US2829596A

US2829596A - Tracking flares

Info

Publication number: US2829596A
Application number: US476017A
Authority: US
Inventors: Alfred C Loedding
Original assignee: Unexcelled Chemical Corp
Current assignee: Unexcelled Chemical Corp
Priority date: 1954-12-17
Filing date: 1954-12-17
Publication date: 1958-04-08
Anticipated expiration: 1975-04-08

Description

April 1958 A. c. LOEDDING 2,829,596

TRACKING FLARES Filed Dec. 17, 1954 uh. m...,- m. nv- Hm.

I -PRESSURE ALUMINUM Fo/ SENSITIVE ADHES/VE INVENTOR Y flfi ed Zaeridzzzg his ATTORNEY 9 TRACKING t nn tus;

. Alfred. C. Loedding, Princeton, .N."J., assignor 't o Un excelled Chemical Corporation, New York, N. Y., a corporation ofNew York Application December 17, 1954; Serial No. 476,017 f slelaims'. c1.10z s7 invention relates to flares and more particularly to a tracking flare forguided'missiles and the like. i I

The invention provides a flare which is relatively small in size and its charge may therefore be fabricated in 1 standard pelleting machines, said charge producing a brilliant substantially smokeless flame clearly visible from a distance ofupto 15,000 feet in clear daylight, having'high combustion stability during required burningduration of between 15-'l9 seconds, and which isstorable for long periods of time up .to 5 years and even longer. The low-cost, simple construction provides great ruggedness andycertainty of operation necessary for use in connection with missiles.

The invention further provides a flare whose electrical l ignition system is simple and reliable, anda safety device which is provided to prevent preignition during storagehandling;

j The novelflare consists essentially of a tubular housing of vulcanized fibre or the likehaving one of its ends closed and its other end sealed by a disc of cardboard or other lightweight material that is easily destructible.

A. pellet of a solid-fuel charge having all its sides or all n butone of its sides inhibited, is inserted into the housing and cemented therein witha layer of elastic material. Thepreferably uninhibited surface of the charge facing the open end'of the housing is covered by a layer of ignitionpowderpaste and the cardboard disc tightly pressed thereagainst to expel anyair which could cause rupture at higher altitudes. In the preferred embodiment, an electric match is embedded in the ignition powder paste and the leads connecting the matchwith a source'of electric energy are led along the periphery of the housing to provide a large contact surface. When i in storage, the' leads are short-'circuitedby a layer of metallic-foil which is removed only before the flare is ;;The pelletf consists of a solid-fuel charge of theme-, chanical mix variety with a preferred composition of about by weight aluminum, by weight of .an-asphalt resin, and about 75% by weight of an oxidizing agent. The oxidizing agent preferably consists of ammonium perchlorate. To achieve the desirable red color and hence long wavelength for tracking purposes, 7

non-hygroscopic'strontium nitrate is added.

U ed States Pur O" 2,829,596 Patente l? 3 1 2 indicate. similar elements, andth'e invention will be final ly pointed out in the appended claims.

In theidrawings, v Fig.1 'is an enlarged perspectiveview of the assembled flare partlybroken away to show the igniton system and the two'leads to a source of electric energy;

Fig. 2 is afront view of the novel flare;

Fig.3 shows an attachment at the nozzle end of a guided missile or the e to receive and retain the flare casing;

Fig. 4 shows a double electric match for ignition of the solid-fuel charge in the flare;

': mounted atthe nozzle end thereof 'askew and exteriorly as an example; and t Fig. 7 is anenlarged view of the nozzle end of the missile shown in Fig. 6.

Referring now in more detail to the illustrated embodi-' ment, there is shown in Fig. 1 a tubular casing 10 made preferably of vulcanized fibre and having one end closed by a disc 11 of like material. Pellet 12 representing the solid-fuel charge is provided with a layer' of inhibiting material on all except one of its surfaces and is cemented to the inner walls of casing 10 and to the disc 11 by a layer of elastic material. However, also this ignition surface could be inhibited with the prime coat only, because the ignition powder paste, when ignited, would be adequate to burn through this coating. In manufacture, the entire exteriorof pellet 12 may be inhibited with the prime coat and the thin 'film'of inhibiting material removed from the surface facing the open end of casing 10.

