Abstract:
An improved wind power device for wind energy conversion or vehicle propulsion. Among many possibilities contemplated, the device may have a moving sail with tethered wings ( 101 ), moving in elliptical trajectory, utilize separate sheave ( 503 ) and cable drum ( 505 ), use a block and tackle ( 411 ), attached to the tether and utilize a cable having a flexible jacket with aerodynamically streamlined cross section ( 603 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application is a continuation of PCT Application No. PCT/US12/67143, filed 29 Nov. 2012, which claims the benefit of U.S. Provisional Applications No. 61/566,681, filed 4 Dec. 2011, No. 61/577,329, filed 19 Dec. 2011, No. 61/621,535, filed 8 Apr. 2012, No. 61/621,593, filed 9 Apr. 2012, No. 61/624,470, filed 16 Apr. 2012, No. 61/662,476, filed 21 Jun. 2012 by the same inventor as herein, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention is generally directed to wind power utilizing systems and methods, using airborne wings or sails. 
         [0003]    Recently, a novel approach to wind power utilization has appeared. A computer controlled kite, flying crosswind, harnesses power of the wind, which is further converted into electric energy or into propulsion of a ship. One example of former is U.S. Pat. No. 8,080,889 by Ippolito et al (assigned to KiteGen). One example of later is U.S. Pat. No. 7,672,761 by Wrage (assigned to SkySails). The common part is that the kite moves cross wind with high speed in so-called ‘figure 8’ trajectory. The tether of the kite also moves crosswind and experiences very large drag, which can exceed the drag of the kite itself. This drag wastes energy and limits possible length of the tether. 
         [0004]    The crosswind flying airborne wing develops high lift forces. In the electricity generating applications, the speed of the tether, transferring this lift to the rotor of the electric generator, is relatively low (typically about ⅓ of the wind speed), resulting in relatively low power output for the force. This issue is further exacerbated by unwinding the tether from a tether drum, and using the same drum as a rotational element, converting linear motion of the cable into rotational motion. The drum is wide, and its width further increases when the tether&#39;s thickness increases. Consequently, drum&#39;s RPM is low and it requires an expensive gearbox with high input torque and large conversion ratio in order to achieve 1,500-1,800 RPM, required by most conventional electric generators. 
         [0005]    One attempt to solve the problem of high cable drag is U.S. patent application Ser. No. 12/154,685 Faired Tether for Wind Power Generation Systems by Griffith et al. Unfortunately, the tether in that application is prohibitively expensive or inefficient. 
         [0006]    This invention is directed to solving these problems and more. 
       SUMMARY OF THE INVENTION 
       [0007]    One embodiment of the invention is a moving sail for use in systems, utilizing wind power, comprising at least two airborne wings; a platform at the ground level; a pulled element attached to the platform; a tether, connecting the wings to the pulled element; an anti-twist device, preventing twisting of the tether by motion of the wings; and the wings move under influence of the wind in the same clockwise or counter clockwise direction, if viewed from the platform, and the motion of the wings has substantial cross wind component. Another embodiment of the invention is a moving sail for use in systems, utilizing wind power, comprising two or more two airborne wings; a platform at the ground level with a pulled element attached to it; an airborne attachment device, having two sides, allowed to freely rotate one relative to another; each wings is attached to one side of the attachment device by a flexible cable; and a tether, attached to another side of the attachment device and to a pulled element of said platform; the wings move under influence of the wind in the same clockwise or counter clockwise direction, if viewed from the platform, and the motion of the wings has substantial cross wind component. 
         [0008]    Related method of utilizing wind power, comprising steps of providing at least two airborne wings, attached to a tether by cables; providing a platform having an element, pulled by the tether at the ground level and controlling the wings to move at least partially cross wind, in the same clockwise or counter clockwise direction relative to the platform for multiple loops, while preventing twisting of the tether. 
         [0009]    Another aspect of the invention is a device for conversion of wind energy into electric energy, comprising an airborne wing or sail, moving under power of wind; a cable, attached to this wing or sail; a block and tackle system, attached to the cable; a ground level platform with a rotational element (like a sheave, a pulley or a sprocket) on it, coupled to the block and tackle system and an electric generator with a rotor rotationally connected to the rotational element. 
