)
(LMODAL
SUPPRESSION

ACCELEROMETER
DFDAU 2

REACTION LINK(3 PLACES) EICAS
1
IRU
(L,C & R)

MECHANICAL RUDDERLEFT CONTROL LINKAGE (REF)YAW DAMPER
AIR DATA MODULE
COMPUTER MANUAL &(L & R) AUTOPILOTINPUT (REF)
LEFT
YAW
DAMPER

HYD SERVO YAW DAMPER PRESS CONTROL (L)
PANEL
INTERLOCKS

RIGHT
PRESS

HYD YAW
(C) DAMPER
SERVO POWER CONTROLACTUATOR (3 PLACES))(R
MODAL
SUPPRESSION

CENTER SPRINGACCELEROMETER
RIGHT
YAM DAMPER

MANUAL &
MODULE

AUTOPILOT
INPUT (REF)  CENTER OFROTATION
1
VALID
HYD PRESS.

AIR/GRD
TEST SW 1AIRPLANES WITH -122 AND ON YAW DAMPER MODULE2 GUN 051,102-999
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 22-21-00
 ALL  ú ú 06 Page 6 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
Yaw Damper Block Diagram
Figure 3

C27585
A
757
MAINTENANCE MANUAL

 (3)  
Yaw Damper Servos

 (a)  Two yaw damper servos are connected in series to the rudder actuating linkage. The yaw damper servos provide the mechanical output to the rudder power control actuator input linkage. The servos receive electrical commands from the yaw damper modules and convert these signals to mechanical commands via an electrohydraulic servo valve (EHSV). The EHSV responds to electrical commands and delivers hydraulic flow proportional to the input signals. Hydraulic fluid then drives the servo actuator piston. The actuator piston drives the LVDT, which provides position feedback to the yaw damper module.

 (4)  
AIRPLANES WITH -122 AND SUBSEQUENT YAW DAMPER MODULES; Modal Suppression Accelerometer

 (a)  The modal suppression accelerometers measure the lateral acceleration of the aft of the airplane. This information is provided to their corresponding yaw damper modules as an analog signal.

 (5)  
System Annunciation

 (a)  The yaw damper ON and INOP annunciation is on the yaw damper panel. System failure status is also provided to the EICAS computers for display on the EICAS display unit (Ref 31-41-00).

 (6)  
GUN 051, 102-999; Digital Flight Data Acquisition Unit (DFDAU) Interface

 (a)  The left and right yaw damper modules provide left and right yaw damper engagement status to the DFDAU (Ref 31-31-00).
 I. Configuration
 (1)  Yaw Damper Module (YDM)
 EFFECTIVITY -109 -124 -125 ~.................................................................
 |GUN 001-008  | BASIC  |  SB 22-18  |  |
 |  |  |  |  |
 |GUN 009-104  |  |  BASIC  |  |
 |  |  |  |  |
 |GUN 105-999  |  |  |  BASIC  |
 |  |  |  |  |

 2......................…...........…..............…...............1
 2. Component Details (Fig. 4)
_________________
 A. Yaw Damper Panel Assembly
 (1)  
The YDS controls and indicators are on the overhead panel (P5). The left and right ON and INOP indicator lamps use 28 vdc provided by the standby and right main bus, respectively. Case cooling is provided by forced ambient cooling air. Two electrical connectors (one for each yaw damper module) are on the back side of the panel.

 (2)  
Each yaw damper module has its own set of controls and indicators on the panel.

 (a)  The ON switch/light controls engagement of the YDS by controlling 28 vdc to the servo solenoid valve on the yaw damper servos. When the switch/light is first pressed, the ON legend is illuminated. Pressing the switch/light a second time turns off the YDS.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 22-21-00
 ALL  ú ú 14 Page 7 ú Mar 20/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757 MAINTENANCE MANUAL
SOLENOID ELECTROHYDRAULIC
VALVE
SERVO VALVE
YAW DAMPER

YAW DAMPER LINEAR
ENGAGE
LR
SWITCHES DIFFERENTIAL TRANSDUCER VOLTAGE ON ON
　
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