Figure 5-11.--Honeycomb-type core repair.
The scarfed method is normally used on small
Cut a piece of replacement core material (or a
punctures up to 3 or 4 inches in maximum dimension
suitable substitute) to fit snugly in the trimmed hole. It
and in facings made of thin cloths (which are difficult to
should be equal in thickness to the original core
peel). The stepped method is usually employed on
material. Brush coat the repair area and the replacement
larger repairs to facings composed of thick cloths.
honeycomb, exercising care to prevent an excessive
amount of resin from entering the honeycomb cells.
Insert the honeycomb repair section and place the
resin-impregnated cloth over the repair area, as shown
in view C of figure 5-11. Cover the repair area with
cellophane sheeting, and cure the repair in accordance
with the resin manufacturer's instructions.
After the repair has been cured, sand the surface to
its original contour. The entire area should be lightly
sanded before refinishing.
FOAM CORE.--The damaged core should be
removed by cutting perpendicular to the surface of the
face laminate opposite the damaged face. Scrape the
inner facing surface clean, making sure there is no oil or
grease film in the area, to ensure good bondage of the
foam to the laminate. Fill the area where the core has
been removed with the filler material specified in the
aircraft structural repair manual. Figure 5-12 shows the
replacement of a foam core.
NOTE: Do not use MEK to clean the damage as it
may soften and weaken the foam.
Repairing Puncture Damage
The repair of punctures differs as to the method
used. Repair of honeycomb cores is different from the
repair of foam cores.
HONEYCOMB CORE.--Repairs to damages
completely through the sandwich structure may be
accomplished either by the scarfed method (similar to
the repair described for damage extending into the
core) or the stepped method.
Figure 5-12.--Foam-type core repair.