if the conveyor belt would run at 3 times the plane’s take-off-speed. (or more – depends on the type/quality of the bearings used in the landing gear which may cause more or less friction)
September 7, 2008 at 3:04 PM“I GUNNED IT” said the pilot! Ok, the guy in the truck limited the velocity of the conveyor belt to the normal takeoff speed of the plane. Therefore it had a terminal velocity while the thrust caused by gunning the plane brought it PAST that velocity. Of COURSE it will take off! Once the wheels were spinning faster than the conveyor the conveyor became a moot point and was, for all practical purposes, a stationary runway! It was a SEVERELY flawed test. The plane has to MOVE to cause lift over the wings. If the runway is moving backwards at the same speed as the wheels are trying to go forward, while bearing all the weight of the plane due to gravity, it will sit still and not move. How can it go UP? If the circumference of the tire is, say 2 feet, and 2 feet of conveyor pass under it as it rolls one revolution it will sit still! This isn’t Voodoo math or physics here. It ain’t happening! Remember, the full weight of the plane goes down thru the wheels as long as it’s sitting still. If the moving runway has a FINAL speed and then additional thrust is applied to exceed that speed then forward motion will start, lift will begin, the plane will get lighter and eventually take off. The guy in the truck gave the runway a FINAL speed which was easily exceeded by the pilot applying extra thrust to achieve takeoff. IF the guy in the truck matched that extra thrust then the plane sits still. It was FLAWED.
September 10, 2008 at 5:04 PMwhat was the actual wheel speed on the plane as it took off? If as they say take off speed was 25mph and the ute was towing the belt at 25mph then with the engine providing enough thrust to hold the plane ’still’ relative to the surrounding ground the wheel speed would be 25mph but the airflow over the wings would be zero. If more thrust was applied by the engine and the plane takes off the final equation is (1) planes wheel speed would be 50mph (2) airflow speed over the wings would be 25mph. Do the experiment again but this time measure the planes wheel speed at lift off.
September 16, 2008 at 4:34 AMA plane does need forward movement to give an airflow over and under the wing to create lift.
September 20, 2008 at 5:58 AMIn the episode of the plane on the conveyor belt, the result is “busted” but this is incorrect to what the myth states. The myth identifies that both plane and conveyor are traveling at the same speed (in opposite directions) – therefore the plane will seem to not move at full throttle due to the conveyor. We can see in this episode in both cases (remote control plane and real plane) that the plane is moving forward (past the cones) therefore giving it lift enabling the plane take off. This myth needs to be tested again and proved correct – that a plane cannot take off when it is not moving forward.
anyone who thinks this experiment wasn’t flawed and thinks an aeroplane can take-off without any flow over the wings creating high and low pressures thus creating lift is a retard. Proper controlled variables would have the plane at a stationary postion-aeroplane speed 0 mph. All that is moving besides the tarp and car in this experiment is thet wheels of the plane are spining at 50 mph. As said wheels are free spinning with no connection to the planes engine, used only for safe landing and safe take off just like a water plane with no wheels. The plane still flies but the wheels don’t dictate the lift produced over the wings, the air speed over the wings does. What i gathered from the experiment is that the propeller produced air flow over the wings along wth the plane wasn’t stationary yet was moving forawrd, this in turn produced the lift needed to lift such a lite aeroplane.
September 20, 2008 at 6:00 AMIn order to take off the plane needs air over the wing to create lift. you have to define moving at the same speed. Ordinarly the plane on a conveyer will not take off if the plane is not going forward, with possible ONE exception. For plane to take off “lift” it needs air over the wings, if there was an air source in front of the plane pushing air over the wings creating lift, then therotically the plane would be able to take off “LIFT” WITHOUT moving forward, providing the engine is keeping the plane stationary into the wind, flaps should be enable the plane to LIFT up off the conveyer without moving forward. But sorry to say, the trail with the model and the ultralight, both craft were MOVING FORWARD which enabled both to take off.
September 20, 2008 at 6:12 AMregards,
Grizzly
I can understand how eople become mislead from this experiment because the believe the propeller is the thing that creates the wind that goes over the wings and this may be 50% of the case for a small aircraft but the dynamics of an aeroplane is that the propeller is designed to “pull” the air craft though the air, making the air pass over the wings producing high and low pressures, creating lift. In the case of an air craft whos propulsion was at the rear of the air craft would not push create any air flow over the wings. The wheels are meaningless to an aircraft, there is no connection between cars and aircrafts. I have lost all faith in mythbusters.
September 20, 2008 at 6:14 AMI wrote that last post extremely bad with mispellings, punctuational and grammerical errors. Ignore them and understand the overall message please. I can’t believe some people can’t grasp the physics of flight. Jaime and Adam aren’t gospel. They’re special effects people, not aeronuatical scientist.
September 20, 2008 at 6:26 AMI am an airline pilot and have taught theory to student pilots for many years. I have a good understanding of aerodynamics. I only just saw this episode tonight. The experiment is flawed. If the conveyor belt and plane were moving at the same speeds (in opposite directions) then the plane would have remained still in relation to the ground (or cameraman). In nil wind conditions there is no airflow over the wings hence the plane will NOT takeoff. In the experiment the plane was moving relative to the ground/cameraman. Ie the plane had more speed than the conveyor belt. Ie the plane had relative airspeed (ie it was moving relative to the ground and air since nil wind). Hence it was able to take off.
As an aside, forget the conveyor belt. When a plane takes off in nil wind, it needs to accelerate to an airspeed where there is sufficient lift (created from the airflow over the wings, which in turn is created by moving the plane relative to the air which is the same in this case as relative to the ground as nil wind).
If there is now a headwind component, then the plane already has some airspeed (airflow over the wings) before it starts moving over the ground. Hence it will need less runway to accelerate to the same airspeed before it can get airborne.
If the headwind component is the same as the airspeed required for lift off (typically very strong winds) then theoretically as soon as power is applied the plane will take off with little or no distance over the ground.
Anyone who thinks the plane could takeoff with no airflow over the wings is WRONG. If you come into my flightdeck trying to tell me that Mythbusters was right then you wont be needing to make the decision to get off my plane, as I will have already made the decision to offload you. So please get over it if you were wrong.
Enjoy your wait in the terminal for the next flight.
September 20, 2008 at 6:35 AMI think the wording of the myth is especially important in this case. It says that an airplane can not take off on a runway that is moving backwards….
It does not say whether, as a result of this moving runway, the plane is able to move forward or not. What we saw on the show was that the planes *were still able to move forward* and hence able to generate lift from air moving over its wings and hence take off. The reason for this is that the force generated by the propeller was large enough to overcome the backward force exerted on the wheels through frictional contact with the backward moving runway.
September 20, 2008 at 8:48 AMI should also mention that the backward frictional force exerted on the plane by the moving runway is fairly small, assuming that the plane’s wheels have good bearings (as you would expect).
September 20, 2008 at 9:06 AMForce= Mass times Acceleration
The airline pilot has of course got it
wrong.
You do not necessarily need air flow over a wing to fly.
Neither rockeds nor helicopters have wings,
they just have very large “F’s” pointing
in the right direction.
Both the model and the ultralight could
September 21, 2008 at 3:08 AMpossibly fly even if tethered, as compared to their self weight they generate such a high thrust and have a large prop wash over the wing surfaces.
Paul, yes I know F=Ma and their is no disputing that rockets and choppers can “fly” but this isn’t what the episode was about. Did you see them putting a helicopter or rocket on the conveyor belt?
Airplanes (not rockets or helicopters) have their thrust aligned in the horizontal plane in normal flight to overcome drag, not to overcome weight. So airplanes need airflow over the wings to generate lift to overcome weight for normal steady flight. The thrust from its powerplant is used to overcome drag and the excess thrust is used to climb.
Airplanes generally have a lift to drag ratio of about 10:1 (a function of wing design). This means the lift force is 10 times greater than the drag force. In steady level flight lift = weight and thrust = drag. You still have excess thrust to climb but it wont be 10 times more. So even if you put the propeller on the roof, you still wouldn’t have enough thrust to overcome weight. That’s why planes fly forward, and not vertically. Have you ever seen an airplane fly vertically in sustained steady flight? No. You can convert kinetic energy into potential energy but you cant hang the airplane off its propeller vertically. Eventually its going to run out of steam.
Rockets, helicopters, rocketpacks are not relevant to this discussion. Why would you even bother putting on of these things on a conveyor belt to start with? It’s not going to prove anything.
Regards,
September 22, 2008 at 6:47 AMAirline Pilot.
Forgot to mention that the propwash, or slipstream, although it does create extra airflow over the wing, is nowhere near enough to create enough lift to overcome weight. It does however as a byproduct give the controls a firmer feel.
September 22, 2008 at 6:55 AMThe airline pilot is RIGHT!
AN AEROPLANE NEEDS AIRFLOW OVER THE WINGS TO FLY. SIMPLE AS THAT!
Perhaps all of you people who “think” you know how to fly a plane should go to your local flying school and do a “stalling” lesson to find this out for yourself. Then maybe you wannabe pilots will realise this fact.
I am a Grade 1 flying instructor with an Airline Transport Pilots Licence (ATPL) and have been flying for 12 years and teaching theory and flight to students for 7 years.
September 22, 2008 at 7:06 AMWell, after getting here via google after what I thought was a disappointing show, I’m NEVER GONNA FLY AGAIN. Seems there are a great many pilots out there that think flight has something to do with ground, or velocity relative to it. That idea’s not even ‘for the birds’. Myth busted.
September 22, 2008 at 10:27 AMIm 15 and even I understand the concept behind this.
September 23, 2008 at 2:50 AMThe Wheels have little to no effect on the plane’s ability to take off when its on a conveyor belt because its merely a bearing. I couldn’t be bothered reading the rest of the 400 comments- but dean, you’re stupid.
SuperGubmy, you really are a GUMBY! Take some flying lessons or do your research before you open your big cyber mouth. Get your facts right.
PLANES NEED AIR OVER THE WINGS TO FLY!
September 24, 2008 at 7:56 AMI think we all know now that they were trying to see if a plane could move forward/go faster than the conveyor belt and then take off (which it could). I think a lot thought (myself included to start with) that they were trying to test whether a plane would take off if it was held stationary in relation to a fixed point off the conveyor belt (which it wouldn’t).
September 24, 2008 at 6:04 PMYou guys who are trying to use airflow to prove that the plane will not fly are overlooking the entire point.
It is true that the plane needs airflow, but a conveyor belt below it will NOT prevent it from getting air flow. It does not matter how fast the conveyor belt is moving – it could move 300x the speed of the airplane, and it would not matter.
This is because the planes forward motion is caused by the force of the thrust, NOT the turning wheels. The wheels can turn as fast as they want, the propellar will still thrust the plane forward. However, a car, a vehicle that DOES propell forward via its wheels, will not move forward. A plane uses its wheels only as contact points to the ground with minimum, and propels forward with thrust.
Physics 101. Go to college, pilots.
September 26, 2008 at 7:35 PMI can’t believe how dumb some people are!
September 29, 2008 at 8:29 PMThe so called pilots and engineers here are full of SHT tell that to your dumb friends.
If you really think the plane will NOT take off you are either under 10 years old and have a limited brain span, failed HS and any other education you faced, or just a waste of space in society with the power of a dumb computer.
Just unbelievable how stpd people are!!
Bernoulli’s principals, aerofoils, newtons laws, are you guys flexing your muscles in front of a mirror?….do you guy have any idea?
People here trying to explain “how this plane would take off” stop trying to educate people that are just PLANE dumb!
Go and watch Ophra!
The only Myth busted here is “Mythbusters” themselves…
Jamie and Adam know as much about science as the BBC TV program “Top Gear” know about cars – ZIP (well almost anyway).
If the Aircraft is travelling in the opposite direction as the tread mill at “normal take off speed – relative to the tread mill” (as I thought the myth was presented in the TV show), the aircraft stays put (with very little engine power required). Period.
If the Aircraft is travelling in the opposite direction as the tread mill at “normal take off speed – relative to the ground” (as it appears to be presented at the top of this web page), the aircraft will take off normally (although a little more engine power than normal will be required). Simple.
The difference in the required engine power is due to the rolling resistance of the wheels and nothing more.
I’m glad we now have this one settled… now we can watch the real exciting stuff on TV… The Advertisements :)
October 1, 2008 at 1:31 AMWe had a considerable discussion on this last night. The biggest issue is that people don’t seem to be able to disconnect the conveyor from the airplane. Since the wheels on the plane really only support the plane and do not drive the plane, then they really don’t enter into the equation.
When power is first applied and the plane starts to move the conveyor belt will start moving in the opposite direction, however the wheels will only roll. The plane moves at 1 mph, the conveyor belt moves at -1 mph, the wheels will be moving at 2 mph. The plane moves at 100 mph, the conveyor belt moves at -100 mph, the wheels are moving at 200 mph, but the plane will fly since it’s moving.
If you take a matchbox car and place it on a belt sander and hold it stationary it will sit there and the wheels will just sit there and spin. Now, push it with your finger and the car will move forward, the wheels will spin faster, but the car will move forward. The thrust is provided by a force external to conveyor belt just like the plane.
Thanks
October 6, 2008 at 7:36 AMChicho, you are retarded. You have shown your level of intelligence through your plethora of spelling, grammatical, and punctuation errors.
October 8, 2008 at 3:25 AMYou should have studied harder at school if you wanted to be a pilot.
Have you you not noticed that without wheels, the plane cannot move forward. The plane can only move as fast as the wheels (except of course when the plane is in the air.) Therefore, if the plane was on a proper treadmill then it would not have moved forward or taken off.
October 10, 2008 at 11:38 AMOK, I Admit, it would move forward a bit, but not enough to get of the ground
October 10, 2008 at 12:09 PMforget everything i just wrote. the illustration with the Rollerblades and the rope really made me think about it properly and now i am a true believer.
October 11, 2008 at 9:41 AMOk..one more time! When the pilot gunned the engine to overcome the FINAL speed of the conveyor he invalidated the experiment. A good question to ask he pilot is WHY did he have to GUN it as he said he did? He had to gun it because the plane wasn’t MOVING fast enough to counter the speed of the conveyor! Why doesn’t anyone else see this??? Had the conveyor NOT had a FINAL terminal speed, as pre-arranged, and the pilot only taken the plane to it’s normal engine RPMs for takeoff the plane would have sat STILL! I was an air traffic controller in the Navy for 4 years and spent two of those years on an attack aircraft carrier…a MOVING runway! Our ship had to move 20+ knots or more depending on surface winds to generate enough lift to get catapulted aircraft airborne. So, when the jet was sitting still at the beginning of the cat it already had 20+ knots of speed generating lift over its wings. ALL of the weight of the aircraft was on the wheels and those who say the wheels are irrelevant have forgotten that gravity still works! Remember…gunning the engine overcame that final speed of the conveyor. If the conveyor would have had unlimited speed matching capability to match the applied thrust then the plane would have sat still. The wheels bear the weight. The WHEELS BEAR THE WEIGHT! ..and they keep bearing the weight of the plane till cancelled out by LIFT caused by forward motion. Wheels DO enter into the equation since they do have a circumference, have contact with the ground and maintain the weight of the plane until lift is generated sufficiently to gain zero weight on the wheels. Myth BUSTED!
October 29, 2008 at 1:58 AMThe really interesting part is that the plane took off using much less ground distance. The physics is clear, if not obvious (that’s why this is interesting & fun)
October 29, 2008 at 12:55 PMWhat I’d be interested in is a comparison of the airspeed from the propeller over the wings on both tarmac and conveyor. It seems that they conveyor reduces the runway length very close to zero velocity, but as the airspeed approaches take off speed the plane moves forward (as discussed ad infinitum) and lifts off. What is the point where the conveyor ceases to matter? Clearly it shortens the run-up distance to air speed.
Neat stuff.
Thanks
Will
You people are all idiots for arguing this… sooo many people…so little understanding of physics…and so much blathering… glad i didn’t read the whole page…
October 29, 2008 at 2:51 PMAre you kidding? this is great! i never laughed out so much as i have reading this!
“Had the conveyor NOT had a FINAL terminal speed, as pre-arranged, and the pilot only taken the plane to it’s normal engine RPMs for takeoff the plane would have sat STILL!”
Lol! no, it would not! the plane would still move forward to it’s takeoff speed no matter how fast the conveyor belt was moving!
Will N: “Clearly it shortens the run-up distance to air speed.”
FAIL! why would it shorten the runway? the plane still needs to reach take-off speed relative to the air!
November 7, 2008 at 9:17 AMThe experiment was FLAWED AND INCONCLUSIVE as the plane still had speed relative to the ground (and air since there was no wind). When the plane reached take off speed, the plane should have been at the same cone that it started at, but it moved down several.
I don’t believe the plane would take off if the plane maintained zero speed relative to the ground (and air).
What gives a plane lift is more pressure under the wing than the top. This is caused by movement of the plane relative to the air. This is why a plane needs more distance to take off in a backwind and less distance in a head wind. Try flying a kite by running with the wind!!!
What irritates me is people stating Newton’s second law of physics, when it has nothing to do with giving a plane it lift. Sure force allows a plane to move forward, but it’s a positive pressure under the wind that gives lift. So those that use Newton’s laws to explain the outcome of the experiment, GO FLY A KITE (by running with the wind)!!!
