The jet control effectiveness of a 5 deg semi-angle cone has been tested at hypersonic speeds. The study has been carried out in the Cranfield hypersonic gun tunnel facility at a Mach number of 8.2, and a Reynolds number based on base diameter of 3.788 x 10(5). Under those conditions, the initial boundary layer in the absence of the jet was laminar. The jet was injected normal to the cone surface at sonic speed. Both sharp and blunted cones were used. The Jet/flowfield interaction, including boundary-layer separation and its influence upon aerodynamic coefficients was determined. Pressure and force measurements were made in the incidence range of -15 deg to 15 deg. The forces were measured with a 3-component balance equipped with semi-conductor strain gauges. The flow structure was studied using high speed schlieren photography. Jet penetration distances have been compared with theoretical estimates.The University