A variable pitch fan, particularly for propulsion, of the type comprising a rotor and at least two stages of stator blade rows positioned upstream and downstream of the rotor, wherein the rotor blades (8) are of the variable pitch type and have a sinusoidal shape, are of the twisted type (1) or of t
A variable pitch fan, particularly for propulsion, of the type comprising a rotor and at least two stages of stator blade rows positioned upstream and downstream of the rotor, wherein the rotor blades (8) are of the variable pitch type and have a sinusoidal shape, are of the twisted type (1) or of the constant deflection type ( 2) and the stator blades (25), positioned downstream of the rotor, are of the twisted type. This rotor blade design allows a reduction of both the torque necessary to activate the variable pitch systems (lither actuator system) and the turning moments due to the centrifugal force. The proposed fan can be set in rotation by a conic couple of gears, contained in a gear oil sump positioned downstream the rotor, by means of one power shaft contained inside the stator blade. The variable pitch fan further provides a stator row upstream the rotor which are twisted in a manner that allows increased efficiency. The stator row downstream the rotor has a movable twisted part actuated by way of a simple electro mechanic system. This invention even further provides a light screw female system, actuated by an electric motor, to rotate the variable pitch rotor blades.
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What is claimed is: 1. A variable pitch fan, particularly for propulsion, of a type comprising a rotor and at least two stages of stator blades positioned upstream and downstream of said rotor, wherein the rotor blades are of a variable pitch type and have a sinusoidal shape, obtained by locating s
What is claimed is: 1. A variable pitch fan, particularly for propulsion, of a type comprising a rotor and at least two stages of stator blades positioned upstream and downstream of said rotor, wherein the rotor blades are of a variable pitch type and have a sinusoidal shape, obtained by locating some pressure centers of the blade airfoils upstream and other pressure centers downstream of a variable pitch rotation axis, so that torques, which are generated by the aerodynamic forces, balance each other, thus allowing use of a low power input to activate the variable pitch; the airfoils on the rotor blade hub and end are disposed so that the axis coincides with a center line of the rotor blade chord, while the other airfoils are disposed so that, under all circumstances, resulting torque changes within a minimum value range, so that a line that joins the centers of all the blade airfoils, has a sinusoidal path. 2. A variable pitch fan according to claim 1, wherein the stator blades, positioned before the rotor, are of a twisted type. 3. A variable pitch fan according to claim 2, wherein the stator airfoils must deviate an advancement speed V so as to generate relative speed vector W always equal, in module and in direction, in all sections to the vector W, closed at the blade end; thus in associated velocity triangles, of all the rotor blades sections, angles are equal in value to angles at the blade end, where it has been demonstrated that there is highest efficiency. 4. A variable pitch fan according to claim 1, wherein the stator blades, positioned before the rotor, are of a constant deflection type. 5. A pitch fan according to claim 1, wherein the stator blades, positioned after the rotor, are of a twisted type. 6. A variable pitch fan according to claim 5, wherein the stator blades positioned downstream of the rotor are formed by a fixed part and by a movable part. 7. A variable pitch fan according to claim 5, wherein a movable part of the stator blades positioned downstream of the rotor are driven by an electric motor; the blades have, at their free ends, projecting folded levers are housed in eyelets obtained in a ring gear; said ring is linked to the fan outer structure by means of the fan shoulders and of pins obtained on the outer structure; by activating the motor, by means of coupling with conic gears, also the ring rotates and, by dragging the levers, causes the blades to rotate. 8. A variable pitch fan according to claim 1, wherein the variable pitch of the rotor blades is activated by an electric motor which controls a screw female thread system contained in the rotor; said rotor is formed by four parts which contain the blades having a polygonal shape, in circular housings obtained in transverse sections; in one of the four parts, helicoidal cavities are obtained which balance the geometry change, from the circular to the polygonal shape, by directing the fluid toward the blades. 9. A variable pitch fan according to claim 8, wherein the motor is directly connected to a planetary gearbox and to an encoder and is powered by a slip-rings; a reduction gear shaft is linked to a worm screw on which a threaded ring nut moves by rotation; bushes, connected to eccentric arms of a plate by means of elastic rings, are retained in a groove obtained in the ring nut. 10. The variable pitch fan according to claim 9, characterized in that axial loads acting on the screw are unloaded on the rotor by way of trust bearings, and not on the reduction gear shaft. 11. A variable pitch fan according to claim 1, wherein the rotor is set in rotation by a conic couple of gears, contained in a gear oil sump, by means of a power shaft contained inside the stator blades which are positioned downstream of the rotor; said rotor is linked to the gear oil sump and to a propeller cuff by means of ball or roller angular bearings mounted with a "O" disposition. 12. A variable pitch fan according to claim 1, wherein actuation and control of the blades are of an electric type; an electronic central unit processes input data consisting of advancement speed and number of revolutions of the fan propeller and, drives two electric motors which move the rotor pitch mechanisms and the pitch mechanisms of the movable stator parts; the blade positions are respectively activated through the feedback of encoders which send a central processing unit a comparison electric signal which is proportional to the blade instantaneous position. 13. A variable pitch fan according to claim 12, wherein control of the propeller pitch is different from the control of the pitch of the stator movable part in order to position the blade at an offset angle with respect to the position controlled by the central unit. 14. The variable pitch fan according to claim 13, characterized in that the central unit has the following flight options: max efficiency, max thrust, and reverse.
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