This article is from the Radio Control (R/C) Flying FAQ, by Shamim Mohamed email@example.com with numerous contributions by others.
There are usually five servos on an R/C heli. One controls throttle, one
controls collective, one controls fore-aft cyclic (analogous to elevator),
one controls left-right cyclic (analogous to aileron), and one controls
tail rotor pitch (analogous to rudder).