WO2008093085A1

WO2008093085A1 - Transfer of fluid to aircraft

Info

Publication number: WO2008093085A1
Application number: PCT/GB2008/000318
Authority: WO
Inventors: Colin Jack
Original assignee: Colin Jack
Priority date: 2007-01-31
Filing date: 2008-01-31
Publication date: 2008-08-07
Also published as: GB0701789D0

Abstract

A method of transferring a fluid to an aircraft from a surface station comprising: the aircraft flying in a coupled circular pattern such that at least a portion of a hose coupled to said aircraft and said surface station adopts a vertically extended spiral configuration which rotates about a vertical axis centred on said surface station, and passing fluid up the hose from a fluid source at the surface station to the aircraft. The method is particularly suited to refuelling an aircraft from the ground or a ship. However other fluids can be transferred e.g. for effecting climate or weather alteration. Also disclosed is method of transferring a fluid to an aircraft from a surface station comprising: the aircraft flying in an acquisition circular pattern such that the lower end of a tether extending from said aircraft is drawn towards an axis passing through the centre of said acquisition circular pattern, acquiring the lower end of the tether at the surface station, using said tether to establish a fluid connection between a fluid source at said surface station and said aircraft and passing fluid up the hose from said fluid source to the aircraft.

Description

Transfer of Fluid To Aircraft

This invention relates to methods of transferring fluids to aircraft, particularly but not exclusively, for refuelling purposes; and to apparatus for use in such methods.

It is often desirable for aircraft, in particular military aircraft, to operate to locations beyond their normal range from land bases. Two methods of achieving this are currently available: air-to-air refuelling and aircraft carriers. Both methods have severe limitations. Aircraft carriers are expensive, and limited in the size and type of aircraft they can operate. Air-to-air refuelling, where an aircraft needing to be refuelled docks on a hose trailed behind a larger, fuel-carrying aircraft, is limited by the range and capacity of the flying tankers themselves: a very large and expensive fleet of aerial tankers is required to provide refuelling at long distance from land bases.

The present invention seeks to provide an alternative method of transferring fluid to an aircraft which can be used in refuelling and other applications.

When viewed from a first aspect the invention provides a method of transferring a fluid to an aircraft from a surface station comprising: the aircraft flying in a coupled circular pattern such that at least a portion of a hose coupled to said aircraft and said surface station adopts a vertically extended spiral configuration which rotates about a vertical axis centred on said surface station, and passing fluid up the hose from a fluid source at the surface station to the aircraft.

When viewed from another aspect the invention provides a method of refuelling a fixed wing aircraft directly from the surface comprising lowering a trailing hose from the aircraft in such a way that the end of the hose touches the surface at lower to zero speed and connecting the hose end to a high pressure fuel pump so that the aircraft can be refuelled via the hose. When viewed from a further aspect the invention provides a method of refuelling a fixed wing aircraft from a surface station comprising lowering a trailing hose from the aircraft in such a way that the end of the hose touches the surface at a lower speed than the speed of the aircraft and connecting the hose end to a fuel pump so that the aircraft can be refuelled via the hose.

Thus it will be seen by those skilled in the art that the present invention provides a way of transferring fluid to a fixed wing aircraft from a point on land or on a ship. Although there are other applications which are discussed hereinbelow, this has clear advantageous application to the refuelling of aircraft since the technique herein described allows an aircraft to acquire fuel from a ship, submarine, or land-based facility while circling. Thus in a set of preferred embodiments the fluid is an aircraft fuel.

By making direct surface-to-air refuelling achievable, the invention has the potential to bring about substantial savings. Specifically, because a fixed wing aircraft can be refuelled from a surface ship or ground facility while in flight, the following missions would become possible at reasonable cost: high performance land based combat aircraft could strike land or sea targets at unlimited distance; AWACS

(airborne warning and control system) aircraft could patrol continuously for very extended periods, hundreds or even thousands of hours; it would become possible to airlift heavy cargo to almost any destination at any distance, needing only a makeshift airstrip without refuelling facilities at the far end since the aircraft could take off for the return leg almost empty, but refuel immediately from a ship offshore; or an unmanned aerial vehicle (UAV) could remain airborne for up to its entire operational life.

It has been known for a long time that if an aircraft tows a long rope, to the end of which a small payload may be attached, and flies in a circle of appropriate radius, the payload is drawn into the centre and hangs essentially stationary along an axis passing through the centre of the circle. This was originally proposed in order to allow cargo to be dropped by fixed wing aircraft in inaccessible places more precisely than though parachute drops. It was subsequently proposed in US 6427944 to adapt the technique to make a fibre-optic connection between a circling aircraft and the surface. It is believed that this has not been widely adopted in practice - presumably due to improvements in secure wireless communications.

However it has not, so far as the applicant is aware, been previously suggested to transfer fluid using such a connection. Prior to the development of helicopters of reasonable performance, a technique was occasionally used whereby a container at the end of a long rope, deployed from an aircraft flying in a circle, could be made to hang nearly stationary at the centre of the circle: thus a payload could be set upon or retrieved from the ground. Trivailo has studied updating this technique for various purposes, including lifting a large container of water for forest firefighting purposes ("Flying circles around the helicopter", David Hambling, New Scientist, 30 April 2005). However there has been no suggestion of using a hose in place of the rope to pump water or other liquid up to the aircraft. This is unsurprising as the rope length needs to be many times the aircraft's turn radius: e.g. Trivailo calculates ~3,000 metres for a medium-sized aircraft. A corresponding hose could be at most a few centimetres in diameter and could upload at most a few litres per second, an ineffective rate for firefighting, and even then would be a major encumbrance to the aircraft.

