Linear Fire Extinguisher

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 charge 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.

FIG. 8 is a cross-sectional view of an alternative embodiment.

FIG. 9 shows FIG. 8 after explosive cutting has occurred.

FIGS. 10A and 10B are perspective views of an alternative embodiment.

FIGS. 11A and 11B are perspective views of an alternative embodiment.

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 contained, 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 and FIG. 5, the line of cutting 27 which line is substantially parallel to the axis 18 of the tube. The type of deformation 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' where the shaped charge 23' 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.degree. to as much as 180.degree..

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 pressured to approximately 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, at minus 65.degree. 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, may also 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-like 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.

In addition to providing the shaped charge 23 external to the container 17, as illustrated in the previous figures, FIG. 8 shows that the charge 23 may be alternatively placed internal to the chamber. Although FIG. 8 shows two shaped charges 33a, 33b, a single charge may be utilized in accordance with the invention as thus far described. This has the advantage of providing protection for the relatively fragile shaped charge within the relatively thick and durable walls of container 17.

However, in accordance with another embodiment of the invention, as illustrated in FIG. 8, a pair of shaped charges 33a and 33b, which are opposed and in fact lie on the diameter 20 of tube 17 (which of course passes through its center 18) may be provided. Thus, these shaped charges provide a cutting action along the lines 31a and 31b, as illustrated in FIG. 9.

As further illustrated, the reaction force, F1, of the escaping HALON is equal and opposite to the reaction force, F2, of the HALON escaping on the opposite side and thus the net reaction force is substantially reduced or close to zero in this case. Reduction of reaction forces may be important in some applications where the wing structure of an aircraft is fragile, since otherwise the fire extinguisher may act like a jet-propelled rocket, depending on pressures, sizes and specific application.

Thus, in the embodiment of FIG. 9 (shown as it is exploding), a pair of fan-like spreadings along the length of the container are provided. And this is provided by the pair of opposed linear shaped charges 33a and 33b which lies in the common plane which also includes the axis 18 of tube 17.

The same result of course of providing a minimal reaction force would be accomplished by installing the linear shaped charges external to the tube, as illustrated in FIG. 3 but, of course, with the placement of a second opposed charge diametrically opposite first.

A further helical installation is shown by FIGS. 1OA and 10B where in FIG. 10A wrapped around the tube 17 in a helical-like pattern is a linear shaped charge 34. FIG. 10B shows the tube after it is exploded or has been cut with the helical pattern 35; as is apparent, the net reactive force when summed along the length of the tube is relatively low or approaching zero. In any case, it's much less than the reactive force which occurs in the first embodiment, as shown in FIG. 3.

Lastly, as FIGS. 11A and 11B show, a helical-like or curved configuration 36 on tube 17. In the exploded version in FIG. 11B, although the net force may have some value (because of the fact that the linear shaped charge does not cover the opposite side of the tube fully) it is still significantly reduced. And of course in both FIGS. 10 and 11 the charge may be placed if desired on the inside of the tube.

Thus, an improved linear fire extinguisher, especially suitable for aircraft application, has been provided.