WO2003082671A1

WO2003082671A1 - Aerofoil with variable camber

Info

Publication number: WO2003082671A1
Application number: PCT/GB2003/001366
Authority: WO
Inventors: Richard Linsley-Hood
Original assignee: Richard Linsley-Hood
Priority date: 2002-03-28
Filing date: 2003-03-28
Publication date: 2003-10-09
Also published as: GB2386884A; GB0207397D0; GB2386884B; AU2003222590A1

Abstract

An aerofoil with variable camber is disclosed. The aerofoil (10) has a first surface (12) and a second, opposing surface (14). The surfaces (12, 14) are fixed to each other at respective leading and trailing ends (28, 29), such that a deflection in one surface is transmitted to the other surface via one or both of the leading (28) and trailing (29) ends. The first surface (12) has a deformable leading surface portion (16) and a deformable trailing surface portion (18), which define adjacent edges (16b, 18a). Both of the surface portions (16, 18) are arranged to be independently moveable with respect to the other. In this way, the aerofoil (10) is capable of assuming a range of positive, neutral or negative aerodynamic profiles. The aerofoil (10) of the present invention may be used in a range of light- to heavy-load applications. In particular, the aerofoil (10) may be employed as a wing, foil, blade or sail in aircraft, motor vehicles, marine vessels and the like.

Description

AEROFOIL WITH VARIABLE CAMBER

The present invention relates to an apparatus for the production of aerodynamic reaction forces, using aerofoils or other bodies with variable camber.

Aerofoils are well-known. A problem with most aerofoils is that the camber and cross-section of the aerofoils are permanently fixed. Flaps and other surfaces are often attached to an aerofoil to provide specific, though limited, variation to its shape.

GB-A-1, 144, 078 discloses aerofoil vanes with variable camber for use in compressors. Rods, which are positioned between the skins of a vane, extend through the span of the vane and are shifted to change its camber. The skins are fixedly coupled to each other so as to maintain them at a predetermined distance apart. The problems with this system are that inner joining members are subjected to bending stresses in order to allow the vane to change shape, and the rods must be shifted by a mechanism external to the vane, resulting in a complicated, multi-component system.

GB-A-2, 332, 893 and GB-A-2, 332, 894 each disclose aerofoil members with variable profile adaptations, in which a rib structure has rigid regions and flexible regions. Rib elements are articulated to one another in a kinematic chain arrangement, with central pivotal connections. The construction is such that the stimulated movement of one rib element may effect the movement of at least one other rib element. This system suffers from a number of drawbacks. In particular, the rib structure has a complex mechanical configuration and needs many moving parts. The angle of incidence of the leading edge also cannot be changed. Moreover, the range of profiles offered is limited to and by the variability of the trailing edge. It is an object of the present invention to provide an improved aerofoil.

In this patent specification, the term "aerofoil" is used to describe any body shaped so as to produce aerodynamic reaction forces and especially aerodynamic lift.

According to a preferred embodiment of the present invention, there is provided an aerofoil comprising a first deformable surface and an opposing second deformable surface, said first and second surfaces being fixed to each other at respective forward and rear ends, one of said first and second surfaces comprising two surface portions defining adjacent edges, said two surface portions being adapted to be moveable with respect to each other such that one or both of said adjacent edges move towards or away from said forward and rear ends so as to cause a deflection in said first and second surfaces, said deflection in the other of said surfaces being transmitted via one or both of said forward and rear ends.

This embodiment includes the possibility of only one of the surfaces comprising more than one surface portion, such that a range of asymmetrical shapes is afforded to the aerofoil. The principal advantage of this embodiment is that the aerofoil offers continuously-variable camber, by virtue of the continuous variability of the first and second surfaces with respect to each other. In addition, the angle of incidence of the leading edge may be varied, offering greater flexibility with regard to the selection of angle of attack of the aerofoil.

According to a preferred embodiment of the present invention, the adjacent edges are adapted to move in a substantially rectilinea motion, in a direction substantially parallel to a cross-sectional tangent line of the first surface in the proximity of said adjacent edges. The first and second surfaces have a respective curvature and, in cross-section, a tangent line may be constructed at any point on either surface. The tangent line of the present embodiment is constructed at the point on one surface of the adjacent edges. In an unactuated, level attitude aerofoil section, this tangent line will be substantially parallel to the chord line of the aerofoil (a straight line passing through the leading edge and the trailing edge of the aerofoil) . Therefore, an adjacent edge does not move in a straight line directed towards (or away from) the exact location of the forward end, but parallel to the tangent line and in the general direction of the forward end.

An advantage of this directed rectilinear motion is that the orientation and position of the surface portions may be more easily defined.

According to a preferred embodiment of the present invention, the first surface and/or the second surface comprises a plurality of surface portions in excess of two. The plurality of surface portions define respectively-adjacent edges being adapted to move in a substantially rectilinear motion towards or away from the forward and rear ends. This embodiment includes the possibility of only one of the surfaces comprising two or more surface portions, such that a range of asymmetrical shapes is afforded to the aerofoil.

This provides the advantage of greater flexibility of the aerofoil and a wider range of cambers which may be produced. The possibility of producing asymmetrical aerofoil shapes is advantageous in that increased variation is provided with regard to the operational applications of the aerofoil of the present invention.

According to a preferred embodiment of the present invention, there. are further provided joining means for associating respective ones of the adjacent edges. The joining means may comprise a sliding joint or an expanding joint, although other types of joint may readily be envisaged, and means for constraining the relative motion of the adjacent edges, such that rectilinear motion is described.

These types of joint are advantageous, since multi- component systems are not necessary, while permitting the desired variable-camber performance of the aerofoil. According to a preferred embodiment of the present invention, there are further provided actuation means for effecting rectilinear motion of the adjacent edges comprising at least one mechanical, hydraulic, or other, actuator per surface portion, being either software- controlled or otherwise, such that the position and orientation of each surface portion,^" or surface portion edge, may be defined. In the embodiment, the actuators comprise a moving arm, a motor, a motor housing and a means for attaching the actuator to a main spar, which extends through the aerofoil. Actuation of the actuator results in the motor driving the moving arm so that the arm either extends from or retracts into the housing and defines rectilinear motion of its respective surface portion edge.

