US3702643A

US3702643A - Means for bounding cushion spaces of gas cushion vehicles

Info

Publication number: US3702643A
Application number: US23829A
Authority: US
Inventors: John James Spillman
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1969-04-02
Filing date: 1970-03-30
Publication date: 1972-11-14
Anticipated expiration: 1989-11-14
Also published as: FR2038170B1; DE2015803A1; FR2038170A1; GB1309745A

Abstract

The cushion of a gas cushion vehicle is contained by a wall structure comprising a horizontal row of rigid members of lamellar form, e.g., discs, mounted for independent vertical movement with respect to each other. The lower surfaces of the members are curved to define a convergent-divergent passage between them and the surface over which the vehicle is to operate, for the escape of gas from the cushion. The members are preferably enclosed in a downwardly open chamber, separate from the cushion space. In use, by suitably controlling the pressure above the members, e.g., in the chamber, the aerodynamic forces exerted on the members due to the flow of cushion gas beneath them, are arranged to maintain the members in an equilibrium position spaced above the surfaces over which the vehicle operates.

Description

United States Patent Spillman [54] MEANS FOR BOUNDING CUSHION SPACES OF GAS CUSHION VEHICLES [72]- lnventor: John James Spillman, Bedford, England [73] Assignee: National Research Development Corporation, London, England [22] Filed: March 30, 1970 [21] Appl. No.: 23,829

[30] Foreign Application Priority Data April 2, 1969 Great Britain ..l7,244/69 [52] US. Cl ..180/127 [51] Int. Cl ..B60v 1/00 [58] Field of Search ..130/126, 127, 128

[56] References Cited UNITED STATES PATENTS 3,204,715 9/1965 Maloof ..180/126 3,288,236 11/1966 Padial ..180/126 3,330,369 7/1967 Hayward ..180/127 Hopkins et a1 l 80/127-X Francis et a1. ..180/127 Primary Examiner-Kenneth H. Betts Attorney-Cameron, Kerkam and Sutton ABSTRACT The cushion of a gas cushion vehicle is contained by a wall structure comprising a horizontal row of rigid members of lamellar form, e.g., discs, mounted for independent vertical movement with respect to each other. The lower surfaces of the members are curved to define a convergent-divergent passage between them and the surface over which the vehicle is to operate, for the escape of gas from the cushion. The members are preferably enclosed in a downwardly open chamber, separate from the cushion space. In use, by suitably controlling the pressure above the members, e.g., in the chamber, the. aerodynamic forces exerted on the members due to the flow of cushion gas beneath them, are arranged to maintain the members in an equilibrium position spaced above the surfaces over which the vehicle operates.

14 Claims, 12 Drawing Figures minimum 14 m2 SHEEI 1 [IF 6 l L I l P'A'TE'N'TEDnuv 14 I972 3.702.643

sun-. 1 2 or e PRESSURE deal/E 14/43/1698 CUSH/ON P2685025 P'A'TENTED Nov 14 m2 SHEET 5 BF 6 GAP/R MEANS FOR BOUNDING CUSHION SPACES OF GAS CUSHION VEHICLES cushions of pressurized air or gas maintained in a space, (the cushion space) beneath the vehicle or other body. In particular the invention is concerned with means for laterally bounding a cushion space.

' According to the invention means for laterally bounding the cushion space of a gas cushion vehicle comprise a plurality of members of self sustaining shape, juxtaposed in a horizontally extending row, arranged for independent movement in a substantially vertical plane, each member having a lower surface which, together with the surface over which the vehicle is to operate, defines a potential convergentdivergent passage beneath the member for the efflux of gas from the cushion, means being provided to control the downwardly acting forces exerted on the members due to the application thereto of pressurized gas from the cushion so that in use, the upwardly acting forces exerted on the members due to the efflux of gas beneath them are such that the members are normally maintained in an equilibrium position spaced above the surface over which the vehicle operates.

Preferably the members comprise rigid plates or laminates having plane parallel side surfaces. Naturally the members will be placed as closely together as possible, to minimize the leakage of air between them, consistent with their having the required freedom of individual movement.

The members may be mounted either for linear movement or for angular movement in the vertical plane. In the former case the members may con veniently have the form of washers or discs loosely mounted on a horizontally extending rod, for the desired degree of linear movement in the vertical plane. Although it is not essential it is advantageous for the washers to be circular so that they may rotate should they come in'contact with the surface beneath the vehicle.

