Aircraft mooring installation

Abstract

An installation comprises a floating platform to facilitate mooring, payload transfer and support operations for waterborne lighter-than-air aircraft such as airships and hybrid lift air vehicles. A floating platform, anchored from below, is equipped with a centrally mounted mooring mast (2). A waterborne aircraft (8) can be secured by attaching its nose to the central mooring mast via an articulated coupling that leaves the aircraft (8) free to rotate in any direction necessary to align with prevailing wave and wind forces. Additionally, the platform includes a rotatable deck and jetty structure (3, 4) incorporating one or more hinged boarding ramps (5) that are arranged to turn freely about the centre of the platform and so maintain heading alignment with a moored aircraft, whilst providing a secure access path (13) between a service boat (12) and the moored aircraft (8), irrespective of movements induced by wave and wind forces.

Description

AIRCRAFT MOORING INSTALLATIONBackground to the Invention

[0001] This invention relates to a mooring installation for a waterborne lighter-than-air aircraft, such as an airship or hybrid air vehicle.

[0002] Airships have operated from installations floating on water since the first flight of the Zeppelin LZ 1 aircraft from Lake Constance in 1900. The utilisation of water for airship mooring, take-off and landing operations is advantageous for a number of reasons:

[0003] Firstly, the aircraft and associated waterborne operating facilities (such as a hangar, boarding jetty and tie-down points) can be re-oriented into the prevailing wind direction, to minimise aerodynamically induced forces and consequent aircraft motion.

[0004] Secondly, large expanses of water provide ample space for an airship to operate from and are generally free from fixed obstructions, concentrations of human population and low- level atmospheric turbulence induced by buildings and undulating terrain.

[0005] Thirdly, water is a convenient ballast material for adjusting aircraft weight during loading or unloading operations and facilitates the damping of aircraft motion induced by wind, using devices such as drag lines, sea anchors and catenary mooring systems.

[0006] In recent decades, a number of hybrid lift air vehicle designs have been developed that utilise proportionately wider "lifting-body" hull shapes to obtain improved aerodynamic lift and control characteristics. An additional benefit derived from the greater width of these hybrid lift air vehicles is the ability to mount a wide-track landing gear directly onto the hull, whilst simultaneously providing ample ground clearance below aircraft centreline for cockpit and payload structures. Relative to conventional airship designs, these features improve the ability of hybrid lift air vehicles to operate from unprepared ground surfaces and routinely land or take-off on water, thus enabling a fully amphibious capability. With this expansion in operating flexibility, however, new challenges arise in developing the equipment and techniques necessary to leverage waterborne operations, particularly in areas of aircraft mooring, provision of external power, transfer of passengers or payload, refuelling and maintenance activities.

[0007] A key issue facing the routine operation of airships and hybrid lift air vehicles from water is how to deal with the near-continuous motion of the aircraft arising from thecombined action of wind and waves. When an aircraft is moored at the nose and ballasted to an appropriate weight, it will generally present a stable platform, provided that it is able to yaw freely to align with the prevailing wind direction. In this single point mooring arrangement, the aircraft will exhibit wind and wave keeping behaviour analogous to that of a moderately large boat. However, because the majority of the aircraft weight is supported by the buoyant action of lifting gas, the mass of water displaced by the landing gear is typically an order of magnitude lower than the aircraft's total inertial mass.

[0008] Consequently, the wave forces acting on the submerged portions of the aircraft's landing gear are opposed by significantly greater inertial mass (and aerodynamic damping forces) than applicable to an object of comparable waterline displacement, but negligible atmospheric buoyancy, such as a boat or floating jetty. Thus, it can be expected that an airship or hybrid lift air vehicle moored on water will be less subject to wave-induced movement than adjacent floating objects, also these movements will occur at lower frequencies and thus typically out of phase. Compounding these differences, the aircraft will be substantially more sensitive to wind forces than surrounding floating objects and there may be little correlation between wave-induced and wind-induced motions.

[0009] The forgoing considerations mean that any interoperation between a waterborne airship or hybrid lift air vehicle and a floating jetty or boat will inevitably need to accommodate significant and unpredictable relative motion between the respective bodies. As a result, it may frequently be unfeasible to gain access to the underside of an aircraft via these means, because of insufficient overhead clearance in typical wave and wind conditions. The solution to this problem constitutes the basis for the proposed invention.

[0010] The emergence of hybrid lift air vehicles suited to routine operation from water has only occurred in recent decades. Prior to this, there are scattered historical examples of waterborne experimentation with conventional airships, none of which appear to have yielded the significant advances in practicality and efficiency needed for long term utilisation.