The advantage of this embodiment is that at least a very close approximation to the shape, if not the precise shape, of the aerofoil produced by adjusting the surfaces may be both determined and prescribed. According to a preferred embodiment of the present invention, any one of the actuators may be actuated separately, or in combination with other actuators. Additionally, any one or ones of the actuators may be actuated, while any other actuators either are employed to constrain an adjacent edge such that the edge is not permitted to be displaced, or, may permit the edge to be displaced to accommodate the displacement of the actuated surface portion.

This embodiment has 'the advantage of offering a greater range of aerofoil profiles and cambers.

According to a preferred embodiment of the present invention, there are further provided internal supports, which extend transversely within^{^} the aerofoil, for joining an inner side of the first surface to an inner side of the second surface. The internal supports may comprise hinged struts, rigidly-fixed struts, extendable struts, or other physical supports, or may comprise an implicit, software-controlled, actuation means, such that the implicit internal supports simulate the effect of physical and fully-extending internal supports.

The advantage of this embodiment is that the aerofoil may have an essentially closed body surface and a sub-divided internal structure, providing support and a coupling system for the aerofoil .surfaces, such that movement of one surface, or surface portion, effects a reciprocal movement in the opposing surface, or surface portion. This embodiment may also advantageously provide an aerofoil with a range of continuously-variable cross- sections .

According to a preferred embodiment of the present invention, each individual internal support may be located between a point on the first surface and a point on the second surface, where the points are either an equal, or unequal, distance from the leading edge or forward end intersection of the first and second surfaces . This embodiment has the advantage of providing a range of symmetrical, or asymmetrical, sub-divided internal structures, where distortions to the aerofoil shape may be deliberately introduced as the camber is varied. According to a preferred embodiment of the present invention, there are provided load-bearing devices, which share the load borne by the aerofoil surfaces and transmit the load to a fixed structure or main spar. These load-bearing and load-transferring devices may also comprise variable load-taking devices, such as rubber blocks, springs, or any other device known for its elastic properties. This embodiment has the advantage of reducing the load borne by the actuation means, which may otherwise become damaged by a load which is too large or which varies too greatly during operation of the aerofoil. If the load-bearing devices are variable load-bearing devices, this embodiment is advantageous in that it is possible to arrange for the variable load-bearing devices to effect an adjustment of the aerofoil surfaces, based on the load being applied to the surfaces, such that the resultant lift approaches a predetermined maximum lift for the aerofoil.

According to a preferred embodiment of the present invention, the fixed structure or main spar comprises at least two sections, adjacent sections of which are pivotally joined. The relative movement of adjacent sections is controlled by actuation means which are disposed between the adjacent sections, and actuatable in the manner described above, and actuation of the surface portions may be achieved by actuation means interfacing between the spar sections and the surface portions or by means of a rigid connection between selected points of the spar sections and selected points of the surface portions, forcing the surface portions to be displaced as the actuators between spar sections are actuated.

This embodiment is advantageous in that it provides a range of varying^' load-bearing aerofoil configurations, the specific selection of one of which may depend on the operational application intended for the aerofoil. According to a preferred embodiment of the present invention, the first and second surfaces comprise a set of planar surfaces, instead of continuous and deformable surface portions, which are joined at each intersection by an internal support. This provides the advantage of flexibility in the construction of an aerofoil of the present invention, depending on the required application for the aerofoil. That is, if full dynamic performance is not necessary, the planar surfaces may be used.

According to a further aspect of the present invention, there is provided an aerofoil comprising a leading region and a trailing region; a first surface, comprising a deformable leading surface portion and a deformable trailing surface portion, the surface portions defining adjacent edges; and a second, opposing surface; the first and second surfaces being fixed to each other at respective leading and trailing ends, such that a deflection in one of the surfaces is transmitted to the other of the surfaces via -one or both of the leading and trailing ends, wherein both of the surface portions are adapted to be independently moveable with respect to the other, such that the leading region may assume a first range of positive, neutral or negative aerodynamic profiles and the trailing region may assume a second range of positive, neutral or negative aerodynamic profiles, the first and second ranges being independent of each other.

According to a further aspect of the present invention, there is provided an aerofoil comprising a first surface, comprising a first deformable leading surface portion and a first deformable trailing surface portion, the first surface portions defining first adjacent edges; and a second, opposing surface, comprising a second deformable leading surface portion and a second deformable trailing surface portion, the second surface portions defining second adjacent edges; the first and second surfaces being fixed to each other at respective leading and trailing ends, such that a deflection in one of the surfaces is transmitted to the other of the surfaces via one or both of the leading and trailing ends, wherein -both of the first surface portions are adapted to be independently moveable with respect to the other and both of the second surface portions are adapted to be independently moveable with respect to the other, such that the aerofoil may assume a range of positive, neutral or negative aerodynamic profiles .

According to the present invention, there is provided An aerofoil comprising a leading region and a trailing region; a first surface, comprising a first deformable leading surface portion and a first deformable trailing surface portion, the first surface portions defining first adjacent edges; and a second, opposing surface, comprising a second deformable leading surface portion and a second deformable trailing surface portion, the second surface portions defining second adjacent edges; the first and second surfaces being fixed to each other at respective leading and trailing ends, such that a deflection in one of the surfaces is transmitted to the other of the surfaces via one or both of the leading and trailing ends, wherein both of the first surface portions are adapted to be independently moveable with respect to the other and both of the second surface portions are adapted to be independently moveable with respect to the other, such that the leading region may assume a first range of positive, neutral or negative aerodynamic profiles and the trailing region may assume a second range of positive, neutral or negative aerodynamic profiles, the first and second ranges being independent of each other.

Other advantages and embodiments of the present invention will become evident from the following description and drawings. A number of embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a sectional view of an aerofoil;

Figs. 2a-h are sectional views of an aerofoil according to Fig. 1, exhibiting variable positive and negative camber;

Fig. 3 is a sectional view of two aerofoils according to Fig. 2f, wherein the aerofoil sections are overlaid;

Fig. 4 is a sectional view of an aerofoil, intended for light-load applications; Fig. 5 is a sectional view of an aerofoil, intended for medium-load applications;

Fig. 6 is a sectional view of an aerofoil, intended for heavy-load applications; and

Figs. 7a-b are sectional views of aerofoils, using variable load-bearing devices.

