Does the helicopter take off?

[voodoodrul]

The turntable is completely irrelevant. If the blades have enough airspeed, yes. If not, then no. Simple. When I say blade speed, I mean blade speed in relation to a stationary point in the air. Trying to think about it in relation to the ground is rather pointless.

If the heli were spinning around at, say, 650rpm and the blades were spinning 650 rpm relative to stationary air and in any direction, yes it would takeoff. Blade speed is all that matters. Nothing else. The body doesn't even need to be discussed as it is not a functional component in flight.

I have flown RC helis for quite a few years and this type of situation is something I have experience with.. You can spin the heli against the blade's direction to descend and you can spin with the blade's rotation to ascend. But this is merely a transfer of energy from the absolute energy source - the engine. Or in the case of a flameout and the engine is dead, the physics of this are quite obvious. The turntable will have no effect.

You might have a problem if the turntable is spinning, say, 325 rpm in the same direction as the heli blades and the heli is adding it's own 325 into the blades. So your total is 650rpm and say that is enough to takeoff. However, the energy from the turntable is lost the second the skids lift off and the heli would no longer have the energy to fly..

 

[Electric Amish]

Originally posted by: mugs
Is this helicopter African or European?

Are you suggesting that helicopters migrate?

 

[Valhalla1]

what if it was one of those huge transport heli's with double rotors

 

[smack Down]

Originally posted by: voodoodrul
The turntable is completely irrelevant. If the blades have enough airspeed, yes. If not, then no. Simple. When I say blade speed, I mean blade speed in relation to a stationary point in the air. Trying to think about it in relation to the ground is rather pointless.

If the heli were spinning around at, say, 650rpm and the blades were spinning 650 rpm relative to stationary air and in any direction, yes it would takeoff. Blade speed is all that matters. Nothing else. The body doesn't even need to be discussed as it is not a functional component in flight.

I have flown RC helis for quite a few years and this type of situation is something I have experience with.. You can spin the heli against the blade's direction to descend and you can spin with the blade's rotation to ascend. But this is merely a transfer of energy from the absolute energy source - the engine. Or in the case of a flameout and the engine is dead, the physics of this are quite obvious. The turntable will have no effect.

You might have a problem if the turntable is spinning, say, 325 rpm in the same direction as the heli blades and the heli is adding it's own 325 into the blades. So your total is 650rpm and say that is enough to takeoff. However, the energy from the turntable is lost the second the skids lift off and the heli would no longer have the energy to fly..

Lol Mr RC plane complete screwed it up

 

[smack Down]

Originally posted by: Valhalla1
what if it was one of those huge transport heli's with double rotors

Doesn't matter.

Nothing matters but what is stated in the question.

There is no net motion (relitive to ground is clearly implied).

The question gives the anwser so it can't take off.

 

[Caveman]

See below...

 

[Caveman]

Lets say you have a helicopter, which is positioned on a turntable.

The turntable is set up so that it monitors the speed of the helicopter's rotor, and matches its speed so that there is no net motion.

Does the helicopter take off?

Ask the Q: How does an airfoil produce lift?

A: By moving at a relative velocity to the air molecules it flows through.

So... is this being accomplished in this problem? Yes. The helicopter is sitting on a turntable and is spinning around and around (as fast as the blade). I think people were having a hard time with this because it's hard to visualize a helicopter rotating as fast as a (very fast) turntable. But the bottom line is still that the blades are producing lift as they move through the still air.

Now, if the turntable/helicopter was in the center of a tornado, and the turntable/blades matched the speed of the tornado, the heli could not lift off because the relative velocity of the blades with respect to the medium they were translating through would be zero. No relative velocity means no lift...

 

[teclado]

Originally posted by: BlueWeasel
It depends on which record is playing.

 

[91TTZ]

Originally posted by: Caveman

Ask the Q: How does an airfoil produce lift?

A: By moving at a relative velocity to the air molecules it flows through.

So... is this being accomplished in this problem? Yes. The helicopter is sitting on a turntable and is spinning around and around (as fast as the blade). I think people were having a hard time with this because it's hard to visualize a helicopter rotating as fast as a (very fast) turntable. But the bottom line is still that the blades are producing lift as they move through the still air.

I think you're getting confused by the question.

The blades would have 0 relative velocity to the air around them, since the turntable is spinning the entire helicopter in an equal but opposite rate that the engine is spinning the blades. If you looked at it in operation, you'd see the body of the helicopter spinning very fast on the turntable and the blades would appear to be stationary. They'd be moving in relation to the fuselage, but that's irrelevant since the only thing that matters is the blades moving in relation to the air, which they aren't.

Normal helicopter:

Fuselage speed: 0 rpm
Blade speed in relation to fuselage: 800 rpm clockwise
Blade speed in relation to ground/air: 800 rpm clockwise

This scenario:

Turntable speed: 800 rpm, counterclockwise
Fuselage speed: 800 rpm, counterclockwise
Blade speed in relation to fuselage: 800 rpm clockwise
Blade speed in relation to ground/air: 0 rpm

 

[newParadigm]

Originally posted by: BrownTown
OK, so since this isn't in HT ill just be blunt about it. The helicopter doesn't take off, if it takes you more than 10 seconds to understand that fact that you are mentally handicapped.

Yes it does. The tail rotor, as like 40 peeps have said, will keep the 'copter stationary in relation to the ground.