Piper Dakota Maintenance Manual page 403

d. For larger damages, an epoxy patching compound is recommended. This type material is a two
part, fast curing, easy sanding commercially available compound.
Increase adhesion by roughing bonding surface with sandpaper
and by using as much surface area for bond as possible.
e. Mix patching compound in equal portions on a hard flat surface. Clean damaged area with
perchlorethylene or VM&P naphtha prior to applying compound. (figure 5 1/4)
f. Use a mechanical sander after compound is cured. Keep sander in constant motion to prevent heat
buildup.
g. For repairs in areas involving little or no shear stress, use hot melt adhesives (polyamids) supplied
in stick form. This type of repair has a low cohesive strength.
h. For repairs in areas involving small holes, indentations, or cracks in material where high stress is
apparent, welding method is suggested.
i. The welding method requires a hot air gun and ABS rods. To weld, hold gun to direct the flow of
hot air into repair zone. Heat damaged area and rod simultaneously. Move the gun continuously in
a fanning motion to prevent discoloration of material. Pressure must be maintained on rod to
ensure good adhesion. (figure 51-5)
j. After repair is completed, sand to obtain a surface finish of acceptable appearance.
4. Cracks: (figure 51-6)
a. Before repairing a crack in thermoplastic parts, first determine what caused crack and alleviate
condition to prevent recurrence.
b. Drill small stop holes at each end of crack.
c. If possible, bond a double plate to reverse side of crack to provide extra strength.
d. V groove crack and fill with repair material such as solvent cement, hot melt adhesive, epoxy
patching compound, or hot air weld.
e. After repair has cured, sand to match surrounding finish.
5. Repairing major damage: (Larger than 1 inch in diameter.) (figure 51-7)
a. Make a patch of same material and cut slightly larger than section being repaired.
b. When appearances are important, large holes, cracks, tears, etc., are repaired by cutting out
damaged area and replacing with a piece of similar material.
When cutting away damaged area, undercut perimeter and maintain a smooth edge. The patch or
plug should also have a smooth edge to ensure a good fit.
d. Coat patch with solvent adhesive and firmly attach it over damaged area.
e. Let the patch dry for approximately 1 hour before any additional work is performed.
f. Fill hole, etc. with repair material. A slight overfilling of repair material is suggested to allow for
sanding and finishing after repair has cured. If patching compound is used, repair should be made
in layers, not exceeding a 1/2 inch in thickness at a time. Allow compound to cure and ensuing a
good buildup of successive layers.
6. Stress lines: (figure 51-8)
a. Stress lines produce a whitened appearance in a localized area. They are generally caused by
severe bending or impacting of material. (figure 51-9)
b. To restore material to original condition and color, use a hot air gun or similar heating device to
apply heat to affected area. Do not overheat material.
PIPER AIRCRAFT
PA-28-236
MAINTENANCE MANUAL
—NOTE—
2F7
51 - 12 - 00
Page 51 - 11
Reissued: August 1, 1986