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,
12-75
