Abstract:
A linear fire extinguisher, includes a high strength elongated tube containing a pressurized fire extinguishant such as HALON 1301. A shaped charge is placed along the exterior of the tube and when actuated provides a rupture line which causes a directed distribution of the fire extinguishant along the rupture line.

Description:
The present invention is directed to a linear fire extinguisher and more specifically to a fire extinguisher especially useful for the dry bays and fuel tanks in airplane wings and fuselages. 
     BACKGROUND OF THE INVENTION 
     High pressure bottles or canister type powder suppressors have been used in the wing areas of aircrafts. These are explosively actuated to provide a quick opening valve, such as illustrated in Tyler U.S. Pat. No. 4,003,395, assigned to the present assignee. In addition to the relatively high weight of the system it has a distribution of the point source type. A linear type distribution of flame-quenching agent has been proposed in Mitchell U.S. Pat. No. 3,482,637, using a detonator cord along a tube containing the fire extinguishing agent. Here the application is in coal mines using tubing such as acrylic plastic materials. It has a distribution time of the flame quenching agent of about 40 milliseconds. Both the material and distribution time are unsuitable for aircraft use. Another similar fire extinguisher of either molded plastic or very light weight metal which is easily rupturable is shown in Finnerty invention registration H141, published Oct. 7, 1986. The Finnerty device is useful for ammunition fires or vehicular fires, but because of the lack of pressure and the material used it is unsuitable for aircraft use. 
     OBJECT AND SUMMARY OF INVENTION 
     It is a general object of the present invention to provide an improved linear fire extinguisher. 
     In accordance with the above invention there is provided a linear fire extinguisher comprising a closed elongated high strength metal tubular container having an axis along which it is elongated and having its interior volume substantially filled with a fire extinguishant. The container is pressurized so that when it is cut open the extinguishant is substantially distributed within a time period of less than 10 milliseconds. Means are provided for explosively cutting the container along the line substantially parallel to the axis and extending substantially the length of the container as measured along the axis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the linear fire extinguisher installed in the dry bay of an airplane wing. 
     FIG. 2 is a cross-sectional view of the fire extinguisher of the present invention, showing it connected to a fire detector system, along with a detonator. 
     FIG. 3 is a cross-sectional view taken along the line 3--3 of FIG. 2. 
     FIG. 4 is a perspective view of a linear shaped charged used in the present invention. 
     FIG. 5 is a perspective view of the tubular fire extinguisher after it has been cut by the linear shaped charge. 
     FIG. 6 is a greatly enlarged view of a portion of FIG. 3 showing the mounting of the linear shaped charge on the tubular fire extinguisher. 
     FIG. 7 is a cross-sectional view of an alternative embodiment of the invention corresponding to FIG. 3. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a wing section 10 with a fuel cell 11 shown in dashed outline which has attached to it linear fire extinguishers 12 and 13 which incorporate the present invention. The unoccupied portions of the wing shown at 14 and 15 are known as dry bays. The invention, of course, has other applications, as for example in an engine compartment, or, in fact, in non-aircraft applications, where a linear uniform distribution of a fire extinguishing agent is necessary along a fairly long axis. Also, although illustrated in a dry bay, the extinguisher may be placed inside a fuel tank. 
     Linear fire extinguisher 12 is illustrated in greater detail in FIG. 2 and is composed of a tubular container 17 having an axis 18 and which is sealed at its ends by plugs 19 and 21 so that pressures of several thousand psi may be applied. It is substantially filled with a fire extinguishant 22. Extending along the outside of the tube 17 along a line substantially parallel to axis 18 is an explosive linear shaped charge 23 which for example is available under the trademark Jetcord. It is filled with an explosive material such as RDX (cyclotrimethylene trinitramine). A detonator unit 24 is provided which is attached at end 19 and the detonator is actuated by a fire-detection system 26 when installed for use. Alternatively detonator 24 may itself be thermally sensitive so that when shipping, excessive temperatures will explode the charge 23 so that excessive pressure buildup does not occur within cylinder or tube 17. Also, there could be a detonator 24 at each end of the charge 23, wherein one could be initiated electrically and one could be activated by excess temperature. 
     FIG. 3 illustrates the cross-section of the tubular container 17 and shows the shaped charge 23 as it would be affixed to the container for example, by a simple adhesive. Alternatively, shaped charge 23 can be provided with a standoff of, for example, a few millimeters from the container by known techniques to provide a gap which is more effective when the shaped charge is used for cutting large diameter tubes. Also, in addition, a cover can be placed over the shaped charge 23 to enhance its cutting capability. 
