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.

1,032 Comments

  1. NewsNik says:

    So it’s not me.
    It’s the web page that is cutting out the midle part….

    So ignore the 2 above,
    I will post each following experiment in pars till the end

    —-
    7) Experiment # 3
    This is a step up on experiment # 2
    But let’s make sure we note the numbers
    The plane is tied out, the motor is off.
    The runway is turned UP to >>60<< knots

    V_air = 0 (Zero)
    V_ground = 0 (Zero)
    V_runway = -60
    S_laser = 0 (Zero)
    V_plane_2_ground = 0 (Zero)
    V_plane_2_runway = 60

    Plane stays in line with reference poles


    8) Experiment # 4

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to 40 knots
    The runway is turned on to 40 knots

    V_air = 0 (Zero)
    V_ground = 0 (Zero)
    V_runway = -40
    S_laser =0 (Zero)
    V_plane_2_ground =0 (Zero)
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NO wind (V_Air) going over the wings – No Flight

    • Alan says:

      Wrong. If the plane accellerated to 40 kts, it did so relative to the AIR, not the ground. If you pull the ground backwards at 40 kts, the wheels now are spinning at 80 kts.
      I take it you do not have a pilots certificate (license), or experience flying aircraft.

      • presto says:

        To be fair to Newsnik he specified in this example that the plane is powered up to the point where it’s wheels are spinning at the same speed but opposite direction of the tradmill.

        He is not incorrect about his experiment #4

        He IS incorrect to think this is the situation the Mythbusters were interested in testing.

        Alan, welcome to the conversation. It definitely sounds like you understand this thing.

        Don’t make the mistake of questioning people’s Piloting qulifications based on this myth. This question does not require knowledge of flight and pilots have no special advantage in solving it.

  2. NewsNik says:

    —-
    9) Experiment # 5

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to >>60<>80<< knots
    The runway is turned on to 40 knots

    V_air = 40
    V_ground = 40
    V_runway = -40
    S_laser =40
    V_plane_2_ground =40
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 20) going over the wings – No Flight

  3. NewsNik says:


    10) Experiment # 6

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to >>80<>81<< knots
    The runway is turned on to 40 knots

    V_air = 41
    V_ground = 41
    V_runway = -40
    S_laser =41
    V_plane_2_ground =41
    V_plane_2_runway = +81

    Plane FLIES and moves forward at 1 knot

    —————————————

    The plane must be moving at a COMBINATION of speeds
    The speed of the runway + it's takeoff speed to be able to takeoff
    Just rolling along on a runway at equal and opposite speeds does NOT create ANY wind speed to be able to fly..

  4. NewsNik says:


    11) Experiment # 7

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to >>81<< knots
    The runway is turned on to 40 knots

    V_air = 41
    V_ground = 41
    V_runway = -40
    S_laser =41
    V_plane_2_ground =41
    V_plane_2_runway = +81

    Plane FLIES and moves forward at 1 knot

    ————————————————————-

    The plane must be moving at a COMBINATION of speeds
    The speed of the runway + it's takeoff speed to be able to takeoff
    Just rolling along on a runway at equal and opposite speeds does NOT create ANY wind speed to be able to fly..

  5. NewsNik says:

    Sorry about that people
    I do not understand why the browser kept cutting out the midle portions of my cut and past..

    Maybe my text editor has some character that gives this page a hiccup..
    :-)

    Experiment #7 is the last and closing step of the proof from which the closing comments are derived…

  6. presto says:

    Newsnik wrote:

    V_air = 41
    V_ground = 41
    V_runway = -40
    S_laser =41
    V_plane_2_ground =41
    V_plane_2_runway = +81

    Plane FLIES and moves forward at 1 knot

    Presto replies:

    So you seem to have gone to a lot of trouble to prove to us that the plane WILL fly. This is the mythbusters conculsion and my conclusion.

    Newsnik also wrote:

    Just rolling along on a runway at equal and opposite speeds does NOT create ANY wind speed to be able to fly..

    Presto wrote:

    Right, again, this is in line with Mythbusters and my statements. There is nothing in this “myth” about a plane standing still.

    So where do you claim to prove mythbusters or myself wrong?

  7. NewsNik says:

    Presto,

    I see what happened

    The descriptions of Experiment # 5 and # 6 are screwed up

  8. NewsNik says:

    Corrected Experiments #5 & # 6

    (I have NO IDEA why it gets changed when I post it…)

    —-
    9) Experiment # 5

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to >>60<< knots
    The runway is turned on to 40 knots

    V_air = 20
    V_ground = 20
    V_runway = -40
    S_laser =20
    V_plane_2_ground =20 (Zero)
    V_plane_2_runway = +60

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 20) going over the wings – No Flight

  9. NewsNik says:

    10) Experiment # 6

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to >>80<< knots
    The runway is turned on to 40 knots

    V_air = 40
    V_ground = 40
    V_runway = -40
    S_laser =40
    V_plane_2_ground =40
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 20) going over the wings – No Flight

  10. NewsNik says:

    I’ve ALSO decide to add an ADDITIONAL experiment were BOTH runway and plane are cranking at 80 knots each

    12) Experiment # 8

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to >>80<>80<< knots

    V_air = 0 (ZERO)
    V_ground = 0 (ZERO
    V_runway = -80
    S_laser = 0 (ZERO
    V_plane_2_ground = 0 (ZERO)
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 0 (ZERO)) going over the wings – No Flight

  11. presto says:

    And as I said you seem to have proven with your experiment #7 that the plane WILL take off.

    • NewsNik says:

      Yes the plane does NOT lose it’s ability to fly just because it’s on a moving surface

      BUT, and this is the but the blows the mythbusters out of the water,
      under the DEFEINITION given by MYTHbusters where the runway rolls at a speed equal to the takeof speed of the aircraf with the aircraft rollng that the same speed, the plane will NOT fly…

  12. presto says:

    Presto quotes the myth from the top of this tread. The one the Mythbusters 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.
    —————————–

    Presto Comments:

    This says te conveyor belt is set to move at the planes normal take off speed (as you did in your experiment).

    Please show me where it says anything about the planes speed durring the take off.

  13. presto says:

    I meant to write “durring the experiment” rather than “durring the take off”

  14. NewsNik says:

    So you’re really about playing weasel word games

    Ok
    I’ll play

    So I’m the pilot of the plane in the above example
    Since I’m an old pilot, that means that I’ve survived by not being a bold pilot

    So I always take off at 10 knots about stall speed that is 50 knots

    As per experiement #

    the numbers are
    V_air = 0 (ZERO)
    V_ground =
    V_runway = -50
    S_laser = 10
    V_plane_2_ground = 0 (ZERO)
    V_plane_2_runway = 0 (ZERO)
    Speedometer on plane 100

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 0 (ZERO)) going over the wings – No Flight

    And that’s according to the Mythbusters definition which CLEARLY states that the runway moves at the takeof speed of the plane but in the opposite direction..

  15. presto says:

    Newsnik wrote:

    So you’re really about playing weasel word games

    Presto responds:

    Weasle words? I only asked you to show me in the myth under question where it says the planes speed is limited.

    So, take your facts. At some point the plane is at equilibrium and is not moving relative to the poles.

    What is to keep the pilot from simply accelerating past this point and taking off?

    You already showed that nothing is stopping him. You showed in your experiment #7 that the plane will fly.

    I’m going to stop here and continue in another post to keep things vey clear

  16. presto says:

    Imagine we are sitting on a couple of lawn chairs and watching the conveyour belt test from the side at a distance.

    Suddenly someone says “There goes the plane!”. We look and see the plane taxiing down the runway and taking off.

    Some one says “Was that with the conveyor belot on or off?”

    My reply: “There is no way to tell from here. Surprisingly the conveyor belt has virtually no effect on the plane. It taxis at it’s normal spped and takes off at it’s normal speed regardless of the converyor belt. There is a very slight change in the rolling friction under the wheels but it is tiny, negligable actually.

    As a matter of fact, the pilot himself would not feel any difference in the handling of his plane, his insturments would nor read any different (he doesn’t have a speedometer on the wheels).”

    Newsnick this little scenario is not offered as proof of my position but only to make it clear what my position is.

  17. presto says:

    Newsnik, from your example above I gather that you believe the conveyor belts speed is somehow connected to the planes speed duriing the experiment.

    Could you refer to the qustion under discussion and show me where you find this?

    • NewsNik says:

      presto says:

      Newsnik, from your example above I gather that you believe the conveyor belts speed is somehow connected to the planes speed duriing the experiment.

      Could you refer to the qustion under discussion and show me where you find this?

      NewsNik Says

      DOH !
      Have you not been paying attention ??

      If as you claim the treadmill have no effect on the plane, or anything with wheels for that matter, you can prove it false with a very simple experiment

      Take a roller skateboard or anything else with a bit of weitht to your nearest airport with one of those people mover belts, or health club with a treadmill
      Tie a string to the front of your device and place it on the treadmill while you stand on solid ground in front of it.

      If as you claim that treadmill will not start moving that object away from you, there should be no pull on the string.

      Experiments #2 and #4 prove your claim to be false
      In one case (#2), it’s the wire attached to the poles that is providing the “thrust” to move the plane forward on the belt, while the belt is moving backwards
      In the other (#4) it’s the thrust from the propeller that is doing EXACTLY THE SAME THING

      On BOTH cases they are overcoming the drag of the runway on the plane that was CLEARLY demonstrated in #1

      Since there was NO CHANGE in the contact between the plane’s tires and the runway, there can NOT be some magical loss that changes from experiement to experiment

  18. presto says:

    Newnik, I think you misunderstand me.

    If you read the “Myth” in question that I have printed several times you will see that the speed of the conveyor belt is fixed. It is equal to the NORMAL take of speed of the airplane (which you set as 40 knots).

    When you reach the equilibrium that you describe the belt is going backward at 40 knots and the plane is moving along the belt forward at 40 knots so there is no movemment, no lift, no flight. We both agree on this.

    Now the question is Can the pilot take off? And the answer is yes. Easily. He just increases the power to the engine and the plane moves forward, achieves lift, and flight.

    The conveyor belt does not change speed to match the plane. It’s speed is fixed at the beginning of the experiment.

    If you disagree I want you to quote the part of the question that you think indicates that the conveyor belt changes speed or matches speed or that the plane is constrained to only go a certain speed.

    • NewsNik says:

      Newnik, I think you misunderstand me.

      If you read the “Myth” in question that I have printed several times you will see that the speed of the conveyor belt is fixed. It is equal to the NORMAL take of speed of the airplane (which you set as 40 knots).

      When you reach the equilibrium that you describe the belt is going backward at 40 knots and the plane is moving along the belt forward at 40 knots so there is no movemment, no lift, no flight. We both agree on this.

      Now the question is Can the pilot take off? And the answer is yes. Easily. He just increases the power to the engine and the plane moves forward, achieves lift, and flight.

      Newsnik says:

      But when the pilots changes the throttle to increase his speed above the “takeoff speed” in effect he has flown away from the Mythbuster question and broken the rules for that question

      By doing so, he has stepped out of the problem and therefore that is not a VALID result..

      That would be like having 2 people compete as to who can make the most money selling 10 apples.
      One of them in the process wins the $200,000,0000 Powerball.
      Can he claim to be the winner by adding that $200,000,000 to his revenues from the apples sales ?

      NO !

      IN the same way, the pilot who changes his “takeoff speed” during the testing of the myth is in effect stepping out of the rules of the myth being tested
      He in effect is out of the contest because the $200,000,000 had nothing to do with selling the apples contest.

      If you’re going to test something, you have to test what is agreed, and anything outside of that definition is NOT part of the test.

  19. presto says:

    The drag that you speak of exists of course. It is greatest when the plane is stopped.

    When the planes wheels are going 40 knots in a normal take off the drag from rolling friction is small.

    When the planes wheels are at 80 knots due to the conveyor belt the new rolling friction is only slightly larger.

    I don’t think you and I disagree on this drag. You acknowledged yourself that the plane will take off when the thrust is increased beyond the equilibrium point to when lift is achieved.

    • NewsNik says:

      Look, it’s really simple
      The myth as defined by Mythbusters is true
      A plane can NOT take off from a runway that is moving backward at a speed equal to the “takeoff” speed of the airplane

      I not only demonstrated that
      I also demonstrated that the airplane needs to be rolling on the “moving” runway at a COMBINATION speed of (takeoff + runway speeds).
      Anything less and it’s physically impossible for the plane to take off.

      ANd the reason why the argument about friction is meaningless, is BECAUSE in the setup we CALIBRATED the throttle to EXACTLY the point just below the takeoff speed

      That calibration INCLUDES BOTH the resistance of the air and the resistance of the plane-runway to the plane moving forward.

      Also a these low speeds, the increase of rolling resistance from air and surface is linear and not exponential, and so small that it really meaningless.

      IN effect the friction resistance, air resistance, have all been factored INTO the calibration of the throttle. So in effect, talking about them is meaningless.

  20. presto says:

    Newwsmik,

    You demonstrated that the plane will not tkae off when it is going 40 knots relative to the conveyor belt. I agree.

    That is not the situation being discussed here.

    There is no reason the plane does not simply move past equlibrium and take off.

    You have never once answered my request that you show me in the myth being discussed where the speed of the conveyor belt is tied to the speed of the plane durring the test. It is equal to the Normal take off speed. It never changes.

    The plane is not constrained to remain in this equilibrium. It simply moves forward and takes off.

    If you are claiming the rolling friction will hold the plane back then say so. I don’t think this is your claim. We both know that the rolling friction is small.

    • NewsNik says:

      There is NOWHERE in the description of the tet ANY statement that for the myth the plane can accelerate past the “takeoff speed”.
      The description of the test is VERY CLEAR
      Runway and plane are BOTH travelling at “takeoff speed”
      ANYTHING else is NOT part of th myth as defined by Mythbusters

      That is YOU trying t change the parameters of the stated myth..

      IN actual fact, this is a common logic problem assigned in many Engineering schools and Math departments
      It is specifically intended to demonstrate how easy it is for a person to read into the question things that are not part of the question. And effectively change the parameters of the problem being solved.

      The term for this is “project creep”.
      You are doing that with your argument that there is nothing to stop the pilot from pushing the throttle to the wall, and taking off.
      But doing so is jumping out of the problem AS DEFINED. And therefore that is NOT and ACCEPTABLE solution for the problem AS DEFINED.

  21. presto says:

    Presto quotes the myth in question:

    ———————————
    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.
    ——————————–

    Yes, the myth says nothing aboout the planes speed durring take off. It simply asks if the plane can take ooff.

    Your statement that “the runway and the plane are both moving at BOTH moving at takeoff speed” is not there. It is something you brought in from outside.

    This problem is not the same one you have encountered before. Surely you conceed that there can be similar sounding problems that have very diffent answers, right?

