What is the purpose of the free-wheeling unit in a helicopter drive system?

The purpose of the free-wheeling unit in a helicopter drive system is to disconnect the rotor from the engine whenever the engine slows down or stops, keeping the rotor turning at its required RPM. This is important for maintaining the helicopter's stability and control, especially in situations where the engine may fail or experience a sudden reduction in power. By allowing the rotor to continue spinning independently, the free-wheeling unit helps to provide lift and control, allowing the pilot to execute a controlled descent or landing, even in the event of an engine failure.

This function is critical for safe helicopter operation because it allows the rotor to take advantage of its momentum to sustain flight characteristics during engine issues, maintaining enough rotor speed for autorotation, which can be a life-saving feature in emergencies.