A layer of ignition powder paste 14, such as for example a black powder paste, is applied to the uninhibited surface of pellet 12 and a specially fabricated double electric match 15 using a pair of single matches, such as those manufactured by the Atlas Powder Company, is embedded in paste;14.' A cardboard disc 16 is air-tightly pressed against the layer of paste 14. The positive and negative leads 17, 18 from electric match 15 are led through

slots

19, 20 at the left-hand end of casing or tube 10, along the periphery thereof, through

slots

21, 22 at the right-hand end of casing 10 and are then bent into the circular recess23 above disc 11, as shown in Fig. 2.

A strip 24 of pressure-sensitive material, covering a thin band 25 of aluminum foil, is applied to the periphery of casing 10 so that the aluminum foil 25 short-circuits both terminals leading to the electric match 15.

When the flare is ready for use, the adhesive strip 24 is [be provided at the nozzle end 28a of a guided missile shown in Figs. 6 and 7. The attachment comprises two substantially parallel resilient metallic conductors 29, 30

having their free ends 31, 32 bent inwardly to retain the flare by acting against the left-hand end thereof, and a ,Further. features and advantages "of the novel flare will beipointed out in the course of the following detailed description of one preferred embodiment thereof, taken in conjunction ,with the description of the figures in the acpair of

lips

31a, 32a made of conductive material fitting into

slots

21, 22 at the right-hand end of tube 10 to in the wires may be shaped as shown, around the edges of tube 10, through slots 19-22 and into recess 23, as they are sufliciently rigid to prevent the electric match 15 from being blown out of the flare during considerable forward speed of the missile. Those portions of leads 17, 18 passing through ignition powder paste 14 and up to

slots

19, 20 are preferably electrically insulated by spraying or the like. The match 15 ignites the layer 14 of ignition powder paste which in turn uniformly ignites the entire uninhibited surface of pellet 12.

The vulcanized fibre casing may blister slightly internally and show traces of slight charring, but will adequately resist the intense heat during combustion of pellet 12. Disc 11 is pressed into tube 10 and retained therein by frictional or mechanical bonding. However, the casing 10 may be manufacturedwith one end closed, the arrangement with a separate disc 11 being shown to indicate that the casing may be cutfrom a longer tubular body for ease of manufacture and lower cost The layer 13 of elastic cement inside tube 10 and on the inner side of disc 11 also securely seals said disc in the tube and prevents pellet 12 from being ejected from the tube under high axial acceleration forces. This elastic material may be the same as the secondary inhibiting coating of pellet 12. In manufacture, the pellet 12 having all but one of its surfaces inhibited to assure end burning (cigarette type), is pressed into tube 10 after the elastic cement 13 has been applied to the inner wall of disc 11 and the pellet will then distribute the cement 13 along its contact surface with casing 10 and disc 11, thereby tightly sealing the same into the tubular body 10 and against the inner wall of disc 11.

The layer of ignition powder paste-14 along the uninhibited surface of pellet 12 is desirable to uniformly ignite the uninhibited surface of the pellet and tov minimize the amount of entrapped air between disc 16 and pellet 12. Such air could cause serious blowout at certain altitudes due to the pressure difference between atmospheric air and that entrapped in the flare.

The pellet 1.2 is actually retained during combustion thereof by the layer of elastic cement, which may be the secondary inhibiting material 13 and also due to the fact that the flare is preferably mounted in a manner shown in Figs. 6 or 7, i. e. with its longitudinal axis at an angle to the axis of the guided missile, target drone, boat or any other object to be tracked.

