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  1. #1
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    Talking Sunday night Brain Bender - Airplane Physics

    Alright here it is.


    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?

    Discuss....

  2. #2
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    Default Re: Sunday night Brain Bender - Airplane Physics

    no!!

    the airplane needs air speed.

    airspeed is the speed of the air over the wing, ground speed is the speed to the airplane over the ground.

    if the airplane was sitting still and a head wind of 160KPH was comming at it then it could take off with no ground speed.
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  3. #3
    In a 1920s time warp Terry Porritt's Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics


    It's a no brainer.

    The only difference to a normal take off is more friction in the wheel bearings. There is no tractive effort applied through the wheels.

    Of course with double the ordinary wheel speed, the bearing grease may break down and the bearings seize, then the plane may not be able to take off
    Remembering Rich Conaty, 1954 - 2016....."and don't you never forget, rhythm saved the world, Aloha"

  4. #4
    Senior Member pine-o-cleen's Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics

    YES!

    Of course it will. The plane doesn't accelerate through it's wheels. It accelerates through the thrust from the jets / propellors.

  5. #5
    Long Time Member drcspy's Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics

    NO NO NO the lift which removes the plane from the ground is supplied by air moving over the wings..........no matter how fast a plane travelled along the ground if there is no airspeed then it wont lift..............try for example getting a plane to lift off the ground on the moon, (no air).........no go !!!
    There are two sides to any question; MY side and the WRONG side (Winston Churchill)

  6. #6
    Long Time Member drcspy's Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics

    in fact the lift is caused because the air has to travel a greater distance over the upper side of the wing than the lower side.....the air on the upper side has a lower pressure thus the higher pressure on the lower side of the wing is what provides the lift.......check out a cross section of a wing to understand this.
    There are two sides to any question; MY side and the WRONG side (Winston Churchill)

  7. #7
    In a 1920s time warp Terry Porritt's Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics



    drcspy, consider this: the moving runway will drag a thin layer of air along with it determined by boundary layer theory which I can't be bothered to look up at the moment But it certainly wouldn't affect the air flow over the wings, the wings are too high. Maybe I will do the boundary layer sums if anyone needs convincing.

    Also now consider that if the wheel bearing friction was zero, like if the wheels had air bearings instead of grease lubricated roller bearings, then no frictional force would be transmitted through to the plane and it would just sit there with the runway conveyor moving past underneath it.

    So as I said, and also so did pine-o-clean, the take off would be as normal as the wheels do not provide tractive effort, it comes from thrust. Thus the airflow over the wings will be the same as if the runway were not moving.

    The wheels bearings may suffer though through roller skidding or grease overheating.

    Edit: I will concede the boundary layer above the runway will help to provide a bit more lift as it will actually increase the airspeed a bit not decrease it, but without doing the sums I'm sure it is quite small.
    Last edited by Terry Porritt; 04-12-2005 at 08:59 PM.
    Remembering Rich Conaty, 1954 - 2016....."and don't you never forget, rhythm saved the world, Aloha"

  8. #8
    Wrinkly Member! B.M.'s Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics

    Am I missing something here?

    Surely if what ever propels it, moves it forward fast enough to get sufficient air flow over the wings we have flight.

    I recon the wheels and conveyer are a red herring.

    I certainly don’t know of any aeroplane that relies on wheel traction for propulsion.

    Whoops, covering the same ground as Terry. Sorry.
    Last edited by B.M.; 04-12-2005 at 09:01 PM.

  9. #9
    Modulator Greg's Avatar
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    Default Re: Sunday night Brain Bender - Airplane Physics

    I guess yes, it'll take off.

    The wheels only provide a means of reducing friction and support of the aircraft versus the ground. Thrust and/or propulsion is provided by the engines and/or props. They're independent of the wheels and ground.
    Last edited by Greg; 04-12-2005 at 09:30 PM.
    Bugger the cancer. I'm suffering from terminal inertia.

  10. #10
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    Default Re: Sunday night Brain Bender - Airplane Physics

    Yep, it will.

    looks familiar

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