    And one more thing. The pilot doesn’t have to “pull the throttle to the wall”. The take off is perfectly normal. The pilot is already used to the normal rolling friction on the wheels and the increased spinning of the wheels caused by the conveyor belt adds very little to it. (Note: I never said nothing, I said very little)

    • NewsNik says:

      presto says:

      Presto quotes the myth in question:

      ———————————
      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.
      ——————————–

      Yes, the myth says nothing aboout the planes speed durring take off. It simply asks if the plane can take ooff.

      NewsNik Responds:
      False !
      IT states CLEARLY:
      “its normal ground speed during takeoff.”

      presto continues:
      Your statement that “the runway and the plane are both moving at BOTH moving at takeoff speed” is not there. It is something you brought in from outside.

      NewsNik Responds:
      False !
      IT states CLEARLY:
      “its normal ground speed during takeoff.”

      presto continues:

      This problem is not the same one you have encountered before. Surely you conceed that there can be similar sounding problems that have very diffent answers, right?

      NewsNik Responds:
      Wrong !
      See above.

      presto continues:

      And one more thing. The pilot doesn’t have to “pull the throttle to the wall”. The take off is perfectly normal. The pilot is already used to the normal rolling friction on the wheels and the increased spinning of the wheels caused by the conveyor belt adds very little to it. (Note: I never said nothing, I said very little)

      NewsNik Responds:
      False !
      The pilot must be rolling at a speed greater than double the “normal takeoff speed” to have ANY chance of taking off.
      THis is proven in experiments #5 to @8

  22. presto says:

    Newsnik, you have explained things well and you proved the point you were trying to prove. (A point that neither I nor mythbusters ever disputed).

    Now look at the question we are dealing with here and be as careful as you were with the answer.

    Does the question as stated at the top of THIS thread involve any matching of speeds?

    • NewsNik says:

      presto says:

      Newsnik, you have explained things well and you proved the point you were trying to prove. (A point that neither I nor mythbusters ever disputed).

      Now look at the question we are dealing with here and be as careful as you were with the answer.

      Does the question as stated at the top of THIS thread involve any matching of speeds?

      NewsNik says:

      Yes
      The phrase “normal takeoff speed” implicits that..
      Any other speed is NOT “normal takeoff speed”…

  23. presto says:

    The myth again:

    —————————
    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.
    —————————-

    The conveyor belt is moving at the Normal Gorund Speed of the plane. You set this at 40 knots for our discussion.

    So you take the Normal Ground Speed of the plane at take off (40 knots) and that the speed of the conveyor belt.

    There is nothing in that sentense about the speed of the plane durring the test. It simply asks if the plane can take off on a conveyor belt going 40 knots in the other direction.

    • NewsNik says:

      go back and read the definitions
      40 knots is NOT the “normal takoff speed”
      It is the STALL speed.
      The point at which the aircraft can NOT fly

      Basically what you are trying to do here is pick nits
      I’m NOT going to waste my time with you doing that.

      I already answered your various questions about “normal takeoff speed”
      I will NOT go in circles with you about it..

  24. presto says:

    Newnic also wrote:

    The pilot must be rolling at a speed greater than double the “normal takeoff speed” to have ANY chance of taking off.
    THis is proven in experiments #5 to @8

    Presto wrote:

    We don’t actually disagree on this. Accept that I have pointed out that this difference is really small. We’re not even talking about the rolling friction because that is always there. We are talking abou the slight increase in rolling friction. it is tiny. Nothing compated to the thrust that makes a plane fly.

    To Illustrate:

    Let’s have a tug of war. I will stand on the ground and you put the biggest strongest weightlifter you can find on the other end of the rope. He is wearing roller skates and standing on a treadmill.

    I will have no trouble defeating him. Neither would my Neice. I’ll even let you increase the speed of the conveyor belt as much as you want.

    It won’t help. He has no purchase. The free spinning wheels of his skates are doing their job and isolating him from the treadmill.

    Again. I didn’t say there was no force involved. I said it was small. And it is. It is well within the normal variables that an airplane might encounter on take off. (Sleightly bumpier surface, wheel bearing getting older, etc etc)

    • NewsNik says:

      ALready asked and answer.
      Whatever resistance there is from the air or the rolling on the runway surface is CALIBRATED INTO THE THROTTLE WHEN YOU SET IT UP..

      ALl you are doing is trying to pick nits to avoid facing the fact that I have proven the myth valid and that test by Mythbusters was UNSCIENTIFIC BULLSHIT

      I’m an NOT going to play your game.

  25. presto says:

    Newsnik,
    Do you see now that “It’s normal speed during take off” is the speed assigned to the conveyor belt?

    The belt has to move at “he planes normal speed during take off” But the plane does not have to move at “the planes normal speed during take off”.

    Look at this sentence:

    Presto can not walk faster than a golf cart which is moving at Presto’s normal walking speed. (Well of course I can. This sentence constrains the golf card not me)

    We are really at the crux of our disagreement. It is the meaning of those words. Those words fix the speed of the belt (during the test)or the plane (during the test). There is no way of interpreting that sentence to apply to both.

    One poster weeks ago insisted that the sentence should be read:

    An airplane cannot take off [at a speed equal to its normal ground speed] from a runway which is moving backwards.

    This is a pretty silly reading because obviously the speed of the conveyor belt must be stated. If not you can just consider a conveyor belt which is not moving at all or which is moving at one inch/year.

    He insisted that it was linguistically valid (probably) but conceeded that it was NOT the myth the Mythbuster tested.

    • NewsNik says:

      Don’t give a rat’s ass about the nonsense posted by someone else
      I’m also gettng tired of you trying to go in circles to pick nits

      Here’s the bottom line
      If you have an airplane that takes of at a “normal takeoff speed” (and do look up the statistical meaning of “normal”), and you try it on a runway going at the same speed in the opposite direction, the plane will NOT fly.
      PERIOD..
      FINITA
      END of discussion

      Good bye

  26. presto says:

    You are quite wrong. The plane will take off.

    AND even though it is not required by the myth, the plane will infact take off at it’s normal take off speed!

    This is because airplane speed is measured by the speed through the air. Not along the ground. Normally on a windless day these two speeds would be the same. But the treadmill changes that.

    So:

    The Treadmill moves backward at 40 knots

    The plane moves forward and when it reaches at a bit over 40 knots (air speed) it takes off.

    The treadmill has almost no effect on the plane. The pilot can not even feel a difference.

    At the time of lift off the wheels of the plane are spinning as if it is going 80 knots (which it is if measured along the conveyor belt).

    So the plane in fact takes of at it’s normal take off speed (ok a tiny tiny bit more, really tiny).

    I didn’t bring this up because the question doesn’t mention the speed of the plan durring the test. So it doesn’t specify what if this is air speed or what. But if you are going to insist that the plane can’t take off while flying at it’s normal ground speed well yes it certainly can.

    It was nice having this discussioon with you. I always try to address each issue brought up s clearly s I can.

    Feel free to resume the discussion anytime. I have a thick skin and I know these discussions can be frustrating.

    • NewsNik says:

      I disgree, you have tried to play fast and loose in this discussion, as you have in all your other discussion with other participants

      I will point out to you, that when I decided to respond to you, I went back and read ALL of your responses to others.
      I made a list of all of the methods by which you tried to game the arguments.
      I then set up the proof I provided to make sure that I addressed ALL of your “trick”, prevarications, side-steps, and outright lies.
      I can knock down every single objection you have come up with in the past, and any you can imagine in the future.

