Elevator Control System
Figure 18
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
22-00-01
ALL ú ú 05 Page 29 ú Mar 20/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
V. Elevator Control Modes (Fig. 19)
(1)
All elevator control is accomplished by movement of a common set of linkages. Both aft quadrant torque tubes operate together. The mechanical linkage translates torque tube movement into PCA control lever movement. The hydraulically powered PCAs move the elevators. Linkage between the PCA output shaft and input linkage centers the control lever when the elevator position corresponds with the input linkage position.
(2)
AIRPLANES WITHOUT CONTROL WHEEL STEERING; pitch control is accomplished by pilot controlled inputs through the control columns and autopilot. Manual input, through the control columns, mechanically moves the PCAs. If the autopilot is engaged outputs are processed by an FCC to control an autopilot pitch control servo. The servo then drives the linkage to the PCAs and backdrives the control cables to move the control columns.
(3)
AIRPLANES WITH CONTROL WHEEL STEERING; pitch control is accomplished by pilot controlled inputs through the control columns and autopilot. Manual input, through the control columns, mechanically moves the PCAs if the autopilot is not engaged in the CWS configuration. If CWS is engaged, the control columns pitch control force transducer's outputs are processed by an FCC to control a pitch autopilot servo. The servo then drives the linkage to the PCAs and backdrives the control cables to move the control columns.
PILOT CONTROLLED INPUTS
PILOT INPUT
AIRPLANES WITH CONTROL WHEEL STEERING
Elevator Control Modes Figure 19
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
22-00-01
ALL ú ú 08 Page 30 ú Sep 28/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(4) Pilot controlled inputs are conditioned by reaction inputs. The feel computer reacts to stabilizer position and dynamic pressure, and then provides appropriate inputs to the feel unit. Neutral shift reacts to stabilizer position and maintains the relative stabilizer-to-elevator position by mechanically moving the feel unit.
W. Elevator Control Conditioning Devices
(1)
Elevator Neutral Shift
(a) The elevator neutral shift assembly recenters the elevators in proportion to stabilizer position to maintain elevator authority. The effective range is between 8 and 12 1/2 degrees of stabilizer leading edge down (airplane nose-up). The assembly moves the feel and centering unit through an override cam and follower. The feel and centering then moves linkages to the PCAs, which reposition the elevators. Elevators move from a normal position of 3 degrees down to a maximum of 1 degree up.
(2)
Elevator Feel and Centering Unit
(a) Mechanical feel and centering is provided by a cam and follower inside the feel unit. They are between a feel actuator and the feel unit control arms. Control arms are connected to the elevator aft quadrant torque tubes. The feel computer varies hydraulic pressure to the feel actuator in proportion to airspeed and stabilizer position. This provides the appropriate pressures for the sense of feel and centering required by the pilots.
X. Elevator Feel Unit
(1)
The elevator feel unit generates increasing force with increased control system movement. The scheduling of force application is determined by the feel computer, which uses dynamic pressure and stabilizer position to meter hydraulic pressure to the feel actuator.
(2) 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：757 AMM 飛機維護手冊 自動飛行 AUTOFLIGHT 1(19)
