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 B.  The beam is attached to the upper of two sets of lugs near the forward end of the shock strut trunnion. The outboard end is attached to a support link, which is hinged to airplane structure. The cylinder end of the actuator pivots in the beam and the piston rod end attaches to a lower lug on the shock strut trunnion. With wing gear down and locked, the trunnion attachment lugs for the walking beam are above and slightly inboard of trunnion centerline. The actuator attachment to trunnion is below a point outboard of the trunnion centerline.
 10. Wing Gear Trunnion (Fig. 2)
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 A.  The trunnion fork of the wing landing gear provides the forward pin of the hinge for retraction. It also transmits landing gear loads from the drag brace into airplane structure. The trunnion fork is mounted between the rear wing spar and upper shock strut. The aft end of the trunnion pivots in a swivel housing and spherical bearing mounted in the wing support beam. The top end of the drag brace is attached to lugs on the underside of the trunnion fork which is machined from a high tensile strength steel forging.
 11. Wing Gear Truck Positioning Actuator (Fig. 4)
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 A.  The truck positioning actuator of the wing landing gear is mounted aft of the shock strut just above the upper torsion link. The head end is attached to lugs on the outer cylinder of the lower aft shock strut. The piston rod end of the actuator points rearward, and is attached to a titanium bellcrank, which is a portion of the positioning mechanism. A high pressure relief valve is located at the head end.
 12. Wing Gear Truck Positioning Mechanism (Fig. 1)
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 A.  The positioning mechanism of the wing landing gear consists of a bellcrank, link and universal fitting, with associated pins and bushings. The forward, lower end of the triangular bellcrank attaches to the apex of the torsion links through a common pin. The top of the bellcrank connects to the rod end of the positioning actuator. The aft hole of the bellcrank is bolted to a link which runs down to a universal fitting located on the truck, directly above the rear axle. The geometry of the bellcrank/link mechanism amplifies the tilting arc supplied by the positioning actuator.
 13. Wing Gear Truck Mechanical Lock
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 A.  The truck mechanical lock of the wing landing gear ensures that the trucks hold their tilt angle if hydraulic pressure is lost. The mechanism has a roller and roller support attached to the upper torsion link, and a hook, lever, and pushrod assembly.
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 ALL  ú ú 01 Page 9 ú Jun 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

IN CHECK VALVE

PISTON
Wing Gear Truck Positioning Actuator
Figure 4

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 32-11-00
 ALL  ú ú 01 Page 10 ú Jun 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 14. Truck Positioning Bypass Reducer Valve
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 A.  The bypass reducer valve of the truck positioning is a three-part hydraulic unit located in the upper wheel well area. It consists of a spool and sleeve assembly, poppet, guide, and two ball and spring-type check valves. Pressure above 2200 psi causes the unit to completely open. The valve closes completely at 1900 psi. The valve supplies hydraulic fluid to the truck positioning actuator of the gear.
 15. Wing Gear Truck Shield and Bumper
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 A.  Both wing gear trucks have a truck shield mounted to the bottom to protect the truck and electrical conduits. The bumper is attached to the truck shield clamps forward of the truck pivot and acts as a guard to keep the truck from touching the inner cylinder when the truck is in the full tilt position.
 16. Wing Gear Shock Strut Charging Valve
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 A.  The charging valve of the shock strut for the wing landing gear is located on the inboard side of the shock strut below the trunnion. The charging valve is used to fill the shock strut with dry air or nitrogen and is also used to deflate the shock strut.
　
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