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  1. #121
    it wont take off..common sense. No drag.

    airports would have designed it to save space.

  2. Join Date
    Jan 2003
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    2,979
    #122
    Quote Originally Posted by OTEP View Post
    From: http://www.4x4wire.com/forums/showfl...4&fpart=1&vc=1

    A plane is standing on a runway that can move (like a giant conveyor
    belt). This conveyor has a control system that tracks the plane's
    speed and tunes the speed of the conveyor to be exactly the same (but
    in the opposite direction) instantly.

    Will the plane be able to take off?
    after reading all comments here, I definitely am sure that the plane would definitely fly. I am also sure that the plane would move forward and gain enough thrust to take of. again, assuming that the conveyor would only match the turning of the wheels of the plane thus relying only on frictional force to hold the plane back on its original position but since the plane is not using its wheels to propel itself and uses a jet propulsion or a propeller system to push the wind, then we could just neglect the effect of the conveyor since the main forces that affects the plain are the engine and the wind. The wheel actually helps reducing the friction being caused by the conveyor... what could happen is that the wheels would be turning a lot faster than running on an ordinary runway
    Last edited by badsekktor; November 10th, 2006 at 05:22 PM.

  3. Join Date
    Nov 2005
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    7,501
    #123
    [QUOTE=OTEP;690167]From: http://www.4x4wire.com/forums/showfl...4&fpart=1&vc=1

    as mentioned in my previous post. it will not be able to take off.

    it clearly states that this conveyor has a control system that
    tracks the plane's speed and tunes the speed of the conveyor
    to be exactly the same (but in the opposite direction) instantly.


    during taxiing and take off, thrust is needed in order for the nose
    wheel and the main landing gear to roll.

    any velocity the aircraft produces is accurately matched by the
    conveyor. since no forward movement is obtained by the aircraft
    therefore no incoming wind is encountered by it's elevator and the
    wing's positive angle of attack.

  4. Join Date
    Aug 2004
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    22,710
    #124
    Quote Originally Posted by xto View Post
    as mentioned in my previous post. it will not be able to take off.

    it clearly states that this conveyor has a control system that
    tracks the plane's speed and tunes the speed of the conveyor
    to be exactly the same (but in the opposite direction) instantly.


    during taxiing and take off, thrust is needed in order for the nose
    wheel and the main landing gear to roll.

    any velocity the aircraft produces is accurately matched by the
    conveyor. since no forward movement is obtained by the aircraft
    therefore no incoming wind is encountered by it's elevator and the
    wing's positive angle of attack.
    Nope. The conveyor doesn't push the airplane... it pushes the wheels back. All that will happen is the airplane will move forward, but the wheels will be spinning faster.

    Please read my previous posts and do the experiments I've listed, which demonstrate why this happens.
    Last edited by niky; November 10th, 2006 at 06:48 PM.

    Ang pagbalik ng comeback...

  5. Join Date
    Oct 2002
    Posts
    19,438
    #125
    Please explain to me how will air flow to and under the wings that will lift the airplane.

    all the engines do is suck in air and thrust it backwards that would supposedly push the airplane forward. but since the airplane is touching the conveyor through its wheels, the engine's work just makes the wheels spin faster and the airplane stays where it was.

  6. Join Date
    Jul 2005
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    199
    #126
    hala! 7 pages na in such a short time.

    i'm afraid i have to change my position regarding this topic..there is no way the plane is going to fly.

    becoz...there's no pilot...there was no mention of a pilot in the original question...not even a turning on of the engine.

    joke lang peeps..to lighten up your day.

  7. Join Date
    Oct 2005
    Posts
    115
    #127
    all that jet engine do is to create thrust to the direction of the exhaust. just like a rocket or jet propelled power boat. it does not create lift unless you point it downwards. the lift is still generated by the air interacting with the wing. so i stand also to my words, that the plane cannot fly.

  8. Join Date
    Oct 2005
    Posts
    115
    #128
    one thing more for all of you to analyze. an F1 car aerodynamics works just like wings but acting on oppsite direction, meaning pushing it down to the ground instead of lifting it up. the higher the speed of the car the stronger is the push downwards. put the car in a dyno or the same conveyor if you want. do you think it can create the downward force, no because there is no wind acting on it. even if you add in a jet engine behind, there will still be no downward force.

  9. Join Date
    Oct 2002
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    2,703
    #129
    After reading thru thread just now, I'm changing my position on the matter. I am now convinced that the plane will fly.

    As pointed out correctly by alpha_one, in my FBD, Fb will only cause the wheel to rotate but will never approach the magnitude to counteract the Ff of the engine. The magnitude of FB will only be limited to rotating the wheel, no matter what the conveyor speed is. Since Ff will always be greater than Fb, The plane will move, accellerate, and fly. If Ff becomes less than Fb, it means the plane has not gained enough thrust to move itself forward against rolling friction, regardless of whether the runway is moving or not.

    I realized, that the wheel bearing, with minimal friction, has effectively rendered the runway, moving or not, to be frictionless! Hence, if there is no friction below the plane, the engine thrust will act on the plane (and the wheel rotates due to Fb) and plane will move and take-off normally.

    So there, the wheels will simply rotate faster when the runway moves in opposite direction. As far as the plane is concerned, it is standing on a frictionless surface, so it won't matter if the surface moves or not.

    Now I can sleep.

  10. Join Date
    Dec 2004
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    1,310
    #130
    Quote Originally Posted by mbeige View Post
    Lastly, let's pretend you didn't say that I'm talking "rubbish" because if you ask me, yes that comes as offensive.
    I'm sorry if you were offended when I referred to one of your comments as rubbish, but I'm not changing anything. Yes, let's just pretend it didn't happen, let's keep it from being personal.

    Give me an airplane that doesn't go forward using engine thrust. It's obvious that engine thrust is needed to push the plane to get enough wind across its wings to generate lift.

    Besides, even a car or a man, which uses the friction between the feet/tires to propel forward, CAN move forward on a platform that matches it's speed backwards. It's simple, get a friend, and a pair of moving platforms (or escalators, but that'll require extra athletic ability/balance). You and your friend stand on the platform at the exact same moment, he goes on the platform that goes forward, just standing (letting the platform move him forward). You go on the platform that goes BACKWARDS, and you try to keep up with him. With extra effort you can easily keep up with him and get to the other side at the same time or even FASTER than him. Gumalaw ka diba? At gumalaw ka ng halos parehong bilis nung platform na tinatayuan mo (your friend is standing on a similar platform, which should be moving at approximately the same speed).

    Of course, you used extra effort. But that's because your feet is directly attached to your legs which is directly attached to your torso. To more accurately model the forces acting on the airplane, it would require that you'd be on rollerskates holding on to a piece of rope (syempre di pwede sa escalator) - if you pull on the rope, you move forward, regardless if the platform is going forwards, backwards, fast, slow, keeping up with your speed or not at all. All the platform does is spin the wheels, because the wheelbearings has effectively isolated your body from the moving platform.

Will the Airplane Fly??????????