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32-09-20
ALL ú ú 01 Page 424 ú Jul 12/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
MAIN GEAR - DESCRIPTION AND OPERATION
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General
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A. Each main gear consists of a trunnion link, a shock strut, a drag strut, torsion links, a damper, a side strut, and a reaction link (Fig. 1). In addition, the right main gear carries ground speed brake operating rods and cable.
B. The shock strut assembly is attached to the trunnion link by a pin joint and the two are mounted between the rear wing spar and a trunnion support beam. The shock strut is charged with oil and compressed nitrogen to provide a shock absorbing medium. The main gear axles and the shock strut inner cylinder are machined from a one piece forging. Replaceable sleeves are assembled over the axles to provide a mounting for wheel bearings and to protect the axles from damage. The reaction link is connected to the shock strut and to the upper end of the side strut. Refer to 32-32-0 for information on main gear extension and retraction.
Main Gear Trunnion Link
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A. The main gear trunnion link provides the forward pin of the hinge for main gear retraction and transmits landing gear loads from the drag strut into airplane structure. The trunnion link is mounted between the shock strut and the rear wing spar (Fig. 2). The aft end of the trunnion link is pinned to the shock strut and the forward end pivots in a spherical bearing mounted in the rear wing spar. The top end of the drag strut is attached to a lug on the underside of the trunnion link near the spherical bearing. A pushrod from a bracket on the underside of the trunnion link operates a shock strut door hinged to the wing. The door covers part of the shock strut aperture in the wing when the gear retracts. A swivel fitting for hydraulic lines is mounted on top of the trunnion link. The trunnion link is machined from a high tensile steel forging.
B. The trunnion forward bearing bolt is designed to fail if the landing gear
receives a severe impact, thus minimizing damage to structure.Main Gear Shock Strut
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A. The main gear shock strut is the primary supporting member of the landing gear. The shock strut is made of steel and consists of an inner cylinder, an outer cylinder, an orifice support tube, and a metering pin (Fig. 3). The orifice support tube is attached to the top of the outer cylinder. Upper and lower bearings provide sliding surfaces and locate the inner cylinder concentric with outer cylinder. A snubber valve located below the upper bearing provides control of shock strut rebound. A packing adaptor with annular grooves is installed between the lower bearing and a spacer. A channel seal in the packing adaptor is in contact with the inner cylider. An O-ring between two backup rings makes contact with the outer cylinder. The channel seal and the O-ring provide an air-oil seal between the cylinders. Annular grooves in the lower bearing are used to store spare seals. The spare seals in the lower bearing can be used to replace active seals without removing the inner cylinder. The shock strut is attached to airplane structure by an extension on the outer cylinder and by the trunnion link. The lower end of the shock strut is held in position by the side strut and the drag strut.
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32-11-00
ALL ú ú 01 Page 1 ú Feb 20/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
The outer cylinder is a single piece forging bored to fit the inner cylinder. The upper portion provides an extension for attachment to airplane structure (Fig. 2). A full shock strut width lug on the opposite side provides an attachment for the trunnion link. Lugs on the lower end provide attachment points for drag strut, torsion links, and universal side strut attachment. The orifice support tube projects through the top of the outer cylinder where it is secured by a nut. A charging valve is installed in the top of the orifice support tube.The inner cylinder, with all lugs and the axle, including brake flanges, is machined from one forging. A diaphragm integral with the metering pin seals off the inside bore of the inner cylinder. A drain tube attached to the metering pin is secured by a nut to the underside of the inner cylinder. A check valve is installed at the bottom of the cylinder for strut servicing. In addition to axles, the lower end of the cylinder has a towing lug and a jacking pad.A snubber valve is installed on the inner cylinder just below the upper bearing. The valve consists of an angular sectioned bronze ring that moves up and down when the shock strut operates to act as a one-way restrictor. When the shock strut is compressing, the snubber valve allows an unrestricted flow of oil from the upper chamber into the annular space between inner and outer cylinders. When the shock strut extends, the snubber valve moves up to close off holes in the upper bearing; this restricts flow from the annular space and so absorbs shock strut rebound.With the shock strut compressed and serviced with oil, the outer cylinder contains oil all around the piston rod and in the space between inner and outer cylinders. The shock strut is then inflated with nitrogen or air to the specified pressure.Shocks are absorbed by the flow of hydraulic fluid through the annular space between the orifice and the tapered metering pin. As the shock strut is compressed, oil flows through the orifice and the movement of the tapered metering pin through the orifice progressively varies the area of the annular space between orifice and pin. The variation in area results in an adjusted rate of hydraulic flow from the inner cylinder chamber to the upper side of the piston, thus providing uniform control of the impact loads on the airplane structure when landing. Landing and taxi shocks are also cushioned by the increasing volume of hydraulic fluid above the piston further compressing the volume of compressed air or nitrogen in the upper end of the outer cylinder. As the shock strut extends, there is a reversal of flow through the orifice. The hydraulic fluid now being forced from the upper to the lower side of the piston must pass through the space around the metering pin and through holes in the orifice support tube. Also, fluid in the annular space between the inner and outer cylinders is forced through the snubber valve restriction and through the upper bearing into the upper chamber. The resulting resistance to hydraulic flow dampens the return movement of the shock strut.
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