GB1594973A

GB1594973A - Air cushion vehicles

Info

Publication number: GB1594973A
Application number: GB4997877A
Authority: GB
Original assignee: British Hovercraft Corp Ltd
Current assignee: GKN Aerospace Services Ltd
Priority date: 1978-05-24
Filing date: 1978-05-24
Publication date: 1981-08-05

Description

(54) IMPROVEMENTS IN OR RELATING TO AIR CUSHION VEHICLES (71) We, BRITISH HOVERCRAFT COR PORATION LIMITED, of Yeovil, in the County of Somerset, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to air cushion vehi- cles, and is more particularly concerned with a flexible skirt assembly that forms at least part of the cushion sealing means on an air cushion vehicle.

For efficiency of cushion containment, the lower edge or hemline of the flexible skirt on an air cushion vehicle must readily conform to terrain variations so as at all times to achieve an effective seal to minimise the escape of cushion air under the skirt. If the skirt drags upon the surface over which the vehicle is operating, or becomes immersed when that surface is water, there is an increase in total vehicle drag so that additional power is required to propel the vehicle.

Whilst the skirt hemline should readily deflect when it comes into contact with the surface, it is important that the deflected portion of the skirt should quickly regain its original shape after deflection in order to minimise the loss of cushion air.

A skirt has conflicting requirements, since it must have good response to contact with the surface so that it will readily deflect, and at the same time it requires high stiffness in order to maintain its operational configuration under normal loading and to aid quick recovery after deflection. To date, on our air cushion vehicles, these conflicting requirements have been met by a two-part skirt configuration, the upper part of the skirt being formed as an inflatable bag that is stiffened by being inflated, while the lower part of the skirt is formed by a plurality of adjacent and independent flexible skirt elements known in the art as segments or "fingers".Each finger comprises a generally triangular shaped sheet of flexible material that is folded so as to comprise an outer arcuate part that is concave with respect to the vehicle supporting air cushion, and two web portions extending one from either side of the arcuate part into the cushion. The upper edges of the web portions are attached to the bag, and the upper edge of the concave portion is attached to an apron that depends downwardly from an outer surface of the bag so as to reduce the escape of cushion air between the bag and the outer parts of the fingers. In operation, the fingers are inflated by cushion air so that the webs of adjacent fingers are brought into contact with each other.

In operation, those fingers along the longitudinal sides of the vehicle are subject mainly to deflections in a fore and aft direction with respect to the vehicle. Whilst the tips of the fingers at the skirt hemline are responsive and will deflect locally to small waves or surface undulations, the stiffness of the fingers in the fore and aft direction increases as they approach their attachment to the bag member. Thus, if high bending loads are applied in the fore and aft direction at the lower parts of these fingers they will not readily deflect over their complete height to relieve these loads. Under such loading that part of each finger which is compressed by the bending, puckers, and if the bending is further increased the finger collapses about a well-defined foldline, so that it lies against the underside of the bag member.This loss of stability delays recovery of the fingers and during this period they behave in a random manner, serving no useful purpose and either contributing to hydrodynamic drag or allowing large amounts of cushion air to escape.

It is an object of the present invention to provide a flexible skirt that is particularly suited for use as the cushion sealing means along the longitudinal sides of the vehicle, and which may be used as the cushion sealing means at other peripheral parts of the vehicle.

Accordingly, in one aspect of the invention cushion sealing means for an air cushion vehicle comprises a flexible skirt of corrugated form adapted to be attached to the vehicle in such manner that each corrugation has an outer part arcuate in plan with the concave side thereof facing the cushion, and webs extending towards the cushion from the sides of the outer parts, characterised in that the skirt is adapted to be attached to the vehicle structure solely by attachment, along lines that slope upwardly and outwardly with respect to the underside of the vehicle, of those parts of the webs that are innermost with respect to the cushion.

Another aspect of the invention provides an air cushion vehicle having cushion sealing means comprised at least in part by a flexible skirt of corrugated form, each corrugation having an outer part that is arcuate in plan view with its concave side positioned to face the cushion and webs extending from the sides of the outer part towards the cushion, each corrugation being attached to the vehicle structure solely by attachment, along lines that slope upwardly and outwardly with respect to the underside of the vehicle, of those parts of the said webs that are innermost with respect to the cushion.

