WO2019135078A1

WO2019135078A1 - A kite apparatus

Info

Publication number: WO2019135078A1
Application number: PCT/GB2019/050011
Authority: WO
Inventors: Reinhart PAELINCK
Original assignee: Kiteswarms Limited
Priority date: 2018-01-04
Filing date: 2019-01-03
Publication date: 2019-07-11
Also published as: GB201800090D0; EP3735531A1

Abstract

The present invention provides a kite apparatus (100), comprising a main tether line (120a), for connection at a first end to a base station (110), a hub (130a) connected to a second end of the main tether line, a sub-tether line (145a, 150a, 160a) connected at a first end to the hub, and a kite (10a) connected to a second end of the sub-tether line, wherein the hub is connected to the main tether line by a swivel connector (131, 133) such that the hub can swivel relative to the main tether line, about a swivel axis. The present invention also provides a hub for a kite apparatus, a kit of parts for assembling a kite apparatus and a method of flying a kite apparatus.

Description

A KITE APPARATUS

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to a kite apparatus.

[0002] The present invention concerns a kite apparatus. More particularly, but not exclusively, this invention concerns a kite apparatus, comprising a main tether line, for connection at a first end to a base station, a hub connected to a second end of the main tether line, a sub-tether line connected at a first end to the hub, and a kite connected to a second end of the sub-tether.

[0003] The invention also concerns a hub for a kite apparatus, a kit of parts for assembling a kite apparatus and a method of flying a kite apparatus.

[0004] Kite apparatus, in particular kite apparatus used to harness wind energy, have been proposed by various authors. In addition, a kite apparatus could be used for lifting or towing a base station, such as a payload. For example, the kite apparatus could be used to tow a ship.

[0005] A typical kite (also known as a kite plane) is shown in Figure la, as reference numeral 10. The kite has control surfaces 11, such as for controlling pitch, yaw and roll. The wings 13 of kites are generally of a rigid construction. The kites also comprise a forward propeller 12.

[0006] A VTOL (vertical take-off and/or landing) kite plane may be used, as shown in Figure lb by reference numeral 20. Here, as well as the propeller 12, are four rotors 25 to aid VTOL.

[0007] Multi -kite systems 30, where kites 33 are branched off a main tether line 31, on their own sub-tether line 32, at a hub point 36, have also been proposed, as shown in Figure 2. The Figure also shows the wind direction 34 and the rotation flight paths 35 of the kites 33 during operation. The main tether line 31 and the sub-tether lines 32 may be extendable/retractable. The extending and retracting of the lines is known as“pumping” and this allows for the system to not get tangled when on the ground. [0008] However, it is often very difficult, especially when the kites are not designed for VTOL, to get the multi-kite system deployed in the air and operating to generate electricity, for example.

[0009] The present invention seeks to mitigate the above-mentioned problem. Alternatively or additionally, the present invention seeks to provide an improved kite apparatus.

SUMMARY OF THE INVENTION

[0010] The present invention provides, according to a first aspect, a kite apparatus, comprising a main tether line, for connection at a first end to a base station, a hub connected to a second end of the main tether line, a sub-tether line connected at a first end to the hub, and a kite connected to a second end of the sub-tether line, wherein the hub is connected to the main tether line by a swivel connector such that the hub can swivel relative to the main tether line, about a swivel axis.

[0011] Having a swivel connector allows the kites to rotate around the main tether line, without twisting it. This is especially useful when there is more than one hub and not all the hubs are extended out from the base station (e.g. if a kite on a hub is using its forward propeller to accelerate around the hub, it will produce lift that can be used to lift other lower hubs) or if kites on different hubs are being rotated at different speeds.

[0012] The swivel connector allows the hub to swivel about an axis corresponding to a longitudinal axis of the main tether line. This allows the hub to rotate through 360 degrees around the longitudinal axis of the main tether line.

[0013] Preferably, the swivel connector comprises a swivel rod, rotatably mounted to the hub so as to be rotatable about its longitudinal axis.

[0014] Preferably, the swivel connector comprises a slip ring.

[0015] Preferably, the main tether line is extendable/retractable. This allows the hub to be deployed out as the lift generated by the kite is increased.

[0016] More preferably, the main tether line is provided with a main tether winch drum for accommodating a variable length of main tether line, when at least partially retracted. [0017] Even more preferably, the main tether winch drum is located within or adjacent the base station or within or adjacent the hub.

