Supersonic area rule

An approximate idea of the optimum volume distribution can be obtained by theoretical analysis on a simple body of revolution. The resulting minimum wave drag body is known as the Sears-Haack body after its originators. To a reasonable degree of approximation the minimum wave drag of a real aircraft configuration of a given volume will be obtained when its cross-sectional area conforms to the Sears-Haack distribution. This requirement for optimum area distribution is known as the area rule.

For the actual aircraft the local cross-sectional area will not only be pro­vided by the fuselage but by the wings and tail assembly as well. It is this com­bined cross-sectional area which must be distributed correctly. Application of the area rule at supersonic speeds is not quite as simple as may at first appear. It is not the distribution of area on planes at right angles to the axis that is important but, as we would probably expect by now, the distribution along the direction of the local Mach cone.

We will encounter another form of the area rule when we come to consider transonic aircraft in the next chapter.