Abstract: Disclosed is a windmill whose impeller and strut are protected from harms by high wind, comprising an impeller; a strut; weight; and means for supporting said strut in such a manner that said strut is capable of rotating and inclining around pivot, wherein said impeller and weight are installed at different sides of said strut, and wherein said strut is supported by said means at the pivot located between said impeller and the center of gravity.

Abstract: A wind turbine having the tips of the blades pivotable to a position in which they act as brakes to slow the turbine down. The pivoting is caused by relative axial movement of the tip and main blade portions which is caused by the action of a spring. The spring action is normally overcome by a hydraulic actuator 16. When the hydraulic pressure exceeds a threshold value corresponding to a desired limit rotational speed of the turbine a pressure switch 83 causes a pressure release valve 84 to dump the fluid pressure in the hydraulic actuator 16, thus allowing the spring to operate and cause the pivoting of the tip.

Abstract: An air foil which is coupled to a wind energy conversion machine is provided with a flexible and resilent trailing spoiler that limits the rotational speed of the machine and prevents overspeeding. The trailing spoiler is a flexible and resilient sheet that is laminated to the upwind side of a rigid blade so that a portion of the sheet extends past the trailing edge of the blade. The portion of the sheet that extends past the trailing edge bends towards the wind during high wind conditions to prevent overspeeding of the machine.

Abstract: A water wheel for operating fully submerged in an ocean current has a rotating frame member supported on the ocean floor for rotation about a vertical axis. The frame member supports a plurality of vertically extending vanes, each vane being rotatably supported on the frame for limited rotation about a vertical axis. It has a hydrofoil shape in cross-section with the axis of rotation parallel to the leading and trailing edges. Rotation of the vanes is limited relative to the frame by a hydraulic piston control system and shock absorbers.

Abstract: An improvement of the device disclosed in U.S. Pat. No. 4,297,075 permits the propeller assembly of a wind energy system to swing in two directions, both left and right with respect to wind direction. The improvement includes a snubber assembly which has a plurality of springs mounted on a central bar.

Abstract: Yaw (fishtail) oscillations in large wind turbines (10) are minimized by damping provided by a drive motor (65) connecting the turbine to the supporting tower (50) therefor at, for example, a yaw bearing (45). The drive motor drives the wind turbine in yaw and maintains desired yaw settings of the turbine. The motor is also capable of being driven by yaw oscillations of the wind turbine and in being so driven, dissipates the energy of such oscillations.

Abstract: Normally feathered propeller blades of a wind power generating system unfeather in response to the actuation of a power cylinder that responds to actuating signals. Once operational, the propellers generate power over a large range of wind velocities. A maximum power generation design point signals a feather response of the propellers so that once the design point is reached no increase in power results, but the system still generates power. At wind speeds below this maximum point, propeller speed and power output optimize to preset values. The propellers drive a positive displacement pump that in turn drives a positive displacement motor of the swash plate type. The displacement of the motor varies depending on the load on the system, with increasing displacement resulting in increasing propeller speeds, and the converse.

Abstract: An air jet spoiler arrangement is provided for a Darrieus-type vertical axis wind-powered turbine. Air is drawn into hollow turbine blades through air inlets at the ends thereof and is ejected in the form of air jets through small holes or openings provided along the lengths of the blades. The air jets create flow separation at the surfaces of the turbine blades, thereby inducing stall conditions and reducing the output power. A feedback control unit senses the power output of the turbine and controls the amount of air drawn into the air inlets accordingly.

Abstract: To generate power from wind economically, a feathering vane is pivotally mounted perpendicular to a tail vane and shifts the orientation of a sprocket assembly controlled by the tail vane in response to wind velocity. The sprocket assembly changes the orientation of blades which orbit about and rotate the main power shaft so that, as wind velocity changes, the blade orientations are shifted in a compensating direction under the control of the tail vane. A lever shifts the position of the blades to positions that balance wind power and brake the rotation for maintenance purposes. The speed-control mechanism includes a damper to avoid being excessively affected by wind gusts. The main shaft is connected through a speed increaser which has less mass at the high-speed end than the low-speed end to an induction generator when used for cogeneration, the field of the induction generator being excited by the cogeneration frequency.