At least in its preferred embodiments the present invention provides a practicable system and method for establishing a connection between an aircraft and a ship or ground facility, for emplacing a hose of dimensions which can be used to transfer fluids at rates useful for certain applications, and those applications.

The invention extends to a hose adapted to transfer a fluid to an aircraft from a fluid source at a ground station.

The hose could be provided on the aircraft. For example it could be paid out directly from the aircraft to make the connection with the surface station. Alternatively a line attached to the hose could be paid out first, the line allowing the hose to be pulled from the aircraft towards the ground or ship.

In preferred embodiments however the hose is provided at the surface station (e.g. a ship or ground station) and a line (e.g. a rope, cable or the like) is paid out from the aircraft which can be used to pull the hose up to the aircraft. For example in the preferred embodiments the end is acquired by the surface station, the line is attached to the hose, and a winch aboard the aircraft winds in the line until the hose has replaced the line. This arrangement is advantageous as in general the physical parameters (length, diameter, stiffness, strength, etc.,) of a hose which are optimal for fluid transfer purposes are not the same as those of a rope or other line which would be optimal for initial end acquisition, and which will occupy minimum space aboard the aircraft. It further means that the aircraft does not have the weight and space penalty of carrying the hose.

Deploying a line to acquire the hose is also advantageous as it permits, in accordance with particularly preferred embodiments, the aircraft to descend as the line is wound in from the acquisition circling pattern required to carry out the initial operation to acquire the end of the rope, to a lower altitude coupling pattern . This allows the length of the actual hose to be shorter than the rope, which is advantageous in terms of cost, weight and fluid transfer time.

Preferably the combination of the height at which the aircraft circles in the coupled circular pattern and the length of hose are such that the length of hose is significantly longer than the distance between the aircraft and the surface station. The deployed length is preferably at least 50% more than said distance, more preferably at least twice as long. The curve formed by the hose then tends to be one that in plan elevation has the approximate shape of a logarithmic spiral so that the configuration adopted by the hose is an approximate logarithmic spiral which is vertically extended. The outermost, hence fastest-moving, portion is then nearly parallel to the airflow it experiences. Since the drag on an inclined cylindrical element is roughly proportional to the cube of the angle between its axis and the airflow, as well as to the square of the airspeed, the total drag on the hose, and hence the work which must be done by the aircraft engines to counter this drag, is very much less than the drag on a straight-line hose connecting aircraft and surface station would be, even though the latter would be shorter - e.g. it is reduced by at least a third, preferably at least two-thirds. The spiral is moreover drawn out in the vertical direction, with the vertical slope steepest near the centre and shallowest at its maximum radius, thus the outer part generates aerodynamic lift with a good lift-to-drag ratio. By adopting the vertically extended spiral shape described herein the lift will counteract the weight of the hose filled with fluid (e.g. fuel) to at least some extent - preferably reducing the effective weight by at least a third, preferably two-thirds.

The tether could just have a plain end, but preferably comprises a payload at the end to serve as ballast. An end payload of significant weight and/or aerodynamic drag plays a useful role, helping the end of the line pull in toward the centre of the circle with a shorter line length than would otherwise be required; it can also provide aerodynamic damping to reduce pendulum swing. The end payload can be landed directly aboard a ship, or can be a buoy which acts as a sea anchor after entering the water at low speed, and is subsequently brought aboard a ship.

The hose may have a permanent circular or other open cross section, or could be configured to be collapsible so as to enable it to be rolled flat onto a reel. The latter is preferable from the point of view of being less bulky for storage on the aircraft but requires inflation and positive internal pressure to give it a cylindrical shape of desired aerodynamic properties. Such inflation may be performed as it is paid out by an air pump attached to the lower end of the hose, which may be part of the ballast payload.

The applicant has appreciated a further benefit achievable in accordance with the invention in that centrifugal force helps to force fluid up the hose, countering both static pressure, due to the aircraft's height above sea level, and viscous drag. Thus only a relatively small fuel pump, e.g. situated aboard a ship, might be required and the pressure in the hose can be kept modest at all points. Indeed it is envisaged that by judicious choice of flight parameters for the fluid transfer phase - in particular, if the aircraft altitude is sufficiently low and its speed sufficiently high - then centrifugal force will cause fuel to flow up the hose with little or no additional pumping required. If in addition the hose geometry is appropriate (ideally, if the hose lies on the surface of an appropriate parabola of revolution) there will be little internal pressure for the hose to withstand, as centrifugal pressure roughly counterbalances static head pressure at every point. If the hose is put under significant tension at the ends, relative to the aerodynamic force on it, it will tend to hang in a shape intermediate between a catenary, (which it would adopt under gravity alone), a spiral (which it would adopt under aerodynamic force alone) and a triptych (which it would adopt under centrifugal force alone); this can be made a reasonable approximation to such ideal geometry.

The preferred refuelling methods in accordance with the invention could be used to refuel directly the aircraft to which the fuel is transferred. In some preferred embodiments however the aircraft is itself a refuelling tanker suitable for refuelling other aircraft, e.g. using conventional air-to-air refuelling. There are advantages to the aircraft employed being an air-to-air refuelling tanker and these will be briefly discussed below.

