sprag clutch

sprag clutch

[′sprag ‚kləch] (mechanical engineering) A clutch designed to transmit power in one direction only.

sprag clutch

Freewheeling unit engaged, with engine driving rotor.Freewheeling unit disengaged, in auto-rotation position.A mechanical clutch used in reciprocating engines and direct-shaft turbine engines. It helps remove the load of the rotor when the engine is being started. In helicopters, it allows the engine to drive the rotor, but when the engine power is reduced, or the engine fails, the clutch allows the rotor to freewheel and prevents it from driving the engine. When the clutch is partially engaged, the RPM needles are split, and when it is fully engaged, the needles are married.