Firewall flange join to boot and engine cowl

[Pbruce]

When constructing the boot cowl sides I noticed “puckering where the side panel overlays the firewall flange. (first pic). At first I thought I had somehow drilled screw holes incorrectly along the top and aft edges of the panel, causing it to buckle. But now I see that the firewall flange is bent more than 90 degrees near the top corners and down the side. The issue does not exist at the bottom near the tunnel (second pic).

Is that 90+ bend required to allow the engine cowl sides to lay flat, or can I bend it back to 90 so my boot cowl panel will attach?

If it is indeed needed to allow fitting of the engine cowl, what are other builders doing to manage the buckling effect of the boot cowl sides at he top corner? Take a shrinker to the flange area and bend it in to match the firewall? ? It will be covered by the engine cowl anyway. Would this work? It would need to bend in about 3/16”. Thanks

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[Lee]

Hi Pat. I laid a straight edge across the two flanges and formed them as necessary to conform. Most of it required very little. The exception was the small radius turns which required a bit of encouragement with the fluting pliers. I'm not in my hanger right now but there might have been a flute or 2 elsewhere the location of which was chosen to not interfere with cowl fasteners. I haven't got to the engine cowl yet. I'll cross that bridge when I get there but I don't anticipate any problems.
Lee

[Pbruce]

Thanks Lee. Unless I hear otherwise I guess I’ll tweak the cowl flange back to a right angle. Hopefully the engine cowl slides over that nicely.

[alaskabearhawk]

Did you use a slip roll to form the sides? I found that necessary to make the side panels fit correctly. I first made a paper pattern, then transferred it to the AL sheet as the panel lines aren’t straight and parallel on a flat surface. Then used a slip roll to do the differential curves.

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3583&log=272683&row=60

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=3583&log=272685&row=57

[Pbruce]

No, I did not use a slip roller. I don’t have access. I did form the top corner panels separately though so that I could place the side panels below the lower corners of the windscreen. This makes them simpler, and easier to handle and allows removal for maintenance. They seem to lay flat except where the flange “pulls away”. I will bend that back to the required angle so the boot cowl panels can be attached without buckling. The panels on the Patrol are slightly different too so this might help. Thanks for the link to your log. Very helpful.