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The tail rotor is mounted on the end of the main
transmission and is driven by the accessory gear
train. A flexible splined coupling provides a means
of attaching the tail rotor drive shaft.
Generator Drive
The generator drive is driven by the main transmission
accessory gear train. The generator is driven
off the main transmission so that, when the
helicopter goes into autorotation and the engine
is idling or stopped, enough electrical power will
be left to operate instruments, radio, and electrical fuel
main transmission is mounted directly on the engine. pumps.
5-4
FM 1-514
Main Transmission Oil System
Most main transmissions are lubricated by a wet
sump oil system which is separate from the engine oil
system (Figure 5-5). However, the engine oil cooler
and transmission oil cooler may be mounted close
together so that they can use the same blower system
to cool the oil. Oil supply from the transmission
sump is circulated under pressure from a gear-driven
pump through internal passages and a filter to the
sump outlet. From this outlet external lines are
routed to an oil cooler with a separate thermal bypass
valve, then to a manifold on the transmission main
case. This manifold is equipped with a relief valve to
regulate system pressure and distribute oil through
jets and internal passages. This lubricates bearings
and gears inside the transmission where the oil drains
back to the sump.
Oil temperature and pressure gage readings are
shown by a thermobulb and a pressure transmitter.
Most transmission oil systems provide a heat switch
and a pressure switch which will light caution lights
on panels lettered XMSN OIL HOT and XMSN OIL
5-5
FM 1-514
PRESS (low pressure) if such conditions occur. Servicing
and draining provisions are provided in the
transmission oil system. Oil level sight gages are
provided on most transmissions; others use the
dipstick method. Chip detectors used in the transmission
oil system are similar to those used on
engines.
Rotor Tachometer-Generator Drive
The rotor tachometer RPM indications are provided
by the rotor tachometer-generator. The tachometergenerator
drive is driven by the main transmission
accessory gear train.
Hydraulic Pump Drive
The hydraulic pump drive is driven by the main transmission
accessory gear train. The hydraulic pump
provides hydraulic pressure for the flight control
servo system. Some helicopters use two separate
flight control servo systems completely independent
of each other. One system is the primary servo system;
it gets hydraulic operating pressure from a
hydraulic pump driven by the main transmission. A
secondary servo system gets hydraulic operating
pressure from a hydraulic pump driven by the engine.
MAIN ROTOR MAST ASSEMBLY
The main rotor mast assembly is a tubular steel shaft
fitted with two bearings which support it vertically in
the transmission (Figure 5-6). Mast driving splints
engage with transmission upper-stage planetary
gear, providing counterclockwise rotation (viewed
from above). The upper bearing retainer plate has
an oil jet fed by an external oil hose. Splints on the
upper portion of the mast provide mounting for main
rotor arid control assemblies.
TAIL ROTOR DRIVE SHAFT
The purpose of the tail rotor drive shaft is to transmit
torque from the main transmission to the tail rotor
gearbox (Figure 5-7). The shaft is made up of a series
of hollow tubes with provisions for statically balancing
and coupling attachments on each end.
Flexibility in the shaft is provided by splined or rubber
couplings. The tail rotor drive shaft is supported
by a series of support bearings and support hanger
assemblies.
INTERMEDIATE GEARBOX
An intermediate gearbox is located on the tail boom
of the helicopter (Figure 5-8). This gearbox provides
5-6
a specific degree change in direction of the tail rotor
drive shaft with no speed change. The gearbox assembly
consists of a case with flexible coupling
provisions for attaching onto the tail rotor shaft fore
and aft. The gearbox is splash-lubricated, and the
case is fitted with an oil filter cap, a vent breather, an
oil level sight gage, and a drain plug equipped with a
magnetic insert. The magnetic insert collects metal
particles coming from inside the gearbox. When
there is a requirement, the metal particles can be
collected and analyzed to determine the condition of
the gears and bearings in the gearbox.
TAIL ROTOR GEARBOX
The tail rotor gearbox is located on the extreme aft
　
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