Puzzle (physics oriented)

[biggy7]

This has been going round and round on a couple of other forums I know, so I thought I'd post it here and see what peoples' thoughts are:

A plane is sat on a runway. The runway is like a rolling road, as the plane moves in one direction, the runway acts like a conveyor belt and moves in the opposite direction - it can do this instantly and exactly matches the speed that the plane's wheels turn.

The question is:

Will the plane take off or not?

fire away!

[Shambles]

Doesn't a plane have to reach v2 to take off? It can't do that if there's no lift across the wings (which there won't be if it ain't moving against the air)

[Mule]

No it wont, the wheels would be moving but the plane would stay stationary.

[/dev/null]

As the AIR isn't moving I'd say no, however there is the fact that according to Einsteins theory of relativity, it is impossible for an observer to say whether an object is moving along the ground or whether the ground is moving beneath the object...

[DB]

No

[casio]

nope there'd be no lift for the wings it'd be lile putting an f1 car on a dyno and expecting downforce, just wouldnt happen

cas

[ZX7R]

If the plane is a harrier jump jet, then yes, I could see that taking off.

[Mule]

If the plane is a harrier jump jet, then yes, I could see that taking off.

Valid point

[Arcolite]

For a Plane to get lift it needs to have a movement of air over the wings, as the plane remains stationary, there is no air flow so the plane wont be able to take off.

[luckydip]

No

[dava123]

this hurts me brain wots the answer then

[Hippie on hill]

IF the runway can create enough friction against the air as to move the air fast enough and create enough wind across the wings then yes the plane could theoretically be lifted vertically.
It's quite a big IF tho so in reality NO

[Cam]

the real question is tho not weather the plane can take off or not its what underwear is the stewardess is wearing and how many drinks will it take for me to see them?

[pcjnr]

Yes the plane will take off , The wheels however will be turning twice as fast as they would normally , as said the plane will be moving !!



I wouldn't like to try it tho!!

[Andy Poobar]

A plane is moved along by the engines which have no relation to the road, the plane will move along and at V2 the wheels will be moving at twice there normal speed, but the engines will generate the thrust that is needed for takeoff, therefore, yes, the plane will take off.

Going to lie down in a darkened room now. My head hurts.

[NiCkO]

from a pilot...

"To generate lift an aircraft needs to have airflow over the surface of the wing. If the aircraft is static in relation to the surrounding air, (because of the road rolling in the opposite direction), then under normal circumstances there will be insufficent airflow over the wing surface to generate lift and achieve flight.

The speed at which the wheels are turning is immaterial, as it is the 'airspeed' which is critical, not the speed of the wheels or the groundspeed.

If an aircraft accelerates along a standard runway then a light aircraft might get airborne at say 60 knots airspeed, if there is no headwind then this would be equal to 60 knots groundspeed. All things being equal if the same aircraft took off with a 10 knot headwind then it would still get airborne at 60 knots airspeed, but the groundspeed needed to achive that would only be 50 knots because the airflow across the wind is already 10 knots.

Therefore leaving aside the case of a Harrier taking off in vertical take off mode, (which is a different principle) , the only way in which the aircraft on the rolling runway described could get airborne would be if the headwind was sufficent to generate lift (e.g. a 60knot wind during a hurricane etc), becasue the aircraft itself has no forward speed."

[Andy Poobar]

But the aircraft has normal forward speed as generated by the engines. When the plane is moving forward at 60 knots, then the road is moving backwards at 60 knots and the wheels are moving at 120 knots.

The road is irrelivant. The plane still has the lift as it's moving forward at 60 knots.

[Shambles]

The road is irrelivant

The road is counteracting the plane's movement

The plane still has the lift as it's moving forward at 60 knots.

The runway is like a rolling road, as the plane moves in one direction, the runway acts like a conveyor belt and moves in the opposite direction - it can do this instantly and exactly matches the speed that the plane's wheels turn.

So the plane ain't moving anywhere.. so no lift generated

You lose

[NiCkO]

think of a static rocket attached to wheels on stabalisers. with wings. on the rolling road. ..if you tilt the flaps will it take off? no. its in front of you going nowhere fast.

[Andy Poobar]

if I put a rocket on wheels on the rolling road and let it go, will the rocket move, yes. The only force involved is the rocket in one direction, thus causing movement. the fact that the wheels turn and at what speed doesn't make a difference. The road is moving at the same speed as the rocket so the wheels move faster. The rocket is still moving.

If there was no friction in the bearings or the wheels etc then the rolling road could be moving all the time and in any direction. The rocket never would, until you lit it.