Single-engine airplanes in particular are susceptible to left-turning-tendencies, especially at low airspeeds. You’re typically taught 4 of these:
- Torque (Newton’s 3rd law from the engine)
- P-Factor (Gravity)
- Spiraling Slipstream (Aerodynamics)
- Gyroscopic Precession
These combine to produce a left turning tendency, all because the propeller is turning clockwise (relative to the pilot).
Standard disclaimer for my other flying notes: I’m not a CFI. Hell, as of this writing, I’m not even a private pilot. Don’t take this as flight instruction.
Pretty simple, Newton’s third law states that for every action, there’s an equal and opposite reaction to that. The engine of the airplane is causing the propeller to rotate, at a certain amount of torque. Newton’s third law states that there’s an equal amount of torque in the opposite direction. Because the aircraft is of much greater mass than the propeller, this is why the propeller rotates at a great rate, whereas the plane... essentially doesn’t, unless you’re at or near full power.
P (or Propeller) factor is, IMO misnamed. Essentially, the propeller blade that is going “down” has gravity to help it out, whereas the blade(s) that are moving horizontal or up don’t. This, fairly minimal extra force, helps the right side (because the propeller is spinning clockwise) to move more air than the left side. This extra force on the right side causes the plane to yaw towards the left.
Note that this is most noticeable at higher pitch angles.
Now we turn towards trying to imagine the airflow. Because the propeller is turning, the wind is also turned by it (the propeller pulls the wind backwards and induces a rotation in the same direction as the propeller). This slipstream now rotates around the aircraft, until it hits a flat surface (typically explained as the rudder), which forces either a bank (wing or elevator), or a yaw (rudder).
Note that this really only happens at slow speeds, because at faster speeds, the wind is moving fast enough that it doesn’t hit the plane.
Only really a thing in tailwheels, or while trying to change pitch angle.