# The Naked Scientists Forum

### Author Topic: How high can a helicopter fly?  (Read 8083 times)

#### GlentoranMark

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##### How high can a helicopter fly?
« on: 16/01/2010 20:05:56 »
And is there a theoretical upper limit that it can reach?

#### Karsten

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##### How high can a helicopter fly?
« Reply #1 on: 16/01/2010 22:59:20 »
Currently:

* International: 40,820 ft; 12,442 m.
* Jean Boulet (France) in Alouette SA 315-001 Lama powered by Artouste IIIB 735 KW engine; Istres, France, June 21, 1972.

No idea what the theoretical limit would be. I guess running out of air is not good for producing lift like a helicopter does.

#### GlentoranMark

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##### How high can a helicopter fly?
« Reply #2 on: 17/01/2010 02:04:06 »

Obviously it needs air to get lift and it needs to work harder and harder the higher it goes. There must be an upper limit under ideal conditions? And if you built a bigger helicopter with bigger rotors could it go higher?

#### graham.d

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##### How high can a helicopter fly?
« Reply #3 on: 17/01/2010 09:46:07 »
It is more to do with power to weight ratio rather than being bigger. It is likely that the maximum height would be achieved in quite a flimsy, and pilotless, machine that, to save fuel weight, would have to be launched at altitude. There is no hard limit that is applicable to helicopters any more than for fixed wing aircraft (well I should say aircraft relying on lift from wings as opposed to using additional rocket thrust). It just gets harder to do as the air gets thinner and is clearly impossible when there is essentially no air at all.

#### chris

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##### How high can a helicopter fly?
« Reply #4 on: 17/01/2010 11:19:02 »
Bear Grylls flew a paraglider over the top of Everest a couple of years ago. Meera interviewed him on the show:

http://www.thenakedscientists.com/HTML/content/interviews/interview/820/

Chris

#### LeeE

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##### How high can a helicopter fly?
« Reply #5 on: 17/01/2010 12:11:04 »
The situation re helicopters is a bit complex.  Ultimately, the amount of lift you can get is limited by the linear speed of the rotor blades through the air, so in theory you could counter the thinness of the air at high altitudes by spinning the rotor faster.  However, not only is the speed of sound a limiting factor, but there's also the issue of the rotor spinning so fast that it encounters the turbulence from the preceding rotor blade.

Increasing the length of the rotor blades would increase the tip speed, and in effect the linear speed of the rotor tips through the air, but then you run into the problem of controlling the blade and keeping it at the right Angle of Attack (AoA).

However, increasing the tip speed of the rotor blades would reduce the top forward speed that the helicopter could achieve because the tip speed of the advancing blade through the air in lateral flight is the sum of the linear speed of the tip of the blade relative to the helicopter plus the helicopter's lateral speed through the air e.g. if the rotor blade tip speed is nearly supersonic while the helicopter is stationary, let's say 700 mph, then once the helicopter approaches a lateral speed of 70 mph the tip becomes supersonic (at ground level).  In practice, the tip speeds must be kept well below supersonic speeds for a number of complicated aerodynamic considerations.

#### ukmicky

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##### How high can a helicopter fly?
« Reply #6 on: 17/01/2010 17:07:29 »
You could go for a twin main rotor design

#### GlentoranMark

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##### How high can a helicopter fly?
« Reply #7 on: 18/01/2010 03:43:03 »