should be manually synchronized before turning the
If the synchrophaser is ON but does
synchrophaser has reached the limits
of its range. Turn the system OFF,
manually adjust the propeller RPM into
The propeller synchrophaser may be used on
takeoff at the pilot's option. If used for takeoff, the
limited range of the synchrophaser will be reduced near
maximum propeller RPM.
b. Control Box. The control box, located forward
of the pedestal, converts pulse rate differences into
correction commands. Differences in pulse rate, and/or
propeller position, causes the control box to vary the
voltage in the primary governor coil, which in turn
increases propeller speed until the correct speed and
phasing is obtained. The system is protected by a 5-
ampere circuit breaker placarded PROP SYNC, located
in the overhead circuit breaker panel (fig. 2-6).
c. Synchroscope. The propeller synchroscope
indicator, located in the pilot's instrument panel,
provides an indication of synchronization of the
propellers. If the right propeller is operating at a higher
RPM than the left, a black and white cross pattern, spins
in a clockwise rotation. Left, or counterclockwise,
rotation indicates a higher RPM of the left propeller.
This instrument aids the pilot in obtaining complete
synchronization of the propellers.
2-48. PROPELLER LEVERS.
Two propeller levers on the control pedestal (fig.
2-11), placarded PROP, are used to regulate propeller
speeds. Each lever controls a primary governor, which
acts to regulate propeller speeds within the normal
operational range. The full forward position of the
REVERSE HIGH RPM. The full aft position of the
levers is placarded FEATHER. When a lever is placed
at HIGH RPM, the propeller may attain a static RPM of
1700 depending upon power lever position. As a lever
is moved aft, passing through the propeller governing
range, but stopping at the feathering detent, the
propeller RPM will correspondingly decrease to the
lowest limit (approximately 1390 RPM). Moving a
propeller lever aft past the detent into FEATHER will
feather the propeller.
2-49. PROPELLER REVERSING.
Do not move the power levers below
the flight idle gate unless the engine is
to the reverse
linkage mechanisms will occur.
Propeller reversing on unimproved surfaces
should be accomplished carefully to prevent propeller
erosion from reversed airflow. Consideration should be
given to reversing propellers when operating in snow or
dusty conditions, to prevent obscuring the operator's
The engine power levers actuate an engine
mounted cambox which is connected to the engine FCU
(fuel control unit) and the propeller reversing cable. The
cambox is arranged so that the reversing cable is not
affected by power lever movement forward of the idle
stop. When the power levers are lifted over the
reversing detent and moved rearward, the reversing
cable is pulled aft. This action resets the Beta valve
rearward, allowing the governor to pump more oil into
the propeller, thus moving the blades through the
ground fine range towards reverse pitch. As the blades
move, the mechanical feedback collar, is moved
forward. This movement is transmitted by a carbon
block on the end of the reversing lever to the Beta
valve, causing it to move forward. When the Beta valve
reaches its initial position, oil flow to the propeller is
blocked preventing further blade angle change. As the
power levers are moved further rearward (into the
striped area), the propeller blades are moved further
toward the reverse pitch stop, and the FCU is reset to
increase engine speed.
2-50. PROPELLER TACHOMETERS.
The two tachometers on the instrument panel
register propeller speed in hundreds of RPM (fig. 2-14).
Each indicator is slaved to a tachometer generator unit
attached to the corresponding engine.
Section VII. UTILITY SYSTEMS
2-51. DEFROSTING SYSTEM.
Description. The defrosting system is an
integral part of the heating and ventilation system. The
system consists of two warm air outlets connected by