      You have accepted my setup
      You have accepted my experiments
      YOu have NO CHOICE but to accept the conclusion derived

      And finally, Mythbusters FAILED to bust the myth, because their test was FLAWED

      And simple analysis using High School Physics (specificaly Mechanics) prove the Myth is TRUE..

      • presto says:

        This is quite a strange thing for Newsnk to say because I agree on almost everything he has said.

        We agree on the actions of the plane and the physics involved. Newsnik has spent a lot of time defining and explaing the stuff that the Mythbusters and I agree with him on.

        The problem is that Newsnik believes the pilot is supposed to conspire to keep the plane at a certain speed.

        This is not in the wording of the myth. It is something he has brought in from elesewhere.

        Newsnik proved that the plane CAN take off. For some reason he believes it is not allowed to take off.

  27. NewsNik says:

    To properly argue this supposed myth and the mythical proof provided by Mythbusters, we need ot fix down a few concepts to avoid all the nonsense that so many have posted
    By also providing a structure, it will make it easier to argue the validity of individual points in a directed and simple fashion.

    For this experiment, we will need 3 things
    1) A table of terminology
    2) A definition of the moving runway-treadmill and it’s operation.
    3) A definition of the test airplane with well defined operating characteristics


    Section 1) Terminology
    1.1 Drag – The force of air against a body moving through it
    – Also any resistance created by two bodies moving agains each other ( e.g axle against bearings, tires against ground)
    1.2 Lift – The upward force create by wind under and over a wing.
    1.3 Resistance, Rolling – the force against a body rolling along on the ground, usually created by the wheels against the ground
    It can also be created by internal parts such as axle, brakes against axle, or
    1.4 Resistance, Internal – any resistance between two moving parts (e.g axle against bearings)
    1.5 Resistance, taxu – the combination of drag and rolling resistance
    This is what the thrust needs to overcome to get to takeoof speed.
    1.6 Speed – speed is how fast something moves with NO DIRECTIONAL REFERENCE
    1.7 Thrust – the force created by various means to propel a body forward through space
    Thrust is created by a propeller in air or water
    Thrust is created by tires agaisnt the ground and the ground against the tire

    1.8 Velcity = speed + direction
    For our purpose – anything moving right to left will have NEGATIVE velocity
    – anything moving left to right will have POSITIVE velocity

    1.30 V_air – actual speed of plane through the air
    1.31 V_ground – actual speed of plane relative to ground
    1.32 V_runway – either ZERO or -40 knots (see section 2)
    1.33 V_stall- velocity below which the plane WILL NOT fly (<=40 knots)
    1.37 V_plane_2_ground – actual speed of plane relative to ground (calculated)
    1.38 V_plane_2_runway – actual speed of plane relative to runway (calculated)

    1.40 S_laser – the plane speed displayed by the laser gun on the right end of the runway-treadmill

    Notes:
    1.50 Drag is the opposite of Thrust
    Drag is NEGATIVE acceleration
    Thrust is POSITIVE acceleration


    Section 2) Runway – Treadmill (from now on just called the runway)
    We are going to build our runway inside a dome so that we can keep constant
    – air temperature
    – air pressure
    – air stillness – NO WIND
    We wiil build a runway with the following characteristic
    2.1 It can either be at rest ( 0 knots) or moving at EXACTLY 40 knots
    2.2 to make things easy for discussion the runway is configured to move from right to left and we will describe it's velocity to be either ZERO or -40 knots (for arithmetic purposes)
    2.3 we will plant a pair of poles on either side of the runway.
    2.4 we will put a very accurate laser speed detector at the right end of the runway aimed at the plane
    2.5 we will connect a very accruate speedometer to the runway.
    2.6 we will install a very narrow field of view telescope that ONLY shows
    the body, but not the engine/propeller
    the wheels to see if they are moving or not
    a portion of the runway where you can see if the runway is moving or not
    (more on this later – may not be needed)


    Section 3) "The Plane, the plane" (RIP – Hervé Villechaize)
    For the plane I propose using a slightly modified Piper Cub.
    The original Piper Cub had a stall speed of 33 knots. That is, if the airspeed fell under 33 knots the Cub turned into a brick and stopped flying.
    We will modfy the Cub in the following way
    3.1 We will modify the plane so that it's V_Stall speed is EXACTLY 40 knots.
    In other words, the wind has to move around the wing at MORE THAN 40 knots for the wing to creat lift and the plane to fly.
    3.2 We will install a VERY PRECISE Pitot Tube that can measure wind speed (V_air) in 1/100 of a knot or better
    3.3 We wil install a very precise speedometer that can measure ground speed (V_ground) in 1/100 of a knot or better

    While the treadmill/runway is at full stop, will will use it to set "cruise control".
    We will use the laser gun to:
    3.4 calibrate and notch the throttle of the plane so that it can be set at EXACTLY 40 knots of ground speed.
    3.41 Since the plane is moving at exactly 40 knots we can also calibrate our Pitot Tube to 40 knots as well.
    3.5 We now tie the plane to a cable strung between the 2 poles to immobilize it and turn on the runway
    When the plane speedometer is at 40 knots we calibrate the runawy speedmeter at 40 kntos
    (At this time both the Laser gun and Pitot Tube should show ZERO knots)
    3.5.1 Once done remove cables.

    ——
    STEP 2:EXPERIMENTS

    —-
    4) Pre-amble and review

    In part one we have established a couple of points

    4.1) We have created a plane with able to takeoff at any speed over 40 knots
    4.2) This speed is most accurately measured with the Pitot Tube which measures the wind over the wings.
    4.3) All the measuring tools have been calibrated to each other

    4.4We have also incorporated all resistances to forward motion by air and ground into the 40 knot takeoff limit.
    At this level of speed the both resistances can be considered linear.

    4.5 Another interesting note is that we have establish the dragging (as opposed to air drag) resistance of the plane by tying it out and running the runway under it to benchmark the runway.
    So all of thse arguments about wheel bearing friction, tire friction, etc have been rendered moot.
    The plane will not roll freely and stay in the same place if the runway is moving
    It will be carried away by the runway in motion

    4.6 this also means that IF the runway is moving, and the plane motor is turned on, to start moving it "upstream" there will be additional rolling resistance
    rolling resitance against the belt carrying it backward PLUS the rolling resitance of moving upstream
    So if the belt is moving backward at 40 knots and the plane is moving forward at 40 knots, the rolling resistance is the sum of the 2, ie is 80 knots and the speedometer will be showing that speed


    5) Experiment # 1
    The plane is just sits on runway, the motor is off.
    The runway is turned off .