[0018] Preferably, the sub-tether line is extendable/retractable. This allows a diameter of a rotational path of the kite about the hub to be increased as the lift generated by the kite is increased.

[0019] More preferably, the sub-tether line is provided with a sub-tether winch drum for accommodating a variable length of sub-tether line, when at least partially retracted.

[0020] Even more preferably, the sub-tether winch drum is located within or adjacent the hub or within or adjacent the kite. The sub-tether winch drum may be located within the hub. The sub-tether winch drum may be located entirely within the hub. The sub tether line may be connected at its first end to the inside of the hub. The sub-tether line may extend out of the hub through an opening of the hub. The sub-tether winch drum may be provided on a portion of the sub-tether line extending between the first end of the sub-tether line and the opening of the hub.

[0021] Even more preferably, the sub-tether winch drum is located within the hub and has a rotational axis, and wherein the rotational axis of the sub-tether winch drum is substantially in line with the swivel axis of the hub. This prevents unwanted vibration and uneven loading within the hub.

[0022] Preferably, the sub-tether winch drum is powered by a sub-tether motor and wherein the sub-tether motor is located within the hub or kite, or wherein the sub-tether winch drum is connected to a mechanical transmission from the sub-tether motor and the sub-tether motor is located externally of the hub or kite.

[0023] Preferably, the sub-tether line includes a length provided by one or more support rods, for ensuring a minimum distance is maintained between the kite and the hub, when the sub-tether line is retracted. The length provided by the support rods provides a minimum length of sub-tether line, even when fully retracted. This means that the kite cannot be retracted too far to hit the hub. The support rods also allow the kites on the hub to“push” the rods around to rotate around the hub and prevent the kites from going and different speeds to each other/over-taking each other. In addition, the support rods support the kites, for example, when the hub is stacked to a ground station or another hub. In other words, a support rod can act as a cantilevered landing point for a kite.

[0024] More preferably, one of the support rods is pivotally mounted to the hub, so as to be pivotable about an axis substantially perpendicular to the swivel axis of the hub. This provides a flexibility in the flight path of the kite and prevents tangling of the sub tether lines.

[0025] Even more preferably, the angle of the support rod that is pivotally mounted to the hub is maintained within a range of angles by mechanical limit stops. For example, the support rod may not be able to pivot lower than about 90 degrees downwards from an upper longitudinal axis of the hub. This prevents the kite from dropping too low where it might hit another kite associated with a lower hub.

[0026] Preferably, the angle of the support rod that is pivotally mounted to the hub is measured by one or more angle sensors.

[0027] Preferably, one of the support rods is attached to the kite by a joint allowing three degrees of freedom. This allows freedom for the angle/orientation of the kite during flight.

[0028] Preferably, one or more support rods are hollow to allow an extendable/retractable portion of the sub-tether line to pass through the one more support rods to the sub-tether winch drum. This allows the winch drum to be, for example in the hub, and for the support rod to be part of the sub-tether line external to the hub.

[0029] Preferably, the adjacent ends of the one or more support rods have correspondingly shaped interface profiles so that, upon retraction of the sub-tether line, the support rods can link together. This provides a linked support rod assembly that is rigid when the support rods are linked up.

[0030] More preferably, the correspondingly shaped interface profiles comprises a cone and a conically-shaped recess. This allows the interface to be urged together, to form a linked support rod assembly, when the sub-tether line is retracted.

[0031] Preferably, the hub comprises a positioning device.

[0032] Preferably, the kite apparatus comprises one or more additional sub-tether lines, similar to the first sub-tether line, connected at their first ends to the hub, each additional sub-tether line having an additional kite, similar to the first kite, connected to its second end. This allows for more than one kite to be flown from the hub. This allows for more energy to be harnessed. It also allows for the one or more kites to be evenly spaced around a rotational path of the kites about the hub, allowing for more even loading of the hub. Each of the additional kites is separate from each other and the first kite. In other words, each of the kites is only connected to any other kite through the sub-tether lines and the hub.

[0033] The kite apparatus may be provided with a number of additional hubs. These hubs may be dissimilar to the hubs with a swivel connection. However, the present invention only requires one such hub with a swivel connection. If such hub is not the adjacent hub to the base station, the intermediate hubs and associate tether lines are simply to be considered part of the main tether line of the invention.

[0034] More preferably, the first sub-tether winch drum and any additional sub-tether winch drums are located within the hub and wherein the sub-tether winch drums are stacked so that the rotational axes of the sub-tether winch drums are substantially in line with the swivel axis of the hub. This prevents unwanted vibration and uneven loading within the hub.

