Here’s a pic of the plug and two of the mold parts. As mentioned earlier, the fuse plug was built using balsa and ply in the same way that you would build a typical kit. I started with a side view cut from 1/8 inch ply, cut my fuse formers down the middle and glued them to the ply profile. This was sheeted with balsa and when finished I flipped it over and repeated the process. I then covered it with fiberglass and started sanding, priming, sand some more, until you begin to think that you’ve lost your mind with what you have undertaken!
Once the fuse has a class A finish it’s time to plan the location of your parting seams, making sure that there will be no reverse curves which would make the mold parts impossible to remove. After several coats of wax and lots of planning, I took 1/8 inch ply, about 2 inches tall, and attached it to the plug, essentially surrounding what was to become the first mold part. A coat of PVA was applied, then 3 layers of resin and 6 oz. cloth (I used polyester because it was cheaper and I was more familiar with it. When that first lay-up cured, I brushed on a layer of very thick resin (pudding consistency) and covered it with ½ inch thick balsa blocks and when cured, covered that with another 2 coats of resin and cloth. The balsa blocks are a cheap and easy way to make the molds much thicker and very strong without having to lay up countless layers of cloth.
When the first mold part was cured, I removed the parting ply from where the next mold part would meet, took a ½ inch drill and bored small indentations into the resulting parting flange (these become alignment buttons for the mold that butts against it) and used the resulting surface to butt the next part.
Once the entire fuse was covered, it was time to say a prayer and hope that the parting preparation (wax and PVA was done correctly. Well, I lucked out and the molds came off.
Once you have the molds it’s a simple matter of laying up cloth and resin in each mold part, trimming it at just the right time <g>, then clamping all the mold parts together and joining the parts with fiberglass tape. Pop off the molds and you have a fuse.
Well, that’s the simplified version. In fact there were a few disasters along the way. There was a release problem with the first fuse I laid up because I didn’t know PVA had a shelf life. That first fuselage was almost completely fused to my molds! Took a month to fix them. Tried again and the next came out fine. I’m glad now that I didn’t put panel lines and rivets on the plug (too lazy at the time) because the molds would not have been repairable.
As far as formers go there are only two main formers running through the wing center section. To these attach the retract rails and the wing brackets. The remainder of the fuse is rigid enough not to need additional formers, with the exception of the tail where the hstabs and tail wheel attach.
If you need more info just let me know,
John Fangohr