Q15-21. During normal aircraft operation, the
copilot's sub-instrument panel operates the shutoff
hydraulically operated generator drive
valve that controls the generator drive system. The
system AC GEN switch is OFF, and the
system consists of a shutoff valve, a hydraulically
solenoid-operated shutoff valve is energized
driven motor, a heat exchanger, a control switch, and a
(closed). What other component is also
relay.
energized?
During normal aircraft operation and with the AC
GEN switch at OFF, the solenoid-operated shutoff
VARIABLE RAMP AND BELLMOUTH
valve is energized (closed). The hydraulic motor
SYSTEMS
lockout relay is also energized. Under this condition,
the generator does not operate, since hydraulic pressure
LEARNING OBJECTIVES: Recognize the
is stopped at the shutoff valve. When the AC GEN
characteristics of the variable ramp and
switch is moved to ON, the hydraulic motor lockout
bellmouth systems. Identify their components
relay and the shutoff valve is de-energized and the valve
and applicable maintenance requirements.
opens. Hydraulic fluid at 3,000 psi is directed to operate
The airflow velocities encountered in the higher
the constant speed variable displacement motor at
speed ranges of aircraft are much higher than the engine
8,000 rpm. When the fluid exits from the motor into the
can efficiently use. Therefore, the air velocity must be
return lines, it is routed through a heat exchanger and
controlled for acceptable engine performance.
ram air cooled before returning to the power system
reservoir. When ram air is not available on the deck, an
The variable inlet ramp system positions the inlet
electrically driven blower is engaged automatically to
ramp (located in the air inlet) so that it will position the
provide airflow.
shock wave to decrease the inlet air velocity to a
subsonic flow with maximum pressure energy. The
Maintenance of the generator drive system nor-
system also provides for the reflection and bypass of
mally consists of servicing, testing and checking for
surplus air not required by the engine with a minimum
proper operation, adjusting, troubleshooting, and
of drag. The inlet system in combination with the
removal and installation of system components,
bypass bellmouth system allows the inlet duct to take
flexible line couplings, and other plumbing. Servicing
aboard the maximum free airstream. The air not
and maintenance procedures and precautions are listed
required by the engine is bypassed by the action of the
in the MIM and respective (03) overhaul manuals and
bellmouth ring.
must be observed at all times to complete the
procedures efficiently and safely. Particular attention
Figure 15-14 shows the ramp sections and
should be given to cautions and warnings and specified
associated hydraulic mechanism and linkage. The aft
quality assurance considerations.
Figure 15-14.--Ramp servo and actuator.
15-16
