Earth spinning

Abraham said:
Only if there's infinite friction keeping the tyres on the treadmill, they would just slip and it will fly.
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But we are assuming they can't within the question, I agree if the tyres slipped so there was forward movement without the wheels actually turning faster than it would take off.

Abraham said:
My brain's hurting trying to picture it, but if the helicopter is centered on the turntable then the blades won't actually be moving relative to the air/ground, the body of the copter will be spinning instead.
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The helicopter would be pulling the air in from above it, which wouldn't be moving relative to the ground, assuming the turntable isn't creating some sort of vortex.
 
if the turntable matched the rotor speed, then the blades would remain stationary while the poor sick pilot and helicopter spun at a few thousand RPM. I'd imagine the g-force would liquefy the pilot and destroy the chopper.
 
Rusty_Noob said:
But we are assuming they can't within the question, I agree if the tyres slipped so there was forward movement without the wheels actually turning faster than it would take off.
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It isn't stated or even implied by the question, it is assumed by people trying to justify an illogical question, as the question is written that is the answer.
The helicopter would be pulling the air in from above it, which wouldn't be moving relative to the ground, assuming the turntable isn't creating some sort of vortex.
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The rotor blades wouldn't move relative to the air around them, or the ground below. Why would they? The turntable spinning the opposite direction at the same speed would exactly cancel out the movement of them.
 
gurusan said:
if the turntable matched the rotor speed, then the blades would remain stationary while the poor sick pilot and helicopter spun at a few thousand RPM.
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O rly? What happens here? :p

oupky9.jpg


or here?

21j7zuo.jpg


Nate
 
Nate--IRL-- said:
O rly? What happens here? :p

http://i50.tinypic.com/oupky9.jpg[IMG]

or here?

[IMG]http://i45.tinypic.com/21j7zuo.jpg[IMG]

Nate[/QUOTE]

Picture unrelated?

Think about the turntable. It spins the body of the chopper such that the blades don't move from the surrounding air's point of view. So no lift is generated...
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What do you mean, what happens? The aircraft is still stationary, the rotors are turning. Imagine you stuck the helicopter on a turntable without it's engines running. The whole thing turns.

If it's turning in a direction which causes the blade to produce lift, then when it reaches that RPM, assuming it hasn't shaken itself to bits, then it will rise into the air slightly. Once it loses contact with the turntable, it will then start to slow down, and then fall back down again.

Imagine it's now sat on the turntable, turning but below that speed. If you start the engines, and the rotors turn, they will appear to the casual observer to start slowing down. Once they reach the same RPM as the turntable, they will appear to be at s standstill.

Increase the speed even more, and providing they are turnign the right way, they begin to produce lift and the helicopter will rise.

What happens after that I wouldn't like to think about...
 
p4radox said:
Picture unrelated?

Think about the turntable. It spins the body of the chopper such that the blades don't move from the surrounding air's point of view. So no lift is generated...
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But in the copter with rotors spinning in opposite directions the one spinning the same direction as the turntable will be spinning twice as fast relative to the air, so it will take off.

The chinook will be the same but I'm not sure what affect just having one rotor lifting it has, I suppose it would rapidly lift off the turntable and then fly normally.
 
I'm not going to begin to think about the physics of the Chinook on a turntable, suffice it to say that you have to remember WHY they have the two sets of rotor blades in the first place.
 
Nate--IRL-- said:
Are they not helicopters?



The blades are contra-rotating, is the turn table spinning the helicopter both ways at once?

Nate
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Oh I get you now. I thought you were just misunderstanding the situation I was proposing, but you were asking what would happen if you stuck a chinook on the same turntable.

I agree, that makes things interesting.:)
 
I admit I'm trolling a bit. The point I'm trying to make is that these questions are nonsensical, in that they define nothing and then expect a definite answer. You'd be better off banging your head off a wall, as the questions are fundamentally broken.

Nate
 
Have we agreed yet that the plane takes off ? (as proven on Mythbusters lol)

because if we are still saying it doesn't I'm to go and boil my head.
 
LOAM said:
Have we agreed yet that the plane takes off ? (as proven on Mythbusters lol)

because if we are still saying it doesn't I'm to go and boil my head.
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Everybody agrees that with the original question the plane takes off (as proven on mythbusters).

The question being asked in this thread was a different question (and a pretty stupid one I think we can agree).
 
neodude said:
Everybody agrees that with the original question the plane takes off (as proven on mythbusters).

The question being asked in this thread was a different question (and a pretty stupid one I think we can agree).
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As I wrote overleaf, but no-one seemed to take any notice of, it all depends on your exact circumstances, which aren't defined in the original question...?:D

Penfold101 said:
Ok, having skipped over 6 pages of this thread - here's the situation as I see it:

You have a few different senarios here, as follows.

1. You have a plane (757) on a treadmill. The treadmill has constant velocity. With no opposing thrust from the engines, the aircraft will move backwards along with the treadmill, it's wheels not moving. It will continue like that forever.

2. You have a plane on the treadmill, but with it's engines set to produce a small amount of thrust. This thrust is enough to keep the aircraft moving along the treadmill at the same velocity as the treadmill is moving, thus cancelling eachotehr out. To the casual observer, the plane is standing still.

3. The aircraft now has enough thrust to power itself to exactly take-off speed (Vr, or Velocity Rotate) under normal circumstances. It will accelerate to this speed in relation to the conveyor belt, but it's speed relative to the air in which it is moving will be insufficient to allow it to take off. If the conveyor was moving at 30 knots, the aircraft would require a speed of Vr PLUS 30 knots to become airborne.

4. The aircraft has enough thrust to accelerate to Vr+30 knots and beyond. Upon reaching this speed, the aircraft will become airborne.

5. The aircraft has enough thrust to reach takeoff speed, but it's speed is exactly matched by the treadmill instantly. Since the aircraft's only contact with the ground is through the wheels, and these are rotating, they will simply speed up with the treadmill and to the observer the aircraft will again remain stationary. The thrust of the engines is unimportant as this is the only opposite force acting against the conveyor belt. Whatever thrust is being produced will be cancelled out by the belt instantly, and all that will change is the rotational speed of the aircraft's wheels.

The mythbusters video is irrelevant - if you had a plane pulling the conveyor belt with the same acelerative force as the plane ON the belt, the two would simply cancel eachother out.
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