TM 1-1510-224-10
annunciator panel indicate a fully armed system. The
annunciator panel annunciators are green and placarded
#
1
AUTOFEATHER
(left
engine)
and
#
2
AUTOFEATHER (right engine). The system will remain
inoperative as long as either POWER lever is retarded
below approximately the 89% N, position, unless TEST
position of the autofeather switch is selected to disable
the POWER lever limit switches. The system is
designed for use only during takeoff or landing, and
should be turned off when establishing cruise climb.
During takeoff or landing, should the torque for either
engine drop to an indication between 19 13%, the
autofeather system for the opposite engine will be
disarmed.
Disarming
is
confirmed
when
the
AUTOFEATHER annunciator of the opposite engine
becomes extinguished. If torque drops further, to a
reading between 13 and 7%, oil is dumped from the
servo of the affected propeller, allowing a feathering
spring to move the blades into the feathered position.
Feathering
also
causes
the
AUTOFEATHER
annunciator of the feathered propeller to extinguish. At
this time, both the # 1 AUTOFEATHER and # 2
AUTOFEATHER annunciators are extinguished, the
propeller of the defective engine has feathered, and the
propeller of the operative engine has been disarmed
from autofeathering capability. Only manual feathering
control remains for the second propeller.
b.
Propeller Autofeather Arm/Off/Test Switch. A
switch placarded AUTOFEATHER TEST - OFF - ARM,
located on the overhead control panel (fig. 2-15), is
provided for arming and disarming the system and for
selection of the TEST function. The TEST position of
the switch checks the readiness of the autofeather
system below 89% N1.
c.
Autofeather
Annunciators.
Autofeather
annunciators consist of. two green annunciators on the
caution/advisory annunciator panel, placarded
# 1
AUTOFEATHER and # 2 AUTOFEATHER. When
illuminated,
the
annunciators
indicate
that
the
autofeather system ig armed. Both annunciators will be
extinguished if either propeller has been feathered or if
the system is disarmed by retarding a POWER lever.
Autofeather circuits are protected by a 5-ampere circuit
breaker, placarded AUTO FEATHER, located on the
overhead circuit breaker panel (fig. 2-9).
2-42. PROPELLER GOVERNORS.
A constant speed governor and an overspeed
governor control propeller RPM. The constant speed
governor, mounted on top of the reduction housing,
controls the propeller through its entire range. The
propeller control lever controls the propeller by means of
this governor. If the constant speed governor should
malfunction and request more than 1700 RPM, the
overspeed governor cuts in at 1802 RPM and dumps oil
from the propeller to keep the RPM from exceeding
approximately 1802 RPM. A solenoid, actuated by the
GOVERNOR TEST switch, located on the overhead
control panel (fig. 2-15), is provided for resetting the
overspeed governor to approximately 1540 to 1580 RPM
for test purposes. If the propeller sticks or moves too
slowly during a transient condition, causing the propeller
governor to act too slowly to prevent an overspeed
condition, the power turbine governor, contained within
the constant speed governor housing, acts as a fuel
topping governor. When the propeller reaches 106% of
selected N2 RPM, the power turbine governor limits the
fuel flow to the gas generator, reducing N1 RPM, which
in
turn
prevents
the
propeller
from
exceeding
approximately 1802 RPM. During operation in the
reverse range, the power turbine governor is reset to
approximately 95% of propeller RPM before the
propeller reaches a negative pitch angle. This ensures
that engine power is limited, allowing a propeller RPM of
somewhat less than that of the constant speed governor
setting to be maintained. The constant speed governor,
therefore, will always sense an underspeed condition
and direct oil pressure to the propeller servo piston to
permit propeller operation in beta and reverse ranges.
2-43. LOW PITCH STOP.
Low pitch propeller position is determined by a
mechanically-monitored hydraulic low pitch stop. The
propeller servo piston is connected by four spring-loaded
sliding rods to the beta collar, mounted behind the
propeller. A carbon brush block riding in the beta collar
transfers the movement of the collar through the
propeller reversing lever to the beta valve of the
governor. The initial forward motion of the beta valve
from its rigged position blocks off the flow of oil to the
propeller. Further motion dumps the oil from the
propeller into the reduction gear box sump. A
mechanical stop limits the forward motion of the beta
valve. Rearward movement of the beta valve from its
rigged position does not affect normal propeller control.
When the propeller is rotating at a speed lower than that
selected on the governor, the governor pump provides
oil pressure to the servo piston, decreasing pitch of the
propeller blades until the feedback of motion from the
beta collar pulls the beta valve into a position blocking
the supply of oil to the propeller, thus preventing further
pitch changes.
2-44. GROUND FINE.
CAUTION
Propeller speeds below 1000 RPM are
not authorized, unless the propeller
is feathered.
Lifting the POWER levers and moving them aft past the
flight idle stop will place the POWER levers into the
ground fine position. Approximately half way back to the
2-54
