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Introduction to Glider Flying > Aerodynamics of Flight > Forces of Flight > Drag > Induced Drag
The airflow circulation around the wing generates
induced drag as it creates lift. The high-pressure air beneath
the wing joins the low-pressure air above the wing at the trailing
edge of the wingtips. This causes a spiral or vortex that trails
behind each wingtip whenever lift is being produced. These wingtip
vortices have the effect of deflecting the airstream downward
in the vicinity of the wing, creating an increase in downwash.
Therefore, the wing operates in an average relative wind, which
is deflected downward and rearward near the wing. Because the
lift produced by the wing is perpendicular to the relative wind,
the lift is inclined aft by the same amount. The component of
lift acting in a rearward direction is induced drag. [Figure
3-10]
As the air pressure differential increases
with an increase in the angle of attack, stronger vortices form
and induced drag is increased. The wings of a glider are at
a high angle of attack at low speed and at a low angle of attack
at high speed.
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