         [0010]    Another aspect of the invention is a device for conversion of wind energy into electric energy, comprising an airborne wing or sail, moving under power of wind; a cable, attached to this wing or sail; a ground level platform with a rotational element (like a sheave, a pulley or a sprocket) in contact with the cable; an electrical generator, having a rotor rotationally connected to the rotational element; and means for holding excess of said cable (like a cable drum). The cable may comprise two dissimilar sections, a top section and a bottom section, and only the bottom section is exposed to said rotational element. 
         [0011]    Related method of converting linear motion of a cable into rotational motion in a wind energy conversion device, comprising steps of providing an airborne wing; a cable, coupled to the airborne wing; a rotational element coupled with a rotor of an electric generator; coupling the cable with the rotational element; storing excess of the cable separately from the rotational element. Further, the top part of the cable, which normally does not come in contact with the rotational element, may have round or streamlined section; and the bottom part of the cable, which does come in contact with the rotational element, may have flat or flattened section. An electronic control system may be utilized to control the electrical generator and/or the rotational element and/or to synchronize reel on/reel off of said cable with the motion of the airborne wing. 
         [0012]    Another aspect of the invention is a cable with aerodynamically streamlined profile, comprising a load bearing core and a flexible jacket having aerodynamically streamlined profile around the core, placed in such way that the center of aerodynamic pressure on the jacket is behind the center of the core, when the profile of the cable is not oriented straight into the relative airflow. 
         [0013]    A method of manufacturing a cable with aerodynamically streamlined profile, comprising steps of providing at least one core cable made of a material with high tensile strength and wrapping a flexible jacket, having aerodynamically streamlined profile, around it. 
         [0014]    Various objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings illustrate the invention. The illustrations omit details not necessary for understanding of the invention, or obvious to one skilled in the art, and show parts out of proportion for clarity. In such drawings: 
           [0016]      FIG. 1  is a schematic view of a vehicle propulsion system with a dynamic sail according to one aspect of the present invention 
           [0017]      FIG. 2  is a schematic view of a rigid wing when used in the dynamic sail 
           [0018]      FIG. 3  is a schematic view of a flexible wing when used in the dynamic sail 
           [0019]      FIG. 4  is a schematic view of a wind energy conversion system according to one aspect of the present invention 
           [0020]      FIG. 5  is a perspective view of a wind energy conversion system with a separate pulley or sprocket and a cable drum 
           [0021]      FIG. 6A  is a sectional view of one form of a aerodynamically streamlined cable 
           [0022]      FIG. 6B  is a perspective view of one form of the aerodynamically streamlined cable 
           [0023]      FIG. 7  is a sectional view of another form of the aerodynamically streamlined cable 
           [0024]      FIG. 8  is a sectional view of one more form of the aerodynamically streamlined cable 
           [0025]      FIG. 9  is a sectional view of yet another form of the aerodynamically streamlined cable 
           [0026]      FIG. 10  is a perspective view of another form of the aerodynamically streamlined cable 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Unless stated otherwise, term “cable” here includes usual mechanical cables, ropes and lines of any form and material. It also encompasses belts, including perforated belts, flat belts, round belts, toothed belts, ribbed belts, grooved belts and V-belts. A tether is a kind of a cable, lower end of which is attached to an object on the ground level. 
         [0028]      FIG. 1  shows one embodiment of the invention, in which a system of airborne wings utilizes power of the wind to pull a ship. This embodiment comprises a pair of wings  101 , attached by cables  102  to an anti twist device  103 . Anti twist device  103  is attached to a ship  110  by a tether (or another cable)  105 . A control system  104  is provided. Ship  110  has a hull  106  and a rudder  107 . Anti twist device  103  is provided in order to allow circular motion of wings  101 . Anti twist device  103  comprises a top part  109  and a bottom part  108  with a ball bearing between them, allowing unlimited rotation of top part  109  relative to bottom part  108 . Optionally, it can be provided with its own direction sensor (gyroscopic, magnetic or GPS) and a servomotor, compensating remaining twisting moment. 
         [0029]    Wings  101  move cross wind in a circle in the same direction (clockwise or anti clockwise, when viewed from ship  110 ) under power of wind for long time. The circle lies in a plane—the plane of rotation. In  FIG. 1 , the plane of rotation is inclined about 45 degrees to the horizon. The aerodynamic forces (mostly aerodynamic lift) act on wings  101  and are transferred to anti twist device  103 . There, force components, parallel to the plane of rotation, compensate each other. The remaining force component, normal to the plane of rotation, pulls tether  105 , which pulls ship  110 . The projection of tether  105  on horizontal plane does not usually match direction of the desired motion. Rudder  107  and hull  106  compensate sideways component of the pull force. Control system  104  selects direction of the tether to maximize the component of the pull force, matching the desired direction of ship motion (tractive component). Control system  104  can vary angle of attack of the wings depending on the wind condition and desired pull, and angle of inclination. Angle of inclination of the plane of rotation to the horizon can vary in wide range, from 30 to 85 degrees. 
