IGNITER PELLET AND RELATED COMPOSITION FOR DECOY COUNTERMEASURE ASSEMBLY

The present technology is directed to igniter pellets for use with an expendable countermeasure flare assembly with an igniter assembly with a pellet receptacle. An igniter pellet of one or more embodiments has a moisture insensitive first layer formed by a first composition comprising a mixture of a fuel material that includes Boron, an oxidizer material that includes Bismuth Oxide and/or Potassium Perchlorate, and a granular matrix binder holding the fuel material and the oxidizer material together. A second layer is formed by a second composition that has a fuel material that includes Magnesium, an oxidizer that includes Polytetrafluoroethylene, and a binder material that includes a fluoropolymer elastomer. The second layer is contained in the pellet receptacle and covered by the first layer, so that the second layer is isolated and protected from ambient moisture by the moisture insensitive first layer.

TECHNICAL FIELD

This patent application is generally directed to pyrotechnic expendable countermeasure decoy flares, and more particularly to ignition systems for pyrotechnic countermeasure decoy flares.

BACKGROUND

Conventional pyrotechnic infrared (IR) expendable countermeasures, such as decoy flares, are used in aircraft self-protection systems as a deployable expendable munition to counter an infrared homing surface-to-air missile, air-to-air missile, or other heat-seeking weapon. Decoy flares commonly include a pyrotechnic composition based on magnesium or another hot-burning powdered metal composition, with combustion/burning temperatures equal to or hotter than engine exhaust or other components of the aircraft. The aim is to make the IR-guided missile seek out the more attractive heat signature from the flare rather than the aircraft's engines or hot components. The countermeasure flares typically include ignition systems configured to ignite or otherwise activate the pyrotechnic and/or propellant materials within the countermeasure once deployed from the aircraft.

Ignition systems often utilize electrically initiated expulsion or impulse cartridges that eject the expendable from the aircraft dispensing system and contain features that ignite an expendable flare ignition material, such as an igniter pellet upon exit from the dispenser system. This ignition pellet, in turn, quickly generates flame and hot gas that propagates ignition to the body of the expendable or countermeasure flare assembly. Some conventional compositions for the ignition material, however, are susceptible to degradation by moisture exposure or intrusion, which can result in poor aging characteristics and reduced performance of the countermeasure, including complete failure and non-transfer of the ignition train to the expendable, rendering it totally ineffective. There is a need for an ignition system with an ignition composition, which may be in the form of an igniter pellet or pellets, that are sufficiently durable and insensitive to moisture and other conditions that can cause ignition delays and propagation failures associated with aging, storage, application, system interaction, and environmental issues.

The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claimed embodiments. Further, the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be expanded or reduced to help improve the understanding of the embodiments. While the disclosed technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the embodiments described. The embodiments are intended to cover all modifications, equivalents, and alternatives falling within the scope of the embodiments.

DETAILED DESCRIPTION

The present technology provides ignition compounds and igniter pellets for use with deployable expendable countermeasures, such as IR decoy flares or other ignitable countermeasures, and associated methods that overcome drawbacks of the prior art and provide other benefits. Examples of the technology introduced above will now be described in further detail. The following description provides specific details for a thorough understanding and enabling description of these examples. One skilled in the relevant art will understand, however, that the techniques discussed herein may be practiced without many of these details. Likewise, one skilled in the relevant art will also understand that the technology can include many other features not described in detail herein. Additionally, some well-known structures or functions may not be shown or described in detail below so as to avoid unnecessarily obscuring the relevant description. For purposes of simplicity of discussion, the technology may be described herein with reference to top and bottom, upper and lower, above and below, and/or left or right relative to the spatial orientation of the embodiment(s) shown in the figures. It is to be understood that the technology, however, can be moved to and used in different spatial orientations without changing the structure of the system.

