WO2012005600A1

WO2012005600A1 - An inflatable wing with inflatable leading edge spar and rib(s) in the form of inflatable truss(es)

Info

Publication number: WO2012005600A1
Application number: PCT/NZ2011/000092
Authority: WO
Inventors: Richard John Roake
Original assignee: Aquadria Kite Design Limited
Priority date: 2010-06-02
Filing date: 2011-06-02
Publication date: 2012-01-12
Also published as: NZ587521A

Abstract

An inflatable wing for a traction kite, the wing including: a flexible envelope having a first sheet and a second sheet, the first and second sheets joined together at a leading edge and a trailing edge; an inflatable leading edge spar located within the flexible envelope and attached to the flexible envelope substantially along the leading edge; and an inflatable rib located within the envelope and extending from the leading edge spar generally towards the trailing edge, characterised in that the inflatable rib includes a first inflatable chord and a second inflatable chord spaced apart from the first chord for at least a length of the rib, and one or more inflatable struts extending between the first chord and the second chord, the rib configured such that, when inflated, the first chord, second chord and the strut(s) form a truss.

Description

AN INFLATABLE WING WITH INFLATABLE LEADING EDGE SPAR AND RIB(S) IN THE FORM OF INFLATABLE TRUSS(ES)

TECHNICAL FIELD

The present invention relates to an inflatable propulsive wing of the type used in traction kites to provide a traction force and/or for lifting or pulling a load via lines attached to the wing. In particular the invention relates to an inflatable wing having an upper and a lower outer skin joined to form a flexible envelope having a leading edge and a trailing edge, and an inflatable rib extending from the leading edge towards the trailing edge of the wing, the wing having a curved profile across the span when inflated. The inflatable wing may be configured as a kite to provide traction to an attached load, and as such may be generally used in a similar manner to other inflatable kites, such as, without limitation, Leading Edge Inflatable (LEI) kites, bow kites and hybrid kites. However, it is envisaged that the inflatable wing may also find applications in devices other than kites and reference to its use as a wing for a kite should not be seen as limiting.

BACKGROUND ART

The use of Inflatable wings is increasingly common in many activities, especially sport and recreational activities involving the use of an inflatable wing configured as a traction kite to provide traction to a person on a device for moving or sliding over water (kitesurfing, kiteboarding etc) or land (kite buggying, kiteskiing, etc). Most traction kites commonly used in these activities use a wing either of the leading edge inflatable (LEI) type or a variant thereof. Sporting activities using LEI kites (and related variants) have become extremely competitive and there is very high demand for a wing/kite that can provide improved performance over existing wings/kites. The basic concept of an LEI wing was disclosed by D and M Legaignaux in US 4,708,078 ("Legaignaux"). Legaignaux discloses a wing configured like a spherical segment, or arc shaped spanwise. The wing has a light weight skin formed from a flexible material. Typically an LEI kite wing has a single skin which forms the canopy for the kite.

An LEI kite wing includes inflatable tubes preformed to create a leading edge spar and generally one or more ribs extending chordwise between the leading edge and trailing edge of the wing. The spar and ribs of an LEI kite wing are generally formed by enclosing an airtight bladder within a more robust outer part that is configured to provide the desired shape of the spar or rib. The leading edge spar is attached to, or more generally enveloped by the flexible skin forming the leading edge of the kite, the shape of the inflatable leading edge spar being chosen and preformed to create the desired spanwise shape of the leading edge of the kite. Likewise, the shape of the outer part of a rib may be preformed to provide a desired shape. A traction kite is formed by attaching one or more control lines to the wing tips of the LEI kite wing, the other end of the lines generally terminating in a control bar. The control bar is typically attached to a harness for holding the person operating the kite.

The LEI kite, while very successful, has a number of disadvantages, including difficulties experienced by users in controlling the kite in flight and in maintaining the desired aerodynamic performance for the wing at all times.

