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  1. Join Date
    Oct 2002
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    9,894
    #101
    Quote Originally Posted by BlueBimmer View Post
    wag mo na ubusin ang buhok mo kapatid. tignan mo ako naubos na buhok ko sakit pa rin ulo ko --> :headache:

  2. Join Date
    Dec 2004
    Posts
    1,310
    #102
    Quote Originally Posted by kinyo View Post
    Let's see your FBD then.

    The forces shown on the FBD are accurately depicting their directions and where they are applied.

    Obviuosly, Fb, being off-center, produces torque which tends to rotate the wheel. Friction force is always against motion, if the wheel tends to move forward with Ff, then Fb will try to oppose it.

    The friction on the wheel bearing is basically negligible and because of this, the wheel is allowed to rotate. When the wheel rotates, it will move forward (and the plane flies) IF the runway is not moving. With a moving runway, the forward motion of the wheel is exactly opposed, hence the wheel, although rotating, stays in place.

    In the FBD, a moving runway is depicted as Fb being significant to oppose Ff. If Fb is made greater than Ff, then the wheel/plane would be moving backward! (meaning, the conveyor/runway was adjusted too fast!)

    The wheel bearing, with almost zero friction, actually plays an important role of the wheel. It is its frictionless property that allows the wheel to move along the road. But with a moving runway, it is also its frictionless property that allows the wheel to stay in place while rotating.

    The wheel is attached to the plane. If it moves, the plane moves. Sure you can have an FBD of the plane, and it will show the same forces. There will be Fb that will oppose Ff. There is no wind resistance when the plane is stationary or just starting to move.

    Yes, its the wheel bearing that is frictionless. It does simulate a frictionless runway in the case of non-moving runway. If the runway is frictionless, the plane can take off with a ski, instead of wheels, and it would not matter if the runway is moving or not.

    If the wheel bearings got stuck, the plane will not move if the runway does not move; the plane will move backwards with a moving runway (even if the engines are at full thrust).

    Then let's see your FBD so you could clarify what "runway speed = plane speed" would imply.
    Contrary to what you assume, if the wheel moves, the plane DOES NOT HAVE TO MOVE! You can try that with your car, jack up a non-driven wheel, let go of the brakes and spin it with your hands. Does the car move?

    What frictionless property?! You can go do the matchbox-on-paper experiment to demonstrate that your assumption is completely wrong.

    The wheels are attached to the plane. Yes. If the wheelbearings got stuck, all force exerted by the runway on the tires would be transferred to the plane, keeping it from moving - IF AND ONLY IF!. However, the wheelbearings serve to minimize friction EFFECTIVELY ISOLATING ANY FORCE EXERTED BY THE RUNWAY ON THE PLANE (and vice versa). VIRTUALLY NONE OF THE ENERGY exerted by the runway goes to the plane. Almost all of the energy exerted BOTH BY THE RUNWAY ON THE TIRES and THE PLANE ON THE WHEELBEARINGS go to MAKING THE WHEEL SPIN. Thus, the wheels spin faster, but the rest of the plane gets to do whatever it wants.

    I'm not saying that your FBD is wrong. It's a perfectly fine representation on what's going on with the wheel. I'm saying that your ANALYSIS of the FBD is wrong. You have not demostrated any relationship between the forces acting on the wheel and any force acting on the plane, you just concluded that since the runway exerts force on the wheel it MUST exert the same force on the plane, which is completely wrong - virtually nothing happens to the plane, except the wheels spin really fast. Two linear forces act on the wheel, the engine thrust and the runway's friction on it. However, whatever torque they create causes angular velocity in the SAME DIRECTION! Meaning all the runway is doing is spin the wheel faster!

    In fact, I believe your FBD is a representation of the WHEEL and the forces acting on it, which makes it irrelevant to the question.

    I can't create an FBD that models runway speed = plane speed, kasi hindi naman force ang pinag-uusapan eh!!! Mahirap ba intindihin yun (apparently oo)? SPEED IS NOT FORCE, FOR THE NTH BLOODY TIME! The runway and the plane speed are NOT a function of the forces the two bodies are acting on each other! Your FBD is a red herring. So is the runway and the wheels, all of these serve as the trick to the question. The wheelbearings make whatever force the runway exerts on the plane negligible. Almost all of the energy exerted by the friction between the runway and the tires go to spinning the tires, almost NONE go to push the plane backwards.

    Quote Originally Posted by niky View Post
    *Kinyo: wheel speed does NOT equal airplane speed.

    The airplane is not wheel driven. The wheels can be moving 1000 mph along the conveyor, and the plane will still be going at the same speed it would be going if the wheels were moving at 50.

    Your analogy on the wheel plane thing is false.

    If the wheel moves, the plane moves, right?

    If the runway moves, does the wheel move? NO. The Wheel is not attached to the runway.

    [size=4]This is the tablecloth trick. The tablecloth is the runway, the wheeled plane is a plate on the table. Pull the runway out from under the plane fast enough, and it won't move.[/size]

    Now do you understand?
    Last edited by Alpha_One; November 10th, 2006 at 01:13 PM.

