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A 737-300/400/500MAINTENANCE MANUAL
PILOT'S INPUT
FEEL AND
CENTERING
TRIM ACTUATOR UNIT
FIN STRUCTURE
RUDDER PEDAL (TYP) CONTROL ROD
QUADRANT AFT
FORWARD QUADRANT TORQUE TUBE LOWER CRANK (BELL CRANK)
BUS ROD
Rudder Feel and Centering Mechanism Schematic
Figure 5
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A 737-300/400/500MAINTENANCE MANUAL
TRANSFER VALVE CAGING SPRING YAW DAMPER SHUTOFF VALVE
CONNECTOR ELECTRICAL C C P PRIMARY VALVE PB SECONDARY VALVE TANDEM ACTUATOR
RB R
YAW DAMPER POSITION TRANSMITTER BYPASS VALVE
COMPENSATOR SPRING
SECONDARY SUMMING LEVER
COMPENSATOR
YAW DAMPER ACTUATOR
PRIMARY SUMMING LEVER
RA PA
INPUT INTERNAL
SHAFT INPUT THERMOSTATIC
CRANK VALVE OR PLUG
(OPTIONAL)(2 PLACES)
Rudder Power Control Unit Schematic
Figure 6
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T80957
A
737-300/400/500MAINTENANCE MANUAL
C. In some airplanes a Rudder Pressure Reducer (RPR) is connected to the "A" system hydraulic line upstream of the main rudder PCU. Hydraulic pressure to the rudder is reduced when the airplane climbs above 1000 feet AGL. Hydraulic pressure returns to normal when the airplane descends through 700 feet AGL, or if "B" hydraulic system depressurizes, or whenever the N1 difference between the left and right engine exceeds 45 percent. The function of the rudder pressure reducer is to reduce the rudder authority by approximately one-third at higher speed condition. The reduce rudder deflection will permit more effective lateral control in countering rudder inputs, and will give the pilot more time to recover from a full rudder input, regardless of the cause. The rudder pressure reducer does not involve the system-B portion of the rudder power and control, and will have no effect on the yaw damper system operation. The Flight Control System-A "LOW PRESSURE" light on the P5 panel indicates "A" system pressure is low when normal system pressure is commanded. Following pressurization of hydraulic system-A with the yaw damper coupler powered and Flight Control A switch on, the Flight Control System-A "LOW PRESSURE" light will be shown for approximately 5 seconds.
D. Pilots' input by rudder pedals is transmitted through cables and linkages to the power control unit input crank. The input crank rotates and moves the control valve which ports hydraulic pressure to the actuating cylinder. The amount of control valve movement is also governed by the yaw damper input. The pilots' input and yaw damper input are combined algebraically by the summing levers, which connect to the the primary and secondary control valves. The power control unit piston rod end is attached to the rudder. Extension or retraction of the rod moves the rudder left or right. An external summing lever attached to the actuating piston provides feedback to return the control valve to neutral and to stop the rudder at the desired position.
11. Standby Rudder Actuator Shutoff Valve_____________________________________
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