A further disadvantage, common to all LEI kites, is the amount of time and effort required to inflate the leading edge spar and the ribs. The leading edge spar, for example, can have a diameter of 80mm or more in the central, midspan, portion. Even with modern pumps it can take many minutes to inflate the spar to the required pressure, which is not only time consuming but can be generally frustrating and inconvenient to a user.

This problem is exacerbated when ribs are inflated as well. It is common for an LEI kite wing to have 5 -7 ribs spaced across the span of the wing. Inflation of the ribs as well as the leading edge spar can increase the inflation time considerably. Partly because of this the size of the rib bladders is generally a trade off between the desire to provide shape and stiffness to the chordwise profile and the need to keep inflation time at an acceptable level. As a consequence the ribs are generally much smaller than required to hold the chordwise profile of the kite wing in an aerodynamically efficient shape.

Further, the shape of the leading edge, without further modification, is generally restricted to a semi circular arc shape. This may not be the best shape for all purposes, and maintaining even that shape in changing conditions, as can be common in flight, can be difficult. Failure to control the shape of the wing correctly can lead to loss of boundary layer stability/lift and/or in extreme cases collapse of the wing, which can lead to injury or fatality, especially if the user was airborne at the time.

Various modifications to the Legaignaux design have been made since it was patented in 1987. For example, US 2002/0185570 A1 (to Winner) discloses the addition of cross bridle lines attached to the leading edge of the wing enable the turning radius of the kite to be altered to suit different wind conditions. Other developments include adding further bridle lines attached to the leading and trailing edges of the wing to improve control and to maintain a desired shape to the wing in varying conditions. US 2009/0277997 (to Shogren et al.) discloses a leading edge formed from a plurality of spaced segments fabricated from a material having a high elasticity in order to allow greater twisting and bending of the leading edge. The shape of the leading and trailing edges in Shogren is controlled by a plurality of additional bridle lines attached at various points along the edges.

While this construction may improve the flexibility of the leading edge, it comes at the cost of increased complexity of construction and hence cost of the wing/kite to the user.

Moreover the additional control/bridle lines add complexity to the control required of a user, as well as adding weight to the kite and increasing the drag forces experienced by the kite, both of which are undesirable where high performance is a requirement.

US 6,837,463 (to Lynn) discloses a double skin, bladderless wing including a plurality of cells formed between the skins by chordwise-extending ribs. The cells are formed as walls of flexible material extending in a chordwise direction between the skins. The wing includes valved openings to the cells, situated near the leading edge, to allow ram air to inflate the wing. The shape of the wing in chordwise profile is held under tension by the walls of the cells.

One disadvantage of the "ram air" wing is that, while the shape may be held when the pressure difference between the skins holds the cell walls in tension, there is little resistance to compression, which can lead to partial or full collapse of the pressure inside the cell under certain conditions. Another disadvantage is the large number of lines used to maintain the shape of the ram air wing and to control it during flight. The lines add weight to the kite, can generate considerable additional drag forces and can become tangled, all of which reduce the performance and usability of the ram air wing. A further disadvantage is that it can be difficult for a user to control the shape of the wing section during flight. It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

It is another object of the present invention to provide an inflatable wing for a kite or other application where the time and effort required to inflate the wing is significantly reduced.

It is another object of the present invention to provide an inflatable wing which allows designers to create an aerodynamically efficient shape for the inflated wing.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

STATEMENT OF INVENTION

According to one aspect of the present invention there is provided an inflatable wing for a traction kite, the wing including:

a flexible envelope having a first sheet and a second sheet, the first and second sheets joined together at a leading edge and a trailing edge; and

an inflatable rib located within the envelope and extending substantially from the leading edge generally towards the trailing edge, characterised in that

the inflatable rib is attached to the first and second sheets.

According to another aspect of the present invention there is provided an inflatable wing for a traction kite, the wing including:

a flexible envelope having a first sheet and a second sheet, the first and second sheets joined together at a leading edge and a trailing edge;

an inflatable leading edge spar located within the flexible envelope and attached to the flexible envelope substantially along the leading edge; and

an inflatable rib located within the envelope and extending from the leading edge spar generally towards the trailing edge, characterised in that

the inflatable rib includes a first inflatable chord and a second inflatable chord spaced apart from the first chord for at least a length of the rib, and one or more inflatable struts extending between the first chord and the second chord, the rib configured such that, when inflated, the first chord, second chord and the strut(s) form a truss.

