Stephan's Sonex #1627 Builder's Log

I worked on the SNX-T09-01 main spar assembly and the SNX-T09-02 forward spar assembly for the vertical stablizer. This required a lot of measuring and checking because I wanted to make sure that the pre-drilled skins were going to fit without too much trouble.

I needed to drill the holes for the AN3 bolts, but could not find any documentation on what the correct drill size is for this. I find it a bit perplexing that there is no universally accepted standard for this. I found a lot of different ways people in various groups suggested on doing this, some say start with #13 and then drill with #12 and then use a #12 reamer. I contacted Kerry at Sonex and he suggested to either use #11 or 3/16" bit. I did not have any #11 drill bits and checked with Aircraft Spruce and they didn't appear to have any either, so I settled on 3/16". I drilled a test hole and the fit was reasonable. However, when drilling the actual main spar, I found that there was way too much slop. I will have to get a #11 and #12 and reamer and see if that provides better results.

The plans indicated the location of the rudder hinge, which I carefully located and then fastened to the main spar, with the eye of the hinge centered on the edge of the spar. After I had it all lined up, I went ahead without thinking and started to drill the holes so I could cleco the hinge. While I was doing this, I realized that the skins were already pre-drilled and unless I had located the holes perfectly, they weren't going to line up! 

I quickly assembled the vertical stablizer and wrapped the skin around only to discover that the 4 holes I had drilled were exactly on the center of the edge of the channel, whereas the skins had the holes located more to the right edge of the channel. I'm not yet sure if I'm going to have to scrap the SNX-T12-03 upper spar channel piece, or if I can salvage it. It looks like the distance between the bad hole and the correct hole is approx. 5.4mm. I believe the minimum edge clearance is supposed to be 6.4mm, so I may have to scrap this piece.