In the second case, in which the members are mounted for angular movement, they may take the form of generally pear-shaped laminates pivotall y secured on horizontal axes so as to depend from the body or a peripheral wall of the vehicle.

Preferably in order to be able to control the pressure above the members a space or chamber, separate from the cushion space, is defined above the members and means are provided to control the build-up of pressure in the chamber due to flow of gas thereto from the cushion space.

The chamber above the members may be defined by a pair of depending walls extending parallel to the cushion boundary to embrace the members. The provision of such walls also serves in the case where the members are in the form of dics loosely mounted on a horizontally extending rod, to restrict horizontal movement of the members at right angles to the rod. In fact it may be arranged to trap the members between the depending walls by, for example, making the walls downwardly convergent, in which event a horizontally extending rod to secure the members may be dispensed with.

The means to control the build-up of pressure in the chamber above the members may comprise a strip of flexible material secured, for example, to the inner wall so as to prevent the direct flow of gas from the cushion to the chamber between the inner wall and the peripheries of the members, and also to restrict flow of gas between the members to the said chamber. The extent to which the sealing strip masks the inner peripheries of the members which are subjected to cushion pressure may be varied to adjust the pressure that would be built up in the chamber as required. Preferably, however, in order to control the pressure in the space above the members, vents are provided communicating either or both withatmosphere or the cushion space, via which leakage of gas into and from the space may be adjusted.

Generally of course the pressure above the members must not be allowed to build up to such a value as would prevent the members from being maintained in the required equilibrium position, or undesirably restrict their freedom for vertical movement. Conversely other than when operating to contain very low cushion pressures, it will normally be necessary to maintain thepressure above the members above atmospheric pressure.

It is to be understood that it is not essential for a cushion to be laterally bounded either to its full peripheral or vertical extent by means in accordance with the invention. It has already been made evident that the means may solely comprise a lower portion of a peripherally extending wall, and equally of course the means of the invention may be employed to bound only a part of the periphery of a cushion, for example only at the front and rear of the vehicle, the remaining lateral boundary of the cushion being provided by other means of known form.

The invention is further described below with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic sectional view of one embodiment of means for laterally bounding the cushion space of a gas cushion vehicle,

FIG. 2 is an elevation of the embodiment of FIG. 1

FIG. 3 is a view corresponding to FIG. 1 of an alternative embodiment,

FIG. 4 is again similar to FIG. 1 indicating a modification of the embodiment of FIG. 1,

FIG. 5 is a plan view of an air cushion supported pallet in accordance with the invention,

FIG. 6 is a plan view of another form of air cushion supported pallet in accordance with the invention,

FIG. 7 is a section on the line VH VII of FIG. 6,

FIG. 8 is a graph explaining the operation of the cushion bounding means of the invention,

FIG. 9 is a sectional view similar to FIG. 1 of a further embodiment,

. FIG. 10 is an elevation of the embodiment of FIG. 9,

FIG. 11 is a fragmentary view indicating how the cushion bounding means of FIGS. 9 and 10 may be arranged at comers of a cushion space, and

FIG. 12 is a graph indicating the manner in which the operation of the cushion bounding means may be controlled.

Referring first to FIGS. 1 and 2, means for laterally bounding the cushion space of a gas cushion vehicle comprise a plurality of juxtaposed washer-like laminates 1, arranged in a horizontally extending row,

being loosely mounted on a rod 2. A pair of walls 3a and 3b are provided depending from the body 4 of the vehicle to embrace the laminates 1 as shown. As indicated in FIG. 2 the laminates 1 are placed as close together as possible to minimize the gaps between them through which air may leak from the cushion space 5. The laminates are not, however, so closely packed as to restrict the laminates from being capable of independent movement in a vertical plane in relation to the vehicle and each other. A flexible sealing strip 6 may be provided at the lower end of the inner wall 3b at least to restrict direct flow of air from cushion 5 to the space or chamber 7 between the walls 3a and 3b above the laminates l. The space 7 may be vented to atmosphere by a series of ports 8 in the outer wall 3a, and a further series of ports 8a may be provided in the inner wall 3b to enable the pressure in the space 7 to be controlled as will be explained below.