Abstract: A windpower system includes a support and a turbine having a shaft rotatively mounted to the support. The turbine has variable pitch blades whose pitch is controlled by the differential motion of a rotary control shaft coaxial with the turbine shaft and the turbine shaft itself so that the blade pitch can be varied by a stationary motor without requiring any slip rings or other such wear-prone couplings. In the event of a power failure, rotary motion of the control shaft is prevented so that the turbine blades are feathered solely due to the force developed by the rotating turbine. Also, if the turbine is used to generate electrical power, an induction generator coupled to the turbine shaft is employed whose shaft speed is indicative of generator output power.

Abstract: A new type of overspeed control system for a rotor driven by wind or some other fluid flow. The rotor support is mounted so that it can move back some small distance along the direction of the fluid flow, the rotor axis remaining in substantially the same direction during this movement. This backward movement is in response to the thrust generated by the lift and drag forces on the rotor impellers. At a predetermined thrust force, indicating that the rotor is operating in a fluid velocity high enough to cause overspeeding, the backward movement of the rotor engages a brake to slow the rotor. Essential to the invention is the use of the backward movement of the rotor to brake the rotor.

Abstract: An offset-axis type wind generator uses a passive cyclic pitch-change rotor whose shaft axis is inclined downward and aft, with its sense of rotation selected so that the yaw component of the shaft torque at least partially of the shaft torque offsets that component of thrust which accompanies power extraction. A wind-alignment vane extends from a boom mounted on a furling hinge, equipped with mechanism to limit the vane's anti-furling moment to balance only the remainder of the moment of rotor thrust. Hence, disengagement of power extraction does not cause the rotor to overspeed, and the machine may idle even in gale-force winds, furled to nearly 90.degree..

Abstract: Damping of the primary bending mode of a tower (12) mounting a wind turbine having a control (36) for providing a pitch blade angle reference signal (40) to modulate the pitch of the turbine blades (1) through a pitch change mechanism (38) for constant power is provided by generating the pitch blade angle reference signal as the integral (104) of the summation (266) of a torque/power controlling blade pitch angle reference rate signal (98) with an estimated acceleration signal (255) generated by filtering (250, 252, 254) the blade pitch angle reference signal (40) with the following transfer function ##EQU1##

Abstract: In order to control the turbine speed of a windmill employed for power generation, the pitch of the turbine blades is based on a dual-deadband control strategy. If the current turbine speed is determined to be outside of a relatively wide deadband, action is taken to correct the speed by changing blade pitch accordingly. If the current speed is not outside of the relatively wide deadband, then the average of the turbine speed over a recent interval is compared with a relatively narrow deadband within the wider deadband. Action is then taken to change the blade pitch if the average speed is outside the narrow deadband. In this way, wide excursions of turbine speed are corrected promptly, but the frequency of control actions is minimized by requiring only the average speed to be kept within tight limits.

Abstract: An accelerometer (1) disposed on the support tower (12) of a wind turbine electric generating system in the vicinity of the rotor (10, 16) thereof provides a signal (1) indicative of acceleration of the tower in the direction of the rotor rotational axis. The signal (2) is passed through a band-pass filter (4) for summation (9) with a torque/power controlled (100) blade pitch angle reference rate signal (98), the integral (104) of which provides a blade pitch angle reference signal (40) to control the pitch angle of the rotor blades (10) through a pitch change mechanism (38), thereby to provide additional, positive aerodynamic damping to the tower while modulating blade angle for constant torque/power in response to wind turbulence.

Abstract: A windmill of the vertical axis type having a plurality of circumferentially and radially outwardly spaced rotatably mounted vanes vertically parallel to the axis shaft wherein means are provided for controlling multistage feathering of the vanes in conjunction with said vanes feathering to rotate on their individual axes in a direction opposite to the direction of rotation of the windmill assembly in increments of 45 degrees twice for each blade before finally feathering a final half rotation completing the rotation of 360 degrees on its individual axis while the windmill makes one revolution, thus repeatedly repositioning the blades to the most optimum resistance angle to the wind as the windmill rotates increasing the power angle to near seventy-five percent of the circle of the windmill rotation, a construction option prevailing to routinely cause all the blades to feather when near a zero angular position to the wind, and having associated therewith a conglomerate of mechanical phenomena to perform said

Abstract: A fiberglass-epoxy flexbeam extends from tip to tip of each opposed blade pair, carrying the blade centrifugal forces so that none of the centrifugal loading is carried by the hub. The primary load-carrying connector between the flexbeam and the hub is a set of elastomeric pads. These provide a soft mount between the flexbeam and the hub to keep the primary bending moments within the flexbeams where the filaments are designed to accommodate them. The elastomeric pads are also effective in isolating the hub from chordwise loads which include the steady driving torque and the "C" mode and "S" modes of coriolis vibration. The elastomeric hub mount damps these vibrations and tunes their frequencies to values well separated from the rotor frequency.

