EP1613530A2 - Airship - Google Patents

Abstract

An airship (10) comprising an envelope and a ballonet (32) positioned within the envelope (30). Drive means is provided for supplying lateral thrust for the airship, to improve lateral control of the airship. The drive means has a dual function as it has an air supply system with an air inlet provided at the bow of the envelope of the airship for supplying air to the balonet (32) to aid pressurisation. A mooring system and detachable gondola (14) is also disclosed.

Description

AIRSHIP

The invention relates to improvements to a variety of applications, which have a small non-rigid manned airship, for example, supporting advertising indicia and patrol work. The invention also relates to improvements in the apparatus for launch (take-off) and capture (landing).

There are many examples of airship, however they suffer from a number of common problems namely, as size increases the suspended mass is more difficult to support if concentrated in one place (the gondola), because the proportion relative to the gross mass is greater and the envelope's pressure stabilised form has relatively reduced capacity to support the load. Furthermore, current designs fail to provide sufficient control for the ground handling operation to be fully automated.

An objective of the development is to minimise ground crew numbers needed for airship ground handling to just one person, essentially for mooring and to overcome difficulties. To satisfy this objective the airship needs to be arranged to provide the pilot with adequate control, particularly at slow speed near to the ground, in order that ground crew may be dispensed with. In addition, the airship needs to be provided with the means to simplify mooring procedures and be arranged to put control for mooring into the hands of the pilot - enabling the airship to moor without ground crew assistance.

The present invention seeks to overcome, or at least mitigate the problems of the prior art. According to one aspect of the present invention, there is an airship comprising an envelope and a balonet positioned within the envelope, wherein there further comprises drive means for providing lateral thrust for the airship, which drive means has an air supply system with an air inlet provided at the bow of the envelope of the airship for supplying air to the ballonet.

A second aspect of the invention provides an airship having an envelope, a ballonet located within the envelope, and a gondola secured to the envelope, wherein there further comprises drive means for controlling the airship at low velocity and a mooring system controlled by the pilot to enable the pilot to control the launch and capture of the airship.

Optionally, the drive means is a bow thruster. Preferably, the bow thruster comprises an air intake, a fan unit mounted in the air intake, a plenum chamber to contain and balance the air taken in, and a plurality of outlet ports radially disposed around the nose of the airship and a controller for controlling the opening of the outlet port to allow the air to be exhausted thereby to provide bow thrust.

There may further comprise drive means mounted on the port and starboard portions of the envelope. In one class of embodiments, the drive means is a cycloidal propeller system.

There may also comprise drive means mounted to the stern of the airship. According to an optional feature of this aspect of the invention there further comprises a ground fender having a roller ball arrangement.

According to a third aspect of the invention, there comprises a mooring system for an air ship comprising a mobile mast adapted to be attached to a vehicle, a winch line attached to the airship and a dongle connected to the free end of the winch line, wherein the mast is provided with a boss shaped to be received in the winch line housing, the boss having a port to allow the dongle to pass therethrough to be engaged with the boss, thereby to secure the airship to the mast.

A fourth aspect of the invention provides an airship having a gondola detachably connected to the envelope of the airship. Preferably, the envelope has an intermediate support collar for receiving and engaging a gondola.

A fifth aspect of the invention provides a ground fender for an airship having a ball rotatable within a socket secured to the airship, which ball is adapted to rotate in any direction.

A sixth aspect of the invention provides a cloak for securing to an airship, which cloak is capable of being fixed between a support surface and the airship, to retain the airship in a fixed position above the support surface.

Exemplary embodiments of the present invention will now be described, by way of example only in which: Figures 1, 2 and 3 are a front view, side view and bottom plan view respectively of an airship according to one embodiment of the invention;

Figures 4 and 5 are end and side views of the nose of the airship shown in Figure 1 ;

Figure 6 is a side view of the main drive means for the first embodiment;

Figures 7A to 7F illustrate how the airship is controlled at slow speeds.

Figure 8A and 8B are a side view and a plan view of the mobile mast for use with the airships described;

Figures 9A to 9F illustrate one example of mooring system;

Figure 10 illustrates a ground fender according to one embodiment of the invention;

Figure 11 A, 11 B, 11 C are a front view, side view and bottom plan view respectively of an airship illustrating the main conduit lines according to one embodiment of the invention;

Figures 12A, 12B, 13A and 13B illustrate respectively the port side elevation, the underside plan view, front elevation and rear elevation of a second embodiment of airship;

Figure 14 illustrates a suspension system for the gondola according to one embodiment; Figures 15 and 16 illustrate apparatus for providing a detachable gondola;

Figures 17A to 17D illustrate a cloak arrangement for use with an airship; and

Figure 18 illustrates a roller-ball arrangement for a ground fender according to one embodiment.

