TM 55-1520-228-10
2-34 Change 11
b. Tail Rotor Gearbox Chip Detector. The chip
detector is located in the lower section of the tail rotor
gearbox. The chip detector is wired to the T/R CHIP DET
caution light and the MASTER CAUTION light. The cau-
tion light is activated when a sufficient amount of metal
particles has been collected on the chip detector to close
the circuit.
c. Transmission Oil Pressure Warning
Light. The XMSN OIL PRESS warning light (figure
2-13 and figure 2-14) is located in the upper center
section
A , and upper right corner C of the instrument
panel. The XMSN OIL PRESS light will illuminate steady
until oil pressure is above 36 psi. Normal operating pres-
sure is 30 to 60 psi with warning light actuation at 30 $
2 psi on decreasing pressure. The transmission oil pres-
sure switch is located on the left side of the cabin roof
near the transmission. The light is protected by the CAU-
TION PNL LTS circuit breaker.
d. Transmission Oil Temperature Warning
Light. The XMSN OIL HOT warning light (figure 2-13
and figure 2-14) is located in the upper center section
A
, and upper right corner C of the instrument panel. The
XMSN OIL HOT light will illuminate when temperature
is 110_C or above. The transmission oil temperature
sensor is located on the transmission oil filter head. The
light is protected by the CAUTION PNL LTS circuit
breaker.
SECTION VIII. MAIN AND TAIL ROTOR GROUPS
2-42. MAIN ROTOR.
The main rotor assembly is a two blade, semi-rigid, see-
saw type rotor called an underslung feathering axis hub.
The blades are mounted in the hub assembly grips with
blade retaining bolts which have hollow shanks for
installation of weights to balance the hub and blade
assembly. Pitch change and pillow block bearings are
lubricated with grease. The rotor blades are all metal,
consisting of an extruded aluminum alloy nose block,
aluminum alloy trailing edge and an aluminum honey-
comb filler. The main rotor is driven by the mast which
is connected to the transmission. The rotor RPM is gov-
erned by the engine RPM during powered flight. The
rotor tip path plane is controlled by the cyclic stick. The
rotor pitch is controlled by the collective lever.
2-43. MAIN ROTOR RPM INDICATOR.
CAUTION
The same audio tone is used for both
the rotor rpm warning and engine out
warning. Check the visual indicators
to determine corrective action ne-
cessary.
The rotor tachometer indicator (figure 2-13
A , figure
2-14
C ) is part of the dual tachometer and is located on
the instrument panel. The rotor RPM reading is indi-
cated on the inner scale and the pointer needle is
marked with an R. The indicator is powered by a
tachometer generator mounted on and driven by the
transmission and is independent of the helicopter elec-
trical system.
C Model aircraft require 28 VDC and are
protected by the DUAL TACH circuit breaker.
2-44. RPM WARNING SYSTEM.
A ROTOR RPM warning system is installed to provide
a visual and audio indication of low rotor RPM. A RPM
sensor is connected to the rotor tachometer. Power is
supplied from the CAUTION PNL LTS circuit breaker
and connections are made to the ROTOR RPM warning
light and to a tone generator which provides an audible
tone in the crews headsets. The warning system is acti-
vated when the rotor RPM drops below 95% $ 1.4%.
2-45. TAIL ROTOR.
The tail rotor is driven by the inner shaft of the freewheel-
ing unit through tail rotor driveshaft and the tail rotor
gearbox. The tail rotor hub and blade assembly consists
of an aluminum alloy forged yoke and aluminum alloy
blades. The spherical bearings provide for pitch change
of the blades. The hub and blade assembly are mounted
on the tail rotor gearbox shaft by means of a splined
trunnion, mounted in bearings in the yoke, to provide a
flapping axis for the assembly. The tail rotor gearbox has
a breather type filter cap, electrical chip detector and oil
level sight gage, all accessible from ground level. Tail
rotor blade pitch is controlled by the anti-torque pedals.
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