Abstract

The wavefront surface produced by a supersonic propeller is constructed in the standard way as an envelope of expanding spheres. Focusing of rays is shown to occur, determined by the curvature of this surface and consequent variation of ray tube areas during propagation. Two important factors, the amount of sweep and the length of edge with supersonic normal component of velocity, are investigated analytically by means of a family of “quadratically swept” edges; the length of the supersonic part may be varied from zero to infinity, to give different waveforms. A straight radial edge, which emerges as a special case, is further analyzed. These results are believed to be a helpful preliminary to applying sonic boom methods, such as those based on Whitham's weakly non-linear theory or the transonic equation.

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