In Chapter 3, the Cozy plans have you do three little “practice” projects that gradually help you dial in the various techniques you’ll need to successfully complete the airframe.
The first layup is just six layers of BID (bi-directional fiberglass) laid up flat on the bench, with some sort of release agent underneath – I used wax paper. You make the thing oversize, and then cut it to a more precise size (about 10″ by 16″ if I remember – I don’t have the plans in front of me). Then you let it cure, and weigh it, aiming for no dry fibers and between 10.5 and 12.5 oz’s. The plans say 11 is perfect, and 10.5 is the lightest you can safely go. Mine ended up at about 10.75, so I’m feeling fine and dandy about that. And my epoxy passed the “scratch test,” so all’s well there.
The second layup is meant to give you confidence that these foam/fiberglass sandwich pieces are really as strong as they need to be to stand up to the loads that they’ll be subjected to while flying. To do this one, you take a piece of foam and shape it into, essentially, a thick ruler, with tapered sizes and ends. (The plans aren’t clear, but I went ahead and used urethane foam, which I don’t think is typically used for anything structural in the Cozy, but what the hey. It’s practice.) Then you lay up four layers of fiberglass, alternating UND (unidirectional fiberglass) and BID on the table, then slurry the foam and press it into the middle, then four more layers, and let it cure. Once that’s done, you try to destroy it but putting a wood dowel underneath and putting all of your weight on the ends. Yep, my 200 pounds couldn’t break it. I was eventually able to get it to start to de-laminate by working it on both sides, but that took some doing and a LOT of weight. There were several places where I had a hard time getting out air bubbles, and those spots proved to be the weakest spots. Go figure. There will be no air bubbles on this plane if I can help it – period.
By the way, I’m not knife-trimming any glass on this project if I can help it. I used the Fein Multimaster on all three of these to cut the fully-cured glass, and it worked like a charm. Very little follow-up sanding to do, and that was only for aesthetic purposes. The edges were always nice and smooth.
The third layup (really it’s the third, fourth, and fifth layup) ends up becoming a bookend, by the most circuitous route possible, in order to allow you to practice all of the major techniques you’ll need to build your airframe: UND layup, BID layup, dry micro inside corner, flox corner, etc. AND you get to mount your favorite photo. So mine isn’t beautiful, mostly because I didn’t obsess over getting everything perfect but I was able to get the various steps done satisfactorily. The only air bubbles in this thing are around the photo. I should have just made it smaller so that the glass could have adhered to itself in the corners – I don’t think micro would have helped. And the flox corner is HUGE. I love flox. Future corners will be smaller And yes, that is a photo of our family in front of FIFI, the only remaining flying B-29 in the world, at OSH this past summer. I remember us being pretty wet and tired when that was taken…