RE: ZIROLI P-61 BLACK WIDOW BUILD
Randy,
I epoxied that fire wall with triangular stock behind the fire wall so there would be a lot of damage done in trying to remove the existing fire wall. Things worked out for the best as any rotation would have moved the carb higher so the hole for that would show on the cowl. This way, there will be some big holes for the engine head and muffler exhaust but it'll all be at the bottom of the cowl.
Thanks for thinking about it.
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Booms (cont)
Planking:
This morning, I started planking the left boom using 1/8" thick by 4" by 4' long sheets.
In order to insure that the booms stays straight, no additional stringers are added to the top of the boom as this allows the crutch to sit on all my risers: I can thus put weights to hold the crutch in place and add planking to get a ridged, straight boom. Once the bottom is planked, the boom will then be ridged enough to remove it from the risers and then finish up the top.
Planking starts along the bottom, center of the boom (boom upside down) and works out along each side, doing both sides at once to remove the possibility of warping the boom, laterally.
I used carpenters glue for all planking.
I put water on the top surfaces of the planking to get better bending.
I couldn't use the micro wave on them as they are too long.
I put tick marks on the planking at each former location so I can put glue, accurately, on the sheeting as well as on the fuse structure.
pic 1:
Bottom center planked using a 1 3/4" wide piece which goes from the front to N-8.
After N-8, there are compound curves, plus the bottom back ends as a ridge.
pic 2/3:
Two sides planks 1 1/4" wide and tapered at the tail were next glued to the boom.
The back of the gear doors has a change of compound curves so the taper was started there and went to a point to N-8.
pic 4/5:
The next two planks are from the back of the gear door to the last former (N-12).
I could use about a 3" wide piece as there are no compound curves.
This planking also extents past the break in planking at N-8, thus giving more strength to the sheeting (with overlapping sheeting).
pic 6-8:
A 'mostly 4" wide' piece of planking was glued from the back of the door to the front of the boom.
Before gluing on the sheeting, I had to add some 1/8" thick ply along the front for the other cowl hard points.
Planking is one of the few places were you don't have to be neat as, in the end, everything gets sanded and "bondo'ed". Even with carpenters glue, speed is more important than neatness as even carpenters glue starts hardening in about twenty minutes.