RHOMBOHEDRAL HYDROFOIL AND CRAFT COMPRISING SAME

Abstract

The rhombohedral hydrofoil (20) for a craft travelling parallel to an axis (46) has a plane of symmetry and comprises front wings (21, 22) that are connected to one another and rear wings (25, 26) that are connected to one another. The end of each front wing that is furthest from the junction of the front wings with one another is connected to one end of a rear wing which is the end furthest from the junction of the rear wings with one another. This assembly of wings has a first orthogonal projection onto a plane referred to as vertical perpendicular to the axis of travel, this projection having the shape of a quadrilateral having an obtuse angle at the junction of the front wings with one another, an obtuse angle at the junction of the rear wings with one another, and two acute angles at the junction of a front wing with a rear wing. This assembly of wings has a second orthogonal projection onto a plane referred to as horizontal orthogonal to the plane of symmetry and having an axis parallel to the axis of travel, this projection having the shape of a quadrilateral having only angles with magnitudes smaller than 180 degrees.

Claims

1. Rhombohedral hydrofoil (20, 50) for mounting on a lower mast (45, 105) of a craft (40) travelling in a direction parallel to an axis (46), this hydrofoil having a plane of symmetry and comprising, in this direction, front wings farther from the craft (21, 22, 53, 54) that are connected to one another, and rear wings closer to the craft (25, 26, 55, 56) that are connected to one another, characterised in that: the end of each front wing that is farthest from the junction of the front wings with one another is connected to one end of a rear wing which is the end farthest from the junction of the rear wings with one another; this assembly (52) of wings has a first orthogonal projection onto a plane referred to as vertical perpendicular to the axis of travel, this projection having the shape of a quadrilateral having an obtuse angle at the junction of the front wings with one another, an obtuse angle at the junction of the rear wings with one another, and two acute angles at the junction of a front wing with a rear wing; this assembly of wings has a second orthogonal projection onto a plane referred to as horizontal orthogonal to the plane of symmetry and having an axis parallel to the axis of travel, this projection having the shape of a quadrilateral having only angles with magnitudes smaller than 180 degrees; and the front wings have a lift profile.

2. Hydrofoil (20, 50) according to claim 1, which also comprises a body (32, 51) that comprises: a fastening for the lower mast (45, 105) of the craft; a wing-root and junction support (23, 24, 57) for the front wings (21, 22, 53, 54); and a wing-root and junction support (31, 58) for the rear wings (25, 26, 55, 56), the front and rear wing-root supports being respectively positioned either side of this body in the plane of symmetry of the hydrofoil.

3. Hydrofoil (20, 50) according to claim 2, wherein the body (32, 51) of the hydrofoil comprises a ballast.

4. Hydrofoil (20, 50) according to claim 2, wherein the body (32, 51) of the hydrofoil comprises a ballast tank.

5. Hydrofoil (20, 50) according to claim 1, which comprises, at least on each wing (25, 26, 53, 54, 55, 56) of a pair of wings, at least one sidewall (29, 30, 63 to 66, 73 to 76) actuated by an actuator.

6. Hydrofoil (20, 50) according to claim 1, wherein, at each junction of the front and rear wing ends, a vertical surface (27, 28, 78) for closing these wing ends is positioned.

7. Hydrofoil (50) according to claim 1, wherein the rear wings have a spoiler profile.

8. Hydrofoil (20) according to claim 1, wherein the rear wings have a lift profile.

9. Hydrofoil (50) according to claim 2 wherein: one end of each front wing (53, 54) is articulated to one end of a rear wing (55, 56); and at least one of the wing-root supports (57, 58) can move along the body of the hydrofoil.

10. Hydrofoil (50) according to claim 9, wherein the length of the rear wings is strictly shorter than the length of the front wings, the angle formed between the main longitudinal axis of the body of the hydrofoil and the main axis of the rear wings therefore being more obtuse than the angle formed between the main longitudinal axis of the body of the hydrofoil and the main axis of the front wings.

11. Hydrofoil (50) according to claim 9, wherein at least one of the wing-root supports is configured to come closer to the other wing-root support so that the front wings form the hypotenuses of right-angle triangles formed by the front wings, the rear wings and the body of the hydrofoil, the main axis of each of the rear wings being, in these right-angle triangles, perpendicular to the main longitudinal axis of the body of the hydrofoil.

