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AAE 334, Fall 2011, Homework 13
Due Friday, September 30, at the beginning of class.
1.
Increasing the aspect ratio of a rectangular wing by increasing span while keeping
chord, velocity, density, and lift force constant causes what change induced drag?
Show
your work.
Induced drag coefficient is given by:
1
2
AR
C
C
L
Di
and thus, induced drag force is given
by:
1
2
2
2
S
q
L
qS
D
i
or
1
1
1
2
2
2
2
2
b
q
L
S
b
qS
L
qS
L
D
i
or,
2
2
1
1
b
q
L
D
i
.
Thus increasing the span reduces induce drag.
Some of you noted that we need to be concerned about changes in the induced drag factor.
I
didn’t intend this step, but yes, it is correct.
The rightmost ends of the curves in Figure 5.20
show that
100
for rectangular wings.
Thus our equation for induced drag becomes,
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 Fall '09
 COLLICOTT

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