Cherokee-M Construction - Fin can
May 11, 2003:
Strangely, the 6" fiberglass coupler tubing from Hawk Mountian was a very sloppy fit in their own 6" airframe tubing. That's OK, another chance to practice my
vacuum bagging technique. Laminating the coupler tube using Aeropoxy (R2032 Resin and PH3660 hardener) and a single layer of 5.7 oz. bidirectional carbon fabric added just the right extra thickness, plus additional strength.
I didn't have coupler tubes to nest inside the coupler tube that I was laminating, so I made a quick-and-dirty substitute using cardboard propped up internally with more cardboard. It collapsed a little under vacuum bagging, but held up well enough. I taped coupler bulkheads on the ends end wrapped the cardboard in waxed paper. The whole thing with the release film and the breather just barely slid into the largest food saver bag.
I peeled off the release ply and did a rough trim of the excess cloth overhang at the 12-hour mark. Once it was fully cured I cleaned up the ends with sandpaper and a file and some sandpaper, sanded down a couple of high spots where the cloth had wrinkled up a little, and sanded the whole thing very lightly to get a perfect fit. Sanding into the matrix isn't what you are supposed to do because it weakens it a little, but I was doing this as much for thickness as strength. The result was a super-strong coupler that was a perfect smooth fit with the airframe tube. Barring some differential expansion out in the desert, no more messing around with sandpaper and masking tape to adjust the fit in the field.
Ready to begin laminating:
Carbon wrap:
Release film:
Polyester breather cloth:
Vacuum bagging:
Bag removed:
Trimmed and sanded:
