GB2188783A - Radar reflector - Google Patents

Abstract

An inflatable frame for a radar reflector, eg for rescue or decoy uses, comprises a number, eg eight, of inflatable struts 4 made of lay-flat plastic tubing extending from a manifold 1 and having their remote ends closed. The struts are sealed to stubs 3 on the manifold so oriented that when made rigid by inflation their remote ends define the apexes of a geometrical figure, eg with eight struts, a cube. The manifold contains a compressed-gas bottle and associated valve gear. The lay-flat tubing is folded zig-zag fashion close to the manifold, and to promote orderly inflation a cord is interleaved between the folds of the struts, crossing itself between adjacent folds, with its two free ends at the near end of each strut. Portions of electrically-conducting sheet material are tied to the remote ends of the struts. <IMAGE>

Description

SPECIFICATION Improvements in or relating to inflatable frames This invention relates to inflatable frames and has one application in inflatable radar reflectors for rescue or decoy uses.

Forms of reflectors are known in which an external frame of inflatable struts supports sheets of electrically-conducting flexible mesh, e.g. of carbon fibre. For example, twelve such identical struts can define the edges of a hollow octahedron within which they support eight concave corner-reflectors of such material. The struts can be made of rubber or plastic tubing sealed at their ends to four-way corner pieces of similar material to form an inflatable frame having a single inlet to which a pressurised gas source can be connected for inflation.

It is one object of the present invention to provide a form of inflatable frame which can be packed into a smaller volume before inflation.

According to the present invention, an inflatable frame comprises a plurality of inflatable struts made of flexible tubing and extending from a manifold, said struts having their remote ends closed and being so orientated with respect to the manifold that, when made rigid by inflation, the remote ends define the respective apexes of a notional geometrical figure.

The figure may be three-dimensional with the manifold located within said figure.

The manifold may be permanently rigid and may be provided with suitably oriented stubs, which may be rigid or flexible, to which the near ends of the struts are sealed. The manifold may be adapted to contain a container of compressed gas and associated control means for inflating the frame.

The struts may be made of lay-flat tubing which, in the non-inflated state, is folded lengthwise in a regular zig-zag manner and held close to the manifold by releasable means. Preferably a flexible linear member, eg.

a cord, is interleaved between the folds of the tubing of each strut transversely to the length of the strut, the member crossing itself between each pair of adjacent folds and having its two free ends extending from the near end of the strut, thereby to cause orderly expansion of each strut, starting at the near end, upon inflation.

The present invention also provides a radar reflector comprising an inflatable frame as aforesaid.

To enable the present invention to be more readily understood, attention is directed, by way of example, to the accompanying drawings wherein: Figure 1 is a perspective view of an inflated frame defining the corners of the cube.

Figure 2 is a perspective view of a part of a non-inflated, partially-folded strut.

Figure 3 is a perspective view of the strut of Fig. 2 fully folded and clamped, and sealed to a manifold stub.

Fig. 1 shows a permanently rigid cylindrical manifold 1, having gas-tight end-caps 2. Extending from the manifold 1 are eight stubs 3 to which are sealed eight struts 4 made of layflat plastic tubing. The stubs 3 are so located and oriented with respect to the manifold 1 that, when made straight and rigid by inflation, the remote ends 5 of the struts 4 define the corners of a cube, indicated by the interrupted lines 6, with the manifold located approximately centrally within the cube.

The remote ends 5 comprise tabs having holes which support sheets of electrically-conducting material (not shown), eg, carbon-fibre mesh, to form a radar reflector. The manifold 1 contains a bottle of compressed gas (not shown), which is opened by remote control to inflate the frame.

In order that the frame shall occupy a small volume in the non-inflated state, and to obtain orderly opening of the frame when the bottled gas is released into the manifold, the noninflated struts are preferably folded zig-zag fashion, as shown partially in Fig. 2 and completely in Fig. 3, so that they lodge close to the manifold. In Fig. 3 the folds are held together temporarily by a clip 8, and the strut 4 is shown sealed to a stub 3 of the manifold 1. Additionally, a cord 9 is interleaved between the folds of the strut, transversely to its length, and crossing itself between each pair of adjacent folds, as shown in Fig. 2. The two free ends 10 of the cord 9 (of which only one is visibie in Fig. 3) extend loosely from the end of the folded strut nearest the manifold as shown.The effect of the cord is to cause the expansion of all eight struts to occur in an orderly manner beginning at those ends nearest the manifold, the cord falling fee as successive folds straighten out.