Abstract: A windmill having blades with both variable pitch and variable spanwise twist. The windmill includes a hub which may be supported on top of a tower for rotation about a substantially horizontal axis. A plurality of blades are provided, each having a root, a tip and a spanwise twistable intermediate section. Linkage mechanisms connect the roots of the blades to the hub to permit selective independent rotation of the roots and the tips of the blades for varying the pitch and the spanwise twist of the blades. An electric power generator is drivingly connected to the hub. A control mechanism is connected to the linkage mechanisms for varying the pitch and spanwise twist of the blades in accordance with a predetermined desired relationship.

Abstract: A wind-wheel for a wind-operated power generator comprises a rotor shaft, carrying the vanes of the wind-wheel, and mounted at its ends in rotary bearings supported by a frame. The frame is mounted on the top of a tower by means of a support member which itself is rotatable about a vertical axis through the tower. The connection between the support member and the frame enables the frame to be rotated about a horizontal axis below the bottom of the vanes. In a high wind, the wind-wheel can, thus, swing out of the vertical plane, spilling wind from the vanes, to avoid damage.

Abstract: The present invention relates to wind turbines and more particularly to such a device having a horizontally disposed power output shaft pivotally supported by a turntable. Attached to the output shaft are a number of circumferentially spaced apart blades which are each hinged along their leading edges with the hinge axes inclined obliquely to the longitudinal axis of the shaft. A spring controlled governor is provided to control the pivotal position of each of the blades around their respective hinge axis of rotation.

Abstract: A system of rotatably and pivotally mounted radially extended bent supports for radially extending windmill rotor vanes in combination with axially movable radially extended control struts connected to the vanes with semi-automatic and automatic torque and other sensing and servo units provide automatic adjustment of the windmill vanes relative to their axes of rotation to produce mechanical output at constant torque or at constant speed or electrical quantities dependent thereon.

Abstract: Opposing windmill airfoil blades extend from a central hub and are connected thereto by a pair of cables secured to the inner ends of the blades and which each freely engages through the opposite ends of a cross member secured to the hub. These cables then extend to a reel on the hub thus forming a triangular configuration to support each airfoil blade. The reel is driven by a small reversible electric motor which extends and retracts the cables and hence the blades depending upon the tension in the cables which is sensed by a sensor which in turn actuates the electric motor. As the wind speed increases in velocity, the cables lengthen and vice-versa. Guide vanes or control tail wings extend from adjacent the inner ends of each of the airfoil blades and are fixed in manufacture thus automatically presenting the desired angle of attack of the airfoil blades to the wind.

Abstract: A wind energy conversion system for converting wind energy into controlled wind turbine torque comprising a wind turbine with an essentially horizontally disposed shaft, a means, rotatably mounted to a chassis, for sensing and reacting to wind turbine torque such that reaction torque acting on the means causes angular displacement of the means, a driven machine drivenly connected to the shaft of the wind turbine, and a means for adjusting wind turbine efficiency which is drivenly connected to the first mentioned means in such a way as to prevent continual angular speed thereof. Angular displacement of the first mentioned means provides the power for the last mentioned means to adjust wind turbine efficiency.

Abstract: A wind turbine adapted to rotationally drive a load such as an electric power generator 50 includes in the turbine drive train, resiliently mounted gearing 55 which isolates and damps the load from drive train disturbances caused by wind gusts and wind stream dyssemmetry and inherent torsional vibration without assistance from modulation of turbine blade pitch.

Abstract: There is disclosed in the present application a wind wheel having a set of movable vanes whose orientation with respect to the plane of the wheel is changed automatically to limit the speed to a safe level in winds of high velocity. The wheel is constructed and shipped in segments and is especially adapted for ease of assembly and truing for minimal eccentricity and lateral run-out.

