Wingsail deflection

Abstract: A selftrimming sailing rig comprising rigid wingsails each comprising a leading aerofoil (1) and a trailing flap (2) that can be deflected relative to the respective leading element. The spacing between the trailing edges of the flaps is maintained less than the spacing between the leading edges of the flaps. The arrangement assists stalling and therefore improves the downwind performance.

Description: This invention relates to aerofoils, and especially to wingsail aerofoils. The wingsail systems with which the present invention is concerned are generally of the self setting type that are mounted freely for rotation about an upright axis and trimmed by a tail aerofoil. A rig of this general type is described in The Motorship Vol 65, No.771 October 1984 GB "Walker Wingsail project rivals Japanese experience" pages 30-31. In a wingsail system with a multi-element wing comprising a leading element and a trailing element or flap positioned closely behind the leading element and pivotable to each side to form respective composite cambered configurations, the moment on the hinge of the flap due to airflow is considerable, and must be resisted if the cambered configuration is to be maintained. If a hydraulic ram is used to drive the flap and maintain its position, this necessitates use of a ram large enough to withstand the maximum moment likely to be encountered. A locking device may be employed in order to relieve the ram once the flap is fully deflected, but the hydraulic ram still has to be large in order to defect the flaps in a strong airstream. Aircraft flaps incorporate devices such as rails and fixed pivots in order to alleviate any analogous problems, however this method is not easily adaptable for wingsail systems because, unlike aircraft flaps, the flap must be capable of deflection in both directions in order to operate on both tacks. The present invention in one aspect is directed towards a method of assisting the flap to reach operating deflection. Accordingly the invention provides a method of operating a self-trimming wingsail assembly comprising a thrust wing having a leading aerofoil and a trailing aerofoil flap and a trimming tail aerofoil in which the flap is pivotable to each side of the leading aerofoil to form respective deflected configurations and the tail aerofoil trims the angle of attack of the wing to the wind, the method comprising pivoting the trailing aerofoil to a desired deflected configuration characterised by the step of first adjusting the angle between the tail aerofoil and the leading aerofoil to rotate the sailset towards a position in which the moment opposing movement of the flap in the desired direction is reduced or reversed and after the flap has been moved, readjusting the tail aerofoil for trimming to the desired angle of attack. The invention also provides apparatus for controlling a self-trimming wingsail having at least one thrust wing with a leading aerofoil and a trailing aerofoil and a trimming tail aerofoil in which the flap is pivotable to each side of the leading aerofoil to form respective deflected configurations and the tail aerofoil trims the angle of attack of the wing to the wind, the apparatus comprising means for pivoting the trailing aerofoil to a desired configuration characterised by a control system that operates first to adjust the angle between the tail aerofoil and the leading aerofoil to rotate the sailset towards a position in which the moment opposing movement of the flap in the desired direction is reduced or reversed and after the flap has been moved, operates to readjust the tail aerofoil for trimming to the desired angle of attack. The forces may be reversed tending to aid movement of the flap in the particular direction. The invention also relates to a control system for moving the flap of the self-trimming rig. The present invention is also directed towards providing a system that will deflect a moving aerofoil with equal speed in each direction, and towards providing a failsafe system for aerofoil movement. Accordingly the present invention additionally provides a wingsail deflection system comprising at least two fluid operated cylinders connected so that a first cylinder operates on an inward stroke and a second cylinder operates on an outward stroke to move a member, the cylinders being interconnected so that fluid is simultaneously conducted to and from each of the cylinders with the rod side of each cylinder being interconnected to the piston side of the other cylinder. DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a two section wingsail showing the hinge moment; Figure 2 is a schematic diagram of a self trimming wingsail rig