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Riddle: Will it take off?

Discussion in 'The Pub' started by 7THSIN, May 19, 2006.

  1. Yes

  2. No

    0 vote(s)
  1. This is a theoretical riddle, so don't post things about tyre's exploding, bearings seizing, or the impossibility of a giant conveyor belt runway.

    Now, the riddle.

    - A plane is standing on a 'runway' that can move (some sort of band conveyer).
    - The plane moves in one direction(under it's own power), while the conveyer moves in the opposite direction.
    - This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

    The question is:

    Will the plane take off or not? Will it be able to run up and take off?

  2. Also bearing in mind of course that a Hawker Harrier Jump Jet and Thuderbird Two would not be affected by the conveyor belt one iota. :LOL:
  3. something to do with thrust, lift and airspeed
  4. no, the lift for any aeroplane or hydrofoil is caused by an area of low pressure above the top wing surface. This is caused by the air having to travel over the top curve of the wing which is a longer route in realtion to the short route air moving below the wing. Its not the rolling speed of the wheels but the air flow past the wings that gives lift.

    I dont know the actual requirement in air speed across the wing but in your scenario the planes acceleration in one direction is being countered 180 against in the other direction by the speed of the conveyor. So the plane stays relativley still... Sitting still means little or no air over the wing and no lift...

    if the conveyor sudenly died and siesed... :shock:
  5. +1 on what he said... you're not generating any thrust, which requires a hell of a lot of wind, so you need to add a big ass fan, or having the plane generate that thrust by actually moving.
  6. You're quite right that the plane won't take off - the wing has zero airspeed. The same thing would occur if the plane was rolling at 100km/h with a 100km/h tailwind - take off is a result of airspeed, not groundspeed.

    BUT...if (as you suggest) a wing flies because the air travels further over the upper curved surface, how can a plane fly inverted? Isn't the curved surface now on the bottom?

    [Inci - don't spoil the fun]
  7. Good question I just know basic theroy, what I described is sesame street basic engineering. :LOL:

    If I guessed I would say that pilot flips the plane... or rolls it upside down then uses the control flaps to tilt the plane that way the wing curve still creates lift... I'm not a pilot but I think wings have an angle of attack to produce lift...

    any pilots out there...?
  8. I'd say that the angling of the wing forces the air downwards, producing lift, it is less efficient than the correct orientation but still produces lift
  9. it wont fly.... :grin: :grin:
  10. no, from my understanding it's the difference between the air speed as it goes over the top and underneath the wing, which causes lift. So as others have said it's air speed not ground speed, which causes lift (from what i know anyway, but hey i am a draftsman not a pilot ;))
  11. That pretty much comes down to having massive amounts of thrust and a positive AoA (nose up).

    In level flight the thrust of the aircraft is one dimensional, it only pushes one way. When given an angle of attack it turns into a two dimensional force, aka, with the nose up, thrust pushes the aircraft up and forward. This works whether the aircraft is upright or inverted, so if that upward push from the thrust can equal or overcome gravity and the lift that the wings are generating downward, then you have inverted flight. Same principle applies to a missile that is flying horizontally.

  12. Ummm.. I actually believe that the plane will take off... This is my take on it... The plane's forward acceleration is governed by the thrust it's engines generate. This thrust generates forward acceleration in the same manner that the wings generate lift, the air pressure in front of the engine is less than the pressure behind the engines. Hense the planes forward acceleration is relative NOT to the conveyor belt but to the surrounding atmosphere. Because of this the plane will accelerate through the atmosphere, generate lift on the wings and take off. The only thing the conveyor belt will do is cause the wheels to spin in a counter clockwise direction (assuming the plane is facing left) faster than they would have if the runway was stationary.

    Any takers???
  13. i love it when you talk like that jafu :p
  14. Did any of you graduate from college?
    :edit: seems parko may have at least...

    The plane will take off.

    just say the plane accelerates to 10k/h. The conveyor will spin backward at 10k/h too.

    Now if this was a car, sure, that'd be a problem, but last time I check planes are NOT driven by their bloody wheels.
  15. you idiots, the plane is not driven through the wheels! they will just spin faster relative to the stationary ground than usual!

    sheeeeesh, year 8 physics!
  16. I'm wating for an engineer or a pilot to come along and set us straight... I'm not certain but someone must know a text book example...

    MYTHBUSTERS!!!!! someone should send this on to mythbusters! it would be great to see if they could do it!!
  17. Yes it will.

    The plane will out accelerate the conveyor belt. The only way it would stay still if the conveyor belt sped up so fast as to counter the acceleration of the aircraft.

    It doesn't matter what speed the plane's wheels turn as the thurst of the engine will still provide the power to start accelerating the aircraft.
  18. no it wouldnt! completey seperate systems.. no affect on the air speed, maybe if it sped up so much as to suck air down the runway into the plane in order to neutralise its airspeed! :p
  19. It will take off. The planes wheels serve only one purpose (theoretically) - to hold it up off the ground. The thrust of the engines will move the plane forward regardless of what the conveyor does. Nothing is actually offering resistance to counter the thrust of the engines. (althought the wheels will spin twice as fast as they normally would).
  20. :rofl:

    ditto what a few others have said.... *IF* the plane was driven by its wheels, then it would have no wind under its wings and therefore would sit right the fark where it is.

    but thats not how planes work, they're driven by the engines that pull air through them. the plane pulls the air through as per normal, the plane get momentum as per normal and the plane takes off as per normal.

    at worst, all you've done by making this massive big conveyer is make the freespinning wheels work a little harder. possibly chewed up a bit of extra rubber and shot a few bearings maybe but thats it.

    now if you were to set up some kind of massive fan behind the plane that pushes wind from behind at the same rate that it accelerate, THEN it will get nowhere....

    this was pissssss funny when i saw it on OSB, lets go ppls, i can see 10 pages of arguments coming on :LOL: maybe chuck norris will get involved.... and the HOFF :shock: