Firewall Part 1

I started mounting components to the firewall. There is a little bit of extra work for me to do since my firewall was pre-punched for a Rotax 914UL engine, but I’m installing a 915iS instead. This means I have some new holes to drill, some holes to cover up, and a few that I can use as-is. To locate the new holes to drill, I printed sections of CAD drawings from the build manual at 1:1 scale and used existing holes to line up the print. Luckily, nothing going on the firewall is especially sensitive to position tolerances, still I’m able to achieve better than 1mm accuracy.

Sample print for locating new holes to drill- here I am marking holes for the throttle cable and for the water lines that feed the heater core inside the cabin

To cover up holes I’m not using: for holes that are rivet-sized, I just install a rivet. For larger holes (e.g. there was a triple set of holes for the throttle, choke, and heater of the 914 engine), I cut a small repair doubler from 6061-T6 sheet stock, and then set it in place using a combination of rivets and JB Weld MinuteWeld epoxy.

M5 rivnuts for the Rotax fuse box assembly – the lower right rivnut was close to other prepunched holes, so I put a 60x60mm doubler to cover the holes
Another patch doubler, covering up the holes for the muffler-cuff heating system that I’m not using
Rotax fuse box and fuel pump assembly mounted
Locating holes for the GPS antennas, trying to re-use existing holes as much as possible

One of the feet on the Rotax fuse box I acquired was broken. Rather than trashing the whole box (which is quite expensive to replace), I made a repair foot and attached with plastic epoxy. The repair foot is 3D-printed with the same carbon fiber polycarbonate filament I used for the wingtip. Although this filament is pretty strong as-is, I took the extra step of annealing the part, which helps bond the layers of plastic. After some experimentation, I found that annealing at 190°F for 40 minutes yielded the best results (increased strength, minimal deformation).

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