After all the holes have been drilled, the
temporary fasteners are taken out and the sheet is
removed from the framework. The burrs left by
drilling must be removed from both sides of all holes
in the skin, the stringers, and the rib flanges. Burring
may be accomplished with a few light turns of a
deburring tool or drill bit. In this way, particles of
metal left around the edges of the drilled holes are
eliminated. If they were not removed, the joint would
not be tight and rivets might expand, or flash, between
the parts being riveted.
Internal
The repair of internal structures concerns the
repair or replacement of extruded parts used as
stringers, webs used as bulkheads, and formed parts,
such as ribs and formers.
After the damage has been inspected and
classified, the next consideration is to plan the repair
so that it may be assembled in the proper sequence,
Before the removal, repair, or replacement of a
structural member is undertaken, the adjacent
structural members of the aircraft must be supported
so that proper alignment is maintained throughout the
operation.
STRINGERS.— A stringer is a spanwise struc-
tural member designed to stiffen the skin and aid in
maintaining the contour of the structure. Stringers
also transfer stresses from the skin to the bulkheads
and ribs to which they are attached. Stringers are not
continuous throughout the structure as are longerons
and are not subject to as much stress. Stringers are
made from both extruded and rolled sections, and are
usually in the form of C-channels, angles, or hat
sections.
Figure 13-67 shows one method used in repairing
a damaged stringer by patching. The repair consists
of a reinforcement splice and a filler splice. The
reinforcement splice should be long enough to extend
a minimum of four times the width of the leg of the
stringer on each side of the damaged area. The
cross-sectional area of the reinforcement splice must
be equal to or greater than the stringer itself. The
damage is cleaned to a smooth contour with corner
radii, and a filler of the proper thickness is prepared to
fit in the cleaned area. If possible, you should always
make both ends of the cutout midway between two
rivets so that the existing rivet pattern can be
maintained in the repair. Cut the filler splice one
thirty-second of an inch shorter in length than the
cutout section. This will allow a 1/64-inch clearance
stringer between each end of the filler splice and the
stub ends of the stringer. This eliminates the
possibility of stress developing from contact between
the two parts.
Figure 13-67.—Stringer repair by patching.
13-49