In one embodiment of the invention the adjacent webs of adjacent corrugations are joined together, and the complete skirt, or a section of the skirt, may comprise a strip of flexible sheet material that is folded to form the outer arcuate parts and the webs of the corrugations. In this embodiment of the invention the skirt may be attached to the vehicle by rods that are inserted into the loops formed by the fold lines in the sheet material where adjacent webs of adjacent corrugations merge to join each other. Preferably, the adjacent webs of each pair of adjacent corrugations are fastened together near to the fold lines between the adjacent webs so as to form a substantially closed loop into which the attachment rod is inserted.

In alternative embodiment of the invention the adjacent webs of adjacent corrugations are not joined together. In this embodiment the skirt comprises a plurality of independent corrugations, and each corrugation may be formed by folding a substantially rectangular sheet of flexible material so as to form an outer part that is arcuate in plan view and two webs extending from either side part of the arcuate part to terminate at edge portions which are arranged for attachment to the vehicle. Preferably, the terminal edge portions of the two webs of each corrugation are turned back on themselves and fastened to form loops into which attachment rods can be inserted for fixing the element to the vehicle.

In a skirt according to the invention having the lower edges of the webs normal to the inner edges of the webs, the dimension by which the skirt extends below the underside of the vehicle is dictated by the slope of the attachment line, a steep slope giving a smaller skirt clearance dimension, and hence cushion depth, than a shallow slope. The skirt clearance dimension may be further increased by profiling the lower edge of the skirt so that the included angle between the lower and inner edges of each web is larger than 90 degrees, however, care must be exercised in increasing this angle since there is a corresponding reduction in the included angle at the lowermost tip of the skirt, i.e. the angle formed by the outer arcuate part and the lower edge of the web, and if the tip included angle is very much less than 90 degrees the stability of the skirt may be impaired.

When the skirt is assembled on the vehicle the upper edges of the skirt comprised by the upper edges of the outer arcuate parts and the webs, abut with structure that extends outwardly from the vehicle to overlie the upper edges of the skirt so as to prevent substantial escape of cushion air therethrough. At least those parts of the skirt that extend generally in the direction of normal motion of the vehicle, i.e. those parts of the skirt extending along the longitudinal sides of the vehicle, are free from attachment to this structure, so that these parts of the skirt are substantially unrestrained in bending in a fore and aft direction about the attachments of the innermost edges of the webs to the vehicle.

The structure that overlies the upper edges of the skirt may comprise rigid structure that extends downwardly and outwardly from the vehicle. If desired, rigid structure of the vehicle to which the inner edges of the webs are attached may be constructed in the form of a downwardly extending skeg that contacts the water when seas over which the vehicle is operating exceed the free height of the skirt. Alternatively, the structure that projects outwardly from the longitudinal sides of the vehicle to overlie the upper edges of the skirt may comprise flexible structure.

This flexible structure may be inflatable, and may be positioned between the upper edges of the skirt and rigid structure extending outwardly from the vehicle.

In one embodiment of the invention the inflatable flexible structure comprises a bag that is inflated to a pressure corresponding substantially to the pressure of the air cushion on which the vehicle is supported. If desired, holes may be provided in the bag at positions corresponding with the open upper part of the skirt so as to provide communication between the interior of the bag and the spaces that are defined by the outer arcuate parts and webs of the skirt and the rigid structure of the vehicle to which the webs are attached. Preferably a strip of flexible material extends downwardly from the bag to form an apron that overlaps the uppermost edges of the outer arcuate parts of the skirt.

In another embodiment of the invention the inflatable structure comprises a plurality of side-by-side flexible members of the kind known in the art as "fingers", these members being attached at their upper edges to rigid structure that extends outwardly from the vehicle. Preferably, a strip of flexible material is attached along the outermost edges of the outer arcuate parts of the fingers so as to form an apron that overlaps the upper edges of the outer arcuate parts of the skirt.

In a further embodiment of the invention the inflatable structure comprises a plurality of side-by-side flexible pocket members inflated to a pressure substantially corresponding to the pressure of the air cushion on which the vehicle is supported. The pocket members may be arranged for inflation by cushion air which passes into them through holes in their lower parts.