    V_air = 0 (Zero)
    V_ground = 0 (Zero)
    V_runway = 0 (Zero)
    S_laser = 0 (Zero)
    V_plane_2_ground = 0 (Zero)
    V_plane_2_runway = 0 (Zero)

    Plane stays aligned with the reference poles

    —-
    6) Experiment #2
    This has already been done in 3.5
    But let's make sure we note the numbers
    The plane is tied out, the motor is off.
    The runway is turned on to 40 knots

    V_air = 0 (Zero)
    V_ground = 0 (Zero)
    V_runway = -40
    S_laser = 0 (Zero)
    V_plane_2_ground = 0 (Zero)
    V_plane_2_runway = 40

    Plane stays in line with reference poles

    —-
    7) Experiment # 3
    This is a step up on experiment # 2
    But let's make sure we note the numbers
    The plane is tied out, the motor is off.
    The runway is turned UP to 60 knots

    V_air = 0 (Zero)
    V_ground = 0 (Zero)
    V_runway = -60
    S_laser = 0 (Zero)
    V_plane_2_ground = 0 (Zero)
    V_plane_2_runway = 60

    Plane stays in line with reference poles


    8) Experiment # 4

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to 40 knots
    The runway is turned on to 40 knots

    V_air = 0 (Zero)
    V_ground = 0 (Zero)
    V_runway = -40
    S_laser =0 (Zero)
    V_plane_2_ground =0 (Zero)
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NO wind (V_Air) going over the wings – No Flight

    —-
    9) Experiment # 5

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to 60 knots
    The runway is turned on to 40 knots

    V_air = 20
    V_ground = 20
    V_runway = -40
    S_laser =20
    V_plane_2_ground =20 (Zero)
    V_plane_2_runway = +60

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 20) going over the wings – No Flight


    10) Experiment # 6

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to 80 knots
    The runway is turned on to 40 knots

    V_air = 40
    V_ground = 40
    V_runway = -40
    S_laser =40
    V_plane_2_ground =40
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 40) going over the wings – No Flight


    11) Experiment # 7

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to 81 knots
    The runway is turned on to 40 knots

    V_air = 41
    V_ground = 41
    V_runway = -40
    S_laser =41
    V_plane_2_ground =41
    V_plane_2_runway = +81

    Plane FLIES and moves forward at 41 knot, and is accelerating to 81 knots IN THE AIR.


    12) Experiment # 8

    The plane is NOT tied but just sits on runway, motor is off
    The plane is powered up to 80
    The runway is turned on to 80 knots

    V_air = 0 (ZERO)
    V_ground = 0 (ZERO
    V_runway = -80
    S_laser = 0 (ZERO
    V_plane_2_ground = 0 (ZERO)
    V_plane_2_runway = +80

    Plane stays aligned with the reference poles
    But because there is NOT ENOUGH wind (V_Air = 0 (Zero)) going over the wings – No Flight

    ————————————————————-
    CONCLUSIONS

    The plane must be moving at a COMBINATION of speeds faster than the speed of the runway + it's takeoff speed to be able to takeoff.

    Just rolling along on a runway at equal and opposite speeds does NOT create ANY wind speed to be able to fly..

    Therefore the Myth stands
    Myhbusters used a flawed test ot make their case.

  28. presto says:

    Newsnik wrote:

    The plane must be moving at a COMBINATION of speeds faster than the speed of the runway + it’s takeoff speed to be able to takeoff.

    Just rolling along on a runway at equal and opposite speeds does NOT create ANY wind speed to be able to fly..

    Presto replied:

    Agreed

    Newsnik also wrote:

    Therefore the Myth stands
    Myhbusters used a flawed test ot make their case.

    Presto wrote:

    Unlike most people who think the Mythbusters got it wrong, Newsnik has the physics right and sees that the plane WILL fly in spite of the treadmill.

    Howerver he believes the plane is not allowed to go faster than it’s Normal Take Off Speed.

    I will quote the Myth for reference:
    ————————
    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.
    ————————–

    As you can see this sentence mentions the Normal Speed of the Plane. But this is give as the speed to set the conveyor belt to.

    There is nothing in that sentence that limits the speed of the plane. It is not limited to it’s Normal Take off Speed.

    Now if Newsnik insists that the plane cannot travel faster than it’s Normal Take off speed, he must explain why he wants to measure this speed at the wheels.

    If you measure the take off speed as air speed, the plane will take off at it’s Normal take off speed. In fact it can’t take off at any other speed.

    Why would you choose to measure the speed of a plane at the wheels rather than as airspeed? On a windless day these would normally be the same but the conveyor belt changes that.

    Welcome back Newsnik,
    We agree on the actions of the plane. I believe your reading of the Mythbusters question is influenced by the Question you have encountered before.

    Try putting your version of the question into words. You will find that you have to mention that the conveyor belt is designed to match the wheel speed of the plane.

    There is nothing remotely like that in the question we are addressing here.

    You only have to address the wording of the question.

  29. presto says:

    Sorry one more thing:

    If you object to using air speed because the speed mentioned is Normal Ground Speed then why not use ground speed in other words the speed of the plane relative to the runway next to the conveyor belt?

    My point is this is not in the question at all so why arbitrily pick a speed that you think works for your argument?

    I don’t have to pick a way of measuring this speed because it isn’t in the question.

  30. NewsNik says:

    presto, you are trying to play word disingenuous word games.

    This is where you start shoveling the bs. ANd when that doesn’t work you either misquote people, quote them out of context,create strawman arguments, or just flat-out lie..

    So let’s make it real simple
    1) Air Speed is the ONLY measure by which a pilot knows that he can fly or not
    2) Because the test is framed in the context of ground speed, I made sure that the ground speed could be tranlasted to air speed.
    3) The test speaks of
    “runway which is moving backwards (like
    a treadmill) at a speed equal to its
    normal ground speed during takeoff.”
    THis CLEARLY IMPLICITS that the plane will attempt to take off at it’s “normal ground speed during takeoff”.
    2) I set up the test so that with the runway STOPPED, both air speed and ground speed are the same
    That is called CALIBRATION.
    3) I also set up the test so that all outside factors like wind are ELMINATED
    4) My results CLEARLY SHOW that the MINIMUM speed necessary for the plane to take off from the moving runway is MORE THAN DOUBLE “the normal ground take-off speed”

    That right there squelches ALL your weasel arguments, word games and misquotes.

    presto, I have read all your bs, outright lies, outright misrepresentations of what others wrote, before setting up my proof.
    I made sure that there was no wiggle room.
    ANY and ALL your bs can be shot down by anyone who reads the full test that I set up.

    YOU ARE BUSTED

    And from now on, you will be ignored.

    • presto says:

      Look closely at Newsniks item 3) in his above post.

      That is where he makes his mistake. There are several versions of this myth floating around on the internet and they do not have the same answer.

  31. presto says:

    Let’s really look at the Myth being discussed here, the one tested by Mythbusters

    __________________________________

    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 let’s replace the phrase “like a treadmill” with a (*)

    So we have :

    __________________________________

    An airplane cannot take off from a runway which is moving bacward (*) at a speed equal to it’s normal ground speed during takeoff.
    ___________________________________

    Now let’s take the phrase “It’s normal ground speed at take off and replace it with X

    so we have:

    __________________________________

    An airplane cannot take off from a runway which is moving bacward (*) at a speed equal to X.

    (*) = like treadmill
    X = The planes normal ground speed durring take off.
    ___________________________________

    If the plane’s normal ground speed at take off is 60mph for instance. Then X=60mph

    and we would have:
    __________________________________

    An airplane cannot take off from a runway which is moving backward (*) at 60mph.

    (*) = like treadmill
    ___________________________________

    60 mph is only an example. But the point is the normal take off speed is determined before the test. It is more or less a constant for a given plane.

    There is nothing in the myth being discussed that constrains the speed of the airplane durring the test. No it is not required to move at it’s normal speed. That is a constraint on the conveyor belt only.

    More than that there is absolutely nothing here about the conveyor belt matching the planes wheel speed. It isn’t there. That wording is used in a completely different scenario.

    Before you post that the Mythbusters were wrong make sure you understand the question.

  32. nano says:

    I’m a huge fan of this show, but I have to see this has disappointed me.

    Firstly, only a very little list if provided by the propeller, no where near enough to get off the ground. If that did work then you could just keep the wheel brakes on and you would get vertical takeoff (which doesn’t work btw).

    it’s clear in both the small and large scale tests that the plane is moving faster than the conveyor belt, as you can see the plane moving forward. If they were going at the same speed, the plane would be standing still.