12. Hydrofoil (50) according to claim 9, wherein at least one of the wing-root supports is configured to come closer to the other wing-root support so that the front wings and the rear wings are in swept-back configurations. Thanks to these provisions, the sweep of the front wings can be increased and the span reduced, in particular for flight configurations at the highest speed.

13. Hydrofoil (50) according to claim 9, wherein at least one of the wing-root supports is configured to move away from the other wing-root support so that the hydrofoil's span is less than the sum of four times the maximum width of the front wings and the rear wings, firstly, and the width of the body of the hydrofoil, secondly.

14. Hydrofoil (50) according to claim 9, wherein each of the wing-root supports can move along the body of the hydrofoil. Thanks to these provisions, the geometric configuration of the wing structure can be adjusted for any distribution of mass or thrust.

15. Hydrofoil (50) according to claim 9, wherein at least one wing-root support is put into motion by a motor, a control unit actuating this motor. Thanks to these provisions, the centre of thrust of the wing structure can be moved from front to back on the body of the hydrofoil, independently of the geometry of the wing structure dictated by the distance between the wing-root supports.

16. Hydrofoil (50) according to claim 9, wherein at least one front wing-root support comprises at least one pivot.

17. Hydrofoil (50) according to claim 9, wherein a rod inside one of the wings keeps the main plane of the vertical surfaces for closing wing ends parallel to the main axis of the body of the hydrofoil.

18. Hydrofoil (50) according to claim 9, wherein the junctions of the front and rear wing ends comprise pivots.

19. Craft (40, 100) comprising a hydrofoil (20, 50) according to claim 1.

20. (canceled)

21. Craft (40, 100) according to claim 19, which comprises means for morphing the wing structure, to alter the inclination of the wings' axes of rotation and cause a variation of incidence, the adjustment means (51) controlling the morphing means.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0042] Other advantages, aims and characteristics of the present invention will become apparent from the description that will follow, made, as an example that is in no way limiting, with reference to the drawings included in an appendix, wherein:

[0043] FIG. 1 represents, schematically and in a perspective view, a first particular embodiment of the craft that is the subject of the invention;

[0044] FIG. 2 represents a detailed view of FIG. 1;

[0045] FIG. 3 represents, schematically and in a side view, the craft illustrated in FIGS. 1 and 2;

[0046] FIG. 4 represents, schematically and in a front view, the craft illustrated in FIGS. 1 to 3;

[0047] FIG. 5 represents, schematically and in a top view, a first particular embodiment of the hydrofoil that is the subject of the present invention;

[0048] FIG. 6 represents, schematically and in a side view, the hydrofoil illustrated in FIG. 5;

[0049] FIG. 7 represents, schematically and in a top view, a second particular embodiment of the hydrofoil that is the subject of the present invention, in a first configuration;

[0050] FIG. 8 represents, schematically and in a top view, the hydrofoil illustrated in FIG. 7, in a second configuration;

[0051] FIG. 9 represents, schematically and in a top view, the hydrofoil illustrated in FIGS. 7 and 8, in a third configuration;

[0052] FIG. 10 represents, schematically and in perspective, the hydrofoil illustrated in FIGS. 7 to 9, in the configuration illustrated in FIG. 8;

[0053] FIG. 11 represents, schematically and in perspective, a movable articulation of a front wing-root support;

[0054] FIG. 12 represents, schematically and in perspective, a movable articulation of a rear wing-root support;

[0055] FIG. 13 represents, schematically and in perspective, an articulation of front and rear wing ends;

[0056] FIG. 14 represents, as a logical diagram, steps in the operation of the hydrofoil illustrated in FIGS. 7 to 13;

[0057] FIG. 15 represents, schematically and in a perspective view, a second particular embodiment of the craft that is the subject of the invention;

[0058] FIG. 16, represents, in a side view, the craft illustrated in FIG. 15;

[0059] FIG. 17 represents, in a front view, the craft illustrated in FIGS. 15 and 16; and

[0060] FIG. 18 represents, in a front view, the craft illustrated in FIGS. 15 to 17.