with all aerofoils aligned; Figure 3 is a diagram of a hydraulically operated pinlock; Figures 4 to 6 are a schematic diagrams of a self trimming wingsail rig undergoing flap deflection; Figure 7 is a schematic diagram of a self trimming wingsail rig with a governor vane set for trimming; Figure 8 is a flow diagram for a control system for changing camber; Figure 9 shows a multi-element wingsail cambered for ahead port tacking; Figure 10 shows a multi-element wingsail cambered for ahead starboard tacking; Figure 11 shows the position reached in changing from ahead port to starboard tack; Figure 12 shows a method of attachment of a cable on a wingsail; Figure 13 shows a preferred embodiment of cable fixings; Figure 14 shows a preferred embodiment of attachment of the cable at the trailing edge of the slat; Figure 15 shows a preferred embodiment of attachment of the cable to the flap; Figure 16 shows a modification to the embodiment of Figure 7; Figure 17 shows a modification to the leading edge of the flap; Figure 18 is a schematic plan view of a two element wingsail in the symmetrical position; Figures 19 and 20 are schematic plan views of the wingsail of Figure 18 in cambered configurations; Figure 21 is a schematic plan view of a hydraulic system according to the invention; Figure 22 is a perspective view of the wingsail assembly of Figure 18; Figure 23 is a schematic diagram of a pair of thrust wings; Figure 24 is a schematic diagram of a pair of thrust wings in the 'toe-in' configuration, and Figure 25 is a schematic diagram of a pair of the wings of Figure 24 with the flaps deflected. DETAILED DESCRIPTION Referring to Figure 1 a wingsail comprising a leading aerofoil 1 and a trailing aerofoil flap 2 is shown with the flap 2 deflected for tacking. The airflow, shown generally by the arrow 3, creates a positive pressure on the flap tending to rotate the flap away from its deflected position as shown by arrow 4. It will be seen that the movement of the flap is resisted by a hydraulic ram 5 (or some other operating device). A pinlock, or other device may be incorporated into the hinge in order to relieve the stress on the hydraulic system during tacking, but never-the-less the flap moving system is still subject to stress when moving the flap in a strong airstream, and unless it is very heavy (and therefore expensive) may become overstressed before the position is reached at which the pin can be inserted. In order to reduce the stress on the hydraulic system when the flaps are being deflected, a method of operating a self trimming wingsail system has been devised in which the trimming system is operated in order to reduce the movement opposing moment about the flap hinge. A self-trimming wingsail is one in which a governor aerofoil, preferably in the form of a tail vane mounted on a boom is used to trim the main aerofoil, the desired angle of attack being set by the relative deflection to the governor which then trims the main aerofoil wings and retrims during changes in wind direction. The method of operating the self-trimming rig to reduce flap hinge moments comprises, for a tail vane governor, deflecting the tail vane to full deflection on the same side as that to which it is intended to deflect the flap on the main aerofoil wings. This will rotate the main aerofoil so that the resistive force on the flap is much reduced, or even eliminated and replaced by a force assisting deflection. The flap is then deflected, locked and the tail vane readjusted to trim to the desired angle of attack. This sequence is shown in Figures 4 to 7, commencing from a position shown in Figure 2 in which the tail vane designated by reference 6 is aligned with the main wing, of which both aerofoil sections 1 and 2 are also aligned and weathercocked to the wind. In general a plurality of wings will be arranged alongside each other and be interconnected to be rotated as a unit by the tail vane, with the flaps interconnected to move together. The device for moving the flaps may then be mounted on a stay interconnecting the wings, as shown in Figure 2 with hydraulic ram 5 mounted on a spar 7. In Figure 4 the tail vane has been deflected to its maximum position in one direction (down as viewed) and by virtue of the tail vane realigning itself to the wind it rotates the main wing system about its axis as shown in Figure 5. Deflection in the downward as viewed direction of the flap 2 to the position shown in Figure 6 is now aided by the wind, and upon achieving maximum deflection the flap 2 is locked in position and the moving mechanism relieved of stress. Figure 7 shows the tail vane set at a different angle to trim the main wing to the desired angle of attack. The same