GB2266944A

GB2266944A - Flare arrangements

Info

Publication number: GB2266944A
Application number: GB9210162A
Authority: GB
Inventors: Timothy Jone
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1992-05-12
Filing date: 1992-05-12
Publication date: 1993-11-17
Anticipated expiration: 2012-05-12
Also published as: GB9210162D0; GB2266944B

Abstract

An infra-red flare, used as a decoy, for example, includes a pyrotechnic charge 4 which, in one embodiment, consists of a solid body 5 of a fuel having apertures 6 therein which contain rods 7 of an oxidiser. In an alternative embodiment of the invention, the body portion is of the oxidiser material and the fuel is located in the aperture or apertures. The material located in the aperture may be in solid or divided form and the body portion may be laminated or a foil, for example. The fuel may be lithium and the oxidiser PTFE. <IMAGE>

Description

Flare Arrangements This invention relates to flare arrangements particularly to arrangements which include infra-red flares.

One type of system for tracking potential targets such as aircraft relies on detecting infra-red emissions from, for example, engines. A comparison is made between the intensity of detected infra-red emissions with background infra-red radiation and the results may be used to guide missiles towards the target.

One mechanical countermeasure which may be used to interfere with infra-red guidance systems involves the deployment of an infra-red flare in the vicinity of the potential target, the flare being ejected from the target itself or some other local platform. The presence of another intense source of infra-red radiation near a target confuses the tracking system and may cause missiles to be deflected from their intended target.

Flares suitable for use as decoys generally include a pyrotechnic charge which, when ignited, generates a large amount of electromagnetic energy, a significant part of which falls within the infra-red part of the spectrum. At present, the pyrotechnic composition used in flares is manufactured by mixing a fuel and an oxidiser, both in powder form, using a binder, which typically occupies 8% to 15% of the volume, to hold the mixture together. Remote handling devices are necessary when preparing the composition as any static build up in the manufacturing area results in an appreciable fire risk.

The present invention arose from an attempt to provide arrangements employing infra-red flares which are less hazardous to manufacture and which more efficient during combustion.

According to the invention there is provided a flare arrangement comprising an infra-red emissive flare having a solid body portion which defines one or more apertures and a material located in the aperture or apertures, one of the body portion and material comprising the fuel part of a pyrotechnic composition and the other of the body portion and material comprising the oxidiser part of the pyrotechnic composition and including means for initiating combustion of the pyrotechnic composition whereby infra-red radiation is emitted.

As part of the pyrotechnic composition is present as a solid body portion, which may be a solid block or a foil, for example, rather than in divided form such as the powdered materials used in conventional compositions, handling during manufacture is much facilitated. Furthermore, as a binder is not required to retain a proper mixing of fuel and oxidiser parts, the efficiency attained during combustion may be greater because all of the volume occupied by the pyrotechnic composition is available to the reaction process.

In a preferred embodiment of the invention, the fuel part is of an element selected from Group I of the periodic table or a mixture or alloy including such an element. A particularly suitable element is lithium.

It is preferred that the oxidiser part of the pyrotechnic composition is a poly alkyl halide. One advantageous oxidiser, which is also particularly suitable for use with a lithium fuel, is polytetrafluoroethene (PTFE).

Other fluorinated polymers may also be suitable as oxiders.

In one advantageous embodiment of the invention, the body portion is a solid block having an aperture or apertures therein. The apertures may be blind or open at both ends.

Where the body portion has a plurality of apertures therein, the material may be located in all of them to give a wide spatial distribution but it may be deposited in only a few of them, depending the effect it is wished to obtain. The distribution, configuration and dimensions of the apertures may be regular or there may be a variation, for example they may be more closely spaced near the outer surfaces of the body portion.

In another embodiment of the invention, the body portion is of a laminate construction. The body portion may be made up of layers of the fuel with non-reactive intermediate layers or of the oxidiser part again with non-reactive intermediate layers. However, the body portion may be formed from laminated sheets of the fuel alone, or of the oxidiser alone.

In a preferred embodiment of the invention, the body portion is elongate and has a plurality of cylindrical apertures therein having longitudinal axes which are aligned parallel to the length of the body portion. In an alternative arrangement, the body portion is a foil which may be, for example, wound to leave a single aperture at its centre or apertures between turns of the foil. It could alternatively be corrugated or folded to define the required apertures.

The material in the aperture or apertures may be in divided form, being finely divided as a powder or in particulate or granulate form. The material may be compressed after it has been placed in the aperture or may be left loose.

Alternatively, the material may be in a solid or continuous form. Thus, where a block includes cylindrical apertures, the material may be inserted into the apertures as rods or the material could be in the form of sheeting, for example.

It is preferred that the body portion and the material are contained within a housing. Suitable materials for the housing are aluminium or PTFE as these may also take part in the pyrotechnic reaction when combustion is initiated. The means for initiating combustion may be remote from the housing or partly or wholly contained within it.

It may be preferred to include a magazine for storing a plurality of flares. This enables flares to be sequentially launched and initiated to give a continuous decoy presence.

