BACKGROUND

[001] The present invention relates to a wind turbine and in particular to a wind turbine that harnesses lift force by means of airfoils.

[002] Some conventional wind turbine stnictures may be categorized as horizontal- axis wind turbines (HAWT) or vertical-axis wind turbines (VA.WT). Although said turbines are practical and in operation for many years, they may pose disadvantages including inefficiency, environmental threat, and visual pollution.

[003] US Patent No. 4186314 describes a configuration that employs sail blades mat change orientation (overturn while revolving around their axes), thereby changing the wind's course through the device. EP Patent No. 1260708 and Wo Patent No. 8705079 describes a wind turbine with two horizontal axes and fixed multiple tongues or blades as sails, with endless support mechanism mat wind can blow onto and move, inefficiently, as it creates drag and reduce the wind speed.

[004] DE Patent No. 381102 and US Patent No. 4536125 describes a wind turbine with muiti horizontal axis and multiple blades or wings, with endless support mechanism that wind can blow and move, inefficiently, mainly as it creates too much mechanical loads and friction.

[005] US Patent No. 4303834 describes a wind turbine which is effective for only one direction of wind feed and in one installation location. It negatively impacts the visual landscape. Its disproportionate horizontal configuration is inherently strained, whereby negatively impacting its operational effectiveness.

[006] US patents Nos. 4859146, 5744871, 5992341, 6672522, and 7075191 describe mechanisms with similarly reduced efficiency, due to the feet that their own structural weight impedes wind loading. US patents No. 6435827, 7591635, and 7573148 describe wind vanes with vertical axes and US Patent No. 7550865 employs me principle of lift force.

[007] The following embodiment and aspects thereof are described and illustrated in conjunction with systems, tools and methods, which are meant to be exemplary and illustrative, not limiting in scope. [008] In accordance with the present invention there is provided a wind turbine mat comprises two pairs of upper and lower pulleys and two endless support elements being each looped over a respective one of the pairs of the upper and lower pulleys, the upper pulleys being adapted to rotate about an upper axis, the lower pulleys being adapted to rotate about a lower axis that is generally parallel to the upper axis and the wind turbine comprises in addition a plurality of airfoils extending each generally parallel to the axes, wherein each airfoil extends between a first end coupled to a first one of the endless support elements and a second end coupled to a second one of the endless support elements.

[009] Optionally, a middle plane of the turbine includes the upper and lower axes and at least some of the airfoils on a first side of the middle plane are adapted to produce lift in an upward direction and at least some of the airfoils on a second side of the middle plane are adapted to produce lift in a ! downward direction.

[010] Typically, the lift formed by the airfoils is adapted to urge the airfoils together with the endless support elements to rotate about the pulleys.

[011] _f If desired, the wind turbine is adapted to rotate about a post axis generally perpendicular to the upper and lower axes, the post axis being not included in the middle plane and having a substantially similar distance from each one of the pairs of upper and lower pulleys.

[012] Optionally, the post axis is located on the first side of the middle plane that includes the airfoils that are adapted to produce lift in the upward direction.

[013] Further optionally, the post axis is located more distal than the middle plane In relation to the airfoils mat are adapted to produce the upward lift.

[014] If desired, incoming wind blowing towards the wind turbine is adapted to rotate the wind turbine about the post axis to locate the airfoils on the first side of the middle plane at a position that their leading edges face the wind.

[015] Optionally, a cover shields the airfoils adjacent the upper or lower pulleys from incoming wind.

[016] If desired, a gap is formed between the airfoils on the first and second sides of the middle plane and the wind turbine comprising louver means located in that gap that are adapted to affect wind flowing theremrough to assume a pattern that improves the lift on the airfoils on the second side of the middle plane.

[017] Optionally, the lower pulleys have a diameter that is different man the diameter of the upper pulleys so that each endless support element along given parts thereof that extend between his pulleys extends transverse to the middle plane to affect the angle of attack of the airfoils coupled to those given parts.

[018] If desired, the lower pulleys have a diameter that is larger man the diameter of the upper pulleys.

[019] Optionally, the lower pulleys have a diameter that is smaller than the diameter of the upper pulleys.

