The propeller synchrophaser system discussed
and to increase hot section life. This trim signal
here is common to the P-3 and C-130 aircraft and
varies in size between 4,000 and 9,000 feet. To
similar to the E-2 aircraft. In this section, you will
ensure correct positioning of the VEN area,
learn about the electrical operation of controlling
the VEN position transmitter LVDT provides
and synchrophasing the hydromatic propellers of
feedback to the ECA. Any error between the
multiengined aircraft.
actual VEN area position and its required position
goes to the bias signal to readjust the VEN area
to its correct position.
PROPELLER GOVERNOR
As the throttle advances into military (MIL)
power (100 percent) and afterburner (AB) ranges,
A propeller governor is a control device that
the VEN area maintains the low-pressure turbine
controls engine speed by varying the pitch of the
discharge temperature within established limits.
propeller. Increasing the propeller pitch adds load
Throttle position establishes this limit. This limit
on the engine and increases propeller thrust. This
is adjustable for ambient pressure for fan inlet
load reduces engine speed. Conversely, decreasing
temperature and for actual low-pressure turbine
the propeller pitch reduces engine load, which
discharge temperature values from the thermo-
increases engine speed. Therefore, engine speed
couple harness.
is a function of propeller pitch. Furthermore, if
As the throttle enters AB range, the VEN area
the propeller governor setting remains unchanged,
reopens slightly above the normal throttle setting,
any variation of power produced by the engine
and low-pressure turbine discharge temperature
translates into a corresponding variation of
resets to a lower value. These conditions are held
propeller thrust. The system does this by varying
until the flame sensor signals the ECA of an AB
the propeller pitch while engine speed remains
light-off. The ECA then releases its hold on the
constant. The best engine efficiency is when engine
VEN area and re-establishes actual low-pressure
speed is constant; therefore, because it controls
turbine discharge temperature values. The VEN
engine speed, the propeller governor achieves
area will adjust to maintain actual low-pressure
engine efficiency.
turbine discharge temperature limits.
The VEN power unit supplies hydraulic power
The pitch of hydromatic propeller blades
for positioning the VEN. The power unit activates
changes by porting hydraulic fluid onto the
on an electrical signal from the ECA to the power
propeller piston in the propeller dome. The action
unit torque motor. The torque motor drives a
on the piston transmits through a geared cam
servo, which supplies high oil pressure to the
mechanism that rotates the propeller blades to the
synchronized actuators to open or close the VEN.
pitch desired.
The governor is the constant speed control
REVIEW SUBSET NUMBER 8
device used with the hydromatic propeller.
The output oil of the pump goes to either
Q1. When the engine is shut down and the
the inboard or the outboard side of the propeller
throttle is in the off position, the variable
piston.
exhaust nozzle is in what position?
There are two separate ranges of propeller
operation--the flight range and the ground
Q2. What unit in the variable exhaust nozzle
operating range. The flight range includes the
adjusts the VEN for atmospheric condi-
takeoff roll after the power levers advance
tions?
forward for takeoff. For the ground operating
range, power levers return aft of the flight-idle
detent. In the ground operating range (taxi range),
power lever position determines propeller blade
PROPELLER SYNCHROPHASING
angle. A hydromechanical system, with linkage
SYSTEM
to the power lever, meters oil pressure to either
Learning Objective: Recognize operating
the increase or decrease side of the propeller
dome. As the power lever moves forward toward
p r i n c i p l e s and features of propeller
FLIGHT IDLE, a simultaneous increase in blade
synchrophasing systems.
