ORIGINAL: bjorngl
The left yaw may simply be due to to little right thrust if you have a big motor. My uplines and hover had a definite left-limp until I added a 3 or 4 shims to increase the R-thrust on my OS 91 FS.
With a 15x4w prop it's a real killer. Have to tune a good low idle, otherwise it can't stay still on the pavement. I used the CA hinges. Very good instructions in the UCD manual. I pinned the hingeswith toothpicks for extra safety.
I think I'm going to handle the left yaw just like they do with full-size single engine aircraft and that's just dial in a little right rudder trim. I think my RD 8000 will allow some right rudder mix slaved to the throttle. And/or, keep my left thumb dancing as I change power settings.
I own on older Piper aircraft and not only does the engine have some right thrust and a little down thrust built into the engine mount, it also has some permanent, designed-in right yaw twist in the vertical stabilzer. During a full-throttle takeoff and climb, some additional right rudder input is still required to counter the torque induced left yaw tendency. The left yaw tendency becomes more noticeable as airspeed decreases. Full throttle in level flight at low altitudes actually requires a touch of left rudder to keep the ball centered (yaw indicator). During normal cruise (75% power or so) things seem to even out and the airplane flies straight, hands and feet off the controls.
Kaos