Abstract: A wind-driven turbine with a self-regulating pitch control system is disclosed. The turbine includes a wheel having a plurality of wings or blades that rotate about a longitudinal pivot axis through a pitch range. The blades are in coned or parallel relation to the axis of rotation of the wheel. Biasing means are provided for biasing the wings toward a starting pitch position. The center of gravity of each wing is spaced from the axis of rotation of the wheel and from the pivot axis of the wing toward its trailing edge. Centrifugal force acting on the wings causes them to move from a starting pitch orientation to a power pitch orientation as the speed of the turbine increases. A system is provided for selectively controlling the pitch of the wings, preferably from a location remote from the turbine.

Abstract: A propeller hub carries pivotally-mounted blades that are linked to a spring-loaded collar on the propeller shaft for automatic coning and feathering under predetermined high velocity movement along the propeller shaft to change the blade pitch angle during low wind velocity conditions. An airfoil support mounts a propeller shaft and turns therewith to reduce tower shadow effects. This is called a "down-wind system" meaning the propeller is behind the tower and causes the assembly to rotate into the wind without a tail vane.

Abstract: An improved wind turbine in which the tip portions of the blades are variable in pitch and are cyclically varied in pitch to control the yaw of the rotor and to relieve bending moments on the blades and are collectively varied in pitch to relieve bending moments on the blades and to maximize the power output of the turbine at a selected constant rotor speed.

Abstract: A wind powered electrical generator having a rotatable wind wheel (21) carrying one of the armature (42) or field structures and a plurality of windvanes (45) connecting the rim to a central shaft (28), a stator (39) carrying the other of the armature or field structures, and a supporting structure (22) for the windwheel rotor shaft and the stator. The armature winding is carried by the windwheel at its perimeter, and the field structure is a ring structure which lies just radially outward of the armature winding and is carried by the fixed housing structure which perimetrally surrounds the windwheel. Bearing support (48) provided at the perimeter of the windwheel by low friction bearings carried by the fixed housing structure minimizes bearing stresses developed at the supporting shaft under wind loading conditions.

Abstract: A speed control system for a windmill having blades which can be feathered for altering speed and with the blades under the control of a mechanism which includes a piston assembly and a fluid governor associated therewith. Spring means are used to feather the blades against the force of the piston assembly which is interconnected with the blades, and the speed of blade rotation actually creates the fluid pressure acting on the piston assembly and a governor is associated with the piston assembly for controlling the position of the piston and thus controlling the feathering of the blades, all according to the speed of rotation of the windmill blades. The windmill can be used for generating electric power, and fail-safe mechanisms are employed for protecting in the event of a windmill blade breakage.

Abstract: A base is provided and a rotor is journaled from the base for rotation about a first upstanding axis. The rotor includes a plurality of vanes journaled therefrom for rotation about second axis spaced about and radially outwardly from the first axis and vane displacement control structure is operatively connected between the base and the vanes for proportionally angularly displacing the vanes relative to the rotor 180.degree. in one direction during each 360.degree. of rotation of the rotor in the opposite direction. The vanes are angularly displaced in optimum positions relative to the rotor and each other to develop maximum thrust by the vanes on the rotor responsive to fluid flow against the vanes from a predetermined side of the first axis.

Abstract: A multi-vane windmill rotating in a horizontal plane on a vertical shaft includes frame supported fabric type vanes with the frame hingedly attached at one end to support arms to swing closed and catch the wind in one position and to swing open under centrifugal and wind forces in another position when coming into the wind to reduce air resistance. Vanes are releasably attached in part to the frame for support in operating position and otherwise slidably secured thereto so as to release and collapse on the frame under extreme wind pressures when the frame is closed and thus spill the wind. Stops on the support arms provide a limit of movment of the vane frames. A second embodiment of the vanes includes two overlapping sections normally held in overlapped or closed position by yielding means that permit the sections to separate under high winds to provide an air passageway through the vane.

Abstract: A reaction-type turbine provided with an output shaft coupled to a power generator, such as an electric generator, and having a plurality of variable-pitch flexible impeller blades, or sails, mounted between the periphery of the output shaft and a concentric tubular shroud rotatable in unison with the output shaft. The pitch of the flexible impeller blades or sails is varied by a centrifugally-actuated pitch controlling unit such that the output shaft has a constant angular velocity irrespective of variations in the velocity of the fluid flowing through the turbine. For actuation by wind, the turbine is mounted on a rotatable platform which is automatically oriented in the direction of the prevalent wind by a servo system controlled by a wind direction detecting device. The mass of air flowing through the turbine is automatically controlled as a function of the wind velocity by an appropriate throttling mechanism controlled by a wind velocity detector.