Fig. 8 is an expanded view of an actuator. Fig. 1 illustrates an aerofoil 10, comprising an upper surface 12 and a lower surface 14. The upper surface 12 comprises an upper front portion 16 and an upper rear portion 18, the upper rear portion being joined to the upper front portion by a sliding joint 20, such that a leading end 18a of the upper rear portion is positioned below a trailing end 16b of the upper front portion. The lower surface 14 comprises a lower front portion 22 and a lower rear portion 24, the lower rear portion being joined to the lower front portion by a sliding joint 26, such that a leading end 24a of the lower rear portion is positioned above a trailing end 22b of the lower front portion. The sliding joints 20, 26 comprise means (not shown) which do not permit the sliding joints to bend or twist. The constraint of rectilinear motion only of the trailing and leading ends 16b, 18a; 22b, 24a, which form part of the sliding joints 20, 26 is afforded by a suitable means, such as rail-and-car joints.

The leading end 16a of the upper front portion 16 is fixedly joined to the leading end 22a of the lower front portion 22, by a fixing means (not shown), such as rivets. Furthermore, the leading ends 16a, 22a of the front portions 16, 22 are fixed to a substantially non- deformable leading edge element 27 and maintain a fixed relative position at the leading edge 28 of the aerofoil The trailing end 18b of the upper rear portion 18 is fixedly joined to the trailing end 24b of the lower rear portion 24, by a fixing means (not shown) , such that the trailing ends 18b, 24b of the rear portions 18, 24 maintain a fixed relative position at the trailing edge 29 of the aerofoil 10.

The upper and lower surfaces 12, 14 thereby define an enclosed internal volume of the aerofoil 10. The internally-facing side of each respective surface portion 16, 18, 22, 24 is associated, by means of a rigidly-fixed joint 40, with an actuator 30, _32, 34, 36, respectively. The construction and functionality of each actuator 30, 32, 34, 36 are substantially the same. Therefore, to facilitate understanding, the upper front actuator 30 will be described (see Fig. 8). It will be understood that the properties relating to the upper front actuator 30 may be appropriately ^λreflected' in order to describe the properties of each one of the remaining actuators 32, 34, 36.

The upper front actuator 30 comprises a moving arm 38, a motor 39, and a motor housing 42. The motor 39, which may be software-controlled or otherwise, is housed within the motor housing 42, which comprises an attaching means 44. The attaching means 44 is rigidly fixed to a main spar 46, which extends into an internal region 60b of the aerofoil 10, such that a load applied to the actuator is transferred to the main spar. The moving arm 38 associates the actuator 30 with the upper front portion 16. One end of the moving arm 38 is connected to the motor 39, such that an actuation of the motor causes the moving arm to be displaced. An opposite end of the moving arm 38 is fixed, at a specific point 31, to the upper front portion 16, by means of the rigidly-fixed joint 40, such that a displacement of the moving arm effects a substantially equivalent displacement of the specific point on the upper front portion.

The moving arm 38 is constrained such that the rigidly-fixed end may only describe rectilinear motion in a direction substantially parallel to a cross- sectional tangent line 21 of the upper sliding joint 20. This constraint may be achieved by means of a predefined track in the motor housing 42, along which the moving arm 38 is driven; by means of runners, which are fixed to the trailing end 16b of the upper front portion 16a and which, on actuation of the motor 39 such that the upper front portion 16 is displaced, slide along a rigid bar; or by any other means ..known to a person skilled in the art.

The moving arm 38 is permitted to be extended from and retracted into the motor housing 42, such that the moving arm effects an associated and defined rectilinear displacement of the trailing end 16b of the upper front portion 16 in a direction substantially parallel to a cross-sectional tangent line 21 of the upper sliding joint 20.

As previously stated, the above description of the upper front actuator 30 may be applied to the upper rear actuator 32, the lower front actuator 34 or the lower rear actuator 36, by appropriate Reflections' of the aerofoil components. For example, the fixing end of the moving arm 38 of the lower rear actuator 36 is rigidly- fixed, at a specific point 37, to the lower rear portion 24 and is constrained to describe rectilinear motion in a direction substantially parallel to a cross-sectional tangent line of the lower sliding joint 26.

Hinged struts 48a-e extend between the upper and lower front surface portions 16, 22 and between the upper and lower rear surface portions 18, 24. Each hinged strut 48a-e has a first hinged joint 50a-e, joining one end of each hinged strut to a specific point 52a-e on the upper surface 12, and a second hinged joint 54a-e, joining the other end of each hinged strut to a specific point 56a-e on the lower surface 14. The distance along the upper rear portion 18, measured between the trailing edge 29 and the specific upper strut-joining point 52e on the upper rear portion, is arranged to be substantially equal to the distance along the lower rear portion 24, measured between the trailing edge and the specific lower strut-joining point 56e on the lower rear portion. This ^vertical' arrangement of the hinged strut 48e adjacent to the trailing edge 29 results in a trailing edge region 58, whose cross- section is a rigid isosceles triangle. In the same way, the distance along the upper front portion 16, measured between the leading edge 28 and the specific upper strut-joining point 52a on the upper front portion, is arranged to be substantially equal to the distance along the lower front portion 22, measured between the leading edge and the specific lower strut-joining point 56a on the lower front portion. This ^Λvertical' arrangement of the hinged strut 48a adjacent to the leading edge 28 results in a leading edge region 59, whose cross-section is a closed, symmetrical parabola. In addition, the distances along the upper and lower surfaces 12, 14, measured between the leading edge 28 or trailing edge 29 and respective specific upper and lower strut-joining points 52b-d, 56b-d are arranged to be substantially equal, such that the aerofoil 10 is symmetrically subdivided (in cross-section) into trapezium-shaped internal regions 60a-d by the hinged struts 48b-d. By virtue of the configuration of the aerofoil 10 with the hinged struts 48a-d, the shapes of the leading edge region 59 and the internal regions 60a-d are capable of being deformed.

