referring to the drawing generally , the preferred blade motion according to the present invention is such that the perpendicular lines to the blade chords intersect the line perpendicular to the fluid flow direction and passing through the center of the blade rim or platform outside the circle described by the path of the blade axis . this point of intersection of the perpendicular n lies on the line which passes through the center of the blade rim m perpendicular to the wind direction , as illustrated by the arrow w . the magnitude of the angular deflections of the blades depends on the distance of the point n from the center of the circular path . if point n is located at infinity , then all the blade profiles are oriented in parallel to the wind direction . in one embodiment of the invention , the principle of a revolving crank slot is exploited in order to obtain the desired blade motion . in one specific embodiment , this is accomplished by providing a structure where : ( a ) each blade 1 is driven with the interposition of a carrier peg or arm 3 and a crosshead or pivot link 4 by a connecting rod or coupler 6 ; ( b ) the couplers of all blades are connected to each other by a belt or chain 5 or by gears or cogwheels or other similar arrangements ; ( c ) the couplers are positioned in a bearing disc or second platform 9 which is driven by a drive arrangement 10 , 11 and 12 and which rotates synchronously with the wheel body or platform 2 inside which the blades are supported ; ( d ) the distance e of the points p at which the couplers 6 are supported from the axes of rotation k of the blades 1 is adjustable , for example by the structure illustrated in fig6 ; ( e ) a coupler of a blade with the interposition of a drive is directly or indirectly connected with a normally stationary central wheel 8 which may be turned by the action of a positioning drive 13 to properly orient the device to a given direction of fluid flow . the blade motion with this arrangement is controllable as desired since each blade is provided with a kinematic drive employing a revolving crank slot in which the length of the crank e is adjustable . this means that the ratio which is so important for blade motion a / e = λ = the pitch , where a is the coupler length or length between the coupler axis p and the axis of the pivot link 4 may be set all the way to infinity by letting e become zero . when λ is infinite , the blades then receive a uniform rotary motion inside the wheel body with an angular velocity equal to the angular velocity of the platform but of opposite sign so that their absolute angular velocity is zero and their alignment remains that illustrated in fig3 . by connecting the couplers 6 of the crank slots of all the blades together by a belt drive , chain drive or similar arrangement , the movement of each blade in a similar manner is accomplished . the magnitude of the angular deflections of the blades is determined by the distance e of the coupler support axes p from the axis of rotation k of the blade under consideration . if the supporting points p of the couplers and their corresponding blades axes k are located exactly above one another , then all of the blades are oriented in parallel . if the coupler bearing points are twisted in the peripheral direction relative to the blade axes , then the angle of incidence or attack of a blade with respect to the wind or water direction changes value during one revolution of the platform 2 . the stationary central wheel 8 functions to define the direction in which all the blades are oriented in parallel or around which they perform their angular deflection . the couplers of the crank slots may , as noted earlier , be constructed as sprocket wheels , and in this manner the individual sprocket wheels may be connected to each other by a chain in a simple manner with one sprocket wheel connected directly to the central fixed sprocket and with the other sprocket wheels connected to one another . there may also be provided a synchronous drive arrangement for connecting the wheel body or platform 2 and the bearing disc or second platform 9 together and this synchronous drive may comprise a pair of gears or cogwheels having different bevel or orientation of the teeth , as illustrated in fig6 with the axial position of the two gears being adjustable with respect to the positions of the gears on the platforms cooperating with them . by this arrangement , axial movement of these idler gears changes the distance between the points of support of the couplers in the supporting disc or second platform and the corresponding blade axes in the wheel body or platform 2 , thereby allowing the easy selection of the magnitude of the angular deflection of the blades . the gears 12a and 12b may be mechanically or hydraulically adjusted in the longitudinal direction . in the illustrated preferred embodiment , either four or six blades 1 are supported in the wheel body or platform 2 . the blades 1 are moved by a carrier peg or arm 3 , each of which slides in a corresponding crosshead or pivotable link 4 . by looking at fig2 one may derive a formula for the blade motion with respect to the tangent to the path of the blade axis : ## equ1 ## in fig1 and 2 , the distance e represents the adjustable stationary crank of the revolving crank slot , the radius a ( the distance of the crosshead 4 from the center of rotation of the coupler 6 ) is the length of the coupler , and the carrier peg or arm 3 represents the revolving crosshead path of the revolving crank slot . α is the tilting angle of the blade relative to the tangent to the blade circle or path of the blade axis . φ is the angle of revolution of the blade relative to a conventional reference direction and α - φ would be the angle of the blade relative to the direction of fluid flow , that is the attack angle . in fig3 the blade positions which arise for λ = a / e =∞ are shown while in fig4 the blade position for λ = 2 . 