It is envisaged that the invention will be mainly of use in decoy apparatus but it may have applications in other fields, such as for signalling purposes.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings in which: Figures 1, 2 and 3 schematically illustrate parts of arrangements in accordance with the invention; and Figure 4 illustrates decoy apparatus in accordance with the invention which incorporates a magazine for storing a plurality of flares.

With reference to Figure 1, decoy apparatus for launching infra-red flares from an aircraft includes a flare cartridge having an outer housing 1 of PTFE which is elongate and has a rectangular transverse section. The housing 1 is shown only in part and broken away in order to more clearly illustrate its contents. It is open at the bottom (as shown) and has five sides.

The housing 1 includes a compartment 2 at one end thereof remote from the opening. The compartment 2 houses a trigger, which may be electrical or mechanical. This is arranged adjacent to a compartment 3 enclosing an initiator in the form of a detonator and black powder. The greater part of the volume enclosed by housing 1 contains a pyrotechnic composition or charge 4.

In this embodiment of the invention, the pyrotechnic charge 4 comprises a solid block 5 of lithium metal having a plurality of cylindrical apertures 6 therethrough, the longitudinal axes of the apertures 6 being substantially parallel to the length of the housing 1. Each of the apertures is filled with a rod of PTFE 7. The lower part, as shown, is taken up by a volume 8 in which a parachute is stored.

In use, the flare cartridge is loaded into a launcher and ejected into the air. The parachute is deployed to slow the descent of the flare. At a predetermined time after launch, when the flare is safe distance from the launch platform, the trigger located in compartment 2 initiates the ignitor contained within compartment 3. This causes heat energy to be produced which is sufficient to cause combustion of the lithium and PTFE of the pyrotechnic composition. The pyrotechnic burning which results from the reaction produces large amounts of infra-red radiation, effectively masking the aircraft from infra-red search and tracking devices.

With reference to Figure 2, the pyrotechnic charge part of another apparatus in accordance with the invention is shown. The charge includes a solid body portion 9 which is cylindrical and is of a laminated structure. The material of the body portion 9 is PTFE and there are no intervening layers between the layers of that material. The body defines a single convoluted aperture 10 which contains lithium in granulate form. The housing (not shown) in this embodiment is of aluminium.

With reference to Figure 3, in another embodiment of the invention the pyrotechnic charge is composed of a metal foil 11 which is loosely wound so as to leave a gap between adjacent turns to define a single spiral aperture 12.

The aperture is filled with PTFE powder and the housing in which the charge is contained is of PTFE.

With reference to Figure 4, in one arrangement in accordance with the invention intended for use on board aircraft, a magazine 13 includes six cavities 14 of rectangular transverse section, each of which houses a flare similar to that illustrated in Figure 1. In this embodiment of the invention the flares are identical but different sorts could be available from the magazine if it is likely that flares having different properties regarding lifetime and intensity will be required. The rear of the magazine 13 includes sections 15 in which propellant charge for ejecting the flares is located. A timing and control circuit 16 generates initiation signals when it is wished to employ flares, these being transmitted via a demultiplexer 17 to the appropriate section of the magazine.

Claims

1. A flare arrangement comprising an infra-red emissive flare having a solid body portion which defines one or more apertures and a material located in the aperture or apertures, one of the body portion and material comprising the fuel part of a pyrotechnic composition and the other of the body portion and material comprising the oxidiser part of the pyrotechnic composition and including means for initiating combustion of the pyrotechnic composition whereby infra-red radiation is emitted.

2. An arrangement as claimed in claim 1 wherein the fuel part is of an element selected from Group I of the periodic table or a mixture or alloy including such an element.

3. An arrangement as claimed in claim 1 or 2 wherein the oxidiser part is a poly alkyl halide.

4. An arrangement as claimed in claim 1, 2 or 3 wherein the body portion is a solid block having an aperture or apertures therein.

5. An arrangement as claimed in claim 1, 2, or 3 wherein the body portion is of a laminate construction.

6. An arrangement as claimed in claim 4 or 5 wherein the body portion is elongate having a longitudinal axis and has a plurality of cylindrical apertures therein having longitudinal axes aligned parallel to the longitudinal axis of the body portion.

7. An arrangement as claimed in claim 1, 2 or 3 wherein the body portion is a foil.

8. An arrangement as claimed in any preceding claim wherein the material in the aperture or apertures is in divided form.

9. An arrangement as claimed in any one of claims 1 to 7 wherein the material in the aperture or apertures is in a solid form.

10. An arrangement as claimed in any preceding claim wherein the body portion and the material are contained within a housing.

11. An arrangement as claimed in claim 10 wherein the means for initiating is contained within the housing.

12. An arrangement as claimed in any preceding claim and including timing means for controlling the initiation of the pyrotechnic composition.

13. An arrangement as claimed in any preceding claim and including a magazine for storing a plurality of flares.

14. An arrangement as claimed in claim 12 and including means for sequentially launching and initiating flares stored in the magazine.

15. A flare arrangement substantially as illustrated in and described with reference to any one of the Figures of the accompanying drawings.