In at least one embodiment, the technology disclosed herein provides an igniter pellet for use with an expendable countermeasure assembly having an igniter assembly with an igniter pyrotechnic pellet receptacle therein. The igniter pellet has a first layer formed by a first composition comprising a mixture of a first fuel material that includes Boron, a first oxidizer material that includes Bismuth Oxide and/or Potassium Perchlorate, a granular matrix binder holding the fuel material and the oxidizer material together, wherein the first composition is insensitive to ambient moisture. The igniter pellet has a second layer formed by a second composition different than the first composition. The second composition comprises a second fuel material that includes Magnesium, a second oxidizer that includes Polytetrafluoroethylene, and a binder material that includes a fluoropolymer elastomer. The second layer is configured to be contained in the pellet receptacle and covered by the first layer so that the second layer is isolated and protected from ambient moisture by the moisture insensitive first layer.

Another embodiment of the present technology provides a method of forming an igniter pellet for use with an expendable countermeasure flare assembly having an igniter assembly with an igniter pellet receptacle therein. The method includes forming a moisture-insensitive first ignition composition for a first layer of the igniter pellet by dissolving a first rubber-based binder in a polar solvent to form a binder solution. The binder solution is mixed with a first fuel material that includes Boron, and a first oxidizer material that includes Bismuth Oxide and/or Potassium Perchlorate to form a first mixture. A low boiling point non-polar solvent is added to the mixture and precipitating the binder from the mixture to form a coagulation composition. The coagulation composition is converted to a first moldable granular composition. The method also includes providing a second ignition composition that comprises a mixture of Magnesium, Polytetrafluoroethylene and a fluoropolymer elastomer binder. The first and second ignition compositions are positioned into the pellet receptacle of the igniter assembly slider, wherein the first composition forms a first layer, and the second composition forms a second layer that is covered and isolated from ambient moisture by the first layer.

Another embodiment of the present technology provides a deployable expendable infrared countermeasure assembly that has a body portion with a payload portion and a base portion. A deployable, ignitable payload is contained in the final configured countermeasure flare assembly. An impulse cartridge is coupled to the base of the outer case of the expendable. The impulse cartridge comprises an electrical initiator adjacent to a pyrotechnic output charge suitable for payload jettison and ignition train transfer to the expendable. The ignition pellet of the igniter contained in the expandable countermeasure flare assembly has a first layer formed by a first composition comprising a mixture of a first fuel material that includes Boron, a first oxidizer material that includes Bismuth Oxide and Potassium Perchlorate, and a granular matrix binder holding the fuel material and the oxidizer material together. The first composition is insensitive to ambient moisture. A second layer is formed by a second composition different than the first composition. The second composition comprising a second fuel material that includes Magnesium, a second oxidizer that includes Polytetrafluoroethylene, and a binder material that includes a fluoropolymer elastomer. The second layer is configured to be fully contained in the flare igniter assembly and covered by the first layer so that the first layer is adjacent to the impulse cartridge output and the second layer is isolated and protected from ambient moisture by the moisture insensitive first layer.

Another embodiment of the present technology provides a method of forming an igniter pellet for use with a countermeasure assembly having an igniter assembly with a pellet receptacle therein. The method comprises forming a moisture-insensitive ignition composition by dissolving a first rubber-based binder in a polar solvent to form a binder solution. The binder solution is mixed with a first fuel material that includes Boron, a first oxidizer material that includes Bismuth Oxide and/or Potassium Perchlorate and a second oxidizer material and burn rate enhancer that includes finely divided Potassium Perchlorate powder to form a mixture. A low boiling point non-polar solvent is added to the mixture and the binder is precipitated from the mixture to form a coagulation composition. The coagulation composition is converted to a moisture insensitive moldable granular composition. The moisture insensitive ignition composition is positioned into the pellet receptacle of the igniter assembly to form an igniter pellet adjacent to output of the impulse cartridge.

