Airfoils and Airfoil Systems of Finite Span

  • William Frederick Durand


The subject of this Chapter is the investigation of the forces experienced by an airfoil of finite span and by airfoil systems. The basic idea for the following deductions has been indicated at the end of III 32. The only point we have to add is that in the case of a single wing of ordinary type we may substitute the lift per unit span l for Λ (see III 31), and consequently take l as the principal unknown quantity. Then III (27.7) becomes:
$$ w = \frac{1}{{{e^V}}}\int\limits_{ - b}^{ + b} {dn\frac{{{{dl} \mathord{\left/ {\vphantom {{dl} {dn}}} \right. \kern-\nulldelimiterspace} {dn}}}}{{4\pi \left( {y - \eta } \right)}}} $$
and III (31.9), neglecting the difference between φ and tan φ:
$$ \varphi = \frac{w}{V} = \frac{1}{{{e^{{V^2}}}}}\int\limits_{ - b}^{ + b} {dn\frac{{{{dl} \mathord{\left/ {\vphantom {{dl} {dn}}} \right. \kern-\nulldelimiterspace} {dn}}}}{{4\pi \left( {y - n} \right)}}} $$
Now suppose that the geometrical angle of incidence of an airfoil section. defined with reference to the x axis, or what comes to the same, with reference to the horizontal velocity V, has the value α; then the effective angle of incidence i, measured from the downward sloping effective velocity, is given by1:i = αφ


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Chapter IV A. Single Wing

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    The reader is referred to Th. von Kábmán, Beitrag zur Theorie des Auftriebes, Vorträge aus dem Gebiete der Aerodynamik usw. (Aachen 1929), p. 98. Also for cases treated with the aid of the theory of two-dimensional motion to T. Sasaki, On the effect of the walls of a wind tunnel upon the lift coefficient of a model, Rep. Aeron. Res. Instit. Tokyo No. 77 (Vol. VI, p. 315, 1931; Japanese with English abstract).Google Scholar
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  27. 1.
    In the case of an airfoil of finite span (see 32) there is also a change in the angle of incidence, causing an increase of the lift. Other effects causing an increase of lift come into play as soon as H is of the order of the chord, or smaller than the chord of the airfoil [see: Tomotika and others, Rep. Aeron. Res. Instit. Tokyo No. 97 (Vol. VIII, p. 1, 1933)Google Scholar
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© Berlin · Julius Springer 1935

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  • William Frederick Durand

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