Referring now to FIG. 3 an alternative form the laminates may take is indicated. Thus the laminates 1' are generally pear-shaped in outline, and are pivotally secured on horizontal axes, indicated at 9 for angular movement in a vertical plane. In the embodiment shown the laminates are pivotally secured to the base of a stub wall 10 depending from the under surface of the vehicle body. Equally however they may be pivoted to the lower end of a more extensive wall. A flexible sealing strip 6 may be provided in this embodiment, as in that of FIGS. 1 and 2, to prevent the direct flow of air from the cushion past the joint between the laminates and the stub wall 10 and hence to the upper surface of the laminates.

The upper surfaces of the laminates 1' are enclosed by a depending wall 3a defining a chamber 7 above them after the fashion of the embodiment of FIG. 1. It would be possible pivotally to connect the laminates to the outer wall 3a rather than to the inner or stub wall 10. As in the case of FIG. 1

ports

8 and 8a may be provided in either or both the inner and outer walls.

Referring next to FIG. 4 a modification of the embodiment of FIG. 1 is shown in which the depending walls 3a and 3b which embrace the laminates 1 are formed with guide surfaces 12 which are inclined to the vertical so as to confine movement of the laminates, in the vertical plane, to an axis correspondingly inclined to the vertical. The advantage of this arrangement over that of FIG. 1 will be explained below.

The manner of operation of the above described arrangements is as follows:

Initially the vehicle will be resting on the surface 13, and assuming it to be supported by the laminates, these will be positioned as indicated in dotted lines in FIGS. 1, 3 and 4. Upon the supply of air under pressure to the cushion space 5, pressure will build up therein until the cushion pressure reaches the minimum value to support the weight of the vehicle, causing the vehicle to rise both in relation to the surface 13 and the laminates l, which will then be in the position indicated in full lines. At the same time the cushion pressure will cause the laminates to lift, to open up a gap between them and the surface 13.

Given suitable control of the pressure exerted on the upper surfaces of the laminates, there will be a height of the laminates above the surface 13 at which the gravitational and aerodynamic forces on each laminate have a zero component along the axis of movement provided for the laminates in the embodiments of FIGS. 1 and 2 or 4, or a zero moment about the pivotal connections of the laminates in the embodiment of FIG. 3.

Should this height, i.e., the dimension of the gap between the lower surface of the laminates and the surface 13 change from this equilibrium position, due for example to undulations in the surface 13, the resultant change in the aerodynamic force will tend to move the laminates back to the equilibrium position, i.e., the gap will be maintained substantially constant. The gap is not significantly affected by the magnitude of the cushion pressure, but is sensitive to the shape of the curved lower surface of the laminates, the type of movement permitted and to some extent the density of the laminates.

The reason for this characteristic can perhaps best be understood by considering extreme conditions. When the gap between the undersurface of a laminate and the surface 13 is large, air will flow from the cushion to atmosphere through the convergent-divergent passage defined by the curved lower surface of the laminate and the surface 13. This is similar to the flow through a venturi tube, where it is known that there is a marked reduction in static pressure at the throat. In this application the marked reduction in static pressure has the effect of sucking the laminate down towards the surface 13.

When the gap between the laminate and the surface is very small the static pressure drop associated with the friction between the air and the surface at the narrowest point becomes large. Since this increases extremely rapidly as the gap tends to zero, it follows that when the laminate is almost touching the surface practically all the pressure drop between the cushion and the atmosphere occurs at the narrowest part of the passage. In the limit all the pressure drop occurs at the point of contact. In this case the inner lower part of the laminate experiences the full cushion pressure and as a result the pressure distribution over the laminate is such as to tend to increase the gap.

It can be shown that when the pressure above the laminates is of the right level the aerodynamic lift must vary with gap somewhat as indicated in FIG. 8, in which R is the radius of the lower surface of the laminate forming the convergent-divergent passage, and point E is a typical equilibrium condition which occurs when the aerodynamic lift per unit length equals the laminate weight per unit length. Precise values are functions of scale, atmospheric and cushion air conditions. The equilibrium gap corresponds to a positive aerodynamic lift (or moment) balancing the negative gravitational lift (or moment).