         [0030]    This system can be used either as an auxiliary propulsion system, as a main propulsion system with an auxiliary engine or, on a small boat, as a sole propulsion system. This system cannot pull ship  110  directly upwind. If upwind motion is desired, the system should be either depowered (wings are let to move with a minimum lift, required to keep wings  101  in the air) and a conventional engine used, or the ship should be tacking. 
         [0031]    More than two wings can move in the same plane of rotation. Multiple anti twist devices  103  can be connected with long tethers on top of each other, with a system of wings connected to each anti twist device  103  and moving in parallel planes. 
         [0032]    Lateral axis of wings  101  have slight inclination to the plane of rotation. Wings  101  are cambered. In one particular embodiment, the lateral axis of the wings  101  are inclined 10° to the plane of their rotation, and the angle of attack is 3°. The angles change, depending on strength of the wind and the required force. In another example, longitudinal axis of each wing  101  has constant angle 5° to the plane of rotation, and angle of attack changes with the position of the wing in the circle. 
         [0033]    The system of wings  101  plays role of a conventional sail, with a big advantage: fast crosswind motion of the wings allows to develop force, many (possibly hundreds times) bigger than wind pressure on static sails of the same size. Another advantage is that it can catch stronger and more regular wings at the altitude above the sea level. Further, tether  105  does not exhibit significant motion and does not create significant drag. Also, circular motion of wings  101  requires lower centrifugal acceleration (compared with figure 8 motion). 
         [0034]    Wing  101  can be any of the following: a rigid wing, like planes, gliders or ground based wind turbines have; a flexible wing; a soft wing; an inflatable wing; an inflatable wing, inflated by the ram air, entering it through holes; a kite wing; a paraglider wing; a wing, using soft materials, spread over a rigid frame or cables; a wing made of elastic fabric, receiving airfoil form from relative air flow; and/or a mixed wing, using different construction techniques in different parts of the wing. 
         [0035]    Wing  101  can be made of various materials, including carbon fiber, fiberglass, wood, aluminum, aramids, para-aramids, polyester, high molecular weight polyethylene, nylon and others. Wing  101  may have wingtips to decrease turbulence and noise. Wing  101  has stabilization and control surfaces and their actuators and possibly its own control system. An example of a rigid wing is shown in  FIG. 2 . It comprises horizontal stabilizers  201 , rudders  202 , a vertical stabilizer  203  and an elevator  204  on a double boom  206 , spoilers  205  and a control system  207 . An example of a kite wing is shown in  FIG. 3 . It comprises flexible inflatable canopy  301 , 4 combined control and suspension cables  302  and a control device  303 . In this form, position of the wing relative to the wind and to the horizon is controlled by dynamically changing the lengths of cables  302 . Wing  101  can be aerodynamically unstable and its stability can be assured by frequent application of corrective forces. 
         [0036]    Control system  104  comprises a central processor or a microcontroller, actuators, sensors and communication means for communicating with the control elements of wings  101 . Preferable communication means is a wireless network, although optical or copper wires, going through cables  102  and tether  105  can be used too. The sensors may include an anemometer, barometer, radar, hygrometer, thermometer, GPS, cable tension meter, RPM meter, cameras for observing the wings and other. 
         [0037]      FIG. 4  shows another embodiment of the invention. A pair of wings  101  connected by cables  102  to anti twist device  103  are is placed in the air and are flying cross wind with a speed, exceeding speed of the wind. Wings  101  can have a high L/D ratio, and move with speed is 4-20 times higher, than the speed of the wind. A cable  401  is attached to anti twist device  103  at one end and to a sheave  403  at another end. A ground platform  410  is installed on the ground, or slightly above the ground. An electric generator  408 , having a rotor and a stator, is installed on the platform. A pulley  407  is rotationally connected to the rotor of electric generator  408 . The connection can be via a gearbox, or pulley can be co-axial with the rotor, or another way of mechanical transmission can be utilized. Platform  410  can be able to rotate in horizontal plane (yaw) to order accommodate changes in direction of wind and movement of the wing. A sheave  405  is installed on platform  410 . A belt  406  is attached by its one end to platform  410 , goes around another sheave  403 , then around sheave  405 , then around one more sheave  404 , and comes into contact with pulley  407 . Belt  406  wraps around pulley  407  at a number of times, necessary to avoid slippage (this number can be between 0.25 and 20, depending on used materials, cable form and other conditions). Remaining part of cable  406  is wound around a spool  409 . 