November 16, 2008 at 11:56 PMIn my previous post I said that, “Newton’s second law of physics…has nothing to do with giving a plane it lift”. I should have said that it indirectly gives a plane lift. Force propels a plane forward which gives speed relative to the air, that causes a positive pressure under the wings, that gives lift.
In a 100mph tail wind, all the force that that plane can give, won’t give it enough force forward to take off, even if it’s moving 100mph.
November 17, 2008 at 12:10 AM“The tarpaulin is completely irrelevant. The propeller is screwing into the air, pulling the plane forward.”
Actually, it makes all the difference. The length of the tarp is what allowed the plane to take off in the first place.
If the tarp had been the size of a normal conveyor belt, the plane wouldn’t have been able to take off *without first moving off the conveyor itself*.
And that’s where I think this particular myth busting exercise failed: by using the long tarp, they didn’t exactly replicate the myth.
On a conveyor that is exactly the length of the plane, the plane will not fly without first leaving the conveyor. It won’t, because it can’t generate enough lift to become airborne.
On a conveyor that is exactly the minimum length that the plane needs to take off at full throttle, the plane will take off.
I think the basic problem here is that the myth isn’t very well defined. Which is why you have pilots with years of experience telling you that the plane can’t take off from a normal conveyor belt.
If they could, the US Navy would’ve started building much shorter aircraft carriers years ago.
November 17, 2008 at 2:40 PMHere is a twist on the idea and why this confuses people (jamie, adam):
A plane or any other wheeled object which has frictionless wheels on a treadmill will remain stationary reguardless of the speed of the treadmill — this is primarily why the logic was flawed and any example comparing planes and automobiles is flawed. The similar/reverse, a frictionless treadmill, is in essence what this question posed and why the plane remains motionless in the question! It would be obvious that the plane will not fly if not for air moving over the wings.
The intent of the original problem could also be matched if you replaced the conveyor belt with a huge vice-grip or huge string and removed the wheels and ground completely from the equation and had the propeller exert whatever force it wanted so again the plane remained motionless… hm, you could even measure the force on the vice-grip or used a string to see if the plane indeed rise to determine if there was any lift. A plane in a vice would fall reguardless of forward force when the grip was released and a plane on a string would not lift off.
The idea of that the propeller pulling you forward like a guy on roller blades and a treadmill pulling on a rope explains why you might go forward but not why you LIFT OFF. With the treadmill matching whatever your speed was because you continued to pull on the rope you still wouldn’t actually move forward and like you wouldn’t take off.
The ultimate proof involves a 100mph car motionless on treadmill trying to fly a kite and that is a proper example trying to compare planes and cars and rollerblades with the effects of speed matching treadmills.
This entire thing is complicated because turbines not only try to pull the plane forward, but they also blow air of the wings… an airplane or a kite in a wind tunnel will also take off regardless of the speed of the plane. But this doesn’t involve a wind tunnel and this isn’t the object of this question, it is the ground speed.
November 22, 2008 at 5:04 AMUltimately, the proper example is this… not a big steel cable, which is another prime and great example… but a bullet… shoot a bullet over a magic treadmill and say it remains motionless relative to the treadmill or the ground. Hm… magic treadmills aren’t as common place as magic bullets so lets say this is a magic bullet… if the magic or normal bullet remains motionless relative the normal or magic treadmill (aka ground) will it ever go forward? No, the question says it doesn’t move forward — FACT, use any magic you want to explain the fact. The question says there is no forward movement and that we are dealing with a magic treadmill/bullet.
November 22, 2008 at 5:56 PMProp plane, maybe. Jet plane, no. Most of the arguments seem to only argue that yes, planes can fly.
The refuted “myth” is whether or not a plane can be airborne from a stationary position while a movable ground prevents it from rolling forward.
As long as the air pressure below the wings is greater than the air pressure on top, the plane will lift, according to the Bernoulli Principle.
A jet plane would require some wind resistance against its leading edge through forward acceleration to gain lift. A propeller, however, might the provide the high/low air pressure differential against the leading edge of the airfoil.
November 26, 2008 at 4:30 AMThe ridiculousness of the experiment becomes obvious when you realize that wheels and treadmills are totally irrelevant.
Imagine a plane fitted to run on a maglev (magnetic levitation) train track. Like a maglev train, the plane floats inches above the track.
Now if the whole train track moves in the direction of the plane, forward or backward, who cares? Generally speaking, it has no affect the plane. What matters is the plane’s airspeed — getting enough air moving over the wings to produce enough lift for takeoff.
The situation is the same for wheels and treadmills, except that there is a bit more friction involved. Yet that friction is not a relevant factor — the maglev thought experiment still applies.
December 6, 2008 at 7:10 PMthe treadmill, tarp, whatever could be going a million miles an hour in the opposite direction and the plane would still move forward b/c its being “pulled” by the prop. thus, it would reach its take-off speed, and fly!!!!
December 7, 2008 at 8:05 AMA plane with no wheels will take off given no friction on the ground.
The ground doesn’t matter, and neither do the wheels.
December 8, 2008 at 1:21 AMSorry – but if there is no airflow over the wings, the aircraft will stall – this means there is no lift and so the aircraft cannot fly. However if the myth was to suggest that an aircraft could not take off on a moving treadmill – then obviously this was clearly busted – it just required a bit more energy.
In fact it is possible to fly an aircraft backwards as I have shown my friends on a couple of occasions when I have managed to take off into an extremely strong headwind, cut the throttle and flown backwards at just above stalling speed (remeber we are talking airspeed not ground speed) along the runway, then by adding more power I was able to land exactly where I took off without completing the circuit – won a good deal of beer on that one..
December 11, 2008 at 9:58 AMSnarky sure missed the point here. For the sake of creating a better example, since it seems the one I gave falls on deaf ears, let’s just say that the plane is stopped and the conveyor starts before the engine is started. Which direction is the air flowing over the wings now? Can it fly? NO! Not hardly! If the conveyor was moving at 200 mph before the engine was started the airflow over the wing would be 200mph in the wrong direction! Now, let’s start the engine and see what happens! The plane is already moving 200mph backwards and will continue to move backwards til its thrust is enough to overcome that 200mph backwards movement. So finally the plane is stationary over a spot on the ground and is doing zero though the thrust component generated is enough to do 200mph on a stationary runway. Ok, so now the plane is doing zero with the applied thrust and the runway still moving 200mph backwards. The plane generates more thrust which is now matched by the conveyor exactly. Remember, at this point of zero speed over the ground the wheels still bear the TOTAL weight of the plane. Speed over the ground of the plane will still be zero as long as it is exactly matched with increasing thrust and increasing conveyor speed. THE WEIGHT OF THE PLANE IS STILL ON THE WHEELS WHICH CONTACT THE GROUND. As long as there is not sufficient lift over the entire wing to decrease the weight on the wheels at some point to zero that plane will continue to sit still. For those that say the wheels don’t matter… WOW! They sure do unless the intial weight of the plane is zero and we all know that aint gonna happen! The experiment was primitive at best and flawed when the pilot “GUNNED IT” to overcome the agreed on final speed of the conveyor. If the conveyor kept on accelerating to match the extra thrust applied by the pilot to overcome that speed the plane would have sat still.
December 19, 2008 at 4:48 AMJohn hit it exactly when he said in the last sentence of his first paragraph “it just required a bit more energy.” which is what happened to the plane when the pilot gunned it, however, there was no corresponding “gunning” of the conveyor at that point to match it. Would the plane have gotten off the ground had the pilot not gunned it to overcome the speed of the conveyor? NO way! I’d bet that the pilot in the experiment would agree.
The full scale test which was performed was not true to the wording of the myth. The reason the plane took off was that the forward force generated by the engine overpowered the backwards force generated by the “conveyor”. The plane moved forward relative to the ground (notice the stationary camera pans to follow the moving plane) airflow and low pressure over the wings generated lift and the plane took off. If you tested it true to the wording, that is: “the backwards motion of the conveyor keeps the plane stationary relative to the ground and the speed of the conveyor increases as the planes engine power increases” the plane would not take off. However, the backwards force of the conveyor is slight and it is almost inevitable that the engine will overpower this, the plane will move forward, and take off. I advise you to contact some aeronautical engineers/ physicists and have them come on the show to explain it mythbusters. Your test was impressive but simply false. Yes, the plane did take off on a conveyor belt, but it was moving relative to the ground.
December 20, 2008 at 11:23 PMWhy do airplanes have wheels in the first place? To propel themselves forward. That is why the wheels are static and remain down while the plane is in flight, if there were a device which raised the landing gear during flight then the wheels would stop moving and therefore the plane could no longer propel itself forward and would fall out of the sky. Duh.
December 20, 2008 at 11:24 PMNewbie: Haha, it’s a good thing that the landing gear isn’t raised.
December 20, 2008 at 11:25 PMHere are the facts of this failed experiment. All you Kool-Aid © drinkers please put down your rose colored glasses and read on:
Lift occurs when air passes across the surface of a wing (airfoil). This test was flawed for that very reason.
1. The conveyor belt was not in a true sense a conveyor belt, but just an instable surface that didn’t truly keep the plane in one place. It was not a constant surface, but instead was acceptable to stretching, throwing off the movement versus opposite movement concept.
2. The components to lift that plane were a 25 mph forward movement for 85 feet.
3. The test to determine speed and distance were under different condition than were present on the day of the final test.
4. The weight of the plane on the unstable surface still had enough contact with the tarmac to still cause forward movement.
5. Any air movement against the plane’s airfoil would contribute in some way towards lift.
6. It was visibly obvious that the plane was moving forward based on the stationary traffic cones along the runway. The cones appeared to be about 8 – 10 feet apart and approximately 10 cones were passed on the way to lift.
7. Once the plane lifts off the conveyor belt, the thrust of the propeller would accelerate the plane adding to its lift.
In order to make this a legitimate test the plan should be on a real conveyor that would not be affected by the weight of the plane pressing on its surface. The forward direction would have to be constant. As was shown in the scaled down test with the car, the conveyer does not have to be 2000 feet long, just long enough to hold the plane and maybe an additional length and a half to make up for the lack of a synchronized startup.
The true flaws of the test were set aside in lew of the excitement of misinterpretation of the results.
Guys, do it on a real conveyor belt in a hanger so all outdoor conditions are reduced.
December 20, 2008 at 11:47 PMOK – we all agree that a stationary plane can never achieve lift-off because that is impossible. But, under what conditions would a hypothetical treadmill on the ground keep an airplane stationary? It seems obvious that if the treadmill could counteract the forward progress of the plane then that condition would be met. So build a large scale diet coke bottle with wings set atop and attached to a tripod on wheels and place that device on a treadmill moving backward. Measure how many Mentos candies would have to be dropped in the diet coke bottle before the forward propulsion caused by the foam reaction moving backward could overcome the treadmill to make the device no longer stationary.
December 21, 2008 at 12:10 AMGreat experiment Newbie! I guess it all comes down to the wording of the myth. A stationary plane (relative to the ground) will not take off, but if the question is simply whether the plane can take off on a conveyor then it is yes. The plane’s engine should be much more powerful than the conveyor, move the plane forward, and achieve lift. All the conveyor is doing is making the plane work harder to lift off…
December 21, 2008 at 12:20 AMOK – Here is the real test of this in small scale. Create a treadmill which is wide enough to have two “lanes”. The left lane will be to test if the airplane can achieve lift or not on a treadmill. The right “lane” will have an automobile on it and also a taxi type vehicle attached to the airplane to keep it from moving in either direction and also with a quick release. Have the airplane speed and the speed of the taxi vehicle and the automobile equal and also equal to the treadmill moving backwards, so the entire system is completely static. When you release the taxi vehicle from the airplane see if the airplane continues to be in equilibrium or if it indeed moves forward and achieves enough lift to get off of the ground. Then we will all know for sure or not. Thank you.
-Newbie.
December 21, 2008 at 1:17 AMDan, after all this time, I can’t believe someone would still post that the test was a failure. Please just take a physics course. It is so simple. Tires have nothing to do with the planes forward movement, or lack thereof (except for a little rolling friction). Thus, since the propeller is moving the plane through the air, and not the tires, then it will create lift on the wings, assuming it is moving fast enough. Once enough lift is created to overcome the effect of gravity, then the plane will take off. Of course, the wheels will be spinning faster in this case then they would be if the plane were just taking off from a normal runway.
December 21, 2008 at 2:12 AMThe people aren’t saying that the plane can’t take off, they are noting that the wording of the entire myth is off, and the test was based on off wording.
The plane was not moving at an equal opposite speed to the treadmill because it was moving forward. The wording of the myth was off.
The myth did not say “a plane can not have more thrust than that of a treadmill and as such achieve liftoff,” which is why people feel it was done incorrectly.
December 21, 2008 at 6:08 AMBut that’s just it. The plane was moving at an equal speed to the conveyor belt, only in the opposite direction. The reason it moved was not because it was moving faster, but because the conveyor was acting on free moving wheels, and the plane’s propeller was acting on the air, not the wheels or the belt.
December 21, 2008 at 11:23 AMHas that pilot had a day of training in his life? Nice 3 point landing at the end. They got a real winner to test this one.
As Jamie said: stupid myth, take a physics class people.
December 21, 2008 at 1:08 PMAnybody remember the Custer Channel Wing.
It was the first VTOL. It had a prop mounted right over its semicircular wings.
There are some great pics of it lifting off when tied to a pole.
December 22, 2008 at 10:20 PMhttp://www.custerchannelwing.com/04_facts.html
It is all about airflow over the airfoil. Whatever the ground it doing just does’t matter
When I saw 500 comments I didn’t think I would have to write anything here, however only a very few people saw through this experiments flawed conclusion. Rick you are the only one I found with correct logic, for anyone else who saw through this, sorry, there were so many comments I may not have seen yours.
Thrust is thrust, in this case it doesn’t matter where it comes from (while the plane is on the ground) because it will have the exact same effect. I’m not sure what Jamie and Adam were trying to prove with the model car. The key to this myth is in the wording as some people pointed out and speed.
The experiment is flawed because:
1.The speed indicator on the truck pulling the tarp was GROUND SPEED.
2.The speed indicator on the aircraft was AIR SPEED.
3.I don’t remember the rotation speed (take off) of the aircraft – but let’s say it was 25 mph. This is the speed the aircraft is traveling through the air when it took off, this is also the speed air is traveling over the wings. The speed of the prop thrust has nothing to do with the experiment – and we won’t get into prop pitch (the distance the prop travels through the air per rotation) because it really has nothing to do with the experiment either.
4.I just had to add that the tarp was between the stationary ground and the plane’s wheels and was moving just like a treadmill belt – not sure why people were commenting about it being flawed.
Here is where math 101 explains why this myth bust is a flop. If the truck (and the tarp) is traveling west at 25 mph (GROUND SPEED) and the air craft is traveling east at 25 mph (AIR SPEED assuming the 0 mph wind speed needed to keep the tarp on the ground) at the time of rotation the aircraft is moving over the ground at 25 mph and over the tarp at 50 mph . This is where the wording issue comes into play. If the aircraft’s tarp speed (wheels on the tarp) was 25 mph the aircraft would have been stationary and would not take off because the airspeed would have been ZERO.
So, of course the aircraft could take off if its airspeed is equal to or greater than its rotation speed, and this is why the plane took off.
To correct this experiment you would need to attach a speedometer to the wheels of the aircraft.
I can’t believe that the pilot didn’t see through this immediately. Be careful taking off buddy.
December 30, 2008 at 2:18 AMYes, Aviator60, the plane was moving 50 MPH (for your example) relative to the tarp. But I (and most people) would assume that when they said that the plane would be moving the same speed as the tarp, they meant relative to the Earth for both. Thus, they were moving at the same speed, as the myth stated, unless I am forgetting something from the wording.
December 31, 2008 at 4:01 AMAviator 60, your reasoning and explanation are good.
The problem is you don’t understand the myth being tested.
Here is the wording at the beginning of this thread:
“An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.
Notice it says “speed equal to its NORMAL ground speed”
Most people who read this think that the result is zero airspeed and they reason (correctly) that a plane can’t take off with zero windspeed.
But the surpise is that the moving runway does not (and can not) effect the airspeed of the airplane in any signifigant way.
You and I agree on the science of what is happen. At this point we just disagree with the myth being tested.
Do you now see that the myth is NOT ABOUT TESTING IF A PLANE CAN FLY WITH NO AIRSPEED?
The real point is that the moving runway can affect the speed relative to air of a car but NOT AN AIRPLANE because car move by wheels against the ground and airplanes move by pulling themselves through the air (even when they are on the ground).
January 1, 2009 at 11:38 PMThis would be cool: Take off at slow ground speed- With a 45 mph headwind, face into wind and gas engine for control, liftoff airstrip at 3mph groundspeed. Wouldnt that look cool?
January 6, 2009 at 3:56 AMBush pilots rock.
You morons! An Airplane is propelled by its propellor (or jet engine), NOT THE WHEELS! Air speed is what makes an airplane fly. GROUND SPEED MAKES NO DIFFERENCE WHATSOEVER! You people who think the plane wouldn’t take off on a treadmill need to think a little.
January 7, 2009 at 11:53 AMDidn’t read all comments, didn’t do much physics, but…(and I may be repeating others) the trick works because of various variables
1. tractor prop
2. high trust to weight ratio
3. speed not equal
The prop itself creates enough air current over the wings to provide part of the lift, add forward movement and high trust to weight and there is enough lift to take off.