If full cushion pressure was applied to the upper surfaces of the laminates, the overall aerodynamic lift would of course be negative, bearing in mind that with the arrangements shown in FIGS. 1, 4 and 12 pressure in the chamber 7 above the laminates acts over approximately half their circumference, whereas pressure in the cushion space 5 will act over approximately a quarter of their circumference. Hence the laminates would be pressed down into contact with the surface beneath them. Conversely, unless the cushion pressure was very low, if the pressure above the laminates was atmospheric pressure, the laminates would float up to their top stops i.e., the aerodynamic lift would be positive for all gap conditions'Hence the need, other than when operafing at very low cushion pressures, to adjust the equilibrium height of the laminates above the surface over which they operate by controlling the pressure exerted above them. There is also the further factor that with arrangements as shown in FIGS. v1 and 4, outwardly directed forces exerted on the laminates by the cushion pressure will cause the laminates to be pressed against the outerwall 3a and tend to cause the laminates to roll up or down the wall. It must accordingly be arranged that the moment about the contact line between the laminates and the wall is zero for the laminates to be maintained in the desired equilibrium position.

Basically all that is required to control the pressure within the chamber 7 is to adjust the rate at which gas leaks between it and the cushion space. With the particular arrangements shown the pressure above the laminates needs to be maintained at a value between that of atmospheric and approximately half the cushion pressure. The leakage rate may, as indicated at the outset, be controlled either by adjusting the extent to which the sealing strips mask that portion of the circumference of the laminates directly exposed to the cushion space 5, but preferably the. leakage is arranged to be controlled by means of the

ports

8 and 8a in'the inner and outer walls which are arranged to embrace the laminates. These ports may, of course, take a variety of forms or shapes and would normally include valve means 14 (FIG. 4) to adjust the rates of flow which could take place through them. Such means may be associated with the ports both in the inner and outer walls, but it may suffice to have only one of these sets of ports, preferably the inner one, controllable.

Tests have in fact indicated that with high cushion pressures laminates may be maintained in an equilibrium position a small distance above the surface over which they operate by arranging for a suitable flow of gas to take place from the cushion through the ports provided in the inner wall 317 only. On the other hand, when operating at low cushion pressures, a vent needs to be provided in the outer wall instead of the inner wall. The graph of FIG. 12 generally indicates what is required. This graph in which the pressure in the chamber above the laminates, e.g., in the chamber 7, is plotted against the cushion pressure in the space 5, indicates by the chain line the pressure which would occur in the chamber 7 if no vents were provided in either the inner or the outer wall. Over the range of cushion pressures indicated on the left-hand side of the graph, it is desirable to control the pressure in the chamber 7, as indicated by the full line, such that it is maintained below the value which it would otherwise have reached, and this may be achieved by providing a vent in the outer wall. Conversely at higher pressures over the range indicated on the right-hand side of the graph, the pressure in the chamber 7 needs to be controlled so as to be somewhat higher than it would otherwise be and this may be achieved by providing a vent in the inner wall. The graph in effect indicates the control necessary with an arrangement such as described in connection with FIGS. 1 and 2 to maintain the laminates in an equilibrium position spaced a constant distance above the surface over which they operate, despite variations in cushion pressure occasioned by, for example, varying loads carried by a gas cushion vehicle or pallet, the cushion of which is bounded by the laminates. To achieve the required degree of control the areas of the vents in the inner or outer wall, as the case may be, must of course be adjustable.

It is of interest to note that there appears (as indicated in FIG. 8) to be a maximum equilibrium gap above which an infinite cushion pressure will not lift the laminate. The nearer the equilibrium gap is to this gap, the less sensitive will be the gap to fluctuations of cushion pressure. As the weight of the laminate tends to zero so the gap tends to this maximum equilibrium value.

Reverting to the embodiments of FIGS. 1 to 4, that of FIGS. 1 and 2 in which the axis of permitted movement of the laminates is vertical, is primarily only suitable for application where pitch or roll stability requirements, and/or center of gravity variations due to varying loads are small. The arrangements of FIGS. 3 and 4 have the advantage that upon tilting of the vehicle body relative to the surface over which it is travelling the cushion will be laterally extended on the down-going side due to outward angular movement of the laminates in the arrangement of FIG. 3, or upward movement along the inclined axis provided for the laminates in the arrangement of FIG. 4. Both of these movements will of course move the lowest point of the laminates horizontally outwards in relation to the vehicle. Hence a restoring force or righting moment will be applied to the vehicle, assisted by a corresponding inward shift of the opposite boundary of the cushion. A suitable angle of inclination of the axis of permitted movement of the laminates in the embodiment of FIG. 4 is 30 to the vertical.

