Stabilizer Trim Ballscrew Actuator Compartment Component
Figure 4 (Sheet 1)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH STAB TRIM LEVERS ON THE ú
27-41-00
CONTROL STAND ú ú 02 Page 10 ú Mar 20/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
SEE A
ARM NOSE-UP SOLENOID
ARM
NOSE-DOWN
SOLENOID
AIRPLANE NOSE-DOWN CONTROL SOLENOID AIRPLANE NOSE-UP CONTROL SOLENOID
MOTOR OPERATED SHUTOFF VALVE
757 MAINTENANCE MANUAL
UPPER STOP
UPPER GIMBAL BALLNUT TRUNNION
SECONDARY BRAKE
DRIVE
HYDRAULIC MOTOR
(2 LOCATIONS)
LOWER GIMBAL
FWD
A
ELEVATOR FEEL PORT
PRESSURE PORT
BRAKE
PRESSURE
SWITCH AIRPLANE NOSE-UP PORT
HORIZONTAL
STABILIZER
BALLSCREW
LOWER
STOP
BALLSCREW ACTUATOR
PRIMARY BRAKE
RETURN 1 PORT
BRAKE RELEASE PORT
RETURN 2 AIRPLANE PORT NOSE-DOWN PORT
Stabilizer Trim Ballscrew Actuator Compartment Component
Figure 4 (Sheet 2)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ALTERNATE STAB TRIM ú
27-41-00
SWITCHES ON THE CONTROL STAND ú ú 02 Page 11 ú Mar 20/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(2)
Each STCM controls a drive hydraulic motor and a secondary brake. The STCM ports fluid to the brake and its associated drive motor. The brake is mounted in-line with the motor and acts upon the motor output shaft. When hydraulic pressure reaches the brake-release pressure level, the spring-loaded brake disc disengages and permits motor operation. The brake is sized to hold the maximum output torque of the drive motor.
(3)
The differential gearbox drives a jackscrew and ballnut assembly. The two motors sum their outputs through the differential. This permits full torque capability with one or both motors driving. When only one side of the differential is driven (one motor operation) the opposite side is held stationary. This results in one-half the trim rate. Full trim rate is accomplished with both motors operating. The gearbox utilizes dual load path design to assure that the braking function of either the hydraulic motor or brake is retained after any single failure.
(4)
The jackscrew is dual load path by virtue of a safety rod inside the jackscrew housing which will hold it intact in the event of screw fracture. The inner rod is torsionally constrained to the primary brake at the base and to the jackscrew at the top. The ballnut consists of four ball circuits all of which are loaded. If one fails, only 25 percent of the load carrying capability of the ballnut will be lost. In addition to the ballnut, there is an acme nut which will ride in the ball races on the jackscrew if all ballnut circuits fail.
(5)
The primary brake consists of a disc of friction material and a ratchet plate on both sides of the jackscrew flange. The ratchet plates and their associated pawls permit ratcheting when the jackscrew is driven in a direction to bring the airplane into trim, and resist stabilizer loads backdriving actuator in the APL out of trim direction.
(6)
The ballscrew actuator is located in the empennage. The actuator is held in place by two gimbal pin attachments. The upper gimbal pin attaches the ballnut to the stabilizer. The lower gimbal pin connects the actuator to bulkhead structure below the stabilizer.
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27-41-00
ALL ú ú 02 Page 12 ú Sep 20/90
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
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