. This positioning at an angle also permits observation of a larger portion of the flame 34 during burning of the charge, when viewed from the launching point, as not only the tail of the flame 34 but also a portion of its side will be observable. Also, by positioning the tracking flare close to the inner nozzle wall 28a of the missile, the flames could destroy the disc 16 and ignite the layer of ignition powder paste 14 without any electrical matches. This is possible due to the extremely short housing 10 of the noval flare, a configuration entirely novel in this art, adding desirable ruggedness to the structure. For example, the outside diameter of the housing 10 is only 1 inch, and the length thereof 1 /4 inch.

In Fig. 7,-the inclination of flares 10 with respect to the axis of missile 2 8 is somewhat exaggerated for better illustration. Also, while flares 10 are shown outside the nozzle wall 28a, they are preferably mounted in suitable grooves or in a circular recess in said wall 28a. The 6-8 inch flame may be protected by a transparent housing against the wind at high speeds and to obtain a greater visual effect. The visual effect could be further improved by mounting the flare into a cone acting in a manner similar to that of the reflector for the bulb in a flashlight.

The novel composition of the pellet insures a burning rate of approximately 0.05-inch per second or less for a total time of about 15-19 seconds and observation of the flame at a distance of 15,000 feet in clear daylight with naked eye. The brilliancy of the flame is achieved by addition of fine aluminum powder in the approximate proportion of 10% by weight. While magnesium and zirconium may also be used to add brilliancy to the flame, the use of these elements should be avoided because of their high afiinity toward ammonium perchlorate, the oxidizing agent present in the pellet mixture. Other advantages of the aluminum powder are ease of ignition, combustion stability, great brilliancy during combustion and good storage life.

A preferred composition of the pellet is as follows:

Percent by weight Aluminum powder 10 Asphalt resin 15 Ammonium perchlorate 37.5 Strontium nitrate 37.5

While the percentage of aluminum powder in the mixture may be slightly varied, a pellet containing more than 15% of aluminum powder is not necessary and does not warrant the reduction in safety. It is believed that the oxide layer surrounding each aluminum particle is partly removed during intimate mixing and grinding of the mixture and that the aluminum may react with the oxidizing agent. This is avoided by preferably first mixing and/ or grinding the asphalt resin with the oxidizing agents and then afterward adding aluminum powder for thorough mixing only with little or no grinding action.

Another mode of preventing the aluminum powder from reacting with the oxidizing agent is to coat the aluminum particles with a suitable oil, such as linseed oil, or with a suitable wax. Calcium stearate may be added in quantities between /2--1% by weight. This substance also serves as a coating and a lubricant especially for aluminum particles and reduces friction of aluminum during the pelleting operation.

The asphalt resin serves as both the fuel component and binder in the mixture, as more fully described in my copending application for Letters Patent of the United States, filed under Serial No. 454,209 on September 3, 1954. This resin is a black, odorless substance characterized by conchoidal and lustrous fracture. It is a low penetration, high softening point resin (with a softening point between 176 and F.), derived from petroleum crude oil by precipitation with solvent. The low volatility (high flash) of this resin makes it suitable for high temperature application. It is low in saturated hydrocarbons, high in resins and contains no free carbon. Its sulphur content is very low, only about 1.4% by weight.

The typical chemical composition of the resin is:

Percent Asphaltenes 8.0 Resins 89.0 Saturated oils 3.0

The resin is readily soluble in coal tar or petroleum naphthas. It is generally compatible with petroleum oils, asphalts, pitches, vegetable and fatty oils, alkyd resins and several rubber types. It has heretofore been used in adhesives, battery boxes, battery sealing compounds, for concrete Waterproofing, in floor tiles, in mastic manufacture, paper coating emulsions, in rubber compounding as a tackifier, etc.

The main advantage of the resin lies in that it serves as the fuel component and the binder at the same time. Thus, no inert binders are required.

When it is desired to have only infra-red light waves actuating tracking devices, aluminum powder could be eliminated and the percentage of asphalt resin increased accordingly, but should not exceed 30% by weight.

