What force is responsible for an airplane's turn?

The force responsible for an airplane's turn is the horizontal component of lift. When an aircraft banks during a turn, the lift vector tilts, creating two components: one that opposes gravity and the other that acts horizontally towards the center of the turn. This horizontal component of lift is what provides the necessary centripetal force to change the direction of the aircraft.

As the airplane enters a turn, the pilot tilts the aircraft, which causes the lift produced by the wings to shift. While the vertical component of lift continues to support the airplane's weight against gravity, the horizontal component effectively pulls the aircraft toward the center of the turn. This allows the airplane to maneuver smoothly along a curved flight path.

In contrast, thrust is responsible for propelling the aircraft forward; gravity pulls the aircraft downward; and drag opposes the aircraft's forward motion. However, none of these forces contribute to the change in direction during a turn in the same manner that the horizontal component of lift does. Thus, it is the horizontal component of lift that plays a crucial role in enabling an airplane to turn.