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GENERATOR DRIVE SYSTEM
(HYDRAULICALLY OPERATED) The ac generator drive system shown in figure 12-64 is hydraulically operated by pressure from the hydraulic power system. The AC GEN switch on the copilots sub-instrument panel operates the shutoff valve that controls the generator drive system. The system consists of a shutoff valve, a hydraulically driven motor a heat exchanger, a control switch, and a relay. During normal aircraft operation and with the AC GEN switch at OFF, the solenoid-operated shutoff valve is energized (closed). The hydraulic motor lockout relay is also energized. Under this condition, the generator does not operate, since hydraulic pressure is stopped at the shutoff valve. When the AC GEN switch is moved to ON, the hydraulic motor lockout relay and the shutoff valve is de-energized and the valve opens. Hydraulic fluid at 3,000 psi is directed to operate the constant speed variable displacement motor at 8,000 RPM. When the fluid exits from the motor into the return lines, it is routed through a heat exchanger and ram air cooled before returning to the power system reservoir. When ram air is not available on the deck, an electrically driven blower is engaged automatically to provide airflow. Maintenance of the generator drive system normally consists of servicing, testing and checking for proper operation, adjusting, troubleshooting, and removal and installation of system components, flexible line couplings, and other plumbing. Servicing and maintenance procedures and precautions are listed in the MIM and respective (03) overhaul manuals and must be observed at all times to complete the procedures efficiently and safely. Particular attention should be      
Figure 12-65.-Ramp servo and actuator. given to cautions and warnings and specified quality assurance considerations. VARIABLE RAMP AND BELLMOUTH SYSTEMS The airflow velocities encountered in the higher speed ranges of aircraft are much higher than the engine can efficiently use. Therefore, the air velocity must be controlled for acceptable engine performance. The variable inlet ramp system positions the inlet ramp (located in the air inlet) so that it will position the shock wave to decrease the inlet air velocity to a subsonic flow with a maximum pressure energy. The system also provides for the reflection and bypass of surplus air not required by the engine with a minimum of drag. The inlet system in combination with the bypass bellmouth system allows the inlet duct to take aboard the maximum free airstream. The air not required by the engine is bypassed by the action of the bellmouth ring. Figure 12-65 shows the ramp sections and associated hydraulic mechanism and linkage. The aft ramp is positioned by the hydraulic actuator. The actuator is controlled by the electrically operated torque motor in the hydraulic servo valve. Movement of the aft ramp positions the perforated ramp through mechanical linkage. The position of ramps is automatically selected through the ramp system by a temperature signal from the air data computer set. The ramp actuator is a double-acting cylinder attached to the ramp linkage in such a way as to be free floating. This arrangement causes equal action on the linkages attached to each end of the cylinder. Figure 12-65 shows the complete hydraulic portion of the variable ramp system, showing the actuator extending. Actuating the torque motor armature positions the flapper valve in the servo valve, initiating the proper servo action to extend, retract, or hold the actuator in position. As the actuator moves, it positions the ramp through its mechanical linkage. Electrical components in the circuit translate an electrical signal, proportional to the ramp movement, to balance the amplifier circuits and hold the servo and ramp at this designated position until a new temperature signal initiates a change. If electrical or hydraulic power failure occurs, air loads on the ramps will tend to cause the ramps to move toward the retract position. The variable bypass bellmouth system monitors the inlet duct operation and indicates any corrective action,
Figure 12-67.Bomb bay door hydraulic schematic. bypassing more or less of the airflow at the engine face, as shown in figure 12-66. The system adjusts the bypass bellmouth ring position to maintain a preselected inlet airspeed and stable mass airflow through the inlet duct throughout the flight range of the aircraft. Movement of the bellmouth ring also controls the amount of secondary air bypassed around the engine for cooling. The valves in the bellmouth controller (fig. 12-66) are positioned by the inlet duct pressure differential and, in turn, direct hydraulic pressure to the bellmouth ring actuator, increasing or decreasing the bypass opening. The holes drilled in the bypass ring assure cooling air to the engine compartment when the ring is in the closed position. Auxiliary air doors (not shown in fig. 12-66) open to supplement the bellmouth bypass system at low airspeeds and during ground operation to prevent overtemperature and/or reverse airflow in the engine compartment. These doors are located on the underside of the fuselage and open in flight, at high speeds, as required to prevent excessive air pressure differential between the engine compartment and outside ambient. The auxiliary doors are held closed by hydraulic actuators, which are sized to develop a force equivalent to the door area times the designated differential pressure. When the pressure limit is exceeded, the door is pushed open (varying amounts) to keep the engine compartment pressure from becoming excessive. As the engine compartment pressure is lowered, the hydraulic actuators will pull the doors closed. The variable ramp, bellmouth bypass, and auxiliary air door systems are powered by the utility hydraulic system. Malfunctions in these systems will normally require personnel of the AE, AD, and AM ratings working together to operationally test the system and provide proper corrective maintenance. |
 
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