DESCRIPTION OF THE EMBODIMENTS

[0061] Note that the figures are not to scale. To simplify the understanding of the drawings and schematics, the wings and vertical surfaces at the junction of the wing ends are represented by thin surfaces. Throughout the description, the directions are oriented based on the flow of water intended to pass over the hydrofoil. When this hydrofoil is mounted on a craft, these directions thus correspond to those of the craft. Therefore, the term front refers to being oriented towards the arrival of the water flow during the navigation, rear to being oriented towards the departure of the water during the navigation, lower to being farther from the surface of the water and thus from the float of the craft, upper to being closer to the surface of the water and therefore to the float of the craft, and side to being farther from the plan of symmetry of the hydrofoil and from the plan of symmetry of the craft. Side therefore corresponds to the sides of the craft, also known as port and starboard.

[0062] The following definitions are noted: [0063] a craft is a Small-sized boat, generally open, proceeding by means of sails, oars, steam or motor, the term craft can be replaced by watercraft; [0064] a hydrofoil is In fluid mechanics, a hydrofoil is a wing positioned and profiled so as to generate, by its movement in the water, a lift force that acts on its speed and its stability.; [0065] a rhombohedron is a three-dimensional polyhedron resembling the cube, except that its surfaces are diamond-shaped not square. By extension, according to the present invention, the four wings are diamond-shaped, but the front and rear surfaces of this rhombohedron cannot be flat, and they have two lower surfaces, respectively the leading and trailing edges of the lower wings, whose length is different from that of their two upper sides, respectively the leading and trailing edges of the upper wings.

[0066] A fin is used to ensure the lateral stability of a craft, whereas a hydrofoil aims to make a craft lift up, or plane, from an aquatic environment.

[0067] FIGS. 1 to 4 show a craft 40 comprising a hydrofoil 20 connected to a hull 41 by a lower mast 45. The hull 41 also bears a mast 42, two sails 43 and 44 being supported by the mast 42. FIG. 3 shows an axis 47 of travel of the craft 40 and a main axis 46 of the hydrofoil 20 parallel to the axis 47.

[0068] The craft 40 moves at least partially in the airborne environment on an aquatic environment, the hydrofoil being submerged in the aquatic environment. The purpose of a hydrofoil is to make the craft rise, at least partially, i.e. to reduce the surface of contact between the craft and the aquatic environment. Although the craft 40 takes the form of a monohull sailcraft in the figures, the hydrofoil that is the subject of the invention applies equally to any craft including, in particular, sailboards, surfboards, motor and/or sail mono or multihull boats. The craft that is the subject of the invention can comprise one or more rhombohedral hydrofoils.

[0069] The hydrofoil 20 for craft 40 travelling parallel to a horizontal axis 46 is symmetrical relative to a rhombohedral, rhombohedric or rhomboidal vertical plane. The rhombohedron is defined relative to this vertical plane and this horizontal axis. It is noted that a rhombohedral (rhombohedric or rhomboidal) wing structure is a variant of a tandem wing in which the ends come together. The front wing fixed on the lower portion of the body of the hydrofoil is in a swept-back configuration, and the rear wing fixed on the upper portion of the fin is in a swept-forward configuration. The wing structure, comprised of the assembly of wings, forms a hollow continuous projected quadrilateral surface, close to a diamond.

[0070] The hydrofoil 20 is intended to be mounted on a lower mast 45 (see FIGS. 1 to 4) of a predefined craft 40. In other words, the geometric configuration of the hydrofoil 20 depends on the physical characteristics, especially the weight and position of the mast 45, of the craft 40. The hydrofoil 20 comprises lower front wings 21 and 22 connected to each other by a junction, or wing root, 23 and 24, and upper rear wings 25 and 26 connected to each other by a junction, or wing root, 31. This means that the front wings 21 and 22 are, once the hydrofoil is mounted on the lower mast of the craft, are farther from the craft than the rear wings 25 and 26.

[0071] The end of each front wing, the farthest from the junction of the front wings, is connected to one end of a rear wing, the farthest from the junction of the rear wings, by a mechanical connection; respectively 27 and 28. The front wings 21 and 22 have a lift profile, i.e. their movement forward in the water generates a lift tending to bring the hydrofoil 20 closer to the surface of the water and raise the mast connecting the hydrofoil to the craft. In the case of a hydrofoil positioned on a mast 45 under the centre of gravity of the craft 40, the rear wings 25 and 26 have a lift profile.