Dealing with the first embodiment of the airship shown in Figures 1 to 3, the airship (10) comprises a hull (12) to which a gondola (14) is mounted. There further comprises an empennage (16), which provides the airship with aerodynamic stabilisation and enables directional control during flight. A nose re-enforcement structure (18), described in more detail below is provided. In this embodiment the main thrust modules (20, 22) are mounted to the side portions of the hull (12). There further comprises a pressure management system (24) mounted to the nose of the airship.

A handling system is provided and designated by reference numeral 26 and there is also ground fender (28) positioned underneath the gondola to cushion the landing and to protect the gondola, and preferably the lower tail surfaces from contact.

The hull (12) is provided with an outer membrane skin (30) (or envelope). The form of envelope is maintained by internal pressure stabilisation of the outer membrane, enabling it to function as a stiff structure able to support other airship features.

In this embodiment the envelope (30) is made from longitudinally laid gores, joined at their edges with tape by the welding process. The material proposed for the envelope is a laminate with structural woven fabric load-carrier impregnated with adhesive, gas retention film and an outer protective film or coatings. The material should have strong rip resistant characteristics. The permeability of the envelope should be better than 1.0 litre/m² per day. Optionally, the envelope material is semi-translucent, enabling an internal light to produce a glowing effect at night.

A single large integral ballonet (32 shown in dotted lines) above the gondola (14) is proposed for air containment, although more ballonets may be used without departing from the scope of invention. The ballonet (32) is provided by an inner envelope membrane sack designed to keep separate and contain air used to pressurise the envelope. The ballonet is interconnected by flexible trunks (not shown), as air passages, for the pressurisation system and for access to the nose. Air management is effected through the envelope pressurisation system, described below. The ballonet and trunking also serve to provide access to systems, motors and equipment at the nose, even in flight - if necessary.

The amount of air contained in the ballonet varies from empty (when the membrane collapses and fits against the envelope) to full, accommodating changes in volume of the envelope's gas fill as atmospheric conditions change. When full, the ballonet should occupy approximately 25% of the gross envelope volume. Depending on envelope gas fill and atmospheric conditions, this enables the airship to reach a pressure altitude of about 2450 m (approx. 8000 ft). When empty the ballonet should lie against the envelope without taking load.

The ballonet membrane and interconnecting trunks join at their edge to the free flange of T tapes in the envelope. Preferably, the ballonet is made from transversely laid gores, joined at their edges by a welding process, using similar techniques and materials as the envelope. The material at the interface with the envelope is arranged to allow continuous flexure.

The ballonet interconnecting trunks or passages may be used to route systems conduit. In the preferred embodiment, the interconnecting trunks are of semi-circular section.

As shown in Figures 1 , 4 and 5, the air ship is provided with a nose reinforcement structure (18). Its primary purpose is to stiffen the forward end of the envelope preventing collapse against flight aerodynamic pressures and mooring loads. It also provides the envelope's bow with structure for the bow thruster systems; mooring systems; envelope pressurisation systems and auxiliary systems.

The arrangement of the nose reinforcement structure (18) proposed essentially comprises a nose ring (38) with a central air intake (41 ) and means for fan (36) and nose mooring installations (26); a plurality of envelope stiffening battens (44) and envelope interface provisions for attachment.

The motor driven fan system (36) is for bow thrust, ballonet fill and possible electrical power generation purposes. The fan system has a fan and stator (40) arrangement. The bow thruster and ballonet fill arrangement necessitates a nose plenum chamber (39) to contain the air from the fan unit (36). The air is then ducted via doors (42) between nose batten elements (44) at four positions for bow thrust purposes and duplicated supply ducts with control valves to the ballonet chamber (32). The plenum chamber (39) is integrally attached to the envelope (12) at its outer edge in a similar manner as the ballonet (32) and provides an air enclosure behind the bow structure and bow thrust ports.

The nose ring (38) is a large reinforcing collar. It is provided with outer rim lugs to attach the battens (44) and connected to the envelope (12) at its rear face with clamp plates (46). The clamp plates (46) overlap with each other around the nose ring and fit on the outer envelope side, thereby trapping and clamping the envelope against the nose ring using through fasteners into captive positions. The clamped faces should be provided with continuous rubber gaskets to protect the envelope and make the joint airtight. Fabric covers laced to the envelope around the nose ring (38) are used to shroud after batten joints have been made to provide a smooth profile.

The nose ring (38) may be produced as a lightweight composite framed structure. It may be skinned with heat shrink doped fabric, acting to provide a fairing for smooth airflow around the forward end.

