(0.229)
0.3115 0.3120 0.3050
X
BOLT OD
(7.912) (7.925) (7.747)
Main Gear Wing Outer Door Wear Limits Figure 601
M62886
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32-13-21
ALL ú ú 01 Page 602 ú Jul 12/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
NOSE GEAR - DESCRIPTION AND OPERATION
_____________________________________
1. General_______
A. The nose gear supports the forward end of the fuselage and provides directional control while the airplane is on the ground (Fig. 1). The nose gear includes a drag brace, shock strut, and torsion links, and is hydraulically actuated to retract forward and up into a wheel well recessed into the lower nose section of the airplane. The shock strut consists of inner and outer cylinders. The upper part of the outer cylinder is "Y" shaped with arms extended to the sidewalls of the wheel well. Trunnion pins connect the gear to airplane structure. The "Y" arms and pins provide lateral stability. The gear rotates about the trunnion pins during extension and retraction. Refer to 32-33-00 for information on nose gear extension and retraction. Shocks and bumps during taxi, takeoff, and landing are absorbed by the shock strut which contains oil and is charged with compressed air or nitrogen. Longitudinal stability is provided by a hinged drag brace which folds upward and aft during gear retraction (Fig. 3). For steering, the shock strut inner cylinder turns within the outer cylinder. Torsion links connected at the upper end to a steering collar and at the lower end to the shock strut inner cylinder transmit a turning moment supplied by hydraulically actuated steering cylinders.
2. Nose Gear Shock Strut_____________________
A. The nose gear shock strut is the main supporting member of the nose gear. The shock strut includes an inner cylinder and an outer cylinder, metering pin assembly, upper and lower orifice assemblies, and upper and lower cam assemblies (Fig. 2). The shock strut is attached to the nose wheel well structure by trunnions which are part of the outer cylinder. Pins are inserted through the trunnion ends into bearings attached to the wheel well structure. A steering collar clamped around the outer cylinder is connected to the upper torsion link and the upper torsion link is connected to the lower torsion link by an apex pin.
B. The inner cylinder and nose wheel axles are machined from a single forging. The fixed centering cam attached to the top of the inner cylinder mates with a similar cam in the outer cylinder when the inner cylinder extends. As these cams engage, the nose wheels will attain a straight forward position to ensure proper fit in the wheel well on retraction. This also ensures the nose wheels to be straight forward when landing. Upper and lower bearings provide sliding surfaces for movement of the inner cylinder in and out the outer cylinder. Annular grooves in the lower bearing provide space for the storage of two sets of spare seals. These spare seals are replacements for like seals installed between the inner cylinder and the lower centering cam, and between the lower centering cam and the outer cylinder.
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32-21-00
ALL ú ú 01 Page 1 ú Oct 20/83
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
C. The outer cylinder has a trunnion on each side near the top. Trunnion pins are inserted from inside outward extending into nose gear support brackets which are mounted on each side of the wheel well. During retraction and extension, the trunnion pins rotate in spherical bearings in the nose gear mounting brackets. Double lugs, to which the lower drag brace is attached, are near the top on the forward side of the outer cylinder. A steering collar encircles the outer cylinder and is bolted to hold the collar in an annular recess. The upper torsion link is bolted to a lug on the steering collar. The lower centering cam is in the outer cylinder to mate with the one at the top of the inner cylinder on inner cylinder extension. This centering cam has an annular groove in which the rebound valve piston ring is located. An upper orifice support tube is connected to the outer cylinder. The rebound valve piston ring in the groove around the upper centering cam is moved against the top of an annular groove as the inner cylinder extends. The fluid, which is compressed by the diminishing cavity between the upper and lower centering cams, is restricted to escape only through the two small holes in a lip on the piston ring. A small portion of fluid will also escape through the piston rings working gap. The escaped fluid enters a cavity between the upper bearing spacer and the outer cylinder wall. The fluid is then forced through twelve holes, lengthwise in the upper bearing, into the cavity above the inner cylinder. This restricted flow of fluid acts as a snubber to slow the inner cylinder during extension.
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