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alternate ECS operation. On the ground and during slow speed flight, the ejector shutoff valve is
opened to direct bleed air to the ram air ejectors to induce cooling airflow through the primary and
secondary heat exchangers. The warm air temperature control valve is used to mix engine bleed air
with primary heat exchanger output air to regulate the temperature of air in the warm air manifold.
2.12.3 Primary Heat Exchanger. The primary heat exchanger is located at the base of the right
vertical tail and is used to reject heat from engine bleed air to ram air from one of two inlets.
During medium to high speed flight, ram air cooling is provided by the main ram inlet which draws
air from the engine intake. During slow speed flight and ground operations, ram air cooling is provided
by an auxiliary ram inlet which draws free stream air from the top of the fuselage. A ram air ejector in
the ram air exhaust duct is used to induce airflow in conditions in which more cooling is required: on
the ground, during slow speed flight, and during windshield anti-ice operation with either throttle
above IDLE.
2.12.3.1 ECS Auxiliary Duct Doors. Two ECS auxiliary duct doors are located on the upper surface
of the fuselage forward of the base of the vertical tails and immediately in front of the primary and
secondary heat exchangers. The ECS auxiliary duct doors are electrically actuated and open into the
free stream, closing the main ram air inlets and exposing the auxiliary ram air inlets.
On the ground, the ECS auxiliary duct doors are open with the BLEED AIR knob in any position
except OFF. Inflight the doors are positioned based on Mach number and throttle setting. The doors
are always open below 0.33 Mach and are always closed above 0.40 Mach. Between 0.35 and 0.40 Mach,
the doors are open if either throttle is near MIL (THA greater than 25°).
The ECS auxiliary duct doors should operate symmetrically. If either ECS auxiliary duct door is not
in the commanded position for greater than 8 seconds, an ECS DR advisory is displayed along with an
ECS BIT indication of DEGD. If the door(s) return to the commanded position, the ECS DR advisory
is removed.
2.12.4 Warm Air Subsystems. Air leaves the primary heat exchanger at a greatly reduced temperature.
Warm air from the primary heat exchanger is routed directly to the following systems: external
fuel tank pressurization, internal fuel tank pressurization, canopy seal, g-suit, radar waveguide
pressurization, and OBOGS.
The ECS controller modulates the warm air temperature control valve (Item 21) to mix air from the
primary heat exchanger with engine bleed air to regulate the temperature in the warm air manifold.
The warm air manifold supplies air for windshield anti-ice and rain removal, gun gas purge, RECCE
bay heating, ECS turbine anti-ice, and cabin heating.
2.12.5 ECS Compressor/Turbine. The ECS controller modulates airflow through the ECS flow
modulator valve (Item 4) to control ECS flow and the speed of the ECS compressor and turbine.
Compressor discharge air is directed to the secondary heat exchanger for additional cooling. Cool air
from the secondary heat exchanger is directed to the ECS turbine and is used as the primary source of
OBOGS air inflight.
Expansion through the ECS turbine drives the compressor and greatly reduces the temperature of
the airflow, typically to below freezing. The ECS controller regulates the ECS turbine output
A1-F18EA-NFM-000
I-2-92 ORIGINAL
temperature and prevents ECS icing by adding warm air through the anti-ice add heat valve (Item 51).
Output temperature is regulated to 0°F during high altitude operations and 35°F during low altitude
operations where ECS icing would be likely. The output of the ECS turbine is cold, dry conditioned air,
used for cabin, FLIR, and avionics cooling.
2.12.6 Secondary Heat Exchanger. The secondary heat exchanger is located at the base of the left
vertical tail and is used to reject heat from ECS compressor air to ram air. Operation of the secondary
heat exchanger is identical to operation of the primary heat exchanger. However, excess ECS system
moisture is sprayed onto the secondary heat exchanger to increase system cooling. This moisture may
be seen exiting the secondary heat exchanger exhaust duct when the throttles are advanced during
ground operations.
2.12.7 ECS Operating Modes. The ECS has three operating modes: AUTO, MAN (manual), and
OFF/RAM. Each mode is selected by the corresponding position of the ECS MODE switch. On the
ground only, APU compressor air may be used instead of engine bleed air to run the ECS and cool the
avionics (BLEED AIR knob in AUG PULL).
2.12.7.1 ECS AUTO Mode. The AUTO mode is the normal operating mode of the ECS. With the ECS
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本文链接地址：
NATOPS Flight Manual 飞行手册 1(78)
