structure's rivet holes should be used when the rivet
be laid out, drilled, and deburred in the identical
pattern is laid out. The flush patch over internal
manner as described for a lap patch. After the required
structure is installed with the same methods as
corrosion-preventive materials have been applied, the
described for a flush patch clear of internal structure,
doubler is positioned in the structure's interior and
except for modification of the doubler.
secured with temporary fasteners. Inspect the rivet
holes for proper alignment, and rivet the doubler in
CHEM-MILLED SKIN REPAIR.--On some
place with solid rivets. The filler can then be riveted in
aircraft the fuselage skin is Chem-Milled or machine
place with blind fasteners.
tapered and highly stressed. Figure 4-63 shows a
Chem-Milled skin repair in a pressurized fuselage
NOTE: If the flush repair is in an open skin area,
section. The skin consists of a shim, a doubler, and a
the filler may be riveted to the doubler prior to installing
filler. The damage area is trimmed and the inside
the doubler.
corners are filed to one-fourth of an inch in radius. The
FLUSH PATCH OVER INTERNAL STRUC-
replaced metal and rivets or other fasteners must be
TURES.--Fabricating a flush patch over internal
equal to or stronger than the original. The structural
structures may become difficult. In some instances, it
repair manual should be consulted for fastener spacing,
may be done simply with a split doubler and a filler, as
edge distance, and repair procedure. During final
shown in figure 4-62. Frequently a split doubler, filler
assembly of the repair, the fabricated parts should be
strips, and filler are used in the repair. The filler strip is
bonded together with an adhesive to ensure
used as a spacer if a structural component under the
skin has been damaged. In all cases, the existing
Figure 4-63.--Chem-Milled skin repair (fuselage pressurized).
4-39