Grob Astir CS G102, Flight Manual

Page: 44 / 48

REPAIR INSTRUCTION ASTIR CS
Rev. 9 28. Nov. 2005
8
After grinding out the splice, the repair must be thoroughly cleaned. Remove the dirt (also
out of the foam pores) with air pressure. Wash the
splice with carbon tetrachloride or
acetone, in case it has been contaminated with dirt or grease.
Fill up
the pores of the foam with resin and micro balloons until it is smooth. Then join
the laminates with the correct cloth, aligning it in the right direction.
Repairs must be dirt and grease free, (Figure 1)
At room temperature the resin will cure in about ca. 8 hours.
The repair can now be ground smooth and be painted.
Warning: Grind only edge of the repaired area
b) Damage of the complete sandwich structure
In case the inner laminate is destroyed, remove outer laminate that has no adhesion to
the foam, enlarge the hole until core is firmly joined to inner skin, then it is possible to
repair the inner laminate. To repair the inner laminate properly, an additional rim of at least
20 mm must be maintained. (splice ratio approximately 1:50).
The outer laminate shall be repaired as described in section a). The inner laminate must
be carefully ground and cleaned from foam residue. (Figure 2). With minor damage a
piece of thin plywood support may be glued onto the inner skin with construction glue,
the cloth patch of the inner laminate can then be positioned. The hole will then be filled
in with resin and micro-balloons mixed with styrene-foam balls. After curing (app. 8 hours
at room temperature) the outer surface can be ground smooth and the outer cloth may be
placed in position.
The plywood support should remain in position as part of the repair. When the hole is
of large or of oblong size the plywood support should be held in place with thin nails
which can be removed later, by pushing then out from the top surface.
Warning:
The plywood support must be properly fastened to avoid any wrinkles in the
cloth. (Figure 3)
Particularly with large holes in the sandwich structure, pre-fabricated foam structures shall
be considered for weight reasons instead of the micro-balloons-resin filler. Prepare a piece
of hard foam to fit exactly into the existing hole. The pores on the inside shall be closed
with resin and micro-balloons, position onto the inner cloth to cure. The structure
remains flexible to some extent (if required, warm up with hot air blower). The pre-
fabricated structure shall be glued into the hole with thickened resin (cotton flocks or
micro-balloons). Micro-balloons are used to close and smooth the outside pores, the
repair area is then ground and the outer cloth is placed into position.