[020] Optionally, the turbine may be tilted about a shaft generally parallel to the axes so as to increase and/or decrease the angle of attack of the airfoils relative to incoming wind.

[021] If desired, a controller is adapted to tilt the turbine about the shaft in response to a parameter associated with the incoming wind.

[022] In accordance with the present invention there is also provided a wind turbine comprising two pairs of upper and lower pulleys and two endless support elements being each looped over a respective one of the pairs of the upper and lower pulleys, the upper pulleys being adapted to rotate about an upper axis, the tower pulleys being adapted to rotate about a lower axis mat is generally parallel to the upper axis and the wind turbine comprises in addition a plurality of airfoils that extend each generally parallel to the axes and are coupled each to the endless support elements, wherein the wind turbine is adapted to rotate about a post axis generally perpendicular to the upper and lower axes to position the airfoils generally perpendicular to incoming wind.

[023] Optionally, the wind turbine has a middle plane that includes the upper and lower axes and the post axis being set aside from the middle plane.

[024] If desired, at least some of the airfoils on a first side of the middle plane are adapted to produce upward lift and at least some of the airfoils on the other second side of the middle plane are adapted to produce downward lift, and the post axis is located on the side of the first side of the middle plane. [025] Optionally, the post axis is located more distal than the middle plane in relation to the airfoils that are adapted to produce the upward lift.

[026] In accordance with the present invention there is also provided a wind turbine comprising two pairs of upper and lower pulleys and two endless support elements being each looped over a respective one of the pairs of the upper and lower pulleys, the upper pulleys being adapted to rotate about an upper axis, the lower pulleys being adapted to rotate about a lower axis mat is generally parallel to the upper axis and the wind turbine comprises in addition a plurality of airfoils that extend each generally parallel to the axes and are coupled each to the endless support elements, wherein a middle plane of the turbine includes the upper and lower axes and at least some of the airfoils on a first side of the middle plane are adapted to produce lift in an upward direction and at least some of the airfoils on a second side of the middle plane are adapted to produce lift in a downward direction, and wherein the lower pulleys have a diameter that is different than the diameter of the upper pulleys so that each endless support element along given parts thereof mat extend between his pulleys extends transverse to the middle plane to affect the angle of attack of the airfoils coupled to those given parts.

[027] In accordance with the present invention there is also provided a wind turbine comprising two pairs of upper and lower pulleys and two endless support elements being each looped over a respective one of the pairs of the upper and lower pulleys, the upper pulleys being adapted to rotate about an upper axis, the lower pulleys being adapted to rotate about a lower axis that is generally parallel to the upper axis and the wind turbine comprises in addition a plurality Of airfoils mat extend each generally parallel to the axes and are coupled each to the endless support elements, wherein the turbine may be tilted about a shaft generally parallel to the axes so as to increase and or decrease the angle of attack of the airfoils relative to incoming wind.

[028] In addition to the exemplary aspects and embodiment described above, further aspects and embodiments will become apparent by reference to the figures and by study of the following detailed descriptions. B IEF DESCRIPTION OF THE FIGURES

[029] Exemplary embodiments are illustrated in the referenced figures. It is intended that the embodiments and figures disclosed herein are to be considered illustrative, rather than restrictive. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying figures, in which:

{030] Figs. 1 and 2 show respectively a perspective back and ¾ perspective slight front view of a turbine in accordance with an embodiment of the present invention; {031] Fig. 3 shows a front view of the turbine;

[032] Fig.4 shows a back view of me turbine

[033] Fig. 5 shows a perspective front view of the turbine in accordance with some embodiments of the present inventio being rotatably mounted on a post;

[034] Figs. 6 to 8 show side sectional views of alternative embodiments of airfoils of uie turbine in accordance with embodiments of the present invention;

[035] Fig. 9 shows a lower section of a portion of the turbine;

[036] Fig. 10 shows another lower section of a portion of the turbine;

{037] Fig. 11 shows a cross sectional view of the turbine;

[038] Fig, 12 A and 12B show perspective and side views respectively of a turbine in accordance with another embodiment of the present invention; and

[039] Figs. 13 to 15 show side views of various orientations of a turbine in accordance with yet another embodiment of the present invention.