The very slight air flow between adjacent laminates is sufficient to ensure that they tend to remain parallel to one another.

Although the cushion bounding means of this invention may be of use in many applications, it is thought that they have the greatest potential in air cushion supported pallets.

Such a pallet may be provided with simple depending side walls, arranged if desired to run along a prepared track, the front and rear cushion boundary being provided by means in accordance with the invention.

While the laminates have very satisfactory characteristics when the direction of movement of a vehicle is parallel to the direction in which the laminates are aligned, plainly when the direction of movement is otherwise, e. g., at right angles to their direction of alignment, as it would be if they were provided at the sides of the vehicle, the laminates may lodge on obstructions or sharp discontinuities in the surface over which they were travelling.

This-tendency may be ameliorated by shaping the leading edge of the laminates such that their initial slope relative to the plane of the supporting surface is greater than the maximum local slope known to occur on a given surface. In addition the laminates can be swept in plan view, e.g., at an angle of 45 to the intended direction of travel, as indicated at the side of the pallet illustrated in FIG. 5 which is intended for travel in the direction of the arrow A. The laminates might further be swept in side elevation.

With a rectangular pallet, as that of FIG. 5, in which the full periphery of the cushion is bounded by means in accordance with FIG. 1, it will be apparent that special provision should be made at the corners, to provide a seal.

Stability of the pallet may be improved by compartmenting the cushion space in known manner, as for example by the simple fixed partitions indicated at 20. Alternatively the partitions can be flexible, e.g., be formed of bounding means in accordance with the invention.

Another form of pallet employing the cushion bounding means of the invention is shown in FIGS. 6 and 7. In this case four cushion spaces are provided. Providing the difference between the radii of the inner and outer walls between which the laminates are held is small in comparison with the mean radius of curvature of the required cushion boundary of the or each cushion space, no excessive loss of air will occur between the laminates.

Referring now to FIGS. 9 to 11 a further alternative form of laminate or washer, which may be employed to form cushion bounding means in accordance with the invention, is shown. Thus, the laminates 21 are in the form of plates, each provided with a straight-sided slot 22 arranged to embrace a depending wall 23. To retain the laminates in place, towards its lower end the wall 23 is provided with a shoulder, as indicated at 24, for cooperation with a complementary shoulder 25 provided at the open end of the slot 22. The lower end 26 of the wall forms a close sliding fit within the slot 22, the slot being of greater depth than the lower part of the wall to allow the laminates to slide vertically with respect thereto to a predetermined extent. To assemble laminates on a wall they will be slid into position from one end. A passage 27 may be drilled through the laminates to vent the closed lower end of the slots 22 to prevent a build up of pressure therein, such as would restrict the required vertical movement of the laminates. A further passage 270 may be provided to establish communication between the cushion space and the lower end of the slots 22. The passages 27 and 27a can of course be arranged to serve the same function as the

ports

8 and 8a of the preceding embodiments. The lower ends of the laminates are curved as indicated to provide the required potential convergentdivergent passage between them and the surface over which they will operate. With this form of laminate, which will operate in substantially the same manner as that previously described, the curve of the lower edges of the laminate may conveniently be made large. It is not necessary for the laminates to be symmetrical about the wall 23. They may, for example, be shaped as indicated in chain lines. Equally the minimum gap between the lower edges of the laminates and the supporting surface need not be arranged to be at the midwidth of the position of the laminates. Clearly the laminates 21 need not necessarily be retained on the wall 23 precisely as shown. Any other suitable arrangement may be employed for this purpose.

If desired the wall 23 may be inwardly inclined so that the axis of movement of the laminates is inclined to the vertical to obtain the benefit explained in connection with FIGS. 3 and 4.

With this form of washer no special provision is necessary at the corners of a rectangular cushion space, as is the case with the washers of FIG. 1, mentioned in connection with FIG. 5. As indicated in FIG. 11 the laminates bounding one side of the cushion space may be arranged directly to abut laminates bounding an adjacent side.