Firstly, because the volumetric rate of flow through a hose is roughly proportional to the cube of its diameter, a large aircraft, such as a refuelling tanker, capable of supporting a large hose can upload fuel faster (even in proportion to its own size) than a smaller one.

Secondly an aerial tanker can act as a cache: able to remain on station for long periods because it is continuously supplied with fuel at a modest rate, it can transfer fuel much more rapidly to individual aircraft which dock for brief periods. Thirdly, any aircraft equipped with a Standard air-to-air refuelling probe can use a ship-plus-aerial-tanker system in accordance with the invention; there is no need for each aircraft to be carry a hose of the type required in accordance with the invention. This means that an effectively unlimited number of aircraft, of any size, can be refuelled by the system. A series of such systems, placed at appropriate intervals, can support missions of effectively unlimited range.

Fourthly, if the aerial tanker periodically disconnects and reconnects from the ship, it can refuel aircraft in straight and level flight, and at some distance from the ship if so desired.

Fifthly, use of an aerial tanker avoids significant delay compared to individual aircraft having to emplace their own hoses before refuelling.

As the aircraft is circling and the hose is connected to the fluid source on the ground, it will experience a twisting tendency. This can be accommodated in several Ways - e.g. by constructing the hose to tolerate the anticipated degree of twisting, reversing the aircraft periodically or allowing the fluid source (e.g. a cylindrical tank) to rotate. Alternatively a rotary coupling could be provided at one end of the hose or indeed anywhere along its length. The hose specified in accordance with the invention may therefore incorporate a rotary coupling.

The tether used during the acquisition phase could be the hose itself, or could be a line - e.g. a rope - which can be used to pull the hose from the aircraft to the surface station, or more preferably, from the surface station to the aircraft.

In preferred embodiments the tether comprises a payload at its free end. Such a payload can assist in drawing the end of the hose/line towards the vertical axis passing through the centre of the acquisition circular pattern so that the end hangs near vertically. It can also assist in acquisition of the end of the hose/line at the surface. The payload could be buoyant in water for example; or could be deformable and/or adhesive or magnetic to prevent recoil upon striking a solid surface.

The acquisition method disclosed herein is considered novel and inventive in its own right and thus when viewed from a further aspect the invention provides a method of transferring a fluid to an aircraft from a surface station comprising: the aircraft flying in an acquisition circular pattern such that the lower end of a tether extending from said aircraft is drawn towards an axis passing through the centre of said acquisition circular pattern, acquiring the lower end of the tether at the surface station, using said tether to establish a fluid connection between a fluid source at said surface station and said aircraft and passing fluid up the hose from said fluid source to the aircraft.

The tether could be a hose and so used to establish the fluid connection directly; or it could be a line used to pull a hose between the surface station and the aircraft to establish the connection.

The applicant has also appreciated that all of the principles and preferred features of the invention apply equally to a cable used to establish an electrical connection to an electrically powered aircraft (such as a UAV) as they do to a hose used to establish a fluid connection.

Thus when viewed from a yet further aspect the invention provides a method of powering an aircraft comprising establishing an electrical connection between said aircraft in flight and a surface station by means of a cable coupled between them and passing electrical current from the surface station to the aircraft via the cable.

Such a method preferably comprises the aircraft flying in a coupled circular pattern such that at least a portion of the cable adopts a vertically extended spiral configuration which rotates about a vertical axis centred on said surface station. The method preferably comprises the aircraft flying in an acquisition circular pattern such that the lower end of a tether extending from said aircraft is drawn towards an axis passing through the centre of said acquisition circular pattern, acquiring the lower end of the tether at the surface station, using said tether to establish said electrical connection.

The tether could be a cable and so used to establish the fluid connection directly; or it could be a line used to pull a cable between the surface station and the aircraft to establish the connection.

Since preferred features of the earlier aspects of the invention apply equally to this aspect of the invention, references to hose and fluid should be understood to apply equally to cable and electrical current respectively.

Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. Ia is a schematic diagram illustrating an aircraft carrying out an embodiment of the method of the invention; Fig Ib is a schematic diagram of an acquisition circular pattern;

Fig. Ic is a schematic diagram of a coupled circular pattern;

Fig. 2 is a schematic illustration of a payload at the end of a rope;

Fig. 3 is a schematic illustration of a hose coupling to an aerial tanker;

Fig. 4 is a schematic illustration of an anti-twist arrangement; Fig. 5 is a schematic illustration of an alternative method of acquiring the end of the tether; and

Fig. 6 is a schematic illustration of an application of the invention for climate modification.

A preferred implementation of the invention will now be described with reference to Figs. Ia, Ib and Ic. Fig. Ia shows an aircraft 2 such as a conventional aerial tanker. The aircraft 2 is fitted with a winch and a rope 4. The rope 4 has a ballast payload 6. In order to make a fluid connection between the aircraft 2 and a ship such as a fleet auxiliary tanker (not shown), the following steps are performed. Firstly the aircraft 2 enters a circular flight pattern as indicated by the dashed line 8. The aircraft pays out the rope 4, to the end of which a ballast payload 6 is fastened, until the payload 6 is travelling in a circle 10 of smaller radius and correspondingly lower speed than the aircraft. For example if the aircraft's velocity is 200 knots, travelling in a circle radius 1000 metres, the payload' s speed might be 20 knots, travelling in a circle radius 100 metres.