[040] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated within the figures to indicate like elements.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[041 Conventional wind turbine structures may be categorized as either horizontal-axis wind turbines (FIAWT) or vertical-axis wind turbines (VAWT), but the embodiraents of the present invention refer to a turbine configuration that is based on the lift force of airfoils as used in winged aircraft flight The wind turbine in accordance with embodiments of the present invention includes wing elements such as airfoils (having a symmetric or an asymmetric profile), vanes, plates, and the like; and utilizes the incoming wind twice, whether at low or high wind speed, firstly upstream as incoming and secondly outgoing downstream. In accordance with some embodiments of the present invention, drag is substantially reduced, as well as visual environmentel pollution. It is noted that the term airfoil as used hereinbelow should be construed in its broadest meaning as any wing element having a profile that may produce a lift force in response to wind that flows thereon.

[042] Attention is first drawn to Figs. 1 and 2. A wind turbine 100 is shown to have two parallel vertically separated apart side holders 4 mat extend each one along a respective holder axis H in an upright direction relative to a ground surface above which the turbine 100 is located. For the sake of description, it is assumed that the wind streams are parallel to surface of the ground. Each given holder 4 has upper and lower pulleys la, lb that are respectively rotatably coupled to upper and lower portions thereof. The two upper separated apart pulleys la are attached to opposing ends of an upper axle 3a of the turbine 100 and the upper pulleys la and the upper axle 3a are adapted to rotate about an upper axis Xa that extends along the upper axle 3a and perpendicularly intersects the centers of the upper pulleys la. The two lower pulleys lb are attached to opposing ends of a lower axle 3b of the turbine 100 and the lower pulleys lb and the lower axle 3b are adapted to rotate about a lower axis Xb that is generally parallel to the upper axis Xa and also extends along the lower axle 3b and perpendicularly intersects the centers of the lower pulleys lb. It is noted that the term pulley as used herein should be construed in its broadest meaning as any rotatable wheeled type structure that is driven by a belt, chain, or the like.

[043] In addition, the turbine 100 has at least one, but preferably two endless support elements 2 that are associated each one respectively with a given pair of upper and lower pulleys la and lb of one of the holders 4. In an exemplary embodiment, the endless support elements 2 are optionally chains and the pulleys la and lb are optionally cog wheels. For example, an endless support elements 2 may also be selected as any kind of belt or cable, and operate in association with an appropriately matchin wheel or pulley la and lb. Each endless support element 2 surrounds a lower portion of the lower pulley lb mat is associated therewith and men extends upward to form a first portion 130 of the endless support element 2 until reaching the upper pulley la that is associated therewith. The endless support element 2 then surrounds an upper portion of the upper pulley la that is associated therewith and further extends back downward to form a second portion 140 of the endless support element 2, until reaching the lower pulley lb that is associated therewith to complete a closed loop and form an endless support element that links one pair of upper and lower pulleys la and lb.

[044] A middle plane M of the turbine 100 is defined as a plane that includes the upper and lower axes Xa and Xb (the middle plane M is seen in Fig. 11), and upstream, a first side (or front side) of the turbine 100 is defined at one side of the middle plane M where the first portion 130 of the endless support elements 2 resides, and a second downstream side (or back side) of the turbine 100 is defined at the opposite side of the middle plane M where the second portion 140 of the endless support elements 2 resides. It is noted that directional terms appearing throughout the specification and claims, e.g. "front", "back", "up", "down" etc., (and derivatives thereof) are used for illustrative purposes only, and are not intended to limit the scope of the appended claims. In addition it is noted that the directional terms "down", "below" and "lower" (and derivatives thereof) define identical directions.

