After plenty of fretting about solid riveting, my results were quite good, for which I am grateful. The one complication I encountered at the end, had to do with the thickness of the center and dual control uprights. The plans call for 3/4" x 3/4 x .093" extruded aluminum. This material is apparently a special run done in high volume for Zenith, so scratchbuilders usually look for readily available alternatives. In the case of this extruded part, the approved equivalent is 3/4" x 3/4" x .125". Normally that wouldn't make much difference, but in this application the extra thickness caused my bolts for the dual control uprights to be too short. Because it would be very difficult to tighten those bolts with the center spar complete, I chose to leave it open until I can get the right AN hardware. At that point I will tighten all the bolts and drill and A5 rivet the overlapping top flanges. That will complete the center spar and should take no more than 60 to 90 minutes. For all practical purposes, I 'm calling my center spar complete. It is remarkably substantial component of the aircraft and I feel very confident that I have made it to the highest standards required for safe operations.
All done except tightening 10 bolts and adding some A5 rivets
