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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




Forces in Climbs
For all practical purposes, the wing's lift in a steady state
normal climb is the same as it is in a steady level flight at
the same airspeed. Although the aircraft's flightpath changed
when the climb was established, the AOA of the wing with
respect to the inclined flightpath reverts to practically the
same values, as does the lift. There is an initial momentary
change as shown in Figure 4-30. During the transition from
straight-and-level flight to a climb, a change in lift occurs
when back elevator pressure is first applied. Raising the
aircraft's nose increases the AOA and momentarily increases
the lift. Lift at this moment is now greater than weight and
starts the aircraft climbing. After the flightpath is stabilized
on the upward incline, the AOA and lift again revert to about
the level flight values.

Changes in lift during climb entry.
Figure 4-30. Changes in lift during climb entry.

If the climb is entered with no change in power setting, the
airspeed gradually diminishes because the thrust required
to maintain a given airspeed in level flight is insufficient to
maintain the same airspeed in a climb. When the flightpath
is inclined upward, a component of the aircraft's weight
acts in the same direction as, and parallel to, the total drag
of the aircraft, thereby increasing the total effective drag.
Consequently, the total drag is greater than the power, and
the airspeed decreases. The reduction in airspeed gradually
results in a corresponding decrease in drag until the total
drag (including the component of weight acting in the same
direction) equals the thrust. [Figure 4-31] Due to momentum,
the change in airspeed is gradual, varying considerably with
differences in aircraft size, weight, total drag, and other
factors. Consequently, the total drag is greater than the thrust,
and the airspeed decreases.

Changes in speed during climb entry.
Figure 4-31. Changes in speed during climb entry.

Generally, the forces of thrust and drag, and lift and weight,
again become balanced when the airspeed stabilizes but at
a value lower than in straight-and-level flight at the same
power setting. Since the aircraft's weight is acting not only
downward but rearward with drag while in a climb, additional
power is required to maintain the same airspeed as in level
flight. The amount of power depends on the angle of climb.
When the climb is established steep enough that there is
insufficient power available, a slower speed results.

The thrust required for a stabilized climb equals drag plus a
percentage of weight dependent on the angle of climb. For
example, a 10° climb would require thrust to equal drag plus
17 percent of weight. To climb straight up would require
thrust to equal all of weight and drag. Therefore, the angle
of climb for climb performance is dependent on the amount
of excess power available to overcome a portion of weight.
Note that aircraft are able to sustain a climb due to excess
thrust. When the excess thrust is gone, the aircraft is no
longer able to climb. At this point, the aircraft has reached
its "absolute ceiling."

Forces in Descents
As in climbs, the forces which act on the aircraft go through
definite changes when a descent is entered from straight and-
level flight. For the following example, the aircraft is
descending at the same power as used in straight-and-level