(b)  
The yaw damper engage switch will remain in the ON position by holding the switch to ON for at least 0.1 second. This allows voltage through the holding coil and the logic circuit timer to complete a path to ground as provided by the logic OR gate circuit.

(c)  
The yaw damper engage relay is energized by a ground through the logic AND gate after going through the 2-second timer. Two sets of contacts apply power to the interlock circuit and to the respective rudder power system. An additional set of contacts open which extinguishes the warning light.

(d)  
Switching between hydraulic power systems causes the yaw damper system to disengage. Transferring between 115-volt ac generators will cause the monitor to momentarily go invalid. However, with a 2-second decay timer in the engage switch circuit, the yaw damper engage relay remains energized.

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H19134
584  Yaw Damper Engage Interlocks 
Feb 15/80  Figure 3  22-11-0 
Page 19 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

(3)  Engaged Mode
(a)  
When the yaw damper coupler is engaged, processed rate gyro signals at summing point 2 produce a valve amplifier output. This output is applied to the series yaw damper actuator transfer valve to command movement. Movement of the yaw damper series actuator results in rudder movement and an output from the position transducer.

(b)  
Position transducer output is demodulated and applied to summing point 2 to cancel the processed rate gyro signal when the corresponding change in rudder position is appropriate for the rate of yaw attitude change. Position transducer output is also applied to control the integrator. The integrator lag is large enough so that the integrator output, which is applied to summing point 2, does not attenuate yaw damper action in the dutch roll frequency spectrum.

(c)  
Rate gyro signals are processed in the rate gyro filter. The rate gyro filter consists of a demodulator, amplifier, and washout network. Filtering accomplished in these circuits eliminates steady-state signals and unwanted high frequency signals. Consequently, the yaw damper coupler does not oppose normal turn maneuvers and does not respond to airplane vibration and bending. Frequency response is tailored to minimize the airplane dutch roll. The rate gyro filtered output is routed to summing point 2 through Q-potentiometer in the ADC. Rate gyro signal gain is varied by this potentiometer to compensate for changes in airplane dynamics as a function of airspeed.

C.  Yaw Damper Test
(1)  The yaw damper indicator, located on the center instrument panel, is a full time operating meter. Whenever the yaw damper system is engaged, the yaw damper indicator will reflect the movements of the rudder. Actuation of the yaw damper test switch to either the left or right applies a voltage to the yaw damper coupler (Fig. 4). Voltage to the coupler is applied to the yaw damper rate gyro torqueing coil which torques the rate gyro and simulates airplane movement. The coupler provides the properly related voltage to rudder power unit for rudder deflection consistent with direction selected. The yaw damper indicator responds to this action as a result of an output from the position transducer.
5.  Autopilot Roll Channel Operation
A.  General
(1)  The roll channel simplified block diagram, Fig. 5, presents the roll axis signal circuits. The various command input signals are summed at summing point 2, routed to the roll computer and combined with feedback signals at summing point 9. This resultant
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H19129
545  Yaw Damper Test Circuit 
Aug 1/74  Figure 4  22-11-0 
Page 21 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

error signal is fed to the aileron power unit to command surface deflections. The system contains three main sections; the input section, the roll computer, and the output and feedback section. Except for control wheel steering (CWS), signal inputs from the input section are summed before going to the bank limiter. Individual input selection includes heading hold, attitude hold, heading select, VOR/LOC course selection. If OMEGA is installed, heading select and OMEGA steering are externally switched into a single input. The output from the CWS force transducer supplies a signal to the rate limiter proportional to pilot force on the control wheel. The vertical gyro senses the change of roll attitude for an input to the computer. The roll computer section provides a composite roll error signal as an output for summing with the feedback section signal. The composite signal at summing point 9 is fed to the aileron power unit.
　
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