FAA Ground School Practice Test

What force is responsible for making an airplane turn?

1. The vertical component of lift

2. The horizontal component of lift

3. The weight of the airplane

4. The thrust produced by the engines

The correct answer is: The horizontal component of lift

When an airplane turns, the horizontal component of lift plays a crucial role in changing the direction of the aircraft. During a turn, the pilot banks the airplane by rolling it to one side. This banking action causes the lift vector to tilt as well, dividing it into two components: a vertical component that helps to overcome weight and a horizontal component that provides the necessary force to alter the aircraft's flight path. The horizontal component of lift acts towards the center of the circular path that the airplane is following. This force is what allows the airplane to make a banked turn and maintain altitude while changing directions. Essentially, this inward force counteracts the inertia of the airplane that wants to keep it moving in a straight line, resulting in a change of direction. While thrust, weight, and the vertical component of lift play important roles in various aspects of flight, they do not directly contribute to the turning motion. Thrust propels the airplane forward, weight acts downward on the airplane, and the vertical component of lift ensures that the aircraft remains in level flight, but it is the horizontal component of lift that is specifically responsible for enabling the airplane to turn.