[0035] Preferably, the kite apparatus comprises an additional second main tether line and an additional second hub, the second main tether line being similar to the first main tether line and the second hub being similar to the first hub, wherein a first end of the second main tether line is connected to the first hub and wherein the second hub is connected to a second end of the second main tether line. This allows for there to be more than one hub (with associated extra kite(s)) in the kite apparatus. This allows for more energy to be harnessed. The hubs can be effectively stacked above each other.

[0036] More preferably, the kite apparatus comprises an additional third main tether line and an additional third hub, the third main tether line being similar to the first or second main tether lines and the third hub being similar to the first or second hubs, wherein a first end of the third main tether line is connected to the second hub and wherein the third hub is connected to a second end of the third main tether line. This allows for there to be more than two hubs (with associated extra kites) in the kite apparatus. This allows for more energy to be harnessed. The hubs can be effectively stacked above each other.

[0037] Even more preferably, there are one or more further additional main tether lines and hubs, connected to the first, second and third hubs in a series relationship.

[0038] Preferably, at least one of the additional main tether winch drums for an additional main tether line is located within the adjacent (lower) hub in the direction of the base station, and wherein a rotational axis of the additional main tether winch drum is in line with the swivel axis of the adjacent hub. This prevents unwanted vibration and uneven loading within the hubs. This also allows for a winch for a hub to be controlled in a hub below.

[0039] More preferably, the additional main tether winch drum is powered by a main tether winch motor and wherein the main tether winch motor is located within the adjacent hub, or wherein the additional main tether winch drum is connected to a mechanical transmission from the main tether winch motor and the main tether winch motor is located externally of the adjacent hub.

[0040] Preferably, the adjacent ends of the one or more adjacent hubs have correspondingly shaped interface profiles so that, upon retraction of the connecting main tether line, the adjacent hubs can link together. This provides a linked hub assembly that is rigid when the hubs are linked up. This means that kites on the hubs are not caused to hit/rest against each other.

[0041] More preferably, the correspondingly shaped interface profiles comprise a cone and a conically-shaped recess. This allows the interface to be urged together, to form a linked hub assembly, when the main tether line is retracted.

[0042] Even more preferably, one or more hubs have a length between their ends, for ensuring a minimum distance is maintained between the kites of the adjacent hubs, when the connecting main tether line is retracted and the adjacent hubs are linked together.

[0043] Preferably, one or more kites of the apparatus are capable of vertical take-off and/or landing.

[0044] According to a second aspect of the invention there is also provided a hub designed for use with the kite apparatus as described above. [0045] According to a third aspect of the invention there is also provided a hub for a kite apparatus, the hub comprising a swivel connector for connection to a main tether line, such that the hub can swivel relative to the main tether line, about a swivel axis, and a connector for a sub-tether line of a kite.

[0046] Having a swivel connector allows the kites to rotate around the main tether line, without twisting it. This is especially useful when there is more than one hub and not all the hubs are extended out from the base station (e.g. if a kite on a hub is using its forward propeller to accelerate around the hub, it will produce lift that can be used to lift other lower hubs) or if kites on different hubs are being rotated at different speeds. Preferably, the swivel connector comprises a drive mechanism to drive rotation of the hub relative to the main tether line. This would allow the hub/main tether line to be driven in relation to the main tether line/hub to ensure the main tether line remains untwisted. The drive mechanism may comprise a motor on the hub for driving rotation of the hub relative to the main tether line. There may be a sensor to sense twisting of the main tether line. There may be a swivel processor to operate the drive mechanism. Upon twisting of the main tether line being sensed, the swivel processor may operate the drive mechanism to drive rotation of the hub relative to the main tether line. As an alternative, or in addition, there may be a weight on the main tether line to resist or prevent twisting of the main tether line and hub in relation to each other.

[0047] The swivel connector allows the hub to swivel about an axis corresponding to a longitudinal axis of the main tether line. This allows the hub to rotate through 360 degrees around the longitudinal axis of the main tether line.

[0048] Preferably, the hub further comprises a main tether winch drum for extending/retracting the main tether line.

[0049] Preferably, the hub further comprises a sub-tether winch drum for extending/retracting the sub-tether line.

[0050] Preferably, the connector for the sub-tether line comprises a pivotally mounted support rod.