If you do the same but with a pusher prop or jet engine, which itself won’t provide air currents over the wings, so zero lift and run the conveyor belt fast enough to cancel ANY forward movement, the a/c will not take off. Zero lift.
Again my apologies for the unscientific approach.
January 7, 2009 at 2:10 PMAs others have noted, the airplane experiment was flawed. Airplanes fly because of lift (which for a fixed-wing plane is a combination of Bournelli’s law and some elementary Newtonian stuff). The wings care about AIR speed. Ground speed is utterly meaningless. The speed of the tarp means nothing at all…it is the speed of the wing through the air that matters.
If the plane took off, it took off because sufficient AIRspeed was obtained. Forget groundspeed. Pilots rotate aircraft based on AIRspeed. Only GPSs and LORANs measure groundspeed.
As others have also noted, this was not a ‘true’ conveyor belt that stabilized the aircraft at a specific point on the ground.
I’ve been a pilot, a Certificated Flight Insructor and a ground instructor for many years, and have many thousands of hours in airplanes. I know what makes an airplane fly. Whether a plane is on a conveyor belt, an aircraft carrier, or a runway, GROUNDspeed means absolutely nothing in terms of life. AIRspeed is the ONLY speed that matters.
January 14, 2009 at 2:29 PMENOUGH ALREADY the wheels on a plane are like roller skates if everybody here puts a roller skate on a level treadmill the damn thing doesn’t move so any kind of thrust like I don’t know an airplane engine is going to move it forward. Forward = airspeed = lift Myth Busted
January 14, 2009 at 6:53 PMChris,
You’re another one who understands what is going on but doesn’t understand the myth being tested. Go back a few postings and read my last post (Presto). Then go to the very beginning of this thread and confirm what I explain.
Ruy Horta,
Fallguy is right that you are way off. You really need to start at the very beginning.
I don’t care how long this thread gets. I’m going to keep checking in. I get a kick out of all the different characters.
January 14, 2009 at 10:33 PMI sorta skipped alot so in case of repeats, I am sincerely sorry but I had to jump in on this because when a work collegue asked the question of me it blew a fuse in my brain. He posed the question that the conveyer is designed to match the speed of the wheels turning exactly in the opposite direction. There was just something that I couldn’t get my head around because the way it was posed appeared impossible or a paradox. I know stuff all about physics and have no idea about relevant equations so I’ll state it as easilly as I can. The wheels are free spinning and therefore are a tertiary force (not a force as they’re free wheeling but bare with me) to the secondary force which is the plane moving forward due to the primary force of the prop pushing forward. The wheels spinning are only true if the plane moving forward is true. The conveyer moving backwards is only true if the wheels turning are true. Therefore, the conveyer can only be true if momentum is true. Therefore it is impossible for wheels and conveyer to be true if momentum is false. The scenario is broken ie a paradox. The only way the ‘equation’ can work is if all factors are false.
January 15, 2009 at 1:37 PMThe concept of the conveyer matching the plane’s velocity is much easier though. The plane will move forward on the conveyer because the plane has no force applied on it by the ground (other than negligible friction of the wheels on the axle) The conveyer will move backwards at the same speed as the plane moves forward but the only force is applied to the speed of the wheels which will simply end up being double the velocity of the plane.
Kinda clumsy description but I think I got it across.
Think of it this way….can a plane with NO wings take off?
Take a plane, with NO wheels, and tie it to a wall with a rope.
Let it rev up to full throttle, then cut the rope, the power of the thrust of the engine will lift the plane immediately. Even without wings, it will rocket off in a mad twisting flight and crash, but it will take off….it won’t just sit there, blowin’ in the wind.
January 24, 2009 at 9:45 PMOk, so we agree that the lift on any plane is created by the the air moving under the wing and “pushing” it upwards (Bernoulli). And if the conveyor was indeed able to match, in reverse the forward speed of the plane, the plane’s speed reletive to the ground should be zero. And if we can assume that the turbo prop engine created enough wind force to create the upward lift on the wings then couldnt this experiment be replicated by removing the wheels altogether and having the plane sit stationary on the ground? We know that this is impossible otherwise we woudlnt need runways. But that wasnt the point. The whole point of the experiment was to determine whether or not the plane would lift off when the speed of its wheels were matched, in reverse, by the conveyor which we can agree that it was (close enough). So the wheels are moving forwards at 25mph and the tarp is moving backward at 25mph. But as you can see on the show the plane’s relative speed to the ground is definetly not zero, it is moving (watch as it speeds past the cones). The speed of the wheels and the tarp doesnt matter. The fact is the plane is moving forward fast enough through the air to create lift. The myth states “An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.” Even if the runway was moving backwards at the planes normal ground speed, the plane could still create enough forward airspeed to take off. The speed of the wheels does not matter. The true nature of the myth I think is “would a plane be able to take off if its reletive ground speed was zero” (i.e. if you were standing perpendicular to it, it would appear as if it were not moving even though the wheels were spinning). The test was flawed or the myth was misunderstood. Its all about the theory of relativity. Think about it, if you are standing by row 1 inside a jet plane flying 700mph and you jump up as high as you can, do you end up landing in row 35? Simple fact is that the wings relative to the ground were moving forward creating lift and thats what makes planes fly.
January 30, 2009 at 11:43 PMYou people assume the lift required to get the plane off the ground is comming from the engine and propeller. This is so wrong. The lift is generated by the airflow over the wings when the propeller pulls it forward. The propeller only pulls the plane forward so that air can flow over the wings AS IT MOVES FORWARD!!!!!!!!! The only problem with the myth busters test was that they did not REGULATE THE AMMOUNT OF THROTTLE the pilot gave to achieve lift off. If they had done this it would never moved forward and never produced lift from the wings and therefore never would have lifted off. This is the only myth i have ever disagreed with from this show.
February 8, 2009 at 8:09 AMto tom, Chris,Matt et al, and all the other non physics people above who think that this was done wrong.
I’m sorry but sometimes people just can’t grasp what is being said!
The myth is about whether or not a plane can take of on a moving runway, thats It.
The conveyor ONLY ACTS ON THE WHEELS!!!!!!
The whole point is, that it matters not whether the wheels are turning, or whether the groung is moving! It is the planes movement relative to the AIR that matters!
There will be no lift without forward motion of the plane. The plane’s forward motion HAS NOTHING TO DO WITH THE WHEELS! I’ll say it again for you, forward motion has NOTHING TO DO WITH THE WHEELS! they are free moving, so why would it matter if the conveyor was moving or not?
The wheels are free moving and not under power so they have nothing to do with the motion of the plane!
The conveyor will not impede the engines’ action on the air! It is the engine, pushing (pulling) the air through the blades that causes the forward force, NOT THE WHEELS!
I’ll say it again, just in case you missed it
It is the action of the engine on the air that provides forward force, NOT THE WHEELS!!! so it matters not whether they are spinning to begin with. THE WHEELS DON’T POWER ANYTHING.
It matters not that the ground is moving, the plane will go forward relative to the air anyway! If the AIR was going backwards, that is a whole other story and not this myth!
That is the best and easiest way i can think of to explian it, if you still can’t grasp it then i’m afraid your one of those people who never will… take that as you will.
Sorry about the capitals but there is no bold or underline function.
February 11, 2009 at 9:06 AMSean Salvador.
Oh, and Dean-the-pilot up at the top there. Your a prime example!
February 11, 2009 at 9:35 AMYou seem to know everything explained but just cannot grasp the fact that the plane moves forward due to the action of the engines on the air! Why would it matter if the ground was moving under it? The plane will still have forward motion!
Planes are not powered by wheels and you know this, but somewhere in between you get lost and start thinking that because the ground is moving backward, the plane will not move forward!!! Why is this? When you clearly state that the whels are free moving… haha
I seriously doubt that you are a pilot but if you are you need some er-education on all matters of physics. That is not an ad hominem attack as clearly there is some expertise lacking.
Sean Salvador
The purpose of the engine on a plane is to provide forward thrust in order to create an area of low air pressure on top of the wings and high pressure below, which generates lift. If the plane is standing still in relation to the air (and the ground), the wings will not be able to generate lift and it cannot take off.
February 12, 2009 at 9:34 AMsaw the episode, agreed with the MBs, myth busted…
i wonder, if you get a big fan the same size as the plane’s propellers, and place it (not attach it) behind a plane, and you turn that fan on with a wind displacement that’s equal to the plane’s propeller’s, then would the plane be able to fly? or move forward at all?
Wind From Fan -> PLANE <- Wind due to Propeller
i wonder if it will fly?
February 12, 2009 at 9:39 AMThis was NOT a true conveyor belt. The plane had forward motion relative to the flourescent cones. If you are running on a treadmill(conveyor belt) you will have no forward motion relative to the room you are in. This is a FLAWED test. FLAWED FLAWED FLAWED
February 18, 2009 at 11:03 PMI agree with Chris. The myth is busted, but for all the wrong reasons. There is a huge logical flaw – if the plane travels at the same speed as the conveyor it would not move, and thus not take off. The planes (regardless of size) accelerated despite the conveyor, thus were going faster than the conveyor, and could take off. Without forward movement there is not enough airflow to take off – forward momentum means the plane is moving faster than the conveyor!
It’s not a myth, it’s a meaningless experiment because for the plane and conveyor to stay at the same speed it would require the plane to decelerate – otherwise the myth has no meaning. Once the propellors “grab” the conveyor is meaningless, thus the myth is true, if you match the speed of the conveyor, or busted if you let the plane do what it was designed to do.
February 18, 2009 at 11:11 PMOkay, I just saw the episode for the first time. I think it’s hilarious that the conversation has reached such length and is STILL going… but I also figured I’d put my 2 cents in and try to clear something up.
First of all, it depends on how the question is worded. The question that Mythbusters tested was whether a plane on a conveyor belt would take off if the belt matched PLANE speed. Now personally, I cannot believe they even took the time to do all the testing that they did, because the answer to this is obvious: the plane has to be moving in order for it to be at a certain speed. Duh. If the plane is moving, lift will be created and it will take off. I suppose the most appropriate way to word it would actually be air speed (air speed really depends on wind, but it’s the idea we’re after, since obviously wheel speed isn’t a very useful piece of information to a pilot).
But here’s the thing: I’ve gotten into this argument before on some other web site about this topic, and I argued that the plane might not take off. Why? Because the question was worded differently. The hypothetical situation that I had came across on that particular web site was that the conveyor belt was constantly and instantaneously matching wheel speed. Clearly, this initial condition would keep the plane in one spot, just like the car that Adam demonstrated that exactly matched the conveyor belt speed.
So would the plane take off? In this case, it might, but it would have to create enough thrust to overcome the friction between the wheels and the conveyor belt, effectively skidding the wheels across the belt. No matter how fast the wheels spin, the belt is matching them and the wheels act as if they are locked. So it would only take the additional thrust to break traction, but I think many planes wouldn’t be able to take off under these conditions.
Of course, this ridiculous scenario is completely nonsensical and impossible to create, but it’s a mental exercise. The myth that the show tested doesn’t make much sense as a mental exercise because it’s so obvious that the plane will take off under those conditions (the wheels will simply be spinning twice as fast). The confusion and arguments about this come into play because of the misunderstanding between the different scenarios.
At least that’s what I hope. Hopefully, people aren’t stupid enough to think that matching plane speed will keep the plane from flying. It’s the confusion between plane speed and wheel speed that gets in the way.
February 18, 2009 at 11:27 PMThe people who are stating that the plane moving forward means that it’s traveling faster than the belt are wrong. The plane has to travel forward to be moving. You’re assuming that wheel speed must equal belt speed. Plane speed isn’t measured by wheel speed, it’s measured by air speed. In order for a plane to have air speed, it needs to be physically moving forward.
February 18, 2009 at 11:30 PMI am also a pilot and trust me it is very difficult while in the air to maintain the speed of the landing gear in order to have enough lift on the wings to stay at altitude.
I can’t tell you how many times all of the engines on my plane were down but we still managed to lift off because we got enough speed on the ground during take-off to produce lift.
One time I was in a plane on water and we could not get any lift because we had no contact with the road – the wheels just kept spinning underwater.
One time I was in Chitty-Chitty-Bang-Bang and we went so fast on the road that we got lift on the wings and we flew but after a few miles in the air we ran out of gas and the wheels stopped moving so we almost crashed. But we got lucky and had some gas in the trunk so we refueled and the wheels started moving again so we were able to fly a few more miles before we landed but there was a conveyor belt on the runway we were landing on moving backwards the same speed we were going forward so the car just floated for a while because it couldn’t land.
I am a pilot so I know.
One time a buddy of mine was trying to take off from an aircraft carrier but the ship was going too fast in the opposite direction of his plane so he could only move backward and not produce lift and the plane fell backward off of the ship and landed in the ocean. But then he took out some oars and paddled hard enough to overcome the effect of the ocean and got lift so he was OK after that. But he got tired after paddling the oars in the air after a while and then he crashed again.
It was the saddest day of my life.
One time I was in a plane that had no wheels at all but it got airborne anyway. It was weird because we weren’t even on a conveyor belt. And someone told me it was called a helicopter. Stupid idiot. It is called an airplane. It was weird because helicopters lift off of the ground because of the wind they blow toward the ground and not lift. Weird. Really weird.
February 18, 2009 at 11:31 PMHey Newbie, if you are a pilot, they should revoke your license. I would never want to be on a plane with you. It’s basic flight dynamics, AIR speed over with wings makes lift, NOT ground speed. If anybody wants to test this, go to Toys-R-Us and buy a 99 cent glider, stand in the wind, and while NOT moving, see that the glider want to leave your hand. WOW, aerodynamics in action. They guys at MythBusters really need to correct their findings. ( sorry guys, you’re wrong, myth confirmed ) The Wright brothers are rolling over in their grave.
February 19, 2009 at 2:19 AMHere is a link to a NASA page that will explain everything. Ummm, they went to the moon, I think they know what they are talking about. If you STILL want to debate this topic, I strongly suggest you return to high school and finish physical science 1.
http://wright.nasa.gov/airplane/move.html
February 19, 2009 at 2:28 AMI’m aware that the wheels have nothing to do with take off. However, if the plane is at full power, but is not moving forward through the air, where is the air thats required to flow over the wings coming from. Isn’t the whole point of the engine and the wings to get up enough speed through the air to generate lift? If it was windy enough a plane could take off without moving if it was pointed into the wind because the wind is creating the airspeed. But if there is no wind then what? If you dont have to be moving forward or the wind isn’t blowing hard enough then why do planes stall when they aren’t going fast enough in the air. Why do they have flaps? To create more lift as lower speeds, thats why.
February 19, 2009 at 3:34 AM“if the plane is at full power, but is not moving forward through the air”
Why are you even assuming this would happen? The only way it would is if the conveyor belt was matching wheel speed, not plane speed, and even then, it would probably move a little bit by overcoming the friction of the wheels.
Read my post above. A plane that is stationary has zero speed, whether it’s on a moving conveyor belt or not.
Read-A-Book: Clearly, you missed the sarcasm in Newbie’s post. Also, I’m confused how you managed to get it right all the way up to the second to last sentence, where you for some reason completely ignored everything you had just stated and dove off the deep end. Puzzling.
February 19, 2009 at 12:08 PMOkay guys, think about this. IF the plane operated by wheels turning, then it would stay still. If the wheels are on the ground and allowed to flow freely, but the propeller is what pushes it forward, then the wheels have nothing to do with it, other than to keep the plane from falling over. The wheels can spin slow, or fast, but if they aren’t pushing the plane, they have nothing to do with the speed of the plane.
The thrust pushes the plane forward at the same speed, the wheels on a flat surface will move at speed A, if on a conveyor belt the wheels will move at speed B, but either way, the plane is still being thrust forward at the same speed, b/c the wheels aren’t pulling the plane.
Since the plane moves the same speed either way, then the air will still move swifter under the wings causing higher pressure under them with lower pressure on top of them. Anyone knows low pressure above with high pressure below causes lift.
February 19, 2009 at 1:59 PMJames, the issue is how the problem is defined, as I pointed out above. If the conveyor belt speed could somehow constantly and instantaneously match wheel speed, then the plane wouldn’t move until enough thrust were generated to break traction between the wheels and the belt, whether they are spinning or not.
Most people who are arguing that the plane won’t fly are equating plane speed to wheel speed. There’s really no reason to do that since wheel speed is pretty much irrelevant to flying a plane. If conveyor belt speed matches plane speed, then the plane obviously has to be moving in order to have speed, and like you said, the lift created will allow the plane to fly.
This whole argument continues because people are confusing terms and not making the distinction between wheel speed and plane speed.
February 19, 2009 at 3:40 PMThe problem is stated imprecisely and the flaw was repeated throughout the experiment. The “myth” never did state that the plane was going to be STATIONARY relative to the AIR. And thus, the plane takes off because it has forward motion. If forward motion was NOT ALLOWED, and the AIR was still, then the airplane would not take off. period.
The test shown by Mythbusters lacked rigor in the following:
1) did the distance required for the airplane to take-off CHANGE when the conveyor belt was added?
2) did the plane’s takeoff airspeed change when the conveyor belt was added.
The answer to both these questions should be “NO”. Thus, it’s not like having a conveyor belt will make you require much less runway to take off. Nor will it decrease your required take off speed.