In addition, the nose structure (18) should provide mountings for forward navigation lights, conduit, ducting, systems routing, and helium fill. It also should provide foot and hand holds plus access for maintenance and personnel use.

The nose ring (38) reinforces the envelope (12) and provides a central aperture as an intake for air into a plenum chamber (39) behind it. To prevent air passing back through the intake a non-return valve or door system is provided at the aft side. The radiating battens (44) (sixteen in the illustrated embodiment) provide envelope stiffening behind the nose ring (38). These are four-sided continuous tubular rib members shaped to the envelope's profile with internal bulkheads along their length to maintain cross sectional shape under bending loads. They are composite mouldings made in two parts (upper and lower) with special forward end fittings that enable a simple pin to be used for connection to the nose ring.

Penetrations and load patches (not shown) of various standardised size (rated load capacity) are proposed for attachment of airship features and equipment to the envelope or for handling line attachments. Each penetration is reinforced with bonded doubters and clamp rings/plates to carry the load across the aperture.

The patches comprise a base fabric to which a load tape or tapes in V or radiating finger form, as appropriate, are stitched and bonded. The load tapes also have a special fitting at their apex (usually a ring), used to attach the airship feature. A reinforcing tape may also be added to the load tape at the fitting position on the bearing surface side to prevent abrasion. Preferably, an outer cover of envelope material should be bonded to the assembly with the apex of the load tape and its fitting passed through a slit. Finally, the exposed load tape should be bound to protect it from weather effects.

The patches are also bonded to the envelope, and aligned to carry tensile loads. In this embodiment, a special spreader shoe of rigid composite construction may be used to distribute the load over several patches around the shoe's perimeter. Alternatively, several patches in a fanned arrangement may be combined, linked by short cables to a ring where the main attachment is made.

The gondola (14) is of known construction and is secured to the hull using load patches and other known connectors.

In one class of embodiments, a rip system (not shown) is used, as an emergency use only method to rapidly release the lifting gas when the airship (10) is at ground level, in order to prevent its ascent and/or free wind motion if emergency evacuation is necessary or the airship breaks loose from the mast. It is achieved by ripping the envelope (12) over a long length - thus allowing the gas to escape through the large opening produced. To this end, three independent lines are installed and attached to separate rip panels such that one line each side at the quarter length position operated by either the pilots or ground personnel from the port or starboard sides, which rip the envelope circumferentially in a near vertical direction from an upper point to the rain curtain and one along the centre-line of the upper surface, which rips the envelope longitudinally at the forward end, operated automatically if the airship breaks loose.

One example of the empennage (16) is depicted in Figures 2 and 3. This shows the surfaces in an X configuration (improving ground clearance and enhancing control surface effectiveness). They also are located at a "forward" position (compared with some known airships) enabling the surfaces to work more in the free stream plus being at a wider envelope station, improving overall lift characteristics and structural support capability. Structural support is by bracing wires and root end envelope attachments. The root end of the fins (52) are provided with a tailored cushioning sole of light material (bonded to the root rib) to avoid envelope abrasion and provide a load spreading method to replace original load paths.

The four fins (52) are fixed in an X configuration, radiating from the envelope centre- line and guyed in position from hard-points near their outboard edge by bracing cables. Inward compressive loads, where the fin presses on the envelope surface, will be resisted directly by membrane tension. Outward tensile loads are resisted by the bracing cables and these should be pre-tensioned to firmly hold the arrangement.

The empennage thus comprises the following sub-groups: fixed stabiliser surfaces (fins) (52), moveable trailing edge control surfaces (54), tail support and bracing system, control mechanisms, stops, tabs and balancing systems.

The clamp plate (46) interface of the envelope to the nose ring (38) has been discussed above. In order to facilitate this, the envelope (12) should be suitably reinforced with doublers and provided with a grommet at the edge of the aperture (similar to that used at other penetrations) to prevent the envelope from being able to withdraw past the clamp plates.

Battens are placed between fabric flanges provided with lacing holes, effectively providing channels along the envelope's outer face. It also is proposed that Velcro tape be permanently attached along the channel and the mating face of the battens to provide shear transfer. The battens should first be connected to the nose ring via a shear pin through mating lugs and then laid into the channels. Lacing with cord may then be used to fix the battens to the envelope. In addition, the aft end of the battens should be fitted into an end enclosure interconnected to reinforce around the envelope. This is to prevent puncture at the end positions should high compressive loads be experienced.

