Aerodynamics of Flight

nose and tail of the aircraft track along the same path. If no decreased, or the angle of bank increased, if a constant rudder is used in a turn, the nose of the aircraft yaws to the altitude is to be maintained. If the angle of bank is held outside of the turn. The rudder is used rolling into the turn constant and the AOA decreased, the ROT decreases. In order to bring the nose back in line with the relative wind. Once to maintain a constant ROT as the airspeed is increased, the in the turn, the rudder should not be needed. AOA must remain constant and the angle of bank increased. An aircraft is not steered like a boat or an automobile. In An increase in airspeed results in an increase of the turn radius, order for an aircraft to turn, it must be banked. If it is not and centrifugal force is directly proportional to the radius of banked, there is no force available to cause it to deviate the turn. In a correctly executed turn, the horizontal component from a straight flight path. Conversely, when an aircraft is of lift must be exactly equal and opposite to the centrifugal banked, it turns provided it is not slipping to the inside of the force. As the airspeed is increased in a constant-rate level turn, turn. Good directional control is based on the fact that the the radius of the turn increases. This increase in the radius of aircraft attempts to turn whenever it is banked. Pilots should turn causes an increase in the centrifugal force, which must keep this fact in mind when attempting to hold the aircraft be balanced by an increase in the horizontal component of lift, in straight-and-level flight. which can only be increased by increasing the angle of bank. Merely banking the aircraft into a turn produces no change in In a slipping turn, the aircraft is not turning at the rate the total amount of lift developed. Since the lift during the bank appropriate to the bank being used, since the aircraft is yawed is divided into vertical and horizontal components, the amount toward the outside of the turning flight path. The aircraft is of lift opposing gravity and supporting the aircraft’s weight banked too much for the ROT, so the horizontal lift component is reduced. Consequently, the aircraft loses altitude unless is greater than the centrifugal force. [Figure 5-35] Equilibrium additional lift is created. This is done by increasing the AOA between the horizontal lift component and centrifugal force until the vertical component of lift is again equal to the weight. is reestablished by either decreasing the bank, increasing the Since the vertical component of lift decreases as the bank ROT, or a combination of the two changes. angle increases, the AOA must be progressively increased to produce sufficient vertical lift to support the aircraft’s A skidding turn results from an excess of centrifugal force weight. An important fact for pilots to remember when making over the horizontal lift component, pulling the aircraft constant altitude turns is that the vertical component of lift toward the outside of the turn. The ROT is too great for the must be equal to the weight to maintain altitude. angle of bank. Correction of a skidding turn thus involves a reduction in the ROT, an increase in bank, or a combination At a given airspeed, the rate at which an aircraft turns of the two changes. depends upon the magnitude of the horizontal component of lift. It is found that the horizontal component of lift is To maintain a given ROT, the angle of bank must be varied proportional to the angle of bank—that is, it increases or with the airspeed. This becomes particularly important in decreases respectively as the angle of bank increases or high-speed aircraft. For instance, at 400 miles per hour (mph), decreases. As the angle of bank is increased, the horizontal an aircraft must be banked approximately 44° to execute a component of lift increases, thereby increasing the rate of standard-rate turn (3° per second). At this angle of bank, turn (ROT). Consequently, at any given airspeed, the ROT only about 79 percent of the lift of the aircraft comprises the can be controlled by adjusting the angle of bank. vertical component of the lift. This causes a loss of altitude unless the AOA is increased sufficiently to compensate for To provide a vertical component of lift sufficient to hold the loss of vertical lift. altitude in a level turn, an increase in the AOA is required. Since the drag of the airfoil is directly proportional to its AOA, Forces in Climbs induced drag increases as the lift is increased. This, in turn, For all practical purposes, the wing’s lift in a steady state causes a loss of airspeed in proportion to the angle of bank. normal climb is the same as it is in a steady level flight at the A small angle of bank results in a small reduction in airspeed same airspeed. Although the aircraft’s flight path changed while a large angle of bank results in a large reduction in when the climb was established, the AOA of the wing with airspeed. Additional thrust (power) must be applied to prevent respect to the inclined flight path reverts to practically the a reduction in airspeed in level turns. The required amount of same values, as does the lift. There is an initial momentary additional thrust is proportional to the angle of bank. change as shown in Figure 5-36. During the transition from straight-and-level flight to a climb, a change in lift occurs To compensate for added lift, which would result if the when back elevator pressure is first applied. Raising the airspeed were increased during a turn, the AOA must be aircraft’s nose increases the AOA and momentarily increases 5-23