Abstract:
A wingsail assembly comprises a main symmetrical aerofoil which is freely rotatable about an upright axis and a control vane which is settable about an upright axis spaced from the axis of the main aerofoil to cause the main aerofoil to adopt an angle of attack to the direction of the wind. A pivoted aerodynamic slot-forming vane assembly is rotatable in response to wind pressure to open and close respective slots, one on each side of the leading region of the main aerofoil. A linkage inhibits movement of the slot-forming vane assembly away from a neutral position when the control vane is set to a neutral position.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to marine thrust wings. Such marine thrust wings are aerodynamic thrust devices broadly similar in principle to the wings of aircraft, but arranged upright (i.e. vertically) instead of horizontally, designed to propel and help to manoeuvre marine craft. 
       BACKGROUND TO THE INVENTION 
       [0002]    A typical design constraint, for marine craft other than certain specialised racing or record breaking boats, is that, unlike the wings of an aircraft, thrust wings must work as well with the wind coming from one side, or tack, as when it comes from the other side. In an aircraft, that is equivalent to the design of a plane capable of exactly the same performance upside down as right way up. In the specialised example of planes specifically designed for aerobatics, this is indeed sometimes the case. 
         [0003]    This means that a thrust wing aerofoil section for marine use must be symmetrical about a vertical plane, or that it must be constructed from more or less vertical aerofoil components, each of which is symmetrical about its own vertical plane of symmetry, and each of which is hinged to another at the intersections of each plane of symmetry, so that any special arrangement of the components to increase thrust, or reduce drag, or both, on one tack may be recreated in a mirror image for sailing on the opposite tack. 
         [0004]    Known examples include the wingsails fitted to the ‘Zefyr’ series of wingsail yachts. In this design a symmetrical wing is provided with a symmetrical external flap hinged to the wing at the intersection of their planes of symmetry. A third element, a symmetrical air directing slat, is also hinged to the wing at the intersection of their planes of symmetry. Careful selection of hinge axes and of the appropriate deflection angles of flap and slat can produce a deeply asymmetrical arrangement capable of extremely high levels of thrust at well-contained levels of drag, and also capable of being turned into its mirror image for sailing on the opposite tack. 
         [0005]    However, the known wingsail has a relatively high level of complexity. For example, the flap is usually power operated by an electric or hydraulic actuator, and in some configurations a further flap locking system has been incorporated. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is intended to provide a simpler and lower cost solution to the challenges of high-thrust, low-drag thrust wing design. It is based on a single symmetrical aerofoil fitted with a leading edge slat and slot arrangement which is composed of two parts. Powered systems will not be required to configure the wingsail components, which can be moved and maintained in place by the airstream alone. 
         [0007]    In one aspect of the invention a wingsail assembly comprises a main wingsail aerofoil and a slot-forming vane assembly pivotally mounted forwardly of the leading edge of the main aerofoil, the vane assembly comprising a pair of lateral vanes positioned on opposite sides of the leading edge of the main aerofoil; and a central vane positioned between the lateral vanes and forwardly of the leading edge of the aerofoil, there being gap locations defined between each of the lateral vanes and the aerofoil and between each of the lateral vanes and the central vane. The vanes are mounted and pivoted such that deflection of the main aerofoil to an angle of attack with respect to the wind allows wind pressure to move the vanes so the leeward lateral vane is moved away from the main aerofoil thereby enlarging its respective gap with respect to the main aerofoil and so that the central vane is moved towards the leeward lateral vane to close that respective gap and enlarge the gap between the central vane and the windward lateral vane. 
         [0008]    The lateral vanes may be mounted on a carrier which has a pivot axis spaced from and fixed parallel relative to a rotary axis of the main aerofoil, the carrier defining a pivot axis for the central vane and the central vane having a pivot connection with the main aerofoil. 
         [0009]    In another aspect of the invention a wingsail assembly comprises a main aerofoil rotatable about an upright axis and a slot-forming vane assembly, the vane assembly comprising a pair of lateral vanes and a central vane disposed along a curve spaced from and extending at least part way around the leading edge of the main aerofoil, the central vane being movable along the curve with respect to the lateral vanes to correspondingly enlarge or decrease gaps defined on opposite sides of the central vane as it moves away from or towards a respective lateral vane, the enlarged gap and the space between the vane assembly and the main aerofoil following the direction of the curve towards the trailing edge of the lateral slot on the opposite side of the central vane thereby forming a slot for airflow. 