[045] A plurality of airfoils 7 are fixedly coupled optionally by pins, or by any means known in the art, to the endless support elements 2 of the turbine 100. Each airfoil 7 extends between a first end 110 and a second end 120 thereof along a path generally parallel to the lower and upper axes Xa and Xb. The first end 110 of each given airfoil 7 is coupled to one of the endless support elements 2 and the second end 120 is coupled to the other endless support element 2. The airfoils 7 disposed on the first side of the turbine 100 that extend between the first portion 130 of the endless support elements 2 are appropriately oriented to provide lift in an upward direction, and the airfoils 7 disposed on die second side of the turbine that extend between the second portion 140 of the endless support elements 2 are oriented provide lift in a downward direction. It should be noted that the orientation of the airfoils 7 which is on both sides of plane M is not created by any kind of mechanism but is due to me coupling of the airfoils to tiie endless support element 2.

(046] Attention is additionally drawn to Figs. 6 to 11. Wind or a flow of liquid indicated upstream by dashed arrows a entering the turbine 10 from its first side flows upo the airfoils 7 associated with the first portion 130 of the endless support elements 2, creating an upward lift force b generally perpendicular to the incoming wind or flow of liquid a. The lift force b propels those airfoils 7 upwards thereby urging movement of me endless support elements 2 of the turbine 100 in an operative direction about the pulleys la and lb. The airfoils reaching the second portion 140 of the endless support elements 2 are oriented upside-down on their downward return, on the second side of the turbine 100. Therefore, wind or a downstream flow of liquid exiting the turbine 100 through its second side flows upon the foils 7 associated with the second side, thereby creating an equally strong downward-directed lift force c mat further propels the endless support elements 2 in the same operative direction about the pulleys la and lb. Therefore, the downward force is not a drag force, but rather a return lift force « that drives the endless support elements 2 in the same operative direction. These dual forces, namely up-lift force b and down-lift force c, continuously turn the endless support elements 2 about their pulleys la and lb when wind blows.

[047] This arrangement may balance both sides of the turbine 100, so that the bearing up lift force b formed at the front first side of the turbine 100 is optionally equal to the down lift force c at the back second side of the turbine 100. As a result, the inherent mass of the airfoils 7 does not directly affect aerodynamic forces applied on the turbine 100, except for a possible load on the upper pulleys la, so that one may use a variety of shapes, materials, and technologies in airfoil manufacture, without having to care too much about weight.

[048] The two endless support elements 2 stretched between the upper and lower pulleys la and lb maintain the airfoils 7 position and angle of attack relative to the incoming wind direction a, while allowing the movement of the endless support elements 2, in reaction to the wind lift forces b and e that drive the endless support elements 2 about the upper and lower axes Xa, and Xb. Optionally, any kind of belt or other appropriate means may function as an endless support element 2 and further, the turbine 100 may optionally employ more than two endless support elements 2 and associated pulleys la and lb in accordance with various embodiments of the present invention.

[049] In accordance with some embodiments of the present invention, the bottom pulleys lb and/or the upper pulleys la may be biased up or down along the holder axis H to affect the tension of the endless support elements 2.

[050] The airfoils 7 may be separated by a gap G that denotes the distance that is formed between two successive airfoils, as indicated in Fig 11, on the first side of the middle plane M and on the second side of the middle plane M. The gap G is sufficient to allow the wind flowing past the front airfoils 7 to resume undisturbed homogenous air stream flow, without turbulences. Once stabilized as a homogenous airflow, th downstream flow of air may more efficiently create downward lift force c on the airfoils 7 at the back of the turbine 100.

[051] As seen in Figs. 6 to 8, me embodiments of the present invention may include airfoils 7 of almost any cross-section or profile design, as long as they create an aerodynamic lift effect, as occurring with winged aircraft but optionally without the shape constrains relating to drag avoidance.

