NAVAIR Ql-F74AAD-I
CHAPTER 2
Systems
2.1 AIR INLET CONTROL SYSTEM
The purposeo f the AICS is to decelerates upersonica ir
and to provide even, subsonic airflow to the engine
throughoutth e aimrat?S ight envelope.T he AICS consists
of two variable-geometryin takes,o ne on eachs ideo f the
fuselagea tt he inters&ion ofthe wing glove and fuselage.
Intake inlet geometry is varied by three automatically controlled
hinged ramps on the upper side of the intakes. The
rampsa m positionedt o decelerates upersonica ir by creating
a compressionfi eld outsidet he inlet andt o regulatet he
amount and quality of air going to the engine. The tectangular
intakes are spaced away from the fuselage to minimize
boundary layer ingestion and are highly raked to
optimize operation at high angle of attack
Inlet ramps are positioned by electrohydraulic actuators
that respond to fixed schedules in the AICS programmers.
Separate programmers, probes, sensors,
actuators, and hydraulic power systems provide completely
independent operation of the letI and right air
inlet control systems. Figure 2-1 shows the basic elements
of AICS mechanization.
Electrical power for the AICS programmers is provided
by the ac and dc essential No. 2 buses. The ramp
stow function is powered by the dc essential No. 1 bus.
Hydraulic power is supplied individually to the left
AICS from the combined hydraulic system and to the
right AICS from the flight hydraulic system. The leg
AICS programmer also functions as a wing-sweep
backup computer.
2.1.1 Normal AICS Operations. No pilot control
is required during the normal (AUTO) mode of operation.
Electronic monitoring in the AICS detects failures
that would degrade system operation and performance
(refer to AICS BIT). AICS caution lights (L and R INLET,
L and R RAMPS) and INLET RAMPS switches
are shown in Figure 2-2.
Sectional side views ofrepresentative variable geometry
inlet configurations scheduled by AICS programmers
and descriptive nomenclature are shown in
Figure 2-3.
2.1.1.1 Ground and Low-Speed Operation. During
ground static and low-speed (Mach dO.35) operation,
the inlet rampsa rem echanically restrainedin the stowed
(retracted)position.T he predominanta irflow is concentrated
about the lower lip of the inlet duct and is supply
mented by reverse airtlow through the fixed bleed door,
around the forward lip of the third ramp. As flight speed
is increasedt o 0.35 Mach, hydraulic power is ported to
the ramp actuators but the ramps are not scheduled out
of the stowed position until Mach 0.5 (see Figure 2-4).
The fixed bleed doorbleeds low-energy, boundary layer
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