Abstract: Apparatus for deriving energy from a moving gas stream, such as an atmospheric air current, and comprising: a rigid body or housing which is generally symmetrical about a single longitudinal axis intended to be oriented in the direction of stream flow, the body or housing defining a longitudinal, coaxial, convergent, frustoconical passageway therethrough for at least a portion of the stream; a gas turbine rotor mounted for rotation about the common axis in a plane rearwardly adjacent the plane of the outlet opening of the passageway in response to the flow of gas through the passageway; an induction fan mounted for rotation about the common axis substantially in the plane of the inlet opening of the passageway; driving means for rotating the induction fan at a fixed speed, or at a variable speed dependent upon gas stream velocity; means for transmitting the rotational energy produced by the turbine rotor; and optional means, such as a generator, for converting the rotational energy into electrical energy.