[052] Attention is drawn to Figs. 5 and 11. Sometimes, the bottom-most portion of the turbine 100 in the general area of the bottom pulleys lb may produce inefficient aerodynamics. Such inefficient aerodynamics are due to the orientation of the airfoils 7 when revolving about the pulleys lb, when the airfoils 7 are not disposed at the desired angle of attack relative to the incoming wind shown as arrow To limit such an undesired effect, a shell cover 11, or partial shroud, may be added to occlude the incoming wind flow a from striking the airfoils 7 when turning around the bottom pulleys lb, before the airfoils return to their appropriately oriented position and angle of attack relative to the wind direction a when associated with the first portions 130 of the endless support elements 2. This optional shell 11 , or shroud 11, is illustrated in Figs.5 and 11 in its very basic and principal shape, but any shape and material may be applicable for the embodiments of the present invention, including such shapes that contribute to channel the wind a (or liquid) stream to the face of the turbine 100 at higher speeds. [053] An optional configuration 170 is shown in Fig 12A. In addition it is noted that the shell 11 may be one portion of shroud (not shown) that surrounds the turbine 100 to block incoming wind at locations of the turbine 100 where such undesired effects may take place. Furthermore, the shroud may operate as an air intake for guiding the wind into the turbine 100. Thus, at least one portion of a shroud ma direct the incoming wind onto the airfoils adjacent the upper portion of the turbine and shields the airfoils adjacent the lower portion of the turbine from the incoming wind. Moreover, the shroud 11 may be disposed appropriately to prevent turbulence to form at the two ends of the airfoils 7, namely 110 and 120 by being perpendicular thereto.

[054] Attention is specifically drawn t Fig. 5. In an embodiment of the present invention, each vertically extending holder 4 of the turbine 100 has a lower portion 160 mat extends ttansverse to the axis H of the holder 4 in a direction that slants downward and sideways to the front away from the middle plane M. The lower portions 160 of the holders 4 may be attached at their lower ends to an optional horizontal bar 8 of the turbine 100 while a vertical pivot 9 is affixed to a center of the bar 8 to allow rotation of the horizontal bar 8 together with turbine 100 about an optional post colum 10 that extends vertically upright along a post axis P. The post column 10 is optionally anchored into the ground, possibly at a height above ground where the wind speed is higher, and the turbine 100 may be disposed eccentrically relative to the pole axis P such that the middle plane M is offset and does not include the post axis P. Optionally, the pole axis P may be offset, out of the middle plane M , at a distance mat is larger than die distance stretching from die first portion 130, of the endless support elements 2 to the middle plane ML

[055] Such eccentric positioning of the turbine 100 upon the post 10 allows the turbine 100 to pivot, sway, or swing, into a position where the front first side generally faces incoming wind as wind bears upon the turbine. In geographical areas where changing wind direction patterns are found, such eccentric positioning of me turbine 100 upon me post 10 will allow the turbine 100 to continuously adjust position and maintain the first side feeing the incoming wind to ensure maximal efficiency of turbine [056] A rotational gear box 5, coupled for example to the bottom pulleys lb may communicates with a wind energy converter (not shown). One or more power harnessing devices, such as an electricity generator, a wind generator, a wind turbine, a wind power unit (WPU), a wind energy converter (WEC), or an aero-generator, may be operationally coupled to the gear box 5 of the turbine 100 so as to convert the energy of the rotational motion into electricity or to any mechanical power.

[057] Attention is drawn to Fig. 11. In an embodiment of the present invention, a louver 12, or a "honeycomb" louver mesh 12 may be installed in the interior of the turbine 100, in alignment with the plane M, and disposed in between the space defined by the front and back revolving planes of airfoils 7. This mesh 12 may be adapted to straighten, smooth, and rectify the pattern of flow of the incoming wind flow a after passage through the front revolving planes of airfoils 7. The thereby enhanced, outflow pattern will effectively act upon the airfoils 7 at the back of the turbine 100 to create the desired down-lift force c. The mesh 12 may be configured in a variety of geometries, and constructed from a variety of materials, in order to redress the outgoing wind flow.

[058] Attention is drawn to Fig. 12A and 12B. In an embodiment, the turbine 100 has an airflow-guiding air intake 17 that forms an air intake entry via Which incoming wind a is collected, directed and/or diverted into the turbine 100. Optionally, the air intake 170 includes upper and lower sections, or upper and lower shell cover Π, that extend axially along upper and lower portions of the turbine 100 respectively however additional sections (not shown) may be provided circumscribing the side of the turbine 100 that faces me incoming wind & order to direct and/or divert incoming wind into the turbine 100.

