Will The Plane Fly?

[Andy Moore]

This will get em arguing at work.

Imagine a plane is sitting on a massive hypothetical conveyor belt, as wide and as long as a runway. The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

Can the plane take off?

[kitten]

you trying to start another wheel bearing thread

[Cookee]

Or reading a highly entertaining thread on OffshoreOnly.com?

[Cookee]

ps. Yes!

[Nasher]

My thoughts

The plane will move forward THROUGH THE AIR at take off speed genetating lift under its wings and take off.

However the undrcarrige wheels will revolve twice as fast for a given speed.

Unless ground force has an effect.
(The actual force, not Charlie and Tommy)

Nasher.

[Nos4r2]

Originally Posted by Andy Moore

The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction.Can the plane take off?

Yes it'll take off. (final answer)

For the conveyer to be able to match the speed of the plane, the plane will have to be moving in relation to the ground.

[Andy Moore]

Originally Posted by Nos4r2

Assuming the tyres don't burst from moving at twice the speed they usually do then yes-the engines are pushing against the air not the ground.

So, if you were observing it from an adjacent field, it would appear to vertically take off?

[Nos4r2]

I think there's an essential parameter missing here.

Is the conveyer designed to match the plane's speed over the ground (in which case it'll take off)
OR
Is it designed to match the plane's speed on the conveyer (in which case it'll never get any airflow over the wings and won't take off).

[Cork Rib]

May'be i'm going against the run of things here, but i don't think it will take off.

An aircraft requires airflow over/under the wings to create lift. In your scenario, the only thing moving is the treadmill and the wheels therefore there is no airflow created.

The thrust of the engines does not become part of the equation as the aircraft is stationary

All IMHO

Jon

[Nasher]

The plane is not stationary, it will move forward as usual, and hence have airflow under its wings.

The conveyer is attached to the ground and only the plane wheels are touching the conveyer, they just need to go faster.

This is all about the planes movement relative to the air around it which is absolutly normal.

Never heard of an air conveyer.

In a wind tunnel where the air was moving the plane would lift vertically.

Nasher.

[Cork Rib]

Originally Posted by Andy Moore

The conveyor belt is designed to match the speed of the plane exactly but moves in the opposite direction. The engines are running at take-off thrust, the brakes are off, etc. Everything is normal save for the fact the plane is on a treadmill.

If the conveyor matchs the speed of the aircraft, then for all intents and purposes the aircraft is stationary.

If the aircraft moves faster than the conveyor then that becomes another story!

jon

[Cork Rib]

if you take the scenario of someone running on a treadmill.

To stay on the thing you have to match the speed of the treadmill. You are using energy running (ie thrust) but you are stationary

Jon

[J S]

I have come across a very similar real situation when flying my model planes. The model trainer cessna i have takes off and lands at about 20mph. I have been in situations where there has been a 20mph headwind so i land stationary. So the airspeed is 20mph but Sog is 0. So i think the plane would take of because it would have the same airspeed as normal.


James

[Nick Hearne]

But the wheels do not propel the plain it is the thrust from the engines, so it will take of as normal moving forward through the air creating lift under the wing!

[Nasher]

Originally Posted by Cork Rib

if you take the scenario of someone running on a treadmill.

To stay on the thing you have to match the speed of the treadmill. You are using energy running (ie thrust) but you are stationary

Jon

Jon

In this case you are matching Ground speed not air speed.
Thats the big differance, as the plane travels through air, and is not driven along the ground by motion of its wheels.

Nasher.

[Cork Rib]

Originally Posted by Nasher

Jon

In this case you are matching Ground speed not air speed.
Thats the big differance, as the plane travels through air, and is not driven along the ground by motion of its wheels.

Nasher.

exactly my point........where is the air speed???

[Nasher]

The air speed comes from the thrust of the engines which are running at take off speed.

The engines are pushing against the air not the conveyer.

I'm not explaining myself very well I know.

Nasher.

[Cork Rib]

Originally Posted by Nasher

The air speed comes from the thrust of the engines which are running at take off speed.

The engines are pushing against the air not the conveyer.

I'm not explaining myself very well I know.

Nasher.

The engines are producing thrust to keep the aircraft at the same speed as the treadmill speed against it. There is no airflow over the wings as the aircraft is stationary because the thrust producing forward motion is Exactly the same as the reverse motion of the treadmill

I'm starting to get confused now!

[Cork Rib]

Originally Posted by Nick Hearne

But the wheels do not propel the plain it is the thrust from the engines, so it will take of as normal moving forward through the air creating lift under the wing!

Only if the speed created by the thrust EXCEEDS the reverse speed of the treadmill. The aircraft will then be moving forward and creating lift under the wings. It would then give a shorter take off run. Conversly, if the thrust is less the aircraft would reverse on the treadmill. Remember in the original question there was no mention of any simulated wind speed.

[kitten]

Originally Posted by Cork Rib

I'm starting to get confused now!

you said it