GB2298173A

GB2298173A - Hover pad

Info

Publication number: GB2298173A
Application number: GB9602453A
Authority: GB
Inventors: John Frances Cownley
Original assignee: Air Log Ltd
Current assignee: Air Log Ltd
Priority date: 1995-02-23
Filing date: 1996-02-07
Publication date: 1996-08-28
Also published as: GB9602453D0

Abstract

A hover pad comprises a rigid diaphragm 10, a flexible inflatable part 13 which forms a lower chamber 14 with the diaphragm and is capable of producing by means of leakage of air from the lower chamber 14 an air bearing which can support the pad clear of an underlying surface, and a rigid member 8 to which the rigid diaphragm is flexibly connected so as to define an upper inflatable chamber 12. The rigid member is adapted for the supply of pneumatic pressure to the upper chamber and the rigid diaphragm is connected to the rigid member by a peripheral skirt 11. In an alternative arrangement, the chambers 12,14, may be inflated independently.

Description

HOVER PADS FOR SURFACE TRANSLATION OF LOADS INTRODUCTION Air bearings for supporting loads on a cushion of air exist in a variety of forms to meet different requirements. A common requirement is for the frictionless movement of loads over a generally horizontal surface. If the surface is irregular, comprising, for example, a natural land or sea surface, the air bearing is preferably achieved by means of an air cushion enclosed within a flexible skirt, as used on air cushion vehicles. If the surface is firm and smooth, permitting small ground clearances, then the use of a number of hover pads, suitably positioned on the under surface of the load or load carrier, may be preferable.One advantage of hover pads with respect to skirted air cushions is that they can be fitted as standard integral units without the need for incorporation into load design as is necessary in air cushion vehicles.

All air bearing devices, skirted or otherwise, depend on the supply of low pressure air to a chamber, the downside of which is open and adjacent to the surface on which the load is to be supported and over which it is to be traversed.

Leakage from the chamber through the open downside is limited by the proximity of the chamber's opening to the supporting surface, thus giving a small annular or peripheral gap through which the air can escape. The essence of such systems is to minimize leakage by keeping the air pressure low in the chamber and to achieve the desired lifting force by a suitable choice of lift area.

The use of a peripheral flexible skirt around the lifting chamber improves the efficiency by further reducing the leakage and also permits a greater lift height, thus allowing the air cushion vehicle to operate over a wide range of terrains and irregular surfaces. Hover pads, generally, do not have the same versatility and their use is usually restricted to relatively smooth, or gently undulating, surfaces. It would give a considerable operational advantage if the range of surfaces over which they can be used could be extended.

It is, therefore, the object of the invention to provide this greater versatility of operation whilst retaining the advantage of an integral, easily filled unit.

According to the invention a hover pad comprises a rigid diaphragm, a flexible inflatable part which forms an annular lower chamber with the diaphragm and includes at least one part through which air within the lower chamber can leak to a region between the said flexible part and an underlying surface and thence radially outwardly between the said flexible part and the underlying surface, to form an air bearing which can support the said flexible part and thereby the pad with respect to the underlying surface, a rigid member which overlies the rigid diaphragm and is of greater lateral extent thereof, the said rigid member having peripheral support members defining a space under the rigid member for the accommodation of the rigid diaphragm and the flexible part in said space when the flexible part is deflated and the said support members rest on the said underlying surface, and a peripheral flexible skirt which connects the rigid diaphragm with the said rigid member to define an upper inflatable chamber.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a known form of hover pad in a deflated state.

Figure 2 illustrates the known hover pad in an inflated state.

Figure 3 illustrates one embodiment of the invention in a deflated state.

Figure 4 illustrates the embodiment shown in Figure 3, in an inflated state.

DETAILED DESCRIPTION A known form of hover pad is illustrated in Figures 1 and 2.

The pad comprises a base plate 1 which may be circular. The plate has a downward, peripheral flange la and a central shallow downward boss 2. A flexible and preferably elastic annular diaphragm 3 is fixed at its outer periphery to the inside of the flange and at its inner periphery to the central boss. The diaphragm 3 has circumferentially disposed holes 4 whilst the base plate has an inlet port 5 communicating with a supply of low pressure air. The base plate may be rigidly attached to the underside of the load or load carrier at its top surface 6.

