Lift Distribution

The lift distribution over the span is defined in analogy to Eq. (2-9b) as

dL = сг{у)с{у)ч dy (3-12)

Here the local lift coefficient has been introduced in analogy to Eq. (2-10) as Ф) & —Су} (y)[12] The lift distribution of a wing in symmetric incident flow is shown in Fig. 3-5b. Finally, in Fig. 3-6 there is also shown the distribution of measured local lift coefficients сг over the span of a rectangular wing at various angles of attack.

By integrating Eq. (3-12) over the span, the total lift L and further, with Eq. (1-21), the lift coefficient are determined as

Cl==a^ = a f c&Wy)dy (3-13)

-s

Only single wings will be treated in this book. Wing systems such as, for example, biplane and tandem arrangements or ring wings (tube-shaped cylindrical surfaces) will not be considered.

In progress reports, more recent results and the understanding of the aerodynamics of the wing are presented for certain time periods, among others, by Schlichting [72, 74], Sears [78], Weissinger [97], Gersten [20], Blenk [7], Ashley et al. [2], Kiichemann [49], and Hummel [35]. The very comprehensive compilation of experimental data on the aerodynamics of lift of wings of Hoerner and Borst [31] must also be mentioned.

Figure 3-4 Most important geometric wing data of actual airplanes vs. Mach number. Evolution from subsonic to supersonic air­planes. {a) Profile thickness ratio 5 — tjc. (b) Aspect ratio A. (c) Sweepback angle of wing leading edge MaCI = drag-critical Mach number (see Sec. 4-3-4).

Figure 3-5 Illustration of lift distribution of wings, (a) Geometric designations, (b) Lift distribution over span.