In yet another embodiment of the invention the flexible skirt is attached to a wall structure that is pivotal with respect to the side of an air cushion vehicle, and whereby the position of the lower tips of the skirt can be controlled. In operation of the vehicle the pivotal wall structure extends outwardly and upwardly with respect to the underside of the vehicle. The pivotal wall structure may be attached to the vehicle by suitable hinge means at either the upper edge or the lower edge thereof, and the angle of the pivotal wall structure with respect to the vehicle may be controlled by variable length jacks extending between the pivotal wall structure and the side of the vehicle. Additional structure extends from the upper edge of the pivotal wall structure to overlie the upper edges of the skirt so as to prevent substantial escape of cushion air therethrough.Preferably, this additional structure is formed as an integral part of the pivotal wall structure.

In operation of an air cushion vehicle over the sea, the passage of a wave through the cushion reduces the cushion volume and the cushion pressure rises. This sudden surge of cushion pressure may result in undesirable vertical acceleration, or heave motion, being imparted to the vehicle. To reduce this heave motion means may be provided for venting the cushion when cushion pressure rises above a predetermined value.In the present invention venting of the cushion may be accomplished by hinging at least part of the structure that overlies the upper edges of the skirt, the hinged structure being biased by resilient means, against the action of normal cushion pressure, towards a position in which is abuts with the upper edges of the skirt, and whereby when the cushion pressure rises above a predetermined value the biasing force of the resilient means is overcome and the hinged structure is moved away from the upper edges of the skirt to allow air to escape from the cushion.

If desired, means may be provided whereby the vehicle commander is able to effect movement of the hinged structure away from the upper part of the skirt when the cushion pressure is normal so that cushion air may be vented for other reasons, such as directional control of the vehicle.

Various embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through part of the rigid structure at the side of an air cushion vehicle, and illustrates a flexible skirt forming cushion sealing means in one embodiment of the invention; Figure 2 is a cross-section through the flexible skirt taken on line X-X in Figure 1; Figure 3 is a similar cross-section to that shown in Figure 1, and illustrates a flexible skirt in a second embodiment of the invention; Figure 4 is a cross-section through the flexible skirt taken on line Y-Y in Figure 3; Figure 5 is a similar cross-section to that shown in Figure 1, and illustrates a flexible skirt in a third embodiment of the invention;; Figure 6 is a part sectioned pictorial view of the embodiment shown in Figure 5; Figure 7 is a similar cross-section to that shown in Figure 1, and illustrates a flexible skirt in a fourth embodiment of the invention; Figure 8 is a similar cross-section to that shown in Figure 7, and illustrates a flexible skirt in a fifth embodiment of the invention; and Figure 9 is a cross-section through cushion-sealing means at the longitudinal side of an air cushion vehicle in accordance with another embodiment of the invention.

The cushion sealing means along at least the longitudinal sides of an air cushion vehicle (not shown in full) comprises a flexible skirt 11 of corrugated form, as shown ii Figures 1 and 2. The skirt 11 extends across the outlet end of a duct 12 defined by structure of a rigid buoyancy compartment 13 and rigid structure 14 forming an upper portion of the vehicle. The duct 12 leads from a lift fan (not shown) which supplies pressurised air to build up and sustain an air cushion 15 between the underside of the buoyancy compartment 13 and a surface 16 over which the vehicle operates.

In this particular embodiment of the invention, a flexible skirt 11 comprises a sheet of fabric reinforced rubber material that is folded to form a plurality of adjacent corrugations, each corrugation having an outer part 17 which is arcuate when viewed in plan and two webs 18 extending one from either side of the arcuate outer part 17. The adjacent webs 18 of each pair of adjacent corrugations are fastened together by fixing bolts 19 (Figure 2) at a position near to the folded edge 20 that is formed where the adjacent webs join each other so as to form a substantially closed loop 21.

The skirt 11 is attached to the vehicle by rigid rods 22 that are inserted into the loops 21. The rods 22 are attached at one of their ends to brackets 23 mounted on the rigid structure of the buoyancy compartment 13, and slope outwardly and upwardly to have their opposite ends attached to brackets 24 mounted on the rigid structure 14. Thus the folded edges 20 of the adjacent webs 18 slope outwardly and upwardly with respect to the underside of the vehicle as represented by the underside of the buoyancy compartment 13, and the lower edges of the webs 18 slope outwardly and downwardly with respect to the underside of the vehicle.

