I can't see the fin being large enough and the tail moment being long enough to cause spiral instability problems even with a
B.Mathews.. This is something you have mentioned before- When I looked at the photo I thought- that rudder looks too small- The fuselage having a lot of side area infront of the centre of gravity, and the big prop, I would have thought problems would be caused by to SMALL a rudder.
You have in the past mentioned problems with large rudders, I`d be interested if you could explain why having a too big rudder is a problem and at what point it starts to becomes so.
J.M