If we are splitting heirs then I'll point out that P-factor is not really an issue in normal flight because you only get P-factor if the propeller disk is significantly misaligned from the direction of travel, and that only occurs in high alpha flight or on the ground with a taildragger. Also P-factor, evenin high alpha attitude,is much less an issue on models than on full size aircraft because of the relative slow forward speed of models compared to full size.

Most of the reason that right thrust is required is because of asymmetric loading on the vertical stabiliser due to spiral slipstream. Also as pointed out by BMatthews on many planes right thrust can help offset rolling momentdue to torque becauase of yaw-roll couple.

http://home.earthlink.net/~x-plane/F...y-PFactor.html

Steve