What purpose does the free-wheeling unit serve?

The correct answer identifies the primary role of the free-wheeling unit in helicopter systems, which is to allow engines to disengage from the transmission under specific conditions. This disengagement is crucial during scenarios like engine failure or in the event of an overspeed condition. By disconnecting the engine from the transmission, the free-wheeling unit helps maintain rotor system functionality, allowing the aircraft to glide safely to the ground rather than forcing the engine to drive the rotor blades. This is essential for safety and helps to enhance the controllability of the helicopter in emergency situations.

The other options discuss various functions that are not aligned with the actual purpose of the free-wheeling unit, such as maximizing torque, adjusting rotor speed, or preventing transmission overheating, which are handled by other systems within the helicopter's design. Understanding the function of the free-wheeling unit is important for recognizing how helicopters manage power and maintain control during critical phases of flight.