Main Rotor Drive
The main rotor drive system provides the transmission of power from the engine to the main rotor of the helicopter.
It consists of the systems that follow:
Engine/Gearbox Couplings
The engine/gearbox couplings system transmits rotational power from the engine to the mast and transmission assembly system. This is a flexible coupling that adjusts to and accommodates for the constant movement of the mast and transmission system as it moves due to changing flight attitudes and buffeting loads. During autorotation, it disengages the engine from the drive train so that the main rotor system can become the rotational power source for the mast and transmission assembly system and the tail rotor system.
The engine/gearbox couplings system has the following components:
Gearbox
The gearbox system transmits the power from the engine/gearbox couplings system to the main rotor and also provides the mechanical means to attach the main rotor to the helicopter structure. It is a right angle single-input drive gearbox which reduces the rotational speed by means of two stages of gear reduction: the first is a spiral bevel gear followed by a planetary spur gear assembly. At the maximum continuous input engine power of 433 HP (323 kW) the RPM reduction is from 5834 RPM to 383 RPM (104% NR) for the mast assembly and to 2613 RPM for the accessory drive gear that drives the oil pump and the hydraulic pump.
The gearbox system also provides pressurized oil and oil reservoir for the lubrication of its components and those of the engine/gearbox couplings system.
The gearbox system has the systems that follow:
Mast and transmission assembly
This assembly is composed of the mast assembly and the transmission assembly. It is located in the main rotor drive compartments and is attached to the aircraft structure by means of the mounts and attachments restraints assembly.
The transmission reduces engine RPM, changes the angle of drive from the engine to the rotor, and serves as the structural member that links the main rotor mast to the airframe. The mast assembly transmits shaft power to the main rotor system.
The mast and transmission assembly system has the components that follow:
Transmission oil system
The transmission oil system controls and monitors the flow, pressure, temperature, and contamination of the oil used for lubrication and cooling of the gears and bearings in the transmission, mast and freewheel assemblies. Refer to Transmission oil.
Mounts and Attachments
The mounts and attachments attach the components of the main rotor drive system to the helicopter structure and attenuate the vibration and shock loads that are transferred from the main rotor to the helicopter structure. Refer to Mounts and Attachments.
Main Rotor Drive Indicating
The main rotor drive indicating system contains transducers and switches that monitor the temperature, pressure, and level of contamination of the lubrication oil in the transmission and freewheel assemblies and provides signals as to the value of these measurements at a point in time or if a pre-set value has been reached. These signals are used by the power control system and the general computers system to monitor transmission running conditions. It also provides a sight glass so that lubrication levels may be checked visually by people on the ground. Refer to Main Rotor Drive Indicating.
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