components housing radar or radio gear must be made
in accordance with the manufacturer’s recom-
mendations. This information may be found in the
aircraft structural repair manual or in drawings and
specifications.
Before a thorough inspection of the damage can
be made, the area should be cleaned with a cloth
saturated with methyl ethyl ketone (MEK). After
drying, the paint should be removed by sanding
lightly with No. 280 grit sandpaper, and then clean the
sanded area with MEK. The extent of damage can
then be determined by tapping the suspected areas
with a blunt instrument. You could use a coin as a
blunt instrument, such as a quarter, to perform the tap
test. This is referred to as the “coin tap” method. You
should never use a hammer as a blunt instrument. The
damaged areas will have a dull or dead sound, while
the undamaged areas will have a clear metallic sound.
Damages are divided into four general classes:
surface damage, facing and core damage, puncture
damage (both facings and core), and damage
requiring replacement.
Repairing Surface Damage
The most common types of damage to the surface
are abrasions, scratches, scars, dents, cuts, and pits.
Minor surface damages may be repaired by applying
one or more coats of room-temperature catalyzed
resin to the damaged area. More severe damages may
be repaired by filling with a paste made from
room-temperature resin and short glass fibers. Over
this coated surface, apply a sheet of cellophane,
extending 2 or 3 inches beyond the repaired area.
After the cellophane is taped in place, start in the
center of the repair and lightly brush out all the air
bubbles and excessive resin with your hand or a
rubber squeegee towards the outer ridge of the repair.
Allow the resin to cure at room temperature, or if
necessary, the cure can be hastened by the use of
infrared lamps or hot sandbags. After the resin has
been cured, remove the cellophane and sand off the
excess resin; then, lightly sand the entire repaired area
to prepare it for refinishing.
PLY DAMAGE (SANDWICH LAMI -
NATES).—When the damage has penetrated more
than one ply of the cloth in sandwich-type laminates,
the repair may be made by using the scarfed method,
shown in figure 14-8.
This repair is made in the
following manner:
Clean the area thoroughly, and
then sand out the damaged laminate plies, as shown in
view B. The area should be sanded to a circular or
oval shape, and then the area should be tapered
uniformly down to the deepest penetration of the
damage.
The diameter of the scarfed (tapered) area should
be at least 100 times the depth of the penetration. You
should exercise care when using a mechanical sander.
Excess pressure on the sander can cause the
sandpaper to grab, resulting in the delamination of
undamaged plies.
CAUTION
The sanding of glass cloth reinforced
laminates produces a fine dust that may
cause skin irritation. In addition, if you
breathe an excessive amount of this dust, it
may be injurious; precautions as to skin,
eyes, and respiration protection must be
observed.
Clean the area thoroughly, brush coat the sanded
area with one coat of room-temperature catalized
Figure 14-8.—Ply repair (scarfed method).
14-7
