and senses engine exhaust temperature. The output
STARTER ASSEMBLY. The starter assembly is
mounted on the forward, upper, right pad of the gear
signal of each element is transmitted to the ESU.
reduction and accessory drive assembly. It is a 24-volt
Overtemperature from the thermocouple to the ESU will
result in either an APU shutdown or operation of the
dc disengaging-type starter, with an integral solenoid
bleed air valve to limit bleed air flow. (See fig. 7-24.)
and contactor assembly that is totally enclosed. The
enclosure protects this unit from exposure to dirt and
MAGNETIC PICKUP. The magnetic pickup is
foreign material. (See figs. 7-24 and 7-27.)
installed in the top center section of the reduction drive
housing assembly. The magnetic pickup generates a
The solenoid, mounted on the motor field frame,
voltage output as the ring gear passes through the
operates the lever mechanism to shift the splined drive
magnetic field surrounding the pole piece at the sensing
into mesh with the mating splint of the starter gear in
end of the pickup. The voltage output is then transmitted
the gear reduction and accessory drive assembly.
to the ESU. An overspeed/underspeed signal from the
START BYPASS VALVE. The start bypass valve
ESU will result in an APU shutdown. (See fig. 7-24.)
is a spring-loaded, normally closed, solenoid valve. The
TIME TOTALIZING METER. The time
valve is installed on the lower portion of the combustor
totalizing meter (hour meter) indicates the total
air manifold. A minimum of 2 to 4 psig compressor air
accumulated hours of APU operation. This unit is
is sufficient to start to open the valve. (A minimum of 7
installed in the fuel valve and the electrical equipment
to 9 psig will fully open the valve.)
mounting bracket, located on the upper left side of the
During the start cycle, the start bypass valve is open
reduction drive. The time totalizing meter operates on
to prevent a surge condition. When the APU reaches 90
12 to 30 volts dc.
percent of rated engine speed, plus 2 seconds, the start
ELECTROPNEUMATIC AIR BLEED
bypass valve is energized to the closed position through
VALVE. The electropneumatic servo actuated air
output current from the ESU upon actuation of the bleed
bleed valve (load control valve) consists of a piston
air valve.
operated butterfly flapper and an electropneumatic
START COUNTER. The miniature start counter
torque motor. Operating air pressure for the butterfly
is installed on the fuel valve and the electrical equip-
piston is obtained from compressor discharge air
ment mounting bracket. This assembly is located on
pressure through a port in the valve body. (See fig.
the upper left side of the reduction drive. The start
7-24.) The air pressure (filtered) is controlled by the
counter records the total APU starts and operates on
electropneumatic torque motor, which regulates the
12 to 30 volts dc.
pneumatic pressure to the piston in the air bleed valve,
thereby positioning the butterfly flapper. This
IGNITION EXCITER. The ignition exciter is
operation is performed as a function of an electrical
bolted to the turbine assembly housing. This capacitor
signal produced by the ESU. Thus, any changes in
discharge-type exciter converts a dc input to a
exhaust temperature will result in movement of the
high-energy ac output. The high-energy ac output is
butterfly flapper to control the bleed air flow from the
supplied to the igniter plug for fuel ignition. The
APU, maintaining exhaust gas temperatures within
minimum igniter rate is four sparks per second at 12
safe operating limits.
volts dc input. (See fig. 7-24.)
We have just discussed the major design and
IGNITION CABLE. The ignition cable connects
operating systems of the Sunstrand APU found on the
the ignition exciter to the igniter plug. The high-energy
LCAC-class ships. In the following sections let's shift
pulse from the exciter to the plug is supplied through the
our focus to the FFG-7 class ship and the Detroit Diesel
ignition cable. The cable is protected by a flexible metal
16V149, which furnishes its electric power.
shielding.
I G N I T E R PLUG. The igniter plug is a
10-millimeter, surface-discharge type. It is threaded into
DETROIT DIESEL 16V149
a boss in the upper left aft section of the combustor. As
If assigned aboard an FFG-7 class ship, you, the
we mentioned earlier, the igniter plug provides the spark
GSM, will need to be familiar with the Detroit Diesel
necessary for initial ignition of the fuel during the
16V 149. The FFG-7 class ship's electric power is
starting phase of the APU. (See fig. 7-24.)
supplied by four ac generators, shown in figure 7-30.
THERMOCOUPLE. A dual-element, chromel/
Each of these generators is driven by a Detroit Diesel
alumel thermocouple extends into the exhaust stream
16V149. These units are also capable of providing
