US3702588A

US3702588A - Device for a flare

Info

Publication number: US3702588A
Application number: US98725A
Authority: US
Inventors: Bjorn Herman Olof Simmons
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1970-01-08
Filing date: 1970-12-16
Publication date: 1972-11-14
Anticipated expiration: 1989-11-14
Also published as: IL35877A0; DE2100489A1; SE339646B; GB1304671A; DE2100489C3; IL35877A; DE2100489B2; NL7100151A; FR2075263A5

Abstract

A braking device for a flare unit including a combustible flare composition attached to a parachute which unit is ejected from a missile a predetermined period of time after firing of the missile and after ejection spins at a high speed about its lengthwise axis, brakes the spinning motion of the unit to a predetermined maximal rotational speed. To effect such reduction of the spinning speed within a minimum of time, the braking device comprises flaps which are initially folded one upon another and upon the body of the flare unit and are unfolded by the centrifugal force acting upon the flaps due to the spinning of the unit after the ejection thereof.

Description

United States Patent Simmons [54] DEVICE FOR A FLARE [72] Inventor: Bjorn Herman Oloi Simmom, Karlskoga, Sweden [73] Assignee: Aktiebolaget Bolors, Bofors, Sweden 221 Filed: Dec. 16, 1970 211 App]. No.: 98,725

[30] Foreign Application Priority Data 5/1857 Sibley ..244/3.29 X

[ 1 Nov. 14, 1972 A Busacker ..244/3.25 617,376

[ ABSTRACT A braking device for a flare unit including a combustible flare composition attached to a parachute which unit is ejected from a missile a predetermined period of time after firing of the missile and after ejection spins at a high speed about its lengthwise axis, brakes the spinning motion of the unit to a predetermined maximal rotational speed. To effect such reduction of the spinning speed within a minimum of time, the braking device comprises flaps which are initially folded one upon another and upon the body of the flare unit and are unfolded by the centrifugal force acting upon the flaps due to the spinning of the unit after the ejection thereof.

9 Clainn, 4 Drawing figures PATENTED 14 W3 3,702,588

SHEET 1 OF 2 INVEYTOR. BJORN HERMAN OLOF .S/MMOM BY Haw Eaafi m S un ATTORNEYS PAIENTEDW B v 3.702.588

' SHEET 2 BF 2 I MTEWTOR. BJOK/V HERMAN OLOF S/MMONS DEVICE FOR A FLARE The present invention relates to a device for a flare that can be enclosed in a projectile, particularly a pyrotechnical flare, which is separated from the projectile at a given time after this has been fired, the flare, at the separation, then being given a rotation around an axis of symmetry extending in the longitudinal direction of the flare. The flare is moreover to be provided with a member for braking said rotation, consisting of two or more flaps, symmetrically arranged in relation to the circumference of the flare and as a rule in the vicinity of the envelope surface of the flare and/or its extension, each flap then being arranged in a bearing so that in connection with said separation it will be turned out or folded out by the centrifugal force caused by the rotation.

In order that the best functioning shall be obtained for the member in question, for instance a flare comprised in a flare unit in the form of a pyrotechnical flare carried in a parachute, it is of importance that the shortest possible time elapses from the time when the flare is separated from the projectile until such a braking of the movements of the flare around and along its axis of symmetry has taken place that ignition, followed by economic combustion of the flare, can be carried out. For instance, it cannot be permitted that a flare is ignited only after a plurality of seconds have passed since the sound from the firing of the projectile has been noticed, as the entire surprise effect will then be lost. Nor is any major advantage obtained if the flare in question is ignited before its movement has been braked down to a sufficient degree, as the light produced by a flare rotating at such a high speed does not meet the requirements stipulated for illumination, and the flare will moreover burn up in comparatively short time. The movement of the flare along its axis of symmetry is taken care by one or several brake parachutes, while the braking of the rotating movement is accomplished by the device according to the invention.

In order to achieve said braking of the rotating movement, it has been proposed, among other things, to enclose the flare unit in a container, on the envelope surface of which, symmetrically around the circumference, flaps are arranged which have one end fastened in the container by welding or brazing, so that their braking surfaces, when the container is placed in the projectile, will substantially coincide with the form of the envelope surface. At the braking, the intention has then been that the centrifugal force caused by the rotation should raise the flaps, so that they can exert their braking effect on the flare unit.

However, such a flap has substantial drawbacks, which among other things cause a long braking time, which is not acceptable in this connection. This is due to the fact that the welded or brazed seam which extends along the envelope surface must be dimensioned to withstand the centrifugal forces arising at high rotating speeds and the air-stream forces, so that no tearing takes place and so that the flap is actually raised at low rotating speeds, which raising can be facilitated by perforating the bending zone. If a shell, when fired, is given a high or a low rotating speed depends upon, in the case of howitzers, for instance, what charges are chosen for the shell in question, and in this connection it can be mentioned that for one and the same howitzer it would be definitely impossible to use shells with different rotating brakes.

