Gearbox Section
power system, and 28-V dc tank power receptacle. The
secondary 28-V dc system is also distributed over a
The reduction gear and accessory drive assembly
common, redundant bus.
reduces the output rotational speed (61,091 rpm) of the
rotor assembly to the speeds necessary to drive the APU
AUXILIARY POWER UNIT
generator and accessories. The two-piece reduction
drive housing is machined from aluminum sand
castings. The reduction drive inlet pinion drives three
As shown in figure 6-18, the gas turbine generator
planetary gears which, in turn, drive an internally
sets are mounted port and starboard on the LCAC. Each
splined ring gear. The ring gear is centrally splined to a
set consists of an ac generator, air inlet chamber,
short output shaft. The external gear of the output shaft
combustor assembly, turbine assembly, and reduction
drives the oil pump drive gear. The internal splines of
gear drive assembly. The gas turbine engine is a radial-
the output shaft connect the driven equipment to the
flow, 150-hp, single-stage compressor, single-stage
engine.
turbine. The APU is a Turbomach Model No.
T-62T-40-7. Filtered air within the compartments is used
The upper portion of the reduction gear drive
for turbine inlet combustion air and generator cooling.
assembly contains the accessory drive. The output
An enclosure assembly houses each gas turbine engine
shaft transmits power through an intermediate gear
and provides mounting of the turbine, exhaust
to the fuel pump drive and starter gears, which
connections, ship pipes, drain connections, and
convert the reduction gear output speed to 6,000
electrical connections. The access doors provided on the
rpm. This is the speed required to drive the APU's
enclosure allow for inspection and maintenance of the
accessories, The fuel pump gear operates at 4,200
gas turbine components.
rpm. With the starter disengaged, the starter gear is
free to rotate with the intermediate gear. When the
starter is engaged, the starter gear drives the
APU Turbine Engine
accessory drive gear train to supply the necessary
starting torque to the GTE.
The major components of the gas turbine engine are
The gears and bearings in the accessory drive are
the generator, turbine, combustor, and reduction gear
lubricated by an air-oil mist from the reduction drive
drive. In addition, electrical control devices,
assembly. To prevent the mist from leaking, seals are
accessories, and associated plumbing and wiring are
mounted in the reduction drive housing at the ends of
also part of the gas turbine assembly. The gas turbine
the output shaft and the fuel pump drive and starter
incorporates an integral lubrication system. The
gears. The fuel pump and engine acceleration control
lubricating oil is contained in an integral oil sump on the
assembly, which is mounted in tandem with the fuel
bottom of the reduction gear and accessory drive
pump, is mounted on the left forward pad of the
housing. A 24-V dc electrical control system provides
reduction gear housing. The starter assembly is mounted
electrical energy for ignition and for operating the
on the right forward pad.
electrical components. Although a fuel system is
integral to the gas turbine engine, a fuel supply must be
APU Lubrication System
connected to the engine.
The APU gas turbine assembly consists of an air
The APU lubricating oil system provides lubrication
inlet assembly, rotor assembly, diffuser, turbine nozzle
to the high-speed input pinion, the reduction and
assembly, and input pinion. The air inlet housing is a
contoured, cylindrical casting with forward and aft inlet
integral lubrication system consists of an oil pump, a
flanges. The flanged forward end of the air inlet housing
filter, a filter bypass relief valve, a pressure relief valve,
is bolted to an adapter. The adapter is bolted to the aft
an oil pressure switch, an oil distribution ring assembly,
end of the reduction drive housing. The aft end of the air
and an oil sump. All components of the APU lubrication
inlet housing is externally flanged to permit attachment
system are contained within the reduction gear and
of the combustor assembly. This configuration allows
accessory drive assembly.
the air inlet housing to serve as a rigid member between
A high oil temperature switch is installed in the
the reduction drive assembly and the combustor
reduction gear drive. The switch is electrically
assembly. An air inlet screen assembly covers the intake
portion of the air inlet housing.
connected to the electronic sequence unit (ESU) to
