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 PMTHE ENGINES PUSH AIR TO CREATE LIFT
January 30, 2008 at 10:38 PMLEARN TO READ UP ON THIS SHIT
A 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, dont try to hide the fact you were wrong. saying that you thought it was something different is bullshit. “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 AMOpinions are like assholes, everyone got one and nobody cares about anyone else’s
January 31, 2008 at 12:05 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 AMso far MR “SHUT-UP” has had the best reply
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 AMAn inclination of the cranium is as beneficial as a spasmodic motion in the optic to quadruped with a void visual capacity - just remember that
January 31, 2008 at 12:55 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 AMPlain standing still in a wind-tunnel, wind is blown onto the plain will at take off force - will it lift (engine and wheels are not powered)
January 31, 2008 at 1:01 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 AMSubmarine engine aganist a stonge (very,very stonge) current?
January 31, 2008 at 1:03 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 AMIt was on tv it must be true.
January 31, 2008 at 1:07 AMit’s on the internet it must be true
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 AMwrong
January 31, 2008 at 1:10 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 AMThe cable on the crane would have to be long if the plain was to fly anywhere??
January 31, 2008 at 1:13 AMThink the crane would provide the lift - cheating
January 31, 2008 at 1:14 AMSHUT-UP: my point was the plane would move. These people are saying that moving the wheels backwards will keep the plane from moving in the air.
January 31, 2008 at 1:16 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 AMthere is a reason that runways are NOT made from treadmills
January 31, 2008 at 1:19 AMStationary surfaces seem the be the way!!
My 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 AMTo everyone who thinkgs that the plain did/should take off - what would happen it the tread mill was moving the other way, in the same direction as the plain?????
January 31, 2008 at 1:23 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 AM“shut-up”. i think maybe you should just go to bed or something. you are way out of your league here. you cant even SPELL plane let alone understand how the basic concept of flight works.
January 31, 2008 at 1:26 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 shit-all, so can you please STFU.
Thanks for your attention.
Love,
The Internet.
XXOOXX
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 dumbass 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, give it up and get some experience.
January 31, 2008 at 1:00 PMAnon–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