Game Development Reference
Figure 15-8. Typical C M versus attack angle
The most widely known family of foil section designs and test data is the NACA foil
sections. Theory of Wing Sections by Ira H. Abbott and Albert E. Von Doenhoff (Dover)
contains a wealth of lift and drag data for practical airfoil designs (see the Bibliogra‐
phy for a complete reference to this work). 2
In practice, the flow of air around a wing is not strictly two-dimensional—that is, flowing
uniformly over each parallel cross section of the wing—and there exists a span-wise
flow of air along the wing. The flow is said to be three-dimensional. The more three-
dimensional the flow, the less efficient the wing. 3 This effect is reduced on longer, high-
aspect-ratio wings (and wings with end plates where the effective aspect ratio is in‐
creased); thus, high-aspect-ratio wings are comparatively more efficient.
To account for the effect of aspect ratio, wing sections of various aspect ratios for a given
foil design are usually tested so as to produce a family of lift and drag curves versus
attack angle. There are other geometrical factors that affect the flow around wings; for
2. Theory of Wing Sections includes standard foil section geometry and performance data, including the well-
known NACA family of foil sections. The appendixes to Theory of Wing Sections have all the data you need
to collect lift and drag coefficient data for various airfoil designs, including those with flaps.
3. Lifting efficiency can be expressed in terms of lift-to-drag ratio. The higher the lift-to-drag ratio, the more
efficient the wing or foil section.