engine), a combustion outer case and a combustion
liner. A spark igniter and a fuel nozzle are installed in
the rear of the outer combustion case.
b. Compressor discharge air is ducted from the dif-
fuser scroll to the combustion outer case by the two
compressor discharge air tubes. Air enters the single
combustion liner at the rear through holes in the liner.
The air is mixed with fuel sprayed from the fuel nozzle.
The fuel-air mixture is then ignited in the combustion
liner to provide combustion. Combustion gases move
forward out of the combustion liner to the turbine.
a. The turbine consists of a gas producer turbine
support, a power turbine support, a turbine and
exhaust collector support, a two-stage gas producer
turbine, and a two-stage power turbine. The turbine is
mounted between the combustion section and the
power and accessory gearbox. The two-stage gas pro-
ducer turbine drives the compressor and accessory
gear train. The two-stage power turbine furnishes the
output power of the engine.
b. Combustion gases from the combustion section
are expanded across the two stages of the gas producer
turbine. Energy is extracted from the gas stream and
converted to shaft torque to drive the compressor and
gas producer gear train.
c. The combustion gases then move forward from
the gas producer turbine and are expanded across the
two stages of the power turbine. Additional energy is
extracted from the gas stream and converted to shaft
torque. This shaft torque is then transmitted through
the power turbine gear train to the output shaft.
d. The expanded gas from the power turbine passes
through the exhaust collector support and is exhausted
upward through the twin ducts The small amount of
energy remaining in the gas stream assists in scaveng-
ing the exhaust gases from the engine.
1-9. Power and Accessory Gearbox.
The main power and accessory drive gear trains are
enclosed in a single gear case. The gear case serves as
the structural support of the engine. All engine compo-
nents, including the engine-mounted accessories, are
attached to the case. At 100% engine speed, reduction
gearing reduces power turbine speed from 33,290 to
6,016 rpm at the output drive pads. The power turbine
gear train has a torquemeter to measure engine output
torque. Accessories driven by the power turbine gear
train are the power turbine tachometer-generator (N2)
and the power turbine governor. The gas producer gear
train drives the oil pump, fuel pump, gas producer fuel
control, and tachometer-generator (N1). The gearbox
has a spare accessory mounting pad which is driven by
the gas producer gear train. During starting the
starter-generator cranks the engine through the gas
producer gear train. After completion of the starting
cycle, the starter-generator functions as a generator.
1-10 Description of Engine Operation
a. The engine is a free turbine engine, that is, there
is no mechanical connection betweem the gas producer
turbine and the power turbine. The power turbine is
gas coupled to the gas producer turbine by the combus-
b. The helicopter uses a conventional control sys-
tem. The collective pitch of the helicopter rotor estab-
lishes the power output demand on the engine. For all
practical purposes, helicopter rotor speed is held con-
stant by the engine and its control system.
c. The fuel control is connected to the twist grip on
the pilots and copilots collective pitch sticks. The
power turbine governor is interconnected to the collec-
tive pitch sticks through a coordinated system of bell-
cranks and linkages. Any change in collective pitch
resets the governor to a new power demand. This
demand is transmitted to the gas producer fuel control,
which resets and varies the N1 speed of the gas pro-
ducer turbine accordingly.
d. A motor-actuated speed trimming device is
installed in the linkage between the collective pitch
sticks and the power turbine governor lever. It is oper-
ated by a trim switch on pilots collective pitch stick,
and allows engine output speed to be varied over a
normal range of approximately 95 to 102% (5896 to
1-11. Fuel and Control System.
a. The gas producer fuel control is located schemat-
ically in the fuel system between the fuel pump assem-
bly and the fuel nozzle. (See figure 1-3.) A power tur-
bine governor, also a part of the control system,
provides control intelligence to the gas producer fuel
b. The system controls engine power output by con-
trolling gas producer speed. Gas producer speed levels
are established by the action of the power turbine gov-
ernor which senses power turbine speed. Power turbine
speed is selected by the operator. The power required to
maintain this speed is automatically maintained by
power turbine governor action on the gas producer fuel