10
HORIZONTAL
I12
STABILIZER
MOF 14
APL
NOSE
F
UP
SP2A SP2B
C
STABILIZER TRIMSHUTOFFSWITCHES SECONDARYBRAKE(EXAMPLE) LIMIT SWITCHAND POSITIONTRANSMITTERSTABILIZER TRIMMODULE (EXAMPLE)DRIVE
CONTROL MODULE
SEE D A HYDRAULIC
(EXAMPLE) MOTOR (EXAMPLE)
B
Horizontal Stabilizer Trim System Schematic
Figure 3 (Sheet 2)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ALTERNATE STAB TRIM ú
27-41-00
SWITCHES ON THE CONTROL STAND ú ú 02 Page 8 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(2)
The "arm" segment of the alternate stab trim switches is connected to a standby trim switch. When the alternate stab trim switches are moved, the standby trim switch sends an electrical signal to the SAM. This signal adjusts the mach/speed trim function to agree with the stabilizer position that is commanded by the alternate stab trim switches. The standby trim switch also prevents an incorrect indication of unscheduled stabilizer trim movement.
D.
Stabilizer Trim Control Module (STCM)
(1)
AIRPLANES WITH STAB TRIM LEVERS ON THE CONTROL STAND; the stabilizer trim system uses two identical hydraulic control modules. They provide direction and rate control to the stabilizer trim ballscrew actuator. Each module consists of an arming valve, control valve, two manually controlled valves, four solenoid-operated valves, rate controller, motor-operated shutoff valve, manual brake bypass valve, and a secondary brake pressure switch used in fault monitoring within the SAM. The simultaneous operation of both STCM's will produce twice the trim rate of just one STCM. The modules are installed just forward of the stabilizer in Section 48.
(2)
AIRPLANES WITH ALTERNATE STAB TRIM SWITCHES ON THE CONTROL STAND; the stabilizer trim system uses two identical hydraulic control modules. They provide direction and rate control to the stabilizer trim ballscrew actuator. Each module consists of an arming valve, control valve, four dual-wound solenoid-operated valves, rate controller, motor-operated shutoff valve, manual brake bypass valve, and a secondary brake pressure switch used in fault monitoring within the SAM. The simultaneous operation of both STCM's will produce twice the trim rate of just one STCM. The modules are installed just forward of the stabilizer in Section 48.
(3)
A manual brake bypass valve is located in each module and will release the hydraulic pressure on the secondary brake when depressed. This action applies the brake. The valve is designed to return to its neutral position when the external force is removed.
E.
Stabilizer Trim Ballscrew Actuator (Fig. 4)
(1)
The ballscrew actuator consists of two sets of drive hydraulic motor/secondary brake combinations which singly or simultaneously drive the ballscrew actuator. The ballscrew actuator consists of a differential gearbox, jackscrew and ballnut assembly, and a primary brake.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
27-41-00
ALL ú ú 02 Page 9 ú Sep 20/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
SEE A
ARM NOSE-UP SOLENOID
"ARM" INPUT
LEVER
ARM NOSE-DOWN SOLENOID
AIRPLANE NOSE-DOWN CONTROL SOLENOID AIRPLANE NOSE-UP CONTROL SOLENOID
MOTOR OPERATED SHUTOFF VALVE
757
MAINTENANCE MANUAL
HORIZONTAL STABILIZER UPPER STOP
UPPER GIMBAL
BALLNUT TRUNNION
SECONDARY BRAKE
BALLSCREW
LOWER
STOP
BALLSCREW ACTUATOR
PRIMARY HYDRAULIC MOTOR DRIVE
BRAKE (2 LOCATIONS)
LOWER GIMBAL
FWD
ST2B
A
ST2A
ST1A ELEVATORRIG PIN FEEL PORTE/ST 2
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