The upper front actuator 30 may be actuated such that the moving arm 38 is forced to extend from the motor housing 42 in the direction of the leading edge 28. The remaining actuators 32, 34, 36 may be operated such that the position and orientation of their respective specific surface portion joining points 33, 35, 37 are maintained. This results in an extension of the upper surface 12, by forcing the point 52b immediately adjacent to the sliding joint 20 on the upper front portion 16 to separate further from the point 52c immediately adjacent to the sliding joint on the upper rear portion 18. Since the upper rear actuator 32 does not permit movement of the upper rear portion 18 of the upper surface 12, this extension effectively increases the cross-sectional length of the upper front portion 16, by reducing the area of overlap of the trailing end 16b of the upper front portion 16 and the leading end 18a of the upper rear portion 18. The trailing end 16b of the upper front portion 16 is forced to slide over the leading end 18a of the upper rear portion 18, up to an extent which is limited such that the leading end of the upper rear portion is maintained below and overlapped by the trailing end of the upper front portion. The lower front actuator 34 does not permit movement of the lower front portion 22, forcing the upper front portion 16 to form an increasingly- convex external surface. To accommodate this extension, the structures of the internal regions 59, 60a-b from the internal region 60b containing the main spar 46 to the leading edge region 59, are forced to change shape. The hinged struts 48a-b act as internal couples between the upper and lower front portions 16, 22, by relating the movement of the upper front portion to the lower front portion. The hinged struts 48a-b effect a controlled and supported deformation of the respective internal regions 59, 60a-b.

As illustrated in Fig. 2b, the leading edge 28 of the aerofoil 72 is therefore forced to assume a downward attitude with respect to. a chord line 70, which is formed as a straight line passing through the leading edge 28 and the trailing edge 29 of the unactuated aerofoil 10 of Fig. 1 and Fig. 2a. The trailing edge 29 is forced to maintain a level attitude with respect to the chord line 70. The aerofoil 72 illustrated in Fig. 2b exhibits increased positive camber.

In order to return this aerofoil 72 to the original, unactuated form of the aerofoil 10, the upper front actuator 30 is actuated such that the moving arm 38 is forced to retract into the motor housing 42 in an opposite direction to the direction of the leading edge 28. The remaining actuators 32, 34, 36 are again operated such that the position and orientation of their respective specific surface portion joining points 33, 35, 37 are maintained. This results, in a reduction' of the upper surface 12, by forcing the point 52b immediately adjacent to the sliding joint 20 on the upper front portion 16 to move towards the point 52c immediately adjacent to the sliding joint on the upper rear portion 18. Since the upper rear actuator 32 does not permit movement of the upper rear portion 18, this reduction effectively decreases the cross-sectional length of the upper front portion 16, by increasing the overlap of the trailing end 16b of the upper front portion and the leading end 18a of the upper rear portion. The lower front actuator 34 does not permit movement of the lower front portion 22, forcing the upper front portion 16 to form a decreasingly-convex external surface. To accommodate this return to the unactuated form of the aerofoil 10, the deformed structures of the internal regions 73, 74a-b are forced to reform the respective original shapes of the internal regions 59, 60a-b. The hinged struts 76a-b, acting as internal couples, relate the reverse movement of the upper front portion 16 to the lower front portion 22 and effect a controlled and supported reformation of the original internal regions 59, 60a-b. The leading edge 28 of the aerofoil 10 reassumes a level attitude with respect to the chord line 70, as illustrated in Fig. 2a. It will be within the understanding of a person skilled in the art that the individual actuation of any one of the actuators 30, 32, 34, 36, to extend or reduce its respective surface portion 16, 18, 22, 24, while maintaining the position and orientation of the remaining three surface portions, may be achieved in a similar manner to that described for the upper front portion 16.

Fig. 2c illustrates an aerofoil 78, wherein the lower front actuator 34 has been operated to extend the lower front portion 22 of the aerofoil. The lower front portion 22 has been forced to form an increasingly- convex external surface. The leading edge 28 of the aerofoil 78 is therefore forced to assume an upward attitude with respect to the chord line 70. The trailing edge 29 is forced to maintain a level attitude with respect to the chord line 70 and the aerofoil exhibits increased negative camber.

Fig. 2d illustrates an aerofoil 80, wherein the upper rear actuator 32 has been operated to extend the upper rear portion 18 of the aerofoil. The upper rear portion 18 has been forced to form an increasingly- convex external surface. The trailing edge 29 of the aerofoil 80 is therefore forced to assume a downward attitude with respect to the chord line 70. The leading edge 28 is forced to maintain a level attitude with respect to the chord line 70 and the aerofoil 80 exhibits increased positive camber.

Fig. 2e illustrates an aerofoil 82, wherein the lower rear actuator 36 has been operated to extend the lower rear portion 24 of the aerofoil. The lower rear portion 24 has been forced to form an increasingly- convex external surface. The trailing edge 29 of the aerofoil 82 is therefore_, forced to assume an upward attitude with respect to the chord line 70. The leading edge 28 is forced to maintain a level attitude with respect to the chord line 70 and the aerofoil 82 exhibits increased negative camber .-

Fig. 2f illustrates an aerofoil 84, wherein the upper front actuator 30 is operated, such that the moving arm 38 is forced to extend from the motor housing 42 in the direction of the leading edge 28, and the upper rear actuator 32 is operated, such that the moving arm 38 is forced to extend from the motor housing 42 in the direction of the trailing edge 29. The entire upper surface 12 is forced to form an increasingly-convex external surface. Both the leading edge 28 and the trailing edge 29 of the aerofoil 84 are therefore forced to assume a downward attitude with respect to the chord line 70. The aerofoil 84 exhibits greatly-increased positive camber. In order to achieve an even greater camber than that of the aerofoil 84 of Fig. 2f, actuators 34, 36 on the lower surface 14 may be operated. Lower front actuator 34 may be actuated such that the moving arm 38 is forced to retract into the motor housing 42 in a direction opposite to the direction of the leading edge 28. Lower rear actuator 36 may be actuated such that the moving arm 38 is forced to retract into the motor housing 42 in a direction opposite to the direction of the trailing edge 29. This configuration is illustrated in Fig. 2g. The leading and trailing edges 28, 29 of the aerofoil 86 have been forced to assume an even greater downward attitude with respect to the chord line 70.

Fig. 2h illustrates another configuration of an actuated aerofoil 88, wherein the moving arms 38 of the upper and lower front actuators 30, 34 are displaced equally, to extend in the direction of the leading edge 28, and the moving arms 38 of the upper and lower rear actuators 32, 36 are displaced equally, to extend in the direction of the trailing edge 29. This results in an aerofoil 88 having a greater longitudinal cross-section, with both leading and trailing edges 28, 29 maintaining a level attitude with respect to the chord line 70. The length of an aerofoil 10, 88 may be reduced in a similar, but reverse, manner to that described above.