Reference to an inflatable wing throughout this specification should be understood to mean a wing constructed in such a way that the wing is formed when air (or some other gas) is pumped into a compartment or compartments within the wing.

Reference to a first and/or second sheet throughout this specification should be understood to refer to an outer skin of the inflatable wing. With reference to a wing in normal (i.e., not inverted) flight, a first sheet may form the upper skin or surface of the wing, and a second sheet may form the lower skin or surface of the wing (or vice versa). The lower sheet forms the primary tension member of the present invention.

Reference to a sheet includes the situation where a surface of the wing is formed from a plurality of panels of flexible material which are joined together to form the sheet.

Accordingly, reference to the first sheet and second sheet being joined together at a leading edge and a trailing edge should be understood to mean that the sheets forming the upper and lower surfaces of the wing are joined at the leading and trailing edges of the wing. This should be understood to include the situation where the join between the first sheet and the second sheet is formed from a continuous section of flexible material - i.e., it may be the surfaces that join in a continuous manner (along an imaginary line), rather than strictly a join in the material forming the sheets.

The sheets of the present invention are formed from flexible material and joined together as described to form a flexible envelope, i.e. having a substantially enclosed space between the first and second sheets.

In one aspect of the present invention an inflatable rib is located within the substantially enclosed space between the first and second sheets and attached to them.

In some embodiments the inflatable rib may include a bladder, or a series of bladders which may be enclosed in an outer sheath, which, when the bladder is inflated substantially fills a volume between the sheets of the envelope.

An advantage of this embodiment is that the rib, when inflated, may provide separation between the sheets and longitudinal (chordwise) stiffness to the inflated wing. The shape of the rib may be chosen to provide an aerodynamic shape (in lateral cross section ie, in the direction from the leading edge to the trailing edge of the wing) of the surfaces of the wing, thus improving the flight characteristics of the wing.

However, generally the size of such a rib is too large to be practical in everyday use, especially if the wing is used sporadically (as in sporting applications for example) and has to be inflated before each use, in which case the amount of time spent inflating the rib may be such that it detracts from the usability of this embodiment.

An inflatable rib, according to another aspect of the present invention, forms a truss when inflated. Reference to a truss should be understood to mean a structural member in the form of a web composed of contiguous triangles. A truss typically has a number of structural members, including longitudinal members, in the form of an upper and a lower chord, and a plurality of straight struts which form vertical of diagonal support members between the upper and lower chords.

An early and relatively simple form of truss, known as the Warren Truss, used only diagonal struts arranged to create a web of contiguous equilateral triangles. However, as those skilled in the art will appreciate, numerous variants of this basic arrangement have been developed and used, and reference to a truss throughout this specification should be understood to refer to any of the numerous variants.

A truss is designed so that the members only act in compression or tension. The region where the straight struts meet with a chord will be referred to as a node. The construction of the truss is such that the forces at a node are balanced (i.e., when all the tensile and compressive forces of each member at the node are added together the result is zero).

A significant feature of all truss structures is that they provide a relatively stiff and stable structure which is able to support considerable loads, while using relatively small amounts of material (in comparison to other load bearing structures).

In preferred embodiments the inflatable wing includes an inflatable leading edge spar as is well known to those skilled in the art, the inflatable leading edge spar configured to provide shape to the leading edge as well as latitudinal (spanwise) stiffness to the leading edge. The leading edge spar may be of the type commonly used in a wing of a Leading Edge Inflatable (LEI) kite, such as a C kite, and in more recent variants of the LEI kite, such as bow kites and hybrid kites.

LEI kites typically have only a single sheet to which the leading edge spar and a plurality of ribs are attached. The present invention differs from such single sheet kites by including two sheets joined together at the leading and trailing edges to form a flexible envelope. The inflatable leading edge spar is attached to the interior of the flexible envelope along the leading edge of the envelope. The leading edge spar may be formed as a single armature, as in the early LEI kite designs, or the spar may be formed from a plurality of segments as in more recent designs.

