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Empennage

HS inner ribs and spars match drilled

I got out to the shed last night to match drill the inner ribs and the spars to the HS skins. Starting from the rear spar I drilled the inner main rib flanges to #30 making sure that my marked centre line was in the middle of the skin holes. Fairly easy and no problems encountered. Then starting from the outboard edge, I match drilled the entire forward spar. Some of the holes are already predrilled in the spar but the inner spar section is not. I used a cleco every 2nd hole to make sure the skin and spar alignment was good. The inner most hole goes through the spar and the inner main rib. I’m a bit concerned about the edge clearance on the rib flange. Looking at a few other builder blogs they appear to have their holes in a similar position. I can’t see how this can be improved as the skin and spar pre-punched holes were clecoed into alignment and the rib was clamped to the forward spar. I’ll measure the clearance when I disassemble but for now … build on.

The plans then called for the reinforcing angles to be clecoed into position to allow for the dreaded inner rib, forward spar, angle, nose rib match drill. I was a bit worried about this drill as I didn’t have an angle drill. As I was making sure everything was aligned, I discovered that one of the angles was not sitting flush with the forward spar as its edge was clashing with the skin. I removed the angle and sanded the edge back a couple of mm’s. I haven’t edge prepped the angle yet so I’ll clean this up when I finish match drilling and disassemble.

Back to the rib/spar drilling. Lots of builders use the 12″ bit which has enough flex to drill this hole. I was very careful, drilled slowly and concentrated on keeping the drill tip as perpendicular to the flange as possible. As I was going slow and being careful, it took a long time to do all 4 holes on each side. It was fiddly but I managed to get the #30 pilot holes drilled ok. I then drilled these out to size using my #40 12″ bit. This was much easier and didn’t take very long at all to drill.

Copper clecoes now in place and the edge clearances on the nose rib flange are great! I’m very glad I left more flange material on, and made the holes closer together then what the plans call for. I only diverged by small amounts but the end result looks good.

I really wanted to get the skin match drilling finished but I built a cradle for my HS and it was getting late so I called it a night. I had some rubber matting which I used to test fit the HS but this is not the permanent solution. I’ll need to find something better on the weekend. I still have the rear spar, main rib, centre nose rib and tip ribs to match drill both sides. I’ll do them next session.

Build time 2.5 hrs.

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About gstrack

Husband and father of 2. Control & Instrumentation Engineer. Flying nut. Gadget geek.

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