[0051] Preferably, the support rod is pivotally mounted to the hub, so as to be pivotable about an axis substantially perpendicular to the swivel axis of the hub. [0052] Preferably, the hub comprises one or more additional connectors for additional sub-tether lines, similar to the first sub-tether connector.

[0053] Preferably, the hub has a first interface profile at one end and a correspondingly shaped interface profile at a second end so that similar shaped hubs can be linked together.

[0054] More preferably, the correspondingly shaped interface profiles comprise a cone and a conically-shaped recess.

[0055] According to a fourth aspect of the invention there is also provided a kit of parts for assembling a kite apparatus, the kit of parts comprising a main tether line, for connection at a first end to a base station, a hub for connection to a second end of the main tether line, a sub-tether line for connection at a first end to the hub, and a kite for connection to a second end of the sub-tether line, wherein the hub is connectable to the main tether line by a swivel connector such that the hub can swivel relative to the main tether line, about a swivel axis.

[0056] According to a fifth aspect of the invention there is also provided method of flying a kite apparatus, comprising the steps of proving a kite apparatus as described above.

[0057] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[0058] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0059] Figure la shows a perspective view of a kite, according to the prior art;

[0060] Figure lb shows a perspective view of an alternative kite, according to the prior art;

[0061] Figure 2 shows a perspective view of a kite apparatus, according to the prior art; [0062] Figure 3 shows a front view of one half of a kite apparatus according to a first embodiment of the invention, with one hub and one kite of the arrangement being shown;

[0063] Figure 4 shows a front cut-away view of the hub shown in Figure 3;

[0064] Figure 5 shows a front view of one half of the kite apparatus as shown in

Figure 3, with three hubs and three kites of the arrangement being shown, at different stages of operation;

[0065] Figure 6 shows a perspective view of a hub of a second embodiment, showing three support rods and three sub-tether lines;

[0066] Figure 7a shows a front view of one half of a kite apparatus according to a third embodiment of the invention, with one hub and one kite of the arrangement being shown;

[0067] Figure 7b shows a front view of one half of a kite apparatus according to a fourth embodiment of the invention, with one hub and one kite of the arrangement being shown;

[0068] Figure 8 shows a front cut-away view of an alternative hub to that shown in Figure 4;

[0069] Figure 9 shows a front partially cut-away view of a second alternative hub to that shown in Figure 4 or Figure 8;

[0070] Figure 10 is a similar view of the hub of Figure 9, showing two sub-tether lines;

[0071] Figure 11 is a close-up cut-away view of the swivel connector of the hub of Figures 9 and 10; and

[0072] Figure 12 is close-up cut-away view of the sub-tether winch drum arrangement of the hub of Figures 9 to 11.

DETAILED DESCRIPTION

[0073] Figure 3 shows a front view of one half of a kite apparatus 100 according to a first embodiment of the invention, with one hub l30a and one kite lOa of the arrangement being shown. The kite lOa is the same or very similar to that shown (numeral 10) in Figure la. [0074] The hub l30a has a lower end attached by a swivel connector 131 to a first main tether line l20a. This main tether line l20a is attached to a winch at a base station on the ground (not shown in Figure 3). A second main tether line l20b extends from the upper end of the hub l30a.

[0075] Extending out from a side of the hub l30a is a hinged long support rod 145. The support rod 145 can rotate up and down, (clockwise and anti-clockwise, as shown in Figure 3). At a far end of the support rod 145 is a conical hole connector 151. A retractable sub-tether cord 150 extends out from the conical hole connector and is attached to a conical connector 152 of a second short, solid support rod 160. The conical hole connector 151 and the conical connector 152 are shaped so as to interface and lock together. At a far end of the second support rod 160 is a gimbal (three degrees of freedom) joint 161, attaching the support rod 160 to the kite 10.

[0076] The kite arrangement 100 contains similar hubs (see later), each hub referred to generally as 130 and shown in more detail in Figure 4.

[0077] Each hub 130 comprises a main body portion 137 at its lower end. The body portion has a lower conical profile 134. The tip of the cone comprises a connector 131 with a conical surface in front of a swivel rod 133. The swivel rod 133 is located in a cylindrical hole 132 of the main body portion. The conical connector 131 has a hole through it for attaching the main tether line l20a.

[0078] Extending from each side of the main body portion 137, as shown, is a support rod 145. The support rod is mounted by a hinge 146 on a bracket 148. The support rod 145 can pivot within the hinge mounting upwards from a position that is horizontal as shown in Figure 4 (stopped by mechanical limit stop 147).

