CHAPTER 38 - Building the Aft Structure

With the F606 bulkhead locked into place, I clamped the F610 to the longerons at the proper fore/aft location and used a pair of J-stringers in the lower longeron slots to hold the F607, F608, and F610 bulkheads square. Then the main longerons were positioned and shimmed to the bulkheads were centered and located correctly in the vertical plane. Next the bottom stringers were cut and trimmed to lap at the F606 and F610 bulkheads. Some builders have made butt joints at those locations, but I expect that the relatively thick tail cone skin will prevent the lap joint from showing at the F610, and I wanted a lap joint at the F606 bulkhead to tie in with the F623 piece (next chapter).

Next I fitted the F611 (without the HS attachment bars) to the longerons and centered and shimmed it, clamping the longerons at the final location. I also added the F612. While the F611 was in place, I marked the longerons for the slots necessary for the HS attachments. Considering the quality of slot the die grinder had achieved, I opted to get some cutoff wheels. With three 3/32" wheels in a mandrel, I was able to quickly cut the slots- requiring only a little cleanup to make the proper position and to round the end of the slot. The F611 was replaced onto the longerons, this time with the HS bars attached. The upper J-stringers were used temporarily to hold the bulkheads in position (the arrow in the photo shows where the end has been obviously offset - this is NOT the final position) while the lower stringers were fitted and trimmed.

The upper J-stringers required a little more effort to fit, because they must be notched to clear the F611 bulkhead while leaving the flange to lap over it. In the closeup of the forward attachments, you can also see that it extends about 5/8" forward of the bulkhead flange in order to tie in with the F622 piece (next chapter). The last couple of photos show how the bulkheads and stringers are beginning to give the project some shape. You can also see that the level has been moved aside for now; it will be used again when reassembling the parts after painting. After that, it will be used from time to time to check the level as I skin the fuselage. You will notice that I have not added the vertical support for F612 (it's laying on the ground in the last photo). It is so incredibly stiff for that last approximately 3" (the longeron clamps are aft of F611), that I cannot easily move it in any direction. I think it's only needed if you follow the traditional sequence of putting in the firewall and F612 on the longerons and then building the rest of the structure to fill.

Anyway, onward to the last of the lower structure....