Main Cargo Door Latching Mechanism 520
52-32-0 Figure 2 (Sheet 1) Aug 15/76
Page 6
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
511 Main Cargo Door Latching Mechanism
Aug 15/68 Figure 2 (Sheet 2) 52-32-0
Page 7
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
and to a bellcrank in the center of the torque tube at the lower end. When unlatching the door, the hydraulic latch actuator retracts. The actuator rod pulls on the torque tube bellcrank causing the torque tube to rotate with the latch bellcranks. The eight latch bellcranks cause the latch hooks to rotate and release the latch pins in the doorsill. As the latch hooks release, they simultaneously push against the latch pins and force the door open to break the pressure seal. Final rotation of the mechanism move the latch actuator rod end slightly overcenter of the torque tube. The compression spring cartridge retains the mechanism in its overcenter position when hydraulic pressure is removed from the actuator. Mechanical stops limit the maximum amount of torque tube rotation. When the door is latching shut, the latch hooks engage the latch pins and pull the door shut to the sealed position. Due to a restrictor in the lift actuator, the door and latch motion is sequenced when opening the door so that the latch actuator operates before the door lift actuator operates. When the door is closing, the latch actuator operates after the lift actuator has lowered the door and the latch hooks engage the latch pins.
(2) Latch Actuator
(a) The latch actuator is composed of a cylinder, piston and rod, necessary seals and a fluid absorber. Two hydraulic ports are near each end of the actuator. The piston responds to hydraulic pressure applied to one of the ports. The remaining port acts as a return line. A felt ring installed on the end of the actuator absorbs any leaking hydraulic fluid. The absorber is retained with a spring. Hydraulic lines to the actuator are coiled near the actuators upper attachment point, thereby minimizing hydraulic line flexing as the actuator moves.
B. Lock Mechanism (See figure 3.)
(1) The lock mechanism consists of an external locking handle assembly, a flexible control cable, bellcrank assembly, pushrod assembly, eight tube assemblies with bellcranks and eight locking pins and links. The external locking handle assembly is mounted flush on the forward outboard section of the main cargo door near the horizontal centerline of the door. The handle assembly has a spring-loaded fairing covering the handhold. The hand can be slipped under the control handle after pushing in on the fairing to gain access to the handle. The locking handle assembly is connected to the flexible cable which, in turn, is connected to the bellcrank assembly. The bellcrank assembly is connected to a series of pushrods and tube-bellcrank assemblies which, when rotated, insert or pull out lockpins outboard of the latch bellcrank assemblies. When the lockpins are inserted, each latch bellcrank is prevented from rotating, thereby locking the door closed. Pulling on the lock handle causes the lockpins to be pulled out. An adjustable stop at lockpin No. 7 prevents the lockpin torque tube from traveling overcenter in the unlocked position. A cam on the aftmost tube operates the main cargo door locked switch. The access panels on the outside of the door provide access for unlocking and unlatching the door in event of a malfunction in the system.
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52-32-0 Page 8 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Aug 15/72
4. Lift Mechanism (See figure 4.)
A. The lift mechanism is installed above the ceiling panels at the aft end of the main cargo door at station 486. It consists of a hydraulic lift actuator, two thrust rods, a bellcrank, an outboard link and two inboard links. The outboard link is held to the cargo door with a single bolt. The remaining assembly is attached to fuselage structure. The outboard link is connected to a bellcrank which is rotated by extension or retraction of the lift actuator rod. The inboard end of the actuator is connected to two thrust rods which transmit loads back to fuselage structure. The inboard end of the actuator and thrust rods are supported by two links bolted to structure. The links prevent any up and down motion of the thrust rods and inboard end of the actuator. Hydraulic tubing is coiled around the inboard end of the actuator to minimize flexing of the tubing. The tubing is also supported with clamps connected to the thrust rods. A strap supported by the thrust rod wraps around the actuator, thereby providing a support for the outboard end of the actuator when installing or removing the actuator. Two canopy position switches are installed adjacent to the bellcrank pivot point. A dual cam lever is operated by the movement of the bellcrank when the door has rotated open 87 degrees or more.
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