MOST Helicopters don’t typically fly high. But there are some choppers which fly higher than most helicopters. I wonder if their engines are designed differently. or their fuselage or rotors are different? I often hear how its difficult to fly helicopters at super high altitudes, but then again there are instances of choppers almost as high as Mt Everest.
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It’s a combination of power and rotor area.
At very high altitudes there isn’t much air density and there’s a limit to how much lift each rotor blade can generate before it stalls. The only way to generate more lift at a particular density, once you’re up against the stall limit, is to make the blades longer or more of them, or both, and then hook on a more powerful engine to spin the bigger rotor.
Almost all helicopters are constant speed rotors so increasing RPM usually isn’t an option. There’s some good research being done on variable speed rotors but it’s not mainstream yet.
Yes, high altitude helicopters are designed differently. The AS350 can be pressurized and has an oxygen system. The rotors also have a larger range of adjustment, as there is less air at high altitude.
Even the AS350 can’t fly at airliner altitudes. The air is simply too thin for a helicopter at 38,000 feet where the 737 is at home.
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Fundamentally, helicopters that fly at higher altitudes need more power to weight as the thin air doesn’t provide as much lift. This means engines with superchargers or turbochargers as well as cutting weight. Helicopters flying as high as Mt. Everest also need oxygen systems or pressurized cabins as the air is thin enough to cause altitude sickness.
Engine design has a lot to do with it. With conventional aircraft their forward motion is responsible for the engines getting enough air to do their work. With helicopters that isn’t always the case, and when you get high enough the air gets thin enough that going too slow can stall the engine out. So the engines need to be designed to not only draw in their own air, but also be able to function with less oxygen.
But the engines aren’t the only problem. When that air gets thin, you don’t get anywhere near as much lift from the rotors as you do in the thicker parts of the atmosphere. So you need longer blades, thicker blades, or more blades to compensate for the reduced lift at higher altitudes, especially when moving slowly or trying to hover.
The “base camp” that is halfway up Mt Everest is as high as helicopters can safely fly under most circumstances. Most rich people fly from Katmandu to base camp and climb Everest from there.
If you get into trouble above base camp, no helicopter is coming for you, no matter how rich you are. Even if there was an electric helicopter (there isn’t) the air is so thin that the blades would have to be wide and spin fast
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