Longerons, side skins, and firewall
Another week with much progress. I attached the forward side skins. I decided to be “bold” and bend the rear curve first. This worked out just fine, although a bit frustrating. I did end up slightly cracking the corner of the sharp bend just like they tell you not to do in the instructions. I stop-drilled the crack and removed the failed material. This is seen as a 1/4″ long notch at that corner. It is fine, just an extra stress-relieved bend. Also seen in some of the images, I needed to adjust my bend to come a little more in line with the bottom of the side skin.
I also cut the holes for the side steps AFTER doing the bend. I think that was a wise choice, as doing it before would have complicated the bend. Have you ever used a fly cutter in a cordless drill? I cut the step holes with the skin on the plane. That was exciting in a terrifying kind of way. Nah, not really, I just turned the fly cutter super slow and used it more as a low speed scribe than a high speed cutter. It worked great.
With the side skins on, I match drilled the arm rests (no brainer) and longerons. Drilling the longerons was one of those processes that requires lots of time and patience. This is also a good process to slow down and do it right the first time, yet not be petrified by the profound nature of what you are about to undertake. Ok, so this seems like an important step. I started from the aft of the fuselage and worked my way forward on both sides. I used a lot of clamps and checked to be sure I was progressing with the top of the longeron flush with the side skin after every couple of holes. I did try to leave just a bit (just a hair) of overhang on the forward skin to account for edge deburring. No big deal, but I’m at least trying to be smart about such things. Alright, so after about six hours and a whole lot of Boelube across two sessions, I completed drilling the length of both longerons. That is a lot of holes. I should note that when I got to longeron alignment at the seat back bulkhead (I forget the part number), it seemed like there should be some consideration for the fact that there is a bracket part that fits between the bulkhead and the longeron angle. It seems that you could get the longeron drilled too close to the top of the bulkhead such that the part that goes between wouldn’t fit later. So, I used a spacer to space the longeron angle off the top of the bulkhead while drilling it.
The forward sharp bends in the longerons came out surprisingly well. They matched the skin just as good as when I did a test alignment against the skin when I was bending them (shouldn’t be any big surprise). I did find that I needed to put some extra twist in the longeron to make it match up to the firewall engine mount angles partly because the side skin wants to take the twist out of the longeron. No big deal, a little extra twist and things came out fine. (picture shown is before extra twist).
Next up was to put on the firewall. Whew, another critical operation. I followed the instructions, used some more Boelube, and the firewall and bottom forward skin are attached.
