NOTE: Acrylic plastics shall never be rubbed with a dry cloth. To remove a light dust film or electrostatic charges, wipe the surface with a clean, damp chamois or a clean, damp cotton-flannel cloth.
(e)
Sand the married plastic surface with progressively finer grits of wet-or-dry abrasive papers (280, 320, 400, 600) to the desired finish. Abrasive papers shall be wrapped around a rubber block having a durometer reading of 35 + 5, Shore A scale, or a wood block covered with cotton- flannel. Keep the surface covered with water while sanding. Use extreme care to avoid overheating. Hold sanded area to a minimum needed to achieve a satisfactory repair. A smooth repair blended with the surrounding area is desirable. However, this blending shall not enter a critical vision area.
(f)
During each step, the deeper scratches left by the preceeding grade of adhesive should be removed. Wash with water each time the grit is changed. After smooth, even surface is obtained, wash with water until grit has been removed.
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57-21-11 Page 802 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 01/01
(g) Polish per the following to produce an optical finish: 1) Machine polishing is preferred when the equipment and a qualified operator are available. Contact pressure, feed rate and wheel speed must be balanced to prevent overheating. For preliminary buffing use a stitched muslin wheel and Learock S-30 buffing compound. Change direction of feed frequently and use only light pressure. For a high luster, finish with a loose, open, unstitched wheel with spacers and Learock 888 buffing compound. (To make spacers, remove all the muslin discs, and with scissors, reduce half of them to 1/2 the original diameter. Re-assemble the wheel, alternating the large discs with the small ones.) This wheel will substantially reduce surface heating due to friction.
2) When polishing machines and qualified operators are not available, hand polishing may be used as follows: Polish the area to the desired finish with 0000 wet rouge applied to a wet cotton-flannel pad. Apply a polish to a clean, wet cotton-flannel pad and polish to desired finish. Wipe with a clean cotton-flannel cloth.
(h) Apply a thin, even film of wax with a clean cotton-flannel pad and bring to a high luster by rubbing lightly with a circular motion.
500
Nov 15/78 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 57-21-11 Page 803
PLATES/SKIN - DESCRIPTION AND OPERATION
1. General
A. The exterior surface of the wing comprises the wing skin and the flight control surfaces attached to the wing. This section describes the wing skin, which can be divided into skin of primary and secondary structural importance.
B. The majority of the wing skin is a component of the wing boxes and the center wing box, of which it forms the upper and lower surfaces.
C. The remainder of the wing skin forms the surfaces of the leading and trailing edge fairings and of the wing tip, and is of secondary structural importance.
2. Primary Wing Skin
A. The left and right wing box structures are continuous and have no production joints. This feature allows the upper and lower wing skin panels to be continuous on each wing from tip to root. The wing inspar upper skin is in two sections, spliced in the spanwise direction. The entire upper inspar skin is made from 7178 aluminum alloy. The wing inspar lower skin is made in three sections spliced in the spanwise direction and pierced by the openings for fuel tank access holes and fuel pump access holes. Refer to Chapters 52 and 57 of the Structural Repair Manual for wear limits on tank doors and tank door openings respectively. All the lower inspar skin is made from 2024 aluminum alloy, the most suitable material for withstanding the heavy tensile loads on the lower surface, and is shotpeened to give additional fatigue life besides forming the curvature of the wing. The inside surface of both upper and lower wing skins is attached directly to the edges of the zee-section wing stringers. The upper and lower skin panels of the center wing box are also attached directly to similar internal stringers. At the outboard ends of the center wing box, the upper and lower skins are connected to the upper and lower skins of the left and right wings by heavy chordwise splice extrusions which follow the lines of the upper and lower edges of the wing root ribs.
3. Secondary Wing Skin
A. Many of the larger areas of fairing skin are laminated honeycomb panels. Several sections of the lower surface are removable for access purposes.
B. The lower wing leading edge skin associated with each slat incorporates one pressure relief door. The door is spring-loaded and will open when cavity pressure reaches 1.5 psig.
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