Bleed air is extracted from the high-pressure compres-sor to perform engine-associated services and to supply hot, high pressure air for operation of auxiliary equipment.
Fifth-stage bleed air supplies hot air for the engine anti-icing system and is used to draw cooling air through the aircraft hydraulic heat exchangers to cool flight and combined fluids and to ventilate the nacelle when weight is on wheels (Figure 2-22). Ninth-stage bleed air supplies hot air to the environmental control system, provides air for crossbleed engine starts, and draws air through the integrated drive generator heat exchanger (ventral fin) when weight is on wheels.
2.6.1 Engine Anti-Ice
The fan IGV and nosedome are susceptible to icing under a wider range of conditions, particularly at static or low speed with high engine rpm, than that which cause ice to form on external surfaces of the airframe. Ice formation at the fan face can restrict engine maximum airflow, which results in a thrust loss, decreased stall margin, and dislodgment of ice, which can damage the compressor. The engine anti-icing system is designed to prevent the formation of ice rather than de-ice the IGV and nose dome. Hot bleed air (5th stage) is passed through the hollow IGV to the nose dome and is discharged into the engine along the vanes and at the rotor hub. Cockpit control of the engine anti-icing system is effected through the ANTI-ICE switch (Figure 2-23).
NAVAIR 01−F14AAD−1
ORIGINAL 2−28
Figure 221.Autothrottle Controls and Indicators (Sheet 1 of 2)
NAVAIR 01−F14AAD−1
NOMENCLATURE FUNCTION
1 THROTTLE MODE switch AUTO Engine thrust is automatically regulated by the throttle control computer to maintain optimum angle of attack for landing.
BOOST Normal operating mode. Reduces effort required to move throttles manually with friction control aft.y
MAN Movement of each throttle is mechanically transmitted to the respective engine cross−shaft by a push−pull cable.
2 THROTTLE TEMP switch Used with the AUTO throttle mode to effect throttle computer gain changes to compensate for air temperature
compensate for air temperature.
HOT Increases normal throttle computer gain.
HOT Increases normal throttle computer gain.
NORM Normal throttle computer gain.
NORM Normal throttle computer gain.
COLD Decreases normal throttle computer gain.
3 AUTO THROT caution light Auto throttle mode is disengaged. During preflight check, remains illuminated for 10 seconds, then goes off and throttle mode switch automatically returns to BOOST.
10 seconds, then goes off and throttle mode switch automatically returns to BOOST.
Note
If the auto throttle is disengaged by deselecting the throttle mode switch, the AUTO THROT light will not illuminate.
4 CAGE/SEAM switch When in TLN master mode with the throttle mode switch in AUTO, selecting the CAGE/BRST position on the CAGE/SEAM switch reverts the throttles to the BOOST mode.
5 Autopilot emergency paddle Reverts throttle system from AUTO or BOOST mode to MAN mode only while disengage depressed and with weight on wheels.
Figure 2−21. Autothrottle Controls and Indicators (Sheet 2 of 2) Note
Because of its adverse effects on engine perfor
mance, the engine anti−icing system should be used only when icing conditions exist or are anticipated.
During engine start, the engine anti−ice valve remains open to bleed the compressor to prevent engine stall. The valve closes when the engine approaches idle rpm. In flight, the valve is normally closed unless the ANTI−ICE switch is in ORIDE/ON, or AUTO/OFF, when the ice detector probe in the left inlet is activated. Ice accumulation on the ice detector illuminates the INLET ICE caution light. The engine anti−icing control valve on the engine is powered closed (fails open) from the essential dc No. 2 bus through the ENG/PROBE/ANTI−ICE circuit breaker (RG2).
2.6.2 Environmental Control System Leak Detection
Thermal detection circuits are routed in proximity to ECS ducts and components to provide cockpit indications of high−temperature air leaks. Normal air temperatures range
from 520° to 1,180_ F inside the bleed air portion of the ECS, and from 400_ to 500_ F inside the hot air portion (400_ F manifold).
The entire bleed air portion of the ECS, from engine bleed air shutoff valves to the primary heat exchanger, is mon
itored by two detection systems. Fire detection circuits moni
tor the bleed air system from each engine to its respective firewall. When a fire detection circuit in an engine compart
ment senses temperatures above threshold, the appropriate L or R FIRE warning light illuminates (refer to fire detection system). The remainder of the bleed air system, from engine firewalls to the primary heat exchanger, is monitored by bleed air leak−sensing elements. When the bleed air leak−detection circuit detects temperatures in excess of 575_ F, the BLEED DUCT caution light illuminates.
The hot air portion of the ECS is monitored by hot air leak−sensing elements. The hot air system extends from the primary heat exchanger through the 400_ manifold to the cockpit floor. When the hot air detection circuit detects temperatures in excess of 255_ F, the BLEED DUCT caution light illuminates.
NAVAIR 01−F14AAD−1
ORIGINAL 2−30
Figure 222.Engine Bleed Air/Compartment Ventilation
2.7 ENGINE COMPARTMENT VENTILATION
Each engine compartment is completely isolated from the primary air inlet, and the efficiency and cooling of the variable−area exhaust nozzle are not dependent upon nacelle airflow. Therefore, within the bounds of the forward firewall (landing gear bulkhead) and the nozzle shroud, the cooling system for each engine compartment is a separate entity.
Cooling requirements for the turbofan engine are mini−
mized by the annular fan bypass duct. Figure 222 shows cooling airflow patterns through the engine compartment during ground and flight operations. Two air−cooled heat exchangers are also shown; however, only the hydraulic heat exchanger cooling airflow is associated with engine nacelle cooling. Fire access doors are on the outboard side of the nacelles at the forward end to permit application of fire suppressing agents by ground personnel in event of an engine compartment fire.
2.7.1 Engine In−Flight Ventilation
In−flight cooling of the engine compartment is accom
plished by nacelle ram−air scoops, circulating boundary−
layer air through the length of the compartment and expelling the air overboard through louvered exits, just forward of the engine nozzle shroud.
2.7.2 Engine Ground Ventilation
With weight on wheels, cooling airflow through the engine compartment is induced by the hydraulic heat exchanger ejector in the forward end of the compartment. Air enters through the nacelle ram−air scoop on the left side, passes through the hydraulic heat exchanger and is discharged into the engine compartment. The air flows through the full length of the nacelle to discharge overboard through a louvered port atop the nacelle on the outboard side of the vertical tail.