EP3589836A1

EP3589836A1 - Kite wing

Info

Publication number: EP3589836A1
Application number: EP18714011.6A
Authority: EP
Inventors: William Hampton; James Taylor
Original assignee: Kite Power Systems Ltd
Current assignee: Kitemill AS
Priority date: 2017-03-01
Filing date: 2018-02-28
Publication date: 2020-01-08
Also published as: GB201703337D0; WO2018158575A1; GB2560179A

Abstract

A kite having multiple sections for use in a power-generation system, the kite comprising a top panel and a bottom panel, and at least one rib connection piece extending between the top panel at a first end and the bottom panel at the second end and which terminates at both the first and second ends end with a respective attachment portion arranged to extend in a plane that is coplanar with respect to the top panel and/or bottom panel and to be attached thereto.

Description

Kite wing

Field

The present invention relates to a method of building kites for energy production. Background

People have tried to harness wind energy for thousands of years. Lately, with fossil fuels running out, techniques for converting energy in the wind to other forms of energy and, in particular, electrical energy have become more popular. It is known to use wind turbines to extract the energy from the wind. It is also known to use kites to extract energy from the wind. Kites can fly at high altitudes where wind speeds are more reliable than the wind speed at the height of the hub of a wind turbine. The hub height of a wind turbine may be at 8o or loom whereas kites can be flown at a typical height of 400 to 700m or even higher. With kite-based power generating systems, the majority of the mass is kept near to ground or water level at a base station, thereby minimising bending moments and reducing the mass of the airborne equipment considerably. Repair and service of the equipment is easier since the bulk of the equipment is at low-level. At sea, the ground based equipment can be mounted on towable barges or buoys allowing retrieval to harbour for major repair or service.

A system for the extraction of power from the wind using a kite typically includes a kite connected to a base station using a tether. A major issue with these systems is producing a kite that is light and strong enough to launch in light airs but still robust enough to survive for adequate service life.

Summary

The scope of protection is defined by the appended claims. Brief description of the drawings

Embodiments of the invention will be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a mould for manufacturing a section of a kite wing;

Figure 2 shows a mould with a first layer thereon;

Figure 3 shows a mould with further layers thereon; Figure 4A shows a woven T-section for a rib connection piece;

Figure 4B shows a noodle;

Figure 5 shows a rib connection piece;

Figure 6 shows an internal view of a wing section;

Figure 7 shows a whole kite section without the bottom skin and the nose section for illustrative purposes;

Figure 8A shows a portion of a kite wing;

Figure 8B shows a portion of a kite wing having a chordwise strip;

Figure 8C shows a portion of a kite having a lateral joint;

Figure 9 shows a kite section having an inflatable tube;

Figure 10 shows an embodiment having a sacrificial layer; and

Figure 11 shows a side view of a nose section of the wing in accordance with some embodiments. Detailed description

When a kite is flying, a variety of forces act on the envelope that generates the flying form, these are substantially: lift forces, hoop forces and drag forces. A hoop force is the load generated by the lift of the wing being within the top skin of the kite. The same term is used in an inflated body where internal pressure translates into tension.

Embodiments of the invention provide a kite whereby hoop forces are introduced in order to ensure a substantially flat surface which is aerodynamically effective. The hoop forces thus introduced can cause a peeling effect between neighbouring kite sections. Embodiments of the invention therefore provide one or more rib connection pieces that are configured to transfer loads away from areas of the kite where the peeling action is greatest.

Embodiments of the present invention further provide a method of building a robust kite wing for power generation where the build accuracy can be controlled and the airtight integrity of the joints can be maintained. Each primary component can be manufactured and then brought together for assembly.

Power generating kites manufactured according to methods described herein allow loads to be distributed throughout the structure to minimise fatigue and maximise the working life of the kite. The skin of the kite may be laminated in a way whereby the fibre layers are exposed at the lateral edges of each section, allowing a bond to form between top and bottom panels and a rib. This is stronger than if there were a film or membrane between the fibres of the skin and the rib.

In some embodiments, the skin is laminated as a composite structure. Therefore, it is possible to lay reinforcing fibres in greater density where required, for example in areas of the kite that will experience greater stress. In areas of lower stress, fibres may be applied in lower densities. Alternatively, in areas of lower stress, fibre layers may be replaced with high strength film layers.

By using a film that is vacuum formable it is possible to produce a 3D skin that has the final form of the billowed structure in flight. Alternatively, the film may be composed of separate panels that are cut individually put in place individually.