Drive means are provided to power the airship. In this embodiment the drive means are provided by a bow thruster (34) and a pair of main thrust modules (20, 22). The thrust modules enable a pilot to accurately control the air ship at low speeds to enable the pilot to launch the airship and to facilitate capture. Figures 7A to 7F illustrate the control directions: x is forward and backward motion; y is Left or Right Sideways motion (looking forward); z is upward or downward motion; p is roll clockwise or roll anticlockwise (looking forward); q is pitch nose down or pitch nose up; and r is yaw nose left or yaw nose right (looking forward).

The main thrust modules (20, 22) provide thrust in any direction around a lateral axis (360°) in order to provide precise control for realisation of the main objectives (just one ground crew person). It is proposed to use a cycloidal propeller system, which has a number of advantages, fitted at pannier positions on the envelope.

An envelope mounting arrangement, shown in Figure 6, is used for installation of the cycloidal propellers (23) and a housing nacelle (25) provides an engine compartment as well as to contain fuel plus associated systems, which is provided as a blister structure. The nacelle may be profiled to suit aerodynamic needs and be attached to the envelope by a system of load patches radially disposed around its perimeter. In addition, tensioning lines across the envelope between the LH and RH propeller units may be used to impart pre-tension against the envelope (12), in order to make the installation firm and to avoid towing-in effects from the offset thrust line (which creates a turning moment effect). The nacelle may be either a skin covered framework or monocoque shell.

Bow thrusters (42) are provided to supply lateral and vertical thrust inputs, needed for precise control of the airship's nose during mooring activities. As shown in Figures 4 and 5, bow thruster ports (42) are located at four 45° positions around the envelope between respective battens (44). The ports (42) may be shaped to suit the space between the battens and to be reinforced. Clamp rings (not shown) are provided with sealing louvre doors to close the apertures and with an actuator mechanism for operation.

The bow thruster (42) proposed largely has been discussed already in the foregoing sections, since it is a collection of parts associated with other airship features that function collectively to provide the effect, rather than a module (as for the main thrust units above). The features involved include: an air intake (41) centrally located at the airship's nose; a motor driven propeller (34) (fan or impeller) in the air intake duct with clutch engagement/ release. The motor may be located in a compartment below the duct and with a belt system to drive the propeller between parallel rotating axes; an automatic non return valve (not shown) at the back of the air intake duct preventing air from escaping back through the duct (spring closing doors); a plenum chamber (39) behind the duct to contain and balance the air taken in; outlet ports radially disposed around the nose (between battens), and mechanically operated doors at each of the outlet ports (opening inwards so that they fail closed). Bounding walls to create the plenum chamber (39) comprise a nose reinforcement structure at the front (the nose ring (39)); envelope membrane all around, as a continuous sidewall; closing membrane at the rear, to separate the chamber from the envelope's helium compartment (integral with the envelope but connected to the nose by a tie).

An operating system is provided to control the fan (36) and open the doors (42) so that the air may exhaust through the desired outlet ports, thus causing the bow thrust reactive force on the nose due to the change in momentum of the air flow under the action of the propeller.

The plenum chamber (39) behind the nose (34) also can be used for air supply to the ballonet, thereby obviating the need for a separate system - thus saving weight.

There should be little conflict from the dual use of the plenum chamber (39), since the bow thruster system (infrequently used) normally is only needed to assist control at low speed near the ground under mooring or handling operations. At these times conditions should be reasonably stable, requiring little input to the ballonet. High rates of flow on the other hand to the ballonet will be under conditions of descent with forward speed and advantage may be gained here from operation of the system, since the dynamic pressure head will assist flow (enabling fast descents to be made without loss of pressure). In order to fill and recharge the envelope (12) with helium at least 2 input points are used. Helium may be supplied either in its gaseous form in bottles or delivered from a semi-trailer tanker filled under cryogenic conditions with liquid helium. So, two types of hose filling couplings are used, together with 3 fill points - one of each type above the gondola (14) and the third for gas bottle filling at the nose (18), enabling periodic top-up at the mast.

Whilst free balloon flight is not normally envisioned this may be a useful aspect under certain conditions and is a method of flight that pilots should be acquainted with, to use as necessary. In order to execute control under these conditions, perhaps without power, the pilot needs a means to reduce the aerostatic lift when flying light (when the aerostatic lift is greater than the total weight airborne) by releasing gas. A small helium discharge valve therefore is proposed to be located just above the ballonet membrane joint to the envelope on the pilot's side.

There are two mooring positions one at the nose (26) and the other at a chin position. The reason for this is to make provision for a strong point at the axis of symmetry (the nose probe), needed to ride out adverse weather (storms) and a general operational use position (the chin housing) that reduces operational costs and is easier to use (although only for normal operating weather conditions). In this way a tall fixed mast may be used under riding out conditions whilst a short mobile mast can be used for general operation.

