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 C.  The lift power unit consists of a 3-phase, 115V AC electric motor coupled to a gear reduction unit with an output shaft splined at either end running through the reduction unit. The forward and aft ends of the output shaft are connected by torque tubes to the respective forward and aft rotary actuator arms through the gearbox and brake assemblies.
 D.  One end of the link which connects the rotary actuator arm to the door includes a slip joint. As the door is driven closed, the links are compressed to minimum length by the weight of the door until the door is stopped by the hooks engaging the hook pins. Further rotation of the actuator arms extends the links at the slip joint until the lift power unit shuts off. As the hooks completely close the door the links are compressed to some point between limits of slip.
 7.  Gearbox and Brake Assembly (Fig. 2)__________________________
 A.  The gearbox and brake assembly contains a spur and pinion reduction gearbox and a multiple disk brake assembly. The brake assembly is installed on the pinion gear shaft and driven by the pinion gear. Four bronze brake disks inside the brake housing are splined to the pinion gear shaft, alternating between four steel disks which are splined to the housing.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL

 B.  The brake disks are forced together by an adjustable spring plate, causing the entire brake housing assembly to rotate with the pinion gear by brake friction. Ratchet teeth cast in the brake housing and spring loaded pawls bolted to the gearbox form a pawl and ratchet mechanism which allows free rotation of the brake assembly in the door up direction, but locks the housing to prevent rotation in the door down direction. This ensures that the door will remain in position when power is removed, and equalizes power requirements to raise and lower the door by forcing the power unit to drive against slipping brake disks to close the door.
 C.  The torque at which the brake will slip is adjustable by adjusting the spring plate in the brake housing. The torque is set high enough that either of the two brakes will maintain door position in the event one side of the lift mechanism fails.
 8.  Rotary Actuators (Fig. 2)
________________
 A.  The lift mechanism rotary actuators are multiple-stage planetary gear reduction units. The input shaft extends through the unit and is splined on both ends to be driven from either side. The output shaft extends out the mounting flange end of the actuator and rotates in the same direction as the input shaft. Overall gear reduction is approximately 250:1. The actuators are installed in pairs, facing each other, with the actuator arm between.
 9.  Manual Drive Mechanism (Fig. 2)
______________________
 A.  Each of the door electrical actuators (latch, hook and, lift) can be driven manually for adjustments or to overcome failures which prevent electrical operation. The latch and hook actuator manual drive ports are accessible by removing plugs in the door outer skin. The lift power unit is driven manually through a flexible shaft connected to the lift power unit at one end and to a manual drive gearbox in body structure aft of the door at the other end.
 10. Control and Sequence Switches (Fig. 2)
_____________________________
 A.  The side cargo door electrical operation is initiated by either of two control switches just aft of the door at window level, one accessible from inside the airplane, one from outside.
 B.  Sequencing of the mechanism is done automatically by limit switches which actuate to shut off power to one mechanism as it reaches the end of its cycle, and transfer power to the next mechanism in the sequence of events. The final switches in the operating sequence remove all power in either the door up or down position. The sequence switches include a door closed switch, master latch lock switch, latch closed switch, latches open switch, two midspan latch open switches, two hook open switches, two hook closed switches, two door up switches, and two door down switches.
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