The open upper part of the skirt 11, as defined by the upper edges of the webs 18 and the outer arcuate parts 17, is closed by a plate member 25. The plate member 25 is attached by a hinge 26 to an outwardly projecting portion of the rigid structure 14, and extends downwardly and outwardly over the open upper part of the skirt 11 to terminate adjacent the outer arcuate parts 17.

An apron 27 formed from a strip of flexible sheet material is attached to the outer edge of the plate member 25 so as to overlap the upper edges of the outer arcuate parts 17.

The plate member 25 prevents a substantial escape of pressurised air from the cushion 15 through the open upper part of the skirt, and is biased towards this closing portion, against the action of normal cushion pressure, by resilient means, in this embodiment torsion springs 28 built in with the hinge 26. In operation of the vehicle, when cushion pressure rises to a value such that the pressure of the cushion air acting on the plate member 25 overcomes the biasing force applied by the torsion springs 28, the plate member 25 will be moved away from its closing position and air will escape from the cushion 15, thereby relieving the surge in cushion pressure, and hence substantially reducing the heave motion applied to the vehicle.

In the embodiment of the invention shown in Figures 3 and 4 the flexible skirt comprises a plurality of side-by-side independent flexible members 31. Each member 31, as shown in Figure 4, comprises a substantially rectangular sheet of flexible material, for example rubber impregnated woven nylon fabric, which is folded to form an outer part 32 that Is arcuate in plan view with two webs 33 projecting one from each opposite side of the arcuate part 32. Those edges of the webs 33 that are spaced from the arcuate part 32 are folded back on themselves and fastened to form loops 34 which facilitate attachment of the member 31 to the vehicle.Each member 31 is positioned so that the arcuate part 32 is concave with respect to the vehicle, and is attached by rods 35 that pass through the loops 34, to structure of the vehicle which is similar to that illustrated in the embodiment of Figures 1 and 2, and is indicated by like reference numerals.

In this particular embodiment, however, the outermost part of the buoyancy compartment 13 extends downwardly and outwardly to form a skeg 36 that terminates below the underside of the buoyancy compartment 13 so that when the height of waves in a sea over which the vehicle is operating exceed the free height of the skirt, or the vehicle is subjected to severe rolling motion, the skeg 36 contacts the water to take a major portion of the impact.

Furthermore, fixed rigid structure 37 extends downwardly and outwardly to cover the operi upper ends of the members 31 so as to prevent substantial escape of cushion air through these upper ends. The rods 35 by which the skirt elements 31 are attached to the vehicle structure have their upper ends connected to brackets 38 mounted on the rigid structure 37, and their lower ends attached to brackets 39 mounted on the skeg 36. As in the embodiment of Figures 1 and 2, the rods 35 slope outwardly and upwardly with respect to the underside of the vehicle, and there is no attachment between the upper edges of the webs and arcuate parts of the members 31 on the one hand, and the rigid structure 37 which closes the upper part of the skirt on the other hand.

In another embodiment of the invention shown in Figures 5 and 6, the cushion sealing means at the longitudinal sides of an air cushion vehicle includes a flexible skirt 50 similar in construction to the flexible skirt 11 shown in Figures 1 and 2, and attached to the vehicle in a similar manner: parts of the skirt, the means of attaching the skirt to the vehicle, and the rigid structure of the vehicle, are therefore given the same reference numerals as those used in Figures 1 and 2 to identify equivalent components.

