Thanks, it is right on 10.5 inches... one of the theories my son and I were bouncing around was to move it back even more because the elevator is not very responsive. I think it is that flat bottom stab causing the inconsistencies, but it seems to be doing the opposite of what aerodynamic theory tells us........

I have to move the engine back a bit...I never accounted for the swept back trailing edge, and the first prop (a bit flexible) smacked the trailing edge. I put the apc on which is a lot stiffer, and it cleared the trailing edge, but not by much.....