Abstract: Windmill apparatus comprises an open framework defining a wheel having means defining a pivot axis and embodying a plurality of radially and closely spaced concentric rows of air foils. The foils in each row are connected for their conjoint movement to and from a pre-set operating position, within defined limits. The movement of each foil is about an axis which is substantially radial to the wheel and it is arranged to automatically feather when subject to impact of winds the speed of which is at a dangerous level. As oriented in the wheel the radial extremities of each foil are substantially flat and bridged by a continuous peripheral surface portion. One portion of said peripheral surface portion is flatted to define the operating face of the foil. The flatted portion is preferably comprised of two planar surface portions one of which leads the other, having regard for the facing of the foil operating surface into the prevailing wind.

Abstract: A windmill of the vertical axis type having a plurality of circumferentially-spaced rotatably-mounted vanes wherein means are provided for controlling the feathering of the vanes so that, upon feathering they rotate in a direction opposite to that rotation of the windmill assembly, wherein means are provided to assure that the entire assembly heads up into the wind, and wherein means are provided for disengaging of the entire vane assembly when the wind velocity reaches a predetermined value.

Abstract: A power generating system includes a wind turbine driven generator, the wind turbine having a wind turbine driven rotor with a variable pitch angle blade. Stresses on the system during startup and shutdown are minimized by scheduling the blade angle as a function of the rotor speed and wind velocity to provide a minimum blade angle relative to the fully powered blade angle during rotor acceleration, and to provide a minimum blade angle relative to the fully powered blade angle during rotor deceleration.

Abstract: A system of rotatably and pivotally mounted radially extended bent supports for radially extending windmill rotor vanes in combination with axially movable radially extended control struts connected to the vanes with semi-automatic and automatic torque and other sensing and servo units provide automatic adjustment of the windmill vanes relative to their axes of rotation to produce mechanical output at constant torque or at constant speed or electrical quantities dependent thereon.

Abstract: A spring-loaded pivoting end plate that is hinged such that it is deployed by centrifugal force into the airstream to thereby act as an aerodynamic brake for wind turbines in overspeed conditions. The brake has a stationary portion fixed on the tip of the turbine rotor and a pivoting portion hinged for movement with respect to the fixed portion. The longitudinal centerline of the brake coincides with the chord line of the turbine blade and the pivoting movement is about a hinge axis that is normal to the rotational plane of the turbine. The planform of the brake has a low aspect ratio shape with the ratio of the fore and aft chordwise length to the width being one or greater. The edges of the brake in the normal running condition extend beyond the contour of the turbine blade to serve as an end plate such that the aerodynamic efficiency of the blade is improved thereby.

Abstract: A conical shaped rotor is described for rotation about a horizontal shaft axis for responding to or creating a moving airstream. The rotor is elongated and conical shaped along the rotor axis with elongated blades extending longitudinally and radially inward from an enlarged end to a reduced end. The blades are angularly offset between 1.degree. and 15.degree. from the rotor axis to cause an inner side edge of each blade to be closer to the rotor axis than an outer side edge without the blades being twisted about their longitudinal axis. In one form an electrical generator is operatively attached to the rotor shaft for generating electrical energy in response to the rotation of the rotor by wind passing therethrough. In a second form the rotor is driven by a motor to create an air flow therethrough to serve as a fan.

Abstract: A windmill with a vertical-axis rotor having thrust vanes which is surrounded by a stationary cage having guide vanes to channel the windstream to the rotor. In the preferred embodiment the rotor is a flow-through type with airfoil vanes.

Abstract: Mounted on a vertical axis there is a horizontal axis and, vertically spaced therefrom, a wind wheel generator and counterweight unit. When the wind speed exceeds a predetermined limit, the unit is swung thereby, in a vertical plane, decreasing the effect of the wind on the wheel and protecting it from overload.

Abstract: The disclosed wind turbine has zero mean camber airfoil blades vertically pivoted at the outer ends of pairs of radius arms. The inner ends of the radius arms are fixed to a rotating mast. Each blade is provided with a steering vane. The deflection of each vane with respect to its associated blade is controlled by a cam toggle mechanism. The disclosed cam toggle mechanism includes a double-faced face cam, having a closed cam track on its upper face and another closed cam track on its lower face. Each cam track consists of two circular dwell portions.

Abstract: A wind driven power plant for the generation of electric power comprising a rotor, a shield, and a fin mounted on a vertical, central shaft, the fin and shield adjustably interconnected via a cog and gear track arrangement affording variable relative alignment of the fin and shield to position the shield relative to the wind. A constant rotor rotation rate is achieved by varying the masking thereof by the shield to compensate for wind speed variations. A hydraulic rotation rate control system senses the rotation rate of the rotor and generates a signal permitting the adjustment of the relative orientation of the fin and the shield. The rotor is coupled to a conventional electric generator for the generation of electric power.

Abstract: The present invention relates to a fluid motor of the turbine class in which a pair of rotatable blades are carried in orbital revolution around the output shaft of the motor and wherein the blades are operably interconnected to the output shaft and to a weathercock vane so as to present an optimum surface to the driving fluid at all times.

Abstract: Apparatus for deriving a rotational motion from air currents including first and second coaxial annular members spaced from each other along their axes by axial struts and a plurality of blade assemblies carried by the struts. In a preferred embodiment, the annular members are formed of circular I beams and the apparatus is supported for rotation about the axes of the annular members by rollers engaging the web of the I beams. The rollers may be carried by first and second posts with one of the posts being rotatable about the other such that the apparatus can accommodate changing wind directions. The blade assemblies may include an impeller hingedly secured to a cross-beam extending between adjacent struts with each impeller being individually spring biased to present more or less surface to the air current, dependent on its velocity.

Abstract: A plurality of blades are rotatably affixed to a rotatably mounted shaft and overlap each other in a plane perpendicular to the axis of the shaft in a strong wind force. In a weak wind force, the blades rotate to large angles with the axis of the shaft.

Abstract: There is disclosed in the present application a windmill including a wheel having a set of fixed blades and a set of movable vanes whose angular orientation with respect to the axis of the wheel is adjusted automatically for limiting the speed of the wheel to a safe level in winds of high velocity. The fixed blades may be installed to cause turning of the wheel under generally prevailing winds of a very low velocity. The movable vanes are connected to a speed sensing governor mechanism which changes their orientation from positive through neutral to negative for reducing the speed of the wheel when the wind velocity is excessive and the mill would otherwise reach damaging speeds. In addition, there is disclosed a mechanism for changing the orientation of the vanes from a remote location to stop the wheel. The mill wheel is also constructed in modular segments adapted to being shipped in sections and assembled at the operating site.

Abstract: This invention is an overspeed control arrangement for vertical axis wind turbines employing normally vertically positioned rotor blades, said control arrangement allows the rotor blades to tilt either forward or backwards to form a swept wing configuration, at wind turbine speeds beyond the design rpm. When the rotor blade is in a highly swept wing configuration its high drag and low lift reduces the turbine rotor torque to zero and eliminates excessive overspeeding and structural damage. The rotor blade can tilt about a radial or nearly so, tilt-support arm, mounted on a concentric bearing, the tilting starts at the feathering design rpm which is controlled by the geometric position of the combined center of gravity of both rotor blade and tilt-support arm. The control arrangement is automatic and passive and does not require the use of springs, pulleys or levers.

Abstract: A vertical axle paddle motor including a support structure with a rotor mounted on the vertical axle, the rotor having a plurality of arms with paddle members pivotally attached to the end of the same. Each of the paddle members include a plurality of adjustable vanes which move from an open to a closed position within the paddle. Vane position in the paddles is controlled by a wind velocity and wind direction control, operating a pair of cams forming a composite cam surface which is engaged by cam followers on each of the rotor arms associated separately with motors on the paddle, to adjust the position of the vanes within the paddles for maximum efficiency in rotation. The wind velocity cam may be adjusted relative to the wind direction cam to increase the amount of time the vanes of the paddles are held in an open position to reduce and stabilize rotation of the rotor.

Abstract: A vertical axis wind turbine comprises one or more aerofoil section blades attached to a support structure. The blade has at least one part thereof which is acted on by centrifugal forces as the blade rotates with the support structure and thereby caused to increase its angle of inclination to the said vertical axis when the speed of rotation increases beyond the normal operating range, whereby the rate of increase of rotational speed with wind speed is reduced.