I could be a CG problem. With my UCD46, it's tail heavy with a Saito 72, and just a tad nose heavy with a Saito 91. Also, the torque rolls are very slow on my UCD46 (without cheating with ailerons)... I'm not 100% on this, but I think it's possible to be too tail heavy. I have a Saito 91 on my UCD46.