TM 1-1510-223-10
Change 3 2-47
NOTE
If the synchrophaser is ON but does not adjust
properly, the synchrophaser has reached the
limit of its range. Turn the system OFF, manually
adjust the propeller RPM into synchronization,
then turn the synchrophaser ON.
The propeller synchrophaser may be used on takeoff
at the pilot’s option.
b. Synchrophaser Control Box. The control box, lo-
cated forward of the pedestal, converts pulse rate differ-
ences into correction commands. Differences in pulse
rate, and/or propeller position, cause the control box to
vary the voltage in the primary governor coil, which in turn
increases propeller speed until the correct speed and
phasing are obtained. The system is protected by a
5-ampere circuit breaker placarded PROP SYNC, lo-
cated on the overhead circuit breaker panel (fig. 2-7).
c. Synchroscope. The propeller synchroscope indi-
cator, located on 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 direc-
tion. Left, or counterclockwise, rotation indicates a higher
RPM of the left propeller. This instrument aids the pilot in
obtaining complete synchronization of the propellers.
2-47. PROPELLER LEVERS.
Two PROP levers on the control pedestal (fig. 2-12),
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 levers is placarded
TAKE-OFF, LANDING, AND 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 le-
ver 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 1200 RPM). Moving a
PROP lever aft past the detent into FEATHER will feather
the propeller.
2-48. PROPELLER REVERSING.
CAUTION
Do not move the POWER levers below the flight
idle gate unless the engine is running. Damage
to the reverse linkage mechanisms will occur.
Propeller reversing on deteriorating surfaces
may cause engine FOD and propeller erosion
from reversed airflow. Consideration should be
given to not reversing propellers when operating
in snow or dusty conditions, to prevent obscuring
the pilot’s vision.
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 af-
fected by POWER lever movement forward of the idle
stop. When the POWER levers are lifted over the revers-
ing detent and moved rearward, the reversing cable is
pulled aft. This action resets the beta valve rearward, al-
lowing the governor to pump more oil into the propeller,
thus moving the blades through the ground fine range to-
ward 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. As the
POWER levers are moved further rearward (into the
striped area), the propeller blades are moved further to-
ward the reverse pitch stop, and the FCU is reset to in-
crease engine speed.
2-49. PROPELLER TACHOMETERS.
Two tachometers on the instrument panel register pro-
pellerspeedinhundredsofRPM(fig.2-16).Eachindicator
is slaved to a tachometer-generator unit attached to the
correspondingengine,installedonthereductiongearbox.