    Can’t believe this was busted.

    • Nissim Levy says:

      That’s the whole point of the debate. Does the plane stay still relative to the air or doesn’t it? You are taking the fact that the plane doesn’t stay still in their experiment as proof that their experiment was flawed. So in your way of thinking your point of view can never be falsified. Very convenient.

  33. Nissim Levy says:

    This is actually a simple problem if you look at it the right way. To get a body moving you just need to provide it with a force greater then other forces acting on it in the opposite direction (assume a one dimensional world for simplicity). Once that force is applied the body will begin to accelerate. The speed of the treadmill is completely irrelevant because the friction between the plane’s wheels and the treadmill is the same no matter what the treadmill speed is. As soon as the airplane engine overcomes the friction between the plane’s wheels and the treadmill the plane will begin to accelerate forward in relation to the surrounding air at a rate that will be the same whether the treadmill is moving at one mile per hour backwards or 1000 miles per hour backwards.

    Now, once the plane starts to accelerate forwards it will initially have a speed equal to and in the same direction as the treadmill’s motion. So for example, if the treadmill is moving backwards at 200 mph then when the plane first starts accelerating in the opposite direction of the treadmill it will have a speed of -200 mph going forwards in relation to the surrounding air. For the plane to take off it will need to overcome this speed of -200 mph and get into the positive air speed it needs in order to takeoff. This will happen because the plane is accelerating forwards.

    In the above argument I am assuming that the plane cannot takeoff when moving backwards no matter how fast the treadmill is moving. This is reasonable because the angle of attack of the wings will not allow the plance to take off if moving backwards.

  34. presto says:

    Nono, you fallen into the trap that most of us fall in when first encountering this myth.

    There is nothing in the wording of the myth that says the plane stands still. That is an assumption you made when you heard the word “treadmill”. Surprisingly the treadmill had no effect on the forward movement of the plane and it takes off in a perferctly normal manner.

    Nissim Levy,
    You explained it perfectly but it won’t help. No matter how plainly we explain it here over and over again people will continue to fall into the trap.

    This puzzle tricks people into getting the right answer to the wrong puzzle.

    • Nissim Levy says:

      Hi Presto

      Thanks for your support.

      Another way to look at it is to consider the situation from the frame of reference of the plane on the treadmill. Imagine yourself standing on the treadmill so the plane is motionless in relation to you. Wouldn’t you agree that the plane can take off?

      • presto says:

        Nissim Levy,
        You kind of cunfused me with that one.

        I think talkinb about the plane moving backward with the treadmill is an unneeded complication.

        It is reasonable to assume that the plane and the treadmill moving at the same time and the plane never moves backward.

        It’s not that you are wrong. I just think it only adds to the confusion to assume the treadmill srarts first and drags the airplane backward for a while.

        • Nissim Levy says:

          I guess it’s just a matter of personal preference. For me it makes things clearer to picture a real world situation where the plane is already sitting on the treadmill when it’s moving rather than picturing the plane being deposited on the treadmill while it’s already moving and then immediately starting its engines.

          • Nissim Levy says:

            Or I guess you can picture the plane sitting on a motionless treadmill and as soon as the treadmill starts moving backwards the plance starts its engines. So I guess you are right. I introduced an unneeded complication :-(

  35. Commercial Pilot says:

    You guys who think this was a bad test don’t get it.

    The airplane doesn’t care how fast the ground under it is moving. The aircaft can be stationary and fly just fine. If the wind is blowing at 50 knots, the plane can fly with zero ground speed.

    We are such terrestrial animals that we do not easily separate ourselves from this environment.

    Presto is quite correct that if you run the treadmill at 50 knots, the aircaft wheel speed will be 100 knots when it rotates at 50 knots airspeed, assuming no wind. The plane takes off. No question. No discussion.

    No one ever argues about the fact that if you hold the airspeed to zero, the plane won’t fly. No crap. You have any other obvious claims?

  36. Dimitrios says:

    Ok. the simple answer is no unless we make one of two assumption.
    1. You are in a hurricane and the wind is blowing in exactly the correct direction and speed to achieve lift off . . . plausible but unlikely!
    2. The airplane can accelerate faster that the treadmill is going to achieve liftoff speed. Very likely for most planes.

    However its all in the wording of the question, the question most people ask is: Can a plane take off if on a treadmill that is going the opposite way and at the same speed as the plane? As long as the plane is not in a hurricane, then NO it cannot achieve liftoff.
    Mythbusters changed the question because it is obvious that there is nothing to try to bust if they left the question as it is most commonly asked.

    • presto says:

      “2. The airplane can accelerate faster that the treadmill is going to achieve liftoff speed. Very likely for most planes.”

      In fact it is a certainty for all airplanes. You sound like you are still laboring under the idea that the plane has to “overcome” the speed of belt. It doesn’t. The belt has almost ZERO effect on the plane. Because a plane pulls itself throught the AIR and the wheels just spin however fast they have to. The pilot not be able to feel any effect from the belt. The increase in friction from the spinning belt is tiny.

  37. Serp says:

    Yeah but what about a helicopter!!!

  38. presto says:

    On hearing this myth most people picture a plane taxiing but standing relatively still as it’s wheels spin at the same speed as the treadmill but in the opposite direction.

    They think they are being asked if this plane will take off and they consider themselves very bright for realizing that it will not take off because there is no lift under the wings.

    Some people think they are really clever when they point out that IF there was a high wind the plane could take off vertically.

    None of this matters because the image of the plane being relatively still while it’s wheels move at the same speed as the conveyor belt is NOT PART OF THIS MYTH. IT IS A FALSE ASSUMPTION CAUSED BY HEARING THE WORD TREADMILL.

    In fact the treadmill can have almost no effect on the plane. It moves forward as normal and achieves lift as normal. The treadmill does not slow it down. It’s wheels spin twice as fast but it’s body moves at normal take off speed and takes off in a perfectly normal manner.

    This is because the plane is not driven by it’s wheels. It pulls itself throught he air. The only thing the conveyor belt does is cause the wheels to spin faster. The increase in rolling friction is negligable.

    If you post please read and respond to this post. I would love to hear from anyone who honestly thinks a conveyor belt can hinder the movement of an airplane.

  39. cookie says:

    how can a conveyor belt uses friction in a useful way

    • presto says:

      A conveyor belt can’t effect the movement of an airplane because the airplanes wheels are essentially frictionless. They don’t transmit any of the belts force to the airplane body.

      A car is completely different. It’s wheels are driven by a motor and they transmit force.

  40. Johnny says:

    Hi, everybody,

    I think this myth depend on the “runway” is long enough or not.

    Assume the conveyor belts(runway) is big(or long) as a WW II aircraft carrier’s deck,
    The airplane will moving forward, run for a distance and take off.
    Just like the Myth Busters did.

    If the conveyor belts is small, just as long as airplane, and set it on a aircraft carrier’s front nose(fore),
    than the airplane will moving forward, and once it leave the conveyor belts, it will fall into the sea.
    Also like the Myth Busters did on the Treadmill.

    Anyway, in this myth, without enough runway,
    the airplane will not take off.(except the helicopter.)

    • presto says:

      In the stated myth printed at the top of this thread we are not given any details about the treadmill so we have to make some assumptions.

      I think the fact that no details are given means that it is a very generic use of the word tradmill. It means a moving runway. It is not a treadmill you would find in a gym with handrails and sleightly elevated above the ground. (I believe on the show they did use a cartoon of this type of trateadmill but that was just a humorous illustration).