The inflatable wing of the present invention includes at least one, and generally a plurality of, inflatable rib(s) which extend from the leading edge, or from the inflatable leading edge spar, towards the trailing edge of the wing. In the preferred aspect of the present invention the inflatable rib forms a truss (to be referred to as a rib truss) when inflated. The rib truss includes a first inflatable chord and a second inflatable chord, which for convenience of visualisation will be referred to as the upper and lower chords respectively, and a plurality of struts, all of which are inflatable. A key feature of the rib truss is that the dimensions of the members that make up the truss are small in comparison with the separation of the chords, especially in the vicinity of the centre of the truss.

In a preferred embodiment the diameter of an inflated chord of the truss is in the range from 8 mm to 15 mm. In a preferred embodiment the diameter of an inflated strut of the truss is in the range from 8 mm to 15 mm.

Use of a chord or strut having a diameter within the above ranges in a rib truss may provide a significantly stiffer structure than a bladder having a diameter of the same width as the rib truss when inflated to the same pressure. As a result, the volume of a rib truss (ie the inflatable volume of the chords and struts) needed to provide a structurally stiff rib may be significantly lower than the inflatable volume of a comparable rib formed from a bladder.

This may reduce the amount of material required to form the rib, thus saving cost and weight, but most importantly may significantly reduce the amount of time required to inflate the rib. The applicants estimate that an inflatable rib truss may be formed with 8%- 30% (for 8mm - 15mm diameter struts and chords respectively) of the volume of a comparable rib formed from a bladder, with commensurate reduction in inflation times.

In a preferred embodiment a plurality of inflatable struts and an inflatable chord are connected together to form a node, the configuration of the struts and chord at the node being arranged such that, when inflated, the forces exerted at the node by the struts and the chord are balanced.

A rib truss may have a plurality of nodes along the upper and lower chords, the specific design depending on the size of the rib and the required stiffness produced by the truss. The amount of stiffness required may vary along the length of the rib and the design of the rib truss may be chosen to achieve the desired stiffness of each section of the rib truss.

In a preferred embodiment a central rib is located along a chord line corresponding to the centre of the span of the wing. In at least one model for analysing the flight characteristics of a wing the sum of the lift forces are considered to act at a single point on the mid-span chord line, known as the centre of lift. The centre of lift is not a fixed point but moves along the mid-span chord line under different flight conditions as the angle of attack (the angle between the apparent wind direction (or wing velocity vector) and the chord line) varies. However, designers may typically design a wing for optimal performance under a prescribed set of conditions, including a preferred angle of attack for a particular wing section. The centre of lift under the design set of conditions will be referred to as the design centre of lift.

In a preferred embodiment the central rib includes a node located at or in close proximity to the design centre of lift of the wing.

An advantage of placing a node at the design centre of lift (in practice at either or both the upper or/and lower chords above and below the design centre of lift respectively) is that it may provide the required stiffness of the wing at the design centre of lift and enable the load at the design centre of lift to be distributed appropriately throughout the rib truss.

In a preferred embodiment at least one of the first and second inflatable chords is pneumatically interconnected to the inflatable leading edge spar.

An advantage of connecting a rib truss, or at least a chord of it, to the inflatable leading edge spar is that the wing may then be inflated from a single air inlet. This may save time as a pump need only be connected (and disconnected) once to inflate the wing. However, in some embodiments several inflation points may be used.

In a preferred embodiment the inflatable strut is pneumatically interconnected to at least one of the first and second inflatable chords.

Once again, the advantage of pneumatically interconnecting each strut to at least one of the chords is to enable the rib truss to be inflated from a single point, since in preferred

embodiments at least one chord is pneumatically connected to the inflatable leading edge spar.

In a preferred embodiment the first inflatable chord is attached to the first sheet of the flexible envelope.