The chin mooring position is the one that would normally be used for handling purposes, hangar docking/undocking, launch, capture and restraint between flights. It also enables the airship to be safely taken to or deployed from the riding out mast and to its launch/capture place - enabling safe transfer.

The method devised is based on lowering a pendant line, the line being taken up and attached to a mobile mast, followed by the airship's descent (drawn by the pendant line as it is recoiled) to engage with the mast.

The airship and mast arrangement proposed for chin mooring are shown in Figures 8A and 8B, and Figures 9A to F.

The mobile mast (56) is set-up ready for use by the ground crewperson. The pilot should then bring the airship to a suitable height and position in front of the mast, facing into wind. The mast head (57) should be orientated correctly for subsequent actions through weather vane (58) control. The pilot next operates the plunger system (60) to push a dongle (62) out of its housing (64) and then lowers the pendant line (66) by winch control so that the dongle (62) is at a suitable height for capture, shown in Figure 9A. The pilot then moves the airship forward (the airship remaining above the mast) simultaneously adjusting dongle (62) height with the winch so that the pendant line (66) passes between the guide arms (68, 70) with the dongle below (but above the vehicle), shown in Figure 9B.

When the pendant line (66) is axially aligned with the mast (56) such that the line is through the conical locating boss (56) at the top of the mast, the pilot should use the winch to draw the dongle up tight against the boss. When the airship's housing (64) has mated over the mast's conical boss (56) and with the winch line drawn tight (so that the dongle is pulled against the plunger), the pilot operates the locking system to engage the locking pins (72) around the housing into the groove (74) of the conical boss - locking the airship onto the mast, shown in Figure 9C.

Apart from checking correct engagement and locking, that completes the mooring operation so that the system may be shut down. For launch the pilot first operates the locking pin (70) system to release the locks, shown in Figures 9D and 9E. This does not release the airship, since it will still be held by the dongle (62) (trapped in the masthead).

Next, the pilot applies a little bow thrust (nose up) to tension the pendant line (66) - maintaining this thrust until launched. To release the pilot simultaneously operates the plunger and winch to draw the dongle (62) through the mast's conical boss (56) into the airship's housing.

Launch follows automatically under bow thrust action, when the pilot should take full control of the subsequent free flight.

A conventional stick mast is proposed for mooring out purposes (long term parking) and to ride-out adverse weather. The mast, which can be made in several pieces (for transport) is simply guyed in position with tensioned cables, fixed using anchors to suit the soil conditions. With the configuration envisaged, ground fenders (80) will be needed to protect the gondola and possibly the lower tail surfaces from contact. Preferred angular clearances of the airship proposal are as shown in Figure 20.

The ground fender works as a bumper bag, as used by airships in the past, to cushion and spread ground impact loads over a wide area. It also provides a means for floatation, enabling the airship to settle on water. In addition, it may be fitted with a roller ball system, shown in Figure 18, to enable rolling takeoff procedures to be undertaken when the airship is heavy.

In Figure 18, there is shown one example of roller ball system (91 ) in which there is a roller ball (93) mounted in a socket arrangement (95) and held in place by a ring (97).

Similar small bump bags also are proposed to be fitted to the lower tail fins lower edge, working in the same way - although without the roller ball. These easily may be aerodynamically shaped to suit the tail surfaces. It also is proposed that the lower ruddervators lower edge be arranged to avoid ground contact.

Conduit (82) for electrical, light, signalling, fuel and pneumatic system lines are provided to all parts of the envelope needing supply. Main routes (84, 85, 86, 88) shown in Figures 11A, 11B and 1 C from the gondola (14) are proposed at the sides of the air passages on the envelope internal surface, within the air passages running to the bow and pannier positions. The power generation and motor units at other locations around the envelope. Electrical power generation units are located at the bow, configured also to serve as the motive source to drive a fan unit (via a belt and clutch system) at the nose for ballonet air supply and bow thruster purposes.

Distribution via separate left and right main power lines (84, 85), with cross feed connections is proposed as shown in Figures 11 A, 11 B and 11 C.

This effectively provides a ring main able to serve all airship parts. The main lines of this system would be retained in fabric channel doublers with either lacing, zip or Velcro connections to retain the power lines.

In addition, the main longitudinal conduit is proposed to be provided with an edge tape that acts as a method to cause rainwater break-off from the envelope as it runs down the sides. It thus would act as a rain curtain, providing a dry area beneath the hull.

