Page 227 - Aerodynamics for Engineering Students

Finite wing theory

A great step forward in aeronautics came with the vortex theory of a lifting aerofoil
due to Lanchester* and the subsequent development of this work by Prandtl.+
Previously, all aerofoil data had to be obtained from experimental work and fitted
to other aspect ratios, planforms, etc., by empirical formulae based on past experi-
ence with other aerofoils.
Among other uses the Lanchester-Prandtl theory showed how knowledge of
two-dimensional aerofoil data could be used to predict the aerodynamic charac-
teristics of (three-dimensional) wings. It is this derivation of the aerodynamic
characteristics of wings that is the concern of this chapter. The aerofoil data can
either be obtained empirically from wind-tunnel tests or by means of the theory
described in Chapter 4. Provided the aspect ratio is fairly large and the assump-
tions of thin-aerofoil theory are met (see Section 4.3 above), the theory can be
applied to wing planforms and sections of any shape.

* see Bibliography.
Prandtl, L. (1918), Tragfliigeltheorie, Nachr. Ges. Wiss., Gottingen, 107 and 451.