[0079] Within each support rod is a sub-tether cord 150 running in a hollow cavity 144 of the rod 145. At the near end of the rod 145, is a cord guider 139 comprising two rotatable rollers either side of the cord 150. Another two cord guiders 139 guide the cord to a winch 138. The winch comprises two drums stacked on top of each other with their rotation axis in line with the swivel axis of the hub 130. The cord 150 of the left hand side (as shown) rod 145 is guided to the bottom winch drum and the right hand side (as shown) cord is guided to the top winch drum. [0080] Above the winch 138 is a second winch 140. It is mounted so that its rotational axis 143 is perpendicular to the axis of the winch 138 and swivel axis. However, the axis 143 crosses with the line of the axis of the winch 138 and swivel axis in the centre of the hub 130. This winch 140 is able to extend and retract a second main tether line l20b. The line l20b is guided (by cord guider 141, similar to cord guider 139) into a shaft portion 136 of the hub 130. At the top of the shaft portion 136 there is a further guider 142 (similar to 139 and 141) which guides the line l20b into a conically shaped cavity 135. The conically shaped cavity 135 is shaped to correspond to the conical profile 134 at the lower end so that similar hubs 130 can be stacked within each other via the conical profiles.

[0081] Figure 5 shows a front view of one half of the kite apparatus 100 as shown in Figure 3, with three similar hubs l30a, 130b, l30c and three similar kites lOa, lOb, lOc of the arrangement being shown, at different stages of operation. This Figure also shows the ground 112 station 110 winch drum 111 for extending and retracting the first main tether line l20a.

[0082] Starting from ground level 112 up, it can be seen that the first hub l30a is adjacent the ground 112, interfaced into an alignment cone 114 of the ground station. This is because first main tether line l20a has been retracted. The kite lOa of this hub is supported in a horizontal position by the retraction of the sub-tether cord 144 and the linking of the support rods 145, 160.

[0083] The second hub 130b is shown retracted (by second main tether line l20b) so to be linked into first hub l30a. The support rod l45b of this hub has been pivoted upwards and the sub-tether cord l 50b has been partially extended so as to allow flight of the kite 10b.

[0084] Finally, the third hub l30c is extended out by third main tether line l20c to be deployed from second hub 130b. In addition, the support rod l45c is pivoted upwards (like rod l45b) and the sub-tether cord l 50c has been fully extended to allow the kite lOc to fly in a large diameter flight path.

[0085] A fourth main tether line l20d is also shown to illustrate how a fourth hub l30d (not shown) could be incorporated. [0086] In use, the apparatus 100 starts in its stowed position, where the main tether lines 120 are retracted and all the hubs l30a, 30b, l03c etc. are stacked so that the conical interface profdes 134, 135 sit within each other and the first hub l30a sits in the alignment cone 114 of the ground station. In the stacked position, all sub-tether lines 150 are retracted and the support rods 145 lowered to sit against the mechanical limit stops 147 so that the kites 10 are orientated substantially horizontally, as shown by kite lOa in Figure 5.

[0087] When it is wished to deploy the apparatus 100, for example in order to generate electricity from wind energy, the upper most hub (say hub l30c) is first deployed. This happens in two stages. In the first stage, the sub-tether lines 150 of the kites on the hub l30c are partially extended and the support rods 145 pivoted upwards, to the position illustrated by kite lOb in Figure 5. The hub l30c still is interfaced with the hub below. In this position, the kite lOc is either using its VTOL function (if it is a kite like as shown in Figure 2) and/or using its forward propeller 12 to fly in a small diameter circles about the hub l30c. In the second stage, the sub-tether cords l 50c are fully extended and the kites lOc fly in a large diameter circle about the hub l30c, as shown by kite lOc in Figure 5. This provides lift and the hub below l30b extends the inter connecting main tether line l20c so that the hub l30c lifts up.

[0088] Once the main tether line l20c is fully extended, the process can then be repeated for the hub below (130b), and then the hub below that (l30a) until all hubs 130 and kites 10 required are flying as per hub l30c and kites lOc in Figure 5.

[0089] Once deployed, the kites 10 can be controlled by their flight surfaces, in order to maximise the wind energy harnessed by the apparatus. The wind energy is harnessed by the tension on the main tether lines 120 acting to rotate a drum (not shown) in the base station. That drum drives a generator/compressor. When the main tether lines 120 have been fully extended, the flight surfaces of the kites are adjusted so that they put a minimum pull on the tether lines. The tether lines are then retracted and the process begins again.

