I bought a used Monarch D-lite at the IHLGF this last weekend. It was in 'really' nice shape. Notice I said "was."

Anyway, today I tried it out for the first time. First flight to check trim worked fine. Second flight... had a friend really launch it.... well, his finger must have slipped over the throwing peg, 'cause he cracked the wing. Inspection revealed that it seemed that it was only creased on the top part of the wing about 1/2 down the first wing panel on the right hand side. It flew fine the rest of the next two hours until I made the mistake of supporting too much of the weight of the plane from the creased wing. It broke the rest of the way down. The top glass basically broke from front to back and the carbon broke too. The foam is cracked all the way to the bottom. The bottom glass and carbon is totally intact, so it folds nicely back into place. Sooo, the question is, what's the best way to fix it? Strong and light, of course.

From : Don Stackhouse

The key issue is the compression and buckling strength of the graphite upper spar cap. Carefully use a Monokote iron to re-expand any crushed foam, then use a little thin epoxy (and maybe some micro-balloons if necessary) in the split in the foam to repair the core. Once that's cured, lightly sand the top of the graphite spar cap on both sides of the break with 320 grit sandpaper, just enough to remove any glossiness from the surface. Now bridge across the break in the spar cap with a spanwise piece of unidirectional graphite cloth about 1.5" long (the chordwise width should match the width of the spar cap), or tows laid side-by-side to accomplish the same thing. It's best if the ends of the graphite strip are trimmed to a rounded shape, so the end of the patch is spread out a bit in the spanwise sense to minimize any stress concentrations. Use a thin, slow-cure epoxy. Now patch the rest of the break with a 1/2" wide strip of 3/4 oz. glass cloth.

One final hint, you can save some weight by wetting out the graphite and glass on a separate piece of paper, squeegeeing off the excess before carefully lifting it off the paper and stippling it into place on the wing with a small disposable brush.

Don Stackhouse
DJ Aerotech