How I Fiberglass a Fin Can

by Wayne Mrazek

Glass the fins before they are mounted, makes them real easy to work and sand. Scrape off the excess wet epoxy with a scraper or old credit card. Not so much to make it light, but to get the excess epoxy out from underneath the glass and flatten the final surface. Power sand when dry with 80 grit to remove wax and to smooth.

Epoxy only forward centering ring(s) to the motor mount. Put into slotted airframe with rear centering ring in place to center the tube, but not glued on. Mount fins to presanded motor mount through the body tube with bead of epoxy on edge of root. After all fins are mounted, remove fin assembly. (Make an index mark so you can reinstall it the same way ) Glass fin to motor mount joint with strips of glass that does not go all the way up to where the body tube will be. (see picture below) Put masking tape on opposite side of joint being epoxied if there is any chance it will leak through the original crummy bead of epoxy you mounted the fin with. Sand the glass that extends up the fin to remove the wax, the glass on the motor mount does NOT need sanding.

Epoxy the fin-motor mount assy into the airframe, leaving the rear centering ring loose. When dry, remove the rear centering ring. Now the fun part. Glass the fin to inside of body tube joint with strips of glass. A long stick helps! No one should ever see this joint, so strength, not appearance is most important. Epoxy the rear centering ring and it's done.

A cosmetic bead of epoxy (with microfibers) down the outside fin-body tube joint can be added, but the strength is already there. If the body tube was also sanded to 80-120, any noticeable imperfections are now puttied, and a final coat of epoxy finishes it.