the variable energy transfer achieved by adjusting the setting of the guide vanes of the cold turbine 8 from the low pressure spool to the high pressure spool is accompanied by a variation in the rate of rotation n 2 of the high pressure spool as a function of the rate of rotation n 1 of the low pressure spool with u03b8 being the setting of the rotatable guide vanes 9 when the setting u03b8 is changed the characteristics flow rate pressure of the secondary flow are modified the presence in this secondary flow of an aerodynamic surface mechanically tied to the high pressure spool results in high effectiveness of setting u03b8 on the rate of rotation n 2 of the high pressure spool and consequently of the primary flow in this manner a high rate n 1 makes it possible to achieve powerful thrusts while a high rate n 2 makes possible good specific fuel consumption fig2 represents another embodiment of the turbojet in which the low pressure spool is constituted by a bypass compressor 10 which is driven by a low pressure turbine 11 the high pressure spool is constituted by a single flow high pressure compressor 12 which is driven by a high pressure turbine 13 the high pressure turbine 13 is provided at its periphery with a cold turbine 14 located in the passage 6 for the secondary flow and preceded by a variable.