I've read in another thread about a CG error on WM's part in their Ultimate's instructions. I read this AFTER I balanced my generic Ultimate (using the supplied copy of the WM instructions). It finished up nice and light (4 lbs. 6 oz.) but I had to add three ounces of lead to the tail to balance it per the instructions.
I think I've posted in that thread about that "error". Near as I can tell, the balance point suggested by the instructions is not in error. Where they suggest seems to be right about 30% of the EFFECTIVE MAC of the a/c. I did some measuring on my Ultimate and some figuring on paper (and in the post in that thread) and what WM's instructions say looks correct, not in error. I think the guy who said there was an error was saying that his figuring had the suggested CG at something close to 40% (like 38% or such) and that was why his crashed. Well, figuring out where the effective MAC is on a biplane isn't exactly simple, but it is easy for a straight taper wing biplane that has identical wings. And there's something else about a 30% CG on a biplane. They often have a bit of enhanced pitch stability from their stagger or somesuch. Don't remember what it is, but do remember that they've got "extra". and....
Nobody has figured out the actual tail volume of the WM Ultimate. CG estimation without considering tail volume isn't actually give you much to go on really. And another thing about the WM Ultimate's horizontal tail and it's contribution to pitch stability. If you notice, the elevators aren't aero balanced. There is a good chance that is going to contribute to pitch stability because the aero balanced elevators that seem to be so popular today actually are more prone to stalling around their tips, and this Ultimate isn't going to have that going on. whatever....