Main Gear Extension and Retraction Components Locations  500 
32-32-0  Figure 1  Feb 20/91 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

500  Main Gear Actuator Schematic 
Nov 15/66  Figure 2 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  32-32-0 Page 3 

B.  When the main gear actuator is pressurized to extend, opposing forces from actuator and walking beam act to rotate the gear. The gear swings inboard and up into the wheel well. When the actuator is pressurized to retract, the forces rotate the gear in the opposite direction to extend the gear.
C.  The main gear actuator restricts the rate of extension and retraction of the gear, just as it approaches the up or down position. The snubbing effect is obtained by the action of a spring-loaded sliding valve snubbing assembly. After the actuator has extended 1.10 inches, the snubbing valve opens and hydraulic flow is unrestricted. When the piston is 1.30 inches from fully extended, a snubber stop on the piston contacts the snubber valve sleeve. Further movement of the piston pulls the sleeve against a compression spring to close off ports. For the remainder of piston travel, hydraulic flow must pass through a diminishing number of holes. The increasing restriction to hydraulic flow steadily slows the actuator extension rate until the piston reaches the end of its travel. The sequence repeats in reverse, when the actuator retracts.
3.  Main Gear Actuator Walking Beam
A.  The main gear actuator walking beam works in conjunction with the main gear actuator to retract and lower the gear. The walking beam serves to reduce the reaction force going into airplane structure from the main gear actuator. Reaction force from the actuator is transmitted back to the shock strut through the walking beam. The inboard end of the beam is attached to a lug on the top of the shock strut (Fig. 3). The outboard end is attached to the walking beam hangar. The hangar pivots on a fitting mounted between the landing gear beam and the rear wing spar. The cylinder end of the actuator is connected to the walking beam. The actuator piston rod is attached to a lug on the side of the shock strut. On gear retraction, the outboard force from the actuator piston rod is applied directly to the gear. The inboard reaction force from the cylinder of the actuator reaches the shock strut through the actuator walking beam. Inboard and outboard forces combined provide a couple to raise the gear. The resulting reaction to the couple tends to rotate the actuator and walking beam combination about the gear retraction axis. Force generated by the attempted rotation is taken to structure through the beam hangar. With the walking beam as a third order lever arm, a much reduced force reaches structure. The piston rod shock strut moment arm increases as the gear moves up. The walking beam, shock strut moment arm, first increases then decreases during retraction.
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32-32-0 Page 4  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Nov 15/66 

4.  Main Gear Lock Mechanism
A.  The main gear lock mechanism positively locks the gear in retracted or extended position. The lock consists of a hook, two hydraulic actuators, spring bungees, a lock strut, and operating linkage (Fig. 4). In the retracted position the hook engages a roller mounted on the universal side strut fitting. In the down position, the lock strut assumes an overcenter position to prevent the side strut from folding. The uplock hook, and the lock strut, are connected to individual actuators. The actuators are mounted on the reaction link. Sensors for the position indicating and warning system proximity switches are located in two places. The downlock sensor is on the side strut, near the lower end of the lock strut. The uplock sensor is mounted between the uplock hook and the lower end of the uplock spring bungees.
B.  Normal operation of both up and down locks is by hydraulic pressure directed to the lock actuators. Provision is made to release the uplock in the absence of hydraulic pressure, by means of a manual extension system. Spring bungees provide a force to hold the locks in the locked or unlocked positions. When the gear is released by the manual extension system, the lock strut swings into locked position as the gear falls. On the final extension movement, the spring bungees pull the lock strut into overcenter position.
5.  Main Gear Lock Actuator
A.  Main gear lock actuators operate the main gear lock mechanism, to permit retraction or normal extension of the landing gear (Fig. 5). Actuators are hydraulic piston type. Two actuators are mounted on the reaction link of each main gear. One on the inboard end to operate the uplock, and one on the outboard end to operate the downlock. The downlock actuator extends to push the lock strut across the overcenter position and to start the side strut folding. Retraction of the actuator pulls the lock strut into the overcenter locked position when gear extends. The uplock actuator extends to swing the uplock hook away from the uplock roller and release the gear. Uplock actuator retraction pushes the hook outboard, to fully engage the uplock roller.
　
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