US3496867A - Thermal radiation weapon - Google Patents

Description

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THERMAL RADIATION WEAPON Filed 001;. 13, 1965 2 Sheets-Sheet 1 IN VEN TOR.

Feh 24, 1979 .c. MacD 3,496,867

THERMAL RADIATION WEAPON Filed Oct. 13, 1965 2 Sheets-Sheet 2 HlJJHMHHJHHHJ W 4w, INVENTOR.

3,496,867 THERMAL RADIATION WEAPON Gilmour C. MacDonald, 55 Warwick Drive, Rte. 1 Shalimar, Fla. 32579 Filed Oct. 13, 1965, Ser. No. 495,626 Int. Cl. F41b /00; C06d 1/00 U.S. Cl. 1026 7 Claims ABSTRACT OF THE DISCLOSURE Field of the invention Napalm bombs and flame throwers employing thickened jet fuel or gasoline as the combustible, are in wide use. While they do specific military jobs, and in many cases do them well, they also have disadvantages. Napalm bombs are difficult to drop precisely because of aerodynamic factors, and are expensive because the tanks are expended with each drop. Since the products of combustion are gaseous rather than solid, the flame has poor radiation characteristics, so Napalm does little damage outside the fireball. Flame throwers are also very effective for special military purposes. However, because they are effective, and because they are short-range weapons, operators of flame throwing equipment receive a great deal of special attention from the enemy riflemen and gunners.

Weapons proposed to date, wherein combustible dusts or gaseous fuels are mixed with atmospheric air and detonated, have, in the main, proposed relatively small individual explosions. The reason for this is that as the size is increased, the problems in attaining homogeneous mixing with atmospheric oxygen in the precise proportions required for most effective detonation become truly formidable. With some fuels, a difference in 1% in the fuel-air ratio can make a difference of several hundred percent in the severity of detonation.

In contradistinction, the subject invention provides for continuous combustion (as distinguished from detonation) of the trailed fuel cloud by providing homogeneous and automatic ignition means within the cloud to provide for ignition when that portion of the cloud has been mixed with suflicient air to support combustion. This assures that all portions of the fuel cloud will eventually ignite and burn, regardless of discontinuities in the flame front and inhomogenieties in the fuel-air mixture. This in turn means that all the thermal energy in the fuel is released.

Detonative-type combustion is not desirable in a thermal radiation weapon. The Atomic Energy Commission has reported that thermal inputs of 3 cal./cm. if delivered in one second, will produce first degree burns and ignite some types of cloth, whereas a thermal input of 6 cal/cm. is required for the same effect 'when the heating occurs over a thirty second period. It thu appears probable that radiation periods of up to ten seconds would cause very little loss in effectiveness. Conversely, the same report indicates that thermal pulse times of less than one second also result in some loss of effectiveness.

The literature reports many efforts, both here and abroad, to develop useable weapons employing detona- 3,496,867 Patented Feb. 24, 1970 tion of fuel-air mixtures. Some attempted to dispense carbon black or coal dust from an airplane and initiate detonation with a delayed high-explosive charge. Others attained only limited success by using a high explosive to disseminate and ignite light metal dusts. Still others have investigated liquefied petroleum gases as dispersant/ fuels for detonation type weapons. To date, none of these have achieved the status of a standard weapon.

Past efforts to develop useable detonation-type weapons employing fuel-air mixtures have failed because of the difficulty in attaining, by militarily practical means, homogeneous and stoichiometric fuel-air mixtures. Unless the mixture is stoichiometric within rather narrow limits, detonation (or even burning, for that matter) will not occur. If not homogeneous within equally narrow limits, propagation of the detonation (or burning) will also not occur. For example, acetylene has a very wide flammability range of from 2.3% to and yet the International Critical Tables indicate that the most effective explosion is achieved with 9% to 10% acetylene in air. This is a tolerance of about 1% of the total range of the explosive limits. By comparison, the lower flammable limit for propane is 2.3% and the upper limit is only 7.3%, a total range of 5%. As pointed out above, only a small fraction of this 5% range will result in a militarily useful explosion. It is thus seen that difficulties in attaining homogeneous mixing of the fuel-air cloud in stoichiometric ratios and in useful amounts presents a most difficult problem.

Objects It is a principal object of this invention to provide a chemical fireball munition that eliminates the problems of achieving homogeneouse mixing of the fuel-air mixture in the precise proportions necessary for effective detonation thereby avoiding extreme criticality of fuel-air mixture ratios permitting combustion to continue for several seconds without seriously reducing the thermal damage done to personnel and material.

