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Pilot's Handbook of Aeronautical Knowledge
Aerodynamics of Flight
Aerodynamic Forces in Flight Maneuvers

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Normal, slipping, and skidding turns.
Figure 4-29. Normal, slipping, and skidding turns.

Good directional control is based on the fact that the aircraft
attempts to turn whenever it is banked. Pilots should keep
this fact in mind when attempting to hold the aircraft in
straight-and-level flight.

Merely 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 AOA until the vertical component of lift is again equal
to the weight. Since the vertical component of lift decreases
as the bank angle increases, the AOA must be progressively
increased to produce sufficient vertical lift to support the
aircraft's 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

At a given airspeed, the rate at which an aircraft turns depends
upon the magnitude of the horizontal component of lift. It is
found that the horizontal component of lift is proportional
to the angle of bank—that is, it increases or decreases
respectively as the angle of bank increases or decreases. As
the angle of bank is increased, the horizontal component of
lift increases, thereby increasing the ROT. Consequently, at
any given airspeed, the ROT can be controlled by adjusting
the angle of bank.

To provide a vertical component of lift sufficient to hold
altitude in a level turn, an increase in the AOA is required.
Since the drag of the airfoil is directly proportional to its
AOA, induced drag increases as the lift is increased. This,
in turn, causes a loss of airspeed in proportion to the angle
of bank. A small angle of bank results in a small reduction
in airspeed while a large angle of bank results in a large
reduction in airspeed. Additional thrust (power) must be
applied to prevent a reduction in airspeed in level turns. The
required amount of additional thrust is proportional to the
angle of bank.

To compensate for added lift, which would result if the
airspeed were increased during a turn, the AOA must be
decreased, or the angle of bank increased, if a constant altitude
is to be maintained. If the angle of bank is held constant and
the AOA decreased, the ROT decreases. In order to maintain
a constant-ROT as the airspeed is increased, the AOA must
remain constant and the angle of bank increased.

An increase in airspeed results in an increase of the turn
radius, and centrifugal force is directly proportional to the
radius of the turn. In a correctly executed turn, the horizontal
component of lift must be exactly equal and opposite to the
centrifugal force. As the airspeed is increased in a constant rate
level turn, the radius of the turn increases. This increase
in the radius of turn causes an increase in the centrifugal
force, which must be balanced by an increase in the horizontal
component of lift, which can only be increased by increasing
the angle of bank.

In a slipping turn, the aircraft is not turning at the rate
appropriate to the bank being used, since the aircraft is
yawed toward the outside of the turning flightpath The
aircraft is banked too much for the ROT, so the horizontal lift
component is greater than the centrifugal force. [Figure 4-29]
Equilibrium between the horizontal lift component and
centrifugal force is reestablished by either decreasing the
bank, increasing the ROT, or a combination of the two

A skidding turn results from an excess of centrifugal force
over the horizontal lift component, pulling the aircraft
toward the outside of the turn. The ROT is too great for the
angle of bank. Correction of a skidding turn thus involves a
reduction in the ROT, an increase in bank, or a combination
of the two changes.

To maintain a given ROT, the angle of bank must be varied
with the airspeed. This becomes particularly important in
high-speed aircraft. For instance, at 400 miles per hour (mph),
an aircraft must be banked approximately 44° to execute a
standard-rate turn (3° per second). At this angle of bank,
only about 79 percent of the lift of the aircraft comprises the
vertical component of the lift. This causes a loss of altitude
unless the AOA is increased sufficiently to compensate for
the loss of vertical lift.