Well, I went out for pizza and beer with a frined last night so I didn't get any work
done on the plane. Today, however, was pretty productive. First, I started by tapering
the aft end of the extra tailcone stiffeners. Since stress risers occur where there
are rapid changes in the stiffness of a structure, tapering the end of the stiffener
like this shoule spread the stress out and avoid skin cracks.
At the forward end, I wanted to see if I would be able to just leave the flange
of the stiffener somewhat long and use it to form a tab which would be riveted to the
F-706 bulkhead. As you can see here, because the stiffener is at an angle, when the
flange would be bent up, it would miss the rivet holes that attach the baggage floor
rib to the bulkhead. So I decided to cut the stiffener off aft of the bulkhead and
make up some custom brackets.
First thing was to cut a scrap of aluminum and put the correct bend in it. This
piece is too wide, but that's intentional. I'll trim up the width after drilling
the holes.
I slipped a piece of .025 aluminum scrap under the bracket to create the correct clearance
for the stiffener flange and held the pieces in place with a couple magnets and a spring
clamp.
The holes are drilled. The ones through the bulkhead are #30 and the ones through the bottom
skin are #40.
I offset the holes to define the edges of the bracket. The #30 holes got 5/16 inch edge distance
and the #40 holes got 1/4 inch edge distance.
After some trimming and filing, here's what the bracket looks like. I think it
came out quite well.
Making up the second one took about half the time.
After that, I started fitting cutting pass-throughs in the F-707 and F-708
bulkheads and fitting the doublers. This is the right doubler on the F-708
bulkhead as viewed from the centerline of the fuselage.
Here's the same one as viewed from the outside. Nice, even clearance all around
the J-channel stiffener.
While I was working on fitting these stiffeners I noticed this note I had
made on this edge of one of the F-708 flanges. I trimmed the edge off so
that it would no longer interfere with another of the J-channel stiffeners.
Both sides got this treatment.
Here's what the additional stiffeners look like as they pass through the
F-708 bulkhead. Note how the doublers tie the stiffener into the bulkhead
structure.
After some more work, I had the F-707 bulkhead and doublers fitted as well.