Ammonium perchlorate is a very active oxidizing agent and its presence in the charge is essential to insure combustion stability. The activity of ammonium perchlorate is believed to be increased by the presence of aluminum powder.

tain at least 25% of ammonium perchlorate, based on The oxidizing agent in the charge should con- The mixing of the charge ingredients is preferably achieved in the Entoleter (trademark) which insures uniform mix for any quantity of the mixture. 7

While I have described one at this time preferred embodiment of my invention, I do not desire to be limited 1 to the exact details thereof, but only by the scopeof the appended claims.

I claim:

1. In a tracking flare having a tubular body with an i open end and a closed end: a solid fuel charge in said sealing said open end of said body, and an electric match embedded in said ignition powder paste, said match having two conductive leads extending along the periphcry of said body.

2. The structure defined in claim 1, wherein said solidfuel charge is a mechanically mixed composition comprising about 10% by weight of aluminum powder,

about by weight of a petroleum base resin and about 75% by weight of an oxidizing agent, said oxidizing agent consisting of approximately equal proportions of ammonium perchlorate and strontium nitrate.

3. The structure defined in claim 1, wherein said solidfuel charge is a. mechanically mixed composition comprising about 25 by weight of a petroleum base resin and about 75% by weight of an oxidizing agent, said oxidizing agent consisting of approximately equal proportions of ammonium perchlorate and strontium nitrate.

4. In a tracking flare having a tubular body with an open end and a closed end: a solid fuel charge in said body consisting of a fuel component and an oxidixing agent, said oxidizing agent containing at least 25 percent by weight based on the weight of the charge of ammonium perchlorate and said solid fuel component containing between 5 and 30 percent by weight based on the weight of the charge of a petroleum resin, a layer of ignition powder paste applied to said charge on its surface facing said open end of said body, a closure member tightly applied against said layer of ignition powder paste for sealing said open end of said body, an electric match embedded in said ignition powder paste, said match having two conductive leads extending along the periphery of said body, and a pressure sensitive tape embodying a conductive element removably applied to the periphery of said body for short-circuiting said leads during storage and handling.

5. In a missile having a longitudinal axis and a nozzle at the rear end thereof, the combination of a tracking flare including a tubular body with an open end and a,

closed end, a solid fuel charge in said body consisting of a fuel component and an oxidizing agent,'said oxidizing agent containing at least 25 percent by weight based on the weight of the charge of ammonium perchlorate and said solid fuel component containing between 5 and 30 percent by weight based on the weight of the charge of a petroleum resin, a layer of ignition powder paste applied to said ,charge on its surface facing said open end of said body, a closure member tightly applied against said layer of ignition powder paste for sealing said open end of said body, an electric match embedded in said ignition powder paste, said match having two conductive leads extending along the periphery of said body, and an attachment for said flare supported at said rear end of said missile, said attachment including at least two resilient conductive members conductively contacting said leads and a source of electrical energy connected with said conductive members.

6. In a missile having a longitudinal axis and a nozzle at the rear end thereof, the combination of a tracking flare including a tubular body with an open end and a closed end, the diameter of said body being greater than the length thereof, a solid-fuel charge in said body consisting of a fuel component and an oxidizing agent, said oxidizing agent containing atleast 25 percent based on the weight of the charge of ammonium perchlorate and said solid fuel component containing between 5 and 30 percent based on the weight of the charge of a petroleum resin, a layer of ignition powder paste applied to said charge on its surface facing said open end of said body, a closure member tightly applied against said layer of ignition powder paste for sealing said open end of said body, and means at said rear end of said missile for supporting said tracking flare in such manner that said body is inclined with respect to said axis of said missile and said open end thereof is closer to said axis than said closed end, whereby said ignition powder paste may b ignited by the gases escaping through said nozzle of said missile.

References Cited in the file of this patent UNITED STATES PATENTS