FUEL SYS SELECTOR LEVER
NO. 2 ENG EMER OFF T.HANDLE
POWER CONT LEVER
2-26 Change 2
2.25.3 Load Demand System. With ENG POWER CONT lever at FLY, the ECU and HMU respond to col-lective signals to automatically control engine speed and provide required power. During emergency operations, when the ENG POWER CONT lever is moved to LOCK-OUT and then to some intermediate position, the engine will still respond to collective signals.
2.25.4 Engine Speed Control System. An engine RPM control switch on the upper console (Figure 2-6) con-
trols the speed of both engines simultaneously. There is no individual trim capability. It is used to supply a signal to the ECU for controlling % RPM 1 and 2 as required. The ENG RPM control switch allows adjustment between 96%
Change 2 2-26.1/(2-26.2 Blank)
and 100%. Power for ENG RPM control system is from the No. 2 dc primary bus through a circuit breaker marked SPEED TRIM.
2.26 HOVER INFRARED SUPPRESSOR SUB-SYSTEM (HIRSS).
The hover IR suppressor (Figure 2-2) provides improved helicopter survivability from heat-seeking missiles through-out the .ight envelope. The HIRSS kit has no moving parts. It contains a three-stage removable core which reduces metal surface and exhaust gas temperature radiation and prevents line-of-sight viewing of hot engine surfaces. The HIRSS channels hot exhaust gasses through the three-stage core and inner baffle to induce the .ow of cooling air from the engine bay and the inlet scoops. The three-stage core and inner baffle cold surfaces are coated with low-re.ectance material. For further cooling, hot exhaust gas is ducted outboard and downward by the engine, away from the helicopter by the exhaust de.ector, where additional cooling air is provided by the main rotor downwash. Instal-lation of each HIRSS module requires removal of the stan-dard engine exhaust module and aft cabin door track fair-ings. HIRSS modules are installed on the basic airframe equipped with HIRSS .xed provisions by two airframe mounts. The aft fairings are installed using existing mount-ing points and hardware. While operating in a non-hostile environment, the inner baffle can be removed to enhance helicopter performance.
2.27 ENGINE INSTRUMENTS.
The instrument displays (Figure 2-8) consist of ENG OIL TEMP and PRESS, TGT TEMP, gas generator Ng SPEED, power turbine speed (% RPM 1 or 2), rotor speed % RPM R, engine torque % TRQ, and FUEL QTY to provide the pilots with engine and subsystem monitoring. Continuous indications of those parameters are indicated on vertical scales, digital readouts and caution lights. Instru-ments without low range turn-off feature: % TRQ, TGT TEMP, Ng SPEED, ENG OIL TEMP and XMSN TEMP will remain on as parameter increases and go out as it de-creases (Figure 5-1). Power for lighting the displays is from the No. 1 and No. 2 ac primary and No. 1 and No. 2 dc primary buses through the signal data converters.
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