Minimum Drag Bodies of Given Length and Base using Newtonian Theory.
by J. Pike.
AIAA Journal, Vol 15, No 6, June 1977, pp. 769-770.

The forebody of a high speed aircraft or missile generates a substantial proportion of the overall drag, such that even a modest reduction in the forebody drag can produce a significant improvement in the performance. The requirement that the forebody blend into a fuselage which is nearly axisymmetric has resulted in an intuitive assumption that any low drag forebody will also be nearly axisymmetric. Indeed, this assumption is built into most optimisation studies [1] by geometric constraints on the forebody. Even when the forebody cross-sections are left unspecified, it is usually assumed that these sections and those of the afterbody are similar, and this approach has lead only to unrealistic star cross-section bodies which are discussed in Ref. 1. In this paper, although the base contour is fixed, the cross-sections upstream of the base are merely required to be convex. The minimum drag shapes which emerge using these constraints are termed "spatular" shapes, because of their flat region near the nose and near circular cross-section downstream. The shapes combine the prospects of significantly lower drag (10-15% lower) and improved pilot visibility.

Ref. 1. Miele A., "Theory of Optimum Aerodynamic Shapes."
Appied Mathematics and Mechanics, Vol 9, Academic Press, New York and London, 1965.

This paper suggests that to achieve low drag, hypersonic aircraft should have noses which are flattened or spatular shaped rather than pointed. Although these flattened nose shapes increase the friction drag (and vehicle volume) compared with a pointed nose of similar length, this increased friction drag is not normally sufficient to make the minimum drag nose become pointed. The increased volume naturally favours the spatular nose when volume constraints are considered, such that the spatular nose remains optimum for a wide range of constraints. The AIAA holds additional material submitted at the same time as the original paper which forms an extension and adjunct to the published work.

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Last amended: Dec 2013.