The laminates in all the embodiments described may be made of any desired material. Steel washers have given satisfactory results. In certain circumstances it may be desirable to use lighter weight laminates e. g., of aluminum or plastics material, since obviously if the extent of a cushion boundary to be formed by laminates or like members in accordance with the invention, is large, their weight may represent a significant proportion of the total weight of a vehicle or pallet on which they are employed. Lighter weight laminates may also more rapidly respond to local variations in the surface over which they operate. For vehicles intended for operation over water the laminates may be made buoyant.

It is to be understood that the precise shape and the relative dimensions of the members or laminates is not critical, but may vary within wide limits. The dimensions of the laminates will be determined amongst other factors by the dimensions of obstacles they are designed to negotiate.

It will be seen that a cushion boundary formed by means in accordance with the invention, will generally act in a manner similar to flexible skirts, in so far as their ability to negotiate obstacles and to conform with surface contours is concerned. The members or laminates are of course independently deflectable as are the members of segmented" skirts.

Because the members or laminates will normally be maintained out of contact with the surface, wear due to occasional contact therewith should not be severe, particularly bearing in mind the relatively robust nature of the laminates compared with for example flexible material commonly used for the manufacture of skirts.

While the cushion bounding means of this invention have only been described as providing a seal with a substantially horizontal surface over which a vehicle fitted with them may travel, they may equally if desired be arranged to provide a seal with vertical or inclined surfaces, for example the walls of a channel along which an air cushion supported pallet may be arranged to run.

Air cushion vehicles and particularly air cushion pallets with flexible skirts are prone to suffer from instability in heave unless the rate of supply of air to the cushion and the cushion pressure are very low. The basic cause of this instability is the discontinuity in the rate of leakage (plenum leak) which occurs beneath the cushion containing skirts.

Varying the height of the skirt around its periphery will result in plenum leak varying smoothly over a range of hover heights corresponding to the range of skirt heights. With cushion bounding means in accordance with the present invention this can readily be achieved by employing laminates of different dimensions to form a cushion boundary. It is believed, however, that heave instability may better be countered by arranging for an increase in the rate of plenum leakage as a vehicle rises to a predetermined equilibrium position or hover height.

With cushion bounding means in accordance with the present invention the required control of plenum leakage may conveniently be provided for by suitably positioning the ports 8a provided in the inner wall defining the chamber 7 in the embodiments of FIGS. 1, 3 and 4. Thus these ports may be positioned so that they are sealed by the laminates when these are in the chain dotted position, but are progressively opened as the vehicle rises. It can then be arranged for the vehicle to be in equilibriumbefore the laminates reach their fully extended position, i.e.,,it will be arranged that when the laminates are fullyextended the leak rate is greater than the supply rate. If desired, venting of the space 7 via the ports 8 may equally be arranged to be controlled by the laminates.

It will be appreciated that this ancillary function of the

ports

8 and 8a must not be allowed to disturb their main function of controlling the pressure exerted above the laminates. Thus the total area for leakage through the inner and outer walls 3a and 3b, and its variation with the position of the laminates relative to these walls should be kept at a minimum consistent with obtaining satisfactory stability. It remains necessary to control the ratio of leakage into the chamber 7 to the leakage out of the chamber to ensure that the laminates may be maintained in the required equilibrium position above the surface over which they operate. The pressure in the space 7 must of course be maintained at a value which causes the skirt to float at the desired height above the supporting surface.

With the alternative form of laminate described in connection with FIG. 9 appropriately controlled venting of the cushion space as the vehicle rose could be arranged to take place via vents as indicated at 28. As indicated in FIG. 10the number, size and position of vents controlled by each individual laminate may be varied in a random or predetermined manner to give the vehicle or pallet concerned the required characteristic. Instead of providing a plurality of aligned vents to be controlled by each laminate it may be more convenient to provide a single elongated vent in the wall 23 aligned with each laminate.

In certain cases it may be unnecessary to provide ventilating slots or ports in the wall 23. The gaps between the laminates may be such as to give sufficient leakage variation with height to ensure adequate stability in heave.