         [0010]    The wingsail assembly preferably further comprises a control vane which is settable to cause the main aerofoil to adopt an angle of attack to the direction of the wind, and a linkage which inhibits movement of the slot-forming assembly away from a neutral position when the control vane is set to a neutral position. 
         [0011]    According to a further aspect of the invention a wingsail assembly comprises a main symmetrical aerofoil which is freely rotatable about an upright axis, a control vane which is settable about an upright axis spaced from the axis of the main aerofoil to cause the main aerofoil to adopt an angle of attack to the direction of the wind, a pivoted aerodynamic slot-forming vane assembly which is rotatable in response to wind pressure to open and close respective slots, one on each side of the leading region of the main aerofoil, and a linkage which inhibits movement of the slot-forming vane assembly away from a neutral position when the control vane is set to a neutral position. 
         [0012]    The linkage may comprise an actuating member which extends to the region of the slot-forming vane assembly and carries a peg which engages an hour-glass shaped cavity, the peg being disposed in a central narrow part of this cavity when the member is in a position for setting the control vane to a neutral position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates schematically one embodiment of a multiple vane slot-forming assembly according to the invention. 
           [0014]      FIG. 2  illustrates schematically a central vane of the aforementioned embodiment. 
           [0015]      FIG. 3  illustrates schematically two lateral vanes of the aforementioned embodiment. 
           [0016]      FIG. 4  illustrates the embodiment shown in  FIG. 1  wherein the main aerofoil is at an acute angle to the direction of the wind. 
           [0017]      FIG. 5  illustrates the embodiment shown in  FIG. 1  wherein the main aerofoil is at an opposite acute angle to the direction of the wind. 
           [0018]      FIG. 6  is a schematic side view of a vane assembly according to the invention. 
           [0019]      FIG. 7  is a schematic side view of a vane assembly according to the invention and including a mechanical interlock. 
           [0020]      FIGS. 8 to 12  are views illustrating the operation of an embodiment including the interlock shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    The invention will now be described by reference to the drawings. In  FIGS. 1 to 5  the wind should be considered as blowing “down the page”, and the phrases “left of wind” and “right of wind” are used to define elements, areas or actions when looking into the wind, which or in this description will be regarded as “up the page”. 
         [0022]      FIG. 1  shows a horizontal cross section through the thrust wing according to this invention, shown with its three principal elements configured to be completely symmetrical about the plane of symmetry of the main aerofoil  1 , so that if the thrust wing is aligned to the relative wind at zero angle of attack no cross-wind force will be reacted on to the vessel on which the wingsail is installed. Two further principal leading edge slot and slat elements are:—a twin vane assembly  2 , consisting of two vanes  4  and  5  and two hinge plates, one at each end,  6 , and a single vane assembly  3 , consisting of a single vane  7  and two hinge plates  8 , one at each end of the main aerofoil. The aerofoil sections of both twin and single vanes are shaped to create, when deflected, a powerful slot effect which is by this invention reproducible on either tack in mirror image as described above. 
         [0023]    The twin vane assembly  2  is pivoted to leading edge brackets  9  on the main aerofoil  1  at pivots  10  which are located in the plane of symmetry of the main aerofoil  1 . The single vane assembly  3  is pivoted to the hinge plates  6  of the twin vane assembly  2  at pivots  11 , and extensions of the hinge plates  8  carry hinge pins  12  which are constrained to lie in the plane of symmetry of the main aerofoil  1  by slot brackets  13 , whose centre lines lie on and are parallel to the plane of symmetry of the main aerofoil  1 . 
         [0024]    In this symmetrical or neutral configuration there are four gaps,  14 ,  15 ,  16  and  17 , through which the air flow (thought of as coming “down the page”) may pass. In the ‘neutral’ configuration shown in  FIG. 1  the airflow will pass symmetrically in through gap  14  and out through gap  16 , and in through gap  15  and out through gap  17 , so that symmetry will be maintained and therefore no cross-wind force will be developed. In the thrusting configuration on port or starboard tack, however, two of these gaps will be closed and the remaining two can form the inlet duct of a powerful leading edge slot and slat arrangement, as detailed below. 
         [0025]      FIG. 2  shows a section through the single vane assembly  3 , showing the pivots  11  at which the unit is pivoted to the twin vane assembly  2 , and the hinge pins  12  which are maintained accurately on the plane of symmetry  1  of the main aerofoil by the slot brackets  13  shown in  FIG. 1 . Both pivots lie in the plane of symmetry of the assembly indicated by  18 . In a possible construction method of construction according to this invention the vane element  7  may be made of two skins of reinforced plastic, as indicated at  20 , over a foam or other lightweight core  19 . Resilient foam rubber or plastic sealing strips  21  may be installed to close the gap between assemblies  2  and  3  when the thrust wing is set to provide thrust. 
