Will a plane take off on a conveyor belt?

Discussion in 'Physics & Math' started by w00t, Jun 12, 2007.

  1. w00t i'm with stupid Registered Senior Member

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    Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
    There is no wind.
    Can the plane take off?
     
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  3. Absane Rocket Surgeon Valued Senior Member

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    Yes. I cannot count how many times this question has been brought up.

    Edit: oh, you added the part about the conveyor belt matching wheel speed. In that case, no.
     
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  5. mikenostic Stop pretending you're smart! Registered Senior Member

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    Uhh, no. The plane needs airspeed. The wings need wind flowing above and below them in order to generate lift.* Now if you put it in a giant wind tunnel and had it blow the wind out at the same knots as the airspeed that the plane needs to rotate (off the runway) then yes, it would lift off the ground.

    *You never had any type of aviation or aerodynamics classes did you?
     
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  7. mikenostic Stop pretending you're smart! Registered Senior Member

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    I took it as the OP meaning that the plane is stationary. But if he means the plane was moving, then yes. The catapult on an aircraft carrier is the same principle.
     
  8. w00t i'm with stupid Registered Senior Member

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    My answer would be no, the plane will not take off due to the absence of lift. Just needed some smart people to confirm it.

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  9. Absane Rocket Surgeon Valued Senior Member

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    See my edit.

    But usually I hear the question like this:

    http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/

    The answer to this question is YES.

    But I just read here that giving the OP's orginal assumptions, then it too can lift: http://www.straightdope.com/columns/060303.html

     
  10. Absane Rocket Surgeon Valued Senior Member

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    8,989
    When I read that last page that I provided... it really depends on what you assume is also true of the question being asked. Depending on your own assumptions, the answer is yes or no. I answered "no" at first because I assumed a perfect system in which the conveyor exactly matches the force generated by the plane at every moment.
     
  11. w00t i'm with stupid Registered Senior Member

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    I agree with you. But this perfect system cannot be attained by experimental purposes, only in theory.

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  12. D H Some other guy Valued Senior Member

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    This stupid topic keeps reappearing, dressed in slightly different clothes. A plane, unlike a car, does not propel itself by applying torque to the wheels. Of course it takes off.

    The goal is obviously is to make the plane always stationary with respect to the ground. The above does not accomplish said end. The conveyor will simply move faster and faster as the plane gains ground speed.

    Suppose the conveyor were coated with ice and the plane had friction-free skates instead of wheels. What would happen? The speed of the conveyor is irrelevant. An ideal wheel operates similarly to the skate on ice.
     
  13. Absane Rocket Surgeon Valued Senior Member

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    8,989
    Well even in real life, we can build a conveyor that will equally match the plane's forward force so that it won't take off. One can do this by first making the treadmill just a little too fast (so the plane is going backward) will accelerating. Then we adjust the speed ever so slightly until there is a perfect match. Then the plane never takes off.

    D H, I guess I am considering that the wheels are not 100% freespining and that any friction on the ground will, in some way, affect the plane.
     
  14. w00t i'm with stupid Registered Senior Member

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    Suppose said conveyor does manage to make the plane always stationary with respect to the ground. What then?
     
  15. leopold Valued Senior Member

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    17,455
    oh shit.
    another "airplane on a conveyorbelt" thread.

    the answer for the umpteenth time is YES the airplane will take off.
     
  16. Absane Rocket Surgeon Valued Senior Member

    Messages:
    8,989
    Maybe you mean a plane with no wheels and the plane on the ground has a coefficient of friction equal to 0.1. Then I would say it's very possible for the plane to remain stationary.

    I was assuming that there was sufficient friction between the wheels and the plane. But with the conveyor going the "same speed" as the plane, I guess this isn't possible. Now it is possible if you make the conveyor go much faster than the plane.
     
  17. temur man of no words Registered Senior Member

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    Wheels of an airplane is not active, the airplane gets its speed by pushing the air. So it does not matter what is happening with its wheels and conveyer, as long as the airplane is standing and there is not much friction, airplane will take off.
     
  18. Oli Heute der Enteteich... Registered Senior Member

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    11,888
    It gets lift by moving through the air.
    If there is no airflow over the wing (usually caused by forward motion) then there is no pressure differential to cause lift.
     
  19. nietzschefan Thread Killer Valued Senior Member

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    LMAO this thread delivers....
     
  20. 15ofthe19 35 year old virgin Registered Senior Member

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    You didn't specify if it was an African or European conveyor belt.
     
  21. Oli Heute der Enteteich... Registered Senior Member

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    11,888
    :roflmao:
     
  22. leopold Valued Senior Member

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    the first post is a little confusing.
    it was stated that the belt moves backwards at the same speed the wheels move forward.

    now, if the are plane doesn't take off the the wheels do not move hence the belt remains stationary.

    for those that say the plane doesn't take off what is it that is holding the plane stationary?
     
  23. nietzschefan Thread Killer Valued Senior Member

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    I guess it could be confusing.

    Basically I read it as conveyor belt acts like a frictionless surface(just moves as fast as the wheels turn no matter what speed).

    With no wind(some a/c CAN take off if given enough wind), would would need a harrier jet or similar type. VTOL
     

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