     FIG. 4 illustrates the linear shaped charge in perspective. In FIG. 5, the line of cutting 27, which line is substantially parallel to the axis 18 of the tube which the shaped charge causes, is shown with the tubular container opened. 
     FIG. 6 shows the shaped charge 23 enlarged as it would be typically affixed to tubing on 17 by a suitable adhesive. From the shape of the charge is readily apparent that the V-shape or chevron-type configuration will provide an accurate linear cut along the line 27. 
     Finally, FIG. 7 is an alternative embodiment showing a tube 17&#39; where the shaped charge 23&#39; is an integral part of the tube. In other words it is manufactured in a single tube drawing. 
     Referring to FIG. 3, the fire extinguishant 22 is pressurized sufficiently so that upon cutting of the tube 17 a direction or vector of discharge will occur on a line drawn from the axis 18 to the line 27 and indicated as 28. Thus, this provides a very controlled direction of radial distribution with a fan-like spreading; i.e., the angle may be typically 90° to as much as 180°. 
     In general, the pressure initially placed in the tube can vary from as little as 200 psi to 2,000 psi. In a preferred embodiment where, for example, the fire extinguishing agent is HALON 1301 which is known more commonly as monobromotrifluoromethane, the tube will be pressurized to aproximately 600 psi with nitrogen gas, and most of the nitrogen will be dissolved in the liquid HALON. The reason for the pressurization of the fire extinguishant in the tube is to improve distribution and most importantly improve the speed of distribution. For extinguishing aircraft fires in the wing section it is required that extinguishers operate in less than 15 milliseconds. In the present invention almost full distribution of the fire extinguishant occurs in much less than 10 milliseconds; for example, less than 5 milliseconds. Thus, time of operation is of critical importance in extinguishing aircraft fires. Another reason for pressurization, especially in the case of the liquid HALON material is that at lower temperatures, for example, a minus 65 degrees Fahrenheit (in other words below freezing) the pressure is considerably reduced from the room temperature at which the tube was filled. 
     Other suitable fire extinguishant materials, in addition, are other varieties of HALON (halogenated hydrocarbon) such as 1211, and 2402 and mixtures thereof. Dry powders and dry chemicals, such as aluminum oxide and the more common potassium and sodium salts, also may be used. 
     In order to minimize gravity effects, especially with liquids such as HALON, the tube should be substantially totally filled to for example 95 to 100%. Such filling also promotes the distribution. Also in the case of powder, a super pressurization causes the powder-type material to perform similarly to liquids such as HALON. 
     Because of the high pressures utilized the tube 17 must of course be of high strength but yet light weight for the aircraft environment. This is provided by the use of high strength stainless steel hydraulic-type tubing. One type of tubing utilized is type 21-6-9 per the AMS 5561 standards. A typical dimension of such tubing would be a wall thickness of 0.016 inches with a length of approximately 4 feet and an overall diameter of 0.5 inches. The stainless steel grade referred to as 21-6-9 refers to the components of chromium, nickel and manganese. With the foregoing type of dimensions and a pressure of 600 psi a HALON-filled fire extinguisher when cut fills a dry bay as illustrated in FIG. 1 in just under 5 milliseconds. With regard to the tube design, a wall thickness of 0.016 inches for smaller diameters of 0.437 to 0.500 is suitable and for larger diameters of 0.625 to 0.750 inches a wall thickness of 0.020 inches is suitable. With tubes of these designs and of the hydraulic type, the proof pressure will exceed 5,000 psi. 
     Such high pressure capability is necessary since the almost total filling of the tube with, for example HALON, under elevated temperature conditions the curve of temperature with respect to pressure is very steep. That is, at elevated temperatures the pressure of a totally filled tube will be several thousand psi; for example, approaching 5,000 psi. Thus to survive expected ambient conditions the tubing must be very high strength. But, however with the use of the stainless type hydraulic tubing of the kind mentioned, a relatively light weight is still achieved so that it is still useful in aircraft applications. 
     With the use of the Jetcord type shaped charge and as applied to the type of hydraulic tubing specified the cutting line 27 as illustrated in FIG. 5 occurs in a few hundred microseconds. In conjunction with the pressurization of the extinguishing material a very uniform distribution takes place immediately as well as entirely along the axis 18 for the length of the tube. 
     Thus, an improved linear fire extinguisher, especially suitable for aircraft application, has been provided.