         [0026]      FIG. 3  shows a section through the twin vane assembly  2 , showing the pivots  10  at which the assembly is pivoted to the upstream extension plates  9  mounted on the main aerofoil, and the pivots  11  at which the twin vane assembly carries the single vane assembly  3 . The vanes  4  and  5  may, as indicated for the single vane  7 , be made from two skins of reinforced plastic over a foam or other lightweight core, connected by the hinge plates  6 . Resilient foam rubber or plastic sealing strips, as in the case of the single vane assembly  3 , may be installed to close the gap between vane assemblies  2  and  3  when the thrust wing is set to provide thrust. 
         [0027]      FIG. 4  shows a horizontal cross section through the wingsail according to this invention, where the wingsail has been re-configured to thrust “left of wind”. The main wing element  1  has been angled anticlockwise by the wingsail control system (not shown and not forming part of this invention) and the freely pivoted twin vane assembly  2  has been blown across, rotating in a clockwise direction until the right of wind vane  4  contacts the main aerofoil  1 . It may be noted that as the twin vane assembly  2  swings “left of wind” relative to the main aerofoil  1  the single vane assembly  3  has been caused to swing in the opposite rotational direction so as to complete a slat and slot arrangement, closing off the slots  14  and  17  shown in  FIG. 1 , while increasing the cross-sectional area of the slots  15  and  16 , as set out in more detail below. 
         [0028]    The control system of the wingsail (not shown in this Figure), which may comprise an upright aerofoil of which the angular position may be adjusted, mounted on a boom or booms extending aft of the main aerofoil, has turned the main aerofoil  1  of the wingsail anti-clockwise from the symmetrical arrangement shown in  FIG. 3  to create an “angle of attack”. The wind, then blowing on the right of wind vane  4  of the twin vane assembly  2 , has turned it clockwise (relative to the main aerofoil  1 ) until the right of wind vane  4  closes the gap  17  on the right of wind surface of the main aerofoil  1 . 
         [0029]    This rotation of the twin vane assembly  2  opens further the gap  16  between the left of wind vane  5  and the left of wind surface of the main aerofoil  1 , the wing and vane profiles being carefully shaped to form a convergent duct. 
         [0030]    Simultaneously, the lever extension  8 , its pivot pin  12  constrained to remain in the plane of symmetry of the main aerofoil  1 , causes the single vane assembly  3  to rotate anticlockwise so as to open further the gap  15  and to close off the gap  17  between the vane  4  and the main aerofoil  1 . 
         [0031]    The air flow passing in through the gap  15  and out through the slot  16  will augment the air flow on the left of wind side of the wing thrust unit, enabling it to maintain progressively increasing thrust levels up to a significantly greater angle of attack before stalling than a typical plain aerofoil, increasing the thrust obtained left of wind accordingly. 
         [0032]      FIG. 5  shows a horizontal cross section through the wingsail according to this invention, shown re-configured to thrust “right of wind”. It may be observed that the elements of the invention have now made an exact mirror image of the arrangement shown in  FIG. 4 , for thrust left of wind. 
         [0033]    In the embodiment described in the foregoing, no control is applied to the slot-forming vane assembly, the wind pressure pushing the twin vane assembly ( 2  in  FIG. 1 ) across to one side or the other, and positioning the single vane assembly ( 3  in  FIG. 1 ) so as to form a slot for one side or other of the main aerofoil. 
         [0034]    A further development is intended to avoid, when the device is in a neutral configuration, possible instability which may result from the twin vane assembly  2  blowing from left to right of its desired position symmetrically disposed about the plane of symmetry of the wing  1 . In the embodiment now to be described with reference to  FIGS. 6 to 12 , such instability is prevented by a mechanical interlock incorporated in the operating system for the control vane disposed upstream or downstream of the main aerofoil. 
         [0035]      FIG. 6  shows a side elevation showing the base or root region of a vane assembly for example as described above and including a control vane  23  which is employed to adjust the angle of attack of the main aerofoil relative to the wind. An actuating member constituted by a rod  22  is shown acting on the symmetrical section control vane  23  which may in general be positioned upstream or downstream of the main aerofoil  1  but in the embodiment shown is downstream of the main aerofoil  1 . A bracket extends laterally from the control vane near the base thereof and the rod  22  is pivoted to this bracket so that to and fro movement of the rod alters the angle of the control vane about its upright pivot axis. 