Through design and experimentation it is possible to predict a final flying form for the kite and it is this form that is used for the skin design. The films and fibres can be coated or pre- impregnated with resin on glue or a glue film can be added. Certain fibres are sensitive to temperature and others are sensitive to UV. The final fibre/resin/setting method can be varied in ways that would be evident to someone skilled in the art. The method for consolidating the panels could, for example, be vacuum or pressure forming.

The hoop forces acting on the kite due to the curvature of the kite allow the skin of the kite to be pulled substantially flat thus aiding the aerodynamic performance. The hoop forces arise because the bridling is not perpendicular to the wing. The bridling is offset, thereby transferring a portion of the force into a hoop force that flattens the individual sections. These hoop forces need to be transferred from one section of the kite to other sections of the kite to achieve an equilibrium. The lift force is at roughly 90⁰ to the hoop force. In kite wings formed from multiple sections arranged laterally there is a tendency for neighbouring sections to peel away from each other because of the hoop force. By building a moulded formed rib connection piece and connecting a panel or panels to this that are capable of transferring the load from the top of the wing to the bottom of the wing, embodiments of the invention provide a transfer piece between the top and bottom panels and bridle connection points. This allows the lift force to be transmitted from regions of the top skin experiencing high loads typically at the front of the wing to regions of the wing towards the rear and towards the bottom panel. The transmittal of the force may be through the rib the connection pieces or through one or more bridle connections to bridle connection points that connect with bridles of the kite. In one embodiment, the moulded formed rib connection piece may be manufactured using a flexible resin and a woven anti-peel profile incorporating a noodle or noodles to overcome the peel issue. The woven piece may be woven to the final form but in this example it is woven as a flat T-shape and then the bottom leg is cut to allow the curvature to develop.

This method of manufacture means that it is possible to create an airtight envelope should a fully inflated wing be desired.

The rib connection piece may comprise a woven section having five legs. It is possible to create an anti-peel vacuum formed section that can have internal v-shaped ribs or internal bridling lines. In some embodiments, the rib connection piece has the top skin attached to it.

Alternatively, attachment points can be bonded on using stitching, riveting, gluing, a combination of these methods or any other method known to someone skilled in the art. By fitting internal structure, it is possible to minimise external bridling as the wing form can be held without a bridle connected to each rib.

Figure 1 shows a male mould ιοο which forms a plug. The mould ιοο is complementary in shape to one section of a multi-section kite wing. The mould 100 is used to lay the films and fibre thereon prior to compression or vacuum forming.

Figure 2 shows the mould loo with a first or base film layer loi applied thereto. The first film layer ιοι can be Tedlar ® or equivalent. The film layer ιοι is moulded and then trimmed to lay flat on the mould loo. The film is rebated from the edge of the male mould by a distance slightly less than the width of the rib moulding top 221 shown in Figure 4. This allows for a direct connection between the rib connection piece and the fibre layers.

Figure 3 shows a lateral fibre layer 102 laid onto the first film layer 101 (which forms an underfilm) and extending to the edge of the mould 100. A linear fibre layer 103 is also provided. Although not shown within this figure for the sake of simplicity, other fibre directions may be present, e.g. there can be bias fibres and extra fibres or tapes laid in where tension loads are highest. Over the fibre layer 104 another film layer may be placed that extends the full width of the section. The layers 102, 103 and 104 cover the full width of the mould 100. This creates a 3D formed top panel 105. The fibre layers 102, 102, 104 are made from any suitable material. For example, the fibres may be Dyneema, carbon, PBO, Vectran, Spectra, Kevlar or any suitable polyester. Dyneema has good UV stability, low density and a good strength/weight ratio.

The fibre layers 103, 104 are placed in regions of the wing where the loads are expected to be higher. For example, fibre layers may be introduced at the leading edge of the kite wing while the trailing edge may be thinner since lower loads are expected in this region. Thus a resilient panel may be formed in areas where high loads are experienced whilst the overall weight of the wing can be minimised in regions where lower loads are experienced.

The difference in width between the lateral fibre layer 102 and linear fibre layer 103 on the one hand and the base film layer 101, on the other hand, creates a rebated portion. This enables a rib connection piece 200 to be attached to the top and bottom panels. The rib connection piece 200 is bonded to the top panel 105 so that the load is in shear and allows loads to be transferred from the top panel to the bridle connection points. This helps to control the peeling force which can act on neighbouring sections since the peeling action between neighbouring sections is converted into a shearing action.

Figure 4A shows a 3D woven T section of a rib connection piece 200 having a noodle 202 around which the fibres 220 are woven. The fibres 220 are woven around the noodle from one leg of the rib connection piece to the other. As can be seen from Figure 4B, the noodle 202 is a rod formed from a strand of sufficiently rigid material around which fibres are bent so that individual fibres 220 in the vicinity of the T-section extend from a vertical panel 222 to a horizontal panel 221.