[0011] Many early airships were equipped with air-inflated "bump" bags on their undersides, prior to the widespread adoption of wheeled undercarriage in the first half of the twentieth century. In addition to absorbing loads arising from ground contact, these bags provided a degree of flotation to enable an airship to land and moor on water in suitably favourable conditions. GB 316554 A extends this approach by proposing to equip the airshipwith a mooring foot structure that locks onto a buoy at water level, with the option of suspending the buoy at the centre of a circular floating platform. Whilst these arrangements may provide convenient access to the airship gondola in calm weather conditions, they restrict the airship to landing at near-zero or negative heaviness and the positioning of the mooring fulcrum point so far below the aircraft's aerodynamic centre means that strong wind gusts will induce tail-down pitching moments that exceed the available aerostatic and elevator pitch trim capability.

[0012] In the offshore oil and gas industry, tethered buoys are used for single-point mooring of large tanker vessels and transferring potentially hazardous products in locations that are remote from land. See US 2771617 A and US 2011 / 107951 Al. In some respects, these operations resemble the deployment of a waterborne airship on a floating mooring mast, as originally undertaken by the British HMA No. 1 "Mayfly" airship in 1911. However, the absence of an attachment mast, or other means of direct coupling renders these mooring systems ineffective for restraining the nose of an airship in the vertical direction, thus greatly diminishing aircraft pitch stability in moderate sea states. Similar limitations apply even when direct coupling is proposed, but the connection is only effective in a horizontal plane as in the arrangements described in US 3442245 A, US 3823432 A and US 3354479 A. Furthermore, these direct coupling mechanisms would need to be aligned to point in the downwind direction prior to engaging with an airship.

