"David Lesher" wrote in message
...
"Simon Robbins" writes:


Rather than lack of oxygen, I imagine it would be that the lower air
pressure simply means the rotor is unable to achieve lift without an
unacceptable increase in rotor speed, which would likely overstress the
engines and gearbox.

I've wondered what keeps you from building a high-altitude version.

I envison big fat blades and an engine design for thin air. Or is there
some other issue I'm not seeing?

Lack of demand most likely.
Not a lot of places to land on mountains that tall.