  41. required says:

    mythbusters is not science, is entertainment. get this.

    • presto says:

      mythbusters does not conduct rigorous scientific experiments but there is a lot of science on the show.

      They get some things wrong but they’ve gotten better over the years. The show is a great starting place for discussion.

  42. Joma-Sama says:

    The reason the plane took off is because its speed exceeded the speed of the conveyer belt. You can clearly see this as the plane moves past the cones at a high rate of speed. It was the same problem with the small scale test. Had it matched it would not have taken off.

  43. presto says:

    Joma-Sama,
    You are right but you are wrong. You are correct in thinking the plane moved past the cones at a high rate of speed.

    You are wrong in thinking this violated the conditions. This is the trap most people fall into.

    Re-read the “myth”. Where does it say the plane must match the speed of the belt?

    No don’t assume it is there. Where is it? Quote it here and repost.

    • M Jenkins says:

      Other conditions must be assumed, like whether the conveyor is level, or up-side down. The problem with the “myth” is that is allows people to insert their own assumptions.

      The primary unstated assumption is that the conveyor is preventing the plane from moving forward relative to the ground (and more important, relative to the air).

      If the plane is prevented from moving forward relative to the air, it will not lift. This is so even if the plane moves fast down a runway–if the wind from behind matches that forward ground speed, the plane will not lift.

      If the plane is perfectly still relative to the ground (whether on a theoretic conveyor or even tied to an anchor)but there is a high headwind, then the plane will lift.

      Everything else on these thousand comments is irrelevant, like talking about the color of the plane.

      • Mike says:

        I agree that some assumptions must be made but they are pretty reasonable. There isn’t a huge boulder in front of the airplane, there isn’t a hurricane etc. The myth is about the belt and the plane so keep things simple and don’t bring in extra complications.

        Your “primary unstated assumption” is actually the false assumption that most people make when encountering this myth.

        That assumption is not warranted by anthing in the wording of the myth. We read “Conveyor Belt” and we picture a person running but standing still. We apply that to the plane. But…it doesn’t apply. Planes are not driven by contact with the ground. They are driven by contact with the air.

    • M Jenkins says:

      I just re-read the “myth” very closely. The problem is the irrelevant assumption that planes take off as a certain ground speed. They do not. They take off at a certain air speed. The Mythbusters worked hard to prove something about a meaningless variable.

      • Mike says:

        Read it again. The myth does not say anthing about the speed of the plane durring the test. It only defines the speed of the conveyor belt durring the test. Do you see it? If you disagree please explain exactly where the myth constrains the speed of the plane durring the test. If you are tempted to say the plane is limited to it’s normal speed durring take off please think about it.

        Can you run faster than a runner who runs at your normal running speed? Of course you can. That sentence limits his speed not yours!

        In fact the plane will take off at it’s normal take off airspeed. It has to. But at that moment the WHEELS will be going at twice their normal speed.

        Consider this: Can a plane take off if it is on a conveyor belt which is moving backward at high speed?

        The answer to this is yes, the plane can always take off NO MATTER WHAT SPEED THE CONVEYOR BELT.

        No conveyor belt can impede the forward motion of an airplane because the propeellers are pulling the plane through the air and wheels are just reducing friction

        I welcome debate but please address my points and keep it as concise as possible and I will do the same.

  44. Joma-Sama says:

    Hey Presto,

    You may be right. But I wasn’t commenting on the original myth per se. I was commenting on the experiment as it was explained by the cast during the episode. Paraphrasing, they said that the test was to see what would happen if you matched the speed of the plane with the conveyer belt. Would the plane take off or would it fail to fly. They didn’t conduct the experiment as it was described. Had they, the plane would not fly.

    Had the experiment been carried out as defined in the episode, there would not have been enough flow over the wings to generate enough lift to attain flight.

    What was most amazing to me was that the pilot in the episode seemed to be convinced. I am a private pilot with > 500 hours of PIC time and I guess would have been scratching my head a little more.

    • Presto says:

      Did the cast really use the word “match” in describing this myth? I haven’t seen the show in a while but I would be surprised if they said anything about matching. That is the false assumption that many people bring into the myth from the outside. (I’m not saying they didn’t, I just would like a more specific quote from the show)

  45. CF says:

    Non-believers of the “Plane on Conveyor” myth, read this: http://www.straightdope.com/columns/read/2638/an-airplane-taxies-in-one-direction-on-a-moving-conveyor-belt-going-the-opposite-direction-can-the-plane-take-off

    It’s basically separating the method of propulsion of the car and airplane and understanding relative motion.

    Propulsion of car are the wheels.
    Propulsion of plane is the prop.

    The wheels move the car forward relative to the GROUND.
    The prop moves the plane forward relative to the AIR.

    The car would care if the ground/conveyor is moving backwards as an outside observer would notice it stationary.
    The plane could care less if the ground is moving backwards as it’s moving the air. If you want the plane to be stationary, just give it an HEADWIND equivalent to its ground speed.
    The wheels are just for taxing purposes, they’re useless from a flying pov.

  46. Engineering Student says:

    There seems to be a problem of definition:
    A plane with a take-off speed of (say) 80 knots will take off when the air-speed is 80 knots.
    If there was (for example) a head wind of 30 knots, then the ground-speed will be 50 knots, but the air speed will still be 80 knots.

    If the ground was ‘moving backward’ at 10 knots, then the speed of the plane, relative to the ground will be 90 knots, but the air-speed will still be 80 knots.

    So the question is: what is your definition of ‘normal take-off speed’?

    Now for the myth: it states that the increasing speed of the treadmill will make it increasingly difficult to take-off.
    This is false, as the major drag of the aircraft comes from the air, rather than the wheels on the ground. The aircraft (and propeller) also has an effective tail-wind (from the reference frame of the aircraft), which will result in more thrust from the prop to achieve the required change in velocity.
    The treadmill will not even have to be longer than a normal runway, as the treadmill itself is not moving relative to the air. More belt-distance will be covered, but as the belt is looped, it doesn’t matter.

    If you want to prevent a plane taking off, the best way would be to have a static runway, and switch on a huge fan to create a tail-wind.

    • Presto (AKA Mike) says:

      Because no wind is speicfied it only makes sense that we are talking about a windless day. This is the only reasonable assumption. We can also assume there are not giant boulders on the runway even though that isn’t spelled out.

      Engineering Student wrote:
      “Now for the myth: it states that the increasing speed of the treadmill will make it increasingly difficult to take-off.”

      Presto replies to Engineering Student:
      Where does it say that in the myth? I think you meant to say that many people ASSUME this, but it certainly isn’t stated in the myth and in fact isn’t true at all.

  47. Daniel says:

    My question: Was that tarp really a treadmill? That is if you parked the plane on the tarp could you pull the plane around? If you can’t then it’s not a real treadmill. I assume the plane weigh’s enough that it still was able to grab traction from the ground to move forward enough to generate air speed (via the propeller)over the wings to achieve lift off. My skepticism is about whether it is a real conveyor belt, nothing else.

    • Presto says:

      That seems like a legitimate question but I don’t share your concern. I think if the plane was “grabbing traction from the ground” it would have to be tearing the tarp to shreds at the same time. Still, I think you make a good point. I’d like to know if the tarp was pretty much in tact at the end.

  48. Lewis says:

    The reason there is still ambiguity about the results of this myth, is because the conditions of the test have not been fully define. Based on the conditions of the test, two results are possible.

    If the plane is allowed to travel at a groundspeed greater than the standard take off groundspeed (25 MPH), then the plane will be able to fly. If the plane is constrained to travel at a groundspeed equal to the standard take off groundspeed then the plane will not be able to fly.

