CHAPTER 36 - Adding the Seat Ribs
I modified the F657 gussets to match the contour of the longerons and then used them to space the F605 bulkhead as I positioned it in the jig. Since the gussets would have gotten in the way of the longeron clamps that the plans show, I used large diameter washers, bent on one side to form a hook, in conjunction with a lag bolt on the outside of the longeron to clamp it in place. I'll try to get a picture of the arrangement on this page soon. With the longeron shimmed and clamped and the F605 bulkhead clamped to the longeron, I used some angle stock and cleco sidegrips to position the lower end at the approximate distance. Then I began to fit the end seat ribs.
For the next couple of days, I did the measurement dance again. I'd clamp the rib in place, measure from the rear of my false spar to the inside of the F605C, then go the the wing to measure spar to spar. Wait, was that the left or right wing? Back to the wing stand to measure again. Back and forth, back and forth. Finally, I was satisfied (after trimming about 1/8" from the seat rib forward flange), so I drilled the ribs. Now the distance was set. Next I checked (again) that the bulkhead was centered and levelled and replaced the angle stock with a yardstick, as you can see in the next couple of photos.
Judi caught me in the process of fitting the remaining ribs; it was easiest to get inside the jig, though the quarters were cramped and I had to juggle things around by removing some ribs to give me room to work. Basically, I started by marking the front of the ribs for their rivets and marking the rib locations on the F604 flanges. You can see from the arrow that I carried the spacing to the ends of the rib flanges. That was Ok, except on the F618 ribs, where the spar holes coincided. Fortunately, the predrilled holes disappeared when the spar holes were drilled through them. I proceeded to drill and attach all the ribs to the F604.
Now everything got removed and I marked the locations of the ribs on the F605 spar. This is when I discovered that some rivets needed to be drilled out. This is also when I discovered that I had measured the outboard seat belt anchors from the center of the bulkhead rather than from the inboard seat belt anchors. As a result, they were 3 1/8" too far inboard! After some discussion (some of it by myself in a closed room, loudly!), I decided to relocate the anchors to their proper position without replacing the spar. This entailed drilling out another couple of rivets and replacing them with countersunk. I will ream the extra holes and fill them with rivets or bolts.
After that crisis, completing the rear attachments of the ribs was fairly simple. Like so many other builders, I found that the rib lengths were off. I was prepared for this and simply rebent the flanges to fit. Throughout this process, I used a steel rule and sidegrip clecoes to ensure that the ribs were flush with the bottom flanges of the bulkheads. Now I was ready to tackle the baggage area.