All combinations of actuations, both extending and retracting, and non-actuations, of the upper and lower, front and rear actuators 30, 32, 34, 36 are envisaged and may be readily understood and achieved by a person skilled in the art.

Fig. 3 illustrates two aerofoil sections 100a, 100b of an aerofoil 100, which have been overlaid. The uppermost aerofoil section 100a has been produced by forcing the lower front and rear portions 22, 24 of the aerofoil 100 to extend, forming an aerofoil with- an increasingly-negative camber. The lowermost aerofoil section 100b has been produced by forcing the upper front and rear portions 16, 18 of the aerofoil 100 to extend, forming an aerofoil with an increasingly- positive camber. The aerofoil 100 is joined, by actuators (not shown), to a main spar 102, which extends into four internal regions 103a-e of the aerofoil 100. The internal regions 103a-e are defined by the subdivisions introduced by internal supports 104a-d. The main spar 102 is a fixed structure, which comprises three transverse accommodating channels 106a-c, extending from an upper surface to a lower surface of the main spar. Each of the three channels 106a-c accommodates a respective one of the three internal supports 104a-c adjacent to the leading edge 28 of the aerofoil 100.

The main spar 102 is either formed of one part or comprises three longitudinally-contiguous parts. Either way, the cross-section of the main spar 102 comprises three sections 102a-c. The first section 102a, adjacent the leading edge 28, is trapezium-shaped, having two transversely-parallel sides. The transverse side immediately adjacent to the leading edge 28 is shorter than the length of the opposing transverse side. The central section 102b is of rectangular cross-section. The two transverse sides of the rectangle are of the same length as the larger transverse side of the first section 102a, such that the contiguous sides of the first and central sections 102a, 102b are flush with each other. The third section 102c, furthest from the leading edge 28, is also trapezium-shaped, having two transversely-parallel sides. The transverse side adjacent to the central section 102b is of the same length as the transverse sides of the central section, such that the contiguous sides of the central and third sections 102b, 102c are flush with each other. The opposing transverse side of the third section 102c; is shorter than the shorter transverse side of the first section 102a. The first and second accommodating channels 106a, 106b adjacent the leading edge 28 are contained within the first section 102a. The upper and lower surface diameters of the first channel 106a are substantially equal, as are the upper and lower surface diameters of the second channel 106b. Inside the first channel 106a, the diameter changes linearly with depth, by changing the profile of the two opposing sides of the channel. From the upper surface to a central longitudinal axis of the section 102a, the diameter reduces to a minimum, and from the central longitudinal axis to the lower surface, the diameter increases back to that of the upper surface. Inside the second channel 106b, the diameter changes linearly with depth in the same manner as for the first channel 106a, except that one side of the channel 106b is contiguous with the central section 102b and therefore remains substantially vertical.

The third accommodating channel 106c is contained within the third section 102c, at the end which is contiguous with the central section 102b. The sides of the third channel 106c are both substantially vertical.

The configurations of the main spar 102 and the channels 106a-c permit the internal supports 104a-d to assume a range of positive and negative oblique attitudes and permit the surface portions to be adjusted to a range of orientations, such that a variety of aerofoil cambers may be produced in a system with a main spar 102 which is more expansive than the main spar 46 of Fig. 1.

Fig. 4 illustrates an aerofoil 110, intended for light-load applications, essentially corresponding to the aerofoil 10 of Fig. 1, wherein the load-transmitting components comprise four actuators 30, 32, 34, 36, one actuator joined to a respective one of each of the surface portions 16, 18, 22, 24. The internal supports 48a-d contribute to the distribution of the load throughout the upper and lower surfaces 12, 14 of the aerofoil 110, so that the load may be borne substantially equally by the actuators 30, 32, 34, 36.

In addition, the aerofoil 110 illustrates a rigid, non-deformable leading edge region 112 and a rigid, non- deformable trailing edge region 114. These regions 112, 114 are not capable of being deformed by extensions or reductions of the surface portions 16, 18, 22, 24, so the aerofoil 110 would only be capable of closely approximating to the profile of an aerofoil offering maximum deformations of internal regions. The aerofoil 110 also illustrates a simpler main spar 116 configuration, being rectangular in shape and containing two uniform accommodating channels 118a, 118b, both having two transverse sides. The first channel 118a contains the internal support 48b, which is adjacent to the upper and lower sliding joints 20, 26 and joins the upper and lower front portions 16, 22. The second channel 118b contains the internal support 48c, which is adjacent to the upper and lower sliding joints 20, 26 and joins the upper and lower rear portions 18, 24. Fig. 5 illustrates an aerofoil 120, intended for medium-load applications. In this embodiment, the spar comprises three parts: a main spar 122, a front spar 124 and a rear spar^" 126. The main spar 122 extends fully into the internal region 128c comprising the upper and lower sliding joints 20,^' 26 and partly into the two adjacent regions 128b, 128d. The front spar 124 extends fully into the internal region 128a adjacent to the leading edge 28 and partly into the adjacent region 128b. The rear spar 126 fully extends into the internal region 128e adjacent to the trailing edge 29 and partly into the adjacent region 128d. The front spar 124 is of essentially rectangular cross-section. The substantially transverse side of the front spar 124 abuts and is flush with the leading edge region 112. The opposing side is centrally angled and comprises a pivotal joint 134 at the apex. The front spar 124 is either formed of one part with the leading edge region 112 or is contiguous with and rigidly-fixed to the leading edge region. The apex of the angled side of the front spar 124 is joined, by the pivotal joint 134, to the main spar 122, at a central point on the transverse side facing the leading edge 28. The upper corner 136 of the opposing side of the front spar 124 is rigidly-fixed to the upper front portion 16 and the lower corner 138 of the same side is rigidly-fixed to the lower front portion 22, at points on the upper and lower front portions where the leading edge region 112 ends .

