A preliminary idealized analysis of a part of the flow field close behind a hypersonic projectile. For the purpose of studying the structure of the inviscid gas flow near the narrow neck of the wake behind a projectile, the formation of a shock by a steady gas stream converging toward an axis of symmetry is investigated. The flow is assumed to be a conical field with vertex at the point where the inner boundary of the stream first reaches the axis and where the shock starts. It is shown that the result concerning the occurrence of vacuum must be expected to be independent of all but one assumption-that the gas impinges on the axis at a nonzero angle. Accordingly, tail-shock formation in two-dimensional and axially symmetrical flows must be expected to differ in significant, still-unknown ways.
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