[0013] The transfer of personnel and supplies between a floating platform and a moored vessel (for example via an articulated gangway or a small service boat) can be vulnerable to adverse weather conditions. This is particularly the case when it is required to provide access to a location on the underside of an airship or hybrid lift air vehicle, with the attendant problems of limited overhead clearance and the near-continuous differential movements induced by waves and wind. US 2011 / 107951 Al and US 3983706 A describe, the application of passive or active measures to minimise the wave-induced heave of the floating platform relative to the moored vessel. In other proposals for dealing with vertical heave, US 4088089 A describes rigid connection of the mooring point to the sea floor and US 9463848 B2 describes a massive semi-submersible structure for lifting the moored vessel clear of the water, which would impose untenable weight and cost penalties for an aircraft mooring mechanism or mooring platform, respectively.US 3354479 A and WO 2017 / 217860 Al describe an established approach for dealing with the differing vertical movement of the floating platform and a moored craft, namely to use a pivoting structure to form an articulated bridge between the two locations. However, the task of engaging a pivoting structure with a target that is continually moving in 3-dimensional space may pose substantial actuation and control challenges.Summary of the InventionIt is an aim of the present invention to provide a floating platform to facilitate the mooring and operation of waterborne lighter-than-air aircraft, such as airships and hybrid lift air vehicles, with greater reliability and / or efficiency than the known installations.The invention provides an installation for mooring a waterborne lighter-than-air aircraft according to claim 1. Optional features of the invention are set out in the dependent claims.Brief Description of the DrawingsFor a complete understanding of the objects, techniques and structure of the invention, reference should be made to the following detailed description and accompanying drawings, given by way of example only, wherein:Figure 1 is a perspective view of a floating platform according to an embodiment of the invention;.Figure 2 is a cross-sectional view of the floating platform of Figure 1, deployed on water, also showing the nose of a hybrid lift air vehicle and a service boat;Figure 3 is a plan view of the floating platform also depicting the service boat, and the hybrid lift air vehicle.Detailed Description of Particular EmbodimentsThe invention provides a floating platform incorporating an array of features which serve to facilitate mooring, payload transfer and support operations for waterborne lighter-than-air aircraft, such as airships and hybrid lift air vehicles.Figure 1 shows a floating platform comprising a buoyant base structure 1, configured with a central mooring mast 2, surrounded by a rotatable deck 3 that incorporates an example arrangement of an offset jetty 4 and a hinged boarding ramp 5.Figure 2 shows the platform of Figure 1 deployed on water, to secure the nose of a notional hybrid lift air vehicle 8, with the boarding ramp positioned above 9 or below 10 the waterline 11 and a service boat 12 moored alongside the jetty 4 located on the opposite side of the rotatable deck.The buoyant base structure 1 forms the core of the floating platform and provides sufficient mass and waterline displacement to significantly restrain the motion of the attached waterborne craft 8, 12. The base structure may possess any advantageous planform shape, such as circular, polygonal, or irregular and be profiled as shown at 14 on its underside surfaces to reduce the forces exerted by wave action in the surrounding water 11.The base structure 1 incorporates a number of internal water-tight compartments 15, which may be utilised variously for ballast, fuel, machinery, equipment, personnel accommodation, or stowage space, as required for the operational support of the client aircraft 8.The base structure 1 is restrained in the water by a number of anchor lines 6 attached to its underside or lower periphery faces. These anchor lines may be actively or passively tensioned to control the location of the floating platform and attenuate any perturbation caused by attached craft 8, 12, changing water depth, water currents, or prevailing wave and wind conditions.The anchor lines 6 restraining the base structure 1 are arranged to remain at a sufficient inclination below the water surface 11 to preserve clear access to the floating platform for surface craft 8, 12 approaching from any direction. Additionally, the anchor lines do not prevent the hinged boarding ramp5 positioned at any point around the periphery of the floating platform from being angled to lie substantially below water level 10.In this example, the base structure 1 is provided with connection points for sub-surface cables and hoses 7 to supply external services such as electrical power, fuel, water, or communications.The centre of the base structure 1 is fitted with a mooring mast 2 that is capable of resisting the forces exerted by the attached waterborne aircraft 8. This geometric layout is advantageous for avoiding the need to align the floating platform with the prevailing winddirection 16 and enabling safe access to the aircraft's underside, thus facilitating docking operations and subsequent aircraft servicing activities.The central mooring mast 2 may be rigidly mounted on the base structure 1, or optionally be attached by an energy absorbing mechanism 18 with spring and damper functionality to diminish the transmission of dynamic forces to the attached aircraft 8, as may be induced by prevailing wave and wind conditions. In either arrangement, the mooring mast may take the form of a freestanding cantilever structure, or utilise radial bracing 19, the elements of which may comprise part of an energy absorbing mechanism.The upper portion of the mooring mast 2 may optionally incorporate a telescopic mechanism, or an analogous feature, that functions to vary the height of the mast, either actively driven by an integral actuation system, or passively driven by the vertical force exerted on it by an attached aircraft 8.The top of the mooring mast provides an attachment feature 20 such as an articulated conical receptacle or spherical ball that is able to engage and interlock with a corresponding feature 17 on the waterborne aircraft 8 to effect a direct mechanical coupling.The mechanical coupling between the mooring mast 2 and the waterborne aircraft 8 is arranged in a manner to permit an attached aircraft to rotate in heading about a vertical axis without restriction. Additionally, the mechanical coupling permit rotations about a set of mutually perpendicular pitch and roll axes to fully accommodate all components of angular motion that may occur between the aircraft and the floating platform, as driven by prevailing wave and wind conditions.The mooring mast attachment feature 20 incorporates a mooring line 21 that can be linked to a corresponding line deployed by a waterborne aircraft 8 to facilitate mechanical assistance with mast docking operations. The associated take-up of mooring line slack and tension control may be undertaken with a winch installed on the floating platform, or by a winch onboard the aircraft.After a waterborne aircraft 8 has engaged and locked onto the mooring mast 2, service lines 22 for the provision of electrical power, fuel and ballast water replenishment may be routed up the mast and connected in close proximity to the aircraft's mooring attachment point 17. Interconnections made in this manner will be immune to rotational motion of the aircraft about the floating platform in normal wind and wave conditions.The upper portion of the base structure 1 is fitted with a rotatable deck 3 that is able to turn freely about a vertical axis centred on the mooring mast 2. An actuation system is also provided for positively aligning the rotatable deck to any desired heading, for example, working by manual or powered means.In planform view, as shown in Figure 3, the rotatable deck 3 includes a circular central cutout 23 to provide unimpeded access to the mooring mast installation 2 and the underlying base structure 1.The outer perimeter of the rotatable deck 3 is configured to mount the jetty structure 4 configured for the alongside mooring of a service boat 12. In this arrangement, a service boat will approach and depart the floating platform in a tangential direction, thus minimising potential contact forces when docking with the jetty. Optionally, the jetty structure may be movable to different angular positions around the outer perimeter of the rotatable deck, to best accommodate ambient wave and wind conditions.The outer perimeter of the rotatable deck 3 is configured to attach the one or more boarding ramps 5 oriented in a radial direction to reach the entry door 24 of the aircraft 8 moored to the floating platform.Each boarding ramp 5 is hinged at the inboard end 25 in a manner that enables the inclination angle of the ramp to match varying aircraft door sill heights 24, including the effect of dynamic movement occurring between the floating platform and the moored aircraft 8.The inboard hinge 25 of each boarding ramp 5 is provided with a sufficient range of movement to permit the ramp to be angled substantially below water level 10, so as to prevent interference with aircraft docking operations. Similarly, in the absence of a moored aircraft, each boarding ramp 5 is capable of being raised completely clear of the water 9, to minimise ramp exposure to waves.Each boarding ramp 5 is provided with means for raising and lowering about the inboard hinge 25, actuated either from the floating platform, or from onboard a moored aircraft 8). The ramp actuation system may be either manual or powered in operation and augmented by counterbalance weighting or compensation springs to minimise the force input needed to change the ramp inclination.The actuation systems for aligning the rotatable deck 3 and varying the inclination of a boarding ramp 5 is capable of being disengaged to permit free movement of the respectivestructures. Immediately prior to disengaging these actuation systems, a winch line 26 is connected between the outboard end of the boarding ramp and the underside of the moored aircraft 8 to enable the ramp to be simultaneously pulled out of the water and caphvely aligned into a door engagement position 24. The tension control of the ramp winch line may be undertaken with a winch installed on the floating platform, or by a winch onboard the aircraft.The outboard end of each boarding ramp possesses a pivoting contact pad 27 and a lockable means of attachment to enable secure connection to a moored aircraft 8. Upon locking, this doorway connection is capable of transmitting interface loads between the outboard end of the ramp and the adjacent aircraft structure 24 whilst simultaneously accommodating a modest degree of angular movement (for example, as will arise from pitching and rolling motion of the moored aircraft relative to the floating platform).The length of each boarding ramp 5 is adjustable by the incorporation of a telescopic mechanism or similar means. This feature enables engagement with differing aircraft types and accommodates any dynamic variation in the distance of an aircraft door 24 from the ramp hinge line 25, as may result from deflection of a mast equipped with an energy absorbing mechanism 18.It will be advantageous to customise the planform shape of a boarding ramp 5 to match the external profile of a moored aircraft 8, to obtain a consistent clearance gap 28 between the two structures when the ramp is locked into position. Ramp edges adjacent to the aircraft may also be configured with compliant material to further reduce the clearance offset and cushion any potential contact.The outboard edges of the rotatable deck 3 and ramp(s) 5 are fitted with safety rails 29 to prevent personnel and large objects from falling overboard. Where necessary, these safety rails can be made retractable to provide increased clearance during ramp docking and undocking operations.Upon engagement and locking of a boarding ramp 5 onto a moored aircraft 8, any subsequent change in aircraft heading about the mooring mast 2 will cause the ramp (and thus also the rotatable deck 3 and jetty structure 4) to turn in unison with the aircraft. By this means, the rotatable elements of the floating platform will function to provide a secure and stable accesspath 13 between the service boat 12 and the entry door 24 of the moored aircraft irrespective of movements induced by wave and wind conditions.Additionally, the foregoing arrangement will ensure that the service boat 12 tied-up alongside the jetty 4 will maintain a consistent heading offset and radial separation with respect to the moored aircraft 8, eliminating any possibility of collision between the two vessels.Furthermore, the boarding ramp(s) 5 constitutes a convenient means to connect electrical, refuelling, air conditioning, or analogous ground services 30 to a moored aircraft, as may be provided by equipment located onboard the floating platform.