The rear spar 126 is of essentially rectangular cross-section. The substantially transverse side of the rear spar 126 abuts and is flush with the trailing edge region 114. The opposing side is centrally angled and comprises a pivotal joint 140 at the apex. The rear spar 126 is either formed of one part with the trailing edge region 114 or is contiguous with and rigidly-fixed to the trailing edge region. The apex of the angled side of the rear spar 126 is joined, by the pivotal joint 140, to the main spar 122, at a central point on the transverse side facing the trailing edge 29. The upper corner 142 of the opposing side of the rear spar 126 is rigidly-fixed to the upper rear portion 18 and the lower corner 144 of the same side is rigidly-fixed to the lower rear portion 24, at points on the upper and lower rear portions where the trailing edge region 114 ends. One actuator 146 is located above and one actuator 148 is located below the pivotal joint 134 between the front spar 124 and the main spar 122, such that controlled relative movement between the front and main spars may be achieved. These two actuators 146, 148 comprise a front actuator set. Similarly, one actuator 150 is located above and one actuator 152 is loca.ted below the pivotal joint 140 between the rear spar 126 and the main spar 122, such that controlled relative movement between the rear and main spars may be achieved. These two actuators 150, 152 comprise a rear actuator set.

The front spar 124 comprises one accommodating channel for an internal support 48a. The rear spar 126 comprises one accommodating channel for an internal support 48d. The main spar 122 comprises two accommodating channels, one for an internal support 48b on the leading edge 28 side and one for an internal support 48c on the trailing edge 29 side of the upper and lower sliding joints 20, 26.

In this configuration, there are no actuators joined to the surface portions 16, 18, 22, 24, so actuation of the surface portions is effected by movements of the upper and lower corners 136, 138, 142, 144 of the front and rear spars 124, 126. These movements are controlled by the actuators 146, 148, 150, 152, between the front and main spars 124, 122 and between the rear and main spars 126, 122, in a similar manner to that described above. However, the actuation of one of the actuators 146, 148, 150, 152 in either the front or rear actuator set must include a reciprocal actuation of the other actuator in that set, such that movement of the front spar 124 or rear spar 126 may be permitted. For example, actuation of the upper front actuator 146, such that the moving arm 38 is forced to extend from the motor housing 42 of the upper front actuator in the direction of the leading edge 28, is accompanied by a reciprocal actuation of the lower front actuator 148, such that the moving arm 38 is forced to retract into the motor housing 42 of the lower front actuator in the direction opposite to the direction of the leading edge 28.

The load in the aerofoil 120 is transmitted to the main spar 122 from the front and rear spars 124, 126, being shared by the actuators 146, 148, 150, 152 and the pivotal joints 134, 140. The aerofoil 120 is therefore capable of being subjected to a greater maximum load than the aerofoil 110 of Fig. 4.

Fig. 6 illustrates an aerofoil 160 intended for heavy-load applications. The aerofoil 160 comprises all of the features of the aerofoil 120 of Fig. 5, and additionally comprises the actuators 30, 32, 34, 36, as located and described with reference to the aerofoil 10 of Fig. 1.

Movement of the surface portions 16, 18, 22, 24 may be effected by actuation of the surface actuators 30, 32, 34, 36 and the spar actuators 146, 148, 150, 152, in a manner similar to that described above. However, the actuation of one of .the front surface or spar actuators 30, 34, 146, 148 or one of the rear surface or spar actuators 32, 36, 150, 152, may include reciprocal and cooperating actuations of the other actuators in the front or rear of the aerofoil 160. For example, actuation of the upper front spar actuator 146, such that the moving arm 38 is forced to extend from the motor housing 42 is accompanied by: a cooperating extension of the moving arm 38 of the upper front surface actuator 30; and a reciprocal retraction of the moving arm 38 of the lower front spar actuator 148. 22 -

movement of the front spar 124 or rear spar 126 may be permitted. For example, actuation of the upper front actuator 146, such that the moving arm 38 is forced to extend from the motor housing 42 of the upper front actuator in the direction of the leading edge 28, is accompanied by a reciprocal actuation of the lower front actuator 148, such that the moving arm 38 is forced to retract into the motor housing 42 of the lower front actuator in the direction opposite to the direction of the leading edge 28.

Movement of the surface portions 16, 18, 22, 24 may be effected by actuation of the surface actuators 30, 32, 34, 36 and the spar actuators 146, 148, 150, 152, in a manner similar to that described above. However, the actuation of one of the front surface or spar actuators 30, 34, 146, 148 or one of the rear surface or spar actuators 32, 36, 150, 152, may include reciprocal and cooperating actuations of the other actuators in the front or rear of the aerofoil 160. For example, actuation of the upper front spar actuator 146, such that the moving arm 38 is forced to extend from the motor housing 42 is accompanied by: a cooperating extension of the moving arm 38 of the upper front surface actuator 30; and a reciprocal retraction of the moving arm 38 of the lower front spar actuator 148. - 23 -

There may also be a^' reciprocal retraction of the moving arm 38 of the lower front surface actuator 34.

The use of eight actuators 30, 32, 34, 36, 146, 148, 150, 152 in this configuration permits deflections of the surface portions 16, 18, 22, 24 to be achieved in a stable and controlled manner.

The load in the aerofoil 160 is transmitted to the main spar 122 from the front and rear spars 124, 126, being shared by the actuators 146, 148, 150, 152 and the pivotal joints 134, 140, and from the upper and lower surface portions 16, 18, 22, 24, being shared by the actuators 30, 32, 34, 36. The aerofoil 160 is therefore capable of being subjected to a greater maximum load than the aerofoil 120 of Fig. 5. Figs. 7a-b illustrate aerofoils 170, 190, which comprise variable load-bearing devices 172a-f; 192a-f, 193a-f, extending from the upper surface to the lower surface. The aerofoils 170, 190 have been pre-arranged such that the initial profiles of the aerofoils are ones with positive camber and with the attitudes of the leading and trailing edges 28, 29 assuming a downward attitude with respect to the chord line 70. The aerofoils 170, 190 comprise multiple upper and lower surface portions and multiple upper and lower sliding joints.

