What is the primary force that causes an airplane to turn?

The primary force that causes an airplane to turn is the horizontal component of lift. When an airplane banks or tilts into a turn, the lift vector is split into two components: a vertical component that acts to counteract gravity and a horizontal component that provides the necessary force required for the turn.

During a turn, as the airplane banks, the angle of attack increases, and the lift generated by the wings tilts with the aircraft. This results in the vertical component of lift acting to oppose gravity while the horizontal component of lift is directed toward the center of the turn. It is this horizontal lift component that causes the airplane to change direction, allowing it to turn effectively.

Understanding this is crucial for pilots, as managing the balance between lift and bank angle directly influences the aircraft's maneuverability and performance during a turn.