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B. The electronic engine control (EEC) controls the system as a function of low pressure rotor speed (N1), high pressure rotor speed (N2), and inlet total temperature (TT2).
C. The major components of the system are the variable stator vane actuator and the mechanical linkage which includes a bellcrank, four adjustable links, four unison rings, and 230 connector links.
2. Variable Stator Vane Actuator (Fig. 1)
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A. The variable stator vane actuator moves the inlet guide vanes of the HPC and the 5th-, 6th-, and 7th-stage variable vanes through bellcrank and unison ring links.
B. The variable stator vane actuator is installed on the HPC forward case at the 4:30 o'clock position.
C. The variable stator vane actuator includes a pilot valve, dual torque motor, dual independent linear variable differential transformers (LVDTs), and an actuator piston.
D. The variable stator vane actuator is controlled by the EEC and hydraulically moved by fine filtered engine fuel from the fuel metering unit. The rod end of the actuator piston prevents fuel leakage by dual-stage ring seals. Fuel, which could leak through the ring seals, is drained overboard through a drain tube.
3. Variable Stator Vane Bellcrank Assembly (Fig. 1)
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A. The variable stator vane bellcrank assembly, which includes the bellcrank, unison rings, and adjuster links, is installed on the HPC forward case at the 3:30 o'clock position.
B. The mechanical linkage operates the inlet guide vanes for the HPC, and the 5th-, 6th-, and 7th-stage variable vanes through operation of the variable stator vane actuator.
C. The bellcrank and adjuster links mechanically transmit linear hydraulic motion of the variable stator vane actuator to the unison rings. The unison rings, in turn, transmit the linear motion to the connector links to position the vanes.
4. Operation
_________
A. Functional Description
(1) The EEC sends a signal to the torque motor of the variable stator vane actuator, which converts an electrical signal into a hydraulic drive signal to move the pilot valve.
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
SEE A
BELLCRANK
VARIABLE STATOR VANE ACTUATOR
DRAIN HOSE
SERVO FUEL RETURN TUBE
SERVO FUEL PRESSURE TUBE
A
Compressor Stator Vane Control System Component Location Figure 1
HPC FORWARD
CASE
UNISON RING (4 PLACES)
ADJUSTABLE LINK (4 PLACES)
FWD
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(2) The position of the pilot valve controls hydraulic pressure (fuel
pressure) to the variable stator vane actuator, and finds the
direction and the travel rate of the actuator piston. The actuator
piston position is found and fed back to the EEC by dual linear
variable differential transformers (LVDTs).
(3) The linear motion of the actuator piston is transmitted first to the
bellcrank, then to the adjustable links, unison rings, connector
links, and finally to the variable vanes.
(4) During engine start, the variable vanes are moved in the closed
direction which permits minimum airflow through the HPC. At
approximately 36 %N2, the variable stator vanes start to open and
continue to open as N2 rpm increases and permits maximum airflow
through the HPC.
(5) The variable stator vanes start to close if an impending surge is
detected by the EEC.
(6) If there is no electrical signal to the variable stator vane
actuator from the EEC, the system is made to open the variable
stator vanes.
(7) If the variable stator vane actuator fails, a record of the messages
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