Depending on the degee of non-inflated compactness required, the stubs 3 can be of rigid or flexible material. For example, the manifold and stubs can be made of a metal such as aluminium. In order to occupy the minimum volume, however, the stubs can be made of a flexible material such as synthetic rubber, to allow the folded struts to be held closer to the manifold. In the latter case the manifold may comprise a rigid inner sleeve, eg, of aluminium, covered by a close-fitting flexible sleeve, eg, of synthetic rubber, with which the stubs are integral as a single moulding.The inner sleeve is perforated with holes to allow inflation of the struts from the bottom within it, and after insertion of the bottle, etc, the caps are fitted to the manifold with the gas-tight O-ring seals (not shown) Where flexible studs are used, the aforesaid flexible sleeve may be bonded to the rigid inner sleeve by a layer of adhesive; in order to ensure that the flexible sleeve does not peel off when the frame is inflated, a closefitting outer sleeve of heat-shrinkable irradiated-plastic (eg. polyethylene) tubing is fitted over the flexible sleeve. This outer sleeve has large holes through which protrude the flexible stubs of the flexible sleeve; the holes are cut in partially pre-shrunk plastic tubing to ensure good registration between holes and stubs before the final heat-shrinking in situ to a rigid state.

The nylon struts can be bonded with adhesive to the inner surface of the stubs (whether these are flexible or rigid) with the aid of a long mandrel which is inserted into each strut from its open end. The mandrel has an inflatable lower tip which is used to press the nylon tubing against the inner surface of each strut while the adhesive layer between them is cured by heating. After withdrawal of the mandrel, the remote end of the strut is sealed, and the tabs attached, by welding.

The clip 8 shown in Fig. 3 clamps the strut in the folded state during assembly. When all eight struts have been sealed to the manifold, each circumferential ring of four clamped struts is held in place against the manifold by an encircling rubber band (not shown) and the eight clips removed. Thereafter four arcuate plates (not shown), each occupying about 90" of the circumference, are placed round the assembly and held together by flanged end-caps (not shown). The underlying rubber bands are then severed at the gaps between the plates, and the frame is then ready for use.

To open the frame, the end-caps securing the arcuate plates are removed, mechanically or otherwise, and the compressed-gas bottle opened. The inflating struts then push the arcuate plates free of the expanding structure.

Other arrangements for holding together, and releasing, the non-inflated frame can be used.

Also it is not essential for the manifold to be rigid, eg, for some applications a flexible moulded rubber manifold may be suitable.

To produce frames having a maximum dimension of the order of 1 metre, lay-flat nylon tubing of about 50 microns thickness and 2.5 cm between edges when flat is suitable. The cord 9 may be of twisted or woven nylon about 0.5-1.0 mm in diameter. Tape may be used instead of cord.

The present frame has the advantage, over those in which inflatable struts define the edges of the geometrical figure, of requiring a reduced total length of tubing, and thus occupying less volume before inflation; it also requires less gas to inflate it.

For ease of inflation (and of exhaustion for packing into a small volume) a length of thin tape substantially narrower than the flat nylon tubing may be enclosed in each strut as indicated at 11 (Fig. 2). For enhanced reflectivity when used in a radar reflector, the tape is made of aluminium or aluminised plastics.

In addition to its use for three-dimensional frames, as described, the present invention can also be used for two-dimensional frames.

The frames of the present invention are not usually suitable for free-standing applications, ie, to "sit" on a surface, but may be suspended from a mast or released from a height, eg, from an aircraft or rocket.

Claims (12)

1. An inflatable frame comprising a plurality of inflatable struts made of flexible tubing and extending from a manifold, said struts having their remote ends closed and being so oriented with respect to the manifold that, when made rigid by inflation, the remote ends define the respective apexes of a notional geometrical figure.

2. A frame as claimed in claim 1 wherein the figure is three-dimensional with the manifold located within said figure.

3. A frame as claimed in claim 1 or claim 2 wherein the manifold is permanently rigid and is provided with suitably oriented stubs to which the near ends of the struts are sealed.

4. A frame as claimed in claim 3 wherein the stubs are flexible.

5. A frame as claimed in claim 3 or claim 4 wherein the manifold is adapted to contain a container of compressed gas and associated control means for inflating the frame.

6. A frame as claimed in any of claims 1 to 5 wherein the struts are made of lay-flat tubing which, in the non-inflated state, is folded lengthwise in a regular zig-zag manner and held close to the manifold by releasable means.

7. A frame as claimed in claim 6 wherein a flexible linear member, eg a cord, is interleaved between the folds of the tubing of each strut transversely to the length of the strut, the member crossing itself between each pair of adjacent folds and having its two free ends extending from the near end of the strut, thereby to cause orderly expansion of each strut, starting at the near end, upon inflation.

8. A frame as claimed in claim 6 or claim 7 wherein a thin tape of width substantially less than the lay-flat width of the tubing extends along the interior of each strut in order to aid evacuation and inflation.

9. A radar reflector comprising a frame as claimed in any preceding claim having a portion or portions of flexible electrically-conducting sheet material attached thereto.

10. A radar reflected as claimed in claim 9 as dependent on claim 8 wherein the thin tape is electrically conducting.

11. An inflatable frame as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

12. A radar reflector comprising a frame as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.