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 27-21-00
 ALL  ú ú 01 Page 8 ú Dec 15/83
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

 (2)  
The rudder ratio changer modules (RRCM) are located in the main equipment center on shelves E3 and E4. The modules receive 28 volts dc from bus L and are controlled by the RUD RATIO circuit breaker located on overhead circuit breaker panel P11.

 (3)  
The ratio changer has an offset torque tube with two inputs and two outputs. The two inputs come from the aft quadrant, feel, centering and trim mechanism through two control rods. The control rods are adjustable for rigging purposes. Output comes from two control rods mounted on the left and right ratio changer cranks. The cranks are tied together by an interconnect rod, and move together at the same time as the actuator extends or retracts. The left crank mounts the ratio changer actuator rod end; both cranks are spring-loaded to return the mechanism to the low speed position (actuator retracted, crank arms swung out) in the event of hydraulic failure. Rig pins R5 and R6 fix the cranks to the torque tube in the high speed position.

 J.
Linear Variable Differential Transformer (LVDT)

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 (1)  
An LVDT is mounted on the ratio changer and driven by the right crank. Dual channels provide position feedback signals to the two rudder ratio changer modules (RRCM). The left LVDT channel supplies signals to the left RRCM and the right channel supplies the right RRCM. The LVDT has an adjustment nut for rigging purposes. The LVDT is powered by 26 volts ac from PSM 1R and 1L.

 K.
Primary Control Linkage - Load Limiting

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 (1)  
A shearout is located on the right ratio changer crank. The shearout protects the primary control linkage between the ratio changer and yaw damper summing lever in the event of a jam.

 L.
Secondary Control Linkage

_________________________
 (1)  
The secondary control linkage includes a pogo between the left ratio changer crank and the yaw damper summing lever. The ratio changer output pogo limits the force fight in the two control paths due to component tolerances and is slightly biased to reduce lost motion by preloading the linkage joints. Rod end bearings are called out on the pogo rod decals. Breakout load is 46-56 pounds (204-249 Newtons) . Extension/retraction is +/-3.3 inches (84 mm). Rig pin hole R7, which controls the amount of pogo bias, is located at the end closest to the ratio changer mechanism.

 M.
Rudder Ratio Changer Actuator (RRCA) (Fig. 6)

____________________________________
 (1)  The RRCA is located on top and to the left of the ratio changer. The RRCA is attached to the ratio changer support bracket mounted on the vertical fin aft spar. The RRCA piston rod end is attached to the left ratio changer crank. The actuator has four line replaceable units: a solenoid valve, an electrohydraulic servo valve (EHSV), and two filter screens. The solenoid valve controls the hydraulic supply to the RRCA. The EHSV controls the rate and direction of hydraulic flow within the RRCA. The filter screens provide filtering of the hydraulic fluid input.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 27-21-00
 ALL  ú ú 01 Page 9 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

SOLENOID
ACTUATOR324BL
VALVE
SEE A ELECTRO-HYDRAULIC SERVO VALVE
BEARING MOUNT TO STRUCTURE
ANTI-ROTATION
MOUNTING

ACTUATOR MOUNT TO CLEVIS
ACTUATOR TO BELL CRANK CONNECTION
A
ACTUATOR BYPASS VALVE
REAR SPAR VERTICAL FIN
ELECTRO-HDRAULIC FILTER
SERVO
TOP VIEW SCREEN  VALVE
RTN
PRESS
PCA
BOOT CONNECTOR
FILTER SCREEN
CONNECTOR
LEFT SIDE VIEW
Ratio Changer Actuator Figure 6
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
　
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