         [0038]    Usual mechanical cables, ropes and lines of many forms and materials can be used for belt  406 . Also, various belts, including perforated belts, flat belts, round belts, toothed belts, ribbed belts, grooved belts, V-belts and other can be used for belt  406 . Control system  412  is provided. 
         [0039]    Operation of this embodiment is controlled by control system  412 . Operation comprises two phases: the active phase and the passive phase. The active phase starts when anti twist device  103  is in a position, closest to platform  410 , sheave  403  is closest to sheave  405 , and almost all of cable  406  is wound on spool  409 . In a coordinate system, moving with anti twist device  103 , wings  101  move in the rotation plane. Relative to platform  410 , wings  101  move in ascending downwind spiral with constant radius, getting away from the platform. Aerodynamic lift of wings  101  pulls cable  401 , which pulls sheave  403 . Belt  406  is pulled up, unwinding from spool  409  and rotating pulley  407 , which rotates the rotor of electrical generator  408 , which produces electric energy. When all cable  406  is unwound from spool  409 , an electric motor or some other means stop spool  409  and start rotating it in the opposite direction, winding cable  406  back on. Winding cable  406  pulls in sheave  403  and extension cable  102 . Wings  101  stop flying cross wind and are commanded by control system  412  to fly in general direction of platform  410 , creating minimum resistance, only to keep cables  102  and  103  stretched. In the end of passive phase, the device returns into the initial position, and a new active phase starts. The passive phase is much shorter than active phase and consumes very little energy. 
         [0040]    Optional block and tackle  411  is employed to mechanical disadvantage. It is used here for two purposes:
   a) increase velocity of belt  406  in contact with the pulley, thus decreasing forces, acting on the pulley and other mechanisms, connected to it, for the same power;   b) decrease tension of belt  406 , thus allowing to decrease its thickness and, consequently, diameter of pulley  407 , while increasing durability of the belt.   
 
         [0043]    Increasing velocity of cable in contact with pulley  407  and decreasing diameter of pulley  407  allow to increase angular speed of pulley&#39;s rotation. A gearbox may still be required, but less expensive one than without use of block and tackle  411 .  FIG. 4  shows block and tackle system with mechanical disadvantage ratio of 4 (i.e., velocity of the cable near the pulley, attached to the rotor, is 4× higher than the speed, with which distance between wing  101  and generator  408  increases). By changing number of the sheaves, it is possible to change mechanical disadvantage ratio from 2 to 20. Block and tackle system  411  or its analogies (a differential pulley, Z-drag line, Spanish bartons etc.) can be used in any wind energy conversion system with airborne blades, where the motion transfer is performed by a cable. Alternatively, belt  406  can be connected directly to cable  401 . If belt  406  is perforated, a matching sprocket can be used instead of pulley  407 . 
         [0044]    An example system with cross wind wing trajectory, in which anti twist device  103  is moving away from platform  410  with an average speed 2 m/s, pulley  407  has diameter 0.25 m and block and tackle provides 10× mechanical disadvantage has 1,500 RPM on pulley, sufficient for almost every 50 Hz electric generator without gearbox. 
         [0045]    It should be noted, that in the active phase cable  401  moves steadily in the direction of its length and neither it nor block and tackle system  411  experience significant sideways motion (thus saving power losses due to air resistance and excessive wear of cable  406 ). Different strategies for control of wings  101  can be utilized by control system  412  in the active phase. One strategy is to attempt to keep wing&#39;s angle of attack in the air constant and low. Another strategy is to attempt to keep constant the wing&#39;s angle to the wings&#39; plane of rotation. These controls actions can be combined with cyclical changing angle of the lateral axis of the wings to their plane of rotation (over each 360 degrees rotation cycle). Anti twist device  103  prevents twisting of cable  401 . 
