received by the International Bureau on 13 July 2015 (13.07.2015)

1. Horizontal axis Wind turbine of propeller type consisting of two separate rotors, a main and conventional rotor consisting of three blade's (1) with symmetrically arranged blades (1) permanent fixed to the main shaft (4) and the generator, and of an additional 4^th blade (2) also of propeller art, of longer length, and selectively coupled to the three conventional blade rotor, both rotating in their coupling phase in parallel planes to each other, in the same direction, and coaxial with the shaft (4) characterized in that: the additional 4^th blade (2) at its coupling phase is positioned in the space between two successive conventional blades (1) and diametrically opposite to the third conventional blade (1) of the said three blade rotor, where the additional 4^th blade (2) during its coupling phase rotates at the same rotational speed with the said three blade rotor, where the additional 4^th blade (2) during its uncoupling phase is remaining in a stand-by position, been stopped and stored in vertical position always along and at the front of the tower (3) toward the wind direction, where the additional 4^th blade (2), during its uncoupling phase, is not connected direct or indirect to the main shaft (4) and to the generator.

2. Horizontal axis Wind turbine of propeller type according to claim 1, wherein the additional blade (2) bears a diametrically opposite counterweight (15) .

3 . Horizontal axis Wind turbine of propeller type according to claim 2, wherein the counterweight (15) bears a telescopic mechanism (16) or a toothed rack and pinion.

4. Horizontal axis Wind turbine of propeller type according to claims 1,2,3, wherein the additional blade (2) is equipped with control systems of "active pitch" or "passive stall" type or of a combination thereof.

5. Horizontal axis Wind turbine of propeller type according to claims 1,2,3,4, wherein the additional blade (2) bears at its hub/jacket (13) two piston/bolts (10) that lie on one level passing thought the axis (4), move parallel to the axis (4), are coupled and uncoupled selectively to the shaft (4) by two radial arms (14) which arms extend diametrically opposite to each other, are built-in firmly perpendicularly to the shaft (4) and are arranged vertically to one of the conventional blades (1) , transmitting a rotational torque to the shaft (4).

6. Horizontal axis Wind turbine of propeller type according to claims 1,2,3,4,5, wherein the additional blade (2) bears an independent brake system.

7. Horizontal axis Wind turbine of propeller type according to claims 1, to 6, wherein the additional blade (2) is fixed and rotatable mounded by means of a Jacket/sleeve (13) and a bearings array (12) around a hollow cylindrical protrusion (11) of the nacelle (8) that surrounds the main shaft (4).

8 . Horizontal axis Wind turbine of propeller type according to claims 1, to 6, wherein the additional blade (2) is fixed, 21 rotatable mounded, and direct supported onto the shaft (4) by means of a Jacket/sleeve and a bearings array.

9. Horizontal axis Wind turbine of propeller type according to claims 1, to 8, wherein the additional blade (2) bears aerodynamic serrated elements (flaps, or tips-vanes) mounted at the airflow breakaway edge.

10. Horizontal axis Wind turbine of propeller type according to claims 1 to 9, wherein the system is equipped with two separate generators: a smaller one for the startup, and a larger one for the operation at rated power.

11. Horizontal axis Wind turbine of propeller type according to claims 1 to 10, wherein the additional blade (2) bears a plurality of vertical aerodynamic protrusions of small height on to the outer convex surface.

12. Horizontal axis W/T turbine of propeller type according to claims 1 to 11, wherein the additional blade (2) is connected and disconnected to the system via an electromagnetic coupling.

13. Horizontal axis Wind turbine of propeller type according to claims 1 to 12, wherein the structure of the additional blade (2) enables the automatic passive twisting and bending, altering simultaneously the pitch angle as well as its diameter under the action of the wind pressure.