What is the term for the turning rotor system by air flow instead of engine power?

Autorotation is the process in which a rotor system gains lift and propulsion through the kinetic energy of the rotor blades as they turn due to the upward airflow created when a helicopter descends. In this scenario, the engine is not providing power to the rotor; instead, the rotor blades are driven by the air flowing upward through them as the helicopter descends. This aerodynamic principle allows a helicopter to maintain control and provide a controlled descent without engine power, making it a crucial technique for emergency landings or situations where the engine fails.

In contrast, hovering refers to a helicopter's ability to maintain a stable position in the air at a constant altitude, which does require engine power. Flight control encompasses the systems and processes that manage a helicopter's movement, commonly reliant on the engine's thrust. Torque stabilization refers to the techniques and systems designed to counteract the rotational forces created by the helicopter's main rotor during flight, again depending on engine power and not airflow alone. Thus, autorotation is the correct term for utilizing airflow for rotor movement instead of relying on engine power.