         [0046]      FIG. 5  shows another aspect of the invention—an enhanced mechanism for conversion of linear motion of a cable into rotational motion of a rotor of electric generator. In one embodiment, this aspect of the invention comprises at least one wing  501 , moving in the air under power of wind and pulling a cable  502 . On the ground, there is an electric generator  504 , comprising a rotor and a stator. A pulley (or a sheave, or a sprocket for a perforated belt)  503  is rotationally attached to the rotor of generator  504 . Optionally, it can be attached through a gearbox (not shown on the picture). Cable  502  is wrapped around pulley  503  at least pre-defined number of turns. Pre-defined number of turns can be fractional and is usually small, typically between 0.5 and 20. After wrapping around pulley  503 , cable  502  is wound around a spool  505 , and cable&#39;s end is attached to it. Means are provided to wind and unwind cable  502  accurately and to maintain pre-defined force on cable  503  in direction from pulley  503  to spool  505  in order to ensure sufficient friction. In  FIG. 5 , these means are a small electrical motor  506 , attached to spool  505 , and a ball screw  507  with associated small electric motor  508 . Further, an optional section of cable  509  of a different kind can be inserted between wing  501  and cable  502 . For example, cable  509  can be a standard round cable, while cable  502  can be a perforated belt. If cable  502  is perforated belt, a sprocket is used instead of pulley  503 . 
         [0047]    Operation of the system consists of two phases—the active phase and the passive phase. In the active phase, wing  501  is moving away from pulley  503 , while rotating the rotor of generator  504 , which generates electricity. It should be noted, that trajectories of the wing may differ as long as the cable length between wing  501  and pulley  503  increases. In the passive phase, wing  501  moves toward pulley  503 , while cable  502  is winding on spool  505 . Electrical energy is not generated in the passive phase, other way around—small amount of electrical energy may be consumed. The arrows on the picture show direction of movement of cable  502 , spool  505  and direction of rotation of pulley  503  and spool  505  in the active phase. In the passive phase these directions are opposite. 
         [0048]    In the beginning of the active phase, spool  505  is in its left most position, wing  501  is in the position, closest to pulley  503  and most of cable  502  is wound on spool  505 . In the active phase wing  501  is moving away, pulling cable  502 . Cable  502  rotates pulley  503  and unwinds from spool  505 . Small motor  506  resists rotation of spool  505 , creating a force on the segment II of cable  502 , opposite to direction of cable movement. Force, acting on segment II, is much smaller than force of wing&#39;s pull, acting on segment I, so that cable unwinds, while rotating pulley  503  without slippage. As cable  502  unwinds from spool  505 , spool  505  moves toward right on ball screw  507 , pushed by motor  508 . Spool  505  moves to right with such speed that unwinding cable remains aligned with pulley  503 . In the end of active phase, spool  505  is in its right most position, wing  501  is in the furthest position from pulley  503  and only few wraps of cable  502  remain on spool  505 . Then passive phase starts. In this phase, motor  506  rotates pulley  506  in the opposite direction, winding cable  502  on pulley  505 , while motor  508  moves spool  505  to the left. In the end of the passive phase, positions of the parts of the system correspond to the positions in the beginning of the active phase. 
         [0049]    The benefits of this embodiment are due to the fact, that forces, acting on segment II of cable  502  are much smaller than forces, acting on segment I of cable  502 . The ratio is determined by belt friction equation: 
         [0000]      T load =T hold  e μφ   
         [0050]    where T load  the force on segment I, T hold  is the force on segment II, mu is the coefficient of friction and phi is the angle of cable wrapping. It is desirable to have higher ratio of forces. In many cases ratio 20:1 is sufficient (i.e., force on segment II is 5% of force on segment I). To achieve such ratio with a high friction ribbed belt over ribbed sheave (mu=0.9), only half turn of the cable is required. To achieve such ratio with Dyneema over smooth steel (mu=0.05), full 20 turns are required. In any case, the force should be sufficient to prevent slippage. Since force, acting on segment II of cable  502  is relatively small and we do not care about angular velocity of spool  505 , spool  505  can be wide and long and cable  502  can be laid in multiple layers on it. 
         [0051]    Among advantages of this aspect and embodiment: very long cables and very long cable motion are allowed (up to tens of kilometers) due to large capacity of spool  505 ; cables and belts, withstanding high tension are allowed due to large capacity of spool  505 ; cable fatigue is decreased due to large diameter of spool  505 ; flat cables and belts can be used; rotational velocity of pulley  503  can be increased for the same linear velocity of cable  502  by decreasing diameter of pulley  503 ; higher power output at lower cost is achieved. 
