INPUT CRANK 757 MAINTENANCE MANUAL SHEAR PIN YAW DAMPER SUMMING LEVER
UPPER COMPENSATING ROD
MULTIPLIER CRANK FIN REAR SPAR
RIG PIN HOLE R7 POGO-SECONDARY CONTROL LINKAGE
RATIO CHANGER MECHANISM
ROD LOWER COMPENSATING B RIG PIN HOLE R8 YAW DAMPER POGO
FIN REAR SPAR
SUPPORT BRACKET A-A Yaw Damper Summing Lever Figure 8 (Sheet 2) C
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27-21-00
ALL ú ú 04 Page 14 ú Jun 15/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
TRUNNION BLOCK
PCA INPUT LEVER
HORIZONTAL INPUT LINK (ADJ)
SHEAR PIN INSPECTION HOLE
757
MAINTENANCE MANUAL
PCA
R
324CL
PRIMARY
CONTROL PATH L
SEE A SECONDARY
CONTROL PATH PCA
SEE B
C
PCA
FROM YAW DAMPER SUMMING LEVERS
A BELLCRANK RETURN LINE
TRANSFER PRESSURE LINE
CONTROL PATH TO UPPER PCA
TRANSFER BELLCRANK
ELECTRICAL CONNECTOR
PCA MONITOR SENSOR
REACTION LINK
HANGER LINK PCA
CONTROL PATH RUDDER TO LOWER PCA
CONTROL PATH (FROM YAW SUMMING OUTPUT)
MIDDLE PCA
B
Rudder Power Control Actuators (PCAs) Figure 9
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27-21-00
ALL ú ú 02 Page 15 ú Mar 20/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(4)
The only line replaceable unit (LRU) on the PCA is the 250 micron screen/filter located in the pressure inlet line. Other parts of the PCA are not LRUs because the tests necessary to make sure the PCA operates correctly use hydraulic pressures and flows greater than those available on the airplane.
(5)
One of the relief valves is an independent unit. The other is integral with the PCA monitor sensor. The sensor senses pressure change across the PCA piston during pre-flight ground check. A control valve jam or disconnect or an input linkage disconnect is then sensed due to abnormal pressure difference and the failure noted on lower EICAS display unit status page (Ref 27-23-00).
(6)
The PCA control valve is biased in the retract direction (left rudder) by a coil spring. This removes backlash in the linkage and assures the control valve is positioned off null in the event of internal linkage disconnect. The control valve input linkage has full overtravel capability from each extreme input position.
Q.
PCA Reaction Link
_________________
(1)
The reaction link provides mechanical feedback from rudder surface movement to reposition the actuator body and null out the valve input. One end is connected to the rudder front spar on the right side of the rudder pivot. The other end is connected to the trunnion assembly. Curved slots on top and bottom of the trunnion assembly provide retention for the PCA in the event of a reaction link or hanger link failure. The trunnion right side is connected to and supported by the bearing mounted hanger on vertical fin rear spar.
R.
PCA Linkages
____________
(1)
The PCA linkages transfer inputs from the yaw damper summing lever to the actuators through control rods and torque tube levers. The primary control path (right side) provides input to the middle PCA torque tube lever. Control input is continued through the primary control path to the lower and upper PCAs via non-adjustable rods. The secondary control path (left side) connects the summing lever to the lower PCA torque tube lever and is non-adjustable.
(2)
Shearout rivets are provided at each PCA input valve lever to protect against a jam in the PCA control valve or linkage.
S.
Rudder Structure (Fig. 10)
________________
(1)
The rudder is constructed of graphite epoxy over a nomex honeycomb. The rudder weighs about 334 pounds (151 Kg) and is about 30 feet tall (9.15 m).
(2)
Eight hinge fittings are mounted between the vertical fin rear spar and the rudder front spar. Two thrust hinges provide rudder positioning. Six hinges are expansion link hinges needed to account for the difference in thermal expansion between the graphite rudder and aluminum hinges. A seal between the rudder front spar and fin rear spar prevents airflow across the hinge line at all deflection angles. Hoisting points are located at the rudder front spar between the bottom two hinges and between the sixth and seventh hinges from the bottom.
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