[059] In some embodiments of the present invention, an airfoil 7 that is adapted to produce lift b, c may feature a cross section profile having a rounded or curved airfoil extrados 71, see Fig. 12, and a substantial flat airfoil intrados 72. The extrados 71 may be selected as desired for optimal performance and such airfoils 7 may be disposed in the turbine 100 with a chord orientation that may be substantially perpendicular or have an angle of attack with respect to the endless support element 2.

[060] In an embodiment, the lower pulleys lb of the turbine 100 may have a larger diameter than the upper pulleys la so that the first and second portions 130 and 140 of [061] each endless support element 2 converge upwardly and extend each transverse relative to the holder axes Ή.. As a result, airfoils 7 such as for example those described hereinabove that are perpendicularly attached to the endless support element 2 may be disposed into a required angle of attack relative to incoming wind a. The achieved angle of attack is a function of the difference between the diameters of the upper and of lower pulleys, respectively la and lb, and of the out of common vertical plane disposition of the axis Xa relative to the axis Xb.

£062] Attention is drawn to Figs. 13 to 15. In an embodiment, the turbine 100 is adapted to rotatably hang from a shaft 180 that extends generally parallel to and above the upper axis Xa of the turbine 100. For example, the shaft 180 may be supported in appropriate disposition higher up and above the turbine 100 by supports 190 that extend down from the shaft 180 and are fixed in the ground above which the turbine 100 hangs. A tilt guide or rail 200 may be appropriately coupled to the structure of the turbine 100 to define an arcuate path having a radius centered at the shaft 180 along which the lower axle 3 b of the turbine 100 may translate. For example, the lower axle 3 may be adapted to travel along a groove forming the path of translation, where the path of translation defines a tilting range of the turbine 100 about the shaft 180.

[063] Tilting of the turbine 100 about the shaft 180 defines the angle of attack of the airfoils 7 of the turbine 100 relative to incoming wind a and consequently the resulting rotational speed of the endless support elements 2 about the upper and lower pulleys la and lb. In an embodiment, the turbine 100 is provided with a driving means (not shown) that is adapted to bias the turbine 100 to assume a desired tilting angle about the shaft 180. For example, a controller (not shown) may define the tilting angle of the turbine 100 and operate the driving means in function of at least one parameter associated with the incoming wind a, such as the speed or direction of that incoming wind a.

[064] In Figs. 12A and 12B the shafts Xa and Xb are shown when disposed in a vertical plane, whereby the angle of attack of the airfoils 7 is controlled by the difference in diameter of the pulleys la and lb. Figs. 14 and 15 illustrate that further control of the angle of attack of the airfoils 7 may be obtained by tilting of the turbine 100 about the shaft 180. For example, in Fig.14 the axis Xb is disposed downstream relative to and out of vertical with the axis Xa, and in Fig. 15, the same axis Xb is disposed upstream relative to and out of vertical with the axis Xa.

[065] The wind turbine 100 described hereinabove thus comprises two pairs of pulleys 1, namely an upper pair of pulleys la and a lower pair of pulleys lb. Two endless support elements 2, such as belts, cables, chains, or ropes, for example, may each be disposed in parallel to each other and each be looped over one upper pulley la and one lower pulley lb out of the pairs of upper and lower pulleys. The pulleys la and lb are configured to rotate about axes, with the upper pulleys l rotating about the upper axis Xa, and the lower pulleys lb rotating about a lower axis Xb, which is generally parallel to the upper axis,

[066] The plurality of airfoils 7 may be disposed generally parallel to the axes Xa and Xb, each airfoil having two ends, namely 110 and 120, where each one end is coupled to one of the two endless support elements.

[067] The wind turbine 100 may also be adapted to rotate about a post axis generally perpendicular to the upper and lower axes Xa and Xb, to position the airfoils 7 generally perpendicular to mcoming wind.

[068] The middle plane M of the turbine 10 includes the upper and lower axes, respectively Xa and Xb, and at least some of me airfoils 7 on the upstream mcoming wind side, thus on the first side of the middle plane M. The airfoils 7 are adapted to produce a lift force in an upward direction and at least some of the airfoils on the downstream turbine-outgoing wind side, thus at the second side of the middle plane M are adapted to produce lift forces in a downward direction.

