c. Fuselage Extension, -On the P-40F model, ship No. 701 and up, there is an extended fuselage. This extension is made up of 24ST aluminum-alloy stressed skin reinforced by stringers and vertical bulkheads. This extension is so designed that only the fin and rudder are moved aft. An illustration of this extension is shown in figure 11.      2.Classification of Damage. -When effecting any repairs on the fuselage structure, carefully examine the extent of the damage and determine a method of repair by classifying it as one of the following:      a. Negligible damage.      b. Damage reparable by patching.      c. Damage reparable by insertion.      d. Damage necessitating replacement.      3.Skin.      a. General. - Aluminum-alloy stressed skin is used to cover the fuselage. Since the skin gages at the various stations have been carefully selected to give the required strength with a minimum of material, it is necessary, when effecting repairs to make all patches, inserts and splice plates of the same gage stock as the sheet being repaired. (See figure 12.) The rivets and rivet patterns to be used for each attachment or around a damaged area should be the same as ln the nearest parallel skin splice or skin overlap.

b. Negligible Damage. - Small dents free from cracks, abrasions, and sharp corners may be neglected provided the adjacent structural members are not damaged and the rivets are undisturbed. Care must be exercised when bumping out dents that the skin is not stretched or buckled otherwise it will have to be reinforced with a patch d the same gage skin or removed and repaired by an insert.      c. Damage Reparable by Patching.      (1) Skin Repair. -Large dents, cracks, holes and skin abrasions are reparable by patching or splicing as illustrated in figure 13, 14, 15, 16, 17 and 18. When effecting skin repairs, note the gage of the skin used in the damaged area by referring to figure 5. Figures 19 and 20 illustrate methods of repairing damages to the free areas of the skin between stringers and bulkheads. The damaged skin area should be cut away to leave a square or rectangular hole with 1/2 -inch radii in the corners and a flush insert should be fitted in the hole and secured by an internal frame as shown in figure 10 or by a patch as in figure 19.      (2) Skin Repair Over Stringer. - Skin patch repair over stringers should be repaired by the method shown in figures 13, 21, 17 and 19. The repair is similar to that described in this section, paragraph 3.9.(1) except that the repair to the stringer is effected by splicing (this section, paragraphs 3.13, and 4.9) and the internal frame must be inserted about the slringer having a 1/32-inch clearance at the stringer. The insert is neatly fitted ln the hole and flush riveted by countersunk rivets.

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