         [0036]    Such a control vane  23  may be mounted on a boom or booms  24  projecting downstream from the main aerofoil  1  to provide a vertical axis pivot or pivots  25  for the control vane, which lies or lie in the plane of symmetry of the main aerofoil  1 . The pivot or pivots also lie in the plane of symmetry of the symmetrical section control vane  23 . The rod  22  and thereby the vane  23  may be actuated by a vertical rod  26 , set generally coaxial with the main support bearing  27 , and connected to the rod  22  by a bell crank  28 . Any adverse effect of the rotational movement of the wingsail on its bearing  27  may be eliminated by the incorporation of a swivel in the rod  26 . Other arrangements for operating the rod  22 , such as an electric or hydraulic actuator, with or without electronic computer involvement, may be provided within the scope of this invention. 
         [0037]    In the embodiment shown in  FIG. 6  the rod  22  is moved in an upstream/downstream direction to operate the control vane; and there is no linkage between the operation of the control vane and the slot-forming assembly. 
         [0038]    In the embodiment shown in  FIG. 7 , the rod  22  is extended upstream until its upstream end is at or somewhat upstream of the upstream elements of the slot-forming assembly. A peg  29  is fixed to the lower end plate of the twin vane assembly  2  in its plane of symmetry projecting downwards from the twin vane assembly  3  and passing through a clearance aperture in the lower support bracket  9 . This peg  29  engages with a cavity in the upstream extension of rod  22  as shown in  FIG. 8 . 
         [0039]      FIG. 8  shows a plan view of this embodiment. The single vane assembly  3  has been omitted to shown the other parts more clearly. The peg  29  runs in an hourglass shaped cavity  30  in the upstream extension of rod  22 , which cavity  30  has a neck which is a close fit on the peg  29  near the neutral position, where the rod  22  is holding the control vane and the slot assembly in the plane of symmetry of the main aerofoil  1 . 
         [0040]    Longitudinal guides  31 , 32  may be incorporated to assist the maintenance of the rod  22  in the plane of symmetry of the main aerofoil  1 . A pivot may be incorporated in the linkage to the downwind tail vane  23  as shown to allow for angular movement of the tail  23  about its vertical axis  25 . 
         [0041]    To provide thrust to the left or right of the wind the rod  22  is moved upstream or downstream, which action rotates the control vane  23  to an angle of attack. The resulting aerodynamic force on the control vane rotates the main wing on its free bearing  27  to its own angle of attack. This actuates the slot-forming vane assembly as described with reference to  FIG. 4  or  5 . 
         [0042]      FIG. 9  shows the setting for thrust left of wind. The single vane assembly  3  is now shown. To permit the actuation of the slot-forming vane assembly the hourglass shaped cavity  30  is flared upstream and downstream of the neutral position as shown, providing lateral freedom for the peg  29 . 
         [0043]    When neutral is reselected the rod  22  returns to the neutral position, the angled faces  34  of the flared extensions upstream or downstream of the hourglass shaped cavity  30  act as a cam to “collect” the peg  29  and ensure that the elements of the slot-forming vane assembly are constrained to lie symmetrically about the plane of symmetry of the main aerofoil  1 . 
         [0044]    The control vane has been shown in  FIGS. 7 ,  8  and  9  as a downstream tail vane  23 . If the wingsail thrust unit is, alternatively, configured with an upstream control vane  37 , the rod  22 , which is now an upstream extension of the member defining the cavity  30 , instead of acting directly on the control vane, may communicate with the control vane via a twin bell crank and swivel arrangement  40 , as shown in  FIG. 10 . A tail vane  36  is mounted to the trailing edge of the upstream control vane  37 , which in this case will be mounted on its own freely pivoting vertical axis bearings  38 . The upper bell crank of the assembly  40  is linked to the tail vane  36  by a rod  39 . 
         [0045]      FIG. 11  shows the arrangement at the base of the control vane to a larger scale for clarity.  FIG. 12  is a plan view which shows how, in such a configuration, thrust is again provided by moving rod  22  upstream or downstream, but now setting the tail vane  36  to an angle of attack which will rotate the upstream control vane  37 , in turn rotating the main aerofoil  1  to an angle of attack. The neck of cavity  30  having released the peg  29  to permit lateral movement, the slot-forming vane assembly is able to configure, and thrust will be developed once the rotational aerodynamic force developed by the vane  37  has set the main aerofoil  1  to the appropriate angle of attack.