To provide, without provision of an after-burner, an inter-turbine bypass variable-cycle engine as an environmentally friendly supersonic engine wherein, as practicable technology, mixing of three flows is accomplished by overcoming difficulties in obtaining a bypass ratio higher than that is previously possible, and bleeding is effected from between the high/low pressure turbines, and the bleed is reintroduced in an exhaust duct by bypassing the low pressure turbine (LPT), and such a problem is resolved that the total pressure of the bleed gas is higher than LPT-outlet gas or the fan bypass-flow to incur serious loss.

In a first mixing system, a tail cone is moved to and fro to make variable the outlet area of the core to mix thereby the three flows at equal static pressures. In a second system, a double-lobe mixer is employed to allow LPT bleed to flow in a state of spokes between the double lobes to achieve a big-scale mixing by enlarging the contact surfaces of the flows.