In the embodiment of Figures 5 and 6, the rigid structure 14 again defines with the buoyancy tank 13 the outlet end of a duct 12 leading from a lift fan (not shown). However, in this embodiment the rigid structure 14 is continued outwardly in a substantially horizontal plane and an inflated bag member 51 is attached to the underside of the rigid structure 14 so as to close the space defined by the structure 14 and the upper edges of the skirt 50. The bag member 51 is conveniently manufactured from three sheets 52, 53, 54, of reinforced rubber material.The first sheet 52 is attached along one edge to the outermost part 55 of the rigid structure 14 by hinged fixings (not shown), such as are disclosed in British Patent Specification No. 969,235, and when inflated, extends in a direction first outwardly away from the rigid structure, and then downwardly, and then inwardly to wards the outer arcuate parts 17 of the skirt 50 where it terminates at a downwardly turned edge portion which is joined with edge portions of the sheets 53 and 54. The second sheet 53 extends from an edge which is attached to the underside of the rigid structure 14 by similar hinged fixings (not shown), at a position near to the brackets 24, downwardly and outwardly to terminate in a downwardly turned edge portion that is joined with edge portions of the sheets 52 and 54.The third sheet 54 extends from an edge that is attached at or near the outermost parts 55 of the rigid structure 14, downwardly to where its lower edge portion is joined with the edge portions ofthe sheets 52 and 53. The joined edge portions of the sheets 52, 53 and 54 form an apron 56 that closes the gap between the upper edges of the outer arcuate parts 17 of the skirt 50 so as to prevent substantial loss of air from the cushion 15 through this gap. The bag 51 is inflated to a pressure which corresponds substantially to the pressure of the cushion 15 by air from the cushion which enters the bag 51 through the holes (not shown), in the sheet 53. Similar holes in the sheet 54 permit air to enter the space that is enclosed by the sheets 52 and 53.Inflation of the bag 51 to a pressure corresponding substantially to the cushion pressure ensures that the sheet 52 is substantially flat because it is not subject to any substantial pressure differential across its faces, and thus the upper edges of the skirt 50 do not come into contact with the sheet 53 so as to be restrained when they are deflected in a fore and aft direction with respect to the vehicle.

In the embodiment of the invention shown in Figure 7, the flexible skirt comprises a plurality of side-by-side independent flexible members 31 similar in construction to those shown in Figures 3 and 4, and their attachment to rigid structure 70 of an air cushion vehicle is also similar to that of the embodiment of the invention shown in Figures 3 and 4. In this particular embodiment, however, the rigid structure 70 does not define a duct leading from a lift fan supplying pressurised air to the cushion, the cushion 15 being supplied instead through ducts (not shown) in the base structure of the vehicle. The space between the upper edges of the members 31 and the rigid structure 70 is closed by a plurality of side-by-side flexible elements or fingers 71, each formed by folding a substantially triangular sheet of reinforced rubber material so as to be U-shaped when viewed in plan.This folded sheet is positioned so as to be concave with respect to the vehicle and has its upper edges suitably attached to the rigid structure 70 by bolting to web members 72 that depend downwardly from attachment to the rigid structure 70. The upper and lower outer parts of each finger 71 are formed with knuckle parts 73 and 74, respectively. The upper knuckle part 73 is attached by suitable means, such as bolts (not shown) to a strip of flexible material 75 which extends downwardly from attachment to the outermost part 76 of the rigid structure 70. A strip of flexible material 77 is attached to the lower knuckle parts 74 of the fingers 71 so as to extend downwardly and close the gap between the lower edges of the outer parts of the fingers 71 and the upper edges of the outer arcuate parts of the members 31.In operation, air from the cushion 15 inflates the members 31 and the fingers 71.

In a further embodiment of the invention, shown in Figure 8, flexible structure closing the space between the upper edges of a plurality of side-by-side independent flexible members 31 forming the flexible skirt and rigid structure 80 at the longitudinal side of an air cushion vehicle comprises a plurality of side-by-side pocket members 81. Each pocket member 81 is manufactured from reinforced rubber sheet material and has its upper edges fixed by bolts (not shown) to web members 82 that extend downwardly from attachment to the rigid structure 80.

The pocket members 81 are inflated by air from the vehicle supporting cushion 15 that passes into the pocket members through holes 83 in their lower parts 84. A strip 85 of flexible material is attached along the lowermost outer parts of the pocket members 81 so as to extend downwardly across the gap between the outer parts of the pocket members and the upper edges of the outer parts of the members 31, thus preventing substantial escape of air from the cushion 15 through this gap.The members 31 are attached to the rigid structure 80 in a manner similar to that described for other embodiments of the invention; however, in this particular embodiment the clearance between the underside of the vehicle and the ground is increased by profiling the lower edges 86 of the webs 33 and outer parts 32 of the flexible members 31 to a shape such that when the skirt element is folded and attached to the vehicle the included angle between the lower edge and the inner edge of a web 33 is larger than 90 degrees, bearing in mind the need to keep the tip included angle, i.e. the angle formed by the outer arcuate part and the lower edge of the webs as near to 90 degrees as possible, so that the stability of the member 31 is not impaired.

