What is the main purpose of the transmission reduction gearbox?

• A. Reduce the main driveshaft RPM and change the direction of drive
• B. Convert mechanical drive to electrical power
• C. Power the aircraft pitot-static system
• D. Counteract induced drag

Answer: (A)

The main purpose of the transmission reduction gearbox in a helicopter, such as the TH-73A, is to reduce the main driveshaft RPM and change the direction of drive. This component allows the engine, which often runs at a much higher RPM, to transmit power to the rotor system efficiently at a lower RPM that is suitable for rotor operation. This reduction not only optimizes performance but also enhances the safety and longevity of the rotor system by preventing excessive speeds that could lead to mechanical failure. The ability to change the direction of drive is also crucial, as it allows for the necessary mechanical configuration to transfer power from the engine to the main rotor and potentially other systems.

While the other options present different systems or functions, they do not pertain to the specific functions of the reduction gearbox. For instance, converting mechanical drive to electrical power relates more to generators or alternators, while powering the aircraft pitot-static system involves different pneumatic or electronic systems. Counteracting induced drag is a consideration in aerodynamic design but not directly related to the function of the transmission reduction gearbox.