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2-42 Change 2
Section VII POWERTRAIN SYSTEM
2.41 POWERTRAIN.
The powertrain consists of inputs from two engines, a main transmission, intermediate gear box, tail gear box and connecting drive shafting. Power from the engines is trans-mitted to the main transmission module through input mod-ules. The main transmission is mounted on top of the cabin between the two engines (Figure 2-1). It mounts and pow-
ers the main rotor head, changes the angle of drive from the engines, reduces rpm from the engines, powers the tail ro-tor drive shaft and drives the accessory module. The main transmission consists of .ve modules: two input modules; the main module; and two accessory modules. The main transmission has a built-in 3° forward tilt.
2.41.1 Input Module. The input modules are mounted on the left and right front of the main module and support the front of the engines. They contain an input bevel pinion and gear, and a freewheel unit. The freewheel unit allows engine disengagement during autorotation, or in case of a nonoperating engine, the accessory module will continue to be driven by the main rotor. The input module provides the .rst gear reduction between engine and main module.
2.41.2 Accessory Module. One accessory module is mounted on the forward section of each input module. Each accessory module provides mounting and drive for an elec-trical generator and a hydraulic pump package. A rotor speed sensor is mounted on the right accessory module and provides signals for the VIDS.
2.41.3 Main Module. The main module contains the necessary gearing to drive the main rotor and tail rotor systems. It provides a reduction in speed from the input module to the main module and the tail drive shaft.
2.42 MAIN TRANSMISSION LUBRICATION SYSTEM.

CAUTION
Prolonged nose-down attitudes of 5 de-grees or more may cause high main trans-mission oil temperature.

The transmission incorporates an integral wet sump lu-brication system that provides cooled, .ltered oil to all bearing and gears. The ac generators on the accessory mod-ules also receive oil for cooling. Oil under pressure is sup-plied through internally cored oil lines, except for the pres-sure and return lines of the oil cooler. Refer to servicing diagram for oil speci.cation and servicing (Table 2-4). The lubrication system includes two lubrication pumps that are combination pressure and scavenge types operating in par-allel. The main transmission may run at cruise .ight for 30 minutes with loss of all oil. Main transmission oil pressure may .uctuate when the aircraft is known to be in a nose-up attitude (i.e., slope landings or hover with an extreme aft CG). Pressure regulating and bypass valves protect the lube system by returning excess high pressure oil back to the inlet side of the pump. A two-stage oil .lter and various strainers in the sump prevent contamination. The oil .lter has a visual impending bypass indicator (red button) that protrudes when the .rst stage .lter becomes contaminated. When the button pops the .lter element must be replaced to reset. A thermal lockout prevents button popping when oil is cold and thick. The oil cooler uses a blower driven by the tail rotor drive shaft to cool oil before it enters the various modules. The oil cooler has a thermostatic bypass valve that directs oil .ow around the cooler when the oil tempera-ture is below 71°61°C. Other warning and monitoring sys-tems on the main transmission are: MAIN XMSN OIL TEMP and PRESS caution legends, and XMSN TEMP and PRESS oil temperature gages. An oil pressure switch on the left accessory module, the farthest point from the pumps, causes the MAIN XMSN OIL PRES caution leg-end to go on when the pressure drops to 1462 psi. The transmission oil temperature warning system is triggered by an oil temperature switch at the oil cooler input to the main module, near the tail takeoff drive shaft .ange. A caution legend, MAIN XMSN OIL TEMP goes on when trans-mission oil temperature reaches 120°C. Temperature for the gage is sensed between the sump and the pump. Pres-sure readings are taken at the main module manifold. Elec-trical power for the warning systems, except chip detection, is from the No. 2 dc primary bus, through the MAIN XMSN circuit breaker on the overhead circuit breaker panel.
　
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