A.  The rudder feel and centering mechanism consists of the feel and centering unit which provides artificial feel to the pilots' pedals and centers the rudder. The feel and centering unit is located below the rudder power unit in the vertical fin (Fig. 3). The feel and centering unit has the following parts: A support shaft, a feel and centering crank, two frames, an arm and roller with a spring assembly, and a cam. The support shaft is bearing mounted on structure. The feel and centering crank is fixed to the support shaft and is connected through the trim and feel rod to the lower crank on the torque tube. The two frames are bearing mounted on the support shaft. The arm and roller and the spring assembly attach to and rotate with the two frames. The cam is fixed to and rotates with the support shaft. The cable drum end of the rudder trim actuator is supported by the forward side of the two frames. When the rudder pedals are displaced, the torque tube rotates causing offset of the trim and feel rod and in turn rotation of the feel and centering crank, the support shaft and the cam. As the cam rotates, the arm and roller are displaced out of the detent position to extend the spring assembly and provide artificial feel. Rudder trim input through the rudder trim actuator rotates the two frames with the arm and roller and spring assembly. The force of the spring assembly holds the arm and roller in the cam detent and causes the cam to rotate also. Rotation of cam causes subsequent motion of the support shaft, the feel and centering crank, the trim and feel rod, the lower crank, the torque tube which then causes input to the rudder power unit repositioning the rudder. At the same time the lower crank causes input to the rudder control system with movement of the pilots' pedals.
500 
27-21-1 Page 10  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/03 

W32348 W32468
500  Rudder Feel and Centering Mechanism Schematic 
May 01/03  Figure 4  27-21-1 
Page 11 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Main Rudder Power Control Unit Schematic  500 
27-21-1 Page 12  Figure 5 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/03 

11.  Main Rudder Power Control Unit (PCU) (Fig. 5)
A.  The PCU moves the rudder right or left when actuated by rudder pedal input, rudder trim, or yaw damper.  It also provides wind gust snubbing when the airplane is parked.  The unit is located in the vertical fin (Fig. 1).  The body is fixed to fin structure and the power head to the rudder. 
B.  The PCU is a dual tandem hydro-mechanical servo, powered by hydraulic systems A and B.  The PCU is internally separated into an A and B side, providing an output force equivalent to two PCUs.  Each half of the PCU consists of a balanced actuator, bypass valve, inlet filter and inlet check valve, all contained in a separate manifold for each system.  The A and B manifolds are bolted together to make up a single PCU package, controlled by two independent input linkages that drive two independent servo valves which are controlled by externally mounted breakout devices for jam protection.
C.  The PCU yaw damper function is to minimize dutch roll during manually and automatically controlled flight.  The yaw damper provides rudder displacement proportional to the yaw rate, and opposing the yaw direction of the airplane.  The yaw damper input is in series with the pilots' input and is not felt at the rudder pedals.
D.  The Force Fight Monitor (FFM) compares the delta pressure of the A system actuator with the delta pressure of the B system.  When the delta-delta pressure exceeds 3150 psi for 5 seconds, the FFM provides an electrical ground to the P5-3 panel to command pressure to the standby actuator, open the rudder standby system shutoff valve, and turns on the STBY RUD ON light.  The FFM contains a latch that can be reset by following the fault isolation procedure for the STBY RUD ON light (AMM 27-21-0/101).
E.  A Rudder Pressure Limiter (RPL) is installed on the main PCU "B" piston to limit output from 3000 psi to 2200 psi when the airplane climbs above 1000 feet above ground level (AGL). Hydraulic pressure is restored from 2200 psi to 3000 psi when the airplane descends through 700 feet AGL.  The RPL is controlled by the yaw damper coupler.  The RPL defaults to full pressure following loss of electric power.
F.  Pilots' input, by rudder pedals or trim wheel, is transmitted through cables and linkages to the PCU input cranks.  The input cranks rotate and move the control valves which port 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 summed internal to the main PCU. The PCU piston rod end is attached to the rudder.  Extension or retraction of the rod moves the rudder left or right.  The external summing levers attached to the rod provide feedback to return the control valves to neutral and to stop the rudder at the desired position.
　
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