A helicopter's rotor has a complex control system that has you changing the pitch of the rotor blades and the angle of the rotor disk, with the rotor behaving s

A helicopter's rotor has a complex control system that has you changing the pitch of the rotor blades and the angle of the rotor disk, with the rotor behaving similarly to the wing of an airplane. Quadcopters usually rely purely on thrust for control. For example to bank, the motors on one side spin faster (more thrust) and the motors on the other side spin slower (less thrust). If you lose a motor, or lose the ability to control a motor, you lose the ability to control the quad. In comparison, a helicopter will have a clutch that can disengage the rotor from the engine and let it turn freely. The pilot still has the ability to control the rotor, so she has some control during the autorotation. At the end, just before landing/impact, she will perform a flare, using the rotational energy in the rotor to slow the helicopter's descent.