This is highly controversial debate that's still raging I think. And I've edited some details to make it clear of the scenario. It is reflected in bold text

The question is that can a plane take off on a conveyor belt moving at the same speed in opposite direction?

In simple form - Can a plane take off while being stationary? Having it's forward rolling momentum elliminated?

Both camp of yes and no are split quite evenly.

The 'Yes' camp argued that :

- Plane do not use wheels to fly, so it can lift off even if the ground is moving away at the opposite direction at the same speed.

The 'No' camp argued that :

- If the plane remained stationary, it wouldn't have forward momentum for air to slice through to the wing to generate lift, hence it won't have lift off.

Sure, Mythbuster tested the myth, but through proper observation you will notice that both model and full scale plane in the myth has some forward momentum.

In my opinion, not definite fact, there's flaws in this debate.

- Propeller propelled air into the wing, thus able to generate lift despite being stationary.
- If plane are able to lift up without moving, why does it still need a runway? VTOL would be laughing stock since it's an invention that fixes nothing!

So IMO, a plane on a conveyor belt wouldn't fly away. I am on the 'No' camp

This post has been edited by wKkaY: Jun 20 2009, 03:33 PM

basically my idea is that the plane to obtain some minimum speed with respect to the AIR (v). So a conveyer (u) will certainly slow down the speed of the plan with respect to the air.

new take off speed = x = v+u

Hence, you will require a higher speed from the plane itself to take off.

Do tell me if i do any stupid mistake here.

Uhh, I don't think you have the setup right

The conveyor belt is moving away in a way that it's making the plane stationary.

what i mean the plane would require a higher speed than normal condition. The extra speed is to overcome the conveyor belt speed and to reach the take off speed.
If it remain stationary, this means the speed of the conveyor belt is the same as the plane. Certainly it wont take off.

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Added on June 16, 2009, 12:58 amactually another important factor would be the type of the plane. Whether it is jet engine, propellor engine also matters.

This post has been edited by ModularHelmet: Jun 16 2009, 12:58 AM

Yeap, I meant the latter, the conveyor belt moves away at the same speed at every condition. Meaning the plane is always stationary.

Consider another body that requires airspeed to fly - a kite. If you were to run on a conveyor belt holding a kite, will the kite take off?

Kites are very light and I think the wind itself can make the kite 'take off' if you just raise it with your arms while tilting it. But for planes I don't think this would be possible.

@TS
I agree with your opinion. If the plane can take off without a runway, why do we still need the runway? Hehe..

Correct me if I'm wrong,

The lift is created by the difference in pressure on the top of the wing and the bottom. This difference in pressure is due to the air velocity which is caused by the jets and also when the plane moves.

But, we're speaking ideally, since the conveyor's velocity is always changing due to the change in the velocity of the plane to keep it stationary right?
So, ideally if there exists a jet that could make the air velocity fast enough to create sufficient lift without moving the plane it should be possible.

What i think is:

A plane fly or take off because of the lift force generated by the pressure difference between the moving fluids around the aerofoil,which is also the reason why most planes need a runway to take off.Ignoring VTOL and vector trusting.Just a typical 747.

Since the conveyor belt always move in the opposite direction of the plane,the relative velocity of the plane and the conveyor belt is zero.This also mean the plane and the more importantly,the air around the plane is stationary.Or,in another words,the velocity of the air is zero.

By the drag force formule,

F = 0.5*C*A*p*v^2

where,
C is coefficient of drag
A is projected area of the plane to the flow
p is density of air
v is velocity of the fluid,which is air here.

Since velocity of the air is zero(boundary condition cant be formed here),there isnt any lift forceprovided by the aerofoil.The plane wouldnt take off.

This is just my 2 cents,as this is what i know.

Do correct me if im wrong.

for me, plane on a conveyor belt, wont take off on opposite direction. so, i think im in no camp.

The answer provided by "Cheesenium" is the most acceptable for your "curiousity", Thread Starter.

It takes an understanding in the concept of Lift Induced Drag.

Regards, Joey

Kite would fly IF you yanked on the string, providing movement for the kite through the air. It's the same why kite fly when it's high up even if you're standing still because there's enough gale in the atmosphere to keep it flying.

So far everybody saying no, I don't believe it's possible to fly either but anyone who's a fan of Mythbuster will notice that their plane took off on a conveyor belt so... explanation?

The video does not seem convincing that the speeds match exactly at every moment. How do they coordinate? Comparing a car and a plane, shouldn't the plane have a higher acceleration?

They did a control test to determine the minimum take off speed of the plane and it's shown that the car can match that speed.

I am not very convinced because I do noticed some forward momentum in the plane. I really hate to prove them wrong because I am a big fan of them but in truth I still don't see how a plane can fly while remaining stationary.

Another possible explanation is the plane design itself. The air pushed by the propeller actually passing through the wing, and there's enough lift to lift the wheel away from the conveyor belt, allowing it to accelerate forward and fly off.

This post has been edited by SeaGates: Jun 16 2009, 06:54 PM

Ah..a control test. But the accelerations would still be different (since they didn't mention the synchronisation method), right? This would cause a net force.

I havent watch the video yet,but what im sure is,the forces around the plane arent scaled properly which might give different result compare to real life.

my thought is as what you mentioned.

if plane going at X speed and belt going at -X speed, then it should be stationary.

in the video, the plane was moving at quite a substantial speed.

when stationary, there's no way a lift can be achieved with little to no air-movement.

im in 'yes' camp..

y i said so? it because the plane use engine thrust (air) to create a lift. it doesnt depends on the rotation of the wheel. this means the wheel just only a tool to supporting the plane to move..so when the conveyor belt moving in opposite direction of the plane at the same speed (theoretically) while the plane is in motion, the only thing different is just the wheel is rotate twice as much compared when the plane take off on normal ground.

or simply, the plane use thrust created by the engine to move forward, not by the rotation of the wheel.

That's my answer for now

@blue
Still...if you only use the machine thrust to move forward, it still need the air-movement to push it up. It's kinda different with Helicopter.

Thanks
Rcode

Once again , you guys do not understand that the wheels are FREE to move in forward or backward direction . The thrust will definitely be able to move the aircraft , regardless of what the conveyor belt is doing . Definitely definitely .

Absolutely no doubt about it !

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Added on June 17, 2009, 12:40 amIf you give this question to the guys at Airbus / Boeing / Bombardier / Embraer . They'd tell you its a NO BRAINER .

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Added on June 17, 2009, 12:42 amIf you are talking about WIND SPEED in the SAME DIRECTION as the aircraft is moving . Then that aircraft would definitely not fly . But this one , tyre's doesn't really affect much . Think about the thrust these engine's produce

This post has been edited by gavind87: Jun 17 2009, 12:42 AM