This article is from the Radio Control (R/C) Flying FAQ, by Shamim Mohamed email@example.com with numerous contributions by others.
What's the deal on auto-rotation?
If a heli's engine quits in flight or you simulate this by going to
throttle hold mode, it is still possible to glide the helicopter down
safely. As the helicopter descends, the wind flows up through the rotor
disk from below. At a low or negative collective pitch setting, the wind
flowing up through the rotor disk keeps the blades spinning. Heli blades
usually have lead weights epoxied into the tips, so as the blades spin they
build up a fair amount of rotational inertia. When you are near the ground
and ready to land, you add in collective to increase lift, and the inertia
maintains head speed sufficient to execute a controlled landing. In
theory. ;-) Auto-rotative glides and landings are beautiful to watch. A
helicopter can sustain as much as a 4:1 glide ratio in auto-rotation.
What about aerobatics?
Helis can do awesome aerobatics: loops, rolls, pirouettes, you name it. My
personal favorite is inverted flight. If looks 'way cool to see a
helicopter hovering inverted right above the grass. I've seen guys do
aerobatic routines flying the whole thing BACKWARD. With a helicopter you
have unbelievable versatility.
How high do they fly? How fast do they go?
Helicopters can go so high they are out of sight. Being able see the thing
in order to control it is the only limit on how high they can fly. R/C
helis can go 60-80 MPH or more.