The envelope and fabric structures along the conduit lines should be protected where necessary with insulation material to prevent burn through if the lines get hot (possible following a lightning attachment or electrical system fault). Electrical shielding braid also should be laid along the conduit lines, where necessary, to protect the system lines from electrical interference or lightning attachments. The external ring main conduit (84, 85) also should be provided with an edge, acting as a rain curtain, which causes water washing down from the envelope's upper sides to naturally break off, so that it does not reach the gondola - creating an umbrella effect.

A second embodiment of airship will now be described by reference to Figures 12 and 13. The second embodiment is similar to the first embodiment and like parts have been designated by the same reference numeral with the prefix '1 '. Only the differences will now be described in any greater detail.

Airships need to be provided with sufficient power to meet minimum forward speed requirements (so that they can make reasonable progress against maximum perceived adverse wind conditions) with sufficient reserves for power take-offs to run their systems. Also, special power requirements need to be provided to deal with adverse power failure conditions and to ensure that they are fully controllable during landing, taxing and takeoff (when aerodynamic control is least effective).

To compete successfully, it is believed that airships must be able to routinely depart from their mooring site and to reach their destination (as heavier-than-air craft do) without always relying on a ground crew. Bearing in mind that lighter-than-air craft are more vulnerable to adverse weather, this may not always be possible. For the majority of the time, however, the weather is not particularly disruptive - so for light weather unassisted landing field operations are seen to be a necessary goal. When the weather is bad this will then make airfield operations much safer, ensure that go-a-rounds are avoided and enable fewer ground crew to handle the situation. For the airship, shown in Figure 10, on normal airship operations the maximum installed power may only need to be used for short periods, the majority of the flight requiring only a small amount of the total power available. The units therefore need to be configured in such a way that performance is optimised. A stern thrusters (190) is believed to improve overall efficiency, by drawing the air around the envelopes rear profile (reducing drag), this unit is selected as the main unit to propel the airship (110). The pannier thrusters (120, 122) may therefore be operated at a low power setting or shut down with propellers feathered during cruising flight.

A stern thruster (190) with reverse thrust also enables the airship (110) to be stopped and, if necessary, flown backwards. Since it also draws air over the empennage (116) it should improve aerodynamic control at the stern. Vectored thrust at the stem is not necessary for most cases, since it is the airship's bow that needs to hold station and this cannot be so easily achieved from the rear. Also, a stem thruster (190) acting along the envelope's centre-line does not cause much pitching moment. Losses due to counteraction of such a moment from thrusters at a lower level therefore are obviated.

A bow thruster (134) enables the airship's nose (118) to be precisely controlled for lateral station keeping purposes. An airship (110) operated mooring method can then be used with confidence. In combination with differential longitudinal thrust from the port and starboard pannier thrusters (120, 122) (balancing the moment about the airship's centroid), the bow thruster (134) also can be used to track the airship (110) sideways, avoiding go-around situations to get the airship in the right place for mooring. Vertical bow thrust is considered to be unnecessary, since airship height is more effectively controlled using the pannier thrusters vectored up with propellers pitched to effect either up or down thrust.

Since a bow thruster (134) normally would only be needed for low speed control near the ground the power unit also is used for other purposes. One of its uses is to supply power to run the airship's normal operating systems. A second function is to provide the means to supply air to the ballonets, for envelope pressurisation purposes. A third use is to supply power for the bow systems, to enable an automated mooring system to be operated.

Vectored thrust has been shown to be a useful feature in modern airship flight control. This feature is therefore employed for the same reasons. Since the stern thruster (190) is used as the primary means to propel the airship the vectorable side units are lighter and used more as quick response units for low speed control. They also help to propel the airship (110) in forward flight for maximum speed, should this be required, improving safety of flight by enabling storm fronts to be outrun.

There are a number of benefits of this approach including the thrust line in forward flight is raised towards the aerodynamic centroid, reducing adverse pitching moment effects (which otherwise would need to be counterbalanced by aerodynamic control from the tail surfaces) and therefore reducing overall drag. Also, the vertical thrust line does not pass through the envelope's profile, improving vertical thrust efficiency by a considerable amount, making them more effective for height control and avoiding propeller wash debris from hitting the envelope (112). In this embodiment, the empennage (116) may be provided with a fixed upper dorsal fin (153) with no moving parts and which does not increase overall airship height. Apart from occasional inspection, to ensure structural integrity, the dorsal fin (153) is virtually maintenance free.

The main surfaces of the fins (152) on each side are arranged symmetrically such that the substantially vertical surfaces (147) hang below the horizontal surfaces (149), attaching at their upper edge to the outboard edges of their respective horizontal surface - forming an elbow (151), shown in Figure 13A. The elbow joint relationship is fixed using struts between the surfaces. The horizontal surfaces are affixed from the envelope (112) using bracing wires (157). Both the horizontal and vertical surfaces carry control surfaces at their trailing edge (154) to manoeuvre the airship in flight.