         [0052]    As a variation of this embodiment, a second wing can be used instead of spool  505 , creating resistance in segment II of cable  502  in its active phase, and pulling cable  502  in the passive phase of the first wing. Also, drag based wind capturing devices can be used instead of wings in this embodiment. 
         [0053]    Another aspect of the invention is a streamlined cable and method of its manufacturing, combining high strength with low drag in cross flow and low disturbance of laminar air flow. The high drag of a usual cable is caused by it being round in section. This causes disturbance of air flow in the area behind the cable. Thus, aerodynamic cable should have a section in the form of a streamlined body. 
         [0054]      FIG. 6A  shows one embodiment of such aerodynamic cable in section. It consists of an off-the-shelf load bearing rope  601  inside of a streamlined jacket or coating  603 , with the remaining space occupied by polyethylene foam  602 . Rope  601  is placed in the widest place inside jacket  603  (or jacket  603  is wrapped around rope  601 ). In some variants of this embodiments, especially when the rope diameter is small, polyethylene foam  602  is replaced by air. Also, electrical or optical wires can pass in the space between core  601  and jacket  603 . Other light weight flexible material can be used instead of polyethylene foam. Rope  601  is made of aramid (including poly aramid or meta aramid) fibers, ultra high molecular weight polyethylene fibers, carbon fibers or another strong material. Jacket  603  is made of nylon or other material, sufficiently durable and flexible. Material of jacket  603  should also be smooth from outside, resistant to water and ultra violet radiation, or have coating with these properties. When the aerodynamic cable is attached to another cable or surface, jacket  603  and foam  602  are removed at the end, and rope  601  is attached as usual. 
         [0055]      FIG. 6B  shows perspective view of the aerodynamic cable according to this embodiment, with rope  601  exposed at the end. In most cases, the cable needs to orient itself correctly in the air stream. The cable in this embodiment does orient itself in the air stream, when it is attached by its end and sufficiently long. In some variations, additional strips  604  are attached to the rear end of the cable at constant intervals, to provide additional stabilization in the air flow. Strips  604  can be rigid or flexible. 
         [0056]      FIG. 7  shows another embodiment of the aerodynamic cable in section. It comprises multiple ropes  601 , possibly of different diameters. In this embodiment, ropes or yarns  601  can fill part or whole space inside of jacket  603 .  FIG. 8  shows another embodiment of such aerodynamic cable in section. It uses one or more sideways compressed ropes  601 . As the result of asymmetrical compression, rope  601  should be wider in the direction of the airfoil axis and narrower in the perpendicular direction.  FIG. 9  shows another embodiment of such streamlined cable, in which sectional form is not airfoil, but round in the forward part and angular in the rear part.  FIG. 10  shows another embodiment, in which a small section of jacket  603  is removed at equal intervals (for example, each one hundred diameters of rope  601 ). It is done for better flexibility and self orientation in the air flow. 
         [0057]    These embodiments of invention will have aerodynamic drag many times (5×-50×) lower, than round cable of the same strength and weight, due to lower form drag coefficient in all embodiments and lower cross section in some embodiments for the same strength. The applications of the streamlined cable are in the airborne wind energy conversion devices, tethered aircraft, suspension cables for airplanes and kites, guy wires for tall buildings, bridge suspensions etc. Jacket  603  may have dimples to damp oscillations. The streamlined cable can be manufactured from conventional round fiber rope by flattening it by pressure from the sides, using the flattened rope  601  as the force bearing core, and then wrapping jacket  603  around it, with optional foam  602  inside of jacket  603 . 
         [0058]    Examples of using streamlined cable in this invention are for cables  102  in  FIG. 1  and  FIG. 4 , cable  509  in  FIG. 5 , suspension cables in the kite wing in  FIG. 3 . 
         [0059]    Multiple embodiments and aspects of the invention are described with reference to ground level. The invention can be practiced in marine environment (oceans, seas, lakes as well), in which case water level replaces ground level. 
         [0060]    Thus, a wind power system with a dynamic sail, streamlined cable or enhanced ground mechanisms is described in conjunction with multiple specific embodiments. While the above description contains many specificities, these should not be construed as limitations on the scope, but rather as exemplification of several embodiments thereof. Many other variations are possible.