I think Mythbusters did a disservice in not emphasizing the difference. They seemed to indicate that the plane would take off EVEN if FORWARD motion was not allowed – which is untrue.
February 19, 2009 at 9:02 PMAmazing.. simply amazing… so many people think this myth is busted. So many idiots capable of reproducing, filling the world with they’re stupid offspring. To everyone who thinks the myth is busted and is arguing that traction is provided by the propeller and not the wheels, STOP TALKING. ok.. i mean.. that part is true. But try using your brain a little. How the hell does a plane lift it’s self? Surely not the propeller alone?! RIGHT?! THEY USE WINGS!
How do wings work? .. they work on a principle: AIR PRESSURE ABOVE THE WING IS LESS THAN AIR PRESSURE BELOW THE WING, GENERATING LIFT. for the difference of air pressure to work the wing needs forward momentum (to move forward, for idiots), and the principle of a treadmill is to eliminate forward momentum. QED.
Shame on the idiots. Shame on the MithBusters. :(
March 3, 2009 at 3:25 PMWell, the point is that the conveyor belt CAN’T limit forward momentum… unless it somehow matches the speed of the plane’s wheels. Air speed has nothing to with keeping the plane still. Mythbusters matched belt speed with air speed, so naturally the plane would take off (it would be impossible for them to make the belt speed match wheel speed).
The first version of this question that I came across posited that belt speed matched wheel speed, and in that case, the plane would have to overcome friction between the wheels and the belt in order to move forward.
March 11, 2009 at 7:37 PMGet on a treadmill with rollerblades on.
Hold onto a rope that’s past the front of it
Now,
The treadmill = the tread mill
You = the plane
The rollerblades = the wheels
The rope = the thrust generated by the planes prop
Pull on the rope, do you move forward ?
By most of your logic a plane with skids (water plane floats) would never take off…
The first question should be, will the plane move at all.
The second question should be, what will stop the plane.
The ONLY thing that the plane needs to overcome is the friction with the ground, this is true with any plane. Wheels and bearings make this a non issue. Just as a float plane only needs to overcome the friction created by the water and the floats.
March 21, 2009 at 11:05 PMHaving just seen it screened in Australia – I came to post the exact same thing as the first couple – if their hypothesis was as stated that a plane travelling the same speed as the treadmill could not take off.
Taking the view that by “the same speed” they meant that it was held stationary (ie measuring the speed of the plane at it’s wheels – or by the speed it was travelling relative to the treadmill) – that theory is correct.
As soon as you allow the plane to move forwards, then it’s pretty much a waste of time, as normal lift/thrust principles apply.
The only thing I could imagine would have been the residual airflow created from the treadmill itself – and whether that would be enough to generate any lift.
If the plane was held stationery, how fast would the treadmill have to travel, before there would be enough windspeed at the wings to generate enough lift?
March 23, 2009 at 11:53 PMCamp #1 – A plane needs relative air speed to take off. A plane is propelled by it’s propellor not by it’s wheels. A conveyor belt cannot impede the forward motion of a plane. Even when the conveyor belt is moving at the normal take off speed of the plane the plane simply pulls itself through the air as normal and takes off.
Presto
Sean Salvador
Ben
Rarson
Matt
HaHaHa
Not A Moron
Guy
Engineer
Camp #2 – A plane needs relative air speed to take off. If the conveyor belt is going backward at the same speed as the planes wheels the plane will remain stationary relative to the air and will not take off.
Andru
Mick
Aviator60
Lulz
The people in camp #2 have taken the bait. The myths wants you to imagine the plane like a car driving at 60 mph on a conveyor belt going 60 the other way. The car would stand still. A PLANE WOULD NOT. In fact no matter how fast the conveyor belt went the plane would simply glide over the belt and pull itself through the air as if the belt was not there.
Camp #3 – People who talk about friction on the wheels and prop wash and planes taking off in the wind. These people are correct about some things and incorrect about others but it all has nothing to do with the subject at hand.
Before any one argues with this post go to the very beginning of this thread and read the myth being tested:
“An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
Camp #2 notice that it DOES NOT SAY “Runway moving backward…at a speed equal to the speed the wheels of the plane are spinning”
Read what it actually says before you comment.
March 24, 2009 at 2:19 AMSo why not take the wheels out of the equation and outfit a plane without wheels? In that situation wouldn’t you have the desired test? No forward motion, and the only air moving over the wings is the air being pulled over the wings by the propellers?
I have no idea whether you could actually design a plane that wouldn’t topple over forward and drive itself into the ground in that situation, but in theory wouldn’t this be an effective test?
Before anyone even says it, no I’m not a physics guru.. Just trying to apply common sense to this question.
March 25, 2009 at 1:38 PMAnonymous,
You don’t understand the question. Go back to the very top of this thread.
It is not a test of wether a plane will fly with no forward motion. That is the trap that you and so many have fallen for.
March 28, 2009 at 12:09 AMThe shame of this myth is that myth busters got it wrong and won’t admit their testing was flawed. Planes fly due to lift created by wind over the wings. If the conveyor belt was moving at exactely the same rate as the airplane but in different directions then the plane would not have any wind over the wings – no lift. Only thing busted is the myth busters lack of integrety to admit their testing was flawed as was their outcome!
March 28, 2009 at 11:38 AMRobert Black,
You re-stated the myth incorrectly:
“If the conveyor belt was moving at exactly the same rate as the airplane but in different directions…”
Here is the myth stated at the top of this thread
“…which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
The difference is everything. You fell into the trap. I did too at first.
Do you see it yet?
Some one “got it wrong and won’t admit it” but it wasn’t the Mythbusters.
March 28, 2009 at 4:05 PMdo you want to know the answer? (I’m gonna regret this, but here you go…)
March 29, 2009 at 7:36 AMthe premise in good faith (non-deceitful language) is that in zero mph headwind a stationary observer (in a non-moving frame of reference outside the conveyor belt) would see the plane as stationary (not moving forward) yet would see the plane lift off the ground (it’s movement forward after “lift-off” is not part of the hypothesis) also not specified is the actual movement of the invisible airflow over the wings. there are only 2 forces acting on the plane in only 2 directions: the prop (essentially just “forward” and the wings (fused to the body) (essentially just up) for the plane to move up more than a few inches (for the wheels to leave the ground aka takeoff) there must be an upward force (not possible from the prop, only possible from the wings) therefore there must be sufficient air movement over the wings.
jame and adam do not have the money for the necessary controls, but they would need to show 1) that the plane does not move forward from a stationary point while the tarp pulls it (not done, difficulties with real world size tarp and plane and cameras)
2) the air movement over the wings (not done, can’t afford massive amounts of colored smoke, can’t control real world size planes/cameras/trucks on any reasonable budget)
only this would show the source of the airplane’s “Lift” (a few inches up is all that is spelled out in the premise), but something is lifting the wings up: some combination of forward movement from imperfect (non-matched) tarp-pulling, head-wind, and wind from props and wind from the tarp.
it’s very interesting that the plane lifted off, but it’s just a question of money as to whether you can trace the sources of the wind over the wings. (if you tied a string to the FRONT of the plane then whipped up the tred-mill to 129 mph, an infinitely light side-bar would register no upward lift, (if you had an infinitely high wheelbase to negate wind from the treadmill)
that’s the answer. I’m sorry to take the fun out of it, and i’m sure i’ll be sorrier soon when somebody calls me an idiot for trying.
p.s.: if you want to know “if a single engine prop plane with a tarp being pulled under it at about the speed of the usual-take-off-ground-speed resulting in greatly reduced forward movement (much below customary take-off speeds) would still lift off the ground”, the answer is “Yes it would” if his wheels had “speedometers”, they would show something like a normal take-off speed, and if there was a second set of wheels off the tarp (on the runway) they would show a much slower speed than usual (not zero, but clearly MUCH slower than a normal takeoff)
March 29, 2009 at 7:48 AM(where is the air over the wings coming from? some combination of prop, headwind,tarp and actual forward-pulling of the whole tarp-plane system)
again, I’m sorry (that’s how we roll in Bangor)
p.p.s. I meant(if you tied a string to the FRONT of the plane in place of propellors) then whipped up the tred-mill to 129 mph, an infinitely light side-bar would register no upward movement, (if you had an infinitely high wheelbase to negate wind from the treadmill): NO WIND OVER WINGS equals NO LIFT-OFF AT ALL. it could spin along at any speed, but would never lift an inch
March 29, 2009 at 8:02 AM(but the system they created in episode 97 HAS wind over the wings and DOES take-off)
thezef,
If you are serious you are wrong.
The plane does move forward. It’s propellors pull it forward through the air and it takes off in a perfectly normal way. The conveyor belt does not and can not impede it’s forward motion.
If you are joking you are not helping
March 29, 2009 at 3:56 PMbut it’s fun messing with peoples’ heads…
March 30, 2009 at 2:17 AMalright, here it is;
the wheels actually mean nothing: it would be the same if you took off on water or ice or a perfect frictionless surface: the propellors pull the plane forward (whether the wheels ROTATE on a stationary runway, or remain stationary on a 55 mph tarp or conveyor belt)
just remember the basic premise: “An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.” it’s just like an amphibious aircraft: there is no “purchase” with a runway, whether it’s pontoons on water, skis on snow, or low-friction wheels on tarmac.
again, sorry (hee hee)
thezef:
Good, now I can put you in Camp #1 (People who understand that the plane conveyor belt cannot impede the forward motion of the plane).
I probably should have given you some slack so close to April Fools Day.
April 1, 2009 at 9:28 PMThe whole premise is false. Test is flawed. The plane has no thrust force when when elevated from the belt. Contact with a gravitational force, the belt in this case, is essential for takeoff in a powered aircraft. Knowledge of thrust vector forces are essential in this aviational field. I know. Not only am I a client of TWA, but Assistant Executive Chairman of Public Relations Marketing and an Aeronautical Engineer. Mythbusters really needs to re-do this test according to proper scientific and aviational standards and they will see, the plane will not takeoff.
April 5, 2009 at 2:26 PMJim wrote:
” The plane has no thrust force when when elevated from the belt. Contact with a gravitational force, the belt in this case, is essential for takeoff in a powered aircraft.”
So the belt is a “gravitational force”? You better write clearer than that if your going to convince any one.
Start by explaining how the thrust, which is provided by the propellor against the air is effected by the wheels.
April 6, 2009 at 9:51 PMAt first look this appears to be a flawed experiment, but you have to consider that the wheel speed is irrelevant.
The prop is in essence a “wing” or airfoil and PULLS the aircraft forward just as the wind lifts the wings aircraft up. No matter what the speed under the wheels (within reason), the plane will still be pulled forward because the air around the plane is always relative. Therefore, the takeoff distance will always be the same, within a small margin, no matter if it is on a conveyor belt or not.
April 7, 2009 at 10:40 AMShaun:
You understand the puzzle completely.
I might argue with your choice of words in explaining how planes fly but it isn’t actually an important part of the puzzle. The point is about the plane getting to take off speed and you explained that well.
April 7, 2009 at 8:24 PMSo if the speed relative to its surroundings stays the same, how does the plane fly? Is it because the air from the prop creates an influx of air towards the wings?
April 8, 2009 at 5:23 PM321:
If the speed relative to it’s surroundings stayed the same it would not fly.
The plane moves forward through the air as normal. The conveyor belt does not and can not impede it’s forward motion because a plane is powered by it’s propellors NOT BY IT’S WHEELS.
April 8, 2009 at 8:46 PMCorrection to above post:
321 the phrase “if the speed relative to its surroundings stays the same” is confusing.
I think you meant “if the speed relative to its surroundings is zero”.
If you meant something else please explain.
April 8, 2009 at 8:57 PMThis is hilarious.
Anybody who says “the test wasn’t valid because the plane didn’t stay in place” or “a plane that’s not moving relative to the air cannot takeoff” has entirely missed the point.
While it is undeniably correct that a plane being held stationary (relative to the air) cannot takeoff, that fact is not relevant for this myth because AN AIRPLANE ON A TREADMILL WILL NOT REMAIN STATIONARY. When people think of a plane on a treadmill, they immediately and wrongly assume that the plane wouldn’t move. If this were the case, they would be right that the plane wouldn’t take off. But the problem is that people can never seem to get beyond the idea that a moving treadmill won’t stop the plane from accelerating normally. Instead they fixate on the fact that a stationary plane won’t fly.
Another way to look at it. If you put a wagon on a treadmill, but you yourself were not standing on the treadmill, could you pull the wagon along? Of course. The wheels might spin like crazy, but wouldn’t have any effect on your forward traction because you’re not standing on the treadmill. It’s the same thing with an airplane’s propeller: it’s not attached to the treadmill so the speed of the treadmill is irrelevant.
April 8, 2009 at 9:01 PMfly_cast:
That is a very well worded explanation.
April 9, 2009 at 9:44 AMExcept…if the acceleration of the aircraft is countered by the acceleration of the treadmill resulting in zero relative wind across the wing. Deviating from the purity of the myth, replace the word propeller with thrust. If the thrust and acceleration generated by the powerplant is effectively countered by the movement of the surface beneath the aircraft then no lift will be generated by the wing. Propwash does not generate sufficient lift to induce aviation
Perhaps the easiest way to prove the myth is through the reciprocal. An aircraft with zero forward motion will begin to lift if the relative wind acorss the wings is sufficient to counter drag and weight – which is why you tie down light aircraft. Zero forward speed relative to the ground is a very common problem in sailplanes and indeed, negative groundspeed is possible with sufficient headwind.
April 13, 2009 at 10:32 AMJohn Wrote:
“Except…if the acceleration of the aircraft is countered by the acceleration of the treadmill resulting in zero relative wind across the wing.”
And just how would this happen since the wheels are free spinning?
You have fallen for the trick. The wheels cannot impede the forward motion of the airplane.
The rest of your post is irrelevent. It is not disputed. It has nothing to do with the myth.
April 13, 2009 at 9:55 PMJohn,
How could you type that after read fly_casts clear explanation?
Or did you read it?
April 13, 2009 at 9:57 PMThese no-flys just don’t get it. They say its a flawed test because the plane “moved relative to the ground”. Well get this dudes…it doesn’t matter if the conveyor belt was moving 100 times the plane’s speed…it CAN’T stop the plane moving relative to the ground. So the plane will MOVE…because it’s sucking air in and pushing it backwards. Newton’s law of motion: For every action and equal and opposite reaction.
The ONLY way for the plane to NOT MOVE “RELATIVE TO THE GROUND”…is for the pilot to apply almost no thrust at all. Now that would be ridiculous. Of course no plane will fly with barely any throttle applied.
A Car pushes against the ground to gain forward momentum. A plane pushes against AIR to gain forward momentum…so it doesn’t matter if it was on a conveyor belt or not. The conveyor belt cannot negate the airplane’s thrust against the air.
April 14, 2009 at 5:11 PMWell said RC
I was getting discouraged because no matter how clearly it is explained the next post is almost invariably “The myth wasn’t tested right because the plane was moving forward…”
But non of these No Flys lately have posted more than once so maybe the message is getting through.
April 14, 2009 at 10:17 PMI’m a rated commercial pilot, an experienced military pilot, and an aerospace engineer. I aced everything that had to do with aerodynamics and physics in all of my flight training. Even so, it took me a long time to understand what the claim of the myth was. I agree and sympathize with the folks who say that the myth wasn’t clearly stated.
Assuming no wind for simplicity, the airplane starts out at zero airspeed and zero groundspeed with respect to both the tarp and the ground. The point is that the airplane will accelerate with respect to the ground regardless of what the tarp does and hence with respect to the local airmass.
If it starts on a conveyor belt that is moving backward (NOT as depicted on the show or claimed in the myth), then the plane will have to accelerate back up to zero speed relative to the ground, and then further to its takeoff speed. (You can almost entirely discount the very minimal additional force of rolling friction and the very minimal effects that the tarp has on the overlying air.)
April 21, 2009 at 6:54 PMWhat a bunch of rednecks the ones claiming it won’t fly.
April 22, 2009 at 5:41 PMThe test was flawed. You should have measured the speed of the aircraft at the wheels like you do in cars. Then to keep the aircraft positioned still relative to the ground with the thrust from the propeller you would measure the same speed from the wheels as that of the conveyor belt.
The airspeed indicated in the aircraft’s speedometer is the speed of the air moving relative to the aircraft. An aircraft hold still on the conveyor belt with it’s wheels spinning at the same speed as that of the belt shows zero speed in it’s speedometer.
Throttling the aircraft to it’s lift off speed read from the speedometer would increase the speed at the wheels past the speed of the conveyor belt relative to the amount of the speed shown in the speedometer.
April 22, 2009 at 6:07 PMHoly wrote:
“I aced everything that had to do with aerodynamics and physics in all of my flight training. Even so, it took me a long time to understand what the claim of the myth was. I agree and sympathize with the folks who say that the myth wasn’t clearly stated.”
You’re explanation on the myth is right on.
As you realize now, knowing a lot about airplanes means nothing in this case. You only have to know the basics.
I don’t agree with the idea that the myth is not stated clearly. Go back to the top of this thread and read it again. It is very clearly stated.
It IS tricky but not because it isn’t stated clearly. It is tricky because people don’t realize a plane behaves differently on a conveyor belt than a car, or a person jogging.
April 22, 2009 at 9:54 PMJavs wrote:
“You should have measured the speed of the aircraft at the wheels like you do in cars. Then to keep the aircraft positioned still relative to the ground…”
Javs, you fell into the trap. You assume that the intention of the myth is that the plane should be still relative to the air.
