TM 1-1510-262-10
maximum RPM differential (capture range), at which the synchrophaser, when turned on, will begin to synchronize
the propellers. For this reason, the propeller should be manually synchronized before turning the synchrophaser on.
NOTE
If the synchrophaser is ON but does not adjust properly, the synchrophaser has reached the limits
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. 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 on the overhead circuit breaker
panel (Fig. 2-12).
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.
2-51. PROPELLER LEVERS.
Two propeller levers on the control pedestal (Fig. 2-19), 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 TAKEOFF , 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 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.
2-52. PROPELLER REVERSING.
Do not move the power levers below the light 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 airlow.
Consideration should be given to not reversing propellers when operating in snow or dusty con-
ditions to prevent obscuring the operator s vision.
The engine POWER levers actuate an engine mounted cam box which is connected to the engine fuel control unit
(FCU) and the propeller reversing cable. The cam box 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 ine 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 low 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.
2-53. PROPELLER TACHOMETERS.
The two tachometers on the instrument panel register propeller speed in hundreds of RPM (Fig. 2-22). Each in-
dicator is slaved to a tachometer generator unit attached to the corresponding engine, installed on the reduction
2-53
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