flows freely from the drilled holes. After the voids
are completely tilled, bring the area down to proper
thickness by working the excess resin out through the
holes, and then cure and refinish.
Repairing Facing and Core Damage
The repair of facings and cores requires more than
one method of repair. Special attention must be given
to the type of core used.
HONEYCOMB CORE.—The repair of facings
and cores requires more than one method of repair.
Special attention must be given to the type of core
used. Damages extending completely through one
facing of the material and into the core require
removal of the damaged core and replacement of the
damaged facings in such a manner that normal
stresses can be carried over the area. The scarfed
method, illustrated in figure 14-11, is the preferred
method for accomplishing small repairs of this type.
Repairs of this type maybe accomplished as follows:
Carefully trim out the damaged portion to a
circular or oval shape and remove the core completely
to the opposite facing. Be careful not to damage the
opposite facing.
The damaged facing around the
trimmed hole is then scarfed back carefully by
sanding. The length of the scarf should be at least 100
times the facing thickness, as shown in view B of
figure 14-11. This scarfing operation must be done
very accurately to a uniform taper.
Cut a piece of replacement core material (or a
suitable substitute) to fit snugly in the trimmed hole.
It should be equal in thickness to the original core
material.
Brush coat the repair area and the
replacement 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 14-11. 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 tiller material specified in
the aircraft structural repair manual. Figure 14-12
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 than the
repair of foam cores.
Figure 14-11.—Honeycomb-type core repair.
14-10
