There is quite a lot of miss guilded info flyin' around here. <div>This isn't about Pfactor. It exists but has absolutely no effect on our small models.</div><div>This isnt about Torque. Torque is a twisting, not a yawing effect and has very little (read non) effect on any, even high powered models.</div><div>This is about the spirelling propeller slip stream hitting the left side of the vertical fin causing it to move over, thus creating the left yaw.
There is no 'one answer', sorry. I suggest you do a search on the 'Aerodynamics'forum.
The factors causing left-turning tendency all exist, and are worse on some types than others depending on design criteria. Being aware and ready to counteract it is most of the battle.
I agree poor rye has enough info, his head must be swimming. [8D]</div>