Piper Aircraft Corporation Cherokee 140 PA-28-140, Service Manual

Page: 169 / 1024

PIPER CHEROKEE SERVICE MANUAL
01/31/08 IV - STRUCTURES
1I5
l. After repair has cured for 24 hours, sand patched area using a sanding block with fine wet
sandpaper. Finish by priming, again sanding and applying color coat.
4-60. FIBERGLASS FRACTURE AND PATCH REPAIRS.
a. Remove wax, oil and dirt from around damaged area with acetone, methylethylketone or equivalent.
b. Using a key hole saw, electric saber saw, or sharp knife cut away ragged edges. Cut back to sound
material.
c. Remove paint three inches back from around damaged area.
d. Working inside the structure, bevel the edges to approximately a 30 degree angle and rough-sand
the hole and the area around it, using 80-grit dry paper. Feather back for about two inches all
around the hole. This roughens the surface for strong bond with patch.
e. Cover a piece of cardboard or metal with cellophane. Tape it to the outside of the structure covering
the hole completely. The cellophane should face toward the inside of the structure. If the repair is on
a sharp contour or shaped area, a sheet of aluminum formed to a similar contour may be placed over
the area. The aluminum should also be covered with cellophane.
f. Prepare a patch of fiberglass mat and cloth to cover an area two inches larger than the hole.
g. Mix a small amount of resin and catalyst, enough to be used for one step at a time, according to kit
instructions.
h. Thoroughly wet mat and cloth with catalyzed resin. Daub resin on mat first, and then on cloth. Mat
should be applied against structures surface with cloth on top. Both pieces may be wet out on
cellophane and applied as a sandwich. Enough fiberglass cloth and mat reinforcements should be
used to at least replace the amount of reinforcements removed in order to maintain the original
strength. If damage occurred as a stress crack, an extra layer or two of cloth may be used to
strengthen area.
i. Lay patch over hole on inside of structure, cover with cellophane, and squeegee from center to
edges to remove all air bubbles and assure adhesion around edge of hole. Air bubbles will show
white in the patch and they should all be worked out to the edge. Remove excess resin before it gels
on the part. Allow patch to cure completely.
j. Remove cardboard or aluminum sheet from outside of hole and rough-sand the patch and edge of
hole. Feather edge of hole about two inches into undamaged area.
k. Mask area around hole with tape and paper to protect surface. Cut a piece of fiberglass mat about
one inch larger than the hole and one or more pieces of fiberglass cloth two inches larger than the
hole. Brush catalyzed resin over hole, lay mat over hole and wet out with catalyzed resin. Use a
daubing action with brush. Then apply additional layer or layers of fiberglass cloth to build up patch
to the surface of structure. Wet out each layer thoroughly with resin.
l. With a squeegee or broad knife, work out all air bubbles in the patch. Work from center to edge,
pressing patch firmly against the structure. Allow patch to cure for 15 to 20 minutes.
m. As soon as the patch begins to set up, but while still rubbery, take a sharp knife and cut away extra
cloth and mat. Cut on outside edge of feathering. Strip cut edges of structure. Do this before cure is
complete, to save extra sanding. Allow patch to cure overnight.
n. Using dry 80 grit sandpaper on a power sander or sanding block, smooth patch and blend with
surrounding surface. Should air pockets appear while sanding, puncture and fill with catalyzed
resin. A hypodermic needle may be used to fill cavities. Let cure and resand.