FIG.1is an illustration of a countermeasure assembly10with a moisture insensitive igniter pellet20in accordance with one or more embodiments of the present technology. The countermeasure10has a body12that contains a deployable, ignitable payload14adjacent to an igniter assembly16adjacent to an impulse cartridge17in the base18of the outer case19of the flare assembly. The impulse cartridge17is electrically activated to ignite igniter assembly16of the expendable flare and eject the payload14from the outer case19upon countermeasure deployment. The impulse cartridge17has an igniter pellet20positioned in a receptacle22of the slider component23of the assembly. The receptacle22is in communication with and activated by the pyrotechnic output of the electrically activated impulse cartridge17. The electrical activator of the impulse cartridge17is configured to ignite the output charge of the cartridge, which generates a flame, heat, and pressure to eject the flare payload, in turn igniting the composition of the igniter assembly16which transfers to the decoy flare payload. The payload14may be a pyrotechnic and/or pyrophoric material, such that, upon ignition of the countermeasure, a tuned and strongly exothermal reaction is started, releasing IR energy and visible smoke and flame with a selected heat signature or characteristic. This is only one non-limiting example of a countermeasure assembly that can include the igniter pellet and/or ignition compound in accordance with the present technology. Other countermeasure assemblies can be used in other embodiments.

FIG.2is an enlarged cross-sectional view of an igniter assembly16with the pellet20in the receptacle22in accordance with an embodiment of the present technology. The igniter pellet20is a dual layered, hybrid energetic composition pellet comprising two different compositions arranged in layers within the slider receptacle of the igniter assembly. Each composition has different characteristics and functional roles for the countermeasure assembly10, so as to provide consistent, quick and reliable ignition train transfer from the impulse cartridge17to the payload (e.g., the decoy flare material).

As seen inFIGS.2and3, the ignition pellet20has two layers that form a unitary pellet body with an interface area28where the layers are pressed together or otherwise interconnected. In one embodiment, the ignition pellet20comprises a layered pressing of two independent pyrotechnic compositions. A first layer30is an ignition or acceptor side in communication with the impulse cartridge17output or other ignition activation device. A second layer32of the pellet is pressed with the first layer30to form a transfer or output side in a unitary pellet for activation of the pyrotechnic or propellant materials upon deployment of the countermeasure.

In the illustrated embodiment, the ignition pellet20is positioned in the receptacle22with the outer first layer30fully covering the inner second layer32. The first layer30engages the second layer32at the interface layer28. In some embodiments, the first layer30is applied to the second layer32so that a portion of the first composition mixes with the second composition at the interface layer28to form an ignition pathway from the first composition to the second composition. The outer first layer30is positioned adjacent to the impulse cartridge17output so to accept ignition from the output of the expulsion or impulse cartridge. When the outer first layer30is ignited, it is lit and burns quickly and at high temperatures, so as to pass the ignition train across the interface area28to the pellet's inner second layer32to pass the ignition train to the flare body/material forming the payload. The composition of the first layer30is substantially insensitive to moisture. The first layer30covers the second layer32, so the inner second layer32is substantially fully isolated from the ambient environment (i.e., air, moisture, particulates, potential contaminates, etc.) via the walls forming the receptacle22and the first layer30. Accordingly, the moisture insensitive first layer30forms an exterior surface34of the pellet20facing the opening of the receptacle22for operative communication with the impulse cartridge's output.

The pellet's moisture insensitive first layer30provides superior reliability in ignition, burn rate and consistency upon activation of the impulse cartridge so as to provide the flame and thermal energy transfer across the interface area28to ignite the inner second layer32. Burning of the igniter pellet20can also generate high temperature gases used to cause ignition of the payload of the countermeasure body upon deployment. As a result, the dual layered hybrid energetic composition igniter pellet20of the present technology ensures consistent ignition propagation to the payload independent of the age, storage conditions, or other environmental conditions surrounding the countermeasure assembly10, such as while installed in an aircraft, in a storage location, or in transit to or from the storage location. The ignition pellet configuration also accommodates reliable ignition activation from a wide range of impulse cartridge outputs, therefore ensuring more reliable decoy flare ignition and function.

As indicated above, the pellet's first layer30is pressed onto or otherwise positioned over the second layer32within the igniter assembly slider receptacle22, so entire second layer32is isolated from the ambient environment by the first layer20and the structure forming the receptacle22. Accordingly, only the exterior surface34of the first layer30may be exposed to air, moisture, and other ambient conditions surrounding the countermeasure assembly10. These ambient conditions may be when the countermeasure assembly10is in a storage location, in transit to or from the storage location, or installed in an aircraft dispensing system.