In a preferred embodiment the second inflatable chord is attached to the second sheet of the flexible envelope. Attaching the chords to the sheets in this manner not only locates and orientates the rib truss in the desired location within the flexible sheet, but also enables the rib truss to be configured to define a desired shape of the wing along the rib.

In a preferred embodiment the first chord is curved when inflated. In a preferred embodiment the second chord is curved when inflated.

In a preferred embodiment the first chord and second chord form an aerodynamic shape when inflated.

Reference to an aerodynamic shape should be understood to mean a shape which provides a high aerodynamic efficiency to the wing.

This ability to design the shape of the chords of the rib truss is a significant advantage in enabling the design of wings (and kites) having high aerodynamic efficiency, something which is difficult to obtain with single skin wings such as used in most traction kites.

In particular the increased stiffness of the wing provided by the rib trusses may enable the use of a leading edge spar having a smaller diameter than is commonly used with LEI kites. This may enable a designer to produce an aerodynamic shape having a relatively small leading edge diameter, rather than the large leading edge diameters common to LEI kite wings (where a relatively large diameter leading edge spar is required to provide the required stiffness to the spar so that the leading edge holds its shape).

The ability to use a smaller diameter leading edge spar, and hence sharper leading edge, may significantly decrease the turbulent flow under and over the wing surface in comparison with wings having larger diameter leading edge spars.

A further advantage may be the ability to shape the rib truss, and therefore the profile of the wing, to further reduce drag forces caused by turbulent flow around the wing. In particular, the use of an inflatable rib truss may allow the sheets forming the surface of the wing to have both positive curvature (ie, convex) and/or negative (i.e., concave) in profile. The curvature may be chosen potentially to induce laminar flow over a larger portion of the wing (measured from the leading edge in a chordwise direction), or at least increase the distance from the leading edge over which the air is accelerating (thus increasing lift) before turbulent flow is initiated (which occurs when the air velocity begins to decrease).

In some embodiments the leading edge spar is formed as a truss.

The advantages of the rib truss may be utilised in the leading edge spar by forming it as a truss. In order to keep the leading edge diameter small, it is preferable for the leading edge spar truss to be a horizontal truss; in other words, the plane of the leading edge spar truss members is at right angles to the plane of the members of the rib truss (which lie in a vertical plane). The leading edge spar truss may be formed into a single truss configured to the desired shape of the leading edge, or may be in the form of a plurality of interconnected trusses forming segments of the leading edge. Forming the leading edge spar as a truss may reduce the inflated volume of the leading edge spar from that of the conventional bladder construction, thus reducing the time required to inflate it. Further, the increased stiffness provided by the truss may enable the diameter of the leading edge of the wing to be reduced considerably, thus improving the aerodynamic properties of the wing.

In a preferred embodiment the flexible envelope includes a closable air vent.

A closable air vent may be a valve, or an opening having a closable cap (such as a screw on cap, an opening in a sheet which is closable with a flap, or any other such device.

A closable air vent in the flexible envelope may be used, when open) to allow air into the flexible envelope when the wing is being inflated (i.e., when the spar and rib(s) are being inflated). This may reduce the suction which may otherwise occur within the deflated envelope when pressurised air (or other gas) is pumped into the spar and ribs. The air vent may be closed when the wing is inflated, so that the air inside the envelope is at atmospheric pressure.

In a preferred embodiment the closable air vent is an access panel.

An access panel may be any (closable) opening in the sheet which allows access into the inside of the envelope. An access panel may enable maintenance to be carried out on the rib and spar inside the envelope without the entire envelope being opened. This may reduce the time taken to repair a spar or rib (for example to repair a puncture or replace a damaged part of the spar or rib) by providing direct access to the damaged area, as well as cost savings as the envelope can be restored simply by closing the access panel (as against the cost of resealing the envelope).

In a preferred embodiment one or more lines are attached to the inflatable wing to form a kite.

A traction kite typically includes two or more control lines attached to the wing of the kite (usually at the wing tips but in some cases including bridle lines attached to the leading and trailing edges of the wing to assist with maintaining a desired profile to wing). These lines are commonly attached at the load end to a control bar which is manoeuvred by an operator to control the flight of the wing.

