H19383
Yaw Damper System Component Location 580
22-12-0 Figure 1 May 15/79
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
E. The yaw computer provides amplification and shaping of the rate gyro signals for operation of the yaw damper hydraulic transfer valve and synchronizes the signal chain prior to engagement.
F. The yaw damper coupler provides control signals to the solenoid valve and transfer valve and receives feedback signals from the position transducer.
3. Yaw Damper Engage Switch and Disengage Light
A. The YAW DAMPER ENGAGE switch is located on overhead panel P5 and is the solenoid held type. When the engage switch is placed to the ON position, and if the yaw damper engage interlocks are satisfied, the solenoid will hold the switch engaged. The yaw damper is then in the yaw damping mode.
B. Whenever the yaw damper is or becomes disengaged, the amber light labeled YAW DAMPER, on overhead panel P5, illuminates steadily. The MASTER CAUTION lights and the FLT CONT master caution annunciator light, located on the light shield, also illuminate.
4. Yaw Damper Test Switch and Indicator
A. The YAW DAMPER TEST switch and indicator are located on center instrument panel P2. When the yaw damper is engaged, hydraulic power is available and the test switch is actuated, a test voltage is applied to the yaw damper coupler that torques the rate gyro. As the gyro is displaced, its output signal is sent through the normal signal chain and the rudder deflects. The position transducer on the rudder power control unit senses rudder displacement from neutral and sends a signal to the indicator which shows rudder deflection. If the test switch is placed and held in L, left (or R, right) position, the bar on the indicator should deflect left (or right) momentarily and return to center. Upon switch release, the indicator bar should deflect right (or left) momentarily and return to center. In flight, the indicator shows rudder deflection from neutral resulting from yaw damper inputs.
5. Rudder Position Transducers
A. A linear position transducer mounted on the rudder power control unit supplies a rudder position feedback signal to the yaw damper coupler. The transducer is a variable reluctance transformer which is excited by 26 volts ac. The magnitude of the output signal varies directly with the length of the input stroke and the phase of the signal changes with the direction of the stroke from the center null position.
6. Rudder Transfer and Solenoid Valves
A. The transfer and solenoid valves control hydraulic flow for yaw damper control of the rudder power control unit.
B. The yaw damper solenoid valve is mounted on the rudder power control unit. It is a solenoid actuated valve which is energized when the yaw damper is engaged; it then completes hydraulic power to the transfer valve.
C. The transfer valve, also mounted on the rudder power control unit, converts the yaw damper electrical signals into hydraulic flow to move the rudder. The unit consists of a torque motor which moves a jet pipe assembly that regulates the hydraulic flow to the control valve.
505
Oct 20/86 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 22-12-0 Page 3
7. Yaw Damper Operation
A. General (Fig. 2)
(1) The yaw damper provides damping of movement about the airplane's yaw axis 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.
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. Prior to yaw damper engagement, the yaw damper actuator remains centered which nulls the position feedback to the yaw damper coupler.
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