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Summary

The elements for stringer repair consists of reinforcement and filler splices and rivets. Reinforcement splices must extend at four times the width of the stringer leg on each side of the damaged area. A reinforcement splice's cross-sectional area strength must equal or exceed the stringer's. Damage must be trimmed to a smooth contour and corner radii. The filler patch must be of proper thickness and shape and 1/32 inch shorter in length than the trimmed out section. This allows 1/64 inch clearance between the stringer stub ends and the filler splice ends to prevent stress development between the ends. When possible, maintain the original rivet pattern in the repair. This is achieved by having the trimmed-out area lie midway between two rivets. This repair is authorized only when the damage does not exceed two-thirds of the width of one leg of the stringer and is not longer than 12 inches. If the damage is greater than two-thirds of the leg width, the repair method shown in Figure 2-11 must be used.

Longeron repair is somewhat similar to stringer repair; however, heavier rivets or bolts are used because of the longeron's greater weight. If bolts are used, bolt holes must be drilled for a light-drive fit. Rivet spacing on longeron repairs must be kept between four and six rivet diameters.

Repair on spars may not be permitted because spars are highly stressed members. If the repair is permitted, the workmanship must be of the highest quality and conform to applicable technical manual instructions. Rib repairs are made by patching and insertion. The bent over position of a rib's flange and the vertical portion is the web.

Specifications for each type of bulkhead damage are given in the applicable manual for the aircraft. Repair categories for bulkhead damages are one-third or less of the cross-sectional area or more than one-third of the cross sectional area damaged. If one-third or less of the cross-sectional area is damaged, a patch plate, reinforcing angle, or both many be used. Details on the required number of rivets can be obtained from the applicable technical manual. For damage greater than one-third the area's cross section, remove the entire section and make a splice repair. For details on the kind of splice and the number of rivets, consult the applicable technical manual.

When repairs are made from flat sheet stock, its cross-sectional tensile, compressive, shear, and bearing strength must be equal to or greater than the original material. Curved repair parts made from the flat sheet stock must be in an annealed state before forming and heat treated before installation.

Leading edge damage generally involves nose skin, nose ribs, stringers, and possibly the cap strip. In such a case, an access door is required to make the repair possible. Such a repair requires installing insertions and splice pieces; making repairs to the cap strip and stringer; and if the damage is severe, installing a new nose rib and skin panel. Leading edge repairs must be made as prescribed in the applicable manual.

Although trailing edges are not structural members, they are highly stressed, and their damage can be limited to one point or extended over the length between two or more rib sections. In addition to collision or careless handling, trailing edges are subject to corrosion from moisture.

Damage between ribs of the trailing edge is repaired with a filler and an insert. Fillers are made of hardwood, fiber, or cast aluminum alloy. Inserts are made of the same material as the damaged section and shaped to match the trailing edge. To secure the repairs, use countersunk rivets and countersink the shop heads for smooth contour. Damage at or near a rib is repaired in much the same way. Sufficient material must be removed for a complete splice between ribs. Generally, this takes two splices joined by an insert made of the same kind of material as the trailing edge or of formed sheet stock.

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