REPAIR INSTRUCTION ASTIR CS
Rev. 9 28. Nov. 2005
7
Repair of GRP material
If the glider is damaged, first examine the outer surface very carefully, frequently other
structural parts are involved, fractures can run hidden under the outer surface. Carry out
repairs with extreme care.
On gliders made of GRP, the outer surface is stressed (load bearing), failure of this
element may lead to structural failure.
Maintain a precise resin-hardener mixing ratio i.e. +/- 0.5% using a clean mixing pot.
The ratio of fibre glass cloth — to resin mix is approximately 1 to 1. Grind or splice the
repair location only shortly before applying damp laminate, so that dirt cannot
contaminate and prevent safe adhesion. As in plywood, the alignment of the fibre glass
cloth (lengthwise or diagonally) is of extreme importance to the strength. The required
amount of fibre cloth and direction in the damaged area may be taken from the
simplified texture plan, so that the damaged area can be restored to the correct wall
strength. If a small piece of the damaged laminate is broken off and burnt, the remaining
glass-fibres can be counted and identified.
Splicing and grinding are time consuming. Grind away as much as necessary so that
the added patches do not protrude from the contour. If it is necessary to shorten the
repair time it may be done with a hot air blower to speed the resin curing time.
Warning. A temperature too high will produce large air bubbles in the cloth / resin. An
improvised warming chamber may be built out of foil, through which hot air can be
guided to avoid local overheating.
Caution must be exercised when repairing control surfaces, be careful not to increase
the weight since this may cause flutter of the respective control surface.
Repair of GRP Foam-Sandwich
(GRP Hard Foam-Sandwich)
Damage may happen to the outer surface only (outside laminate) as well as the whole
skin (outside and inside hard foam laminate).
a) Superficial damage
With a split or fracture, the laminate may detach from the supporting foam. Start by
removing loose laminate until firm laminate is reached. To remove the foam laminate use
a grinding disk, grinding block or sharp knife. With a grinding block or sharp knife only
remove the cloth around the damage. Splice ratio per cloth covering approximately 20
mm ratio laminate thickness to splice: approximately 1:50.
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