We know the four basic forces that act on an aircraft that make it fly. There are however a combination of physical and aerodynamic forces that contribute to a left-turning tendency in propeller driven airplanes. The forces of P-factor, torque, slipstream, and gyroscopic precession all work to create a left-turning tendency during high-power, low-airspeed flight.
P-Factor is a force from the propeller. It is also known as Asymmetrical Thrust. When you are flying an airplane at high angles of attack, the descending blade (right side) of the propeller takes a greater ”bite” of air than the ascending blade(left side). This then causes the airplane to yaw to the left about the vertical axis. P-Factor is most pronounced when the engine is operating at a high power setting, and when the airplane is flown at a high angle of attack. In level flight, P-Factor is not apparent, since both the ascending and descending blades have almost the same AoA and are approximately creating the same thrust.
Torque is greatest at low airspeeds, high power settings, and high angels of attack. Torque is better remembered by knowing Newton’s third law of motion. “For every action there is an equal and opposite reacion.” Most single engine aircraft where the motor is mounted on the front, the propeller rotates clockwise when viewed form the cockpit. When the engine puts a force on the propeller turning it to the right, the airplane reacts and rolls in the opposite direction about the longitudinal axis.
As the propeller creates thrust and produces a backwards flow of air, or slipstream, the air “wraps” around the airplane. Since there is a clockwise rotation of the propeller, the resultant slipstream flows over the top of the fuselage back around and underneath, then comes around to strike the left side of the vertical stabilizer. Which then yaws the aircraft to the left. As airspeed is increased, the slipstream tends to “stretch” out and the left turning force is less...
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