TM 1-1510-262-10
SECTION VII. POWER TRAIN SYSTEM
NOT APPLICABLE
SECTION VIII. PROPELLERS
2-44. DESCRIPTION.
A four-blade aluminum propeller is installed on each engine. The propeller is of the full feathering, constant speed,
variable-pitch, counterweighted, reversible type; controlled by engine oil pressure through single action, engine
driven propeller governors. The propeller is lange mounted to the engine shaft. Centrifugal counterweights, as-
sisted 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 propellers have 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, hy-
draulic stop. Ground ine and reverse blade angles are controlled by the POWER levers in the ground ine and
reverse range.
2-45. 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 un-feather, the PROP lever is pushed forward into the
governing range. The automatic feathering system will sense loss of torque and will feather an unpowered propeller.
Feathering springs will 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 action of the blades in
the event of an engine failure. Although the system is armed by a switch on the overhead control panel, placarded
AUTOFEATHER TEST - OFF - ARM , the completion of the arming phase occurs when both power levers are ad-
vanced above 89% N 1 , at which time both annunciators on the caution/advisory 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 1 , position, unless TEST position of the AUTOFEATHER switch is selected to dis-
able 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 of 19-13%, the autofeather system for the opposite engine will be disarmed. Disarming is conirmed when
the AUTOFEATHER annunciator of the opposite engine becomes extinguished. If torque drops further, to a reading
of 13-7%, 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 Switch. A switch placarded AUTOFEATHER TEST - OFF - ARM , located on the
overhead control panel (Fig. 2-13), 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% N 1 .
c. Autofeather Annunciators. Autofeather annunciators consist of two green annunciators on the caution/advi-
sory annunciator panel placarded #I AUTOFEATHER and #2 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 one 5-ampere
circuit breaker placarded AUTO FEATHER , located on the overhead circuit breaker panel (Fig. 2-12).
2-46. PROPELLER GOVERNORS.
Two 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