You then propose what must be done to keep the plane still.
The problem is that the myth has nothing to do with a plane standing still. The conveyor belt will not and can not impede the forward motion of the plane.
The myth states clearly that the conveyor belt moves at the same speed as the NORMAL take off speed as the plane. So that speed is determined before the test. Let’s just say the plane normally takes of at 60mph.
The conveyor belt rolls backward at 60mph, the planes propellors push the plane forward THROUGH THE AIR at 60mph, the wheels spin freely against the conveyor at 120mph.
(Frictional forces on the wheels might change the calculations but only slightly. Prop wash and wind are non issues)
April 22, 2009 at 10:08 PMWell stated, Presto. I like fly_cast’s analogy to pulling a wagon that’s on a treadmill (while the puller is not on the treadmill).
April 23, 2009 at 6:12 PMProper way to test it would be to actually start by pulling the plane backwards and not allowing it “roll” forward on the ground at all and see if it can still generate its own lift even in that condition. If that were to work then clearly the myth would be busted. But due to the fact that the plane was still moving forward across the ground before any lift was created is not saying anything against the myth at all. Try it again.
April 26, 2009 at 10:07 PMG,
I couldn’t make heads or tails out of what you wrote. Maybe it’s me.
Seems to me the “Proper way to test it” would be to do what the myth says.
Why you want to pull it backwards is beyond me.
Care to try again?
April 26, 2009 at 10:54 PMG,
If by “Pulling the plane backwards” you meant “apply a backward force that holds the plane still”, then you are another one who has fallen for the trick.
The myth has nothing to do with a plane standing still. The plane moves forward just as usual. A conveyor belt will not and can not impede the forward motion of the plane because a plane gets it’s power from it’s propellors NOT from it’s wheels.
April 26, 2009 at 10:58 PMI realize the myth only specifies that it is on a belt, and that the wheels alone will not stop it from moving forward. However the base of the myth would be that the belt is already moving, therefore the plane moving backwards before it starts to move on it’s own. The myth is ‘plane on a conveyor belt’ which generally would be assumed that the belt is always moving, not just turned on as the plane starts to move.
April 27, 2009 at 7:02 PMG wrote:
“…Wheels alone will not stop it moving forward”
What are you talking about? Who says the wheels stop it from moving? If anything it would be the belt that would stop it from moving.
I think you are not being very careful with your words which makes it hard to argue a point.
Here is the exact wording of the myth from the top of this thread:
“An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
Now my interpretation of this would be that the plane and the belt start off not moving or that the belt is moving and the plane drives onto it.
Now you are correct that it doesn’t exactly spell that out but I think if they meant”A plane cannot take off if it is sitting on a treadmill being dragged backward at the same speed it normally takes off at” they would have said that.
In any case it doesn’t matter. The plane would easily move forward and take off. It is just an unnessesary complication of the issue.
April 29, 2009 at 8:31 PMI’m really surprised that anyone thought the conveyor belt would have any effect on the airplane. The only thing that happened was the wheels turned faster, ie, the airplane forward speed plus the speed of the conveyor.
April 30, 2009 at 10:04 PMI just watched this and it really bugged me. The plane was traveling forward when it took off. It seems to me that the myth is more about whether or not a plane can take off when it is sort of hovering in place.
It seems to me that the plane should not be traveling forward when it takes off in order for the myth to be confirmed.
May 9, 2009 at 3:08 PMEmily wrote:
” It seems to me that the myth is more about whether or not a plane can take off when it is sort of hovering in place. ”
You fell for the trap. You are supposed to think that. But in fact the myth is not about the plane standing still.
The suprise is that the conveyor belt can NEVER hold the plane back.
A conveyor belt WOULD cause a car to stay in place because a car is powered by it’s wheels. This is the situation most people imagine.
But remember, a plane is powered by it’s propellor. The propellor pulls it through the air exactly as normal and the conveyor belt doesn’t matter at all.
May 12, 2009 at 1:21 PMEmily,
plane on treadmill, treadmill starts at 50mph.
airplane throttle set just enough (lets call this speed X) so it remains stationary to an observer.
Fact- X is significantly less that 50mph
Fact- X is too slow to launch plane on solid ground anyway, a plane at X speed on solid gound would be a plane at taxi speed.
Fact- X does not change AT ALL when the treadmill is increased to 100mph, 200mph, 300mph.
Fact- increasing X to takeoff speed is accomplished just as easy as if it were on solid ground.
the plane will launch, no IFs ANDs or BUTs
May 14, 2009 at 2:22 PMpeetee32,
Very well said. Maybe your way of explaining the situation will get through to some of the ones who aren’t helped by previous attempts.
May 15, 2009 at 10:11 PMI originally googled this episode to unleash some wrath myself in regards to the constraints of the test, its clear that so many other people have already. Main concern: the plane still had forward movement on the belt
Now I UNDERSTAND that you can not stop a plane from moving forward because of the dynamics of the prop driven movement energy – HOWEVER its is VERY clear that the show did not explain these dynamics in anyway understandable by the general audience.
IF 10% of people go to the EFFORT of complaining, then this episode deserves a righteous clarification on another episode. Period.
June 13, 2009 at 7:36 PMKeep it simple wrote:
“Now I UNDERSTAND that you can not stop a plane from moving forward because of the dynamics of the prop driven movement energy – HOWEVER its is VERY clear that the show did not explain these dynamics in anyway understandable by the general audience.”
I completely agree. It definitely needs a revisit. They did try to explain it but I think they underestimated just how confusing the whole thing is.
They further compounded the confusion by using a cartoon of a full sized plane on an exercise treadmill rather than the runway length treadmill required.
June 14, 2009 at 8:15 PMThink of the experiment in different terms. What if the airplane was floating on a cushion of air, like a puck on an air hockey table.
June 21, 2009 at 9:11 AMThe planes propeller would still generate enough force to move the plane forward. Otherwise, if one moved the table in any direction (x & y axis) it would not effect the forward movement of the airplane. Hence, the force generated by the propeller (which is connected to the airplane) pulls the plane through the air INDEPENDENT of the ground. Myth ‘CONFIRMED’
The prop is pushing against the air. The plane will move forward regardless of the treadmill.
The wheels spinning on a treadmill will just spin faster than they normally would for takeoff.
July 23, 2009 at 4:29 PMhahahahaha.
Everyone is right!!!!.
The plane propelled itself forward due to what propellers do. (make it go forward) this made air over the wings that made lift. The propellers moved the plane faster than the tarp.
The tarp was at such a speed it could not keep up with the propellers. But if it could the plane would not be moving therefor no lift.
July 26, 2009 at 6:49 PMOk ok, everyone just breath and lets re-cap.
Airline pilots: The myth was not to test to see if an airplane needs air over the wings to fly.It is obvious that you do need air over the wings! In other words, the test was to see if you CAN ACHIEVE ENOUGH forward momentum to generate the air over the wings needed for lift. That makes your argument irrelevant.
I believe, and as do many other viewers who agrees with the outcome of the myth, that the confusion came in with the initial wording of the myth. I must admit, I initially thought that they wanted to see if you can use a conveyor belt as some sort of a “miracle device” to shorten take-of distances, say from an aircraft carrier!!!!
OK, so
1. Did the plane achieve enough forward momentum to generate enough flow over the wings? YES
2. Why and how? The propeller PULLED the plane forward. It can not care less about what the wheel are doing.Even if the conveyor belt moved at 500 km/h, the wheels will just spin at 500 km/h. When the plane moves forward at 100 km/h, the wheels will be spinning at 600 km/h.
People, think of it this way. WHEN A BOEING COMES INTO LAND, AND SAY THAT IT IS LANDING ON A SPINNING CONVEYOR BELT (both at the same speeds), THERE IS NO WAY IN HELL THAT THE PLANE IS GOING TO INSTANTLY MOVE BACKWARDS or just stand still. How great wouldnt it have been if that was the case, because then we could have shorten all runways!!!So if you believe that planes will not takeoff from a moving runway, then surely you must disagree with the landing-theory!!The wheels will compensate for the moving runway. How??? BY SPINNING FASTER and because it is not relative to the plane’s forward momentum!!!!
3. So when will the plane not be able to takeoff?? I am contridicting myself, but there is actually a scenario when the plane will not be able to take of. How? It is called “initial friction”. Imagine supporting an “object with 4 wheels and with no propulsion” in it. I say object, to eliminate any confusion with a car. Place it on the treadmill, and gradually increase the speed. It WILL move backwards. Why? Initial friction between the wheels and the belt. Now, support it with your finger at the back (or pull the object at the front, it is all the same), you will find that it is very very easy to move forward, because you need very little force to move it forward (Dependant of the quality of the bearings)That force is far less than 0.2 Newtons (dependant of the weight of the object, in other words, VERY small and not even worth mentioning. Now, the faster the belt is moving, the more force you will require to overcome the initial friction. Therefor, the belt must must spin at 1 trillion km/h to overpower the planes engine (propeller) (which will always be powerful enough to overcome the initial friction) if the initial friction was not able to be overcome
Now, imagine, just imagine, that your finger which is pushing, or pulling the “object with 4 wheels” is the planes propeller!! Now, put some wings on the object, and because it can move forward very easily, it will generate flow over the wings, and WILL TAKEOFF!!!
And, before anyone protests about the pulling/pushing of the object, it is all the same!You do get planes with propellers at the back that pushes the plane through the air, as apposed to pulling. The same applies to a Boeing.
When will this ever end??
July 29, 2009 at 8:40 AMJason M and Rudi have it right.
iam2pc4u is still falling for the trick because he believes the plane would stand still if the conveyor belt went faster. For one thing the myth says the conveyor belt is going at the planes normal take off speed NOT that the conveyor belt is going so fast the plane doesn’t move. For another thing there is no speed at which the plane wouldn’t move.
July 29, 2009 at 2:38 PMThis is quite interesting. Ignoring vector thrust, there are 2 main forces dicussed here to achieve takeoff – thurst and lift.
Thurst in normal planes is primarily used to generate forward movement and force air to pass over/under the wings to create “lift”.
Your takeoff speed is determined by the how much air needs to pass under the wings to create a low pressure effect. Once the low pressure threshold exceeds the plane’s weight, the wings “lifts” the body of the plane upwards, and you take off.
Meaning, as long as enough air passes under the wings to create enough “lift” to offset the plane’s weight, the plane can even be moving backwards and still take off.
Taking someone’s earlier example of trying to fly a kite while running on a tread mill – If you just run on it, of course the kite will never take off. However, if you have a gust of wind blowing towards you, say, from a huge fan – the kite will catch it and will fly.
Similarly, I can put a stationary plane in a huge wind tunnel, turn on the fans and it will also “lift” off once enough air is passing over the wings to create lift.
It’s not simply the forward movement of the plane at all. A good way to nip the argument is to test this -
Would the plane still take off if the treadmill runway is turning backwards so fast that the plane goes backwards?
Basically just anchor an ultralight to a bulldozer, and have the bulldozer move the other direction.
The ultralight will still “lift” off. Controlling it will be a problem though.
Why? Because alot of the air being pused by the propellers are flowing over/under it’s wings. Once enough “lift” is achieved, the plane leaves the ground.
To isolate this effect, they can try using a jet can be used, or maybe running it in a vacuum…
July 30, 2009 at 3:52 AMJust to clarify,
I mean anchor an ultralight to a bulldozer, and have the bulldozer move the other direction while the propellers move the ultralight towards the oppsite direction.
The ultralight’s engine needs to be powerful enough to drive enough air over the wings and create lift.
July 30, 2009 at 6:56 AMLee wrote:
“It’s not simply the forward movement of the plane at all. A good way to nip the argument is to test this -
Would the plane still take off if the treadmill runway is turning backwards so fast that the plane goes backwards?”
Sorry Lee,
You also fell for the trap. It doesn’t matter how fast the treadmill is going. The plane moves forward because of the force of the propellors and the fact that the wheels are free spinning.
The treadmill could be going 500 mph in either direction and the plane would just casually move forward as usual through the air and take off.
This is the trap that is hidden in this “myth”.
August 2, 2009 at 5:16 PMWow. I can’t believe how many people can’t grasp that no matter how fast the conveyor belt goes, as long as the prop/jet engine can keep up, and the wheels are free turning, the belt CAN NOT stop the plane. Go back to the human example. Tie a rope around your waist, have a friend stand in front and hold the rope. Put on skates. Turn treadmill on full speed and have your friend pull. Get rid of the friend (representing the planes engines) or the skates, representing the FREE wheeling plane wheels, and good luck. Wow. You “not busted” people make me feel smart.
August 10, 2009 at 11:02 AMWell, of course the wheels does provide SOME friction, so purely theoretically, IF the conveyorbelt could move _incredibly_ fast, all the energy the engine provides would be spent to overcome the friction between the wheels & the ground, but how fast this would have to be, I really have no idea, but if you can find the rolling friction of the wheels, you can calculate it quite simply. Would probably be quite high though, since any aeroplanes engine is able to overcome the drag and still keep the plane moving at a fairly high speed, and the drag at normal airspeeds are WAY higher than the friction from the wheels.
August 10, 2009 at 4:08 PMritchie and torstein are of course correct but I’m a little more understanding than ritchie toward people who fall for the trap. I think it is just a great thought problem in that it is so counterintuitive and such a great argument starter.
torstein, you are correct but you really don’t need to try to explain the wheel friction issue because it isn’t part of this myth. Here is the myth at the top of this thread:
“An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
So the runway is moving at the “normal ground speed” of the plane. It is NOT trying to keep up with speed of the plane. So the normal ground speed of the plane is determined beforehand. If it is, for example 60mph then that is how fast the treadmill goes.
The idea that the treadmill tries to match the wheel speed of the plane is a completely different scenario that probably grew out of a misunderstanding of the original problem.
August 10, 2009 at 10:54 PMWow, people are still posting on this. I understand people falling for this the first time, everytime I ask this of a friend, they all fall for it, but quickly grasp it.
“it can’t move because the threadmill moving back at the same speed”
“ok, that makes sense, but what is the propellor pushing against”
“well, it’s pushing against the air……. ohhh!!!”
I think most people here are smart enough to see the truth as well, and just like to make a deal out of it to rile people up :P
August 14, 2009 at 2:48 PMKal,
If you can explain this so your friends quickly grasp it then we could sure use your explanation here.
In your post you were much too brief. It’s not possible to tell what you actually are saying about the myth.
Could you go ahead and explain it in full?
August 16, 2009 at 8:10 PMPresto wrote:
“Sorry Lee,
You also fell for the trap. It doesn’t matter how fast the treadmill is going. The plane moves forward because of the force of the propellors and the fact that the wheels are free spinning.”
Yes, that’s effectively what I am saying, lift off is from airflow being pushed under the wings. Got nothing to do with how fast the treadmill is moving, the plane can even be moving backwards.
I am trying to take the forward movement out of the equation so that all the folks will understand that the speed of the treadmill (or even forward movement of the plane doesn’t matter.
August 20, 2009 at 6:32 AMLee,
You wrote “Would the plane still take off if the treadmill runway is turning backwards so fast that the plane goes backwards?””
So you clearly fell for the myth. (No big deal, so do most people at first, including me).
Now trying to prove that a plane can fly even if it is standing still as long as air is flowing over the wings is arguing a point that (almost) no one disagrees with. Intelligent people who are fooled by this myth understand basic aerodynamics but make the false assumption that the intention of the myth is that the plane stands still.
Your just dragging in a side issue to confuse things. I mean suppose someone said “Oh yeah well the plane couldn’t take off if there was a brick wall on the runway in front of it”.
Well it’s hard to argue with that logic but the myth doesn’t mention a brickwall (or a headwind).
August 22, 2009 at 9:08 PMLee Also Wrote:
“The ultralight’s engine needs to be powerful enough to drive enough air over the wings and create lift.”
Wow I actually missed this in your earlier post. I don’t know what the definition of an ultralight is but planes don’t fly by “engine…driving air over the wings”.
I was mistaken to think you were bringing a headwing into this. I see now that you were trying to say that the propwash alone would raise the plane. Which is incorrect as well as being a side issue.
I should have read your post more carefully. Now I’ve really confused things.
August 22, 2009 at 9:17 PMThe entire problem here was a crummy explanation. If plane with takeoff speed of 30 will move relative to the ground at 30 while the treadmill moves the other way at 30 (also relative to ground) of course it takes off.
However, their graphics all suggested the goal was to get plane to match speed relative to treadmill. If you held the plane steady and just yanked the treadmill under it at 30, the plane would be moving 30 relative to the treadmill, but zero relative to ground (and surrounding air, right?) and therefore would sit like a brick.
If they explained it better, there’s be no confusion. No one believes a treadmill can keep a plane from taking off (or shouldn’t). But this was a crappy experiment because of how they explained it.
August 29, 2009 at 7:01 PMMister cyance,
The question as stated at the top of this page has caused much debate on it’s own before before the show.
I agree though that the picture they used of a plane on a small exercise treadmill was misleading.
PS. Great name Mr Cyance.
August 31, 2009 at 4:06 PMThe speedo on the plane measures air speed; the one on the car measures ground speed. The wheels on the plane were spinning at a speed that would be 50 MPH – IF IT WERE BEING MEASURED. The plane is only reading the speed of the air passing over the sensor. Seriously.
