prerotator

A prerotator is a device used in aviation, specifically with autogyros and sometimes helicopters, to spin the rotor blades before the main engine provides power for flight. The primary function of a prerotator is to bring the rotor system up to a sufficient rotational speed for autorotation to be achieved when the aircraft lifts off the ground. This initial spin is crucial for generating the lift required for the aircraft to become airborne.

There are several types of prerotator systems. One common type is a mechanical prerotator, which often uses a clutch and a gearbox connected to the aircraft's engine or a separate motor. When engaged, this system spins the rotor. Another type is an air-driven prerotator, which uses a fan or small turbine powered by the main engine's exhaust or a dedicated air source to spin the rotor. Some simpler autogyros might not have a dedicated prerotator and rely on the airflow over the rotor disc during the takeoff roll to gradually build up speed.

The importance of the prerotator lies in its ability to reduce or eliminate the need for a long takeoff run. By pre-spinning the rotor, the wings are already generating lift at a lower airspeed, allowing for shorter ground operations. This is particularly beneficial for operations from confined areas. The prerotator system is typically disengaged once the rotor reaches its operating speed and the main engine is providing sufficient power. Its reliable operation is a key factor in the safe and efficient performance of autogyros.