The descent rate and trajectory of the payload 6 are controlled by adjusting the aircraft's height and course, and/or varying the rate at which the rope 4 is paid out, so that the payload 6 reaches a chosen touchdown point at a chosen time travelling with a chosen velocity vector. It has been appreciated that if the end payload 6 were to be near stationary with respect to the surrounding air, there would be very little aerodynamic damping force to prevent pendulum swing and other unwanted motion. The best strategy to keep control of the end's position, altitude and velocity vector in real-world conditions is to aim not for zero airspeed, but motion at a chosen airspeed. Also, a receiving ship can more readily be positioned if it has good steerage way than if it is stationary. Maintaining a significant descent rate, rather than hovering, allows more precise control of landing point and time.

The acquisition circular pattern of the aircraft 2 and the corresponding configuration of the rope 4 are shown in Fig. Ib. The lower end of the rope 4b is drawn towards the central axis of the aircraft's circular flight pattern 8 so as to hang near-vertical

The ship 11 manoeuvres so that it will reach the touchdown point at the chosen time travelling at speed and direction such that the payload will land with approximately zero lateral speed relative to the deck. The manoeuvre should allow for wind speed. For example if the ship is capable of 20 knots, and the payload is designed to orbit stably at a 20 knot airspeed, then in zero wind the ship should be steaming at top speed in the same direction as the payload motion at the moment of touchdown. If - l i ¬

the wind speed is 40 knots, the ship and payload should both be travelling downwind at touchdown. At intermediate wind speeds, there is a choice of ship speed and direction for zero relative touchdown speed.

A schematic illustration of a possible payload is given in Fig. 2. This design is intended to ensure that the payload moves as little as possible after touchdown. The payload in this embodiment comprises a three-sided prism 12, with an inflated crash balloon 14 or piston-like shock absorber (not shown) at the lower end to avoid damage upon impact. After impact the payload comes to rest on one side of the prism 12. The rope 4 can be attached by means of a universal joint 16 so that the rope end may turn freely after impact. If the payload 12 is sufficiently massive, the rope 4 will not become slack after impact, nor touch the deck at any point.

The rope 4 is attached to the end of the refuelling hose (not shown) which is provided on a winched drum on the ship. If necessary the payload with rope still attached can first be moved to an appropriate point.

The winch aboard the aircraft 2 can then reel in the rope as the aircraft descends and adjusts its course until the aircraft is in a new flight pattern, typically a circle of larger radius and lower altitude than before. This manoeuvre minimizes the hose length required: the hose can if required be much shorter than the rope.

The winch continues to reel in the rope until the end of the hose is aboard or close to the aircraft. The hose 13 is connected to the aircraft 2 so that fuel may be transferred. This is shown in Fig. Ic. Here can be seen the vertically extended spiral configuration of the hose 13 which rotates about the central axis of the coupled circular pattern 15 of the aircraft 2. It can be seen by comparison of Figs. Ib and Ic that the coupled circular pattern 15 is lower in altitude and greater in diameter than the acquisition circular pattern 8.

The aircraft 2 can now be refuelled. If it is an aerial tanker which is equipped with one or more refuelling points additional to that required for the hose, it can also refuel other aircraft from an effectively unlimited supply, as a ship can provide a capacity 1,000 or more times that of an aircraft. It also means that the aircraft can continue to circle indefinitely.

The fuel is heated to reduce its viscosity. This could be done on the ship or in the hose - e.g. by passing an electrical current along the hose and using resistance heating along part or all of the hose.

If the aircraft is an aerial tanker equipped with a steerable boom, then the boom may be docked with the end of the hose without the hose actually being brought aboard the aircraft. This is shown in Fig. 3. In this case the rope 4 may connect to the hose 18 via a yoke 20, the rope 4 being split at its end to connect to the ends of the yoke 20. At the join of the yoke 20 is a receiving cup 22 attached to the end of the hose 18, the cup 22 being designed to accommodate the aircraft's steerable boom 24. A weight 26 may be provided, attached beneath the yoke 20, to prevent the arrangement from spinning. An advantage of never bringing the hose aboard the aircraft is safety: any leak in the hose cannot affect the aircraft 2. The rope 4 can pass through a guillotine 28 so that in emergency the rope may be instantly cut at any time.

Clearly if the hose is fixedly attached at both ends it will gradually become twisted as the aircraft circles. This can be avoided by providing one or more rotary couplings at some point along the hose or at one or both ends.

An alternative to using rotary couplings is to employ an arrangement like that shown in Fig. 4. In this arrangement, a pump 30 is provided at the lower end of the hose 32. The pump 30 is mounted on or within a turret 34 which can rotate. The hose 34 is connected to this pump 30. Fuel maybe sucked up into the turret 34 from a tank 36 beneath via a pipe 38 mounted at or near to the centre of the turret 34. In the embodiment shown the surface of the turret 34 is set flush with the deck 40 so that the ballast payload 42 may readily be moved onto it after touchdown. The turret 34 may also house any handling equipment (not shown) and/or winch(es) or drum reel(s) 44 used to deploy or retrieve the hose 32 and/or any rope used.

There are many further alternative ways to deal with the twisting tendency imparted to the hose by the circling motion of the aircraft, noting that turning the aircraft, and/or the ground station to which the hose is connected, about any axis can prevent the hose becoming twisted. In one example the hose is attached to a wheeled vehicle (e.g. a tanker lorry with a tight turning circle, equipped with a pump) which turns as the plane orbits, either driving slowly in a circle or making consecutive forward-and-reverse turns. The wheeled vehicle may be periodically substituted, and/or replenished by being connected to a high-flow external fuel supply for brief periods. The wheeled vehicle can operate on the deck of a ship if required.

