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Stringer Repair

Made from extruded or rolled metal alloy, stringers are generally in the form of C-channel, angle, or hat-shaped sections. Figure 2-10 shows one method of repairing a damaged stringer by patching. The repair elements consist of reinforcement and filler splices and rivets. The reinforcement splice must extend a minimum of four rivets plus edge distance on each side of the damaged area. The reinforcement splice's cross-sectional area and strength must be equal to or greater than the stringer's. The damage must be trimmed to a smooth contour with corner radii, and a filler patch of proper thickness and matching shape must be prepared. If possible, maintain the original rivet pattern in the repair. This can be done by having both ends of the trimmed damage lie midway between two rivets. Cut the filler splice 1/32 inch shorter in length than the trimmed out section. This allows a 1/64 inch clearance between each end of the filler splice and the stub ends of the stringer. This clearance prevents stress from developing through contact between the filler splice and the stub ends.

Figure 2-10. Patch Repair of Stringer (For Damage Less than Two-Thirds of One Leg Width).

The repair just described is permissible when the damage does not exceed two-thirds of the width of one leg of the stringer and is not over 12 inches in length. When damage is greater than two-thirds of the leg width, use the method shown in Figure 2-11. A repair by insertion, shown in Figures 2-12 and 2-13, is required if the damage is so long that an unusual amount of material and work is required.

Figure 2-11. Patch Repair for Stringer (For Damage Greater Than Two-Thirds of One Leg Width).

Figure 2-12. Insertion Repair (For One Stringer).

Figure 2-13. Insertion Repair (For More Than One Stringer)

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