I didn't get much done this Labor Day weekend. We had a family wedding to attend. I wanted to get something done so I worked on lengthening the stringer past the standard shipping length of 8 feet. I cut off 36" and added 41" which puts the splice between F9 & F 10. I'll let you know what my final length is when I install F12. I'm leaving the cleco's in place until I know for sure I have enough length to work with.
I used a 5" piece of 3/4" x 1/16" aluminum angle (same material as the stringer) for the splice. You have to round off the outside corner edge to get it to fit inside the 6061-T6 aluminum angle due to the inside radius. I used an aggressive file to knock off the corner edge and then used sand paper to give a nice radius until it matched perfectly with the inside radius. I will use 1/8" rivets to secure from the top only, so as to save the side rail for attaching the skin to.
While talking to Dave Thatcher on the phone on "what I do next", he reminded me that there are two anchor nuts that hold the front fin spar to F10 which get mounted later on to the front side of F10. He said not to rivet the side skin on until I have mounted these nut plates. I leave little notes like the one above to help remind me of these things!