In another alternative the ground station could turn at the same angular rate as the orbiting aircraft, e.g. a ship turning with the aid of rudder, twin screws and/or a bow and/or stern thruster.

In another example the ground station can roll about its horizontal axis once per aircraft orbit. While not practicable for a conventional ship, this is achievable if the ground station is a cylindrical fuel tank with attached pump, either floating in the sea or mounted on bearings on the ground, even if its long axis is horizontal.

In other alternatives the aircraft could be manoeuvred to avoid twisting - e.g. by rolling it through 360 degrees once per orbit, or several times in a row, to untwist the hose; or the aircraft can reverse direction after a certain number of orbits, e.g. by performing a half-loop followed by a half-roll.

Alternatively the hose may be designed so that it can survive substantial twisting. For example if the structural fibres are set at 45 degrees to the axis, the hose will be stiff in twisting; but if the fibres are divided between pure circumferential and pure longitudinal, there is little resistance to twist. At -30-60 orbits per hour, it may take hours for the twist limit to be approached. At this point pumping could be stopped, a valve at the base of the hose sealed, the hose uncoupled and the end spun to de-twist (and if desired counter-twist) it before recoupling.

In yet another example there may be a rotating collar at the attachment to the aircraft at the upper end of the hose, where the internal pressure is typically less than at the lower end.

After the refuelling has been completed or whenever it is desired to break the connection between the aircraft and the ground station, the hose could be recovered by reeling it back onto the ship or aircraft by essentially reversing the sequence of actions by which it was emplaced. Alternatively the aircraft could drop its end of the hose into the sea, the hose subsequently being reeled aboard the ship; or the end aboard the ship could be released, so that the aircraft flies off trailing the hose; it may subsequently reel it aboard. Alternatively the hose could simply be jettisoned.

An alternative method of acquiring the end of the rope (or other form of tether such as the hose itself) on a ship to landing it directly aboard the ship will now be described with reference to Fig. 5. For this method the ballast payload is be designed so that it floats, at least when the tension in the tether (line or hose) to which it is attached is taken into account, and will act as a sea anchor after being dropped into the sea. For example it could be a plastic cylinder (solid or hollow) to the lower end of which a metal weight is attached. Many other forms are possible, e.g. a bucket or open-ended bucket. After the payload is floating and effectively stationary (as it will quickly become, irrespective of whether it initially enters the sea at significant vertical and/or horizontal speed) the attached tether (rope or hose), which may be vividly coloured for maximum visibility, will rise taut approximately vertically above the payload. The ship steers towards the tether. Smooth rails 46 - 54 (or a plurality of vertically displaced such rails) may be fitted to one side of and/or all around the ship's bow 56. The tether is guided by the rails 46 - 54 into one of the retaining clips 58, 60 located on either side of the bow 56, and secured. If the ballast payload is denser than water, it can optionally be allowed to sink sufficiently deep beneath the surface that it is minimally affected by wave motion and hence the attached tether is easier to capture. If the ballast payload is denser than water and the end of the tether is rope, said rope may be cut after capture: the end portion attached to the ballast payload will sink rapidly, avoiding any danger of entangling with the ship's propellers.

The line deployed first and used to pull the hose could comprise any suitable tensile member such as rope or cable. The rope may take the form of a thin- walled tube, including a layflat hose inflated as described above. Such a tube may be desired in place of a conventional rope because it has a large aerodynamic cross-section in proportion to its weight, even if the tube is not used as a fuel-transmitting hose.

The methods and apparatuses described above could be used to transfer fluids other than aircraft fuel. In such a case, the aircraft involved can still be kept aloft for long periods if required. For example the hose could be used to pump aircraft fuel and the other fluid(s) required in sequentially, draining the hose if necessary before a switch is made. Alternatively an additional hose or hoses could be provided, either separate or attached to the main hose, so that more than one kind of fluid can be transferred simultaneously. For example this could be achieved by means of a composite hose comprising two or more independent conduits. Of course conventional air-to-air refuelling could be used instead, the hose being used only for transferring other fluids.

A particular application envisaged by the applicant involving the transfer of other fluids is in weather and climate control. Methods have been proposed whereby the injection of material into the atmosphere at altitude could alter the weather at scales ranging from the local to the global. For example, sliver iodide crystals have been scattered from aircraft to induce raindrop formation in clouds. Materials which reflect or absorb radiative energy could have particularly useful effects. At a small scale, 'harnessing the butterfly effect,' Hoffmann and Almaro have suggested (http://www.foxnews.com/story/0,2933,306201,00.html) that scattering a few hundred tonnes of soot particles from aircraft could (by absorbing sunlight from above and/or infrared from below, hence changing the local vertical temperature profile of the atmosphere at carefully chosen places and times) be used to steer a weather system, e.g. to steer a hurricane away from land. At a large scale, Crutzen (Albedo enhancement by stratospheric sulfur injections, Crutzen P, Climatic Change (2006), doi:10.1007/sl0584-006-9101-y) has suggested that introducing 1-2 million tonnes of sulphur or sulphur compounds per annum into the stratosphere, where their residence time would be about one year, could by causing the formation of high clouds of reflective ice particles offset the entire global anthropogenic greenhouse effect. Crutzen has suggested artillery shells fired from the ground, rockets, or high altitude balloons as methods of injecting this material into the stratosphere.

