This article is from the Radio Control (R/C) Flying FAQ, by Shamim Mohamed email@example.com with numerous contributions by others.
Helicopters with collective are now inexpensive and reliable. Every
reasonable modern heli, from beginner-trainers up to FAI world-beaters, has
collective. In a fixed-pitch heli, lift is controlled by varying engine
RPM, just as in an airplane. This is an outmoded technology, and you will
outgrow such a heli very soon. Virtually no aerobatics, no auto-rotation
(if the engine quits at altitude, the heli becomes a brick), not as much