The applicants envisage that one application for the inflatable wing of the present invention may be as the wing of a kite of the type commonly used in many recreational and sporting activities. These include the use of a kite to provide traction to a person on a device configured to move over water (kite surfing and kite boarding), snow (kite skiing) and land (land yachts and buggies).

An inflatable wing according to the present invention may provide many advantages over wings of the prior art, including: reduced time to inflate the rib as the inflatable volume of the rib truss is significantly less (8% - 30%) than the volume of a comparable rib formed from a bladder; increased stiffness of the rib due to the truss structure, enabling a reduction in the diameter of the leading edge spar, thus improving the aerodynamic profile of the wing; providing designers greater freedom in designing the shape of the rib truss to produce an aerodynamically efficient aerofoil profile for the wing, thus increasing performance of the wing during flight.

BRIEF DESCRIPTION OF THE DRAWINGS Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a schematic view of an inflatable wing according to one embodiment of the present invention; and Figure 2 shows a schematic cross section view along a chord line of an inflatable wing according to one embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

An inflatable wing according to one embodiment of the present invention is generally indicated by arrow 1 in Figure 1. The wing 1 is configured as a traction kite having control lines 2, 3 attached to the wing tips 4, 5 of the wing. Further control lines 6, 7, 8 and 9 are attached to the leading edge 10 of the wing.

The wing 1 has a first sheet 11 and a second sheet 12 which define an upper and lower outer surface for the wing, the sheets joined at the leading edge 10 and a trailing edge 13 to form a flexible envelope. The sheets (11 and 12) are formed from a light weight fabric made from any suitable material, such as ripstop nylon, Cuben Fibre™ or other synthetic material as is well known in the art. When the wing is used as a traction kite for use on or over water (as in kite surfing for example), it is important that the material is waterproof.

The leading edge 10 is formed by an inflatable spar 15 (shown in part figure 2) typical of the prior art leading edge inflatable wings. The leading edge spar 15 is typically in the form of an air (or other gas) filled bladder encased in a stronger external casing attached to the leading edge 10 of the wing. The leading edge spar may be formed as a single bladder where the outer sheath or casing is configured to provide the spanwise shape of the leading edge, or may be composed of a series of sections joined together to form the spar. The leading edge spar 10 is enclosed within the envelope formed by the sheets (11 and 12) and defines the spanwise shape of the leading edge 10. The wing 1 includes an inflatable rib in the form of a truss (a rib truss), generally indicated by arrow 16 in Figure 2. The rib truss 16 includes a first chord 17 and a second chord 18 and a plurality of struts which form vertical 19 and diagonal 20 members of the truss between the first and second chords. The regions where the vertical and diagonal members join with a chord form the nodes 21 of the truss. The structure of the rib truss 16 is a web composed of contiguous triangular shapes 22, each triangular shape formed by a node on one chord which is linked to two nodes on the other chord by diagonal and/or vertical members.

The first and second chords, 17 and 18, and the vertical and diagonal members, 19 and 20, are formed from thin walled flexible tubes having a diameter in the range from 8 to 15 mm, depending on the design and the size of the rib truss/wing. The tubes have a wall thickness of around 0.08 mm and are formed from extruded polyether TPU.

The tubes are joined together at the nodes 21 so that the rib truss 16 can be inflated by pumping air into the rib through a single valve(not shown). To achieve this the rib truss 16 is pneumatically connected to the inflatable leading edge spar 15, so that the leading edge spar and the connected rib truss 16 can be inflated through a single valve (not shown). The first chord 17 is attached to the first sheet 11 by loops of material 25 fixed to the first sheet and tied or otherwise attached to the first chord. Similarly, the second chord 18 is attached to the second sheet 12 by loops of material 26 fixed to the second sheet and tied or otherwise attached to the second chord.

