Transmission Assembly

The transmission assembly is installed in the lower main rotor drive compartment. It is a two-stage reduction, single-input drive gearbox which transmits the 433 Hp (323 kW) maximum continuous power from the main driveshaft to the mast pole. It reduces the rotational speed at the maximum continuous power from 5610 RPM to 369 RPM (100% NR) for the mast assembly and to 2613 RPM for the accessory drive. The transmission assembly has provisions for installation of components of the main rotor, main rotor drive, and flight controls systems and includes the primary parts that follow:

• Top case

• Main case

• Input quill

• Spiral bevel gear

• Planetary assembly

• Accessory drive gear

The input quill at the rear of the transmission assembly mates with the main driveshaft which brings power from the engine via the freewheel assembly. At the bottom of the main case is the first reduction stage 90 degree spiral bevel gear. Immediately above this is the second reduction stage planetary gear assembly which reduces the speed of the output of the first reduction stage. At the first reduction stage there is a pinion accessory drive gear that drives the oil pump and provides the drive shaft for the hydraulic pump. The output of the second stage reduction is directed to the rotor mast.

The casing of the transmission assembly is made of a top case and a main case, both made of magnesium. The top case has provisions for attachment of the transmission assembly to the pylon link assemblies, for attachment of the swashplate and support assembly, mast assembly, oil filter housing and manifold assembly, and cyclic and collective linkage. A filler cap is installed on the right side of the top case for the servicing of the transmission assembly. Together, the top case and the main case have provisions for installation of components of the transmission oil and transmission indicating systems and provisions for the lubrication oil reservoir in the transmission assembly. A sight gauge is installed on the right side of the main case to give an oil level indication to the crew and personnel on ground.