Claims

CLAIMS1. An installation for mooring a waterborne lighter-than-air aircraft, the installation comprising a platform arranged to float on water, and a mooring mast located at a centre of the platform, for the direct mooring of a waterborne lighter-than-air aircraft, such that the aircraft can rotate through 360° about a vertical axis.

2. An installation according to claim 1, wherein the mast is provided with an energy absorbing mechanism.

3. An installation according to claim 1 or 2, wherein the platform comprises: a deck rotatable about the centre of the platform together with the moored aircraft, and an aperture through which the mast extends.

4. An installation according to claim 3, including a jetty for a boat, rotatable with the deck at a constant distance from the moored aircraft.

5. An installation according to claim 3 or 4, including one or more boarding ramps for boarding the aircraft, rotatable with the deck.

6. An installation according to claim 5, wherein the or each boarding ramp is hinged to the deck such the ramp can be raised and lowered whilst remaining laterally aligned with the moored aircraft.

7. An installation according to claim 6, wherein the or each boarding ramp can be lowered below a waterline of the platform and raised to engage the aircraft from below.

8. An installation according to claim 6 or 7, including one or more winch lines for raising the or each boarding ramp to a boarding position.

9. An installation according to any one of claims 5 to 8, wherein the or each boarding ramp is lockable to the aircraft.

10. An installation according to any one of claims 5 to 9, wherein the or each boarding ramp is adjustable in length.

11. An installation according to any preceding claim, including service lines for the provision of services to the aircraft.

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