Ch. 5 - Fuselage sides RH - Part 4

Proper positioning of LWX and LWY  (2.0 hrs)

Aligning the wood pieces LWX and LWY on the left sidewall was challenging to say the least, and even with the sidewall cut to the exact plan dimensions, the scale drawings were a bit off (more than I would have liked). I did get them as close to the drawings as possible, but total fidelity was not in the cards. I'm blaming the 1980s reproduction technology.

While a bit disappointed in the quality of the drawings, a lot of the inaccuracies will be magically corrected during final assembly with careful alignment.

Perhaps one of the more important points is that, however inaccurate the geometry of LWX/LWY positioning on the left sidewall turned out, the same should be replicated on the right sidewall, to ensure even fitting of the wing spar.

Because the drawings could not be counted on for absolute precision, and since positioning by hand tends to introduce its own errors, I needed to devise some sort of apparatus to enable me to precisely mirror this wooden geometry on the opposite sidewall.

While considering such a thing, I decided that the most important LWX/LWY dimensions should be the ones measured from the top of the longeron, and from the aft edge of the sidewall, both acknowledged reference points. The jig I was considering would thus have to be able to capture these dimensions, and reverse them, like a mirror, without losing any accuracy.

These requirements were enough to cause quite a bit of head scratching, but I eventually settled on what turned out to be a simple solution, that required no actual measuring, while providing total accuracy, even when transposed.

I decided to place strips of wood on top of, and in tight contact with the longeron (#1), LWX (#2), and LWY (#3), then capture their relative positions by laying a flat a board over them, and driving screws into them from the top.

Laying out the jig

Pattern captured with board

Rear view

Front view

I basically created a wooden pattern for replicating the LWX/LWY geometry. To make it usable on the right sidewall, it had to be reversed though. So, I flipped what I had at this point upside down, and placed another flat board over it. I then drove a new set of screws into the wooden strips from this side, flipped it over again, and removed the original screws, and the original board.

Left sidewall jig flipped over to make the right sidewall jig

New board applied to the top

Jig flipped over and original board removed, yielding the opposite side jig.

Just like that, I had the perfect mirror image I was looking for.

All I had to do now was to secure the jig to the right sidewall, and fill in the new LWX and LWY.

Right side jig in position

New jig in action, positioning LWX and LWY.

After an initial dry fit, followed by many measurements to confirm my expectations, I floxed LWX and LWY in position, confident that I had achieved the closest possible left to right match.

LWX and LWY floxed to the right sidewall

Final measurements after the flox dried revealed no measurable differences between the two sidewalls.

Jig removed, LXY and LWY curing.

Finished product

UPDATE: Here's what I discovered reading through the 1800 pages of Canard Pusher newsletters late last night:

☐ CP #27 page 6 (Builder Hints) Aft fuselage side shape, plans page 5-2

A number of builders have noted that the A-5 drawing has a different shape the that obtained when fabricating the fuselage sides per the page 5-1 dimensions. This approximately 0.2" error will not present a problem if you follow these instructions: Carefully follow all the dimensions on page 5-1. This will assure that the firewall will fit. Do use the 5.8 and 6.9 dimensions on A-5 and be sure the extrusions are perpendicular to the top longeron. Ignore the small difference between the bottom shape and that on A-5.