Whilst there are other ways of creating a similar effect without a noodle, the weave in such embodiments is generally required to be more complex. In kites that do not employ a noodle, the fibres need to be connected mechanically through twisting, knotting or other means to stop the separate arms from parting.

In contrast, providing a noodle allows for a stronger connection between a horizontal panel and a vertical panel since the fibres are integral within both panels. Figure 5 shows a rib connection piece 200. The rib connection piece 200 shown in Figure 5 has had a bottom leg 222 cut and overlapped before placing into a multi-piece mould. This may then be vacuum formed using flexible epoxy. Alternatively, the rib connection piece 200 may be injection moulded using a plasticiser.

Figure 6 shows an internal view of a section of the wing with a flat rib membrane 203. The flat rib membrane 203 has holes 204 therein to allow a balance of pressure and reduction of weight. The moulded formed rib piece 200 can be continuous from the leading edge to the trailing edge, around the nose portion or it may be sectional.

Figure 7 shows a whole kite section without the bottom skin and the nose section for illustrative purposes. The embodiment shown here has a five leg moulded formed connection piece 200 with internal bridle connections 224 shown as webbing bonded between the top and the bottom moulded formed connection pieces 200. This may be a continuous V rib or webbing. In an individual section the diagonal connections 224would normally be in one plane only and would not cross. The bridle connection points 225 may be in line with the internal bridle structure.

The design of the bridles 224 allow a balancing of forces within the kite. If all of the bridle lines are tangential to a perfect arc kite then there are no or low hoop forces. If there are lines from the tips of the kite only then there are high hoop forces. There is a requirement of some hoop force to maintain the aerodynamic form of the kite, the tension thus created acts to flatten the sections.

The balance of forces within the kite when in flight gives rise to a defined 3D shape. By building the kite to this shape, a kite can be produced that is able to withstand greater loads.

Figure 8A shows a portion of a kite wing comprising a first section 801 and a second section 802 laterally adjacent and connected to each other via a rib connection piece 200a. The first and second sections 801, 802 are each attached to the rib connection piece 200a. The first section 801 is also attached to a rib connection piece 200b. The second section 802 is also attached to a rib connection piece 200c. The connection pieces 200b, 200c allow the first and second sections 801, 802 to be connected to other sections of the kite wing. The sections closer to the lateral ends of the kite wing are of a lower height (i.e. separation between top panel 105 and bottom panel 106) than sections towards the centre of the kite wing so that the kite wing tapers towards the lateral edges of the kite wing.

Figure 8B shows a portion of a kite wing having a chordwise strip 850 of non-permeable protective material (such as Tedlar) to seal along the T-section where the two adjacent top layers 105-1 and 105-2 meet. Strips 850 maybe provided at the intersection of each pair of laterally adjacent section. This is to prevent leakage of internal pressure that may occur if small gaps open between the weave of the T-section.

Figure 8C shows a portion of a kite having a lateral joint 860 in the wing top panel 105. Behind the lateral joint and towards the trailing edge of the wing a 2D fabric is provided. The material provided at the trailing edge may be a film with up to 2GPA in a single direction. Such a film laminated would suffice for the majority of the wing where stresses are less than those experienced at the leading edge in the nose section.

Figure 9 shows an alternative embodiment where an inflatable tube 300 is attached to the trailing edge of the section. This can allow active control surfaces a mounting point on the wing. In other embodiments, the wing is partially flexible and formed from a partially rigid composite.

A middle section of the wing in the spanwise direction may be solid with flexible composite wings attached on either side. The leading edge of the wing or parts of it may be rigid composite with the rest of the wing made of a flexible composite structure.

Figure 10 shows an alternative embodiment whereby a sacrificial layer is provided. In accordance with this embodiment, a wing section ιοοο may be substantially similar to that described above with reference to Figures 1-9. However, a top panel 1001 comprises a first skin 1002 and a second skin 1003. The second skin 1002 functions as a sacrificial layer. The sacrificial layer or second skin 1002 is spaced away from the first skin by a predefined distance. The separation between the first skin and the second skin forms a pocket in the nose section (i.e. the section towards the front of the wing). The second skin 1002 may be removable so that it can be replaced without replacing the underlying first skin 1001 or other components of the wing IOOO. The first skin 1001 and second skin 1002 maybe manufactured as described above. It should be understood that the bottom skin 106 may also be provided with a sacrificial layer in substantially the same way. In the pocket formed between the first skin 1001 and second skin 1002 one or more ice crack bladders may be provided. If ice forms on the nose section of the wing then the ice crack bladder may be inflated via an internal pump to increase the volume of the nose section. This leads to the ice cracking so that the ice can be easily removed.

