After getting the cowling mostly done (all
the necessary flanges in place), I decided to finish up the firewall. I removed all
the hardware, wires, tubing, etc. I then fabricated the four rudder cable pulley
assemblies and fit them to the screws on the firewall. I cut two pieces of foam to
fit on the main spar out to the first wing attach bolts, and micro'ed them in place.
Next, I found that I didn't have enough fiberfrax, but I started cutting it to fit the firewall/spar while I waited for more to arrive. After the fiberfrax arrived, I used the white silicone to attach it to the firewall, per the recommendations of many people on the COZY mailing list, who claimed that the white glue supplied per plans just doesn't cut it.
After applying the fiberfrax, I began cutting the 0.016" stainless steel sheet for the firewall. First, I cut the two pieces that fit over the foam. Next, I cut out the bottom section. Since I have a slight joggle in the firewall where it meets the spar, I decided to make the firewall stainless in two main parts, and have a slight overlap sealed with caulk. I cut the bottom section to fit and then positioned all the through holes for the wires, mounting bolts, fuel lines, and conduits. You can see the bottom section in place in the picture above. Next I did the same for the top section of the firewall and another piece cut to cover the vent lines near the top of the firewall.
After ensuring that everything fit well, I caulked all the seams with CP25WB fireproof caulk (it expands when exposed to flame) and red high temperature silicone RTV. I then went back to Chapter 23.
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Copyright © 2000, All Rights Reserved, Marc
J. Zeitlin
e-mail: marc_zeitlin@alum.mit.edu