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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
BEAM 
HANGER  WALKING 
BEAM 
DOWNLOCK 
MAIN GEAR  ACTUATOR 
ACTUATOR 
DOWNLOCK 
TRUNNION  SPRING BUNGEE 
LINK 
UPLOCK 
ACTUATOR 
UPLOCK 
SPRING BUNGEE 
SHOCK 
STRUT 
UPLOCK HOOK 
DRAG  UPLOCK SENSOR 
STRUT  (PROXIMITY SWITCH) 
LOCK STRUT 
(DOWNLOCK) 
DOWNLOCK SENSOR 
(PROXIMITY SWITCH) 
SIDE STRUT 
UPLOCK ROLLER 

FWD INBD
Main Gear Extension and Retraction Component Location Figure 1
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500
MAINTENANCE MANUAL

TRANSFER TUBE
GEAR DOWN PORT PISTON
METERED
ORIFICE

SNUB VALVE SLEEVE
SNUB VALVE
OUTER CYLINDER
GEAR EXTENDED GEAR UP PORT (SNUB VALVE CLOSED)
GEAR IN TRANSIT
(SNUB VALVE OPEN)

GEAR RETRACTED
(SNUB VALVE CLOSED)
Main Gear Actuator Schematic
Figure 2

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 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 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 hanger. The hanger 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 hanger. 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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