Where is the intermediate gearbox located on a typical rotary aircraft?

• A. At the base of the tail pylon
• B. In the main rotor hub
• C. Under the cockpit floor
• D. In the nose section

Answer: (A)

The tail rotor drive system is what this asks about. In a typical rotary aircraft, power from the engine is reduced by the main gearbox to drive the main rotor, while a separate tail rotor drive path takes a portion of that power to the tail rotor. The intermediate gearbox is the gear stage that sits in the tail section to receive power from the drive shaft and supply the proper speed and direction to the tail rotor. Placing this gearbox at the base of the tail pylon keeps the tail-rotor drive shaft short, aligns the gears with the tail rotor, and supports maintenance access and structural integration at the tail where loads are concentrated. Other locations would require awkward long drives and create routing and structural challenges, so they’re not typical.