The method herein described could allow very large amounts of material to be injected into the atmosphere for such-like purposes at very low cost, using a comparatively small number of aircraft. A single large conventional aircraft with a towed hose could inject up to 100 kg/sec (3 million tonnes/year) at 10 km altitude. A 'daisy chain' of two or more aircraft could be used to transport even larger flows to higher altitudes as shown in Fig. 6.

In the method illustrated in Fig. 6, a first aircraft 62 is initially set in straight flight trailing a first hose 64. A further aircraft 66 docks with the end of the hose 64 using a probe (not shown) similar to a standard air-to-air refuelling probe but mounted so that it can be rotated through 180°. The second aircraft 66 ascends and both the first and second aircraft 62, 66 fly similar circles at different altitudes as shown, with the centre portion of the first hose 64 substantially vertical and close to the system's central axis of motion. A second hose 68 is connected to a surface station such as a high-pressure pump mounted on a ship 70 using the methods described hereinabove.

The substance uploaded could comprise freshwater or seawater. No supply vessel is necessarily required at the base of the hose in this case: the payload at the end of the hose might consist of a turbine-driven pump, which is deposited into the water. Fuel to power the pump might be supplied downward from the aircraft by a smaller secondary hose, attached to the main one which conveys the water upwards. Or the aircraft might similarly provide power down wires attached to or embedded in the hose to an electric pump.

Alternative substances to be uploaded could include: a slurry, emulsion, mixture, solution etc. of soot or other particles, suspended or dissolved in water or hydrocarbon or other liquid; molten sulphur; sulphuric acid; liquid metal which is expelled through nozzles so as to form particles, needles or fine wires; or sufficient fuel to allow deliberately inefficient combustion in the aircraft engines to produce soot particles (or extra fuel burned separately to produce soot particles). Of course any other liquid, gas or aerosol, e.g. soot in air, could be used.

The injected substance can be distributed by being sprayed from holes or nozzles set into the hose itself, as well as (or instead of) from the tow aircraft, to distribute it more widely.

Combustion to produce a convection current can lift the injected substance further. The column of air within which the aircraft circles will anyway be heated by waste heat from its engines. The rising-convection-column effect can be increased by combustion of sulphur, combustion of additional fuel pumped for the purpose, etc. Thus a substance distributed at normal aircraft operating height ~10 km, below the equatorial tropopause, can be made to rise above the tropopause into the stratosphere.

One specific application is to prevention of Arctic warming. Water, sulphur or sulphur compounds can be injected directly above the more modest polar tropopause height. Although the stratospheric residency time of the clouds produced would be shorter than for equatorial injection, cover for ~3 months of the Arctic summer would be almost as effective as year-round cover, as insolation at other times is low to zero. Another specific application is to providing rainfall to avert drought. Water could be injected directly into the air which, taking into account wind direction and vertical convection, would then be transported substantial distances inland before raining out. Alternatively, systems could be used to generate areas or lanes of cloud or opaque material above the ocean, separated by areas or lanes of clear air. Sunlight would heat the water surface in the open areas or lanes more than that beneath the occluded areas or lanes, so inducing air convection currents which could lift large quantities of saturated air from just above the sea surface to high altitude.

It will be appreciated that only certain preferred embodiments of the invention have been described thus far. There are many possible variations, some examples of which are given below:

• Rather than an aerial tanker being used, individual aircraft (e.g. combat aircraft) can carry their own hoses or winch-and-rope equipment to refuel directly from a ship or ground facility etc.

• The payload is designed to land on the ground or other solid surface, possibly taking the form of an anchor.

The payload, possibly taking the form on an anchor or grapple, is landed on a net, deployed vertically horizontally or at an intermediate angle.

• The payload is retrieved from the air or water with the aid of a line-throwing gun or harpoon gun, grab mounted on a moveable arm, suction system, magnetic attraction/levitation system, etc.

• The fuel-providing ship is replaced by a submarine or by a land-based facility.

• The tanker aircraft is replaced by an AWACS which is thereby enabled to remain continuously on station for an extended period. Alternatively an appropriate aircraft can serve as both an AWACS and a refuelling tanker.

The payload contains a system enabling its position to be actively controlled during the final stages of descent: for example a set of compressed air jets, compressed air being provided by the aircraft via the hose; or the payload can carry electrically driven fans powered either by a battery onboard the payload or power supplied by the aircraft via wires attached to or embedded in the line.

The payload is of variable mass, for example capable of jettisoning ballast weights and/or liquid contained in a tank within the payload and/or the endmost part of the hose, and/or by the end part of the hose or a tank within the payload being filled with liquid poured down the hose, and/or by solid weight(s) slid down the interior or exterior of the line.

The payload is of variable aerodynamic drag, for example by means of deploying and/or jettisoning drogue parachute(s) and/or inflatable airbag(s), and/or by the payload taking a form whose drag intrinsically varies with airspeed, for example a weighted cylinder which passively orients substantially horizontal at high airspeed but substantially vertical at low airspeed.

• The payload incorporates fixed aerodynamic surfaces, and/or moveable aerodynamic surfaces so that it can be actively steered. • The circling aircraft is unmanned, an autonomous and/or remote controlled vehicle.

• The circling aircraft has electrically powered engine(s), the connecting rope or hose being equipped with conducting wires, instead of or as well as a fuel hose, so that the ground station or ship may provide electricity, continuously and/or to recharge batteries aboard the aircraft. This applies particularly where the aircraft is a UAV.

