Which feature is essential for the functionality of the freewheeling unit in a helicopter?

• A. Reduces weight
• B. Prevents engine stall
• C. Allows rotation during autorotation
• D. Enhances speed control

Answer: (C)

The essential feature of the freewheeling unit in a helicopter is that it allows for rotation during autorotation. In the event of an engine failure, the freewheeling unit disengages the engine from the rotor system, allowing the rotors to continue spinning. This is crucial because it enables the pilot to safely glide to the ground by utilizing the lift generated by the rotor blades as they rotate in the airstream, even without engine power. This capability significantly enhances the safety of a helicopter during emergency situations when the engine loses power, allowing for controlled descent and landing.

The other options, while potentially relevant to helicopter performance, do not directly pertain to the critical function of the freewheeling unit. Weight reduction, engine stall prevention, and speed control are important factors in helicopter design and operation, but they are not the primary focus of the freewheeling unit's role within the rotor system.