Traditional circular nozzles when used in airbreathing engine applications are generally placed on the rear face of a backwards facing step (Fig. A). At low speeds the high speed rocket exhaust acts to entrain air into the engine which then needs to mix within the rest of the engine so that it can be used to generate thrust (either through additional combustion or expansion). The annular rocket exhaust of the Exchange Inlet can also be placed on the rear face of a backwards facing step as in Fig. C. Experimental measurements of the Mach number at the exit of each configuration are shown in Figs. B and D for the traditional and annular configurations respectively. As can be seen, in the traditional configuration (Fig. B) the rocket exhaust remains near the upper wall and retains a high Mach number core, while the annular configuration produces a more diffuse Mach number pattern at the exit. The result is that the annular configuration is better able to entrain atmospheric air as shown by an increased massflow of air for a given rocket chamber total pressure in Fig. E (which is proportional to the massflow of rocket exhaust within the engine).