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1. Type of Construction. The P-40 Airplane is of all metal construction, consisting of a semimonocoque fuselage and full cantilever wing and empennage, manufactured by Curtiss-Wright Corporation, Buffalo, New York. The main structure is a network of bulkheads, spars, and stringers, which are covered with a thin stressed aluminum-alloy skin. The ailerons,rudder, and elevators are of metal structure which is fabric covered. The engine mount is a welded and bolted tubular structure of X-4130 steel and is detachable from the fuselage. See figures l and 2 for major disassembles. 2. Types of Repair. a. General. (1) Due to the construction of the airplane, it is important that any repair to the skin, stringers, and bulkheads be given careful consideration. Simple operations, such as repairs to dents, small skin holes, and exterior injuries may be accomplished readily and easily; however, internal structures must be repaired by means of patches, inserts, or by splicing to reinforce the damaged sections or areas before the outer skin is attached. Caution must be exercised to maintain the original contour and to eliminate excessive increases in weight. (2) A simple procedure to follow for all repairs is: Analyze the extent of the damage to the part before proceeding to repair it, devise several methods for its repair by referring to the repair schemes in the back of the test, and with the aid of the illustrations and the book, proceed to use the most convenient and easiest method. (3) Where a specific repair is not given it is generally permissible to assume that either the member in question or its attachment has been designed to a zero margin. Due consideration must, however, be given to the probable types of loading to which the member is to be subjected and to the eccentricities of the applied loads. Repairs for the most part consist of replacing the damaged material with material of equal strength and section properties. Attach this material with the same type of attachment as used for the damaged piece or with sufficient attachment to permit the new piece to take its full allowable load. Care must be taken in attaching repair pieces to arrange the attachment so as not to reduce the structural efficiency of the member to which the repair piece is attached. b. Classification Damages have been divided into four groups to facilitate the classification of repair methods. The classlficatlon and general description of the various damages is as follows: |
(1) Negligible Damage. - Small dents, holes, or cracks in the sheet material requiring no addition of material or reinforcement. The dents must be bumped out, cracks stopped by a 1/8-inch hole at each end, and small holes rounded out to a 1/4-inch radius to prevent formation of cracks. (2) Damage Reparable by Patching. - Holes and cracks which impair the strength of the structure but which may be repaired by the use of sheet reinforcements attached by a specified number and arrangement of rivets or bolts. Patches must be shaped and arranged in such a manner as to permit the required rivet or bolt pattern to extend completely around the damage or to the edges of the original stock. Where fittings or other structure is near the damaged area, the patches may have to be extended beyond these in order to obtain the required attachment. In many cases the damaged material must be replaced to give support to the patch and to other parts of the structure, or to obtain continuity, as in repair of the fuselage skin, this added material is designated as a filler or insert. (3) Damage Reparable by insertion. - Extensive damage requiring large inserts which may be attached by means of splices. When the damage is extensive or the presence of fittings and other structures make it difficult to use patches, the damaged material must be removed and replaced by formed inserts of the same or equivalent material, gage, and shape, Where practical, the inserts should be made to extend to the edges of the original sheet and should be attached by using the original rivet or bolt pattern. In cases where complete replacements are impractical, splices may be effected by using patches. Patches used in splicing must be continuous along the length of the splice and of sufficient width to take the rivet or bolt pattern Specified for patching on each side of the cut. Continuous patches for splices that are not straight, that is, for angles, rectangles or circles, are designated as frames. Frames are frequently used in repairing small sections of damaged fuselage skin, Where continuity is not essential, splices may be effected by overlapping the insert and undamaged material. The attachment for an overlap should be the same in Pattern as that used on one side of a patch splice (4) Damage Necessitating Replacement. -Damage to fittings, highly stressed material , a small pieces such as clips and gussets which may be easily replaced. Fittings which are cracked, sprung, or nicked must be replaced. Certain portions of the sheet structure are highly stressed and cannot be successfully repaired. These must be replaced. Small sheet fittings, gussets, clips, brackets, etc., are easily duplicated and should be replaced if damaged or stretched out of shape. |
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