In order .to avoid tearing, a flap of the design described above must be made so that it does not extend far tangentially, i.e. it must be made so that, when raised, it does not extend far radially. Hoping to be able to increase the braking effect with a flap that has this extremely limiting factor, it has hitherto been proposed, for the purpose of obtaining compensation, to give the flap a great extension axially. However, this measure has not given the braking efiect intended, as the air stream, through the movement of the unit along its axis of symmetry, hits the leading edge of the flap, which has the consequence that the main braking effect will be obtained at the leading edge of the flap, while there will be turbulence rearwards along the major portion of the flap, which thereby will not have any major effect on the total braking effect of the flap. It is therefore an essential requirement for really good (optimum) braking effect that the flap can be given a great extension tangentially, i.e. a great extension radially after having been raised, while on the other hand the extension axially is of secondary importance. In other words, it is of the greatest importance that the flaps can be given a form that radically differs from the one described above and which it has hitherto not been possible to use, among other things owing to the fastening arrangements shown for the flap.

It has therefore been proposed that said fastening arrangements for the flaps should be replaced by bearings, for instance in the form of bearing axles that extend substantially parallel with the envelope surface of the flare unit. Around each bearing axle, a flap in the form of a tongue has then been fastened at one end, by simply having been bent around the bearing axle, so that the edge of the end has come into contact with or has been directed towards the surface of the tongue at the bearing. The advantage of such fastening is that there will be no problems involved in having the flap rise even at low rotation speeds, but in spite of the fact that the tongue in this connection has been made of hardened steel and notwithstanding the care taken when choosing material and fastening means, as well as careful inspection at the manufacture, it has proved that this type of flap cannot be designed for optimum braking effect either, particularly not if it is a question of high centrifugal loads acting on the flap. It has proved that the flap is torn off where it is fastened, which has had the consequence that, in order to reduce the centrifugal load, it has been necessary to reduce the radial extension of the tongue. As a compensation for the braking surface thus reduced, the width of the tongue where it is fastened has had to be increased as described above, which has involved the above-mentioned drawbacks and limitations at the dimensioning of the projectile and the flare, as an extension of the longitudinal bearing axles will take up some of the space available for, for instance, the flare.

The present invention gives an indication of a device that permits flaps with a design that gives the optimum braking effect shortest possible braking time) even when there are comparatively high centrifugal loads on the flap, which makes it possible, for instance, to have all ammunition of this kind provided with a common type of flap, without having to employ special designs in individual cases of the flap or its fastening means with consideration to the rotation that occurs. In other words, the device according to the invention provides for a flap that is extremely suitable for use for projectiles with both low and high rotating speeds. At the same time, the drawbacks of having material that is difficult to work with and is expensive are eliminated, and the careful inspection procedure that thas hither-to been necessary can be practically omitted. The invention also involves that, although cheaper material can be used, the thickness of the flap can be reduced, which is of extremely great importance for the dimensioning of the flare unit in its entirety. The feature that can be considered to be characteristic for a device according to the invention is that a flap comprises two sheetformed parts which extend from the bearing and at least partly cover each other, which moreover are joined together at the bearing along one of their end edges and that the two parts are also made in such a way that a difference between the total centrifugal load on one part and the total centrifugal load on the other part is zero or is less than or equal to a bending resistance of the material used for the parts, and a further resistance caused by the parts possibly being fastened together, so that, at the rotation, the parts remain in a predetermined position.

The embodiments proposed at present which have the characteristics that are significant for the invention will be described in the following, with reference to the attached drawings, in which FIG. 1 shows in perspective, examples of the positioning in principle of four flaps on a flare unit;

FIG. 2 in a side view shows the fastening of the flaps in a member attached to the flare, whereby the flaps will be arranged in the vicinity of the extension of the envelope surface of the flare;

FIG. 3 is a side view and in cross-section shows a cross-section of the device according to the invention;

FIG. 4 in a diagram form shows examples of the braking time for a device of a known design and a device according to the invention.

In FIG. 1, 1 shows a unit containing a flare unit, separated from a projectile after this has been fired, which unit is then rotating around an axis of symmetry 2 which it has been given. The unit has a member for braking up the rotation in the form of four flaps 3, symmetrically arranged around its circumference, which are raised at or after the separation, which are located in the vicinity of the envelope surface 4 of the flare unit by being somewhat recessed in relation to this. The recess in question can be made greater or lesser. A centrifugal force caused by the rotation actuates the flaps, and depending upon, for instance, the rotating speed, the air stream and the material used in the flaps, these will extend from the unit to a greater or lesser extent in relation to what is indicated in FIG. 1. An arrow Rp indicates the direction of rotation of the unit.