[0072] The assembly of these wings 21, 22, 25 and 26 has a first orthogonal projection onto a plane, referred to as vertical, perpendicular to the axis of travel 46. The first projection has the shape of a quadrilateral having an obtuse angle at the junction of the front wings with one another, an obtuse angle at the junction of the rear wings with one another, and two acute angles at the junction of a front wing with a rear wing.

[0073] The assembly of these wings 21, 22, 25 and 26 has a second orthogonal projection onto a plane, referred to as horizontal, orthogonal to the plane of symmetry and having an axis parallel to the axis of travel 46. The second projection has the shape of a quadrilateral having only angles with magnitudes smaller than 180 degrees.

[0074] In the first embodiment shown in FIGS. 5 to 6, the hydrofoil 20 comprises a body 32. In other embodiments, the hydrofoil that is the subject of the invention does not comprise a body, the wings being connected to each other to form a rhombohedron, a figure in which two orthogonal projections onto orthogonal plans (here a vertical plane perpendicular to axis 46 and a horizontal plane), form quadrilaterals in which the magnitudes of all the angles are smaller than 180 degrees. The root supports 23, 24 and 31 of the front wings 21 and 22 and rear wings 25 and 26 are respectively positioned either side of this body 32 in the plane of symmetry of the hydrofoil 20. The body 32 thus provides rigidity for the hydrofoil 20 and allows the thickness of the wings 21, 22, 25 and 26 to be reduced. More precisely, the linkage of the front wings 21 and 22 is in the lower portion of the body 32 and the linkage of the rear wings 25 and 26 is in the upper portion of the body 32.

[0075] The hydrofoil 20 comprises, at least on each wing of a pair of wings (here the rear wings 25 and 26), at least one sidewall, respectively 29 and 30, actuated by an actuator (not shown). An active stabilisation system of the craft 40 is therefore especially effective. In some embodiments, the front wings 21 and 22 therefore have control surfaces (not shown), ailerons or sidewalls and the rear wings 25 and 26 have control surfaces (not shown), ailerons or sidewalls.

[0076] At each junction of the ends of the front wings 21 and 22 and rear wings 25 and 26 a vertical surface is positioned, respectively 27 and 28, one axis of which is parallel to the axis 46. These vertical surfaces 27 and 27 for closing wing ends allow the drag of the wing structure to be reduced. The closing of the wing ends, to obtain a wing with an almost infinite aspect ratio, thus consists of a vertical hydrodynamic surface 27 or 28 (profiled or not). One of the characteristics of rhombohedral wings is the absence of a vertical surface, and therefore a tangible improvement in profile drag. This vertical surface 27 or 28 that joins the two wings at their ends makes it possible to close the space and therefore, in theory, have a wing similar to an infinite-span wing.

[0077] In some embodiments, the body 32 of the hydrofoil 20 comprises a ballast. The hydrofoil thus has a dual function. In some embodiments, the body 32 of the hydrofoil 20 comprises a ballast tank. The ballast tank can therefore be emptied when the hull of the craft 40 rises out of the water. Each of the wings 21, 22, 25 and 26 shown in the figures are broadly rectangular in shape. They are therefore constant-chord wings, their leading edges and trailing edges being parallel. Of course, the present invention is not limited to this type of general form but extends to all wing shapes other than delta wings.

[0078] The inventor has discovered that the rhombohedral configuration makes it possible to keep an almost constant lift/drag ratio over a broad range of speeds by varying the camber of the front wingsand the rear wings to maintain a balanced flight. This particularity has been confirmed in wind-tunnel tests. The use of wing morphing is especially suitable since a small angular variation in the front and rear wings can introduce significant variations in incidence and/or in camber over their span. This makes it possible to limit the use of sidewall deflections, which have the drawback of the complexity of the mixes of the eight sidewalls and the lack of precision/resolution of the servomotors and of the mechanical controls of these servomotors.

[0079] Morphism is a very elegant solution for fine-tuning the adjustment of the wing structure to the flight conditions without having the drawback of solutions that are cumbersome and hydrodynamically not very suitable for the multiple sidewalls on the trailing edge and/or the slats and other appendages on the leading edge. The rhombohedral type of wing structure lends itself particularly well to this type of control.

