I give up ! All I want to do is make an airplane that has a tendency to return to wings - level if disturbed to a few degrees of bank angle, one that does not constantly need to have uncommanded roll angles taken out by hand, and can stay on a steady 90 degrees due east heading without continual course corrections.
I build a simple test plane
big tail fin, yaw stability
plenty of dihedral
Despite the above, roll angle gets bigger the longer i leave it uncorrected, plane would spiral dive into the ground if i let it.
However, the smallest elevons are having trouble putting any bank on that i do ask for, it's almost impossible to turn this plane at all without the rudder - so maybe it is doing something after all?