The aerofoil 170 of Fig. 7a illustrates the use of rubber blocks 172a-ⁱf as variable load-bearing devices. Each of the rubber blocks 172a-f is essentially identical, although the exact size and shape of individual blocks may vary. For ease of understanding, only the rubber block 172a closest to the leading edge 28 will be described. The cross-section of the rubber block 172a comprises two opposing substantially triangular sections 174a, 174b. The ^λbase' of the upper triangular section 174a is fixed to a trailing end portion 176b of a first upper portion 176 and to a leading end portion 178a of a second upper portion 178b, - 24,

immediately adjacent the first portion but further from the leading edge 28. The base of the lower triangular section 174b is fixed to a trailing end portion 180b of a first lower portion 180 and to a leading end portion 182a of a second lower portion 182, immediately adjacent the first portion but further from the leading edge 28. In this initial configuration, the rubber blocks 172a-f are substantially unstressed. As a load on the aerofoil 170 increases, with increasing lift, the rubber blocks 172a-f are increasingly stressed. The lower triangular section 174b is therefore placed under increasing tension and the upper triangular section 174a is placed under increasing compression, such that the rubber blocks are forced to change shape. The sliding joints accommodate the resulting surface portion displacements and the overall camber of the aerofoil 170 becomes decreasingly positive, reducing the lift on the aerofoil. This process continues until the lift produced by the aerofoil 170 has decreased to such an extent that the loading of the rubber blocks 172a-f causes no further change of shape. If the lift on the aerofoil 170 is then reduced, the restoring force of the rubber blocks 172a-f acts to return the rubber blocks to their original shape. This, in turn, increases the camber and produces increasing lift, until the loading of the rubber blocks 172a-f is balanced by the restoring force.

A designed maximum lift, which can be made independent of operational variables, such as speed, is thereby achieved. A range of desired maximum lifts for an aerofoil 170 can be produced by selecting the specific composition, size and shape of the rubber blocks 172a-f and the initial aerofoil section profile at the time of manufacture of the aerofoil. Other parameters, such as the number of rubber blocks used, may also be varied.

Fig. 7b illustrates the use of springs 192a-f, 193a-f as variable load-bearing devices. The aerofoil - 25 -

190 comprises pairs of pivotally-mounted crossed struts 194a-f, 196a-f, each respective pair comprising two springs 192a-f, 193a-f. For ease of understanding, the crossed struts 194a, 196a immediately adjacent the leading edge 28 will be described, since each of the pairs of struts 194a-f, 196a-f behaves in a substantially identical manner.

The first strut 194a of the pair has an upper end pivotally-joined to a point 198b near a trailing end of a first upper portion 198, adjacent the leading edge 28. A lower end of the first strut 194a is pivotally-joined to a point 204a near a leading end of a second lower portion 204, adjacent a first lower portion 202 immediately adjacent the leading e'dge 28. The second strut 196a of the pair has an upper end pivotally-joined to a point 200a near a leading end of a second upper portion 200, adjacent the first upper portion 198. A lower end of the second strut 196a is pivotally-joined to a point 202b near a trailing end of the first lower portion 202. The crossed struts 194a, 196a are pivotally-joined at the intersection of the struts. There is an upper spring 192a fixed between the upper ends of the crossed struts 194a, 196a and a lower spring 193a fixed between the lower ends of the struts. This configuration of springs 192a-f, 193a-f and crossed struts 194a-f, 196a-f behaves in a substantially identical manner to that described above, in which the variable load-bearing devices are rubber blocks 172a-f, but, in the present embodiment, it is the springs which are subjected to tensile and compressive forces.

It is envisaged that the sliding joint 20, 26 may be replaced by an expanding joint, or any joint which would permit rectilinear motion of the trailing and leading ends of the surface portions adjacent the joint in a direction substantially parallel to a cross- sectional tangent line 21 of the joint. One example of an expanding joint is rubberised sheeting. In such an - 26

embodiment, the trailing end of a first surface portion adjacent the joint would no longer overlap the leading end of a second surface portion adjacent the joint. Instead, the surface portion trailing and leading ends would lie substantially within the same plane, being separated from and attached to each other by the rubberised sheeting.

It is envisaged that some of the internal supports 48a-e described above may be rigidly-fixed. Alternatively, the internal supports 48a-e may be extendable internal supports. Additionally, the supports 48a-e may be any combination of hinged, rigidly-fixed or extendable supports. The extendable supports may change length automatically, to accommodate the actuation of the surface portions 16, 18, 22, 24. The extendable supports' 48a-e may also change length in response to actuators which control the supports. This embodiment provides a further range of continuously-variable cross- sections of the aerofoil. It is also envisaged that the internal supports

48a-e may not fully extend from points 52a-e on the upper surface 12 to points 56a-e on the lower surface 14. Instead, an internal support 48a-e may be replaced by at least two actuators, at least one actuator being joined to the upper surface 12 and at least one actuator being joined to the lower surface 14, such that these actuators simulate the effect of a fully-extending internal support.

Additionally, it is envisaged that the actuation means for displacing the upper and lower surface portions may comprise a gear wheel, which is mounted on a transverse side of the main spar and which may be actuated, and an engageable rack, being rigidly-fixed between an upper surface portion and its respective lower surface portion and having a virtual pivot located within the spar and between the upper and lower sliding joint . - 27

If full aerodynamic performance is not required, it will be understood that the continuously-curving surface portions 16, 18, 22, 24 may be replaced by a set of planar surfaces. These planar surfaces may be joined at each intersection by an internal support 48a-e, as described above, such that the surfaces may approximate to the continuous surface portion 16, 18, 22, 24 profiles .

It is envisaged that the aerofoils described in accordance with the invention may be used in various applications .

For example, the aerofoils may be used as aircraft wings. In this application, the aerofoils would be capable of providing variable camber, from positive through to negative, and therefore, variable lift. One advantage of the aerofoils in this embodiment is the possibility of providing a differential lift between the wings of an aircraft, to facilitate aircraft roll, although many other advantages have been outlined above and will be apparent to a person skilled in the art.

In a second example, the aerofoils may be used as battens in the sailcloth of a sailing vessel. In this application, the aerofoils would be capable of improving the profiles of sails and providing sails which may be controllably-tacked.

In a third example, the aerofoils may be used as spoilers in motor vehicles, and especially in racing cars. In this application, the aerofoils would be used to reduce or eliminate lift and/or provide down force on the vehicles. Additionally, the aerofoil comprising variable load-bearing devices could be used to provide a designed down force on a vehicle at high speeds, which is substantially independent of speed.

Any application in which a wing, a sail, a foil or a blade may advantageously comprise the features of the present invention is envisaged.