In an embodiment of the invention shown in Figure 9, a flexible skirt 11 similar to the skirt shown in Figures 1 and 2 is attached to a rigid member 90 that extends along the longitudinal side structure 91 of an air cushion vehicle (not shown). The rigid member 90 comprises a first part 92 pivotally attached along a hinge line 93 to the vehicle side structure 91, so that in operation of the vehicle it projects outwardly and upwardly with respect to its attachment on the structure 91. A second part 94 projects from the upper edge of the first part 92 so as to be substantially normal thereto. The angle of the first part 92 with respect to the vehicle side structure 91 is controllable by variable length jacks 95 which extend between pivotal attachments on the first part 92 and on the vehicle side structure 91, respectively.The skirt 11 is supported by rods which pass through loops formed at the folded edges of the adjacent webs of each pair of adjacent corrugations, the lower end of each rod being attached to a bracket 96 mounted on the first part 92, and the upper end of the rod being attached to a bracket 97 that in this embodiment is mounted on the second part 94. A strip of flexible material 98 is attached to the outermost edge of the second part 94 of the member 90 so as to project across the gap between the upper edges of the outer arcuate parts of the skirt 11 and the second part 94, thus preventing substantial escape of air through this gap.

By adjusting the variable length jacks 95 the position of the skirt 11 may be changed and by this means the trim of the vehicle may be adjusted. Furthermore, the jacks 95 may also be designed to act as a spring/damper system that allows deflection of the whole skirt in adverse wave or scooping conditions.

Of course, the embodiments of the invention described with reference to and shown in the accompanying drawings are by way of example, and modifications are possible without departing from the scope of the invention. For example, the skirt construction embodying the invention is not limited to use at the longitudinal side of an air cushion vehicle, it may be used at the bow and stern: for instance, the skirt construction illustrated in Figures 1 and 2 may run continuously around the complete periphery of the vehicle.

Furthermore, the hinged plate member that extends across the upper part of the skirt in the embodiment of Figure 1, may be arranged for movement away from the upper part of the skirt by control means, such as a servo-assisted cable and pulley system, that may be operated by the vehicle commander to vent air from the cushion for directional control or other purposes.

In a non-illustrated modification of the invention having inflated structure projecting across the upper end of the skirt so as to prevent the escape of cushion air, the inflated structure may be arranged for movement away from the upper end of the skirt when there is a sudden surge in cushion pressure, so as to permit venting of the cushion through the skirt. In one such arrangement the structure is inflated from a pressure source on the vehicle, to a pressure corresponding to normal cushion pressure, whereby any surge in cushion pressure will act upon the inflated structure to move it away from the upper end of skirt so that air can escape from the cushion.

WHAT WE CLAIM IS: 1. Cushion sealing means for an air cushion vehicle, comprising a flexible skirt of corrugated form adapted to be attached to the vehicle in such manner that each corrugation has an outer part arcuate in plan with the concave side thereof facing the cushion, and webs extending towards the cushion from the sides of the outer parts, characterised in that the skirt is adapted to be attached to the vehicle structure solely by attachment, along lines that slope upwardly and outwardly with respect to the underside of the vehicle, of those parts of the webs that are innermost with respect to the cushion.

2. Cushion sealing means as claimed in Claim 1, wherein the webs of adjacent corrugations are joined together.

3. Cushion sealing means as claimed in Claim 2, wherein the skirt comprises a strip of flexible sheet material that is folded to form the outer arcuate parts and the webs of the corrugations.

4. Cushion sealing means as claimed in Claim 3, wherein the adjacent webs of adjacent corrugations are fastened together near to the fold line between the adjacent webs so as to form substantially closed loops.

5. Cushion sealing means as claimed in Claim 1, wherein the webs of adjacent corrugations are not joined together, and each corrugation is formed by folding a substantially rectangular sheet of flexible material so as to form an outer part that is arcuate in plan view and two webs extending one from either side of the arcuate part to terminate at edge portions which are arranged for attachment to the vehicle.

6. An air cushion vehicle having cushion sealing means comprised at least in part by a flexible skirt of corrugated form, each corrugation having an outer part that is arcuate in plan view with its concave side positioned to face the cushion and webs extending from the sides of the outer part towards the cushion, each corrugation being attached to the vehicle structure solely by attachment, along lines that slope upwardly and outwardly with respect to the underside of the vehicle, of those parts of the said webs that are innermost with respect to the cushion.

