This is an attempt to answer the frequent question "Why is my aircraft turning left all the time?"
Propeller Torque
Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.
P-Factor
P-factor is the term for asymmetric propeller loading, causes the airplane to yaw to the left when at high angles of attack.
The descending right side of the propeller (as seen from the rear) has a higher angle of attack (than the upward-moving blade on the left side) and provides more thrust.
According to What You Need to Know About Aerodyanics... by Franklin Gutierrez.