When side force is produced by the injection of a secondary gas into the supersonic region of an axi-symmetric nozzle, the body shape of the obstruction caused by the secondary flow induces a cone-shaped separation region upstream of the port. From the apex of the cone a conical shock front is developed. Part of the total side force produced is due to the excess static pressure acting on the nozzle wall in
(a) the separated region, and in
(b) the wall area lying between the separated region and the trace of the shock on the nozzle wall.
In such a field the static pressure is not uniform downstream of the shock but varies from point to point on the nozzle wall areas in question. This aspect of axi-symmetric flow makes attempts to correlate theoretical and experimental work difficult. It was considered that basic information about the important parameters, which influence side force, could best be obtained in experiments with two-dimensional nozzles. Here the circular secondary port is replaced by a rectangular port, the separation zone is wedge-shaped, the shock has a plane front, and in theory, the static pressure is uniform between the port and the point at which the boundary layer separates.