Today I worked on fitting the firewall recess. The purpose of this recess is to allow room for the engine oil filter and prop govenor. Otherwise these the firewall would interfere with these items. Most of the aircraft is made out of aluminum but the firewall, the panel between the engine area and the cockpit, is made out of stainless steel. The purpose of this is for fire protection (steel withstands higher temperatures in the event of an engine fire). Drilled, deburred and riveted the joints in the recess and then cleco'd, matchdrilled, deburred and dimpled the recess and the firewall holes. I'm not going to rivet the recess on yet as I may need access to other areas through the hole in the firewall.
