Abstract: A convertible auxiliary turbine capable of providing turbopropeller thrust interchangeably with pure jet propulsion, comprising a controllable fluid deflector element, and an inverted free-floating rotor having planular drive-vanes aligned with the normal flow direction of the engine's gas stream. Thus, no rotative force is imparted to the turbine until the flow direction is varied. At a given change, the turbine begins to spin, outboard swingable propeller blades are urged to open by action of centrifugal force, and propeller thrust is generated in ratio to the angle of deflection, with jet power in inverse ratio thereto.