Debate!

[Jakemaster]

People are starting to look to deep and not concentrating on the basic fundementals...

To be even more simplified...

The aircraft is on a very long ( As long as you want ) tredmill...
As the wheels rotate forwards the treadmill counteracts this and begins to move backwards.
(Imagine your on a treadmill where it responded to how fast you were going so as you speeded up so did the treadmill.)

So now, if you understand that, will the aircraft be able to take-off?  :P

In that case, NO!  It will not takeoff unless the plane itself has forward velocity to generate airflow over the wing.

[Sir_Crashalot]

No the airplane will not take off. In fact it will not move at all. Like the running machine, you can run what ever you like, you will not move forward. The conveyer is counteracting the movement of the wheels, thus moving backwards at the same speed the wheels are moving forwards. That way the plane will never leave it's place, never build up any airspeed and never take off.

Crash

[Hagar]

[quote]I still don't get it.

Lets get away from planes for a moment...

Say I take my car out to a similar conveyer belt strip.

[dcunning30]

LOL, if anything, the bearings of the wheels will burn out and we have a spectacular crash.

[Chris_F]

Right i'll try to go into more detail...

The conveyor belt is x miles long....
The conveyor belt counteracts the motion of the wheels. i.e As the wheels roll forward the conveyor moves back.
Try not to think about the aircraft limitations, including tire limitations and engine endurances just yet...

All you need to picture is any aircraft (I just said a 747 for ease) on a conveyor where the motion of the aircrafts wheels are counteracted by the conveybelt, (Sort of like a person on a tread mill) But will the aircraft ever take-off?

Some posts here are along the right lines but missing some key points....

I still don't get it.

Lets get away from planes for a moment...

Say I take my car out to a similar conveyer belt strip.

[Jakemaster]

Well yes the wheels don't move the plane.  But until the plane generates enough lift the wheels are in contact with the ground.  So if the plane starts moving and the conveyer moves opposite of it, the plane won't go anywhere because until the plane builds up enough airspeed then the wheels will remain firmly planted on the ground.  

No matter what, the plane needs to move forward.  If it doesnt, it won't fly.  Period.

[Chris_F]

[quote]Well yes the wheels don't move the plane.

[expat]

You are all making this way tooooooooo complicated. The clue is in the question.

Conveyor belt type device, that counteracts the movement of the aircrafts wheels as they move.

Definition of counteracts is, To oppose and mitigate the effects of by contrary action

So if the aircraft is doing  1 knot, then the conveyor is traveling in the opersite/agaist direction at 1 knot.
If the aircraft is doing  10 knots, then the conveyor is traveling in the opersite/agaist direction at 10 knots.
If the aircraft is doing  100 knots, then the conveyor is traveling in the opersite/agaist direction at 100 knots.
If the aircraft is doing  10000000  knots , then the conveyor is traveling in the opersite/agaist direction at 10000000 knots.

Counteracts: nullify, annul cancel, cancel out, counterbalance, countervail, counterwork, defeat, foil, frustrate, go against, halt, hinder, invalidate, negate, neutralize, offset, oppose, prevent, resist, thwart.

Matt

[Woodlouse2002]

I have only read the first few posts, and I'm sure the answer has been posted many many times already with many different attempts to explain to those who can't see how it works.

But the answer, yes. The jet engines create thrust which moves the plane forwards. The wheels are just freewheeling and all that happens on a conveyor belt is that they just spin faster while the engines continue to push the plane forwards.

Only catch is that the plane might need a slightly longer take off roll to over come the extra friction on the wheels by the fact that they're spinning so much quicker.

[elite marksman]

Assuming frictionless wheels, yes, they plane will take of as the conveyor can affect the wheels and only the wheels.

Assuming friction, it becomes a matter of physics. Depending on the coefficient of friction between the wheels and the runway, and the bearing in the wheels, the thrust of the engines may or may not be able to overcome the drag induced by forward motion and the friction combined.

Without hard numbers, it is impossible to tell.

[Hagar]

Without hard numbers, it is impossible to tell.

Well, this is purely a theoretical exercise. It's kept the "experts" busy arguing for years & I'm not convinced there is a correct answer to it.

Matt is the only one here to have carried out some practical experiments. I found his results surprising.

[C]

Of course, when you build in the factor that there will be lag in both the conveyor belt control system, and in the motor system itself it becomes all the more complicated. Depending on that I believe, will be the take off distance required, which will be quite a long way.

[Mobius]

The point here is that we're not talking about cars. Aircraft wheels don't provide traction.

Doug is right.  Since the wheels are not providing thrust, and you can assume they are frictionless (as EGNX said), the treadmill will have no effect on the takeoff of the aircraft, and it will fly normally.

[expat]

The point here is that we're not talking about cars. Aircraft wheels don't provide traction.

Doug is right.  Since the wheels are not providing thrust, and you can assume they are frictionless (as EGNX said), the treadmill will have no effect on the takeoff of the aircraft, and it will fly normally.

You have to assume some friction with the wheels. The frictionless part must refer to the wheel bearings otherwise if there is no friction at all produced by the wheels then the aircraft is in effect levitating and the conveyor will have no effect. If however all friction in the system, that being conveyor and wheel bearings is eliminated (theory only) and friction only exists between wheel and conveyor then if the speed of the conveyor equals the thrust of the engines then you have a tread mill and the aircraft will not move forward.

If the aircraft was bolted to the ground, the we would all agree that it would go nowhere. So when we put a system under the aircraft that says forward thrust is neutralised by the reverse motion of the conveyor on the wheels do people then think that the aircraft will fly. If we put the aircraft at the end proposed takeoff end of the conveyor and turned the conveyor on with the engines off, we would all agree that the aircraft will travel backward with the conveyor. If we then started the engines and applied power and slowly increased that power the aircraft would then overcome the backwards travel of the conveyor due to the turning action of the wheels. If we increased the power of the conveyor, the aircraft would still have the same wheel rolling motion, but would start to travel backwards on the conveyor. If we then increase the thrust of the aircraft, the wheels under thrust action would then be forced to turn faster than the conveyor letting the aircraft creep along the conveyor. If we get to a point where thrust forward matches conveyor speed backward the aircraft would sit in once place. So if we increase to max thrust and the conveyor matches this thrust backward in our perfect world why would a stationary aircraft suddenly produce lift???

Matt

[Stormtropper]

...'course the plane will be able to take off

...take a hot wheels car, and put it on your threadmill (actually, balance a dictionary on it, to add more friction so it doesn't just fly away...)...

...if there is perfect contact between the wheels and the treadmill belt, no slipping or anything, the toy car should remail perfectly stationary...

...now apply it to a plane, on idle power, sitting on the conveyor, it should be stationary...so any added thrust should will become forward momentum, and the aircraft will be able to make a normal takeoff, no matter how fast the conveyor belt is moving...unless it comes to the point where the conveyor is moving so fast that the wheels pop off...

...under ideal conditons, the take off should be identical to a take off on a normal runway, with the exception that the wheels will be spinning much faster...

...the more weight there is on the wheels, the heavier the aircraft, the more friction between the wheels and the conveyor...the more true this is...

...well, until when you hit the point when your aircraft is heavier than the earth...then the engines will just generate momentum for the earth in the opposite direction...