7. An air cushion vehicle as claimed in Claim 6, wherein the webs of adjacent corrugations are joined together.

8. An air cushion vehicle as claimed in Claim 7, wherein the skirt comprises a strip of flexible sheet material that is folded to form the outer arcuate parts and the webs of the corrugations.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. vehicle it projects outwardly and upwardly with respect to its attachment on the structure 91. A second part 94 projects from the upper edge of the first part 92 so as to be substantially normal thereto. The angle of the first part 92 with respect to the vehicle side structure 91 is controllable by variable length jacks 95 which extend between pivotal attachments on the first part 92 and on the vehicle side structure 91, respectively. The skirt 11 is supported by rods which pass through loops formed at the folded edges of the adjacent webs of each pair of adjacent corrugations, the lower end of each rod being attached to a bracket 96 mounted on the first part 92, and the upper end of the rod being attached to a bracket 97 that in this embodiment is mounted on the second part 94.A strip of flexible material 98 is attached to the outermost edge of the second part 94 of the member 90 so as to project across the gap between the upper edges of the outer arcuate parts of the skirt 11 and the second part 94, thus preventing substantial escape of air through this gap. By adjusting the variable length jacks 95 the position of the skirt 11 may be changed and by this means the trim of the vehicle may be adjusted. Furthermore, the jacks 95 may also be designed to act as a spring/damper system that allows deflection of the whole skirt in adverse wave or scooping conditions. Of course, the embodiments of the invention described with reference to and shown in the accompanying drawings are by way of example, and modifications are possible without departing from the scope of the invention. For example, the skirt construction embodying the invention is not limited to use at the longitudinal side of an air cushion vehicle, it may be used at the bow and stern: for instance, the skirt construction illustrated in Figures 1 and 2 may run continuously around the complete periphery of the vehicle. Furthermore, the hinged plate member that extends across the upper part of the skirt in the embodiment of Figure 1, may be arranged for movement away from the upper part of the skirt by control means, such as a servo-assisted cable and pulley system, that may be operated by the vehicle commander to vent air from the cushion for directional control or other purposes. In a non-illustrated modification of the invention having inflated structure projecting across the upper end of the skirt so as to prevent the escape of cushion air, the inflated structure may be arranged for movement away from the upper end of the skirt when there is a sudden surge in cushion pressure, so as to permit venting of the cushion through the skirt. In one such arrangement the structure is inflated from a pressure source on the vehicle, to a pressure corresponding to normal cushion pressure, whereby any surge in cushion pressure will act upon the inflated structure to move it away from the upper end of skirt so that air can escape from the cushion. WHAT WE CLAIM IS:

1. Cushion sealing means for an air cushion vehicle, comprising a flexible skirt of corrugated form adapted to be attached to the vehicle in such manner that each corrugation has an outer part arcuate in plan with the concave side thereof facing the cushion, and webs extending towards the cushion from the sides of the outer parts, characterised in that the skirt is adapted to be attached to the vehicle structure solely by attachment, along lines that slope upwardly and outwardly with respect to the underside of the vehicle, of those parts of the webs that are innermost with respect to the cushion.

9. An air cushion vehicle as claimed in

Claim 8, wherein the adjacent webs of adjacent corrugations are fastened together near to the fold line between the adjacent webs so as to form substantially closed loops.

10. An air cushion vehicle as claimed in Claim 9, wherein the skirt is attached to the vehicle by attachment rods passing through the closed loops and having their ends attached to the vehicle structure.

11. An air cushion vehicle as claimed in Claim 6, wherein the webs of adjacent corrugations are not joined together and each corrugation is formed by folding a substantially rectangular sheet of flexible material so as to form an outer part that is arcuate in plan view and two webs extending one from either side of the arcuate part to terminate at edge portions which are arranged for attachment to the vehicle.

12. An air cushion vehicle as claimed in Claim 11, wherein said terminal edge portions of said two webs of each corrugation are turned back on themselves and fastened to form loops, and the corrugation is attached to the vehicle by attachment rods that pass one through each loop to have the ends thereof attached to the vehicle.

13. An air cushion vehicle as claimed in any one of Claims 6 to 12, wherein rigid structure of the vehicle to which the inner edges of the webs are attached is constructed in the form of a downwardly extending skeg when the vehicle is operating over seas that exceed the free height of the skirt the skegs contact the water.

14. An air cushion vehicle as claimed in any one of Claims 6 to 13, including rigid structure overlying the upper edges of the skirt and extending downwardly and outwardly from the vehicle.

