H.  Force Transducers
(1)  
The force transducers supply control wheel steering signals to the pitch and roll control channels which are proportional to the amount of force applied to the control wheels by the pilots when manually flying the airplane with the autopilot channels engaged.

(2)  
There are two force transducers in the pitch axis and one in the roll axis. The two pitch force transducers are mounted in the forward control quadrants below the captain's and first officer's control columns. The roll force transducer is mounted between the control shaft and aileron drum below the captain's control column. Each force transducer assembly consists of two independent electrically isolated E pickoff type transducers. The transducer provides a signal output proportional to the force applied to the control wheels.

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I.  Force Limiter
(1)  
The force limiter is splined to the aileron drum at the bottom of the captain's control column. The force limiter consists of an electromechanical clutch, switch and a spring-loaded arm and cam assembly. The electromechanical clutch and switch are activated when the roll axis is engaged. The force limiter mechanically limits the control wheel angle to 17 degrees by progressive increase of force within the system to cam out the autopilot control at the power control unit. This limits the rate of roll which the autopilot can command; thereby, ensuring against autopilot hardover maneuvers. The switch ensures the force limiter clutch is engaged. If the clutch disengages, the switch opens the aileron engage switch holding coil circuit.

(2)  
The captain or first officer may override the force limiter by applying sufficient force on the control wheel to drive through the limiting mechanism. The autopilot continues to drive the power unit throughout the control wheel steering regime after the control wheel is returned to less than 17 degrees. Manual control is used if the control wheel is turned greater than 17 degrees.

(3)  
The force limiter is deactivated when the autopilot is disengaged, regardless of control wheel position.

4.  Yaw Damper Operation (All except coupler P/N 4084042)
NOTE: For aircraft with coupler P/N 4084042 installed (incorporating SB 27A1206), see 22-12-01.
A.  General
(1)  
The yaw damper provides damping of the airplane's yaw axis movement by shaping, amplifying, and coupling rate gyro and yaw damper actuator position signals to control the rudder through the hydraulic actuator. Yaw damper operation is confined to synchronization mode and engaged mode.

(2)  
The description of yaw damper operation is based upon the schematic shown in figure 2. Summing points on this schematic are coded with reference numbers to aid in the discussion.

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593  Yaw Damper Block Diagram 
Feb 20/90  Figure 2 (Sheet 1)  22-11-0 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Yaw Damper Block Diagram  593 
22-11-0  Figure 2 (Sheet 2)  Feb 20/90 
Page 18 
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H19077
519  Yaw Damper Pictorial Diagram 
Nov 15/79  Figure 2A  22-11-0 
Page 18A 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

B.  Operating Modes
(1) 
 Synchronization Mode

(a)  
Prior to yaw axis engagement, the yaw damper coupler is in the synchronization mode. The purpose of synchronization is to provide a null output to the electrohydraulic transfer valve to prevent yaw damper coupler engage transients.

(b)  
Synchronization is accomplished by routing the demodulated, parameter-controlled signal from summing point 2 through switch Sl, summing point 4 and integrator, and back to summing points 3 and 2. Output from summing point 2 results in temporary output from the valve amplifier. The valve amplifier output is reduced to a null as the integrator output increases and cancels the signal at summing point 2.

(c)  
Prior to yaw damper engagement, the yaw damper actuator remains centered which nulls the position feedback to the yaw damper coupler.

(2)  
Engage Interlocks and Logic (Fig. 3)

(a)  
Prior to engaging the yaw damper system, the yaw damper disengage warning light is illuminated (Fig. 1 and 3). Before the yaw damper engage switch will remain engaged, the power supply must be good from the 115-volt ac power supply and the flight control B switch must be on.
　
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