On the design of wing-body combinations of low zero-lift drag rise at transonic speeds

Abstract

This paper has been prepared for publication from several papers written some years ago. It is essentially a new presentation of the more important features of the earlier papers. The paper is about the transonic area rule, which states that the variation of zero-lift drag of an aircraft configuration at transonic speeds depends primarily on its axial distribution of cross-sectional area. The detailed discussion concerns a more restricted but more explicit result, namely that the drag jump (the discontinuity in zero-lift wave drag predicted by linearised theory at sonic speed) of a smooth wing-body combination is given by a formula which involves only the area distribution of the combination; this result is called the sonic area rule. The present treatment of the sonic area rule is one of exploitation rather than explanation. The paper does not consider in detail the relation of the sonic area rule to the entire problem of drag rise, but makes some contributions to the use of the sonic area rule in the design of wing-body combinations of low drag rise. Results for several optimum area distributions for minimum drag jump are given, in a more compact and enlightening form than hitherto. Some simple, yet fairly general, cases of the design of wing-body combinations of low drag jump are discussed, and a numerical example is given; the cases investigated illustrate some of the principal features of design for low transonic drag rise.