In the illustrated embodiment, the outer first layer30is made of a moisture insensitive ignition composition comprising a fuel material and an oxidizer that are held together by a binding material. In one embodiment the fuel material is Boron or other suitable fuel material. The Boron is combined with the oxidizer, such as Bismuth Oxide, and Potassium Perchlorate, or other suitable oxidizer material. The binding material holding fuel and oxidizer materials together is a granular matrix formed by an elastomeric rubber binding material such as Fluorel™, Kraton®, or suitable rubber material. In at least one embodiment the composition of the first layer comprises approximately 3-5% by weight of the fuel (e.g., Boron), 88-96% by weight of the oxidizer (e.g., Bismuth Oxide and/or Potassium Perchlorate), and 3-5% of the binder (e.g., Fluorel™ or other elastomeric rubber binder). In one embodiment, the composition of the first layer can comprise approximately 3-5% by weight of the fuel (e.g., Boron), 86-92% by weight of the Bismuth Oxide (oxidizer), 3-5% of the Potassium Perchlorate (oxidizer), and 3-5% of the binder (e.g., Fluorel™ or other elastomeric rubber binder).

This composition of the first layer30of at least one embodiment can be blended using a high-shear style mixer according to a shock-gel process that results in a granular material after mixing. For example, this first layer30is formed by a mixing process that comprises dissolving the binder in a low boiling point polar solvent, such as ketones or ketone mixtures, to provide a binder solution. The binder solution is then mixed with mixing the fuel material and the oxidizer material(s). A low boiling point non-polar solvent, such as saturated hydrocarbons, is added to the above mixture to precipitate the binder and form a coagulation composition. The coagulation composition is dried and converted into a granular composition using any suitable method, such as one or more conventional screening/granulating processes. The resulting granular ignition composition of the first layer has a calorific output of approximately 300 calories per gram, is stable to approximately 375° C., and has a burn rate of approximately 3.3-4.5 seconds/inch.

In another embodiment, the composition of the first layer30can be mixed using a static mixer process. For example, a first stream of the binder, the low boiling point polar solvent, the fuel material, and the oxidizer mixture are introduced to the static mixer. This first stream is intersected with a second stream of the low boiling non-polar solvent in the static mixer to precipitate the binder. Granules of the ignition compositions are then formed through the turbulence of the static mixer to provide the composition with the above caloric output, stability and burn rate characteristics.

The second layer32forming the transfer or output side of the dual layered hybrid energetic composition igniter pellet20comprises a second composition different than the composition of the first layer30. In the illustrated embodiment, this second composition comprises a mixture of a second fuel material different than the fuel material of the first layer, a second oxidizer different than the oxidizer of the first layer, and a second rubber binder. In at least one embodiment, the second fuel is a finely divided Magnesium powder. The second oxidizer is a finely divided Polytetrafluoroethylene (PTFE) powder. The binder is a rubber binder, such as a rubber and fluoropolymer elastomer (e.g., Fluorel™) binder. In some embodiments, the second composition for the second layer is a combination of Magnesium, Teflon, and Viton® (MTV). The composition is blended using a high-shear style mixer according to a shock-gel process that results in a granular material after mixing. In at least one embodiment the composition of the second layer comprises approximately 74-80% by weight of the fuel (e.g., Magnesium), 16-22% by weight of the oxidizer (e.g., PTFE), and 2-6% of the binder (e.g., fluoropolymer elastomer).

A mixing method in accordance with at least one embodiment for making this second composition comprises dissolving the binder in a low boiling point polar solvent, such as such as ketones or ketone mixtures, to provide a binder solution. The binder solution is mixed with the second fuel material and the second oxidizer. A low boiling point non-polar solvent, such as such as saturated hydrocarbons, is then added to the second fuel/oxidizer/binder mixture to precipitate the binder and form the coagulation composition. The coagulation composition is converted into a granular composition. The resulting granular ignition composition has a calorific output of approximately 700 cal/g calories per gram, is stable to approximately 490° C., and has a burn time of approximately 1.25-1.75 seconds/inch.

In another embodiment, the second composition for the second later of the ignition pellet of the present technology can be formed by using a static mixer to mix the ignition composition. For example, a first stream of the binder/low boiling point polar solvent/fuel material/oxidizer mixture is introduced to the static mixer. The first stream is intersected with a second stream of the low boiling non-polar solvent in the static mixer. Granules of the ignition compositions are formed through the turbulence of the static mixer with the above caloric output, stability and burn rate characteristics.