[0080] FIG. 7 shows a hydrofoil 50 comprising a body 51 of the hydrofoil and a rhombohedral-shaped wing structure 52. The hydrofoil 50 is intended to be mounted on a lower mast of a predefined craft. In other words, the geometric configuration of the hydrofoil 50 depends on the physical characteristics, especially the weight and position of the mast, of the craft. The hydrofoil 50 comprises a lower left front wing 53, a lower right front wing 54, an upper left rear wing 55 and an upper right rear wing 56. This means that the front wings 53 and 54 are, once the hydrofoil is mounted on the lower mast of the craft, are farther from the craft than the rear wings 55 and 56. The front wings 53 and 54 come together on a front wing-root support 57 located below the body of the hydrofoil 51. The rear wings 55 and 56 come together on a rear wing-root support 58. The left wings 53 and 55 come together on a left wing junction 59 situated above the body of the hydrofoil 51. The right wings 54 and 56 come together on a right wing junction 60. The front wings 53 and 54 have control surfaces 63 to 66, ailerons or sidewalls. The rear wings 55 and 56 have control surfaces 73 to 76, ailerons or sidewalls. The front wings 53 and 54 have a lift profile when the control surface 63 to 66 are in neutral position, i.e. their movement forward in the water generates a lift tending to bring the hydrofoil closer to the surface of the water and raise the mast connecting the hydrofoil to the craft.

[0081] The junction of the left wing ends 59 is articulated, which enables a relative angular movement of the left front wing 53 relative to the left rear wing 55. In the same way, the junction of the right wing ends 60 is articulated, which enables a relative angular movement of the right front wing 54 relative to the right rear wing 56.

[0082] At least one of the wing-root supports 57 and 58 can move along the body of the hydrofoil 51, which makes possible a deformation of the rhombohedral wing structure 52, a variation in the sweep of each wing and therefore of the span of the wing structure 52. Thanks to these variations, the wing structure 52 can be adjusted for different speed envelopes. FIG. 8 shows the hydrofoil 50 in a wing structure configuration with a low sweep angle and extended span. FIG. 9 shows the hydrofoil 50 in a wing structure configuration with superposed wings, high sweep angle and reduced span.

[0083] As can be seen in FIGS. 7 to 9, in particular FIG. 8, in the embodiment shown in it, the length 81 of the rear wings 55 and 56 is strictly shorter than the length 88 of the front wings 53 and 54. The angle 82 formed between the main longitudinal axis 84 of the body of the hydrofoil 51 and the main axis 83 of the rear wings is therefore, in all flight configurations, more obtuse than the angle 86 formed between the main longitudinal axis of the body of the hydrofoil and the main axis 85 of the front wings. Note that the length of the wings is the largest dimension of the wings measured parallel to their main axis.

[0084] Therefore, the front wings 53 and 54 are always in a swept-wing configuration and the rear wings 55 and 56 can be in a swept-forward (FIG. 7), straight (intermediate between the configurations shown in FIGS. 8 and 9), i.e. perpendicular to the body of the hydrofoil, or swept-back (FIG. 9) configuration, or in any of the intermediate configurations. In other embodiments, the length of the rear wings is equal to or greater than the length of the front wings.

[0085] In the embodiment shown in FIGS. 7 to 9, at least one of the wing-root supports 57 and 58 (the two wing-root supports, in FIGS. 7 to 9) is configured to come closer to the other wing-root support so that the front wings 53 and 54 form the hypotenuses of right-angle triangles formed by the front wings, the rear wings 55 and 56 and the body of the hydrofoil 51. The main axis 83 of each of the rear wings is, in these right-angle triangles, perpendicular to the main longitudinal axis 84 of the body of the hydrofoil.

[0086] As can be seen in FIG. 9, at least one of the wing-root supports 57 and 58 (the two wing-root supports, in FIGS. 7 to 9) is configured to come closer to the other wing-root support so that the front wings 53 and 54 and the rear wings 55 and 56 are in swept-back configurations. Therefore, the sweep of the front wings 53 and 54 can be increased and the span 89 reduced, in particular for configurations of use at the highest speed.

