mixture by the start fuel nozzle during a start. Fuel to
compressor wheel and secure it to the rotor shaft flange.
the combustor is supplied through an external fuel
The turbine wheel is pressed onto the aft end of the rotor
manifold assembly. The outlet tips of the fuel manifold
shaft and aligned by three dowels. A threaded bolt
assembly are equally spaced around the combustor
fastens the turbine wheel to an internally threaded plug
housing. The tips are swagged to form an orifice at their
in the aft end of the rotor shaft.
ends. The fuel manifold assembly provides six jets of
A circular, compressor-to-turbine air seal separates
fuel into the throats of six small venturis, which atomize
the compressor section from the turbine section. The
the fuel at the aft end of the combustor liner. A combustor
seal is radially positioned on the nozzle assembly. The
drain port in the lowest point of the combustor housing
axial position of the seal on the rotor shaft is maintained
provides a drain for the fuel that might accumulate in
by compressor pressure, which forces the seal against a
the combustor during a false start or other malfunction.
shoulder on the turbine nozzle. The cantilevered
Thermocouple. A dual-element thermocouple is
arrangement of the rotor assembly in the air inlet
housing places both the forward and aft bearings in areas
mounted in a boss at the aft, right side of the combustor
of minimal temperature. Cooling and lubrication of the
housing. The function of the thermocouple is to sense
rotor shaft bearings are accomplished by a air-oil mist
exhaust temperatures. The two elements of the
from the reduction gear and accessory drive housing,
thermocouple are mounted on bosses at the aft, right side
through the output pinion (within the rotor shaft),
of the combustor housing. One element functions as an
through the aft and forward bearings, and back into the
overtemperature detector. The other element functions
gear reduction and accessory drive housing.
in conjunction with the load control valve.
COMBUSTOR ASSEMBLY. The combustor is
DIFFUSER AND TURBINE NOZZLE ASSEM-
an annular air atomizing-type. It encases the combustor
BLY.- The diffuser is a circular casing consisting of 36
liner assembly. The combustor liner is secured in the
vanes on the outer periphery and 17 vanes on the
combustor housing by four locating bolts. An external
forward face. The turbine nozzle is a brazed, matched
flange at the forward end of the combustor housing
assembly consisting of a forward circular plate and an
mates with an external flange on the aft end of the
aft circular plate. The diffuser is secured in the aft
turbine assembly. The combustor is secured to the
position of the air inlet housing by six threaded nozzle
assembly by a quick-release, V-type clamp (marmon)
retaining pins. These pins pass through the diffuser and
that fits over the flanges. The outer wall of the
also secure the turbine nozzle assembly concentric with
combustor liner fits snugly under the outer aft edge of
the rotor assembly. The turbine nozzle assembly seats
the turbine nozzle assembly. The mating of the
against a mating of the diffuser at the fore and aft ends
combustor housing inner wall with the aft end of the
only (not radially).
turbine nozzle assembly forms a circular exhaust duct
GEAR REDUCTION AND ACCESSORY
for the flow of the exhaust gases as they leave the turbine
DRIVE ASSEMBLY. The gear reduction and
portion of the rotor assembly and flow out of the APU.
accessory drive assembly reduces the output rotational
(See fig. 7-24.)
speed (61,091 rpm) of the rotor assembly to the speeds
Airflow. Intake air passes through the vanes of the
necessary to drive the APU generator and accessories.
diffuser, flows between the walls of the combustor
The two-piece reduction drive housing is machined
housing and liner, and reverses direction to enter the
from aluminum sand castings.
burner section of the combustor. This flow of air cools
Input Pinion Assembly. The reduction drive input
the combustor housing and liner. Air is also directed
pinion drives three planetary gears that drive an
between the inner walls of the combustor housing and
internally splined ring gear. The ring gear is centrally
liner; then it flows to the aft surface of the turbine nozzle
splined to a short output shaft.
assembly. Additional cooling of the turbine nozzle is
accomplished by a flow of cooling air that is forced
Output Shaft Assembly. The external gear of the
around the aft, internal edge of the diffuser, through
output shaft drives the oil pump drive gear. The internal
equally spaced holes in the ring on the combustor inner
splines of the output shaft provide for connecting the
liner assembly, and over the aft side of the forward plate
driven equipment to the engine. The aft end of the output
of the nozzle assembly.
shaft is supported by a ball bearing in the bearing carrier
of the planetary gear system. The middle of the output shaft
Fuel Delivery and Combustion Process. An
is supported by a ball bearing mounted in the forward,
igniter plug, which is mounted in a boss at the aft, left
internal support web of the reduction drive housing.
side of the combustor housing, ignites the fuel-air
7-30
