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Because air is thin up there, toy helicopters usually have a maximum operational altitude. If the toy brought up by a real aircraft, higher than its intended maximum altitude, would it be able to hover inside the real aircraft? If so, what would happen if the real aircraft would now vanish magically, so that the toy helicopter is hovering in the middle of thin air?

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As altitude increases, density of air decreases. As air density decreases, the lift of the helicopter blades decreases (for a given angle of attack and RPM). As long as the "real aircraft" is open to the atmosphere (doesn't have a pressurized cabin), performance of the toy helicopter would be the same as if it were outside the "real aircraft".

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"performance of the toy helicopter would be the same as if it were outside the 'real aircraft'", which is...? – user1032613 Mar 28 '14 at 18:06
which would depend on the altitude, if you're up at 39km with Felix Baumgartner it's not going to work. Every helicopter would have a different maximum altitude, and it would vary with temperature, humidity, etc. – DavePhD Mar 28 '14 at 18:25

A helicopter is an airplane whose wings happen to go in circles.

As an airplane goes higher into thinner air, its wings get less lift and less drag, so with the same power, it just goes faster - bringing its lift and drag up to what it is at lower altitude. That's why jets fly high.

Of course with jets there's a limit because as the air gets thinner the speed of sound decreases. When the plane's speed approaches the speed of sound at that altitude, it has to back off, unless it's built for supersonic flight.

In your toy helicopter, the electric motor loses power as it goes faster, so there's a limit to how fast the blades can go, therefore a limit on how high it can fly. If it has a gas motor, same thing, plus thinner air has less oxygen, so less power.

So if you take it up in an unpressurized aircraft, above the helicopter's maximum altitude, the air will be too thin for it to hover.

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@GlenTheUdderboat: Maybe a bit. What ground effect does is increase the lift/drag ratio. – Mike Dunlavey Mar 28 '14 at 21:49

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