An experimental and analytical investigation was carried out to determine the character of the lee side flow field over a slender delta wing with sharp leading edges in a hypersonic free stream. The experiments of the initial phase of a two part experimental program were for the purpose of obtaining qualitative data to identify the dominant features of the flow field. Schlieren, vapor screen and surface oil flow were useful experimental techniques in this application. The surface pressure, surface temperature, and impact pressure were measured at the points of an extensive array in the lee side flow to determine the magnitude and extent of the flow phenomena. Analysis of the experimental results led to a description of the principal features of the flow field. The character of the flow was identified in three regimes by a specific and dominant property of the flow. The principal concern of this research program was for regime number 2 which had the following characteristics. The viscous flow field on the lee side of the wing caused a significant interaction with the inviscid flow which caused an effective change in the wing geometry. The flow expanded to the displacement boundary layer across the wing leading edge, causing a deflection of the velocity vector toward the plane of symmetry (a plane through the central chord and normal to the surface of the wing), which caused the occurrence of a realignment shock imbedded in the inviscid flow. This shock was sufficiently strong to cause the viscous layer to separate. Results of an impact pressure survey indicated that to a good approximation, the flow field was conical. (Author).