September 2, 2009 at 7:07 PMI just saw this episode as a repeat and agree the experiment definition was a bit confusing. Here’s my explanation. A plane’s wing generates lift when air passes over the wing. If air passes over the wing at greater than the take-off speed it can take off. This has NOTHING to do with ground speed. The eariler post about a tail wind is a good explanation. A plane with a take off speed of 55 will have a ground speed of 55 and air speed of 55 with no wind when it takes off. With a head wind of 20 mph it will have a ground speed of 35 mph and an air speed of 55 mph when it takes off. With a tail wind of 20 mph it will have a ground speed of 75 mph and an air speed of 55 mph when it takes off.
The first question to answer is what happens when the treadmill runs at take off speed and the plane engine is off. If the plane sits still (no friction on the wheels) the treadmill should have no effect. If the plane moves backward, the treadmill should have the same effect as a tail wind. As long as the plane can generate enough thrust to overcome the tail wind it will take off.
September 2, 2009 at 7:42 PMCarl,
You started off strong but then you digressed.
Tailwind is not part of the initial problem and the effects of tailwind are not disputed.
There is no tailwind on the day of the test (or the myth would have mentioned it). There is no tailwind and there is no brickwall on the runway and there is no crosswind and no tornado and he’s not flying over an erupting volcano.
Your final paragraph just adds to the confusion. If the engine is off there is no forward thrust and the plane either stands still (theoretical condition of zero friction) or it moves backward (real condition of slight friction). Either case is irrelevent. The engine IS running and the wheel friction IS negligable.
September 2, 2009 at 10:20 PMLL,
September 2, 2009 at 10:24 PMAnd your point is?
I would like to nominate fly_casts post as the most succinct explanation so far.
I challenge any one who thinks the mythbusters blew it to address this post directly:
________________________________________
fly_cast:
This is hilarious.
Anybody who says “the test wasn’t valid because the plane didn’t stay in place” or “a plane that’s not moving relative to the air cannot takeoff” has entirely missed the point.
While it is undeniably correct that a plane being held stationary (relative to the air) cannot takeoff, that fact is not relevant for this myth because AN AIRPLANE ON A TREADMILL WILL NOT REMAIN STATIONARY. When people think of a plane on a treadmill, they immediately and wrongly assume that the plane wouldn’t move. If this were the case, they would be right that the plane wouldn’t take off. But the problem is that people can never seem to get beyond the idea that a moving treadmill won’t stop the plane from accelerating normally. Instead they fixate on the fact that a stationary plane won’t fly.
Another way to look at it. If you put a wagon on a treadmill, but you yourself were not standing on the treadmill, could you pull the wagon along? Of course. The wheels might spin like crazy, but wouldn’t have any effect on your forward traction because you’re not standing on the treadmill. It’s the same thing with an airplane’s propeller: it’s not attached to the treadmill so the speed of the treadmill is irrelevant.
September 3, 2009 at 6:25 AMOK, Mythbusters are right… if not clearly defined. My first instinct was to call foul, but just needed to think through the poor definition of the myth.
Anyway, It is the wheels that allow the plane to fly in this case. Because they are bearings They allow the plane to move forward under it’s natural thrust of the prop. The tarp / conveyor only practically affect the rotational velocity of the wheels. Most of that energy is not transferred to the plane.
Switch out the wheels for pontoons of a water plane and we have a very different result. Because the friction between the tarp and pontoon has not been overcome the velocity (read vector (direction and value)) are transferred to the plane. The plane would have to generate additional power to overcome the friction between it and the tarp in addition to that needed to reach takeoff velocity.
Turn the plane around and turn the planes engine off. Drag the pontoon plane on the tarp at takeoff velocity with the engine off and it will fly. Put the wheels back on, pull the tarp in the takeoff direction and the plane will not fly because the wheels, again acting as bearings, won’t transfer the forward velocity to the plane.
The the case with the wheels and a conveyor going with the plane the engine will have to go at the same power it normally would. At the point the plane lifted off, the wheels would not be spinning at all.
Does anyone still think the wheels have anything to do with this myth?
September 3, 2009 at 1:58 PMActually I get it now. They do word this VERY poorly. Eventually the plane will move faster than the conveyer and will take off. They make it sound like the plane is taking off with no wind velocity.
September 8, 2009 at 2:09 PMThe “Myth” stated at the top of this thread is very clear. It IS tricky but not because it isn’t clear. People make a wrong assumption and then reason from that. That is the fun.
September 9, 2009 at 12:19 PMI don’t know if anyone has mentioned this, but try to wrap this around your wee-little minds…some planes do not have wheels, and land on water…they take off just fine. All the wheels are used for is to allow the plane to move along the ground. The only way they apply to the actual take off is that they allow the plane to move…they’re not causing the actual movement.
September 13, 2009 at 8:54 PMFor those that still don’t believe me, try this experiment: get a wheelbarrow, and place it on a treadmill. Just hold it there, allowing the wheel to spin. Now push forward..if what you’re saying is true, the wheelbarrow should not move…a plane’s engine works in a similar fashion.
I am sick and tired of people trying to say that the tarp was not a true treadmill…a treadmill is a strip of fabric that moves…the workout treadmills at gyms are just a single loop, allowing them to continue moving. Jamie and Adam did the best they could without building a gigantic treadmill, which would cost way too much money to spend on a single myth.
To all of you non-believers of this theory, get over it…it happened, it’s true, and there’s nothing you can say to make it otherwise.
Dragonfye, well said
September 13, 2009 at 11:11 PMThank you.
September 14, 2009 at 2:11 PMI think that the myhtbuster will need to repeat the “airplane on a treadmill” but in a Wind Channel (tunel de viento). More, I think they should try the experiment again, this time keeping an airplane flying in the same place within a “wind tunnel”.
September 25, 2009 at 3:15 PMJOSE DI SARLI typed:
“I think that the myhtbuster will need to repeat the “airplane on a treadmill” but in a Wind Channel”
Would this be a giant wind tunnel big enough and powerful enough to fly a real plane in? It would make the treadmill part of the experiment easier but I’m not sure the trade-off would be worth it.
Or would it be a small wind tunnel with a model plane inside? In that case I don’t see how it would improve over a model airplane and a real treadmill and no wind tunnel.
September 25, 2009 at 10:19 PMHello. The myth is false, the airplane takes off!, Because the wheels are free and have no traction. The plane moves forward because the propeller does push back on the air. The aircraft’s wheels more laps than usual, since the tape rolls, like the forward progression of the plane by the momentum of the propeller. The MythBusters have to repeat this myth, with 3 variants:
1) place the toy airplane on the belt (even on the floor), but with a fan in front of the wind blowing at the same speed that makes the propeller backward. The aircraft should not move forward as the wind fan counteract the thrust of the plane forward made by the propeller.
2) put the aircraft on the conveyor belt, just like they do in the program, but in a box to “empty”. In the absence of “air” will not push, so the plane will not move forward, indeed, would fall back in the direction of the band.
3) It would be interesting if MythBusters, could hold a toy airplane in flight within a wind tunnel, at one point. Because this if it would be a real challenge!, As in the wind tunnel, you should keep the aircraft in flight at one point.
I wish I could do this to get MythBusters, but it has been impossible. my email is “disarli@cantv.net.
Another thing! that can end this discussion is: Why did the planes have skis snow they leave?, if they not have wheels?, and are on a surface that does not move (like the band)?. As you can see, there are no wheels or rolling road, only two surfaces (the skis and the snow dome)!
Jose Di Sarli (disarli@cantv.net)
September 27, 2009 at 1:42 AMChip, I sincerely hope you have neither an “MS (in) Aeronautical Engineering” or “37 years of pilot experience”.
A plane’s lift has NOTHING, NOTHING, NOTHING, whatsoever to do with its speed relative to the ground. The relative speed of the air passing over the wings is the only thing that matters. It’s entirely possible to fly an ordinary plane BACKWARDS relative to the ground, given a fast enough headwind. Speed relative to the ground plays no part in the whole system. Sheesh…
September 29, 2009 at 2:56 PMPaul C,
Not sure why you are replying to Chip Lancaster. His posts were in January.
Your statements are correct but…
The myth assumes a windless day. If there were a headwind it would have been mentioned in the myth. There is no headwind, no tailwind, no hurricane, we aren’t on the moon or any other variable that isn’t mentioned.
That is why chip talked about speed relative to the earth. He could have been more careful with wording.
September 29, 2009 at 4:41 PMPresto, I just wanted to make the point that ground speed is irrelevant to flight, only airspeed matters.
My example of being able to fly backwards relative to the ground was just that – an example. Ground speed does not matter (Chip referred to ground speed more than once as the deciding factor in flight). It was not based on the experiment itself, it was to illustrate the irrelevance of ground speed to flight.
Judging by the crazy explanations being put forth on this page (several by purported pilots and various other ‘experts’), I thought it should be pointed out – again – that ground speed does not matter. Indeed it is a most unusual metric for a pilot to use in reference to lift, as it has precisely nothing to do with it. Airspeed is the only factor to consider.
September 30, 2009 at 2:29 PMIf there is no wind then groundspeed=airspeed. In the myth being discussed there is no wind.
I don’t think any one here is suprised to hear that a plane can fly backward if there is sufficient headwind.
You’re interpretation of chips comments is that he needed straightening out on this issue.
My interpretation is that he was refering to airspeed on a windless day which is the same as groundspeed.
September 30, 2009 at 9:45 PMYes, yes, in the specific case where there is no wind (which is to say, never), then air speed = ground speed. Ask the following question to any pilot who understands how a wing works: “At what ground speed does your plane take off?” – and see what reaction you get.
It is an utterly irrelevant metric to use, and having reread his posts, it very much seems that he believes it to be the crucial factor. And I haven’t even got to the part where he believed contact with the ground to be important. None of what he wrote sounds anything like the thoughts of an aero engineer or pilot.
October 2, 2009 at 5:51 AMThe myth itself is flawed.
October 28, 2009 at 2:17 AMThe treadmill would have to reach infinite speeds to go fast enough to prevent the plane from moving.
The wheel bearings would grind off before the plane even moved an inch, because the treadmill would have to move so fast, so quickly and reach top speed (infinity mph) almost instantly.
But, if Einstein was wrong and you COULD make the treadmill go infinitely fast, then the plane would have no forward movement whatsoever and not be able to take off.
hyphen782,
The myth has NOTHING to do with the plane NOT MOVING.
Nothing to do with infinite speed. (The treadmill moves at the NORMAL take off speed of the plane. For example 60mph. It isn’t programed to adjust to the speed of the plane. Re-read the myth if you don’t understand this).
The treadmill moves at (for instance 60mph), the plane pulls itself through the air at 60mph just as it always does, the wheels move at 120mph because they are free spinning, and the plane takes off just as normal. The effects of added friction on the wheels from spinning fast are negligable.
I’m not sure from your post if you were just kidding or not.
October 28, 2009 at 11:51 PMWatched this episode last night and felt let down by the guys. I love this show and buy the DVDs, but this episode left me wondering two things: Are these guys losing their integrity and starting to just churn out episodes (jumped the shark) or did I miss the point of the myth?
I see it one of two ways:
If the myth is that the conveyor speed matches the planes forward motion precisely (probably never reproducible in real life by the way), then you effectively have a real fancy “fan” blowing air backwards. You could literally stand right beside the plane and talk (scream) to the pilot all day long in this unachievable magical fantasy simulation. He/she “ain’t goin’ nowhere”. Forward airspeed, thus air passing over the wings, is zip. Eff the wheels, Eff the ground, I don’t care about either. Put that airplane up on blocks, tie a rope to an immovable object, and rev that engine to redline. You’ve got the same results. A brick. Believe me, if this could be done, the militaries all over the world, long ago, would have put airplanes on treadmills, done this exact thing, and launched airplanes in place. They’d just magically float straight up. They have not, because you MUST have air passing over the wings.
Now, on the other hand, if the myth is that the plane cannot overcome the effects of the conveyor belt, and go faster than the “reverse pull” created by the conveyor, then yes, myth busted, and flight occurs. I clearly saw the plane move past the cones and forward motion was achieved. I did not think this was the premise of the experiment though. Rather than call people idiots, I will stay humble, and say that I misunderstood the premise of the myth. But if this was the premise, I say” so what?” to the Mythbusters. You revved the airplane engine up a tiny bit more. I don’t know how much extra power was added, but here was more engine power used than during normal takeoff. Probably not double though since the wheels are free spinning and not a source of forward motion as many have stated. I say, “Big deal”. Now we are just playing “tug of war”. The plane won, this time.
I think WAY TOO many people here believe their interpretation of the initial myth is the correct one. I’ll need to re-watch the episode this weekend to fully understand the myth. I hope that the MB guys didn’t adequately define the myth correctly in the beginning and I am confused. However, my gut tells me I am right and that they just may have defined it correctly in the beginning of the episode (stationary plane, engine revved to takeoff speed) and then were dishonest in the end (non-stationary plane, engine revved beyond takeoff speed to overcome conveyor, cones going by airplane) to make good television.
October 30, 2009 at 12:31 PMJust read the myth at the top of this thread.
It is stated clearly but people still analyze the situation wrong. Not be cause they are stupid or because it wasn’t stated clearly. It is a brainteaser, a puzzle, it is supposed to be tricky.
You essentially analyzed it correctly accept for you feeling that the pilot had to “rev the engine up a bit more”. The pilot just flys the plane as normal. The controls will not feel any different than a normal take off. That is the supriseing fact. It is hard to wrap your brain around. That is the whole reason that this myth exists and is talked about.
(Note for theorists. If there is any effect due to the treadmill on the wheels it is negligable. It does not effect this myth. Read the myth as stated at the top before you post some nonsense.)
October 30, 2009 at 10:34 PMi can’t be bothered reading all of this, but in my opinion if a plane was on a massive treadmill, and assuming that the propellor or jet engine was pulling the plane along (which I beieve to be the case but may be very wrong), as opposed to the wheels PUSHING it, then the plane would just zip along the treadmill and take of as normal, the treadmill wouldn’t be spinning at all as there would be no force from the wheels to turn it.
November 6, 2009 at 1:16 PM“What a massive treadmill!”, would be the cry.
Mark:
You don’t have to read the whole thread. But at least read the myth stated at the top.
“An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
So the treadmill IS moving.
November 8, 2009 at 6:28 PMlemme clear up the subject- THERE IS NO WAY TO DO THE OFFICIAL TEST! The original rcgroups thread says that the wheels move as fast as the treadmill, which means you have the jet engine effect- te wheels speed up, which means the tarp speeds upm wich means the wheels speed up. This is the closest thing to a good test.
If it were done correctly, the treadmill would accelerate to the speed of light as soon as the test started, the treadmill would cease to exhist in a flash of light, and the plane would fall untill it gained enough speed to pull out of stall.
if you have a problem feel free to contact me (i’m b-29er on rcgroups.com) and i’ll be happ to help you waste your time.
November 8, 2009 at 11:53 PMThere is absolutely no relevance at all to the treadmill moving at impossibly high speeds…All the myth requires is that the treadmill moves at the same speed as the takeoff velocity of the plane…the Mythbusters mimicked that, and the plane took off…nothing else to it.
November 9, 2009 at 11:02 AMHey, b-29er on rcgroups,
READ THE MYTH AT THE TOP OF THIS THREAD BEFORE POSTING NONSENSE.
(or you could have just read my post which is RIGHT ABOVE YOUR POST)
November 9, 2009 at 6:57 PMNo one’s an idiot…I think we can ALL agree that a plane with no motion relative to air (i.e. airflow over the wings) doesn’t take off.
Simple analogy is you standing on a treadmill wearing skates. Your skates have motors that let you control their speed. You could set your skates to 10mph, and the treadmill to 10mph, and you wouldn’t move. If you were wearing wings, you wouldn’t take off regardless of what speed you set your skates to (if the treadmill matched it).
BUT THATS NOT HOW PLANES WORK. If you were a plane your skates wouldn’t have motors. It’d be like you holding the handlebars and pulling yourself forward. Wheels are freerolling, and no matter how fast the treadmill goes you can still pull yourself forward, and you can take off. Planes propel themselves by “pulling on the air” in some shape or another…not “pushing on the ground”, like cars do.
November 19, 2009 at 9:05 PMI Like how there are soooo many “pilots” and “engineers” that know everything about aviation in the world, and yet they can’t get this simple myth.
There are so many good examples on here as to why the wheels have NOTHING to do with it, how can they STILL not get it?
All I can say is, mythbusters did a great job and accurately tested the myth, period.
If these pilot’s and engineers can’t get this simple myth on aviation, I SINCERELY hope they never design anything I ever fly or am around!
November 25, 2009 at 10:42 PMtds, good explanation
Sven, There is no reason pilots or engineers SHOULD grasp this faster than anyone else so there is no reason they deserve singling out.
It is a brain teaser. It’s a very good brainteaser BECAUSE intelligent people will fall into it’s trap and engage in long debates.
November 26, 2009 at 12:02 AMThe test was stupid. How something like this can make it to air without somebody on the set with an ounce of common sense to speak up and say it is stupid I’ll never know.
The plane had forward motion that was only being hindered by the tarp which probably resulted in a longer takeoff roll to get to speed. A PLANE CANNOT TAKEOFF WITHOUT FORWARD MOTION TO CREATE LIFT VIA AIR PASSING FASTER OVER THE TOPS OF THE WINGS THAN THE BOTTOM. If a plane is stationary on a true treadmill then essentially you are saying if the wheels spin fast enough it will eventually take off. Ridiculous and not even necessary to run an experiment. IF however the treadmill was in a WIND TUNNEL then yes the plane could take off.