A lower dorsal fin (155), similar to the upper surface, also may be provided. This would be fitted with a bumper bag (157) at the lower edge to provide a reaction point to settle against the ground on and to protect other systems during launch or capture when the tail may strike the ground.

The principal benefits of this arrangement are that the main surfaces are much more easily inspected from ground level prior to flight and maintenance operations are greatly eased, since very high reach equipment is unnecessary. Indeed, with provision of hard points along the rear spar for personnel use, access onto the surfaces for maintenance or close inspection purposes at the mast is easily afforded, making high reach equipment obsolete. Clearly, both personnel and airship safety issues are greatly improved by the arrangement. Other aspects of the arrangement not discussed are common to other airships. In reality, whilst large, airship tail surfaces are very light structures. The additional cantilevered mass therefore should not cause problems for the support system. Also, with the enlarged rear envelope end (needed for the stem thruster) the envelope should have sufficient membrane tension to resist additional load at the root end.

Ground fenders (128) are used instead of wheeled undercarriages since these are considered to provide the most suitable, safe, maintenance free and reliable reaction system for the airship. Pontoons also enable the airship to settle on water - an aspect believed to enhance airship-operating uses.

Four reaction positions generally are provided, disposed as follows: one beneath the gondola and one at the lower edge of each (3 off) vertical tail surface (discussed above). With such a widely disposed arrangement stability in a free landing situation to keep the airship essentially level will be possible - although the tail unit fenders are only designed for settling loads and as bump stops to protect the propeller units if too much pitch or roll occurs. The fender (128) beneath the gondola (114) is the main unit used for reaction of normal landing loads.

To enable the gondola (114) to be routinely removed requires an interface that can be disconnected easily, without damage, and then reconnected by reversal of the process. The preferred apparatus is illustrated in Figures 14, 15 and 16. This fundamental aspect enables the gondola (114) to be treated as a module or piece of equipment, just like any other large or heavy airship item (such as tail surfaces and engines) which may need to be removed and then reinstalled for whatever reason (replacement, repair, maintenance, access, reconfiguration, etc).

The height of a non-rigid airship envelope (112) is very difficult to predict due to the nature of the pressure-stabilised form, which varies due to changing conditions. Due to this, an adjustment facility (192) is required to rig the suspension system - enabling the cables (194) to be correctly set by adjusting the pulleys (196) on the collar (133), to support the gondola (114). Rigging the suspension system can be a laborious and difficult task if each cable has to be treated separately. By grouping the cables (194) at four lower positions (2 each side) as shown in the Figures 12A and 14, so that they fan upwards from a forward and aft position with the gondola's centre of gravity roughly midway between, structural redundancies of the system may be overcome and a simplified adjustment facility provided, as shown below, enabling the rigging to be performed quickly.

With the cables (194) grouped as shown a large area inside the envelope (112) is made available to install operators' special equipment (such as radar antennae), without compromising suspension system integrity.

In Figure 15, there is shown an intermediate support collar (1 13) between the envelope (112) and the gondola (114) from which the gondola may be disconnected whilst leaving the intermediate collar's attachment to the lower envelope and the vertical suspension system intact. In this way the interface may be closely matched and mechanical fasteners used to make the interface joint. The joint between the intermediate support collar (113) and the envelope (112) is similar to that of a simple clamp ring (115), as used at valve penetrations.

This simple method enables the envelope (112) to be replaced if this should be necessary. It also efficiently transfers load from the gondola (114) enabling both vertical support and shear to be borne uniformly around the long perimeter of the support collar (113) without slippage. The gondola (114) itself carries the envelope membrane tension across the envelope (112). The joint also will be able to support the gondola should there be complete failure of the vertical suspension system, although envelope deflections would be much larger.

When the gondola (114) is removed envelope super-pressure would be reduced to zero. Load across the aperture would then be very much reduced. The gondola intermediate support collar (113) should then be able to carry the residual envelope membrane tension without further assistance, providing a clear passage through the aperture for special installations. Also, since the super-pressure is zero there would be no loss of helium other than that caused by circulation and draughts.

