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the wing, making for a slower airspeed and critically higher air pressure. The
differences between the low pressure on the upper side of the wing and the
lower face of the wing, although slight at times, are enough to create lift.
Fast air speed - low air pressure
Left
FIG 4.48 The asymmetric profile
of a wing produces lift through the
differences in air pressure.
Slow air speed - high air pressure
This basic model is useful to explain how the force of lift works for
asymmetrical airfoils, though bats and some airplanes use symmetrical wings.
The orientation of the wing in relation to the direction of movement is the
angle of attack. It is the adjustment of this angle that enables an increase
or decrease in lift. The shape of the cambered airfoil creates lift even when
the angle of attack is at zero. As the angle of the airfoil's leading edge moves
upward from the horizontal, more air is deflected across the upper surface of
Air flow
A
(a)
(b)
(c)
B
Air flow
(a)
(b)
(c)
FIG 4.49 A: The angle of attack of the wing determines flight behavior. a: Level flight. b: Upward
angle of the leading edge creates lift for a climb. c: Downward angle of leading edge creates downward lift for
a dive. B: As the upward angle of attack increases, the flight behavior changes. a: Level flight. b: Climb. c: The
increase in angle creates an increase in drag and turbulence on the trailing edge of the airfoil. This will slow
down the flight to a point where all lift is lost and the flight will stall.
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