TM 1-1510-225-10
2-77
set by the control lever. The maximum synchrophaser
range is approximately 20 RPM. This limited range
prevents either propeller from losing more than a
limited RPM if the other propeller is feathered with the
synchrophaser ON.
There is a limited range for synchronizing, called
the "holding range". There is a maximum RPM
differential
(capture
range),
at
which
the
synchrophaser,
when
turned
on,
will
begin
to
synchronize the propellers. For this reason the
propellers 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 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
during takeoff at the pilot's option.
b. Synchrophaser 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,
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, located on the right sidewall
circuit breaker panel, refer to Figure 2-6.
c. Synchroscope. The propeller synchro-
scope, 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 direction. 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,
placarded PROP, are used to regulate propeller
speeds. Each lever controls a primary governor to
regulate
propeller
speeds
within
the
normal
operational range. The full forward position of the
levers
is
placarded
TAKEOFF
/
LANDING
/
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 1200 RPM). Moving a
PROP lever aft past the detent into FEATHER will
feather the propeller.
2-49. 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
unimproved
surfaces should be accomplished carefully
to prevent 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 that is connected to the engine Fuel
Control Unit (FCU) and the propeller reversing cable.
The cambox is arranged so that POWER lever
movement forward of the idle stop does not affect the
reversing cable. 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 toward 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
toward the reverse pitch stop, and the FCU is reset to
increase engine speed.
2-50. PROPELLER TACHOMETERS.
a. Propeller
Tachometer
R
F3.
Two
tachometers on the instrument panel register propeller
speed in hundreds of RPM. Each indicator is slaved to
a
tachometer-generator
unit
attached
to
the
corresponding engine, installed on the reduction
gearbox.
b. Propeller Tachometer T3 . The indicator
shall display the measured N2 concurrently in a 1
alphabetic, 3 ½ -numeric character digital display, and
a 38-segment bar graph display. The indicator has a
digital display range of 0 to 2500 RPM while displaying
current N2 and 0 to 4000 RPM while displaying
