Making the firewall for the Snoopy

Suomeksi

The firewall between the engine and cockpit of the OH-XEA “Snoopy” has not survived, so one had to be made. Fortunately, we have one photograph in which Snoopy’s engine is shown without its engine cowlings, and the firewall is partly visible. Based on the photograph, we determined what the firewall had looked like in terms of its shape and installation method in order to build a new one.

Most likely, the firewall had been made of thin sheet steel. At its upper edge, the firewall curves a few centimetres over the lower edge of the windshield plexiglass, and at its lower edge it is bent over the lower tube of the nose structure. On the side of the nose, the edge of the firewall likewise bends a few centimetres over the fabric covering of the nose.

At each corner of the nose’s steel tube frame there is a structure for attaching the engine mount to the fuselage. These attachment lugs and their supporting structures make shaping the metal sheet challenging, when making the firewall. We therefore decided to proceed with making the firewall in stages.

When we began making the firewall, we wondered how the firewall had originally been installed, given that all its edges had been folded, or bent. A firewall with folded edges is difficult to press as a flat sheet against the nose end frame, because the engine mount attachment lugs at the corners of the frame prevent the firewall from being pressed flat against the end of the fuselage. We therefore chose a method in which we first make the firewall without the side folds, and create the side folds from separate angle strips that will be riveted to the firewall.

To make the firewall, we first took sturdy cardboard and gradually shaped it into a template for the first version of the firewall. The shape of the cardboard template was then transferred onto a thin, 0,3 mm thick aluminium offset printing plate that is easy to shape. This 0,3 mm aluminium sheet is also easy to cut with scissors.

Photo: Osmo Väisänen

Once the thin aluminium sheet had been cut to the shape of the cardboard template, we test-fitted it to Snoopy’s nose. We found that the sheet still needed further adjustment. We then taped additional cardboard to the edges of the sheet where material was missing and cut away aluminium where there was too much. On this basis, we made a third version of the firewall from the thin aluminium sheet. We were already satisfied with this version, so it will serve as the template for Snoopy’s firewall, which will be cut from 0,7 mm sheet steel.

Photo: Osmo Väisänen

Because the Finnish Aviation Museum has better tools for cutting thin sheet steel to shape than our Puusepäntie workshop, we went there. At the museum, a rectangle was first cut from the steel sheet with a “guillotine cutter” to serve as the firewall blank. The shape of the aluminium firewall, including all its notches, was then transferred to the steel sheet. The notches were cut into the steel sheet with a jigsaw, and the cut edges were filed smooth. Once all the detailed shapes of the firewall had been cut, we returned to our Puusepäntie workshop.

Photo: Juha Veijalainen

There, the steel sheet was test-fitted in place on Snoopy’s nose. The steel sheet that would become the firewall was threaded into position by bending it vertically. The sheet already fitted surprisingly well, but it still needed further shaping and filing of the edges. After a little shaping and filing, the steel sheet was made to sit well in place.

As mentioned at the beginning, we made the firewall sheet so that flanges were left along its upper and lower edges, allowing the sheet later to be bent at the top over the lower edge of the windshield plexiglass and at the bottom around the lower tube of the nose frame.

To make the side flanges, missing from the firewall, we made angle strips from 0,7 mm sheet. They will be riveted to the edge of the firewall sheet only once the firewall is finally in place and its upper edge has been bent over the edge of the windshield and its lower edge over the transverse fuselage tube.

Photos: Lassi karivalo, unless otherwise mentioned

Translation to English: Erja Reinikainen