Note on the lift slope, and some other properties, of delta and swept-back wings

Abstract

In studying anct comparing various theories for the determination of the distribution of loading on wings, Garner has given values for the lift slope of several families of swept-back and delta wings deduced from several different lifting-surface theories. In Fig. 8 of Ref. 1, Garner has plotted these lift slopes as functions of the aspect ratio A, for different values of the angle of sweep. It occurred to the writer to try plotting the ratio of the lift slope to that for elliptic loading instead of the lift slope itself, and when this was done it was noticed that the above ratio was very nearly independent of aspect ratio A, and gave a unique curve for all the available results when plotted against sweepback angle, A. The curve is shown in Fig. 2 and it will be seen that none of the points is more than 3 per cent from the mean curve and most are much closer than this. The cases given by Garner cover an aspect-ratio range from 2 to 8 and a sweep range from 20 to 70 deg, as will be seen from Fig. 1, reproduced from his report. The value of the twodimensional lift slope used in deducing that for elliptic loading at any given aspect ratio was, of course, 2pi, since comparison is with potential calculations on wings of zero thickness. In using the mean curve to predict a lift slope for practical purposes it might be more logical to use the most probable value of the two-dimensional lift slope for the case in question rather than the value for an ideal fluid and zero aerofoil thickness.