[0087] As can be seen in FIGS. 8 and 9, at least one of the wing-root supports 57 and 58 (the two wing-root supports, in FIGS. 7 to 9) is configured to move away from the other wing-root support so that the span 89 (shown in FIG. 9) of the hydrofoil 50 is less than the sum of four times the maximum width 87 (shown in FIG. 8) of the front wings 53 and 54 and the rear wings 55 and 56, firstly, and the width 90 of the body of the hydrofoil 51, secondly. Note that the width 87 of the wings is the largest dimension of the wings measured perpendicular to their main axis 83 or 85. In the embodiment shown in FIGS. 7 to 9, the maximum width 87 of the front and rear wings is located on the front wings 53 and 54. As shown in FIG. 10, the wing-root supports are preferably positioned respectively below and above the body of the hydrofoil 51, this configuration being optimum for several aspects.

[0088] Preferably, as shown in FIGS. 7 to 13, each of the wing-root supports 57 and 58 can move along the body of the hydrofoil. For this purpose, each wing-root support, respectively 57 and 58, is set in motion on a rail, respectively 67 and 68, by an electric motor, respectively 69 and 71, fitted with a worm screw, respectively 70 and 72.

[0089] An electronic control unit 77 (see FIG. 9) comprises a central processing unit which actuates the motors 69 and 71 in a coordinated way. The electronic control unit 77 also performs control functions commanding control surfaces 63 to 66 and 73 to 76. In addition, the electronic control unit 77 forms a means for adjusting the position of each wing root to suit the speeds of movement, for example to the payload, speed, altitude, target autonomy, target manoeuvrability. The adjustment means 77 alters the geometric configuration of the wing structure by moving at least one wing root.

[0090] In some variants, the hydrofoil 50 comprises means for morphing the wing structure, to alter the inclination of the wings' axes of rotation and cause a variation of incidence, the adjustment means controlling the morphing means. Preferably, in these variants, the electronic unit alters the incidence of the wing structure during the travel of the craft, based on the payload, speed, altitude, target autonomy, target manoeuvrability.

[0091] As shown in the right portion of FIG. 8 and in FIG. 13, at each junction 59 and 60 of the front and rear wing ends, a vertical surface for closing these wing ends 78 is positioned. A rod 79 inside one of the wingsa front wing in the FIGS. 7 to 13keeps the main plane of the vertical surfaces for closing wing ends 78 parallel to the main axis of the body of the hydrofoil 51.

[0092] As shown in FIG. 13, the junctions 59 and 60 of the front and rear wing ends comprise pivots. To give a third degree of freedom, over several angular degrees, this pivot link has flexibility or a swivel link.

[0093] As shown in FIGS. 11 and 12, at least one, and preferably both, wing-root support 57 and 58 comprises pivots and a baseplate 80 moved along the body of the hydrofoil 51 by the motor, respectively 69 and 71.

[0094] Below is a description, with reference to FIG. 9, of an operating mode of the hydrofoil 50. The front and rear wings are articulated at the wing root at the point where they are joined to the body of the hydrofoil, and the right front and rear wings, and similarly the left front and rear wings, are articulated to each other at the ends (tip edges).

[0095] This articulation point of the wing root and/or end can be located, or not, in the hydrodynamic loft of the wing. The hydrodynamic loft is the 3D surface of the hydrofoil used for studies, modelling and simulations. This 3D model can also be used to produce the model for wind-tunnel tests. It is the perfect hydrodynamic version of the hydrofoil, which will subsequently be adjusted for the production, use, maintenance, regulatory, etc. constraints. Therefore, it is essential to conform to this shape/surface as closely as possible in order to have a device whose performance levels are as close as possible to this initial theoretical design. The wing-root articulations with the body of the hydrofoil can be moved from front to back and independently to obtain the desired geometry while respecting the position constraints for the centre of gravity required by the transitional and/or desired planar shape.

[0096] These wing-root articulations, while moving longitudinally, can also be moved up and/or down to, for example, obtain the angle of incidence adjusted according to the sweep of the wing. The incidence of the wings is changed according to the configuration of the wing structure so that the profiles of the wings (cross-section parallel to the flow) are always within the values suitable for this configuration. The variations in angle of incidence are, in general, of slight, even very slight, amplitude. This variation in incidence is achieved by the inclination of the wings' axes of rotation. The effect of this inclination on the dihedral (positive or negative) is taken into consideration. On the model shown in FIGS. 7 to 13, the variations in incidence are of the order of 0.5 angular degrees in a range of variations in incidence extending up to five angular degrees.