The rib truss 16 is configured to define an aerodynamically efficient shape and to provide the required stiffness to the rib truss when inflated. This is achieved by configuring each node such that the sections of tube connecting linked nodes, either between adjacent nodes on the same chord or between linked nodes on different chords, are angled to provide the desired shape for the first and second chords (to provide the desired shape to the attached first and second sheets) and to distribute the loads experienced by the wing in flight along the vertical and diagonal members. In this way a relatively stiff rib truss is formed having the desired curvature for the first and second chords (and hence the profile of the first and second sheets of the wing respectively along a chord line).

The rib truss 16 shown in Figure 2 has a node 28 in the vicinity of the design centre of lift, indicated by dashed arrow 27. The node 28 in this position is connected to a vertical member 29 (as well as diagonal members 30 and 31). A plurality of rib trusses 16 are attached to the first and second sheets in a chordwise direction spaced apart in a spanwise direction, the number of rib trusses and their spacing being determined by the span of the wing and design criteria. Each of the plurality of rib trusses is pneumatically connected to the inflatable leading edge spar 15 so that the entire internal structure of the wing (ie leading edge spar 15 plus the plurality of rib trusses) can be inflated through a valve (not shown).

A plurality of closable air vents, in the form of access panels 32 are located in the first and second sheets towards the trailing edge 13 in the vicinity of a rib truss, as shown in Figure 1. The access panels are formed as apertures in the sheet and are closable by a flap using Velcro™ strips. An access panel is opened to allow air to enter the interior of the envelope during inflation, thus reducing the suction within the closed envelope that could occur otherwise. The placement of the access panels 32 in proximity to a rib truss 16 also enables a person to access the rib and rib members to carry out maintenance (repair a puncture or replace a damaged truss member) as and when required. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT I CLAIM IS:

1. An inflatable wing for a traction kite, the wing including: a flexible envelope having a first sheet and a second sheet, the first and second sheets joined together at a leading edge and a trailing edge; an inflatable leading edge spar located within the flexible envelope and attached to the flexible envelope substantially along the leading edge; and an inflatable rib located within the envelope and extending from the leading edge spar generally towards the trailing edge, characterised in that

2. An inflatable wing as claimed in claim 1 wherein a plurality of inflatable struts and an inflatable chord are connected together to form a node, the configuration of the struts and chord at the node being arranged such that, when inflated, the forces exerted at the node by the struts and the chord are balanced.

3. An inflatable wing as claimed in either one of claims 1 or 2 wherein a diameter of an inflated chord of the truss is in the range from 8 mm to 15 mm.

4. An inflatable wing as claimed in any one of claims 1 to 3 wherein a diameter of an inflated strut of the truss is in the range from 8 mm to 15 mm.

5. An inflatable wing as claimed in any one of claims 2 to 4 wherein the rib includes a node located at or in close proximity to the design centre of lift of the wing.

6. An inflatable wing as claimed in any one of claims 1 to 5 wherein at least one of the first and second inflatable chords is pneumatically interconnected to the inflatable leading edge spar.

7. An inflatable wing as claimed in any one of claims 1 to 6 wherein the inflatable strut is pneumatically interconnected to at least one of the first and second inflatable chords.

8. An inflatable wing as claimed in any one of claims 1 to 7 wherein the first inflatable chord is attached to the first sheet of the flexible envelope.

9. An inflatable wing as claimed in any one of claims 1 to 8 wherein the second inflatable chord is attached to the second sheet of the flexible envelope.

10. An inflatable wing as claimed in any one of claims 1 to 9 wherein the first chord is curved when inflated.

11. An inflatable wing as claimed in any one of claims 1 to 10 wherein the second chord is curved when inflated.

12. An inflatable wing as claimed in any one of claims 1 to 11 wherein the first chord and second chord form an aerodynamic shape when inflated.

13. An inflatable wing as claimed in any one of claims 1 to 12 wherein the flexible envelope includes a closable air vent.

14 An inflatable wing as claimed in claim 13 wherein the closable air vent is an access panel.

15. An inflatable wing as claimed in any one of claims 1 to 14 wherein one or more lines are attached to the inflatable wing to form a kite.

16. An inflatable wing substantially as described herein and with reference to and as

illustrated by the accompanying description and drawings.