procedure can be repeated in reverse for the other tack. Preferably the sailing conditions are monitored continually and a control system including a microprocessor ascertains whether a change of camber, such as for changing tack, is required. Figure 8 shows a simplified flow diagram for the change of tack control system. In the diagram the tail and flap movements are linked, however in practice it may be preferable to treat these separately and interrogate 'is tail lock out' with the command 'move tail' following the affirmative, and the interrogation 'is flap lock out' followed by 'move flap' for the respective affirmative response. A wingsail comprising a leading element 1, a flap 2 and slat 23 is shown in Figures 9 and 10 in the configurations that may be adopted respectively for sailing on port and starboard tack. Similar sailset configurations, but with the boat direction rotated by 180° correspond to astern sailing on starboard and port tacks. Preferably, as shown, the leading element is a sail in the form of a rigid, preferably symmetrical, upright aerofoil rotatable about an upright axis. The trailing element, or flap (2), may be similar and the air-directing slat 23 may also be a rigid aerofoil. The general arrangement may be as disclosed in European Patent specification No.0062191. It will be seen from Figure 11 that when the flap 2 passes through the central position the slat 23 is pressed against the leading edge of the flap, and the position shown in Figure 11 is that which is adopted when the flap is centralised from the ahead port tack shown in Figure 9 prior to achieving the starboard tack of Figure 10. The slat continues to be pushed by the flap until flap 2 has been deflected far enough for the gap between the element 1 and flap 2 to permit the slat 23 to pass through, which it does by virtue of wind pressure and centering springs Generally the slat 23 is made as long as possible and so the change of side of the slat occurs just before the flap has reached maximum deflection. The cable 24 is made of a length determined by the desired nozzle configuration. If the cable 24 is clamped at the trailing edge of the slat and attached to the leading edge of the flap by a thimble or similar arrangement, for example as shown in Figure 12, then the cable may suffer from chafe and also 'hanging up' during tack change, the mounting also obstructing the passage of the slat. A preferred arrangement according to the invention for the cable is shown in Figure 13. The cable, which is made of stainless steel and may be plastics covered, is swaged at 25 to a solid thimble 26 at the slat end and swaged at 27 at a special fitting 28 for attachment to the flap. Preferably the slat is made of metal with a riveted or welded trailing edge, although other arrangements are possible, and has a cut out position indicated generally at 29 in Figure 14. A pivot 30 is located within the cut out, being secured in position by side plates 31. The solid thimble 26 has an aperture 32 in the centre portion, and this aperture is threaded on pivot pin 30 between spacing washers 32. Two wheels 33 are also threaded on the pivot pin, one on each side of the thimble, the rim of the wheel extending beyond the trailing edge of the slat. At the other end of the cable 24, the object is to provide an unobtrusive fixing flush with the surface of the flap. The fitting 28, shown in more detail in Figure 14, comprises a plate 34 of a curvature that conforms with the leading edge of the flap, and preferably the leading edge of the flap is recessed so that the plate fits flush with the rest of the surface of the flap. The centre part of the plate has a recess with substantially flat upper and lower walls and and inwardly curving side walls 37 and 38 so that viewed from above the walls 37 and 38 define a 'horn' shape. The separation of the upper and lower walls and is just larger than the thickness of the cable 24 and any covering, and curvature of the walls 37 and 38 are chosen so that the radius of curvature is more than the minimum radius of curvature to which the stainless steel cable should be subjected. At the inward (narrow) end of the recess there is preferably a tubular section to which the cable may be swaged, but if the recess is formed from a material unsuitable for swaging a separate swage 39 may be made as shown in Figure 15. The horn recess may be formed separately from the plate and joined to it. A modification to the plate and horn recess is shown in Figure 16, where a tool is plunged through the plate to form two curved ramps 37a and 38a to which the swage on the end of the cable may be mounted. In order to facilitate such attachment the swage portion may have a turned