• The payload or parts of the payload are covered with glue, or equipped with magnets, so that it sticks to the surface upon which it impacts.

The payload takes the form of malleable adhesive material such as glue which will deform upon impact so that a large area of it is in contact with the surface of the deck etc. on which it impacts, and it then sticks to said surface.

• The end payload serves as an air anchor, e.g. provides an inflatable shape or drogue parachute which becomes essentially stationary with respect to the air.

• Payloads are passed up or down the rope or hose, e.g. by gripping it with motor-driven wheels. • The end payload is deposited on a target ship's helipad, which provides the advantages that it is usually a high friction surface with no overhanging structure presenting a clearly visible target.

• An end payload in the sea, or the rope or hose attached to it, is retrieved by the use of a helicopter or a small boat or a diver (either retrieved directly, or by having a line attached to it) and/or by being harpooned and/or captured with the use of a line-throwing gun or boathook.

• If the end payload is in the sea the attached tether (line or hose), rather than the payload itself, is captured by a ship: note that the line or hose will rise vertically, so it can be captured by relatively simple means such as a boathook wielded by a sailor on a deck at whatever height above the sea.

• In place of a fuel -providing ship, one or more fuel caches on or beneath the sea surface are allowed to drift with the current to the target site; they can be disguised as mines, dead whales, icebergs, etc. • The hose has its outer diameter increased by the addition of bristles, foam plastic, aerogel etc. so as to increase the aerodynamic force on it, for example to damp the motion of the lowermost part.

• Fuel is pumped down the hose from an aircraft to the surface.

• The end payload is omitted. • The end payload touches down at relatively high speed, being brought to rest only after impact. The curvature of the tether due to the aircraft turn will help prevent an excessive longitudinal shock wave from being transmitted along the tether to the aircraft.

• The tether is made of an elastic material e.g. nylon, to reduce the shock transmitted along the hose when the end strikes the surface.

The tether is deployed from the aircraft in flight, e.g. by being unreeled from a drum; and/or similarly recovered aboard the aircraft before landing.

• The tether is deployed in flight by releasing the coiled or folded tether from an initial station inside or attached to the aircraft. • A drogue parachute attached to the end causes and/or assists the tether's deployment from the aircraft. • The already-deployed tether may simply be dragged along the runway after landing and/or upon takeoff. It may be protected from abrasion e.g. by angled wire bristles which also reduce the coefficient of friction with the ground..

• The hose may be jettisoned before the aircraft lands; it may be dispensable, or survive being dropped to the ground or sea surface. A parachute could be deployed from either end of the hose to reduce its fall speed.

• The fuel is preheated to lower its viscosity before transit through the hose; the hose may also be equipped with means of warming the fuel, e.g. electrically.

• Much or all of the pressure gradient necessary to make fuel flow up the hose is provided by centrifugal force, reducing or eliminating the need for a pump at the lower end.

An outer core around the hose e.g. of foam rubber provides thermal insulation and/or mechanical protection, and also increase aerodynamic force on the hose: this may be desirable to drag the hose into a tight spiral as the aircraft turns.

The actions described herein may be performed in an order different from that given in respect of the examples described herein, and some actions may, in accordance with the invention, be overlapped in time or omitted altogether.

Rather than deploying a rope which is used to retrieve the hose from the ship's deck, the aircraft may simply deploy the hose itself, with a ballast payload at the end which is acquired by the ship as described.

Rather than descending after a connection with the ship is established, the aircraft may remain at the same height or ascend to a higher altitude. This is appropriate if, for example, the aircraft is an AWACS.

Especially if deployed from aboard the aircraft, the hose used may be a layflat hose. A layflat hose can be stored compactly aboard the aircraft.

The aircraft may carry a hose to which an additional length of rope is attached at either or both ends. After the end of the rope-plus-hose is retrieved by the ship, winch(es) aboard the ship and/or aircraft reels in the rope(s) until the hose end is acquired.

The aircraft may pay out the tether before it enters the acquisition circular flight pattern.

Claims

Claims:

1. A method of transferring a fluid to an aircraft from a surface station comprising: the aircraft flying in a coupled circular pattern such that at least a portion of a hose coupled to said aircraft and said surface station adopts a vertically extended spiral configuration which rotates about a vertical axis centred on said surface station, and passing fluid up the hose from a fluid source at the surface station to the aircraft.

2. A method as claimed in claim 1 comprising an initial acquisition stage in which the aircraft flies in an acquisition circular pattern such that the lower end of a tether extending from said aircraft is drawn towards an axis passing through the centre of said acquisition circular pattern

3. A method as claimed in claim 2 wherein said coupled circular pattern is lower than the acquisition circular pattern.

4. A method as claimed in claim 2 or 3 wherein said coupled circular pattern has a larger radius than the acquisition circular pattern.

5. A method as claimed in any preceding claim wherein said tether comprises a line which is used to pull the hose from one of the aircraft and the surface station to the other.

6. A method as claimed in claim 5 wherein said line is longer than said hose.

7. A method as claimed in claim 5 wherein said line is at least 50% longer than said hose.

8. A method as claimed in claim 5 wherein said line is at least twice as long as said hose.

9. A method as claimed in claim 2, 3 or 4 wherein said tether comprises the hose.

10. A method as claimed in any of claims 2 to 9 wherein said tether comprises a payload at the end thereof to serve as ballast.

11. A method as claimed in any of claims 2 to 10 comprising landing the end of the tether on a solid surface.

12. A method as claimed in claim 11 when dependent on claim 10 wherein said payload is one or more or deformable, adhesive or magnetic.