  3. Join Date
    Jul 2005
    Posts
    199
    #103
    Quote Originally Posted by boybi View Post
    i stand by my answer that the plane WILL NOT TAKE OFF.

    the jet engine is just like a vacuum cleaner upfront. it sucks in air, which means all the air will go straight into the turbine and NOT PASS UNDER THE WINGS which CREATES THE LIFT necessary for the airplane to take off.
    sir, sabi nga nila..."in every action there is always an opposite equal reaction"..saan naman sa tingin nyo mapupunta yung thrust generated by the jet engine? maa-absorve ng conveyor?

  4. Join Date
    Oct 2002
    Posts
    19,438
    #104
    yes, it will be counter-acted by the conveyor.

  5. Join Date
    Aug 2006
    Posts
    636
    #105
    IMO, (di naman ako pilot at zero bokya ako sa physics) the airplane will fly kahit na moving in opposite direction yung runway. by the sheer power of the airplane's engines, the engines will cut/bite into the air and the plane will fly.

    yung mga VTOL (vertical take-off and landing) airplanes...di nila kailangan ang runway. pwede silang mag hover a few feet above the ground and then take-off. so immaterial kung me ground contact yung wheels nila o wala, dahil so powerful yung engines nila, magkakaroon ng lift yung wings nila kaya lilipad din sila.

  6. Join Date
    Jul 2005
    Posts
    199
    #106
    Quote Originally Posted by boybi View Post
    yes, it will be counter-acted by the conveyor.
    then again sir, i think you missed the point that much of the thrust generated by the jet engine is directed against the wind (medium) to propel it forward and not so much on the tarmac.

    would you agree that a hydroplane resting on water..water being so slippery offering not much resistance and acting much like a "conveyor belt" will be able to take off? if your answer is yes, then i guess the confusion is pretty much resolved.

  7. Join Date
    Jul 2006
    Posts
    3,601
    #107
    Quote Originally Posted by nerbyoso View Post
    naku! hindi pa pala tapos ito.

    ok am gonna say it again..."imposible yun"...
    Pare, that was the premise. If the original premise was wrong to start with, then my answer is right. Why? Because I am basing it on the premise, while yours is wrong, because you said imposible yon. While it may be true na imposible yon, that was the original premise, and that's what we should follow in order to answer the question properly.

    Like I replied on one of the pages, "read the original question" and let's get back on topic. The premise is that the plane should lift off the ground to be considered flying, correct?

    From there I will leave it up to you guys who have more patience than me, because frankly, I think that this question is like the chicken and egg thing. Either way has a good point but both have an error.

    1. The error in my arguement is that it does not take into account that the plane's engine pushes against the air. There is another idea beside this, that the air that goes across the wings should not come from the engine, but rather from the environment. The reason I did not include this is because there was no mention of it. I am focusing on the lift, not on the forward movement, because the question is if the plane will fly or not, and the key point for the plane to fly is the Bernoulli principle, which should generate lift when the plane moves forward. But it remains stationary.

    2. On the other hand, the error in your arguement is you are negating flight. You are focusing on the forward movement, not on the lift. You cannot just forget that the plane has to fly, because that is the question. If you are basing it on forward movement, then you are not answering the question.

    However, the original premise still remains, that whatever speed the plane acquires forward, the conveyor belt matches it so that it runs at an equal but opposite direction.

    *Lolo pepe, the VTOL is different. The wings are now located at the large rotors, which move because they have axial rotation. The plane, on the other hand, has to move forward, which is the basic arguement of this thread. Because once it moves forward, it will generate lift if the speed is sufficient.

    *Niky regarding table cloth pulling: did you mean that the plate will not move, and hence, since the plane rests on the plate, therefore the plane will NOT move?

    The reason we're all having this arguement is because we're talking of two different points of views! One point of view is focused on the lift, while the other is whether or not the plane will move forward.

    1. If I focus on the lift, I will not consider the engine thrust because the premise of the original question is that the conveyor belt will match the speed in the opposite direction. This means, whatever speed the plane acquires, the conveyor belt matches it, be it impossible or not. Therefore this keep the plane STATIONARY.

    2. If I focus on the forward movement of the plane, the engine thrust has to be taken into account and this will provide the external force for the plane to move forward, and therefore, FLY.

    End of discussion!
    Last edited by mbeige; November 10th, 2006 at 01:57 PM.

  8. Join Date
    Jan 2003
    Posts
    2,979
    #108
    hehehe! pasakitan ng ulo dito ah! buti yun saranggola lumilipad kahit di ka tumakbo ng mabilis basta may hangin lang which i think can be dealth with propeller or jet engines... support lang talaga ang purpose ng gulong....

  9. Join Date
    Aug 2005
    Posts
    227
    #109
    :threadmil

  10. Join Date
    Jul 2005
    Posts
    199
    #110
    mbeige, you made some good arguments i must agree...hey no problem sir..this is just an exchange of opinions among guys i must pressume not involved in the aeronautics industry...its all good.

    i think i already expressed enough of my opnions regarding this topic..sige kayo naman..i rest my case...cool lang kayo peeps.

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