the engine mounted accessories, are attached to the case, which has four mounting pads, one on each
side, one on the top, and one on the bottom. The side pads must be used, and the helicopter
manufacturer has his choice of using the top and bottom pads. The accessory gearbox contains most of
the lubrication system components and houses the power turbine and gas producer gear trains. The
power turbine gear train, shown in figure 7.5, reduces engine N2 speed from 35,000 to 6,000 rpm. The
power turbine gear train drives the torquemeter, N2 tachometer-generator, and N2 governor. The gas
producer gear train, illustrated in figure 7.6, drives the oil pumps, fuel pump, gas producer fuel control,
N1 tachometer generator, and starter-generator. During starting, the starter-generator cranks the engine
through the gas producer gear train.
As shown in figure 7.1, the turbine section is mounted between the combustion section and
the power and accessory gearbox. The turbine section consists of a two-stage gas producer turbine,
shown in figure 7.7, and a two-stage power turbine, shown in figure 7.8. Power to drive the compressor
rotor is furnished by the gas producer turbine rotor through a direct drive. The power turbine rotor
converts the remaining gas energy into power which drives the power output shaft. The exhaust gases
are directed into the exhaust collector support and through the twin exhaust ducts on the top of engine.
The power turbine is a free turbine, because it is free to rotate at a different speed than the
gas producer turbine rotors.
The gas producer turbine nozzles (1st and 2nd) are housed in the gas producer turbine
support. The power turbine (3rd and 4th stage) nozzles are housed in the power turbine support and the
aft end of the exhaust collector support. These nozzles may be seen by looking at figures 7.7 and 7.8.
These nozzles increase the velocity of the expanding gas and direct the gas at the proper angle onto the
The oil system is a circulating dry-sump type with an external oil tank and cooler. The
engine oil-system schematic is illustrated in figure 7.9. This system is designed to supply oil for
lubrication, scavenging, and cooling as needed.