Further objects of this invention include:

(1) The provision of a high-temperature thermally radiating weapon that is free from ionizing radiations and radioactive fallout in which the energy release consists of direct thermal radiations, together with visible light and infrared radiation.

(2) The provision of a weapon capable of exposing personnel and material within the effective range of coverage to a thermal radiation intensity which would produce effects varying from first degree burns and the ignition of some. types of cloth to third degree burns and the instantaneous defoliation of trees.

(3) The provision of such weapons wherein much of the energy is radiated in the visible spectrum, to produce damage to the visual receptors in the eye, causing instantaneous temporary blindness (dazzling) or permanent blidness at distances possibly several times that producing skin burns.

(4) The provision of dispensing systems for such weapons that may be reused indefinitely unless jettisoned for air combat reasons with the elimination of bomblets, canisters, or Napalm tanks and providing major savings in costs.

(5) The provision of precise placement of the weapon effect by delivery at very low altitudes of high-speed horizontal fly-by of a trailed dust cloud which slows down almost instantaneously on release.

6) The provision to improve pilot survival by delivering as many munitions as possible on the first pass over the target and making it possible for a pilot to fire his guns and/ or rockets at the target, simultaneously with the use of the new Weapons of the. invention.

(7) The provision of means for producing a fireball with a higher thermal output than an airplane, thus diverting heat-seeking anti-aircraft missiles to the fireball.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

General description These desirable results are accomplished according to the invention by employing airborn dispenser means to continuously deliver a suitable fuel at a relatively high rate of flow, employing turbulence to mix the fuel with atmospheric air, and providing ignition means within the fuel-air cloud to insure that each increment of the trailer fuel cloud ignites and burns as soon as it is mixed with enough oxygen for combustion.

Since aluminum burns to A1 a solid, develops 7.4 Kcal./ g. and has an adiabatic flame temperature of 4770 K., it is a prime choice as a fuel for a thermal radiation weapon, in spite of the fact that the emissivity of A1 0 is only 0.3 at 1100 C.

Magnesium presently costs 50% more than aluminum, and produces only 5.9 KcaL/ g. It is preferred mainly as an additive because it has a high adiabatic flames temperature, and particles of it are easier to ignite and burn faster than aluminum. It is a valuable additive to improve the ignition and combustion of other fuels.

In addition to aluminum and magnesium in various finely divided forms, boron, boron carbide, zinc, and zirconium dusts are suitable fuels for radiation-type weapon contemplated by the invention.

In consideration of the increased combustion time permitted by this invention, it is contemplated to mix a substantial percentage of aluminum or magnesium pellets with the powdered fuel. The heavier pellets will fall when released to lower the thermal center of radiation by producing a fiery rain. This addition of metallic pellets will also increase the overall loading density of the weapon.

Detailed description As mentioned above, the emissivity of A1 0 is only 0.3 at 1100 C., so additives which raise the emissivity of the fireball will likewise improved the thermal radiation output. Commercial gellants comprises of pyrogenic submicron silicon dioxide having an emissivity of 0.85 at 1100 C. are available, e.g., Cab-O-Sil. When these are added to powdered metal fuel, they increase the. fireball emissivity. In addition, such materials may gel a hydrocarbon fuel (if used with the metal dust) and minimize dust settling problems in the weapon.

Polytetrafluoroethylene powder is a possible gellant/ oxidizer when added in small quantities. Magnesium dusts and Teflon may detonate when mixed in air, but are reported to be compatible when mixed in a liquid hydrocarbon.

There are a number of reasons why a combustible liquid such as jet fuel or gasoline should be used to supply a portion of the themal energy in the weapon. For example, aluminum dusts can be compacted to a much higher density when slurried in a liquid, and the liquid fills the intertitial spaces that would otherwise not be used. Both of these elfects improved efficiency by increasing the. thermal energy carried in a given volume. Further, use of a liquefied petroleum gas such as propane mixed with the aluminum dust provides a propellant-dispersant to eject the metal dust and disperse it in the air. Deagglomeration of the aluminum dust during delivery poses no problem, as the propane will boil vigorously (pressure 115 p.s.i.a. at 60 F.) when the fuel container is opened at delivery, breaking up agglomerates.

