Forces in a Turn

An aircraft requires a sideward force to make it turn. In a normal turn, this force is supplied by banking the aircraft so that lift is exerted inward, as well as upward, as shown in the figure below. The force of lift during a turn is separated into two components at right angles to each other. One component, which acts vertically and opposite to the weight, is called the “vertical component of lift.” The other, which acts horizontally toward the center of the turn, is called the “horizontal component of lift” or centripetal force.

During a turn lift is divided into two components. One component acts vertically and opposite to the weight, the other acts horizontally toward the center of the turn.

The horizontal component of lift is the force that pulls the aircraft from a straight flight path to make it turn. Centrifugal force is the “equal and opposite reaction” of the aircraft to the change in direction and acts equal and opposite to the horizontal component of lift. This explains why, in a correctly executed turn, the force that turns the aircraft is not supplied by the rudder. The rudder is used to correct any deviation between the straight track of the nose and tail of the aircraft into the relative wind. A good turn is one in which the nose and tail of the aircraft track along the same path. If no rudder is used in a turn, the nose of the aircraft yaws to the outside of the turn. The rudder is used rolling into the turn to bring the nose back in line with the relative wind. Once in the turn, the rudder should not be needed.

Banking the aircraft into a turn produces no change in the total amount of lift developed. Since the lift during the bank is divided into vertical and horizontal components, the amount of lift opposing gravity and supporting the aircraft’s weight is reduced. Consequently, the aircraft loses altitude unless additional lift is created. This is done by increasing the angle of attack until the vertical component of lift is again equal to the weight. An important fact for pilots to remember when making constant altitude turns is that the vertical component of lift must be equal to the weight to maintain altitude.

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