We have three UCD's in our club (number 4 on the bench) They all use YS91FZ's for power and have CG's about 5 1/2 back. Mine and one of the others needs very little mixing for knife edge flight. Mine needs only a little down and the other needs a little up mixing. The third one, however, pitches much more violently down and rolls opposite the rudder. With the control surfaces centered it will fly straight and level with almost no trim changes. He already has a lot of correcting mix in it but it keeps happening (especially the pitch down) Does anyone have any ideas why this plane is so different? What else should we look for? We've been scratching our heads trying to figure it out. When side by side the control surfaces seem identically positioned and are centered. The pushrods are all 4-40. Loops are straight and rolls are axial, hovering is easy.

Chris