An alternative to providing ice cracking bladders is to provide a wire mesh across the surface of the wing. A current may then be passed through the wire mesh to melt the ice through resistive heating.

A multi-section kite wing may be provided with a carapace so as to flatten the profile and provide improved aerodynamic performance.

Internal spars may be fitted to support the wing. These spars may be rigid, tensairity beams or multiple small inflatable beams. These spars are substantially parallel to the rib connection pieces 200.

The nose section of the wing may be provided with several small laterally extending tubes that are inflatable to around 15 mbar of pressure. These may be provided in the leading edge of the wing in the nose section and provide mechanical strength. This can also have the effect of reducing drag.

Figure 11 shows a side view of a nose section of the wing in accordance with various embodiments of the invention. The nose section has a shark nose profile. One or more sections of the wing may be provided with a shark nose profile. For example, central sections of the wing may be provided with a shark nose profile whilst sections located on the lateral edges may be provided with a plain profile. The section having a shark nose profile may be provided with a gauze section 1105. The gauze section allows air to enter the wing and provides for inflation of the wing. As such, stability of the wing and aerodynamic performance can be improved.

Several advantages of kite wings provided by embodiments of the invention in comparison with conventional kite wings will be apparent to the skilled person. Conventional kites use a ripstop polyester or nylon material and stitch all joints of the kite together. The fabric itself is mobile and stretches to take the final flying form of the wing but both the material and the jointing method is not strong enough for flying kites at the sort of loadings and speeds that are required in modern kite power systems.

Due to the stretch of traditional kite building materials, the fibres in traditional kites generally balance the loads and because of the ripstop nature of the materials, the stitching suffices at the lower loads at which conventional kites operate. The other major issue with conventional build methods is that there is a peel point between each of the sections where the only fibres that transfer the load from one section to the other are the stitching fibres. As the wing operates at higher loads, the stitching starts to become strained and the wing becomes porous along the stitch lines due to the peeling action. As mentioned above, the peeling action is removed in embodiments of the invention by providing the rib connection pieces which transfer the load away from the top panel into the bridle.

It is very difficult in a standard two-dimensional fabric to have different weights of

reinforcement in different areas. This has conventionally been done by stitching on more layers of fabric. One of the principal disadvantages of this is that when the kite takes its flying form the areas with reinforcement have less stretch than the areas without reinforcement and maintaining a clean aerodynamic surface becomes challenging.

The airtight integrity of the wing sections is fundamentally a property of the films that are used both internally and externally in the fabrication of the panels. A film with elastic properties can be used on the top of the T-section between each of the horizontal legs so as to maintain gas tight integrity should the fibres move and small pores appear in the resin between the fibres.

Claims

1. A kite having multiple sections for use in a power-generation system, the kite comprising a top panel and a bottom panel, and at least one rib connection piece extending between the top panel at a first end and the bottom panel at the second end and which terminates at both the first and second ends end with a respective attachment portion arranged to extend in a plane that is coplanar with respect to the top panel and/or bottom panel and to be attached thereto.

2. The kite of claim l, wherein the top panel and the bottom panel are each formed from a laminated structure comprising multiple layers wherein at least some of the layers are applied selectively in predetermined regions of the kite to withstand high aerodynamic loads in said predetermined regions.

3. The kite of claim 1, wherein the rib section is formed from a woven composite.

4. The kite of any preceding claim, wherein the rib section has one of: a T-section, an X- section or a multi-leg section.

5. The kite of any preceding claim, wherein the top panel and the bottom panel are each multi-sectional, comprising a plurality of sections arranged laterally with respect to each other.

6. The kite of claim 5, wherein each section comprises at least one bridle piece extending diagonally from the top panel to the bottom panel.

7. The kite of claim 6, wherein each section comprises a plurality of bridle pieces, each of said plurality of bridle pieces extending substantially parallel with respect to each other.

8. The kite of any of claims 2-7, wherein a base layer of the multi-layer laminated structure has a shorter width than the width of the kite section.

9. The kite of claim 8, wherein the base layer of the multi-layer laminated structure is overlaid with a second layer having fibres extending in a lateral direction.

10. The kite of claim 9,wherein the second layer is overlaid with a third layer having fibres extending in a chordwise direction. it. The kite of any preceding claim, wherein the top panel and bottom panel are formed separately and attached to each other.