Patent Publication Number: US-2011061556-A1

Title: Methods and apparatus for a gas outlet port clog inhibitor

Description:
TECHNICAL FIELD 
     The present invention generally relates to projectiles with gas outlet ports, and more particularly relates to inhibiting clogging of outlet ports associated with base burn and rocket motor systems. 
     BACKGROUND 
     Base burn technology was developed to reduce the amount of drag on a projectile, and to thereby increase its range. Specifically, the drag is reduced by a (base) burner unit that consists of a relatively small amount of combustible material in an enclosure that is attached to the base of the projectile. After firing, the combustible material is exhausted through one or more gas outlet ports in the base of the projectile, thereby increasing pressure in the base region and increasing the range of the projectile. Once ignited, the base burner unit ejects hot gas, which reduces the turbulence in the flow of air at the base. This decrease in turbulence reduces base drag, which is significant percentage of the total drag on a projectile. 
     Presently known base burn structures are unsatisfactory in a number of respects. For example, during the initial launch thrust, it is not uncommon for the structure to experience acceleration on the order of thousands or tens of thousands of g&#39;s. The resulting forces can stress the relatively frangible base burn material such that portions of it (e.g., regions lining its inner bore) break up and fracture into “chunks” that can clog the gas outlet port as it attempts to escape the structure. 
     Accordingly, there is a need for improved methods of preventing clogging of outlet ports used in base burn and other such systems. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     BRIEF SUMMARY 
     A projectile in accordance with one embodiment includes a combustible material structure (e.g., a base burn assembly or rocket motor assembly) having a longitudinal bore extending therethrough, wherein the longitudinal bore defines a gas outlet port on a first end of the combustible material structure. An igniter is provided adjacent to a second end of the longitudinal bore. A clog inhibitor provided within the longitudinal bore, the clog inhibitor including a plurality of openings. The openings may be selected to block extraneous portions of the combustible material structure that are greater than a predetermined size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures. 
         FIG. 1  an isometric overview of an exemplary base burn assembly in accordance with one embodiment; and 
         FIGS. 2  is a cut-away view of the base burn assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion generally relates to methods and apparatus for preventing the clogging of gas outlet ports in base burn structures and the like. In that regard, the following detailed description is merely illustrative in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. For the purposes of conciseness, conventional techniques and principles related to propulsion, base burn systems, aerodynamics, rocket motors, and the like will not be described herein. 
       FIGS. 1 and 2  depict an exemplary embodiment implemented in the context of a base burn assembly  100 . As a preliminary matter, however, it should be noted that the present invention may be used in connection with any number of other systems, such as rocket motors and the like. The illustrated base burn assembly  100  is thus described without loss of generality. 
     As shown, base burn assembly  100  generally includes a combustible material structure (or “base burn material”)  102  having a longitudinal bore extending therethrough. The longitudinal bore defines a gas outlet port  210  on a first end  103  of the base burn material  102 . Base burn assembly  100  may have any suitable shape, depending upon the nature of the projectile with which it is to be used. Furthermore, those skilled in the art will recognize that base burn assembly  100  will typically be installed in a surrounding structure and will be accompanied by conventional projectile components, such as nozzles, retainers, and the like. 
     A variety of materials may be used for base burn assembly  100 , including for example, various polymeric compounds combined with one or more incendiary compounds. In conventional base burn assemblies, for example, a rubber or plastic material combined with phosphorus or the like is used. The present invention is not so limited, however, and may be used in conjunction with any type or configuration of base burn structure. 
     An igniter  104 , which may comprise any suitable conventional igniter component, is typically provided adjacent to the opposite end  105  of the base burn material  102 . Igniter  104  is configured to trigger combustion of material  102  at the appropriate time, as is known in the art. 
     In accordance with the present invention, a clog inhibitor  200  is provided within the longitudinal bore—e.g., in contact with the inner surface of the longitudinal bore within assembly  100 . Clog inhibitor  200  may be inserted within base burn material  102  after formation of the internal bore. In one embodiment, clog inhibitor  200  is secured via a standard compression fit. In an alternate embodiment, however, clog inhibitor is secured using a suitable adhesive. 
     The size and shape of clog inhibitor  200  may be selected depending upon the nature and geometry of base burn material  102 . In the illustrated embodiment, clog inhibitor is generally cylindrical. However, it may have any suitable rectilinear or curvilinear shape. The wall thickness t of clog inhibitor  200  may also be selected depending upon expected forces, but in one embodiment is about 0.125″ to 0.25″. 
     Clog inhibitor  200  includes a number of openings  205  provided within its body for allowing gases to escape through the gas outlet port  210  during combustion. In the illustrated embodiment, openings  205  are circular. But in various embodiments openings  205  may be rectangular, elliptical, or any other suitable shape. In accordance with one aspect, the openings  205  are configured to block extraneous portions of base burn material  102  that are greater than a predetermined size. 
     That is, as described above, it is common in prior art systems for chunks or portions of base burn material  102  to break away and become lodged within the longitudinal bore, thereby blocking the escape of gas through gas outlet port  210 . Thus, it is desirable that the shape and size of openings  205  are based in part on a dimension (e.g., diameter) of the gas outlet port  210 . For example, in a preferred embodiment, openings  205  have an opening area that is approximately ˜10% to ˜50% of the area of gas outlet port  210 . 
     For example, in various embodiments, gas outlet port  210  is generally circular and has a diameter of about 0.25″ to 1.5″, preferably about 0.5″ to 1.0″, depending upon the application. The overall longitudinal length of assembly  100  will also vary widely depending upon application, e.g., about 3-10″ long. 
     Clog inhibitor  200  may comprise any suitable metallic, ceramic, or composite material. Such materials include, for example, aluminum, ceramic, steel, titanium, and magnesium. In one embodiment, however, clog inhibitor  200  comprises an ablative material (such as phenolic resin and cellulous or magnesium) selected to be consumed after launch of the projectile and after the base burn material has been substantially consumed. 
     One or more internal structures  215  may be coupled to the interior surface of the clog inhibitor  200  to provide structural support, and prevent or reducing deformation, e.g., “caving in”, of clog inhibitor  200  during acceleration. 
     While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient and edifying road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention and the legal equivalents thereof.