In my opinion This is being way over thought. Its real simple and absolutely zero math involved. A simple board wing 1/2a airplane with a half A bellcrank (2 inch or thereabouts) and it seems a bit twitchy to the user drop down from that to about two inch at the handle, problem solved.

Davey I do feel that your forty two foot of line is a bit much line for a board wing half A trainer There is absolutely no reason to put a humongous 3.5 inch bellcrank on that little wing heck what is the wing cord?

John