15. An air cushion vehicle as claimed in any one of Claims 6 to 13, including flexible structure overlying the upper edges of the skirt and extending downwardly and outwardly from the vehicle.

16. An air cushion vehicle as claimed in Claim 15, wherein the flexible structure is inflatable.

17. An air cushion vehicle as claimed in Claim 16, wherein the flexible inflatable structure is positioned between the upper edges of the skirt and rigid structure extending outwardly from the vehicle.

18. An air cushion vehicle as claimed in Claim 16 or Claim 17, wherein the inflatable structure comprises a bag adapted to be inflated to a pressure corresponding substantially to the pressure of the air cushion on which the vehicle is supported.

19. An air cushion vehicle as claimed in Claim 18, wherein holes are provided in the bag at positions corresponding with the upper parts of the skirt so as to provide communication between the interior of the bag and spaces which are defined by the outer arcuate parts and webs of the skirt and rigid structure of the vehicle to which the webs are attached.

20. An air cushion vehicle as claimed in Claim 18 or Claim 19, wherein a strip of flexible material extends downwardly from the bag to form an apron that overlaps the uppermost edges of the outer arcuate parts of the skirt.

21. An air cushion vehicle as claimed in Claim 17, wherein the flexible inflatable structure comprises a plurality of side-byside independent flexible members of the kind known in the art as fingers, the upper edges of the fingers being attached to the rigid structure that extends outwardly from the vehicle.

22. An air cushion vehicle as claimed in Claim 21, wherein a strip of flexible material is attached along the lowermost edges of outer arcuate parts of the fingers so as to form an apron that overlaps the upper edges of the outer arcuate parts of the skirt.

23. An air cushion vehicle as claimed in Claim 17, wherein the flexible inflatable structure comprises a plurality of side-byside flexible pocket members arranged for inflation to a pressure corresponding to the pressure of the air cushion on which the vehicle is supported.

24. An air cushion vehicle as claimed in Claim 23, wherein the pocket members are arranged for inflation by cushion air which passes into them through holes in their lower parts.

25. An air cushion vehicle as claimed in any one of Claims 6 to 12, wherein the flexible skirt is attached to a wall structure that is pivotal with respect to the side of the air cushion vehicle, and whereby the position of the lower tips of the skirt can be controlled.

26. An air cushion vehicle as claimed in Claim 25, wherein the pivotal wall structure is attached to the vehicle by hinge means at the lower edge thereof.

27. An air cushion vehicle as claimed in Claim 25 or Claim 26, wherein the angle of the pivotal wall structure with respect to the vehicle is controlled by variable length jacks extending between the pivotal wall structure and the side of the vehicle.

28. An air cushion vehicle as claimed in any one of Claims 26, 27 or 28, including structure overlying the upper edges of the skirt and formed as an integral part of the pivotal wall structure.

29. An air cushion vehicle as claimed in any one of Claims 6 to 28, including structure overlying the upper edges of the skirt, hinged with respect to the vehicle and biased by resilient means, against the action of normal cushion pressure, towards a position in which it abuts with the upper edges of the skirt, said structure being adapted to move away from the upper edges of the skirt to allow air to escape from the cushion, in response to cushion pressure rising above a predetermined value.

30. An air cushion vehicle as claimed in any one of Claims 6 to 28, including structure overlying the upper edges of the skirt and hinged with respect to the vehicle, and control means adapted to move said structure away from the upper edges of the skirt when required, to vent from the cushion for directional control or other purposes.

31. An air cushion vehicle having cushion sealing means comprised at least in part by a flexible skirt substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.

32. An air cushion vehicle having cushion sealing means comprised at least in part by a flexible skirt substantially as hereinbefore described with reference to and as shown in Figures 3 and 4 of the accompanying drawings.

33. An air cushion vehicle substantially as hereinbefore described with reference to and as shown in Figures 5 and 6 of the accompanying drawings.

34. An air cushion vehicle substantially as hereinbefore described with reference to and as shown in Figure 7 of the accompanying drawings.

35. An air cushion vehicle substantially as hereinbefore described with reference to and as shown in Figure 8 of the accompanying drawings.

36. An air cushion vehicle substantially as hereinbefore described with reference to and as shown in Figure 9 of the accompanying drawings.