TM 55-1510-215-10
Autofeathering is controlled by a PROP AUTHFEATHER
propeller operation in the reverse range, the engine
switch on the subpanel (fig. 2-7). The three-position
power turbine governor will automatically be reset to
switch is placarded ARM, OFF and TEST, and is spring-
allow a maximum of 2040 RPM.
loaded from TEST to OFF. The ARM position is used
only during takeoff and landing. At ARM, if an engine
2-48. Propeller Governor Test Switches.
loses power above 88% to 92% N , two torque-sensing
1
switches of the affected engine are actuated by loss of
Two, three-position switches on the left subpanel,
torque pressure.
Switch actuation applies current
are provided for operational test of the propeller systems
through an autofeather relay to a corresponding dump
valve, causing the release of oil pressure which held an
TEST, LEFT, RIGHT (above) and SECONDARY IDLE
established pitch angle on the blades of the affected
STOP TEST (below). Each switch is a double unit,
propeller Following the release of oil pressure, feathering
controlling two different test circuits for the
movement is accomplished by the leathering springs
corresponding propeller. In up position, the switches are
assisted by centrifugal force applied to the blade shank
used to test the function of the corresponding overspeed
counterweights.
The TEST position of the switch,
governor. In the down position, the switches are used to
enables the pilot to check readiness of the autofeather
test function of the corresponding secondary low pitch
systems, below 88% to 92% N1 and is for ground
stop. Each switch is spring-loaded to the OFF (center)
checkout purposes only. Refer to chapter 8.
position. Refer to chapter 8, for steps of both test
procedures. Propeller test circuits are protected by one
c. Autofeather Lights. Two amber lights on the
5-ampere circuit breaker, placarded PROP GOV IDLE
instrument panel, placarded AUTOFEATHER LEFT and
STOP, located on the fight subpanel (fig. 2-7).
RIGHT, when illuminated indicate that the autofeather
system is armed (fig.
Both lights will be
2-49. Propeller Levers.
extinguished if other propeller has been autofeathered or
if the system is disarmed by retarding a power lever.
Two propeller levers on the control pedestal,
Both lights may be dimmed by rotating the cover.
placarded PROP, are used to regulate propeller speeds
Autofeather circuits are protected by one 5-ampere
circuit breaker placarded PROP FEATHER, located on
acts to regulate propeller speeds within the normal
the right subpanel (fig. 2-7).
operating range. The full levers forward position is
placarded TAKEOFF, LANDING AND REVERSE, and
2-47. Propeller Governors.
also HIGH RPM. Full levers aft position is placarded
FEATHER. When a lever is placed at HIGH RPM, the
Each propeller system utilizes three governors, one
propeller may attain a static RPM of 2200, depending
"primary" and two '"backup", to control propeller RPM.
upon power lever position. As a lever is moved aft,
Each propeller lever establishes RPM for the respective
passing through the propeller governing range, but
propeller by altering the setting of a primary governor
stopping at the feathering detent, propeller RPM will
attached to the engine gear reduction housing. It is the
correspondingly decrease to the lowest limit. Moving a
primary governor which controls RPM through the entire
propeller lever aft past the detent into FEATHER will
range.
Should a primary governor malfunction
feather the propeller.
(exceeding 2200 RPM) an overspeed governor cuts-in
(2248 to 2328 RPM), dumping oil from the propeller to
2-50. Propeller Reversing.
prevent RPM from exceeding safe limits. A solenoid
actuated by the PROP GOV TEST switch enables the
overspeed governor to be reset for test purposes (1980
CAUTION
to 2060 RPM). If a propeller should stick or move too
slowly during a transient condition, the corresponding
governor would be unable to prevent an overspeed
Moving the power levers into reverse
condition. To provide for this contingency, the engine
range without the engine running will
power turbine governor acts as a fuel topping governor.
result in damage to the reverse
Thus, when the propeller RPM reaches 2332 RPM, this
linkage mechanisms.
governor limits the fuel flow into the engine thereby
reducing the power during the propeller.
During
2-36 Change 7