[069] In the turbine 100, the lower pulleys lb may have a diameter d, not shown in the Figs., that is different from the diameter D, not shown in the Figs., of the upper pulleys such that each endless support element portion that spans between the upper pulleys and the lower pulleys is disposed transverse relative to the middle plane M and controls the angle of attack of the airfoils along that span.

[070] Evidently, the lower pulleys lb may have a diameter d that is either larger than the diameter D of the upper pulleys la, or have a diameter d that is smaller man the diameter D of the upper pulleys. It is thus the respective diameter of the pulleys la and lb that may be used to control the angle of attack of the airfoils 7. [071] However, it is possible to achieve further control of the angle of attack of the airfoils 7. For example, the turbine 100 may be tilted about a shaft disposed generally parallel adjacent one of the upper axis Xa and the lower axis Xb, to controUably increase or decrease of the angle of attack of the airfoils 7 relative to incoming wind. Fig. 13 shows the shaft 180 whereabout the turbine 100 may be controllably tilted, to obtain a desired angle of attack of the airfoils 7. When the turbine 100 is pivoted upstream into the incoming wind, the angle of attack increases, and when tilted in the contrary downstream direction, the angle of attack decreases: Such a tilting configuration requires appropriate coupling of the electricity generation device that is driven directly by the lower axis Xb, as in Figs. 12a to 15. The electricity generation device may also be driven directly by the upper axis Xa. When driven by either one of the axes Xa or Xb, the electricity generation device may be driven through the intermediary of a transmission, or by use of any such appropriate mechanism exploiting the moving parts of the turbines 100, which transmission or appropriate mechanisms it is superfluous to describe in detail since well known in the art

[072] The tilting of the turbine 100 may be controlled manually, or preferably by a controller, not shown, that may be operated by a control program adapted to command pivoting of the turbine about the shaft in response to one or more parameters. It is understood that the controller operates a drive mechanism, not shown, to controUabl pivot the turbine 100. For example, tilting to obtain a desired angle of attack for optimal energy derivation from the turbine 100 may be associated with the velocity of the incoming wind. Measurement of wind velocity is well known in the art and need therefore not to be described.

[073] In one embodiment, the turbine 100 may be configured to normally tilt forward into the upstream direction, and to be pivoted backward downstream relative to and proportionally to the force of the incoming wind. Thereby, the forward tilt cares for a higher angle of attack at nil or low wind speed, and the force of the wind create higher drag forces on the turbine, to tilt the turbine backward downstream to diminish the angle of attack proportionally to higher wind speeds. Such an embodiment may be achieved by ap ropriately balancing the turbine 100. [074] Although not depicted, the turbine 100 may be tilted at the bottom instead of being pivoted at the top as described regarding the shaft 180. A bottom shaft may be disposed in parallel to the shaft 180 but below the pulley lb for use as a pivot about which the turbine 100 will tilt Such a configuration will require structural arrangements to appropriately guide the path of translation of the upper axis Xa about the bottom shaft. Control of the tilt of the turbine 100 to achieve control of the angle of attack may thus also be realized by the use of a bottom shaft.

[075] Any of the embodiments of the turbine 100 described hereinabove may be accommodated with at least one portion of a wind guide, shell cover 11, or partial shroud, if not with an all-surrounding shroud configuration, to become an air intake 170 for guiding incoming winds. Additionally, the shroud 11 may be disposed appropriately to prevent turbulence to form at the two ends of the airfoils 7, namely 110 and 120 by being perpendicular thereto.

[076] Any of the embodiments of the turbine 100 described hereinabove may be configured as desired regarding the length of the airfoils 7 and the distance between both axes Xa and Xb. Hence, width and height are selected as desired to accommodate requirements. Evidently, a tensioning wheel or tensioning element may be added to provide desired tension to the endless support elements 2.

[077] It is understood that the turbine 100 as descried hereinabove works not only when driven by the wind, but is operative with fluids in general, such as gasses and liquids.

[078] In the descriptio and claims of the present application, each of the verbs, "comprise" "include' ^* and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb .

[079 Although the present embodiments has been described to a certain degree of particularity, it should be understood that various alterations and modifications could be made without departing from the scope of the invention as claimed hereinbelow.