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drive geartrain. All engine components, including the purge blower. The induction cowl and two particle
engine mounted accessories, are installed on the separator panels form a plenum chamber that supplies
clean air for the engine air inlet. The fan purge blower
gearbox. The power and accessories gearbox
will eject all foreign matter through the fan purge
incorporates two monopole pickup units to sense gas blower ducting.
producer turbine and power turbine speed. Accessories
driven by the gas producer drivetrain are: the fuel The induction cowl is equipped with an inlet blast shield
pump/fuel control HMU (8), pressure/scavenge oil to prevent engine surge due to rocket blast entering the
pump, and the starter-generator (7). The power turbine engine inlet under certain rocket firing conditions.
2-22
TM 1-1520-248-10
Figure 2-11. Engine T703-AD-700A (250-C30R)
2-23
TM 1-1520-248-10
Figure 2-12. Engine (250-C30R/3)
2-24
TM 1-1520-248-10
2-21. ENGINE INLET ANTI-ICING SYSTEM. (3) Filter Bypass Valve. The filter bypass valve
opens when the filter element becomes clogged,
a. The engine anti-icing system provides anti-icing allowing fuel to bypass the filter element.
for the compressor inlet guide vanes and the front
bearing support hub. The system uses hot compressed c. Fuel Pressure Differential Switch. The switch is
air from the diffuser scroll. located on the bottom of the power and accessory
gearbox. It activates the FUEL FILTER BYP caution
b. Major components of the anti-icing system are message when the fuel filter is clogged.
the anti-icing air valve mounted on the diffuser scroll,
anti-icing solenoid valve mounted on the turbine section d. Fuel Control Unit (FCU). The FCU is mounted
firewall shield, and ENG ANTI ICE switch located on on the aft side of the fuel pump. Fuel enters the fuel
the forward overhead console panel (fig. 2-8). control unit after passing through the fuel pump. The
fuel control unit meters fuel to the combustor section of
c. The anti-icing system is activated by placing the the engine. The fuel control unit incorporates a PY
ENG ANTI ICE switch to the ENG ANTI ICE position. torquemotor which controls gas producer speed. Fuel
This de-energizes the anti-icing solenoid valve, causing entering the fuel control unit passes through an
air from the anti-icing air valve to be vented out the additional filter and is then conveyed to the metering
solenoid valve. This, in turn, opens the anti-icing air valve. The fuel control unit has a pressure relief valve
valve allowing hot compressed air from the diffuser to to protect the system from excessive fuel pressure. A
flow to the engine inlet, where it is dispersed through bypass valve maintains a constant pressure differential
the inlet guide vanes and over the front bearing support across the metering valve and bypasses excess fuel
hub. In the event of an electrical failure, the system will back to the fuel pump through an external line
remain on or will activate to on if the system is off at connecting the pump bypass inlet to the bypass outlet
the time of the failure. port of the fuel control.
e. Fuel Injector. The fuel injector is mounted in the
2-22. (OH-58D) ENGINE FUEL SYSTEM. The aft end of the outer combustion case. The fuel injector
engine fuel system delivers fuel to the engine for sprays metered fuel into the combustion section of the
combustion. The major components are the engine engine where it is mixed with air for combustion.
driven fuel pump, fuel filter, fuel pressure differential
switch, fuel control unit (FCU), and fuel injector (fig. 2- 2-23. (OH-58D) ENGINE CONTROLS. Engine
11).
controls consist of the throttle, electronic supervisory
a. Engine Driven Fuel Pump. The engine driven control (ESC), fuel control panel, and an RPM trim
fuel pump is a positive displacement gear-type pump switch.
driven by the gas producer section of the engine. It a. Throttle. The throttle is a rotating twist grip
incorporates a single gear-type pumping element. Fuel located on each collective. It establishes fuel flow
passing through the pump is delivered to the fuel requirements which determine power turbine speed.
control unit. The fuel pump is installed on the power The throttle has three primary positions: off, idle, and
and accessory gearbox and is driven by the gas full open. An IDLE REL button on the pilot collective
producer turbine. Access to the pump is gained through prevents the throttle from being turned to the off
the right engine access door. position from idle. When the button is pressed in, the
throttle can be rotated from idle to off.
b. Fuel Filter. The fuel filter is mounted on the
lower rear portion of the power and accessory gearbox. b. Electronic Supervisory Control (ESC). The
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TECHNICAL MANUAL OPERATOR’S MANUAL FOR ARMY OH-58D HELICOPT(11)
