Each propeller has a pulse generator that
angle and fuel flow occurs, providing increased
consists of a permanent magnet on the propeller
power, As the power lever moves aft from
spinner and a stationary coil installation in the
FLIGHT IDLE, blade angle decreases and fuel
governor control. Each time the permanent
flow decreases, reducing power. Fuel flow begins
magnet passes by the coil it generates a pulse. In
to increase when the blade angle decreases to the
other words, each revolution of the propeller
point that the propeller is delivering negative
generates one pulse.
thrust. Reverse power continues to increase until
the power levers reach the full aft position. During
Phase and trim control. The phase and trim
operation in the ground operating range, there is
control functions as a means of setting phase
no electronic governing.
relationships between mast er and slave propellers.
In the flight range of operation, the power
It also trims the master engine.
lever is forward of the flight-idle detent. In
this range, a flyweight governor, driven by
The phase and trim control consists of seven
propeller rotation, mechanically controls propeller
potentiometers that receive a fixed dc voltage from
speed. In normal operation, the pitch-change
the synchrophaser. The wiper of the master trim
oil goes through the feather valve to either
potentiometer supplies a voltage through the
the increase or- decrease pitch portion of the
master select switch to the synchrophaser to trim
propeller.
master engine speed. The other six wipers connect
to relay contacts that separate the wipers into two
groups of three per group. One group corresponds
SYNCHROPHASING
to engines 1, 3, and 4 when engine 2 is master.
The other group corresponds to engines 1,2, and
The synchrophaser has different functions,
4 when engine 3 is master. These wipers supply
depending upon the mode of governing selected
bias voltages to the phase correction circuits of
by the flight crew. The synchrophaser does not
the synchrophaser to set propeller phase angles
function in the mechanical governing mode, but
of other than 0 degree.
the mechanical governor controls the blade pitch
and so propeller RPM. In a normal governing
Speed-bias servo assembly. The speed-bias
mode, the synchrophaser helps the mechanical
servo assembly functions as a means of translating
governor by limiting engine transient speed
synchrophaser electrical signals into a mechanical
changes, or to changes in flight conditions
bias on the mechanical governor speeder spring.
affecting propeller speed.
The synchrophaser supplies the servomotor
In a synchrophasing governing mode, the
with a reference voltage that is 90 degrees out of
synchrophaser helps the mechanical governor by
phase with the aircraft 400-Hz source. The
maintaining all propellers at the same RPM. It
synchrophaser also supplies a control voltage that
does this by maintaining a preset phase relation-
is either in phase or 180 degrees out of phase
ship between the master propeller number 1 blade
with the aircraft 400-Hz source. Therefore, the
and the number 1 blades of the slave propellers.
in-phase control voltage lags the reference voltage
This serves to reduce noise and vibration in the
by 90 degrees. This lag results in counterclockwise
aircraft. In the synchrophasing governing mode,
motor rotation when viewed from the output gear
the synchrophaser also provides the limiting of
of the electric brake. The 180-degree out-of-phase
transient speed changes as it does in normal
control voltage leads the reference voltage and
governing mode.
causes clockwise rotation. The amplitude of the
control voltage determines motor speed and
The synchrophaser consists of four main
components--a pulse generator, a phase and trim
torque output.
control, a speed-bias servo assembly, and the
The motor drives a reduction gear train,
synchrophaser.
which, in turn, drives a potentiometer wiper and
Pulse generator. The pulse generator provides
the electric brake. The potentiometer receives a
the information needed by the synchrophaser
fixed dc supply from the synchrophaser across its
system to produce speed and phase control of the
resistive element. When the motor rotates, the
wiper transmits a corresponding feedback voltage
aircraft propellers.
