The Latin letters indicate United States parameters in which the area is in the numerator. These parameters have values greater than one. The European parameters are indicated with Greek characters. These parameters have values less than one. Splan is the planform area (i.e., the area of the body projection on a planar surface).
Figure 3.9 shows the value of S for a broad spectrum of hypersonic configurations. The values of S corresponding approximately to those in Figure 3.8 are 12.5 through 8.3. This shows that the preferred configurations are all pyramidal shapes with different cross-sectional shapes that includes a stout wing-body, trapezoidal cross-sections, and blended body cross-sections. Figure 3.10 shows that the value of S can be uniquely determined from Kuchemann's tau for an equally wide variety of hypersonic configurations, including winged cylinders. So whether for hypersonic cruise configurations, airbreathing launchers, rocket-powered hypersonic gliders, or conventional winged cylinders, Kuchemann's tau can be a correlating parameter for the geometric characteristics of a wide range of configurations. This means that specific differences in configurations are second-order to the primary area-volume characteristics. Supersonic cruise configurations using kerosene (such as Concorde) are in the 0.03 to 0.04 range of tau. Supersonic cruise configurations using methane are in the 0.055 to 0.065 range of tau. Hypersonic cruise configurations are in the
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