I claim:

1. Means for bounding, at least in part, the periphery of a cushion space of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape, juxtaposed in a horizontally extending row, arranged for independent movement in a substantially vertical plane, each member having a surface which defines a potential convergentdivergent passage between the said member and the surface over which the apparatus is to be supported for the efflux of gas from the cushion wherein the pressure of the gas is maintained above atmospheric pressure, means being provided to control downwardly acting forces exerted on the members due to the application thereto of pressurized gas from the cushion so that, in use, upwardly acting forces exerted on the members due to the said efflux of gas are such that the members are normally maintained in an equilibrium position spaced from the said surface.

2. Means for bounding, at least in part, the periphery of a cushion space of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape, juxtaposed in a horizontally extending row, arranged for independent movement in a substantially vertical plane, each member having a surface which defines a potentially convergent-divergent passage between the said member and the surface over which the apparatus is to be supported for the efflux of gas from the cushion, defining above the said members a space or chamber, separate from the said cushion space, including means to control the build-up of pressure in the chamber due to the flow of gas thereto from the cushion space, so as to maintain the pressure therein at a value between that of atmosphere and about half cushion pressure, so that, in use, upwardly acting forces exerted on the members due to the said efflux of gas are such that the members are normally maintained in an equilibrium position spaced from the said surface.

3. Means as claimed in claim 1 in which the said members comprise rigid plates having plane parallel side surfaces, each member being formed with a slot slidably engaging the free end of a wall structure from which the members are arranged to depend.

4. Means as claimed in claim 2 in which the said members comprise rigid plates having plane parallel side surfaces, the members being mounted for angular movement in the vertical plane with respect to the vehicle.

5. Means as claimed in claim 2 in which the said chamber is defined by inner and outer wall structures between which the said members are mounted.

6. Means as claimed in claim 5 in which the members are in the form of discs loosely mounted for linear movement in the vertical plane on a horizontally extending rod.

7. Means as claimed in claim 5 in which the said members comprise rigid plates having plane parallel side surfaces, the members being mounted for angular movement in the vertical plane with respect to the vehicle.

8. Means for bounding, at least in part, the periphery of a cushion space of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape, juxtaposed in a horizontally extending row, said members comprising rigid plates having plane parallel side surfaces and being mounted for independent linear movement in a vertical plane with respect to the vehicle, each member having a surface which defines a potential convergent-divergent passage between the said member and the surface over which the apparatus is to be supported for the efflux of gas from the cushion, means being provided to control downwardly acting forces exerted on the members due to the application thereto of pressurized gas from the cushion so that, in use, upwardly acting forces exerted on the members due to the said efflux of gas are such that the members are normally maintained in an equilibrium position spaced from the said surface.

9. Means for bounding, at least in part, the periphery of a gas cushion of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape and lamellar form, juxtaposed in a horizontally extending row, and arranged for independent relative movement in a substantially vertical plane, each member having a lower surface which, together with the surface over which the apparatus is to be supported, defines a potential convergent-divergent passage beneath the member for the efi'lux of gas from the cushion, the members being enclosed between depending inner and outer wall structures defining a downwardly open chamber, separate from the cushion space, means being provided to control the build up of pressure in the chamber above the members due to leakage of gas thereto from the cushion, so as to maintain the pressure therein at such a value that, in use, forces exerted on the members due to the said efflux of gas normally maintain the members in an equilibrium position spaced above the surface over which the apparatus is supported.

10. A gas cushion vehicle in which the vehicle-supporting cushion is contained, at least in part, by a wall structure depending from the vehicle body, the wall structure comprising a plurality of members of selfsustaining shape and lamellar form, contiguously arranged in a horizontally extending row, means 'rnounting the members so as to depend from the body for independent relative movement in a substantially vertical plane with respect thereto, the members having a convex surface to define, in use, with the surface over which the vehicle is to operate, a convergent-divergent passage for the efflux of gas from the cushion wherein the pressure of the gas is maintained above atmospheric pressure, means being provided to restrict flow of gas from the cushion to the upper surface of the members, operative to maintain the pressure above the members at a value less than that of the cushion pressure but above atmospheric pressure, so that forces exerted on the members due to the said efflux of gas beneath them, normally maintain the members in an equilibrium position spaced above the surface over which the vehicle operates.

