Plane on a coneyor belt
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The conveyor does not push backwards against the plane, only the wheels which can spin freely. So the conveyor does not inhibit the planes forward progress as it would a car.
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so if we apply this to cars. . .what does that do for the price at the pump?
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It gets expensive insert a plane maetaphor/similie/pun
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Ive got a variation on this conundrum, if anyones interested...
Its a bit trickier than this one
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oh, ok another thought. Its not at all like a treadmill in that sense. Think of it as being on treadmill on a skateboard. If you use your legs to push against the treadmill to move at the same speed as the treadmill, then you stills stay stationary. A plane however is not using the wheels to accelerate. It is using something not connected to the ground - the air. So its more like standing on the sakteboard and pulling forward with your arms. No matter how fast the conveyor moves below your board, and how fast your wheels turn, it is the speed at which your arms can pull that move you forward. One arm pull distance is the same whether the conveyor is running or not. The same as the plane pulling itself forward through the air.
Maybe thats a better analogy?
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@plot-paris said:
ok. we agree with the fact that the plane, if it's engines are turned off and the conveyor is moving, will be transported backwards, right?
so if the plane accelerates and tries to move forward, the conveyor accelerates likewise. wo we have a forward-motion of the plane and a backward-motion of the conveyor, which results in the plane being stationary compared to the people standing arround the whole machinery.
this is exactly like pav running on his treadmill. no matter how fast he runs, the treadmill is always keeping him in the same place.we know the plane can only be lifted up by air pressing aginst it's wing (because that is how planes fly).
we also know, that the plane stays stationary in relation to the spectators around (otherwise the conveyor would have failed it's purpose and the whole experiment would have gone wrong).
and because the air arround the spectators is stationary (unless there is a fierce wind due to weather), it does not move in respect to the plane (except the air, that is sucked in and blown out by the jet enginge of course. but that does not pass by the wings of the plane).regarding these facts we have prove that there is no upwards thrust of the plane's wings by air.
and that means, that the plane is not able to fly
you're wrong
pav
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I think Plot-Paris is right. The plane does not fly . ..
I mean --not if it's a Delta Flight . ..and you don't get peanuts either.
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You can't keep a powered plane in one place by pulling the ground from under it....even at a matched speed.
Even the pilot himself thinks he's going to sit there like a brick.
http://www.youtube.com/watch?v=YORCk1BN7QY&feature=related -
Well that answers that.
Next!
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you know. .. Dave Barry had the theory that flight as in airplane flight was all a myth. .. and was really jsut an example of mass-hallucination. . .his thinking was that an airplane is much heavier than say . .. a piano . .. and yet when he and a bunch of his friends pushed a piano down the runway they couldnt get it to take off, so logic being what it is, a plane can't fly either.
Hmmm.
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ok. so one half of us approached the whole experiment theoretically (with a high speed conveyor that uses the minimal frictional resistance of the tyres to keep the plane in place)
and the other half expected the plane to actually move forward (because an ordinary conveyor can't put up enough speed)...next challenge!
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You asked for it: imagine the same situation again (plane on a conveyor belt) except this time the conveyor belt matches the speed of the planes wheel rather than the speed of the plane itself.
Can it take off?
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yes!
As it uses its jets to propel forward, even if it had it's brakes on the jet would take off.
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well, because the wheels have no motor, the speed of the wheels is defined by the speed the conveyor has to put up to keep the plane (that is trying to move forward) in place...
this time the plane does not take off
and now it is official, I completely misunderstood the first question
[Edit] understood the first question like the second one is meant...[] -
Im with jakob on this one, although i'll see what weird and wonderful explanations everyone comes up with before offering my own interpretation.
Jakob, me too. it took me a good half a day (before posting this thread) to understand what was happening properly.
And just so we're clear about the question, when i say wheel speed i mean the speed at which the wheel is rotating, rather than the speed at which it is moving forward (or not.)
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I fail to see how this is a different question? We've established that the conveyor belt can move however fast it wants. The rotational speed of the wheels has nothing to do with the plane moving forward, as long as the brakes aren't on and there's nothing physically holding the plane to the ground.
So the plane still takes off.
Chris
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@chris fullmer said:
I fail to see how this is a different question? We've established that the conveyor belt can move however fast it wants. The rotational speed of the wheels has nothing to do with the plane moving forward, as long as the brakes aren't on and there's nothing physically holding the plane to the ground.
So the plane still takes off.
Chris
i agree
pav
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I also agree .... however! see if brakes stop an F16 from taking off.
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Ok, well just focus on the system of the wheel for the moment.
For the plane to take off it must have forward velocity relative to the ground (assuming its a still day.) If the plane has forwad velocity so do the wheels...
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but the conveyor belt moving backwards doesn't push backwards at all on the plane. The wheels are free spinning, they will just spin faster to accommodate the conveyor belt while the plane moves forwards.
Here's what I think it would take to stall the plane on a conveyor belt:
The conveyor belt would have to move backwards at the speed at which the propellers/turbine are capable of moving air through them. So if the propeller speeds up air to 1000mph (or km/h), then the conveyor would have to move the plane backwards at that rate, so that their would be air rushing backwards into the prop/turbine at the same speed at which it could be sucked in. That seems more like it. So the conveyor has to move at the speed of the air rushing through the propeller.
Chris
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