5 are illustrated . it will be recognized that for the case λ =∞, the wind or other fluid flow will not cause the platform to rotate because there is no aerodynamic buoyancy or lift acting on the blades . however , for the case ∞& gt ; a / e & gt ; 1 , buoyancy or lift will occur which will turn the rotor , and the angular velocity of the rotor or platform will become greater the smaller the value of a / e . it becomes obvious from fig1 and 2 that for the desired blade motion to occur , there must be a rotation of the coupler 6 with the crosshead 4 by - ω inside the supporting disc 9 around the point p . that is , the average angular velocity of the coupler must be the same as the average angular velocity of the platform 2 but in the opposite direction or sense . additionally , the value e should be adjustable so as to be increased from a starting value of zero up to about 0 . 8 × a in a continuous fashion . a value of e which is = a is not possible with this constructive arrangement . with this arrangement then all the blades on the wheel body assume the same relative position at corresponding points of the revolution of that body , as is illustrated in fig3 and 4 . the arrows w always signify the direction of the wind or fluid flow while the angle of attack of a blade is the angle between that fluid flow direction and the chord or center line 20 which defines the profile axis of a blade . fig5 illustrates how the uniform angular positioning is achieved . the coupler 6 is constructed as a sprocket wheel . a chain 5 which passes across all the sprocket wheels of the couplers 6 , brings about a uniform angular velocity of all the crossheads 4 . an additional chain 7 which passes over a central relatively fixed sprocket wheel 8 and a sprocket wheel of a coupler 6 with the number of teeth of the sprocket wheel 8 and of the sprocket wheel of the coupler 6 being identical , results in the desired angular velocity relative to the wheel body 2 and which has the opposite sign of the angular velocity ω shown by the wheel body and by the supporting disc or second platform 9 . this angular velocity is identical in value for all the couplers 6 . to achieve the desired similar tilting motion of all the blades during a revolution , the axes of rotation k of all blades 1 are turned in the sme direction with respect to the axes of rotation p of the couplers 6 . a turning of the point k , for example in the clockwise direction relative to the point p , would result in the positions illustrated in fig2 and the blade positions shown in fig4 and 5 . this brings about a rotation of the whole assembly in the counter - clockwise direction . the construction of an entire windpower installation in principle is illustrated in fig1 . the sprocket wheels , that is the couplers 6 of the blades 1 , are positioned in a supporting disc or second platform 9 . the supporting disc 9 is driven by a synchronous drive made up of a gear 10 which has an internal toothing about the platform 2 . the synchronous drive also includes a gear 11 of internal toothing located about the supporting disc or second platform 9 , and two gears 12a and 12b which are helical gears mounted on a common shaft 8 and functioning to couple the platforms 2 and 9 together . thus , the supporting disc 9 revolves with the same angular velocity as the wheel body or platform 2 . as is most easily seen in fig6 the angular position of the supporting disc 9 with respect to the wheel body 2 , may be changed by shifting the two helical gears 12a and 12b in the axial direction . this change in relative angular position is , of course , due to different pitches on the two helical gears , and which is illustrated as different senses or orientations of the teeth of those gears . because the bearing of these two gears is rigidly placed upon the foundation or pedestal of the device , the required axial shifting is brought about mechanically or hydraulically in a simple manner . as has been illustrated here , the axial displacement may occur under the action of a lifting piston 16 . in this manner , a certain distance becomes adjusted between the center of rotation p of the coupler and the blade axis k under consideration and in this way the magnitude of the angular deflections of the blades is determined . due to this shifting , one may change the angular velocity of the wheel body 2 and the power harnessed . if necessary , regulators may be installed which affect these parameters according to the wind velocity to achieve different settings . to compensate for changes in wind or flow direction , it should be possible to adjust the blades 1 so that they point with the leading blade edge into the wind or flow and are thereby able to execute the desired tilting motions relative to the wind or fluid flow direction . this adjustment is achieved by turning the central sprocket wheel 8 under the action of a worm drive 13 . this turning by way of the chain 7 causes a corresponding turning of each of the blades . of course , the chain 7 , like the chain 5 , may engage the sprocket wheel of the coupler 6 of the blade or may engage another wheel provided in addition which is rigidly connected ( immovably with respect to it ) to the coupler 6 . the output of the wheel body or platform 2 , by way of a drive gearing arrangement 14 , may be passed on to a generator 15 for producing electrical energy , thereby harnessing the natural energy of the fluid stream . from the foregoing it is now apparent that a novel device for harnessing the energy of a fluid stream has been disclosed meeting the objects and advantageous features set out hereinbefore as well as others and that modifications as to the precise configurations , shapes and details may be made by those having ordinary skill in the art without departing from the spirit of the invention or the scope thereof as set out by the claims which follow .