Did you stagger the clecos from one side to the other?
I found that when putting all the clecos on one side, it would pull the flight controls into a slight bend.
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Then when it came time to rivet them up, I half set one in the very middle, one on each end, and then split the difference between the middle rivet and the end rivet and half set that one. I also marked each hole and alternated the direction the rivets were installed, again to keep them from "pulling" the control surfaces. After all the rivets were in and half squeezed, I went back and finished squeezing them.
The trick to squeezing them was to grind a pair of rivet sets to an angle that matches your control surfaces.
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RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC