planetary gears which, in turn, drive an internally
electrical control system provides electrical energy for
ignition and for operating the electrical components.
splined ring gear. The ring gear is centrally splined to a
Although a fuel system is integral to the gas turbine
short output shaft. The external gear of the output shaft
engine, a fuel supply must be connected to the engine.
drives the oil pump drive gear. The internal splines of
the output shaft connect the driven equipment to the
The APU gas turbine assembly is shown in figure
7-17. The APU gas turbine consists of an air inlet
The upper portion of the reduction gear drive
assembly, rotor assembly, diffuser, turbine nozzle
assembly, and input pinion. The air inlet housing is a
assembly contains the accessory drive. The output shaft
transmits power through an intermediate gear to the fuel
contoured, cylindrical casting with forward and aft inlet
flanges. The flanged forward end of the air inlet housing
p u m p drive and starter gears, which convert the
reduction gear output speed to 6,000 rpm. This is the
is bolted to an adapter. The adapter is bolted to the aft
end of the reduction drive housing. The ail end of the air
speed required to drive the APU's accessories. The fuel
inlet housing is externally flanged to permit attachment
pump gear operates at 4,200 rpm. With the starter
of the combustor assembly. This configuration allows
disengaged, the starter gear is free to rotate with the
intermediate gear. When the starter is engaged, the
the air inlet housing to serve as a rigid member between
t h e reduction drive assembly and the combustor
starter gear drives the accessory drive gear train to
assembly. An air inlet screen assembly covers the intake
supply the necessary starting torque to the GTE.
portion of the air inlet housing.
lubricated by an air-oil mist from the reduction drive
assembly. To prevent the mist from leaking, seals are
mounted in the reduction drive housing at the ends of
The reduction gear and accessory drive assembly
the output shaft and the fuel pump drive and starter
reduces the output rotational speed (61,091 rpm) of the
rotor assembly to the speeds necessary to drive the APU
assembly, which is mounted in tandem with the fuel
generator and accessories. The two-piece reduction
pump, is mounted on the left forward pad of the
d r i v e housing is machined from aluminum sand
reduction gear housing. The starter assembly is mounted
castings. The reduction drive inlet pinion drives three
on the right forward pad.
Figure 7-17.--APU gas turbine engine assembly.