Low-speed theoretical and experimental aerodynamic loading on highly-swept curved-tipped wings of two thicknesses

Abstract

An approximate theoretical formula for the distribution of aerodynamic load over arbitrary thick wings in incompressible flow is developed by combining three-dimensional results from thin-wing theory with twodimensional results from thick-aerofoil theory. The formula is applied to two wings of identical planform, with 60 degrees trailing-edge sweepback and differing aerofoil thickness, which have been extensively pressure plotted at low speeds. After critical analysis of available calculations for the curved-tipped planform by lifting-surface theory and exposition of the matching process underlying the approximate formula, it is demonstrated by comparison with experiment that the allowance for thickness gives qualitative improvement in the estimation of both chordwise and spanwise loading, with particular reference to an increasing effect of thickness near the curved tip. Quantitative differences are substantially reduced by considering results for a given lift coefficient rather than a given incidence. Inboard of the curved tip the discrepancies can be reconciled with those estimated for the two-dimensional aerofoil sections normal to the sweep line. For the purpose of wing loading the formula is regarded as a versatile theoretical framework that should be capable of extension beyond the field of steady inviscid incompressible flow. A semi-empirical approach to problems of unsteady viscous compressible flow is envisaged.