[0090] Of course, some of the power extracted can be used to power on-board electronics (e.g. autopilot, flight surface control functions), if needed. [0091] Figure 6 shows a perspective view of a hub 130’ of a second embodiment, the hub 130’ having three support rods and three sub-tether lines, rather than two.

[0092] Figure 7a shows a front view of one half of a kite apparatus 200 according to a third embodiment of the invention, with one hub and one kite of the arrangement being shown. The difference of this arrangement 200 from arrangement 100 is that the first support rod 245 of a hub is short and the second support rod is long, rather than the other way round.

[0093] Figure 7b shows a front view of one half of a kite apparatus 300 according to a fourth embodiment of the invention, with one hub and one kite of the arrangement being shown. The difference of this arrangement 300 from arrangement 200 is that the sub-tether cord is extended and retracted by a winch 238 in the kite 10, rather than in the hub. For this, the second support rod 260 is hollow.

[0094] Figure 8 shows a front cut-away view of an alternative hub 130’. The hub 130’ is similar to hub 130, but here a slip-ring arrangement can be seen. The slip-ring arrangement is used to pass electricity generated (or required) by the kites to a ground station or a hub below. The slip-ring arrangement comprises a slip-ring cable 400 connected at its top end to the cable l20b (connected at the winch 140 axis 143). This slip-ring cable 400 is run around the winch drum 138 and then attached to a slip-ring connector 401 adjacent the cylindrical hole 132 for the swivel rod 133 of the swivel connector.

[0095] The slip-ring connector 401 is electrically connected to a transfer cable 402 that transmits electricity and is incorporated into cable l20a below its connection to the swivel connector.

[0096] The slip-ring connector 401 is also electrically connected, by second transfer cable 403, to a second slip-ring connector 404 which can transmit electricity to and from the sub-tether cord 150 to provide power and take generated power to/ffom the kites.

[0097] Figure 9 shows a front partially cut-away view of a second alternative hub 530 to that shown in Figure 4 or Figure 8. Here, it can be seen that the hub 530 has a different shape. It comprises a main arm 531 and two lower arms 532, 533. The lower arms 532, 533 are attached to a lower side of the main arm 531 at an angle and connected to each other to from a lower hub portion of the hub 530. At a lowermost portion of the lower hub portion is mounted a swivel connector 540. This will be described in more detail in relation to Figure 11.

[0098] At a central region of the main arm 531 is a main tether line attachment point 534. This is in the form of a spherical body 534 that connects to a main tether line extending above the hub 530. The body 534 also includes a sub-tether line attachment mechanism 550, as will be described later.

[0099] At each end of the main arm 531 is a support arm 536, 538 pivotally mounted to the main arm at pivot points 535, 537. An abutment portion 536a, 538a on each support arm 536, 538 prevents the support arm 536, 538 pivoting lower than level with the main arm 531.

[00100] Figure 10 is a similar view of the hub 530 of Figure 9, showing two sub tether lines 539a, 539b. The first sub-tether line 539a extends through the right side of the main arm 531 and is curved up into support arm 536. This sub-tether line 539a is connected to a first kite. The second sub-tether line 539b extends through the left side of the main arm 531 and is curved up into support arm 538. This sub-tether line 539b is connected to a second kite.

[00101] Both sub-tether lines 539a, 539b are attached to the sub-tether attachment mechanism 550 in the central region of the main arm 531. Figure 12 is close-up cut-away view of the sub-tether attachment mechanism 550. Here, it can be seen that the mechanism 550 comprises a winch drum stem 551 extending vertically in the mechanism 550. Upon the stem 551, are mounted two sub-tether winch drums 552, 553. These drums are used to winch in and out the sub-tether lines 539a, 539b. The mechanism 550 also comprises two sub-tether line guides 554, 555. The first line guide 554 is used to guide the passage of the first sub-tether line onto the first sub-tether winch drum 552. The second line guide 555 is used to guide the passage of the second sub-tether line onto the second sub-tether winch drum 553.

[00102] Figure 11 is a close-up cut-away view of the swivel connector 540 of the hub 530. Here, it can be seen that the swivel connector 540 comprises a swivel rod 541 (that is attached to a main tether line below the hub 530) that is rotatable within a bore 543a of a top holder 543. The swivel rod 541 comprises an enlarged portion 532 at an upper end to prevent the swivel rod 541 falling through the bore 543a. A bottom plate 544 is attached around the swivel rod 541 below the top holder 543, such that the bottom plate rotates with the swivel rod 541. There is a drive mechanism 545 in between the bottom plate 544 and top holder 543 that drives rotation of the bottom plate with respect to the top holder and thus drives rotation of the main tether line (below the hub 530) with respect to the hub 530.