Continuous automatic ignition of the trailed fuel cloud as it becomes mixed with air can be accomplished by several means. For example, white and yellow phosphorus ignites in air at about 86 F. and is very soluble in carbon disulfide. An igniter consisting of phophorus dissolved in CS can be added to the liquid propane and aluminum dust in the fuel tank of the weapon, Where it remains until the fuel is released. When released, the fuel cloud, including the carbon disulfide, evaporates, the phosphorus particles mix with air, oxidize, and ignite, touching off the CS vapors, the propane and the aluminum dust.

Because the ignition energy required by carbon disulfide is very low, and because of the ability to dissolve large quantities of phosphorus, CS is an attractive fuel additive for this purpose. Alternately, the limited solubility of phosphorus in liquid propane may be used for ignition purposes without an intermediate such as CS Other pyrophoric substances can be used to insure complete ignition of the gas cloud. For example, the trialkyl boranes (trimethyl, triethyl, tripropyl and tributyl boranes) have been investigated as possible additives for jet fuel to prevent flameouts. Organo boron compounds known to be spontaneously flammable in air include triethylboron and tetraethyldiborane. Useable pyrophoric trialkylaluminum compounds include trimethylaluminum and triethylaluminum.

During the early dissemination of the fuel cloud, there will be little atmospheric air mixed with the fuel, and the resultant mixture will be very rich. Since the upper explosion limit for propane is only 7.3%, it is advantageous to use additives with a wider range of explosive limits, e.g., acetylene. It is inexpensive, has a very high heat content, requires very little energy for ignition, and has flammability limits of from 2.3% to Further, it is very soluble in acetone, especially at the pressures necessary to liquefy propane. Acetylene as an additive may also improve the ignitability of the aluminum dust. Initial combustion of the acetylene would be under fuelrich conditions, forming carbon black, which would deposite on the metal dust particles. This black coating would increase the absorption of thermal radiation and improve ignition. Somewhat the same effect can be attained by the addition of carbon black or similar substances directly to the aluminum powder.

When compatible with the fuels selected, other possible additives having a wide range of flammable limits include unsysmmetrical dimethylhydrazine (flammable limits 2 to and diborane which has flammable limits of 0.9 to 98% and ignites spontaneously in air at room temperature. Diborane may serve as an automatic ignition source as discussed above. Propyl nitrate has flammable limits from 2 to 100% and its ignition energy is very low, being comparable to hydrogen, acetylene and carbon disulfide. Ethyl nitrate, and highly explosive methyl nitrate, are also in this general category, as are ethylene oxide, nitromethane, and diethyleneglycol dinitrate.

Examples and drawings For a more complete understanding of the nature and scope of this invention, reference may be had to the following detailed description thereof taken in connection with the accompaying drawings, in which:

FIGURE 1 is a side sectional view of a form of this invention which is adapted to external carriage on fighter aircraft. A liquefied petroleum gas such as propane serves as a propellant/dispersant to dispense a primary fuel of aluminum dust. :In this simplest form of the invention, a pyrophoric substance such as white phosphorous is dissolved in the liquid propane to provide for continuous, automatic, and homogeneous ignition of all portions of the dust cloud as soon as the propane has vaporized and mixed with air on release. It will be recognized that this simple form of the invention is not without some hazard, in that it is always under pressure, and that any leak,

however small, will aways catch fire. However, by the same token, there can be no explosion, as the fuel will burn as fast as it leaks out into the air.

FIGURE 2 is a similar sectional view, differing only in that the fuel is delivered by a pump instead of the vapor pressure of propane. Jet fuel or gasoline would be the liquid portion of the fuel. If this construction is struck by a bullet, some of the fuel mixture could run out of the hole (unless the liquid portion of the fuel was gelled as mentioned above), and would burn as above. However, this fuel flow at worst would be only a very small portion of that from the construction of FIG- URE 1, wherein the internal pressure will be of the order of 100 p.s.i. Safety is increased at a cost in efficiency and complexity.

FIGURE 3 is a schematic diagram of an alternate construction adapted for internal carriage in large cargo aircraft. In addition to providing for pump delivery of the fuel, the pyrophoric igniter solution is mixed with the primary fuel just before being sprayed into the air. Thus, the fire hazard should be about the same as any other aircraft with a large amount of fuel aboard. Under some circumstances, it might even be safer, because the main fuel tank of the weapon can be emptied in seconds by the pump if necessary.