December 3, 2009 at 10:49 PMcont…if say there was a huge treadmill with a jet on it. The treadmill is moving at 140 kts backwards and the jet is moving at 140 kts forward so it cancels out and is stationary.
So these idiots are saying this jet will take off? HOW? It doesn’t matter how much thrust is given or how fast the wheels are turning…if the plane is not getting air over its wings (forward motion) it will not fly. Period.
December 3, 2009 at 11:16 PMhahahahaha
Hey I guess its fortunate that planes don’t go through aircir or they would all be getting airborne during the test!
I’m almost embarrassed to be Canadian…I really hope this show doesn’t broadcast in other counties …
December 3, 2009 at 11:21 PMI just have to post this again, as the guy above did…
http://wright.nasa.gov/airplane/move.html
Read it and _then_ re-enter the debate. North Americans have an inability to change their minds and admit that they may have been wrong. We’re taught at an early age that its better to stick to our guns and fight than it is to concede defeat; one of our main cultural flaws.
The mythbusters did a horrible job of explaining and busting this myth, yes, its almost impossible to re-create for one… but they are right.
Please carefully read the above link before responding.
December 3, 2009 at 11:49 PMArmchair Aviator,
You fell for the trap. You think the myth is about the plane standing still but it isn’t. That is your faulty assumption. Read a few of my posts.
The plane moves forward as normal and takes off as normal. The treadmill Can not impede the forward motion of the plane.
Don’t feel bad or get defensive. It is supposed to be tricky. Just read my posts and think more about it.
December 4, 2009 at 12:35 AMwhat? When you run on a treadmill does it impede your forward motion? It is the same for a plane. That is the whole point to the question in the first place. If the treadmill is moving backwards at the same rate as the plane is moving forward then the plane will not have forward motion and will not have lift. How are you not understanding this fact?
December 4, 2009 at 2:32 AMIn the test the tarp was not moving backwards at the same rate the plane was moving forward so the plane still had forward motion enough to gain lift. It was a crude experiment.
December 4, 2009 at 2:36 AMPresto are you familiar with aircare for cars? Are you telling me that if a plane was put on that aparatus that it would take off??? Please.
December 4, 2009 at 2:45 AMHEY GUYS I just thought of something…if an Aircraft Carrier had a treadmill runway moving at the same speed as an approching airplane but in the opposite direction..that plane could essentially touch down and remain in that position! Right? No need for the tail hook?
December 4, 2009 at 3:15 AMMy bad…I have jumped ship. Here is my explanation why:
Hey guys I have been arguing to the fact that the plane will not take off from the treadmill because no forward motion means = airflow over the wings = no lift.
I think both sides are in agreement of this fact.
Where this argument exists is will the plane achieve forward motion regardless of the treadmill?
The answer is yes because as was mentioned the wheels are “just along for the ride” and the plane is pulled forward by its propellors/jets.
To visualize this in action just imagine the plane flying over the treadmill before touching down. At this point the plane is moving forward at thrust speed. At the moment of touchdown, as long as the plane maintains thrust it could remain travelling in the same forward motion, the same as it could on a regular runway…albiet with the wheels spinning twice as fast.
A real life scenario that proves this theory in reverse is the old stunt of a plane landing in the back of a moving flat-deck truck.
December 4, 2009 at 10:36 AMThe problem with the question is that it is accompanied by a picture of a plane on a treadmill which clearly does not supply the necessary room needed to take off so it is assumed that the plane will remain in a stationary position.
If you were standing between two runways..one normal and one large treadmill version and were watching two planes come in to land…both landings would be identical except that with the treadmill plane its wheels will be spinning twice as fast.
This naturally will be the same for takeoff.
December 4, 2009 at 11:13 AMArmchair Aviator,
Your a big man for reviewing the situation and changing your mind.
I completely agree with your statement that the picture they used on the show of a plane on a small treadmill was misleading. I think they would say that was only a cartoon illustration done by the art department and not to be taken literaly.
I decided a while ago to stick with this discussion even though it had become ludicrously long. I’m interested in how people discuss this sort of thing. You get all kinds of characters.
You had the fastest turn around from one extreme to the other of any one I think.
December 4, 2009 at 10:08 PMya as soon as I realized that the argument was about if the plane could propel itself forward on the treadmill and not about the physics of lift then it became clear that I had to rethink my position. :)
December 5, 2009 at 2:39 AMImagine a plane **in a wind tunnel**, on a treadmill, the treadmill is moving backwards at the plane’s takeoff speed, and the wind tunnel is blowing air backwards at the plane’s takeoff speed. The plane’s engine is providing enough forward thrust to keep it stationary in the wind tunnel. We will be a bit naughty and call the wheels frictionless for now, we can revisit that in a second.
Everybody should agree that
a) The plane will remain stationary relative to the ground
b) the plane will be moving forward at takeoff speed relative to the surrounding air.
c) the plane will be moving forward at takeoff speed relative to the treadmill surface.
d) The plane will only be in contact with the treadmill if the pilot wants it to be, by pulling up, or nosing down, without bothering with increasing/decreasing the plane’s prop speed.
Right, now we have established that, leaving everything else the same, ramp up the speed of the treadmill. Ramp it up to 10 times the takeoff speed of the plane. What happens? Bear in mind, at this point, the plane does not care if it is touching the treadmill or not.
Now knock the plane’s takeoff speed off of the speed of the treadmill and the speed of the wind tunnel.
The treadmill is now moving backwards at 9 times the speed of the plane, and the plane is moving forwards at its takeoff speed.
Now all we have to do is figure out what happens if we add wheel friction to the equation.
When the plane is airbourne, nothing
When the plane is in contact with the treadmill, we have to overcome that friction, and to spin the wheels up to the speed the treadmill is going + the speed of the plane. The inertia of the wheels is not much compared to the overall mass of the plane, hence landing planes do not suddenly stop when they hit a runway just because the wheels started spinning. The coefficient of rolling friction is also low, again noted by the lack of planes immediately stopping when they land.
To overcome the friction the pilot would have to throttle forward a minuscule amount. The amount the pilot would have to throttle forward being equal to The coefficient of rolling resistence of the wheels, multiplied by the normal force, or the proportion of the weight of the plane that the wheels are taking compared to the wings, which at takeoff speed is… as much as the pilot wants. The only difference between the plane in contact with a treadmill and the plane flying is how fast the wheels are spinning, and the will of the pilot.
The question could be better phrased.
“If a pilot was in a plane in the middle of an arbitrarily long treadmill, and he wanted to take off, could somebody in control of the speed of the treadmill stop him, assuming the treadmill can move at speeds and accelerations available to modern treadmill technology?”
“If a pilot was in a plane in the middle of an arbitrarily long runway, could somebody in control of the speed of the treadmill force the plane to take off assuming the treadmill can move at speeds and accelerations available to modern treadmill technology?”
Essentially the question is ‘if a plane is on a treadmill who gets to decide if the plane stays still or takes off?’ The pilot.
December 7, 2009 at 7:20 PM‘does the treadmill get a say in this?’
only if it is running first and running fast enough to melt the bearings in the plane’s wheels. Not if it is going even twice the plane’s takeoff speed.
subha man,
You’re explanation is good and might convince some who aren’t convinced by the others.
I prefer the explanations that don’t bring in extra’s like windtunnels and excessive speeds but it may work for some.
The wording of the puzzle is quite clear. People analyze it wrong because they make a hasty assumption based on common experience. That’s what makes it a brainteaser.
December 9, 2009 at 2:02 AMsubha man,
Let me also point out that when you say the myth could be better phrased you then give an incorrect statement of the myth.
The myth does NOT say that some one is controlling the treadmill and can change the speed in an effort to stop the plane. It says the treadmill moves at the NORMAL take off speed of the airplane.
The myth is stated at the very top of this thread.
December 10, 2009 at 10:58 PManyone who thought this myth was true (including the pilot that tested it) is a moron. thrust moves a plane, not wheels or runways. the plane doesn’t know (or care) what direction it’s wheels are spinning or if it’s even moving over the earths surface. planes move through an airmass. i’ve seen a helio courier fly stationary into a headwind and it wouldn’t have made any difference if a runway was moving backwards at 200kts under it. i wonder how some of you function in a society or even sit correctly on a toilet
December 12, 2009 at 10:18 PMseat.
sa227/emb145:
You’re wrong. Many intelligent people fall for the trap hidden in this puzzler.
If you didn’t, congratulations.
December 12, 2009 at 11:28 PMalright, maybe not everyone but certainly every pilot and probably anyone with any scientific or engineering knowledge should have known what would happen. i watched that episode with my friend who never flew anything bigger than an rc job and he knew the belt wouldn’t matter. his mail-order wife who can’t find her butt with both hands even knew. the faa should have pulled that pilot’s certificate as soon as they heard him say he thought it was true. aerodynamics 101.
December 13, 2009 at 11:15 PMi contend that the pilots and engineers here claiming this myth to be true are not who they claim to be (pilots or engineers etc) but only trying to inflate their credentials to bolster their opinion in the face of devastating fact. if i’m wrong, then for the sake of public safety, please turn in your wings or degree.
December 13, 2009 at 11:29 PMWhy would “A Pilot or any one with any scientific knowledge” know what would happen?
This puzzle isn’t tricky because people lack knowledge of airodinamics as you seem to think. The folks who fall for this fully understand that
a “helo courier” can fly stationary into a headwind.
If you really understand this puzzle as you seem to think you do then there is no need to go ever every little detail.
But if you can’t see that it IS tricky and if you think it is aerodynamics 101 then you don’t really understand the puzzle
December 14, 2009 at 11:03 PMso i’m the slow one for not being puzzled by this? rationalizing the stupidy of others is a pretty high paying job these days. you have a bright future.
December 15, 2009 at 1:48 PMWhat tripped me up at first was thinking about the power level necessary to overcome a fast conveyor moving in the opposite direction.
Say the plane is a Piper Cub or something, with a max airspeed of about 80 MPH and a take-off speed of 40.
If it’s riding backwards on a conveyor going 100 mph, you would think, at first glance, that the plane could not get enough forward momentum to take off – 100 mph backwards minus 80 mph forwards equals negative 20 mph.
But this is wrong.
All the plane needs is enough power to overcome friction. Once the wheels are spinning, a little bit of power is all that’s needed to allow the plane to remain stationary – the conveyor moves 100 mph backwards beneath the spinning wheels.
There will always be plenty of power left over to accelerate the plane to takeoff airspeed, no matter how fast the conveyor moves, unless you start talking about rediculous speeds and bearing failure in the wheels.
December 15, 2009 at 3:57 PMChris,
I think it is reasonable to assume that the plane and treadmill start at the same time.
This avoids the issue of the plane moving backward. But I think you are correct in explaing that the plane would have no trouble with this.
Imagine a man standing next to each wing and holding the plane still while the treadmill moves backward. This would require very little effort because that is what the wheels are there for. To reduce friction.
December 16, 2009 at 10:27 PMMy problem with these results is this.
January 1, 2010 at 5:10 PMYou matched the conveyor speed to the indicated airspeed at which the airplane took off. Not the ground speed.
From the way the myth was explained it sounded like the airplane should not be moving relative to the stationary ground and take off. With a knowledge of elementary aerodynamics it would not take off in that case because there is very little air flow over the wing.
So in conclusion I say it’s flawed because the conveyor speed and indicated airspeed were the same but the ground speed of the airplane was not zero and thus it took off normally.
Jamie and Adam said that the reason that this worked is that the prop generates enough air flow over the wings to allow for lift. So, you could test this if you had a way to hold the airplane stationary from forward motion and it would allow it to move up and down freely. Then you would engage the engine and increase speed of the prop to max slowly to see if you can generate enough airflow over the wings from just that to cause lift.
If you do what they did and pick a fixed speed to move the surface below the plane but allow the plane to run at any speed, it can add some amount of airflow from forward motion to that of the prop. To truly test the myth, you have to ensure that you have no forward motion. On a small scale you could (in theory) have something sense the position of the airplane and adjust the speed of the treadmill to ensure that it stays in one place, at least as long as it is on the ground.
Just a thought anyhow.
January 1, 2010 at 5:19 PMFirst time I’ve seen this episode. Obvious to me from basic fluid mechanics that these are seriously flawed tests, because the “belts” themselves create boundary layers that provide lift for the ultralights. Try it with a run-of-the-mill Beechcraft, control the relative speed better, and you should have a legitimate bust.
January 1, 2010 at 5:20 PMIt’s simple folks, the plane gains speed by forcing itself through the air. THE AIR !! Anything on the ground would need to create a force to oppose it’s forward momentum and a ground moving in the opposite direction (Treadmill) with nothing of the plane but the free spinning wheels connecting with the ground, there is no counterforce.
January 1, 2010 at 5:24 PMWhen I first watched this episode I admit I thought the challenge involved an aircraft rendered stationary by a moving treadmill, and I thought the experiment was flawed when I saw the plane moving forward. True, I am NOT a pilot, nor do I claim to have a firm grasp on the laws of aerodynamics, but I should not have jumped so quickly into such an erroneous conclusion. I soon realized my mistake when I read the phrase ” A treadmill CANNOT prevent a free-rolling plane from moving forward. The propellers PULL the plane through the air, thus creating lift. The plane WILL take off!”
The analogies of attaching a rope to the back of the aircraft, or holding a toy car stationary with your hand do not apply. THE PLANE WILL MOVE FORWARD AND TAKE OFF! Luckily, I realized my mistake before I posted any letters to the contrary.
I cannot call it a trick question, like the rooster laying an egg on top of a barn, but at first glance it can mislead.
Kind of reminds me of this one…If a space ship traveling at the speed of light turns on its’ headlamps, how fast does the light from the headlamps travel!
Well, maybe not.
Anyway…Naysayers, for a short time I was one of you. YOU ARE INCORRECT !
January 1, 2010 at 8:19 PMBryan fell for the trap. He thinks the plane is supposed to stand stil.
Floozy is confused. He thinks the mythbusters attribute lift to prop wash.
Bob is wrong
Matt1970 right
Triffid sums it up perfectly
January 1, 2010 at 9:09 PMthere is no “trap” to fall for. this isn’t a trick question. if you think the plane flew because the test was flawed your just plain old wrong. and the weight of the plain relative to any boundary layer affecting this test, was almost irrelevant. as is any vertical lift component related to prop-wash. the result would have been the same on any scale.
January 2, 2010 at 10:54 AMPresto, is one of your hobbies flying kites while running a treadmill?
They cheated by using a powerful ultralight capable of a near-STOL takeoff, assisted by uplift from a billowing 2000-ft airfoil (aka “tarp”). And the video clearly shows the plane isn’t lifting off from a zero position.
Try it with a Beechcraft on a zero-length treadmill and get back to us. Bet you could do it in your back yard, because all you need is about twenty feet of “runway”!
January 3, 2010 at 12:09 AMQ. Why didn’t they model the test for an average weight & power ratio aircraft in the first place?
January 3, 2010 at 12:27 AMPresto, I may have been mistaken when I stated in my previous posting that this is not a trick question, like the rooster laying an egg on top of a barn. People HEAR the word “rooster” but ignore its’ implication when they hear the words “lays an egg”. They then set their mind to solving the problem of which side the egg rolls down.
In the question at hand, some people have it fixed in their mind that the “treadmill-airplane” scenario has resulted in an aircraft that is “stationary” in relationship to its’ surroundings. Even though the original myth makes no such determination. It only states that “An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”
They ignore the fact that it doesn’t matter whether the surface under the planes’ wheels is moving backwards, forwards or standing still…THE PROPELLERS ON THE PLANE ARE PULLING IT FORWARD AND THE AIRCRAFT WILL TAKE OFF WHEN IT REACHES THE PROPER AIR-SPEED. It doesn’t matter if it’s a toy plane, an ultra-light, a Beechcraft, or Howard Hughes’ Spruce Goose, the result will be the same.
As I was saying, having now overlooked this, they set their minds to the other fact of fixed-wing flight. “Without airflow there can be no lift”. Since they now believe that this plane is “stationary” how can there be airflow? They have reached a correct conclusion, but to an incorrect premise.
I’ve enjoyed myself immensely reading these postings. I hope they continue!
January 3, 2010 at 2:40 AM…but PLEASE stop comparing the airplane to cars, joggers and so on.
Picture this:
A very large airplane is flying 1000 feet above the ground. Beneath it are dangling a number of ropes. Attached to the ropes are an automobile (engine running hard), a jogger (legs pumping),a bicycler (peddling like crazy),a roller skater (well, I guess he’s just hanging there), and lastly, a smaller airplane (propellers spinning).
Let’s cut the ropes, shall we? The car, the jogger, the bicycle, and the roller skater plummet
earthward. The small plane flies off into the sunset.
The others require a surface to maintain motion. The plane is in its’ element. The plane will always move forward even if it never takes off. It will just run off the end of that damned treadmill. It will not stay in place.
I was going to add a surfboard, but that might be a bit much!