recess so that it may be sprung over the curved ramps, clamped and then welded or brazed to fix it in place. The leading edge of the flap may be provided with a recess (Figure 17) to accommodate the ramps or horn and swage, and this is particularly desirable if the ramp structure is used, in order to prevent ingress of water into the flap, and in this instance either the plate or the flap is provided with a relieved portion for drainage. In operation the flap end of the cable is firmly fixed and can take up configurations with the cable lying over the surface of either of the surfaces 37 or 38, but is prevented from adopting too great a curvature. The leading edge of the flap remains smooth except for the protrusion of the cable and so presents minimum interference to the slat as it moves from one side to the other. Passage of the slat over the leading edge of the flap is eased by the wheels attached to the trailing edge of the slat, the wheels rolling on the flap surface to reduce scuffing. At the slat end of the cable, the thimble may be modified or replaced by a hollow thimble (or loop) filled by a solid stub with an aperture, and the stub may then be formed integrally with one or both of the spacing washers. The object of a solid or filled thimble is for the pivot pin to be a close but free fit, and of course this could be provided by modifying the pivot pin rather than the thimble. Referring now to Figure 18 a wingsail is shown that comprises a leading element 1 and a trailing flap 2. The flap 2 can be deflected about a pivot to adopt the positions shown in Figures 19 and 20, the deflection being controlled by a system incorporating a fluid cylinder, such as a hydraulic ram. A problem with using a hydraulic ram is that during the inward stroke of the ram into the cylinder an area the size of the piston head is acted upon by the hydraulic fluid and during the outward stroke the area reacting on the fluid is the annulus defined by the piston head perimeter and the ram perimeter, and thus for a given flow rate of supply of fluid the speed of advance differs from the speed of withdrawal, leading to different rates of deflection depending upon whether the ram is on the inward or outward stroke. Figure 21 shows a system in which two cylinders are utilised to provide equalisation of the deflection speed in each direction, and also to provide a failsafe system. Two hydraulic cylinders 43 and 44 are mounted on opposite sides of the flap 2, in a symmetrical arrangement, and hose lines 45 and 46 represent respectively the pump and tank lines for the hydraulic fluid. The pump line divides into branches 47 and 48 and each branch continues to a valve 49. Branch 47 then connects to the annulus side of hydraulic cylinder 43 and branch 48 connects to the full bore side of hydraulic cylinder 44. The tank line 46 divides similarly into branches 50 and 51 which connect respectively via more valves 9 to the full bore side of hydraulic cylinder 43 and the annulus side of hydraulic cylinder 44. Thus in operation when a spool valve 52 is set to permit pressure flow the pressure is supplied to the full bore of cylinder 44 and the annulus of cylinder 43, while hydraulic fluid escapes to the tank from the full bore of cylinder 43 and the annulus of cylinder 44. This moves the flap in a given direction with a speed determined by the annulus/full bore combination and a reversal of the flow directions moves the flap in the opposite direction with the same speed. The valves 49 are flow sensitive devices and are designed to shut if flow exceeds a predetermined rate, such as would occur if a pipe burst. Upon shut down of a valve 49, the flap movement continues, but at reduced speed powered only through the other cylinder. The two cylinders may be displaced from one another vertically. For example, in a structure as shown in Figure 22 one cylinder (not shown) may be placed at one hinge assembly indicated generally at 53, and the other at a different hinge assembly. More than one pair may be provided either in an alternate arrangement or in pairs on the hinge assembles. During deflection the loads are shared by the cylinders in the ratio of their full bore and annulus areas, the imbalance being distributed by the torsional stiffness of the flap. The apparatus has been described in the context of a multi-element wingsail, however a similar arrangement could be used for deflecting other aerofoil members of a wingsail system, for example a governor such as a tail vane as shown in Figure 23. In Figure 23 a twin plane set of thrust wings is illustrated, each thrust wing comprising a leading element 1 and a trailing flap element 2. The flaps 2 are pivotable about an axis 54 located