[0097] The inclination of the wings' axes of rotation where they are joined to the wing root can introduce or eliminate angular variations in incidence. If this axis is perpendicular to the plane of the wing, the dihedral will naturally generate an angular variation in the chord of the wing relative to the frame of reference of the flow of air (the chord of a wing being the cross-section corresponding to the cross-section of the wing dissected by a vertical plane perpendicular to the plane of the wing and parallel to the flow/longitudinal axis X of the hydrofoil). It is necessary to ensure, in the case of a change of incidence introduced by the inclinations of the axis of rotation, that the variations are in phase between the front and rear wings so as to minimise any stresses at the ends that might be introduced by the geometry and the choice of degrees of freedom at the level of the mechanism connecting the ends of the front and rear wings to each other.

[0098] In some embodiments, the hydrofoil 50 comprises means for morphing the wing structure, to alter the inclination of the wings' axes of rotation and cause a variation of incidence. In these embodiments, a torsional moment is imposed on the wing roots, by means of their articulation/mounting, and thus a morphing phenomenon is produced by the use, for example, of composite materials and/or a suitable internal structure of the wing.

[0099] Morphism is aimed at having a structure whose skin deforms, so as to replace or supplement the controls (ailerons, sidewalls, etc.) and thus minimise drag (profile and induced). On a cantilever wing, a reshapable internal structure is provided which produces the deformation at the level of the skin (loft) required to obtain the desired/necessary modification in performance (drag, lift). Another solution consists of deforming skins using electromagnetic currents.

[0100] In the case of the rhombohedral wing structure, because of the rigid structure thanks to the bracing on three axes it is possible to introduce stresses in the ends of the wings fairly easily (e.g. for the change in incidence). In some embodiments, a wing is provided whose structure twists to increase (or reduce) its incidence at the wing root and/or end. This enables the lift of this wing to be altered, and thus makes it possible to replace the sidewalls. These variants are, for example, used to modify the characteristics of the wing according to the speed of motion of the craft 40. As detailed earlier, the inclination of the axes of rotation around the points where the wings are joined to the wing roots/ends, and the control and arrangement of the degrees of freedom at the mounts, can introduce stresses either in the longitudinal direction (span) or in the transverse direction (chord) and thus introduce torsional stresses which make possible, for example by acting on the angles of the axes of rotation and with a suitable structure, a constant or scalable twisting over the span of the wing structure. Buckling of the wing structure over its span can also be introduced, if considered necessary.

[0101] It is also possible to impose a torsional moment on the ends of the wings, by means of their articulation, and thus introduce a morphing phenomenon by using, for example, composite materials and/or a suitable internal structure of the wing. Rigid, semi-rigid and/or flexible fairings can enclose the various articulations to ensure good hydrodynamic sealing and/or a correct hydrodynamic flow. In some embodiments, the body 51 of the hydrofoil 50 comprises a ballast. In some embodiments, the body 51 of the hydrofoil 50 comprises a ballast tank operating as described with regard to the first embodiment shown in FIGS. 5 and 6.

[0102] FIG. 14 represents steps in the operation of the hydrofoil shown in FIGS. 7 to 13. During a step 91, the desired flight altitude of the craft 40 is determined, based on the navigator's flight controls or supplied by a flight optimisation system. During a step 92, the conditions of the corresponding flight envelope is determined, taking into account the flight conditions (speed, wind, payload, remaining autonomy, etc.). During a step 93, the configuration (dihedral angles and angle of incidence) of the wing structure is determined for this flight envelope and/or desired speed (according to the objectives of stability, reduced consumption, manoeuvrability, etc.). For example, starting from information for certain geometric configurations of the wing structure, including extreme configurations (FIGS. 7 and 9), this information is interpolated for all the other configurations.

[0103] During a step 94, the movements of the two wing roots to bring the centre of thrust to the desired place, and the movements of the morphing means providing a variation in angle of incidence, are calculated. During a step 95, the stepping motors and servomotors are controlled, in a simultaneous and coordinated way, so that the geometric configuration of the wing structure is obtained.

[0104] In its second embodiment shown in FIGS. 15 to 18, the craft 100 takes the form of a surfboard that comprises a float 101 and a lower mast 105 supporting a hydrofoil 20. Of course, the hydrofoil of the second embodiment of the craft has smaller dimensions than those of the first embodiment of the invention. The rear wings of the hydrofoil 20 configured for a surfboard or sailboard have a spoiler profile.