My DLG carbon horns are about 0.015" thick and are
plenty stiff and virtually bulletproof. They are laid up from 3 layers of
3.0oz CF cloth, sheared to +/-20. The layup is clamped between two aluminum
plates for compaction. I can get away with such a small thickness for several
reasons:
1) The horn hole is made by poking a wire through matched
holes in the Al plates when the layup is still wet, not by drilling the
cured carbon. This avoids cutting the fibers, and makes a smooth bearing
surface. Drilling the hole in carbon produces fuzzy mush for the bearing
surface, and the hole will easily enlarge with wear.
2) The horn has a tiny 0.035" wide boss at the hole,
which more than doubles the bearing surface. The boss is automatically
formed during layup via a 0.015" deep conical indendation on one of the
plates at the hole. The indendation is easily made with the very tip of a
1/8" drill.
3) I put a loop of 1K carbon tow around the pin poking
through the layup. This ensures that the hole won't burst open.
With these features, a 0.03" thick horn should be
adequate for a 3m ship. Such horns are about as thin as can be made, short of
steel plate. With 4-6 horns in the breeze, the small thickness is probably a
significant drag advantage. A whole batch of horns can be easily made at once
between two 1"x8" Al plates.
Some photos of these horns on my SuperGee-II are here:
http://groups.yahoo.com/group/SALglider/files/SuperGee%20II/Photos/
The boss at the pushrod hole is hard to see, though.