on the centre chord of the respective leading elements, so that each flap is capable of being deflected laterally to each side of its respective leading element. The spacing of the leading element is fixed and maintained by members interconnecting the two leading elements at intervals in the upright direction, so that the leading elements are maintained parallel to one another. Deflection of the flaps may be achieved by a control system including fluid cylinders: each flap may have its own fluid cylinders or one may be driven and the others connected to follow as slaves, this latter arrangement being more suitable for systems with three or more wings with a central (or a central pair) of flaps being driven and the outer flaps being slaves. In all cases the operation of such a system of wings generally requires the flaps to be moved together and so whether by virtue of physical interconnection or by a control mechanism the flaps are moved in unison. The natural arrangement is for the flaps to be maintained parallel to one another, so that the camber presented by each leading element and its flap is the same. However it is now proposed for the flap arrangement to be made non-parallel so that the position shown in Figure 24 is adopted in the symmetrical position, with the trailing edges of the flaps being slightly closer together than the spacing of the leading edge: this arrangement is termed 'toe-in'. The effect of toe-in in the symmetrical position is that once the flaps are deflected, as shown in Figure 25, the leeward flap is deflected to a greater angle than the windward flap, and thus as stalling is approached the leeward wing stalls first and more deeply than the windward wing. The extent of the 'toe-in' determines the difference in the flap angles, a difference of about 2° between the angles of adjacent flaps being preferred. With a three wing system, the central flap will be left parallel with the leading elements and the outer flaps toed-in in the symmetrical positions to give for example angles of +38°, +40° and +42° when deflected, or on the oppostite tack angles of -38°, -40° and -42°. For configurations with four or more wings, pairs of wings may have differing degrees of toe-in in order to maintain the leeward progression to deeper stalling.

Claims: A method of operating a self-trimming wingsail assembly comprising a thrust wing having a leading aerofoil (1) and a trailing aerofoil flap (2) and a trimming tail aerofoil (6) in which the flap is pivotable to each side of the leading aerofoil to form respective deflected configurations and the tail aerofoil trims the angle of attack of the wing to the wind, the method comprising pivoting the trailing aerofoil to a desired deflected configuration characterised by the step of first adjusting the angle between the tail aerofoil and the leading aerofoil to rotate the sailset towards a position in which the moment opposing movement of the flap in the desired direction is reduced or reversed and after the flap has been moved, readjusting the tail aerofoil for trimming to the desired angle of attack. A method according to claim 1 wherein the flap is locked in position after movement in said direction. A method according to claim 1 or claim 2 in which the tail is adjusted to its maximum deflection in one direction and the flap is deflected in the same direction. A method according to claim 2 or claim 3 in which the movement of the tail and flap are commenced simultaneously. Apparatus for controlling a self-trimming wingsail having at least one thrust wing with a leading aerofoil (1) and a trailing aerofoil (2) and a trimming tail aerofoil (6) in which the flap is pivotable to each side of the leading aerofoil to form respective deflected configurations and the tail aerofoil trims the angle of attack of the wing to the wind, the apparatus comprising means for pivoting the trailing aerofoil to a desired configuration characterised by a control system that operates first to adjust the angle between the tail aerofoil and the leading aerofoil to rotate the sailset towards a position in which the moment opposing movement of the flap in the desired direction is reduced or reversed and, after the flap has been moved, operates to readjust the tail aerofoil for trimming to the desired angle of attack. Apparatus according to claim 5 in which the flap is locked in position after movement in said direction. Apparatus according to claim 5 or claim 6 in which the flap is moved by a hydraulic ram.

Inventors: WALKER JOHN GRAHAM, WALKER, JOHN GRAHAM
Applicants: WALKER JEAN MARGARET, WALKER JOHN GRAHAM, WALKER, JEAN MARGARET, WALKER, JOHN GRAHAM
Application year: 1989
Main classification: B63H9
IPC codes: B63H9