A plane on a conveyor belt

[The Dread Pirate]

I realised "cretins" was probably a bit harsh afterwards Still, you have to be pretty dense to figure that a plane takes off using its wheels.

I'm not dense I just didn't think about it correctly I got so hung up on the fact that the plane is technically not moving anywhere that I forgot the engines acted as propulsion for the air

 

[WillyNelson]

Not this again.

I still can't believe how stupid some people are.

 

[NickK]

a) the plane will move forward as the plane does not use the traction of the runway to gain speed. The wheels will actually spin the other way and the conveyor belt will just spin the wheels. A small frictional component will result in a slow movement along the conveyor (ie plane backwards) if the engines where not running.

b) the plane will not take off vertically without horizontal movement as there is no air over the wings to induce lift. Note the conveyor belt only moves the ground not the air above it.

Ask if you put a massive wind generator infront of the plane then you'd not need a conveyor belt and the plane would be able to take off vertically - until it moves out of the moving airstream at which point the wings will not be moving forward and there will nolonger be any lift resulting in a stall. Probably crashing..

 

[MookJong]

I don't think it's the wheels that is the sticking point in peoples heads though, It's the fact that the plane is not moving forward and nobody is helping those who do not understand that bit.

Surly the best way to explain it is that if the engines could go from 0 to full power at the flick of a switch the plane could take off from a standing start on the tarmac.

 

[Confused]

NickK - is your answer a) or b) ?

One is correct, one is partially correct.

 

[Confused]

I don't think it's the wheels that is the sticking point in peoples heads though, It's the fact that the plane is not moving forward and nobody is helping those who do not understand that bit.

Surly the best way to explain it is that if the engines could go from 0 to full power at the flick of a switch the plane could take off from a standing start on the tarmac.

But the plane WILL move forward - because people are thinking the wheels are like them on a treadmill, rather than them on a skateboard on a treadmill.


Edit: It states in the original question that the plane moves, so the plane being stationary is a pointless argument!! Of course, it doesn't state whether the engines are on or not - but we assume so, as we're being asked whether it'll take off - and it requires the engines to be on to take off on a static runway.

 

[Mat]

I don't think it's the wheels that is the sticking point in peoples heads though, It's the fact that the plane is not moving forward and nobody is helping those who do not understand that bit.

Surly the best way to explain it is that if the engines could go from 0 to full power at the flick of a switch the plane could take off from a standing start on the tarmac.

The plane does move forwards, that the thing. People get stuck on the wheels and ignore the engines.

 

[Helium_Junkie]

I realised "cretins" was probably a bit harsh afterwards Still, you have to be pretty dense to figure that a plane takes off using its wheels.

Thats not the point, the plane takes off by moving air over its wings, and it generates air movement by moving forward through the air, which is in turn done by generating thrust to push the plane forward (afaik, the air movement from the jet engines doesnt move over the wing...?).

If the thrust that is generated is countered by a conveyer belt moving the plane at an equal speed in the opposite direction, there would be no air movement across the wings. The conveyer belt would have to generate air currents...

The plane will be travelling along the conveyer at a rate determined by the thrust, but the air movement will not, since in relation to the environment the plane is still...

So, what have I misunderstood here?

 

[izzy eckerslike]

Would not the tyres burst from overheating ?

 

[SwishSpencor]

EFG did a nice demo of this working and I saved it as a gif.
Can't find the gif though.

 

[MookJong]

But the plane WILL move forward - because people are thinking the wheels are like them on a treadmill, rather than them on a skateboard on a treadmill.


Edit: It states in the original question that the plane moves, so the plane being stationary is a pointless argument!!

Yes I KNOW, I'm trying to help explain for those who see the plane being static.

 

[Confused]

Thats not the point, the plane takes off by moving air over its wings, and it generates air movement by moving forward through the air, which is in turn done by generating thrust to push the plane forward (afaik, the air movement from the jet engines doesnt move over the wing...?).

You are 100% correct to this point.

If the thrust that is generated is countered by a conveyer belt moving the plane at an equal speed in the opposite direction, there would be no air movement across the wings. The conveyer belt would have to generate air currents...

Highlighted bit is where you're going wrong - the conveyor belt moves in the opposite direction, but it doesn't mean the plane's forward movement is reduced to zero.

The plane will be travelling along the conveyer at a rate determined by the thrust, but the air movement will not, since in relation to the environment the plane is still...

So, what have I misunderstood here?

 

[Confused]

Yes I KNOW, I'm trying to help explain for those who see the plane being static.

Sorry, my mistake

 

[strudey]

If the thrust that is generated is countered by a conveyer belt moving the plane at an equal speed in the opposite direction, there would be no air movement across the wings. The conveyer belt would have to generate air currents...
?

It's not moving the plane in the opposite direction. It's turning the wheels.

 

[semi-pro waster]

If the thrust that is generated is countered by a conveyer belt moving the plane at an equal speed in the opposite direction, there would be no air movement across the wings. The conveyer belt would have to generate air currents...

The plane will be travelling along the conveyer at a rate determined by the thrust, but the air movement will not, since in relation to the environment the plane is still...

You aren't taking off in a vacumn (you'd also need to use engines that don't require oxygen) and therefore there is still air movement.

 

[Munkeh]

Ok, imagine the engines are off and the wheels have zero loss bearings (i.e. frictionless). The conveyor belt turns, will the plane move with the conveyor belt? If you think yes then that is where you are going wrong. The plane will remain stationary as only the wheels will wheel and not move the plane.

 

[andyp]

Of course it won't bloody take off.

Basic physics tells you this fact.

 

[NickK]

NickK - is your answer a) or b) ?

One is correct, one is partially correct.

Well that depends on the description of "take off".

If take off is a normal horizontal fashion -then yes it would. The conveyor will cause more work for the engines (but not much) and the wheels would turn quicker. Basically the plane would gather speed and the wings would develop lift as the air over them would be going fast enough to create the required low pressure region.

If take off is a direct vertical take off with no horizontal movement then the result is no. There is no air passing over the wings to create the required low pressure to create lift.
Note also the plane will move forward as the engines are using air not the ground to gain speed.

 

[andyp]

oh good god, this appears like every month on here lol. The plane WILL take off.

Are you the one who files 737-800's?

Forgive me if I've got the wrong person

 

[Confused]

NickK - Why complicate the matter with your hypothetical "direct vertical take off" option? No "normal" plane (ie, non VTOL ala Harrier) would do this whether it was sat on a static runway, conveyor belt or suet pudding