Jet Fighter Madness! Physics people come here!

[MikeS]

The problem with everyone's arguement FOR the plane taking off is the assumption that the wheels rotate freely without friction. No where in the question does it actually say this. If you take into account this friction, the problem becomes much more complex.

The wheels don't have to be frictionless. So long as the thrust of the jets overcomes the friction force of the wheels and the plane reaches an airspeed that generates enough lift to take off, the plane will fly.

A bigger issue I see is one that Tor brought up, and was brought up the first time this was discussed, of the wheels physically being capable of spinning at twice the speed necessary for take-off.

[garublador]

The problem with everyone's arguement FOR the plane taking off is the assumption that the wheels rotate freely without friction. No where in the question does it actually say this. If you take into account this friction, the problem becomes much more complex.

Remember that the wheels are there to have high friction with the ground and low friction with the plane. The frictional force between the wheels and the ground does not act in a backwards direction with the plane, it only keep the wheels from skidding. The frictional force between the wheels and the plane is neglegable. If it were really high (higher than the frictional force between the wheels and the ground) then the plane would skid along the belt, but still move forward. The only way I can think of keeping the plane from moving is by attaching it to the belt. The joint would have to be very strong to keep from breaking from the force of the engines, though.

[sosomething]

hahaha! I can't believe you guys are doing this.

Remember that this is an experiment in the MIND. In real life, there are innumerable variables that would likely cause things to go awry. In the mind, one may assume perfectly frictionless wheel mechanisms and perfect contact to the ground/conveyor.

This was designed to be a trick question, anyway. The catch is what has been pointed out a bunch of times already - that a jet's force of movement is not applied to the wheels, but to the wings (or wherever the engines are mounted). That means that, not only would the jet take off, it would move forward down the conveyor (covering actual physical distance) like it were a runway.

If the conveyor were somehow able to move in reverse relative to the jet's thrust, it would only result in the wheels spinning twice as fast against it as it moved forward over the earth before taking off.

The problem is that people assume, based on the wording of the original question, that the conveyor mechanism was designed to (and is able to) keep the plane stationary relative to the earth. Like garublador says above, it is not. For all intents and purposes the plane (with exception to the faster-spinning wheels) will completely ignore any reverse motion of the conveyor belt.

The conveyor belt is moot.

[Davey]

I think that Tims skateboard being pushed by the hand on a treadmill is a perfect analogy of what would happen

[Earl Bypass]

Chimay ... Yes, the plane will fly. It is not an automobile, and you do not have to put it in D to taxi. It is designed, wants to leave the ground. Ah, the world is at peace.

As a participant in aviation, I found the discussion to be much fun. Just waiting for the next fly in the ointment. There are many smart people here, and the internet can be used for things other than pickup selection and wanking. Google is easy.

Now, think about how a sailplane, or glider, can stay aloft for hours -- without an engine. Or, how does an airplane fly upside down, or knife edge, until the fuel tanks are dry? Or, how far will a bullet travel before it is affected by gravity?

[3'scompany]

Olde thread from yonder, riseth from thy grave!!!!





Watched mythbusters tonight, where they tested this myth and it automatically made me think of this thread

Goodness, gracious. If only my memory was filled with more useful things other than the recollection of heated threads.

And for the record, yes, the airplane took off

[GoldenVulture]

Try this way of looking at it.

You need a constant force[jet engine thrust] to maintain zero acceleration.

Presuming the aircraft has greater force available to accelerate, it will.[and take off]

The ability of the conveyor to adjust to the planes change of wheel motion ,will only happen "if it moves"[the plane]

If the conveyor adjusts, it is only because the plane is moving,backwards or forwards

[YJM_Rocks]

The plane won't take off, it has no airspeed. The groundspeed in relation to the conveyor may be high, but no air is moving over the airfoil if the plane is not moving in relation to the air.

[Rich_T]

The plane won't take off, it has no airspeed. The groundspeed in relation to the conveyor may be high, but no air is moving over the airfoil if the plane is not moving in relation to the air.

It does have air speed. The wheels are spinning twice the speed of the forward motion.

[YJM_Rocks]

It does have air speed. The wheels are spinning twice the speed of the forward motion.

The wheels don't matter. Think of it this way: The conveyor is moving backwards under the airplane, but the airplane is staying in place. The wheels don't have anything to do with it. We're talking airspeed here, wheels spinning = ground speed.

[YJM_Rocks]

Another reason:

Newtons third law states that every action has an equal and opposite reaction. The thrust of the airplane is merely countering the movement of the conveyor.

[Rich_T]

Have you read any of this thread? You are wrong. That is the answer. The conveyer is moot.

[YJM_Rocks]

Have you read any of this thread? You are wrong. That is the answer. The conveyer is moot.

Right, the conveyor is moot. If you are looking at the plane from the side, the plane will not move in relation to you. In other words, the plane will not move in relation to the air. The only way a stationary (in relation to ground speed) plane could take off is if there was a headwind above the plane's stall speed. Of course, then we are talking about the plane having air speed.

Without air moving over the wings and the plane moving forward in relation to the atmosphere, no lift is created.

[Rich_T]

It isn't stationary.

[YJM_Rocks]

It isn't stationary.

Explain?

[Rich_T]

Read the thread. It is covered a lot.

[Rich_T]

The wheels negate the effect of the conveyor. Therefore the conveyor does not effect the force from the jet engines, rather the wheels turn faster to compensate.

See Zerb's Skateboard on a treadmill analogy. It takes little force from your hand to keep it stationary, and it is quite possible to push the skateboard forward. Think of the jet engines as your hands pushing the skateboard forward.

[Redmist]

The plane does move forward!!!
Why the hell wouldn't it?
It's got two F%£" off jet engines under its wings.
You think a conveyor belt is gonna change a thing?

[Rich_T]

The plane won't take off, it has no airspeed. The groundspeed in relation to the conveyor may be high, but no air is moving over the airfoil if the plane is not moving in relation to the air.

The plane does move forward!!!
Why the hell wouldn't it?
It's got two F%£" off jet engines under its wings.
You think a conveyor belt is gonna change a thing?

Well sure, you could put it that way too...

[GoldenVulture]

A plane is standing on a runway that can move (some sort of conveyer belt of something). The plane moves in one direction, 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?

You need a constant force[jet engine thrust] to maintain zero acceleration.

Presuming the aircraft has greater force available to accelerate, it will.[and take off]

The ability of the conveyor to adjust to the planes change of wheel motion ,will only happen "if it moves"[the plane]

If the conveyor adjusts, it is only because the plane is moving,backwards or forwards


If the plane starts at no acceleration,the wheels are not moving,so neither is the conveyor.

It will only start moving,if the wheels move and they will only move if the plane does.

If you started the conveyor at a certain speed and then put the plane on it,it would go backwards,unless it had an accelerating force.

Once you reached an equal and opposite acceleration the plane would no longer move backwards but maintain zero acceleration.

Presuming there is more acceleration available the plane will move forward.

The conveyor will only adjust if the plane moves, backwards or forwards.

The conveyor responds to the wheels moving faster because the plane is moving.

The acceleration factor of the plane will be greater than the conveyor.

This should rapidly rise ,creating enough momentum to take off.