    I will describe the two separate conditions based on the episode.

    Condition 1. Plane will not lift off.
    A. The conveyor belt travels at a speed of 25 MPH.
    B. the plane travels at a groundspeed, relative to the conveyor belt, of 25 MPH.
    C. To an observer, away from the conveyor belt, the plane appears to be stationary.
    D. There is no airflow over the wings. Therefore, no lift is generated. The plane stays on the ground.

    Condition 2. Plane will lift off.
    A. The conveyor belt travels at a speed of 25 MPH.
    B. the plane travels at a groundspeed, relative to the conveyor belt, of 50 MPH.
    C. To an observer, away from the conveyor belt, the plane appears to be traveling at 25 MPH.
    D. There is airflow over the wings. Therefore, lift is generated. The plane lifts off the ground.

    In the episode, it was obvious that the plane was allowed to travel at a groundspeed greater than 25 mph. If conditions were described accurately, the plane traveled at a groundspeed, relative to the conveyor belt, of at least 50 MPH.

    For the purposes of a myth, the conditions should be set so that the plane remained stationary relative to the ground. If the plane is allowed to accelerate to a speed that is greater than the that of the conveyor belt, no matter how fast it is going, then it will be able to take off.

    The way it was described made it sound like they were going to allow the plane to move on the conveyor belt at the same speed the conveyor belt was moving in the opposite direction. If that had happened, the plane would have remained stationary relative to the ground.

    • Lewis says:

      I think they should redo this myth using coditions where the plane travels at the same speed as the conveyor belt, relative to the conveyor belt.

      • Presto says:

        Lewis,

        I think you describe the two scenarios very well. You understand the physics and have taken a lot of the confusion out of the situation.

        BUT…I think you are wrong to think both of these scenarios fit the “Myth” as described on the show.

        What’s fun about this “myth” is that people think it is your (1) but it is really your (2).

        The “Myth” as stated at the top of this thread asks if the plan CAN take off and puts no constraint on the plane. It simply defines the speed of the conveyor belt. Any idea that the plane is supposed to match the speed of the belt is a false assumption made by the reader (or listener).

        Some have suggested that the mythbusters weren’t as clear about the myth and didn’t stick to the written myth at the beginning of this thread. If that is true I would like specific examples.

        In this thread I am defending the wording at the top of this thread and I think if is fairly clear.

        I would love to have further discussion on this. Your post is one of most lucid so far.

    • Andrew says:

      Thank you Lewis! I came to the same conclusion. It is an english problem not a physics problem. It is also a very good example of how people can rip each others heads off over a simple misunderstanding. Faith in humanity lost…

  49. Dan Yager says:

    I watched this episode last night on Netflix and I also think they got it wrong. I am definitely in the “no fly” camp.

    Plane relative to ground (treadmill belt) doesn’t matter. Plane relative to air creates lift.

    Here’s a thought experiment that might help some of the people in the “fly” camp.

    On a calm windless day, would the plane be able to LAND on a treadmill?

    I am a pilot, I think the answer is a resounding NO.

    Thanks for listening.

    • Presto says:

      Dan,
      The plane will fly because it will move forward.

      A treadmill cannot impede the forward motion of an airplane because the airplane is pulled through the air by it’s propellor and the wheels are free spinning.

      Like most people who first encounter this situation you think this myth has something to do with a stationary plane on a treadmill. It doesn’t. That is a an assumption that you jumped to when you heard the word treadmill.

      A plane on a calm windless day would have no trouble landing on a moving runway.

      This thread gets a lot of very confident one post wonders. If you agree with my point let me know. If you have a counter argument please stay on point and I will do the same.

      • The Mythkeeper says:

        Presto, I think the problem people have is this. They are CONVINCED that the plane is travelling faster than 25 MPH, and that’s how it can take off because the treadmill is at 25 MPH. I can see how it would appear that way to people. But in fact, the plane is not going faster than 25 MPH. The plane is still travelling at 25 MPH and the pilot will read it correctly on the gauges as 25 MPH. Only the wheels, which spin freely, are spinning at 50 MPH.

        For people to really understand it, they need to understand the difference between a car and a plane. A car propels itself by sending power to the wheels, which moves it along the ground. In fact, a car on a 25 MPH treadmill in this situation WOULD have to accelerate to 50 MPH in order to appear to move forward at 25 MPH. And the driver of the car would see this as 50 MPH on the speedometer. People understand that about a car and falsely believe that it applies to a plane.

        A plane on the other hand propels itself by sending power to the propeller, which moves the plane through the air. The wheels have nothing to do with this; again, they spin freely and independently of this propulsion. The treadmill moving backwards does not affect the plane moving forward, nor the plane’s speed; it only makes the WHEELS spin faster. The plane is still able to move forward and take off at 25 MPH, just like it can without the treadmill.

        Let me say that again for all who still doubt this test. “The treadmill moving backwards does not affect the plane moving forward, nor the plane’s speed; it only makes the WHEELS spin faster.” The plane was not “allowed” to travel faster than 25 MPH to take off. It’s travelling through the air at 25 MPH. Its gauges will read 25 MPH, not 50 MPH like in the car. The treadmill has no effect, because the plane does not use its wheels for propulsion. It takes some people a very long time to GET that idea. But once they get it, they get it.

        • Adam says:

          I just watched this last night again, and can’t help but to comment. It has probaly already been stated, but the problem with all of this is simply the difference in reference. The part that bugs me is when Jamie says people can’t wrap their head around it, because one is powered by its wheels and the other by a prop. The power has nothing to do with it. The reason people can’t understand is because there are two references to speed. Wind speed and wheel speed. It is really that simple. You can put a prop on the car if you want and get it up to 25mph wheel speed on the 25mph conveyor and it will stay in one place, which means basically zero wind speed = no flight.

          Summary. It is not about a difference in propulsion, it is about a difference in measurement.

        • Presto says:

          I lost track of this thread after a computer meltdown but I just re-discoverd it.

          Mythkeeper, Your analysis is very good. Your first paragragh is a little confusing to me but you nailed it on the next three paragraghs.

  50. Chuck says:

    Ok, just saw the episode. Here are a couple of thoughts.

    1 When you run on a treadmill at 8 MPH do you feel wind passing over your body…No. When you run out side on a calm day do you feel wind passing over your body,,,Yes. The wind you feel or do not feel would be able to create lift in a airplane.

    2. Say you are in a plane (which requires 25 MPH of wind for lift) and you take off with the wind in a 25 MPH wind (not into the wind as required) You would need to achieve 50 MPH for the lift to happen.

  51. sam5887 says:

    why the airplane moving forward on the ground when try to take off??? the airplane not run on the same spot!
    the airplane not running on the same place…they moving forward fast and then take off.

    sorry for my bad english

  52. Presto says:

    This is a test post. I’ve tried to post a few times but the posts don’t show up. Is this thread locked?

    • Presto says:

      Ok seems to be working now

  53. Presto says:

    In response to the last few posts:

    If you are bothered by the fact that the plane move forward it is because you misunderstood the question. (Almost every one makes this mistake at first). This question is NOT about a plane trying to take off while standing still on a treadmill. It is actually about whether or not a treadmill can impeded the motion of an airplane. It can’t. The plane moves forward as normal and takes off as normal in spite of the treadmill. And it’s not because the treadmill isn’t going fast enough. The airplane has a propeller or jets that push it through the air. The wheels have nothing to do with this accept to hold the plane up and to glide over the runway.

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