Abstract: The invention relates to a propulsion engine, particularly for supersonic aircraft. An internal propulsion system comprises an envelope displaying a tapered center portion, around which is coaxially mounted an external propulsion system which lacks a separate compressor. According to the invention, mechanisms are provided to divert toward the combustion chamber of the external propulsion system an adjustable fraction of the compressed air arriving from the last compressor stage of the internal propulsion system. A blower which is driven by the external turbine exhausts in parallel with the latter into an annular conduit which emerges between the internal nozzle and external nozzle and an exhaust nozzle, all of these nozzles being of variable geometry. The purpose of the invention is to improve variable cycle propulsion engines for second-generation supersonic aircraft.