[00103] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[00104] The first main tether may be connected to a payload rather than a ground station 110 with a generator.

[00105] The hubs 130 may have any suitable numbers of kites and corresponding sub tether cords and support rods. The examples here have shown 2 and 3 kites, but there could be four or more kites per hub.

[00106] The kite apparatus may include a lifting body, such as a rotorcraft, to help with the deployment (providing initial lift) of the kites.

[00107] Using the slip-ring arrangement, it is possible for the slip-ring cable 400 to be run thought the central axis of winch 138, instead of around it.

[00108] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A kite apparatus, comprising:

- a main tether line, for connection at a first end to a base station,

- a hub connected to a second end of the main tether line,

- a sub-tether line connected at a first end to the hub, and

- a kite connected to a second end of the sub-tether line, wherein the hub is connected to the main tether line by a swivel connector such that the hub can swivel relative to the main tether line, about a swivel axis.

2. A kite apparatus as claimed in claim 1, wherein the swivel connector comprises a swivel rod, rotatably mounted to the hub so as to be rotatable about its longitudinal axis.

3. A kite apparatus as claimed in claim 1 or claim 2, wherein the swivel connector comprises a slip ring.

4. A kite apparatus as claimed in any preceding claim, wherein the main tether line is extendable/retractable.

5. A kite apparatus as claimed in claim 4, wherein the main tether line is provided with a main tether winch drum for accommodating a variable length of main tether line, when at least partially retracted.

6. A kite apparatus as claimed in claim 5, wherein the main tether winch drum is located within or adjacent the base station or within or adjacent the hub.

7. A kite apparatus as claimed in any preceding claim, wherein the sub-tether line is extendable/retractable.

8. A kite apparatus as claimed in claim 7, wherein the sub-tether line is provided with a sub-tether winch drum for accommodating a variable length of sub-tether line, when at least partially retracted.

9. A kite apparatus as claimed in claim 8, wherein the sub-tether winch drum is located within or adjacent the hub or within or adjacent the kite.

10. A kite apparatus as claimed in claim 9, wherein the sub -tether winch drum is located within the hub and has a rotational axis, and wherein the rotational axis of the sub-tether winch drum is substantially in line with the swivel axis of the hub.

11. A kite apparatus as claimed in any of claims 8 to 10, wherein: the sub-tether winch drum is powered by a sub-tether motor and wherein the sub-tether motor is located within the hub or kite, or wherein the sub-tether winch drum is connected to a mechanical transmission from the sub-tether motor and the sub-tether motor is located externally of the hub or kite.

12. A kite apparatus as claimed in any preceding claim, wherein the sub-tether line includes a length provided by one or more support rods, for ensuring a minimum distance is maintained between the kite and the hub, when the sub-tether line is retracted.

13. A kite apparatus as claimed in claim 12, wherein one of the support rods is pivotally mounted to the hub, so as to be pivotable about an axis substantially

perpendicular to the swivel axis of the hub.

14. A kite apparatus as claimed in claim 13, wherein the angle of the support rod that is pivotally mounted to the hub is maintained within a range of angles by mechanical limit stops.

15. A kite apparatus as claimed in claim 13 or 14, wherein the angle of the support rod that is pivotally mounted to the hub is measured by one or more angle sensors.

16. A kite apparatus as claimed in any of claims 12 to 15, wherein one of the support rods is attached to the kite by a joint allowing three degrees of freedom.

17. A kite apparatus as claimed in any of claims 12 to 16, wherein one or more support rods are hollow to allow an extendable/retractable portion of the sub-tether line to pass through the one more support rods to the sub-tether winch drum.

18. A kite apparatus as claimed in any of claims 12 to 17, wherein the adjacent ends of the one or more support rods have correspondingly shaped interface profiles so that, upon retraction of the sub-tether line, the support rods can link together.

19. A kite apparatus as claimed in claim 18, wherein the correspondingly shaped interface profiles comprises a cone and a conically-shaped recess.