Figure 1 shows the hover pad deflated. The pad and any load which it supports rest on the flange la. The supply of pneumatic pressure to the port 5 inflates the annular chamber formed between the base plate and the diaphragm.

Air from this chamber leaks from the holes 4 to a leaky chamber formed between the pad and the underlying surface and out to the atmosphere between the inflated diaphragm and the underlying surface, establishing an air bearing which supports the pad just above the underlying surface. The flow of air is denoted by the arrows A and B.

The hover pad shown in Figures 3 and 4 comprises a rigid plate 7 which has peripheral flanges 19 capable of supporting the plate 7 clear of the ground surface. The plate may support or be attached to the underside of a load by its top surface 8. An air inlet 9 is connected to a low pressure source of air (not shown); a typical pressure would be 1 Bar. A rigid diaphragm 10 is connected to the plate by means of a flexible peripheral elastomeric skirt 11 so as to constitute with the plate 8 an upper chamber 12.

The rigid diaphragm 10 in conjunction with a flexible diaphragm 13 of elastomeric material forms a lower chamber 14. The upper chamber 12 is connected to the lower chamber 14 by a series of pressure reducing orifices 15 in the rigid diaphragm 10 and the lower chamber is connected to the underside of the flexible diaphragm by a series of bleed holes 16.

In use, when low pressure air is introduced into the inlet 9, it flows as shown by the arrow C into the upper chamber 12 and then into the lower chamber 14 through the orifices 15. Due to the pressure drop through the orifices, the pressure in the upper chamber is initially higher than in the lower one. Preferably the area of the upper chamber is greater than the lower one and preferably the arrangement is such that the upper chamber inflates first, thereby raising the load clear of the rigid diaphragm 10 which is still resting on the deflated flexible diaphragm 13, which is lying on the ground.

When the upper chamber is fully inflated the pressure rises in the lower chamber, inflating it also. The air flow passes through the bleed holes 16 in the flexible diaphragm 13, entering the space 17 below it and raising the whole assembly just clear of the floor surface as an air cushion forms. The air flow is discharged to the atmosphere through the circumferential escape path 18 formed between the flexible diaphragm and the ground surface.

In the embodiment just described the lower chamber is inflated by way of the upper chamber. In an alternative embodiment, the lower chamber may be inflatable separately by means of a tube which may be flexible and which extends through the attachment plate 8 and through the rigid diaphragm. A sliding seal may be provided where the tube passes through the plate 8 and there may be a seal around the tube where it passes through or is in communication with a hole in the rigid diaphragm.

The tube may be connected to a source of pneumatic pressure.

In this latter embodiment there is no need for the pressure reducing orifices in the rigid diaphragm.

Claims

CLAINS

1. A hover pad comprising a rigid diaphragm, a flexible inflatable part which forms an annular lower chamber with the diaphragm and includes at least one port through which air within the lower chamber can leak to a region between the said flexible part and an underlying surface and thence radially outwardly between the said flexible part and the underlying surface, to form an air bearing which can support the said flexible part and thereby the pad with respect to the underlying surface, a rigid member which overlies the rigid diaphragm and is of greater lateral extent thereof, the said rigid member having peripheral support members defining a space under the rigid member for the accommodation of the rigid diaphragm and the flexible part in said space when the flexible part is deflated and the said support members rest on the said underlying surface, and a peripheral flexible skirt which connects the rigid diaphragm with the said rigid member to define an upper inflatable chamber.

2. A hover pad according to claim 1 wherein the rigid member is adapted for the supply of pneumatic pressure to the upper chamber.

3. A hover pad according to claim 1 or claim 2 wherein the upper chamber and the lower chamber are pneumatically connected by means of pressure reducers.

4. A hover pad according to claim 4 wherein the pressure reducers comprise holes in the rigid diaphragm.

5. A hover pad according to any foregoing claim wherein the chambers are relatively arranged so that a supply of air to the upper chamber inflates the upper chamber before the lower chamber.

6. A hover pad according to claim 1 or 2 and comprising means for inflating the lower chamber separately from the upper chamber.

7. A hover pad according to claim 7 wherein the said means comprises a tubular connection extending through the said rigid member and the rigid diaphragm to the lower chamber.