Plane on a treadmill...

[coco]

of course the plane will take off , has no one heard of steam catapult launches

[JPreston]

...

The jets push the plane at 1mph, so the treadmil moves at 1mph. This makes the wheels run at 2mph. So the treadmill increases it's speed to 2mph... etc.


...

No that's not right. With the plane taxiing at 1mph, the treadmill runs at 1mph in the oppsite direction, and the wheels spin at the same speed they would as if the plane were on a normal runway at 2mph. The treadmill would not increase its speed

BUT.....the speed of the wheels makes no difference at all to the acceleration of the plane, or whether it will take off. Nor does the speed of the ground, which normally of course is stationary but in this case is not. All that matters is the jet propulsion and the relative speed of the wings through the air. The plane moves - really moves, not just relative to the treadmill - down the 'runway' and takes off entirely as normal.

[JPreston]

It wont take off, the plane itself is stationary ...

No, the plane moves as normal because on a plane the wheels aren't driven but instead the acceleration comes from the engines on the wings. It doesn't matter how the wheels spin.

[MonkeyBum]

The plane moves yes, but surely if it remains stationary on the treadmill, there is no air flow over the wings or very little for it to take off?

Only the wheels are getting air speed, but they do not provide lift for the plane.

[mart_haj86]

The plane moves yes, but surely if it remains stationary on the treadmill, there is no air flow over the wings or very little for it to take off?

Only the wheels are getting air speed, but they do not provide lift for the plane.

Which is exactly what I have been saying all along... hurrah!

[chuckskull]

To take off the plane wont need to accelerate off the treadmill. If the treadmill is matching the intended speed of the plane. The plane will remain perfectly still.

This arguement presumes the treadmill keeps the plane stationary. If the plane can move it will take off, but thats not the point of the arguement, the point is, if the engines are on full and the plane cant move forward will it take off? the answer is no.

[[GSV]Trig]

No, the plane moves as normal because on a plane the wheels aren't driven but instead the acceleration comes from the engines on the wings. It doesn't matter how the wheels spin.

I've not read the other threads, but from what you say if the treadmill is driven by the plane and not the other way round then yes, it will take off as normal and the tread mill wont move much at all as theres little resistance between the plane and the treadmill...

[JPreston]

...if the engines are on full and the plane cant move forward ....

So...why can't it move forward? The acceleration does not come from the wheels...

[iranu]

It is simple - it is the RELATIVE velocity of air over the wing that matters. If the air is not moving at sufficient speed over the wing then the aircraft cannot take off. In this scenario this is exactly what occurs, therefore the plane cannot take off.

The air is not part of the conveyor belt.

[MonkeyBum]

Isn't the theory that the plane remainss stationary in relation to the ground though?

[mart_haj86]

Jpreston the wheels are irrelevant the fact of the matter is it doesnt matter how the aircraft is propelled. It is the wings which create the lift.

[JPreston]

...if the treadmill is driven by the plane and not the other way round then yes, it will take off as normal and the tread mill wont move much at all as theres little resistance between the plane and the treadmill...

It's a normal electric motorised treadmill (albeit one the size of a runway) and a normal, fuelled and piloted plane.

Lets take as given the normal assumptions that the wheel bearings are frictionless, the tyres are perfectly grippy, the treadmill can change speed instantaneously (before anyone starts talking about feedbakc loops), the meteorological wind speed is zero, the mass of the plane stays constant even as the fuel is burnt up, etc etc etc.

[JPreston]

You do know there is such an invention as a sea-plane? How do they ever take off?

[mart_haj86]

Seaplanes take off exaclty the same way an aircraft would take off on a standard asphalt runway except with floats and not wheels.

[MonkeyBum]

You do know there is such an invention as a sea-plane? How do they ever take off?

Say the sea plane needs 80 knots for take off. Then, a current rarely moves at 80 knots in the opposite direction of the plane. Because if it did, the sea plane would not take off.

[kreeeee]

The plane will take off, it's incredibly simple physics as the wheels are free spinning and produce zero thrust. The engines are not affected by the rotation of the wheels.

C'mon guys! *insert brick wall smiley*