How does a freewheeling unit contribute to autorotation capability?

A freewheeling unit, or freewheel, is a mechanical clutch that allows the rotor system to continue spinning even when the engine is no longer providing power. This is essential for autorotation. During normal powered flight, the engine drives the rotor system through the main transmission. The freewheeling unit is engaged, allowing the engine to transmit power to the rotor. However, if the engine fails, the freewheeling unit automatically disengages the engine from the rotor system. This allows the rotor blades to continue rotating independently, driven by the upward airflow through the rotor disk as the helicopter descends in autorotation. Without the freewheeling unit, the drag of the engine and transmission would quickly slow the rotor blades to a stop, making autorotation impossible. The freewheeling unit is a critical safety feature that allows the pilot to perform a controlled autorotative landing in the event of an engine failure.