Rough and Ready Aerospace: Step 9.6, Aft deck plate and gussets

At this point the fuselage is like a cardboard box with no top. Like an open box, the main longerons can move forward or backward relative to each other and this movement will cause a twisting of the fuselage. In order to prevent this the main longerons are tied together at the rear of the fuselage using the F-714 aft deck plate.

Before the longerons can be locked together by the F-714, any pre-existing twist in the fuselage must be removed. The first step is to level the fuselage horizontally across the two longerons at the F-705 bulkhead which is just behind the seats. This is near the widest point on the fuselage and it will make the measurement much more sensitive to have a longer distance measured.

The second point to be measured is at the rear of the fuselage over the F-714 aft deck plate (blue). If the fuselage is level at both points, it is assumed to not have any twist. So with the deck plate in place, the fuselage is tweaked as necessary to bring both points measured into level and the deck plate is match drilled to the longerons.

The fuselage is checked for level one last time before the now primed aft deck plate is riveted on.

Here is some more structure that holds the vertical stabilizer on and is also an elevator stop.

Next on the to do list is the F-757 gussets. These two parts tie the F-705 bulkhead to the main longerons. They require some layout to locate a square hole in the middle.

I cut the hole to the sides with a step drill and used a #30 drill for the inside corners.

A little bit of filing and we've got a square hole.

Here is the part in place. Over the F-705 bulkhead and under the longeron.

The F-721 side rails are next. These were previously trimmed and match drilled so there is nothing to do but rivet them on. They strengthen the top of the center section and provide a flat surface for the canopy to close against. Shown below, F-721 at the top and the arm rest in the middle. At left, is the F-705 bulkhead.

It's a nice quiet Sunday afternoon in the shop, the racket of the occasional rivet being driven not withstanding. I couldn't help but stand back and admire the progress so far. It's beginning to look like an airplane!

Back to work now with the F-695 gussets that tie the main longerons to the firewall.

And finally, the shoulder harness anchor points are attached to the longerons.

There are gussets on the F-706 and F-707 bulkheads. The purpose of these gussets is to maintain the web of the bulkhead's channel construction perpendicular to the surface of the skin. The bulkhead is very rigid in the direction parallel to the web (towards the center of the fuselage), but not strong at all in any other direction. So the gusset restrains the bulkhead from twisting under stress into a less strong geometry.