As seen in FIGURE 1, a preferred embodiment of the invention comprises aerodynamically-shaped fuel tank 11, which contains the fuel, a slurry of aluminum dust in liquid propane, together with pyrogenic additives, and is attached to its supporting pylon on the airplane by means of shackles 12. This fuel mixture boils violently when the outlet valve 14 is opened, the said fuel mixture passing through the outlet pipe 13, the outlet valve 14 and the divergent nozzle 15, where a portion of the flow impacts the diverter 16. This diverter has a duel function, the first being to produce a maximum of furbulent mixing of the fuel and air, and the second being to develop enough reverse thrust to exactly cancel the rocket-type thrust developed by the fuel flow. This will permit firing under-wing dispensers individually without causing the aircraft to yaw.

In a second embodiment of this invention as depicted in FIGURE 2, an aerodynamically-shaped fuel tank 21 contains the fuel, a slurry of aluminum dust in gasoline or jet fuel. The fuel includes additives to produce selfignition when mixed with air. Actuation of the pump 24 draws fuel through section pipe 23 and forces it out divergent nozzle 25. A portion of the How impacts diverter 26, which functions as above.

In the event that safety considerations, such as the amount of heat radiated to the carrier aircraft, make it necessary to drop the dispenser before actually dispensing and igniting the fuel, the diverters 16 and 26, may be designed to produce substantial reverse thrust when fired. When released, the dispenser will then slow rapidly with respect to the carried aircraft while dispensing the fireball.

A third embodiment of this invention, adapted to deliver large quantities of fuel from cargo-type aircraft, is shown in FIGURE 3. The main fuel tank 31 contains a slurry of aluminum dust in gasoline or jet fuel, and will usually be mounted in the fuselage of a cargo aircraft. To operate the weapon, the main fuel pump 33 is actuated, drawing fuel through suction pipe 32, and forcing it through the pump 33, and the injector body 34. Concurrently, igniter fuel pump 37 sucks a solution of phosphorous in carbon disulfide from tank 35 through pipe 36 forces it through the pump 37 and out through injector nozzle 38 where it is mixed with the main flow of fuel. This mixed flow passes through outlet pipe 39 into distribution manifold 40 which sprays it into the air as indicated by the arrows.

The foregoing specification discloses a new and useful thermal radiation weapon. While specific examples have been given, applicant claims the benefit of a full range of equivalents within the scope of the appended claims.

I claim:

1. An airborne thermal radiation weapon comprising in combination with an aircraft, a fuel container, a homogeneous mixture of a liquid combustible fuel, a combustible finely-divided metal and an ignition material, said ignition material being a substance which automatically ignites on contact with air, means to discharge said mixture from said container at a high rate of flow and means to produce turbulent mixing of said mixture with air as said mixture discharges from said container.

2. A radiation weapon as claimed in claim 1 wherein said turbulent mixing means comprises a deflector to cause at least a part of said mixture to flow in a manner to cancel the net thrust resulting from said mixture discharge.

3. A thermal radiation weapon comprising in combination a fuel container enclosing combustible fuel material comprising combustible finely divided metal, combustible organic liquid and an incombustible additive to improve thermal radiation characteristics of the fuel material, means to continuously discharge the fuel material from said container, mixing means to produce turbulent mixing of said material with. air as said fuel material is discharged from said container and ignition means to ignite the resulting fuel material and air mixture.

4. A weapon as claimed in claim 3 wherein said additive is finely divided silicon dioxide.

5. A weapon as claimed in claim 3 wherein said fuel material comprises polytetrafluoroethylene powder as an oxidizer/gellant.

6. A weapon as claimed in claim 3 wherein said turbulent mixing means comprises a deflector to cause at least a part of said fuel material to flow in a manner to at least partially cancel the net thrust resulting from said fuel material discharge.

7. In a device for producing aerial fireballs, the combination comprising an aircraft carrying fuel container means, a combustible fuel material contained in the fuel container means, said fuel material comprising finely divided primary fuel selected from the group consisting of aluminum, magnesium, boron, boron carbide, zinc, zirconium and carbonaceous material in a liquid hydrocarbon, fuel discharge means adapted to vaporize said fuel material and to intimately and continuously mix said fuel material with ambient air as the fuel material is discharged from said fuel container means, said fuel material including means to continuously and automatically ignite all portions of the mixture of said fuel material and ambient air.

References Cited UNITED STATES PATENTS 2,372,264 3/1945 Firth 1026 2,535,309 12/1950 Mari 1O234.4 3,106,238 10/1963 Bruce 891 X 3,150,848 9/1964 Lager 102-344 X 3,188,954 6/1965 Roach et al. 1026 SAMUEL W. ENGLE, Primary Examiner US. Cl. X.R. 1029, 66

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