The story on how this got figured out is a good one.
Well Dan, let us in on it.

Frank Parmenter had built a new gas plane, finished it on a Friday night. He noticed that the stab was glued on with a tilt but didn't fool with straightening it. Flew the plane on Saturday. It flew with a beautiful glide turn. He was unable to live with the tilted stab and fixed it overnight. On Sunday he had lost the turn. The only change was the stab tilt. The engineer mind took over and here we are.