Changes the angle of drive from the engine to the main motor assembly. Provides RPM reduction through a train of spiral bevel gears and planetary gears. Provides a means of driving the tail rotor and the transmission accessories. Supports the main rotor assembly. The main transmission is mounted in a variety of ways according to a particular manufacturer's design.
Some transmissions contain a support case.
The case is an integral part of the transmission mounted directly to the transmission deck. The transmission may be secured to the transmission deck by a system of tubular support assemblies. In one power train system, the transmission is secured to the main rotor mast support structure. Input Drive Engine torque is transmitted through the main drive shaft to the input drive, which drives the main transmission gear trains. On systems not using a clutch assembly, a freewheel coupling is provided in the input drive assembly, which automatically engages to allow the engine to drive the rotor or disengages the idling engine during autorotational descent.