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.
BOMB BAY SYSTEM
The bomb bay system is shown in figure 12-67. The
doors are actuated by mechanical linkage at each end.
12-77
