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5.8 For the Wrights’ 1900 glider, AR1 = 3.5. For the Lilienthal data, AR2 = 6.48.
Eq. (5.70), written for the Wrights’ 1900 glider, is
and for the Lilienthal data.
Hence,
We set ao = 2 . Also, for the rectangular wing planform (taper ratio = 1.0) of the
Hence, to apply the Lilienthal data the Wrights’ 1900 glider taking into account
(Note: We continue here Lilienthal’s use of η for the normal force coefficient, as
seen in Figure 1.65. It is defined in conjunction with Eq. (1.63).)
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5.9 (a) AR = = = 5.385
From Appendix E, at 18,500 ft, ρ∞ = 0.0013329 slug/ft3. In steady, level flight,
L = W. Thus
or,
CL = 0.128
From Eq. (5.62)
For the elliptical wing of the Spitfire, e = 1. Thus
(b) D = T = P/V∞ = = = 979 lb.
Thus,
The induced drag is only 4.5% of the total drag. This is no surprise because at
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5.10 Since only the wing planform shape is different from that in Problem 5.9,
everything else being the same, the lift coefficient and aspect ratio are the same
The value of obtained from Problem 5.9 is 0.000968. By changing the
planform from an elliptical shape to a tapered wing with taper ratio 0.4, the
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5.11 V∞ = 70 = 102.67 ft/sec
At standard sea level, ρ∞ = 0.002377 slug/ft3. Thus,
For this low-speed case, the induced drag coefficient is much larger than in the