11. A gas cushion vehicle in which the vehicle-supporting cushion is contained, at least in part, by a wall structure depending from the vehicle body, the wall structure comprising a plurality of members of selfsustaining shape and lamellar form, contiguously arranged in a horizontally extending row, means mounting the members so as to depend from the body for independent relative movement in a substantially vertical plane with respect thereto, the members having a convex surface to define, in use, with the surface over which the vehicle is to operate, a convergent-divergent passage for the efflux of gas from the cushion, means being provided to restrict flow of gas from the cushion to the upper surface of the members, operative to maintain the pressure above the members at a value less than that of the cushion pressure, so that forces exerted on the members due to the said efflux of gas beneath them, normally maintain the members in an equilibrium position spaced above the surface over which the vehicle operates, and inner and outer walls depending from the vehicle body, between which walls the said members are mounted and defining above the members a chamber, gas vents being provided in at least one of said inner and outer walls to provide for a controlled leakage of gas from the cushion through the said chamber to maintain the pressure in the said chamber at the required value.

12. A gas cushion vehicle as claimed in claim 11 in which the members comprise discs mounted so as to be free to rotate upon contacting the surface over which the vehicle operates.

13. A gas cushion vehicle as claimed in claim 12 in which it is arranged for the discs only to be directly subjected to cushion pressure over their inner lower quadrant and the pressure in the said chamber is maintained at a pressure between that of atmosphere and half cushion pressure.

14. A gas cushion vehicle as claimed in claim 11 including means for varying the rate of said controlled leakage from the cushion in dependence upon the hoverheight of the vehicle, the means being operative to increase the rate of leakage as the vehicle rises to a predetermined hoverheight.

Claims

9. Means for bounding, at least in part, the periphery of a gas cushion of a gas cushion supported apparatus, the said means comprising a plurality of members of self-sustaining shape and lamellar form, juxtaposed in a horizontally extending row, and arranged for independent relative movement in a substantially vertical plane, each member having a lower surface which, together with the surface over which the apparatus is to be supported, defines a potential convergent-divergent passage beneath the member for the efflux of gas from the cushion, the members being enclosed between depending inner and outer wall structures defining a downwardly open chamber, separate from the cushion space, means being provided to control the build up of pressure in the chamber above the members due to leakage of gas thereto from the cushion, so as to maintain the pressure therein at such a value that, in use, forces exerted on the members due to the said efflux of gas normally maintain the members in an equilibrium position spaced above the surface over which the apparatus is supported.

10. A gas cushion vehicle in which the vehicle-supporting cushion is contained, at least in part, by a wall structure depending from the vehicle body, the wall structure comprising a plurality of members of self-sustaining shape and lamellar form, contiguously arranged in a horizontally extending row, means mounting the members so as to depend from the body for independent relative movement in a substantially vertical plane with respect thereto, the members having a convex surface to define, in use, with the surface over which the vehicle is to operate, a convergent-divergent passage for the efflux of gas from the cushion wherein the pressure of the gas is maintained above atmospheric pressure, means being provided to restrict flow of gas from the cushion to the upper surface of the members, operative to maintain the pressure above the members at a value less than that of the cushion pressure but above atmospheric pressure, so that forces exerted on the members due to the said efflux of gas beneath them, normally maintain the members in an equilibrium position spaced above the surface over which the vehicle operates.

11. A gas cushion vehicle in which the vehicle-supporting cushion is contained, at least in part, by a wall structure depending from the vehicle body, the wall structure comprising a plurality of members of self-sustaining shape and lamellar form, contiguously arranged in a horizontally extending row, means mounting the members so as to depend from the body for independent relative movement in a substantially vertical plane with respect thereto, the members having a convex surface to define, in use, with the surface over which the vehicle is to operate, a convergent-divergent passage for the efflux of gas from the cushion, means being provided to restrict flow of gas from the cushion to the upper surface of the members, operative to maintain the pressure above the members at a value less than that of the cushion pressure, so that forces exerted on the members due to the said efflux of gas beneath them, normally maintain the members in an equilibrium position spaced above the surface over which the vehicle operates, and inner and outer walls depending from the vehicle body, between which walls the said members are mounted and defining above the members a chamber, gas vents being provided in at least one of said inner and outer walls to provide for a controlled leakage of gas from the cushion through the said chamber to maintain the pressure in the said chamber at the required value.