I began fitting and drilling the Y tail and tail post structure to the aft fuselage tonight. It's a tight fit and the plans call for that. Once I got everything lined up I realized that there is not enough clearance for the rivets that will attach the skin to the tail post channel. The service bulliten doubler doesn't allow for enough room to insert and pull rivets, or clecos for that matter.
After reading a few builder logs and searching the sonexbuilders.net forum, I found that other builders had to trim/grind about 1/16" off each side of the service bulliten doubler. So I'll have to remove the structure and unbolt the tail straps in order to grind the doubler down. Not a bit deal, but I have to remove all the bolts and nylon lock nuts.
