ground fine gate, a mechanical linkage at the propeller
governor will begin to bleed Py air from the fuel control
unit, provided the PROP levers are positioned to the
minimum RPM position. This results in a decrease in
both engine N,, torque, and propeller RPM. With the
POWER levers at the ground fine gate, engine N1
should be within the range of 62% to 67%, and propeller
RPM should not be less than 1000 RPM.
2-45. PROPELLER SYNCHROPHASER.
matches left and right propeller RPM as well as propeller
phase relationship. This phase relationship is designed
to decrease cabin noise, and is not adjustable in flight.
A toggle switch, placarded PROP SYN - ON - OFF,
installed adjacent to the synchroscope on the pilot's
instrument panel (fig. 2-18), turns the system on/off.
Signal pulses occurring once per revolution of the
propeller are obtained from magnetic pickups (located in
the front of the engine on the deice brush mounting
bracket) when the target (mounted on the aft side of the
spinner bulkhead) passes the magnetic pickup. The
signal pulses are sent to a control box installed forward
of the pedestal. The control box receives these signal
pulses and compares them for pulse rate and relative
position. 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.
A governor coil increases the speed set by the
propeller control lever, but never decreases the speed
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
There is no master or slave engine in this system.
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
synchronized before turning the synchrophaser on.
If the synchrophaser is ON but does
synchrophaser has reached the limit
of its range. Turn the system OFF,
manually adjust the propeller RPM
into synchronization, then turn the
The propeller synchrophaser may be used on takeoff at
the pilot's option.
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 overhead circuit breaker
panel (fig. 2-9).
Synchroscope. The propeller Synchroscope,
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. Left, or counterclockwise, rotation indicates a
higher RPM of the left propeller. This instrument aids
the pilot in obtaining complete synchronization of the
2-46. PROPELLER LEVERS.
Two PROP levers on the control pedestal
(fig. 2-14), 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 1200 RPM). Moving a PROP
lever aft past the detent into FEATHER will feather the
2-47. PROPELLER REVERSING.
Do not move the POWER levers
below the flight idle gate unless the
engine is running. Damage to the
Propeller reversing on deteriorating
surfaces may cause engine FOD and
Consideration should be given to not
reversing propellers when operating
in snow or dusty conditions, to
prevent obscuring the pilot's vision.