The gondola intermediate support structure provides capacity as tanks for water ballast and, fitted with rails, may be used to hang additional ballast bags to compensate for the mass of the gondola when removed. It can be used to handle the envelope with the gondola removed. It also provides the structure to mount internal envelope equipment, which can then remain installed when the gondola is removed. Access to the automatic systems at the bow (for mooring) and the power units mounted at extreme positions on the envelope, needs to be provided for in-flight rectification purposes (should this be necessary). This is enabled through use of the air passages and the ballonet system - accessed from the gondola (114). Since the gondola (114) is partially inserted into the envelope (112), entry into the passages is simply accomplished through hatches or doors - the air passages being connected directly to the gondola. A simple air-lock system on the envelope side is used at the door to prevent the pressurised envelope air from flowing into the gondola.

The air passages give access into the ballonets (132), enabling the air valves to be inspected. Also, special air passages may give access to the upper envelope surface (a vertical trunk with climbing frames) and, if necessary, to the pannier mounted power units. Otherwise, the ballonets are used to gain access to the extreme envelope positions, the ballonets being designed so that they envelop the bow and stern.

At least two ballonets (not shown) are supplied, one forward the other aft. These may be differentially inflated to move the centre of buoyancy position enabling out of trim pitching moments to be balanced for level landing. A transfer fan between the forward and aft ballonets, normally needed to pump the air entering at the bow to inflate the stern ballonet, enables the ballonets to be inflated to different levels.

Electrical systems, fuel, ballast, fire protection, lighting and environmental control systems are provided for the aforementioned embodiments, by using known systems and are not therefore described in any greater detail. In Figures 17A to 17D, there is shown a cloak 200 which is fixed to a support surface 202, for example the ground. The cloak is designed to enclose the lower portion of the airship 110, and to hold it in a fixed position, thereby to protect it and allow access for maintenance. An aperture 204 allows part of the airship 110 to pass there through, as shown best in Figures 17B.

The airships, described above, surpass the standards of both previous and current airships of their size, and achieve new standards in being able to:

• Unmast, taxi, take-off, land, and moor without any ground crew support.

• Operate and be maintained from small unprepared grass fields with minimal ground handling facilities or crew in weather gusting to 30 kts.

• Unassisted, settle onto and take-off from water.

• Go into a large number of existing hangars or be ground fixed within their own transportable cloaking facility - able to endure severe weather.

• Rapidly remove and replace modularised units for off-airship maintenance.

• Reach external attachments for systems, parts and equipment, with facilities no higher than the horizontal plane at the envelope's centreline.

• Remove snow easily whilst the airship is moored, because of draped features that do not entrap or enable accumulation on upper surfaces.

• Provide minimally, airline business standard passenger comfort, safety, boarding and emergency evacuation.

Furthermore, the airships are more controllable at low airspeed, since the propulsion units may be arranged to provide the most effective control and with greater overall airship operating efficiency.

Claims

1. An airship comprising an envelope and a ballonet positioned within the envelope, wherein there further comprises drive means for providing lateral thrust for the airship, which drive means has an air supply system with an air inlet provided at the bow of the envelope of the airship for supplying air to the ballonet.

2. An airship having an envelope, a ballonet located within the envelope, and a gondola secured to the envelope, wherein there further comprises drive means for controlling the airship at low velocity and a mooring system controlled by the pilot to enable the pilot to control the launch and capture of the airship.

3. An airship as claimed in claim 1 or claim 2, wherein the drive means is a bow thruster.

4. An airship as claimed in claim 3 wherein the bow thruster comprises an air intake, a fan unit mounted in the air intake, a plenum chamber to contain and balance the air taken in, and a plurality of outlet port radially disposed around the nose of the airship and a controller for controlling the opening of the outlet port to allow the air to be exhausted thereby to provide bow thrust.

5. An airship as claimed in any preceding claim further comprising drive means mounted on the port and starboard portions of the envelope.

6. An airship as claimed in claim 4 wherein the drive means is a cycloidal propeller system.

7. An airship as claimed in claim 5 or claim 6 wherein the drive means mounted to the stern of the airship.

8. An airship as claimed in any preceding claim further comprising a ground fender having a roller ball arrangement.

9. A mooring system for an air ship as claimed in any preceding claim, comprising a mobile mast adapted to be attached to a vehicle, a winch line attached to the airship and a dongle connected to the free end of the winch line, wherein the mast is provided with a boss shaped to be received in the winch line housing, the boss having a port to allow the dongle to pass therethrough to be engaged with the boss, thereby to secure the airship to the mast.

10. An airship having a gondola detachably connected to the envelope of the airship.

11. An airship as claimed in claim 9 wherein the envelope has an intermediate support collar for receiving and engaging a gondola.

12. A ground fender for an airship having a ball rotatable within a socket secured to the airship, which ball is adapted to rotate in any direction.

3. A cloak for securing to an airship, which cloak is capable of being fixed between a support surface and the airship, to retain the airship in a fixed position above the support surface.