January 3, 2010 at 3:41 AMBob said: “They cheated by using a powerful ultralight capable of a near-STOL takeoff, assisted by uplift from a billowing 2000-ft airfoil (aka “tarp”). And the video clearly shows the plane isn’t lifting off from a zero position.”
nope. in fact one could argue that the almost nil increase in the relative wind would likely be very near the surface (reducing lift by increasing airflow and reducing pressure under the wing instead of above it). any disrupted air by that tarp would not have created anything like some sort of man-made ground effect. the STOL capabilies and weight of the plane are irrelevant regarding this test. yes a STOL plane will get airborne quicker. the treadmill is still effectively irrelevant.
January 4, 2010 at 12:08 AMI can understand that a plane will take off from a runway that is a giant treadmill.
But the treadmill still needs to be long enough to allow the plane to achieve the airspeed needed to generate lift, right?
In other words, if a certain plane requires 85 feet of runway for takeoff, it needs a treadmill 85 feet long.
It can’t take off from, say, a 30 foot treadmill, right?
January 4, 2010 at 5:41 PMBob wrote:
“And the video clearly shows the plane isn’t lifting off from a zero position.”
Case closed. You fell for the trap. (as I stated before)
Here is what I mean by the trap:
When you heard the phrase “Plane on a treadmill…” you instantly pictured a plane standing still.
You then listened to the rest of the puzzle and solved the question “Can a plane take off when it is standing still?” You correctly answered THIS question “No it can’t”.
The problem is you are answering a question that was never asked. Suprise! The treadmill can not keep the plane still. No matter how fast it moves. This is where the trick lies. Right here.
Triffid explains it very well. Read.
Triffid, I really appreciate your posts. Please stick around and help convince Bob.
January 4, 2010 at 6:07 PMSlightly confused,
January 4, 2010 at 6:10 PMYou are correct. The treadmill has to be giant. The same size as the runway needed. The mythbusters used a misleading cartoon at one point that showed a plane on a small treadmill. I think they would excuse this as a cute illustration by the art department and nothing more.
I think I just came up with the ultimate way to explain this whole thing
A) For a moment forget the original myth and discuss this one: If a plane with no wings is on a long treadmill which is moving backward at the planes normal take off speed, what will happen?
Since the plane has no wings we don’t have to be distracted by all the talk about prop wash lift, and taking off into the wind and they used an ultralight blah blah blah.
It should take less time to convince every one that the treadmill cannot impede the forward motin of the plane because the plane is moving throught the air and the wheels are free spinning.
B) Now put the wings back on the plane. Obviously since we all agree the plane is moving forward as normal, we can all agree that the plane will take off!
January 4, 2010 at 6:25 PMThanks Presto! The cartoon used by the Mythbusters definitely confused me… it reinforces the mistaken assumption that the treadmill would be much shorter than a runway. I really wish they had explained this one better!
January 4, 2010 at 6:40 PMOk. The myth was done wrong! If u look at the clip again, you’ll see that…
1) The plane was going faster than the “tredmill”.
2) In order to see that look at the plane passing the orange cones. That itself shows the plane was creating lift to take off.
3) If the plane was at the same speed with the “terdmill” the plane WOULD be on a standstill and to prove that which i can, have u ever heard of a Dynamometer? the busting guys used one in the myth on Episode 80: Big Rig test.
In the inclosed area they used a car on the dynamometer which was going at the same speen as the car, if someone was in the car they will NOT feel air passing over them, the car was on a standstill. The “tredmill” was a Dynamometer.
In conclusion, thr plane would not be able to take off due to the missing element, AIR.
January 5, 2010 at 9:00 AMIan (Trinidad & Tobago):
Just read a few posts above. Start with mine.
You fell for the trap just like almost every one does at first.
January 5, 2010 at 10:46 AMIan (Trinidad & Tobago),
Be sure and post again after reading a few of my posts. Also read Triffid’s recent post.
January 5, 2010 at 10:56 AMPresto, thanks for the kudos, but it’s an uphill battle. Just look at this last posting by Ian. After all these discussions he’s back at the beginning, reading more into the myth than is stated.
I’ve been doing the same thing at work. It’s fun to watch the confirmed “Natsayers” when they have their sudden epiphany, and finally can picture in their minds’ eye what’s actually taking place. It disturbs them to have their confidence so utterly shaken.
Some try to cover it up by saying the answer doesn’t follow the “spirit” of the myth. Meaning, they read more into the challenge than is actually there. As if a plane could actually “hover” in place as the treadmill moves beneath its’ wheels. A car…yes, a bicycle…yes, a jogger…yes, an airplane…NO It doesn’t work that way, and Trying to overcome its’ forward inertia with imaginary ropes, pins, chains, wind tunnels, glue, bubble gum, or pie (as in pie in the sky dreaming) goes against the true “spirit” of the challenge.
Ian says:
“The plane was going faster than the treadmill”
For one thing the “treadmill” was going in the opposite direction, so “faster” is inappropriate. If you mean it was moving forward in relation to its’ surroundings, YES, Ian, it HAS to move forward. It’s an AIRplane! It moves forward in the air. The treadmill will have no effect on that.
As far as the rest of Ians’ posting, he’s just repeating himself, and trying to use the car analogy again.
Presto, I liked your “wingless plane” setup. Keep fighting the good fight.
January 5, 2010 at 11:14 AMLately the “Mythbusters got it wrong” guys who show up here inevitably make a quick burst of posts and then either vanish or post a mia culpa.
January 5, 2010 at 6:41 PMPresto,
It appears to me that the people who are posting on this site and others fall into three catagories.
1) Those who “get it” like you and I, and understand that there is a major blind spot causing some individuals to arrive at an incorrect conclusion.
2) Those who don’t “get it”, and stick to the premise that the plane behaves like an automoble or jogger. That is, will somehow remain in place when the speed of the plane and the treadmill are matched.
3) Those who initially began as catagory 2’s, but later realize they are wrong. These people are most interesting because rather than outwardly “jumping ship” they stick to their original declaration, and try to convice others that there is an underlying “spirit” to the myth that substantiates their claim.
I could argue that there is a 4th group of individuals who belligerently declare that it is a stupid myth and we shouldn’t even be discussing it. Evidently, the hundreds of postings we have seen disprove that position. If nothing else, it an intriguing insight as to how people perceive and go about solving a brain teaser.
All in all, it’s great fun. You might want to check out some of the videos on YOUTUBE relating to this myth. I had a few good laughs myself.
January 6, 2010 at 1:29 PMIan (Trinidad & Tobago)?
January 6, 2010 at 1:54 PMHere’s an experiment to conduct to anyone who’s got the scratch laying around(it’s not much but it could leave you with one expensive wrecked toy plane).
Tether a toy plane to a ceiling or otherwise suspend it from the ground. Turn on the propeller. If the “IT CAN’T WORK!” crowd are right, it’ll produce no forward thrust and not fly off. If the “It worked, deal with it” guys are right, then it will fly forward, and probably make one hell of a mess as it gets wrapped up in the tether(or not, if you cut the cord as it shows that it’s lifting off, either way it’s going to make an impressive YouTube video).
Seeing as how a cheap foam plane can be had for less than 30 bucks, I don’t think anyone would be too broken up if it well, breaks.
I’m in the “It’ll work” crowd. Mostly because it follows the same principles as throwing a helicopter in the air and kicking on the engines. Momentum from thrust generated by the engines are what’s important, not the speed relative to the ground.
Besides, in the 50’s when they were experimenting with breaking the sound barrier, they launched the first experimental craft from another plane. They launched some of the first space bound objects that way too. Speed relative to the ground has nothing to do with how this thought experiment works, just the fact that forward movement generated by the engines, sufficient to negate the effects of the conveyor belt will be sufficient to launch a plane. My big question is, why haven’t they built air craft carriers with this concept in mind.
January 6, 2010 at 11:30 PMI had a gentleman in my place of business yesterday that I happen to overhear tell one of my associates that he had flown his own aircraft down south to visit relatives over the holidays. So naturally I told him the myth.
I was astonished when he replied that the plane would NOT take off! When I asked him why it wouldn’t lift off he said “I’ve studied aeronautical engineering and the plane would need lift to fly” When I asked why there wouldn’t be lift under the conditions of the myth he said,”Because a stationary airplane would not have airflow over its’ wings”. “But I explained that the plane was moving forward at the same speed that the treadmill was moving backward” I replied. “Exactly” he said, “… so it’s stationary relative to the ground”
I couldn’t believe my ears. It took five more minutes of explanation before I saw the dawn of realization in his eyes. He first tried to say that I had explained it wrong, but finally gave in and sheepishly admitted I was correct.
Who says this topic isn’t worthy of discussion?
January 7, 2010 at 7:14 AMEverybody that doubts that the aircraft needs to ask themselves one thing: Why do the wheels on an aircraft turn at all? Is there a linkage to a drivetrain? No.
January 7, 2010 at 11:39 AMThe wheels turn because the engine is pulling or pushing (depending on a/c design) that aircraft through the air. If you spin the wheels of an aircraft under power, all you have is a moving aircraft with rapidly spinning wheels. The wheels don’t have any connection to the rest of the aircraft, so any actions on them has no effect on the aircraft.
The brakes, on the other hand, ARE connected to the aircraft. When the brakes lock on to the wheel hubs, that aircraft can be running at full power and wont move an inch. Release the brakes and the wheels freewheel without any further effect on the aircraft.
Think about it. The aircraft flies because the engine is so strong that it pulls the aircraft through the air despite the forces of gravity and wind resistance. The wheels keep the aircraft from dragging it’s belly on the ground. There is no linkage, it’s bearings against a hub, so there is no drag on the aircraft.
taiki: I don’t know if you understand or not but you sure confused the issue. Your final comment about aircraft carriers leads me to think you misunderstand the myth.
Triffid: If you want anothr argument starter try this one: “Start with two identical glasses of wine except one is red wine and one is white wine. Take exactly one spoonful of red wine from the first glass and put it in the second glass and stir. Then take exactly one spoonful of wine from the second glass and put it in the first glass. Now, is there more red wine in the white, or more white wine in the red?
JD, Correct explanation. I think some people might think airplanes have a motor that drives the wheels but the funny think is even when they are straightened out on this issue it doesn’t really help.
January 7, 2010 at 11:26 PMGood one,Presto.
My initial thought, after about 15 seconds of deliberation (because I’m about to hit the sack and will probably be up half the night wondering if I’m right) is that there will be more red wine in the white, since you’ve just diluted the white with the red. Hence, less white is being transferred to the red. Plus, you are transferring more of the red back to the first glass. Do you have the correct answer, or just putting it forward?
I think I’ll have a glass of wine before turning in.
January 7, 2010 at 11:45 PMhaha,presto, thats a trick question isnt it?
January 8, 2010 at 2:52 AMtheres an equal amount in each glass
anyways, i dont understand how ppl misunderstand it, the simple reason that this myth is busted is cuz the wheels on a plane are free spinning
January 8, 2010 at 2:58 AMI see it, I think. My answer is correct in one sense,I you’re looking at it from the determination of how much wine was transferred.
However, there can’t be more red in the white, or more white in the red, since you started off with full glasses of each.
The white will have more white, and the red will have more red.
Tricky phrasing. Thanks Presto.
January 8, 2010 at 6:49 AMKeic is correct. After the transfer the amount of white wine in the first glass is exactly equal to the amount of red wine in the second glass.
To see this, try it with coins. Put 12 pennies in one pile and 12 nickels in another pile.
Transfer 4 pennies from the first pile to the second. Then transfer 4 random coins from the second pile to the first. No matter how you do it the number of nickels in the first pile will equal the number of pennies in the second pile when you are done.
Triffid, you used the exact reasoning that most people do to get this wrong. It’s hard to explain why it’s wrong but it is. You just have to do it.
Oh and it’s not tricky phrasing. You sound a little like those people you were complaining about earlier :)
January 8, 2010 at 7:10 PMKeic,
Most people hear the phrase “On a treadmill” and interpret that as “standing still”.
This is based on our experience with treadmills. That is what a treadmill does. It makes something that is moving stay in place.
So people think that it is a given that the plane stands still. They think that is defined in the puzzle so they feel cheated when you say the plane moves.
They are being fooled before they even thought the puzzle started.
True…If they would just focus on that one issue they would find it rather simple and obvious. But they gloss over it and get into the other stuff where they think the puzzle lies.
January 8, 2010 at 7:23 PMNo need to get pissy, Presto, by making such a comparison. The phrasing I was speaking of is “Is there more red wine in the white, or is there more white wine in the red?” Rather than, “Is there more more red wine in the white THAN there is white wine in the red”? There is a major difference. I’d explain it to you, but I’m pressed for time today.
However, I’ll let it go. Since you evidently read some of the postings concerning the puzzle before, and it was my first encounter.
Unlike some of the “treadmill” gang, I will concede if I’m in error.
January 9, 2010 at 9:44 AMyikes. triffid, no offense intended.
I thought my use of the smiley face made by a colon and a parenthesis at the end of that sentence would have made it clear that I was kidding.
I do concede that your wording of the question is more precise than mine.
January 9, 2010 at 9:58 PMI apologize, Presto. Bad day yesterday, and I DID miss the smiley face.
I jumped to a quick resolution to the “wine” puzzle, as I originally did on the “treadmill” question.
As far as the wording goes, “is there more red wine in the white, or more white wine in the red”
January 10, 2010 at 11:36 AMThere won’t be more red in the white until you add more than 50%, and vice versa.
No problem Triffid.
Your original interpretation of my wording was the intended one as can be seen from your explanation:
” …is that there will be more red wine in the white, since you’ve just diluted the white with the red. Hence, less white is being transferred to the red. “
January 10, 2010 at 4:47 PMI watched this episode and wondered immediately why it would even be a debate. I’m losing more and more faith in humanity with my ever increasing years.
January 25, 2010 at 1:12 AMBrainwashed, Most people, when given the problem as stated at the top of this thread will get it wrong. Not all, apparently not you, but most.
It isn’t a very good intelligence test. It’s a brainteaser.
January 26, 2010 at 12:18 AMSo can I just clarify
The plane is propelled forward using air movement, nothing to do with wheels, so will move forward regardless of a treadmill pulling it back, and one could ignore the wheels etc.
So would the wheels in fact be moving at 2 times normal speed? the sum of the treadmill pulling it back and the plane moving forward would require the wheels to move at 2 times the speed as normal, but forget the wheels anyway.
Also, alternative experiment, if one suspends a plane on a rope, then powers the engine up to take off speed or cruising speed, would it immediately be flying if we remove the rope? I guess the plane would actually move forward moving the air through it so would pull on the rope. If we remove the rope the plane would just go forward I think.
January 27, 2010 at 9:04 AMJust had a thought,
Have you ever seen in a toy shop a model plane attached to a string on a roof, it just flies round in circles and has no contact with the ground, limited in motion by the string.
Thanks to presto and other people for explaining all this so well for us mere mortals
January 27, 2010 at 12:47 PMthinking,
“So would the wheels in fact be moving at 2 times normal speed?”
YES
As for suspending a plane from a string or cord the plane would be pulled upward at first and then would probablly flounder around on the cord. Flight is a delicate balance. You can’t just fly at an angle without adjusting a lot of things.
January 29, 2010 at 1:38 AMThis is why i don’t like mythbusters at most times, they strive to beat myths down instead of considering how to acheive them. Would have made much more sense to have a static model measuring how much lift is generated directly by the prop’s airflow as opposed to the dynamic real model where the prop pulled the aircraft and induced air flow over the whole area of the wing. I.e. in the fixed position the prop moved air much faster over smaller area of wing.
February 5, 2010 at 6:13 PMrealistic,
You fell for the trap. When you heard “Treadmill” you thought “plane standing still”
The plane doen’t stand still. It isn’t supposed to stand still. It can’t stand still. No treadmill can ever impede the foward motion of an airplane.
It has nothing to do with “lift generated directly by prop’s airflow”. The lifted is generated by the wings moving through the air as in any normal take off (because it is a normal take off).
Before you reply (and I hope you do) please read my post of Jan 04.
February 6, 2010 at 11:09 PMTo really end this, if the plane were on the treadmill, a person on either side could probably hold the plane in place. The treadmill/conveyor belt is really not exerting that much force on the plane and the plane can easily break free of that force with little opposing motion since it is on wheels.
February 7, 2010 at 1:20 PMMatt1970,
Well said. It seems so simple once you get past the initial misconception.
The myth seems to ask “Can a plane take off if it is standing still?”
But it is really asking “Can a treadmill stop a plane from moving forward?”
February 7, 2010 at 6:54 PMrealistc?
Cmon realistic. Follow up on your post. I know you didn’t post once and then never checked up on it.
Tell me you stand by your post or you changed your mind or I misinterpeted you or something.
February 8, 2010 at 8:03 PMThe plane takes off because the wheels really don’t matter all that much, if the wheels are spinning at a certain rate of speed, the propeller is always going to pull the aircraft further forward from where it currently is – the only way a conveyor belt can prevent the aircraft from being pulled further forward is if the force of friction of the wheels is equal to the force pulling the plane forward. The result is entirely consistent with mathematics. The whole notion of the conveyor belt keeping the plane at the same place relative to the ground is flawed.
Mythbuster WIN
February 9, 2010 at 2:58 AMTo say it more simply, The speed of the conveyor belt is independent of the speed of the plane. The conveyor belt cannot slow the plane down it is as if the conveyor belt is completely irrelevant.
The only difference between a plane that takes off from a conveyor belt and one that takes off from a runway is the speed of the wheels.
February 9, 2010 at 3:03 AM