20. A kite apparatus as claimed in any preceding claim, wherein the hub comprises a positioning device.

21. A kite apparatus as claimed in any preceding claim, wherein the kite apparatus comprises one or more additional sub-tether lines, similar to the first sub-tether line, connected at their first ends to the hub, each additional sub-tether line having an additional kite, similar to the first kite, connected to its second end.

22. A kite apparatus as claimed in claim 21, when dependent on claim 10, wherein the first sub-tether winch drum and any additional sub-tether winch drums are located within the hub and wherein the sub-tether winch drums are stacked so that the rotational axes of the sub-tether winch drums are substantially in line with the swivel axis of the hub.

23. A kite apparatus as claimed in any preceding claim, wherein the kite apparatus comprises an additional second main tether line and an additional second hub, the second main tether line being similar to the first main tether line and the second hub being similar to the first hub, wherein a first end of the second main tether line is connected to the first hub and wherein the second hub is connected to a second end of the second main tether line.

24. A kite apparatus as claimed in claim 23, wherein the kite apparatus comprises an additional third main tether line and an additional third hub, the third main tether line being similar to the first or second main tether lines and the third hub being similar to the first or second hubs, wherein a first end of the third main tether line is connected to the second hub and wherein the third hub is connected to a second end of the third main tether line.

25. A kite apparatus as claimed in claim 24, wherein there are one or more further additional main tether lines and hubs, connected to the first, second and third hubs in a series relationship.

26. A kite apparatus as claimed in any of claims 23 to 25, when dependent on claim 6, wherein at least one of the additional main tether winch drums for an additional main tether line is located within the adjacent hub in the direction of the base station, and wherein a rotational axis of the additional main tether winch drum is in line with the swivel axis of the adjacent hub.

27. A kite apparatus as claimed in claim 26, wherein: the additional main tether winch drum is powered by a main tether winch motor and wherein the main tether winch motor is located within the adjacent hub, or wherein the additional main tether winch drum is connected to a mechanical transmission from the main tether winch motor and the main tether winch motor is located externally of the adjacent hub.

28. A kite apparatus as claimed in any of claims 23 to 27, wherein the adjacent ends of the one or more adjacent hubs have correspondingly shaped interface profiles so that, upon retraction of the connecting main tether line, the adjacent hubs can link together.

29. A kite apparatus as claimed in claim 28, wherein the correspondingly shaped interface profiles comprise a cone and a conically-shaped recess.

30. A kite apparatus as claimed in claim 29, wherein one or more hubs have a length between their ends, for ensuring a minimum distance is maintained between the kites of the adjacent hubs, when the connecting main tether line is retracted and the adjacent hubs are linked together.

31. A kite apparatus as claimed in any preceding claim, wherein one or more kites of the apparatus are capable of vertical take-off and/or landing.

32. A hub designed for use with the kite apparatus of any preceding claim.

33. A hub for a kite apparatus, the hub comprising:

- a swivel connector for connection to a main tether line, such that the hub can swivel relative to the main tether line, about a swivel axis, and

- a connector for a sub-tether line of a kite.

34. A hub as claimed in claim 33, wherein the hub further comprises a main tether winch drum for extending/retracting the main tether line.

35. A hub as claimed in claim 33 or claim 34, wherein the hub further comprises a sub-tether winch drum for extending/retracting the sub-tether line.

36. A hub as claimed in any of claims 33 to 35, wherein the connector for the sub- tether line comprises a pivotally mounted support rod.

37. A hub as claimed in any of claims 33 to 36, wherein the support rod is pivotally mounted to the hub, so as to be pivotable about an axis substantially perpendicular to the swivel axis of the hub.

38. A hub as claimed in any of claims 33 to 37, wherein the hub comprises one or more additional connectors for additional sub-tether lines, similar to the first sub-tether connector.

39. A hub as claimed in any of claims 33 to 38, wherein the hub has a first interface profile at one end and a correspondingly shaped interface profile at a second end so that similar shaped hubs can be linked together.

40. A hub as claimed in claim 39, wherein the correspondingly shaped interface profiles comprise a cone and a conically-shaped recess.

41. A kit of parts for assembling a kite apparatus, the kit of parts comprising a main tether line, for connection at a first end to a base station, a hub for connection to a second end of the main tether line, a sub-tether line for connection at a first end to the hub, and a kite for connection to a second end of the sub-tether line, wherein the hub is connectable to the main tether line by a swivel connector such that the hub can swivel relative to the main tether line, about a swivel axis.

42. A method of flying a kite apparatus, comprising the steps of proving a kite apparatus according to any of claims 1 to 31.