until it matches the feedback signal. When this
potentiometer setting and the phase-difference
occurs, the potential at the summing point is zero
voltage. This is how phase-error voltage and its
and the motor stops moving, leaving a portion
size depend on the slave propeller's degree of lead
of the error uncorrected. This is insignificant for
or lag from the 10-degree lead condition. The
errors that occur about a set point--leading
manual phase control is adjustable to allow a slave
and lagging errors. However, for errors that
lead or lag of 45 degrees.
continually occur in one direction, the error
accumulates, and can become large enough to
SPEED-ERROR CORRECTION. --During
reduce system efficiency. To overcome this, a
the phase-error correction, Zener diodes VR405
procedure provides a lock on the mechanical
and VR408 isolate the speed-error potentiometer
governor bias, while the servomotor recenters at
from the signal summing point. When an
a zero-volt feedback position; this is resyn-
off-speed occurs, these diodes conduct and
chrophasing.
connect the speed-error circuit to the summing
As you read this paragraph, refer to figure
point. For large speed errors, the speed-error
5-19. While in synchrophasing mode, place the
signal is a pulsating dc of very low frequency. At
prop resynchrophase switch in the RESYNCH
the same time, the phase-error signal is a rapid
position. This energizes the electric clutch-brakes
dc step voltage consisting of sharp potential
on the slave engine speed-bias servo assemblies.
changes, which trigger the speed-error circuit. The
The brakes lock the output shafts and the clutches
dc step voltage changes developed in the cathode
decouple the input and output shafts. This action
circuit of V206A (fig. 5-20) are averaged and
leaves the input shafts free to turn. Locking the
effectively blocked by resistor R268 and capacitor
C251. The sharp potential changes passing resistor
output shaft retains whatever mechanical bias is
present on the mechanical governor. At the same
R268 and capacitor C251 leak to ground by
time, relay K503 energizes. This opens the signal
resistor R272 and capacitor C256, leaving the
winding number 1 circuits on the magnetic
speed-error signal in control. When the engine
modulators. (The master channel remains in
reaches on-speed condition, but is still out of
normal governing mode through a parallel ground
phase, the speed-error signal drops off until a
provided by the master relay to signal winding
point where the Zener diodes stops conducting
number 1 of the master channel modulator.) After
and the phase-error signal assumes control.
a time delay sufficient to assure brake and clutch
TWO-PERCENT LIMITING. -- T h e
actuation before allowing the recentering action,
relays de-energize, removing the phase- and speed-
potential at the summing point has a limit of plus
error circuits from the slave channel magnetic
or minus 5 volts. The limiting circuit (R442, R443,
modulators and connecting the dummy loads.
R444, R445, CR409, and CR410 as shown in fig.
The only input to the slave channel magnetic
5-23) accomplishes this by clipping any signal
modulators is now the feedback potentiometer
outside of the range limit. In the off-speed circuit,
acting into the dummy load through signal
this limited signal provides only enough output
winding number 2. The generated signal then
to drive the speed-bias servomotor to correct a
drives the motors until the feedback voltage is
two-percent speed change. This occurs because the
zero. Upon releasing the prop resynchrophase
motor movement results in a feedback voltage that
switch, all circuits return to the synchrophasing
cancels the speed-error signal. The slave propeller
mode. Correction of the accumulated phase error
cannot follow large speed changes of the master
can now occur.
engine. This prevents a slave from following an
overspeeding or underspeeding master.
TROUBLESHOOTING HINTS
Resynchrophasing
When trouble occurs in the propeller system
electrical controls, the first troubleshooting step
The need for resynchrophasing arises from the
you perform is determining which part of the
nature in which phase angle correction circuits
system is malfunctioning. You can determine this
operate. As phase errors occur, the servomotor
by completing an operational check. The next step
rotates to correct the error. At the same time, the
is to refer to the electrical schematic and the
feedback potentiometer moves and cancels a
troubleshooting chart in the aircraft maintenance
portion of the error signal. As the phase-error
instructions manual, and then analyze the trouble.
correction occurs, the phase-error signal decreases