Claims

28Claims :

1. An aerofoil comprising: a first surface, comprising a deformable leading surface portion and a deformable trailing surface portion, the surface portions defining adjacent edges; and a second, opposing surface; the first and second surfaces being fixed to each other at respective leading and trailing ends, such that a deflection in one of the surfaces is transmitted to the other of the surfaces via one or both of the leading and trailing ends, wherein both of the surface portions are adapted to be independently moveable with respect to the other, such that the aerofoil may assume a range of positive, neutral or negative aerodynamic profiles.

2. The aerofoil of claim 1, wherein said surface portions are adapted to be moveable with respect to each other such that one or both of said adjacent edges move towards or away from said leading and trailing ends so as to cause a deflection in said first and second surfaces .

3. The aerofoil of claim 2, wherein said adjacent edges are adapted to move in a substantially rectilinear motion in a direction substantially parallel to a cross- sectional tangent line of said first surface in the proximity of said adjacent edges.

4. The aerofoil of any preceding claim, wherein said first surface comprises a plurality of surface portions in excess of two, said plurality of surface portions defining respectively-adjacent edges being adapted to move towards or away from said leading and trailing ends . - 29 -

5. The aerofoil of any preceding -claim, wherein said second surface additionally or alternatively comprises a plurality of surface portions in excess of two, said plurality of surface portions defining respectively- adjacent edges being adapted to move towards or away from said leading and trailing ends.

6. The aerofoil of any preceding claim, further comprising joining means for associating respective ones of said adjacent edges.

7. The aerofoil of claim 6, wherein said joining means comprise a sliding joint or an expanding joint, and means for constraining the relative motion of said adjacent edges, such that rectilinear motion is described.

8. The aerofoil of any of claims 3 to 7, further comprising actuation means for effecting said rectilinear motion of said adjacent edges.

9. The aerofoil of any of claims 6 to 8, wherein said rectilinear motion is effected by a constraint either in the joining means or in the actuation means.

10. The aerofoil of claim 8 or claim 9, further comprising a main -spar, wherein said actuation means comprises actuators, each comprising a moving arm, a motor, a motor housing and an attaching means, wherein each one of said moving arms of said actuators is fixed to a specific point on a respective one of said surface portions and said attaching means of each of said actuators is rigidly attached to said main spar.

11. The aerofoil of claim 10, wherein an actuation of said motor causes said moving arm to be either extended from or retracted into said motor housing, such that an 30 -

associated and defined rectilinear- motion of at least one edge of said adjacent edges is effected, and the position and orientation of each displaced one of said specific points is defined.

12. The aerofoil of any of claims 8 to 11, wherein said actuation means is actuatable a selected one of: (a) mechanically, (b) hydraulically, and (c) electrically.

13. The aerofoil of any of claims 8 to 12, wherein said actuation means is software-controlled.

14. The aerofoil of any of claims 8 to 13, wherein any one of said actuators may be actuated separately, or in combination with other ones of said actuators.

15. The aerofoil of any of claims 8 to 14, wherein ones of said actuators may be actuated, while other ones of said actuators may either be employed to constrain said adjacent edge such that said edge is not permitted to be displaced, or, may permit said edge to be displaced in accommodating response to a displacement of said actuated surface portion.

16. The aerofoil of any preceding claim, further comprising a plurality of internal supports having a first end and a second end and extending between said first and second surfaces, said first end of each of said internal supports being joined to said first surface and said second end of each of said internal supports being joined to said second surface, wherein said internal supports are adapted to act as internal couples between said surface portions of said surfaces.

17. The aerofoil of claim 16, wherein said internal supports are a selection of or combination of: (a) hinged, (b) rigidly-fixed, and (c) extendable. - 31 -

18. The aerofoil of claim 16 or claim 17, wherein, in an unactuated aerofoil, the distance between said first end of each respective one of said internal supports and said forward end of said aerofoil is substantially equal to the distance between said second end of each respective one of said internal supports and said forward end.

19. The aerofoil of claim 18, wherein, in an unactuated aerofoil, said distances are substantially unequal.

20. The aerofoil of any of claims 17 to 19, wherein said extendable internal supports are adapted to extend automatically, such that said extendable internal supports may accommodate an actuation of said surface portions, or in response to additional actuators controlling said extendable internal supports.

21. The aerofoil of any of claims 16 to 20, wherein said internal supports do not extend fully between said first and second surfaces and each of said supports comprises a support actuator in association with said first surface and a support actuator in association with said second surface, such that the effect of said fully- extending supports is simulated by said support actuators .

22. The aerofoil of any of claims 10 to 21, wherein said main spar comprises transverse accommodating channels, extending from a first surface of said main spar to a second opposing surface of said main spar, wherein ones of said internal supports extend therethrough.

23. The aerofoil of any of claims 10 to 22, wherein said main spar further comprises at least two spar sections, wherein adjacent sides of said sections are - 32 -

pivotally joined^" to each other by a pivotal joint, outer sides of said sections are fixed to said first and second surfaces by rigid joints, and said actuation means comprise at least one actuator disposed on a first side of each of said pivotal joints and at least one actuator disposed on a second side of each of said pivotal joints, either in addition to or in substitution of said surface portion actuators according to an intended load for said aerofoil.

24. The aerofoil of any of claims 16 to 23, wherein load-bearing and load-transferring devices comprise said actuators, said internal supports and said main spar, and may further comprise variable load-taking devices, for example, rubber blocks or springs.

25. The aerofoil of claim 24, wherein said variable load-taking devices are adapted to be substantially unstressed in a pre-arranged positive or negative camber aerofoil, such that a predetermined maximum lift may be achieved.

26. The aerofoil of any of claims 10 to 25, wherein said actuation means alternatively comprises an actuatable gear wheel, mounted on an outer and transverse side of said main spar, in engagement with a rack, rigidly-fixed between said first surface and said second surface, having a virtual pivot located within said main spar.

27. The aerofoil of any of claims 16 to 26, wherein said surface portions alternatively comprise a set of planar surfaces being joined at each intersection by said internal supports.

28. The aerofoil of any preceding claim, as employed in a selection of: a) wing, b) sail, c) foil, and d) blade. - 33, -

29. One of: a) an -aircraft, b) a marine vessel, and c) a motor vehicle, in which the aerofoil of any preceding claim is employed.

30. An aerofoil, as substantially herein described with reference to the accompanying drawings.