13. A method as claimed in any of claims 2 to 10 comprising landing the end of the tether on water.

14. A method as claimed in claim 13 when dependent on claim 10 wherein said payload is buoyant in water.

15. A method as claimed in any preceding claim wherein in plan elevation said vertically extending spiral is an approximate logarithmic spiral.

16. A method as claimed in any preceding claim wherein said inclined spiral is such as to reduce the aerodynamic drag on the hose by at least a third compared to the drag on an equivalent hose passing directly between the aircraft and the surface station.

17. A method as claimed in any preceding claim wherein said inclined spiral is such as to reduce the aerodynamic drag on the hose by at least two thirds compared to the drag on an equivalent hose passing directly between the aircraft and the surface station.

18. A method as claimed in any preceding claim wherein said inclined spiral and said hose are configured such as to produce an aerodynamic lift on the hose equal to at least a third of the weight of the hose when full of said fluid.

19. A method as claimed in any preceding claim wherein said inclined spiral and said hose are configured such as to produce an aerodynamic lift on the hose equal to at least two thirds of the weight of the hose when full of said fluid.

20. A method as claimed in any preceding claim wherein said inclined spiral and said hose are configured such that centrifugal force provides at least a third of the pressure required to pump said fluid up the hose against gravity and viscous friction.

21. A method as claimed in any preceding claim wherein said inclined spiral and said hose are configured such that centrifugal force provides at least two thirds of the pressure required to pump said fluid up the hose against gravity and viscous friction.

22. A method as claimed in any preceding claim wherein said inclined spiral and said hose are configured such that centrifugal force provides all of the pressure required to pump said fluid up the hose against gravity and viscous friction.

23. A method as claimed in any preceding claim wherein the hose is configured to be collapsible, the method comprising the step of applying a positive internal pressure to the hose to restore an open cross-section thereto.

24. A method as claimed in any preceding claim comprising heating said fluid.

25. A method as claimed in claim 24 comprising heating said fluid using the hose.

26. A method as claimed in any preceding claim wherein the aircraft is an aerial refuelling tanker suitable for refuelling other aircraft.

27. A method as claimed in any preceding claim wherein the aircraft is at least part of an airborne warning and control system.

28. A method as claimed in any preceding claim wherein the aircraft is unmanned.

29. A method as claimed in any preceding claim wherein the aircraft is electrically powered.

30. A method as claimed in any preceding claim wherein said hose is coupled to a rotatable structure at one end to reduce twisting thereof.

31. A method as claimed in any preceding claim wherein said hose is coupled to a rotatable pump at one end to reduce twisting thereof.

32. A method as claimed in any preceding claim wherein the ground station comprises a boat or ship.

33. A method as claimed in any preceding claim wherein the fluid comprises aircraft fuel.

34. A method as claimed in any preceding claim comprising injecting a substance into the atmosphere from the aircraft and/or from the hose.

35. A method of controlling weather and/or climate comprising transferring a fluid from a ground station to an aircraft according to the method of any preceding claim and injecting said fluid or a substance derived therefrom into the atmosphere from said aircraft or said hose.

36. A hose suitable for use in the method of any preceding claim.

37. A hose adapted to transfer a fluid to an aircraft from a fluid source at a ground station.

38. A hose as claimed in claim 36 or 37 comprising a payload at one end thereof to serve as a ballast.

39. A hose as claimed in claim 36, 37 or 38 comprising a rotary coupling at an end thereof or along its length.

40. A hose as claimed in any of claims 36 to 39 comprising means for carrying an electrical current.

41. A hose as claimed in any of claims 36 to 40 comprising means for heating fluid therein.

42. A hose as claimed in any of claims 36 to 41 comprising a plurality of independent fluid conduits to allow respective fluids to be conveyed independently therethrough.

43. A method of refuelling a fixed wing aircraft directly from the surface comprising lowering a trailing hose from the aircraft in such a way that the end of the hose touches the surface at lower to zero speed and connecting the hose end to a high pressure fuel pump so that the aircraft can be refuelled via the hose.

44. A method of refuelling a fixed wing aircraft from a surface station comprising lowering a trailing hose from the aircraft in such a way that the end of the hose touches the surface at a lower speed than the speed of the aircraft and connecting the hose end to a fuel pump so that the aircraft can be refuelled via the hose.

45. A method of transferring a fluid to an aircraft from a surface station comprising: the aircraft flying in an acquisition circular pattern such that the lower end of a tether extending from said aircraft is drawn towards an axis passing through the centre of said acquisition circular pattern, acquiring the lower end of the tether at the surface station, using said tether to establish a fluid connection between a fluid source at said surface station and said aircraft and passing fluid up the hose from said fluid source to the aircraft.

46. A method of powering an aircraft comprising establishing an electrical connection between said aircraft in flight and a surface station by means of a cable coupled between them and passing electrical current from the surface station to the aircraft via the cable.

47. A method as claimed in claim 46 comprising the aircraft flying in a coupled circular pattern such that at least a portion of the cable adopts a vertically extended spiral configuration which rotates about a vertical axis centred on said surface station.

48. A method as claimed in claim 46 or 47 comprising the aircraft flying in an acquisition circular pattern such that the lower end of a tether extending from said aircraft is drawn towards an axis passing through the centre of said acquisition circular pattern, acquiring the lower end of the tether at the surface station, using said tether to establish said electrical connection.