TM 1-1510-225-10
2-75
the center subpanel. The approach and full down flap
positions are 14 and 35, respectively. The flap
position indicator is protected by a 5-ampere circuit
breaker, placarded FLAP CONTROL, located on the
left sidewall circuit breaker panel.
Section VI. PROPELLERS
2-41. DESCRIPTION.
A four-blade aluminum propeller is installed on
each engine. The propeller is full feathering, constant
speed, variable-pitch, counterweighted, and reversible;
and is controlled by engine oil pressure through single
action, engine driven propeller governors. The
propeller is flange mounted to the engine shaft.
Centrifugal counterweights, assisted by a feathering
spring, move the blades toward the low RPM (high
pitch) position and into the feathered position.
Governor boosted engine oil pressure moves the
propeller to the high RPM (low pitch) hydraulic stop
and reverse position. The propeller has no low RPM
(high pitch) stops; this allows the blades to feather
after engine shutdown. Low pitch propeller position is
determined by the low pitch stop, which is a
mechanically actuated, hydraulic stop. Ground fine
and reverse blade angles are controlled by the
POWER levers in the ground fine and reverse range.
2-42. FEATHERING PROVISIONS.
Both manual and automatic propeller feathering
systems
are
provided.
Manual
feathering
is
accomplished by pulling the corresponding PROP
lever aft, past a friction detent. To unfeather, the
PROP lever is pushed forward into the governing
range. The automatic feathering system senses loss
of torque and feathers an unpowered propeller.
Feathering springs feather the propeller when it is not
turning.
a. Automatic Feathering. The automatic
feathering system provides a means of immediately
dumping oil from the propeller servo to enable the
feathering
spring
and
counterweights
to
start
feathering the blades in the event of an engine failure.
Although the system is armed by a switch on the pilot's
subpanel, placarded AUTOFEATHER ARM / OFF /
TEST, the completion of the arming phase occurs
when both POWER levers are advanced above 89%
N1. At this time, both annunciators on the
caution/advisory annunciator panel indicate a fully
armed system. The green annunciators are placarded
L AUTOFEATHER and R AUTOFEATHER. The
system will remain inoperative as long as either
POWER lever is retarded below approximately the
89% N1 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 21% and 16% R , 468 to 356 foot
pounds T3 F3 , 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 14% and 9% R ,
312 to 200 foot pounds T3 F3 , 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 L AUTOFEATHER and R
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
ARM / OFF / TEST, located on the pilot's subpanel, 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
L
AUTOFEATHER and R AUTOFEATHER. When
illuminated,
the
annunciators
indicate
that
the
autofeather system is 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 right sidewall circuit breaker panel.
2-43. PROPELLER GOVERNORS.
A constant speed governor and an overspeed
governor cont rol 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 2000 RPM,
the overspeed governor cuts in at 2080 RPM and
dumps oil from the propeller to keep the RPM from
exceeding approximately 2120 RPM. A solenoid,