The first and second compositions can be pressed together in the layered arrangement to provide the hybrid layered pellet20with the interface area28between the two layers30and32. For example, in one embodiment the second composition can be mechanically pressed into the receptacle22of the slider of the igniter assembly to form the second layer32. Then the first composition can be mechanically pressed into the receptacle22atop the second layer32to form the first layer30that fully covers the second layer and insolates the second layer from moisture and other ambient conditions. When the first layer30is pressed onto the second layer32, a portion of the first composition forming the first layer30mixes with the second composition forming the second layer32at the interface area28to provide full and consistent ignition propagation between the layers upon activation of the countermeasure assembly10. In other embodiments, the hybrid dual layered ignition pellet20can be formed in a mold by pressing the first and second compositions into the mold to form the first and second layers30and32. The pellet20can then be removed from the mold and inserted into the impulse cartridge16, such as during assembly of the countermeasure assembly10. In yet another embodiment, the first composition can be applied to the second layer32in a slurry application to cover selected portions of the exterior surface of the second layer30, as shown inFIG.4.

The above description are examples of some embodiments of the present technology. In other embodiment, the composition weights can be varied within allowable tolerances while still achieving the identified performance characteristics. The fuels, oxidizers, mixture ratios, and particle sizes can be adjusted according to the desired output performance of the moisture insensitive ignition composition, i.e., by varying the ratios of Boron, Bismuth Oxide, Potassium Perchlorate, binder, as well as the Magnesium/Teflon (PTFE)/Fluorel (MTV), etc.

Another embodiment of the present technology provides a moisture insensitive ignition composition for an igniter pellet that can quickly and reliably ignite the pyrotechnic or propellant materials in the countermeasure assembly without ignition delay or propagation failures. The ignition material can be molded or otherwise formed into a pellet format for use in the igniter assembly16in the base of the countermeasure assembly10. This composition comprises a first fuel, such as a Boron powder, a first oxidizer, such as finely divided Bismuth Oxide powder, and a binder, such as a Fluorel™ rubber binder. This composition also includes a second oxidizer and burn rate enhancer, such as a finely divided Potassium Perchlorate powder.

This ignition composition can be blended using a high-shear style mixer according to a shock-gel process that results in a granular material after mixing. For example, the mixing method for making the moisture insensitive ignition composition can comprise dissolving the binder in a low boiling point polar solvent, such as acetone or other ketones or ketone mixtures to provide a binder solution. The binder solution is mixed with the fuel material and the first and second oxidizers. A low boiling point non-polar solvent, such as hexane or other saturated hydrocarbons, is added to the mixture to precipitate the binder and form the coagulation composition. The coagulation composition is converted into granular composition using one or more conventional screening/granulating processes. The resulting granular ignition composition has a calorific output of approximately 300 calories per gram, is stable to approximately 375° C., and has a burn time of approximately 3.3-4.5 seconds/inch.

In another embodiment, the ignition composition can be mixed using a static mixer process. For example, a first stream of the mixture of the binder, the low boiling point polar solvent, the fuel material, and the first and second oxidizers is introduced to the static mixer. The first stream is intersected with a second stream of the low boiling non-polar solvent in the static mixer. Granules of the ignition compositions are formed through the turbulence of the static mixer with the above caloric output, stability and burn rate characteristics. The fuels, oxidizers, mixture ratios, and particle sizes for these alternative compositions can be adjusted according to the desired output performance of the moisture insensitive ignition composition, i.e., by varying the ratios of Boron, Bismuth Oxide, Potassium Perchlorate, and binder materials.

Remarks

The terms used in this specification generally have their ordinary meanings in the art, within the context of the disclosure, and in the specific context where each term is used. It will be appreciated that the same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, and any special significance is not to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for some terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification, including examples of any term discussed herein, is illustrative only and is not intended to further limit the scope and meaning of the disclosure or of any exemplified term. Likewise, the disclosure is not limited to various embodiments given in this specification. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the case of conflict, the present document, including definitions, will control.