FIG. 2 is intended to show the fastening of the flaps 3 to the unit with the flare unit that can be separated from the projectile in more detail. During the braking time, the flare 5 and the parachute 6 of the flare unit are held together by a container 7, a carrying member 8 and a plate 9. The unit formed by the parts 5-9 rotates as indicated above around its axis of symmetry 2, and the movement of the unit along its axis of symmetry 2 is braked by a brake parachute which is released at the separation, and the cords of which are indicated by 10. In order that the cords 10 shall not be twisted by the rotation of the unit, the brake parachute is attached to the parts 5-9 via a ball bearing 11.

The flaps 3 are fastened and somewhat recessed in the member 8, and will thereby be movably arranged at the extension of the envelope surface 12 of the flare. It is, of course, possible to recess the flaps further in the carrying member 8, but such a measure would reduce the space available for the parachute 6. On the contrary, in the example of the embodiment, the endeavour is to have the flaps recesses as little as possible, and there are therefore essential requirements that they can be made with little thickness. The parts 5-9 are kept together until the braking has been completed, when a delay composition 13 on one end of the container 7 achieves a separation of the flare unit (flare 5 and parachute 6) from the other said parts of the unit, at the same time as ignition of the flare takes place, which can thereafter descend to the ground, depending from its parachute 6.

FIG. 3 shows a cross-section of the bearing for the flap and its fastening in relation to the carrying member 8. The bearing consists of a bearing axle 14 which extends in the recess of the carrying member, substantially parallel with the envelope surface 12 of the flare (FIG. 2). The flap 3 then consists of two sheet-formed

parts

15 and 16, which extend from the bearing so that they cover each other, the parts also being joined together at the bearing along one of their

end edges

15 and 16a. The sheet-formed

parts

15 and 16 will consequently extend one from each

side

17 and 18, respectively, of the bearing axle 14, and in the example of the embodiment, the parts, for the rest, are substantially identical, at the same time as the sections that are located outside the bearing can be fastened together, for instance by spot welding, soldering or glueing. In its most simple embodiment, the

parts

15 and 16 appropriately consist of a sheet of steel or light metal placed under the bearing 14, and are then bent around the bearing so that their ends will correspond to the

parts

15 and 16. In their extensions from the

sides

17 and 18 of the bearing, one of the parts 15 of the two parts and/or the other part 16 can follow the surface or the bearing axle to a greater or lesser extent. In the same way, the

parts

15 and 16 can be designed so that, when turned down, they conform to the shape of the outer surface of the carrying member.

Another specific feature of the device described is that the two

parts

15 and 16 are also designed in such a way that any difference between the total centrifugal load on one side, for instance 15, and the total centrifugal load on the other side 16 is less than or equal to a bending resistance in the material used for the parts so that, at the rotation, the parts will remain in a predetermined position. If a fastening together is utilized, for instance in the form of riveting, welding, soldering and/or glueing between the parts, the resistance from the fastening together, in conjunction with said bending resistance of the material, will contribute by absorbing any possible difference in centrifugal load, and it is thereby possible to allow one of the sheet-formed parts to extend outside the other sheet-formed part, for instance so that in a simple way it will be possible to obtain a thinner outer part of the flap in question for overlapping of two flaps.

In the above-mentioned example of the embodiment, it has proved, at tests that have been carried out, that ordinary steel plate with a thickness of approx. 0.3-0.5 mm is entirely sufficient to give the functioning with a short braking time that it is endeavored to obtain with most types of ammunition. For certain ammunition, however, it can be advisable to use a material other than steel plate, for instance light metal, which is particularly favorable for projectiles having a small caliber and a high rotating speed. A total thickness of the flap of approx. 0.6 mm will involve that certain overlapping between the flaps can be permitted, without, for instance, having to reduce the space available for the parachute, which is of essential importance in cases when the total length of the flaps exceeds the circumference of the carrying member 8. In devices previously used, there was a certain limitation in this respect, as it was then necessary to use hardened steel plate with a thickness of at least 1 mm. If the sheet-formed parts are fastened together, the last-mentioned effect will be further amplified.

FIG. 3 also shows, with dash lines, a flap in the raised position, which coincides with the direction of a total force Tp acting upon the flap, which is determined by the air-stream force Ap as well as the centrifugal load Cp on the flap. Examples of said forces are given with a force parallelogram at the raised flap indicated with dash lines.

HO. 4 shows the braking time in a diagram form for a flare unit which, as the separation from the projectile, has been given a rotating speed of 9,000 r.p.m. and a velocity of 300 m/sec. Before the flare can be ignited, the rotation of the flare should be reduced to, for instance, 500 r.p.m. and the velocity to 60 m/sec., which values can be obtained within approx. 8 sec. with a previously known device, see curve 19, within such a short time at less than 2 sec. with the device according to the invention, of which an example is given by curve 20.

The invention is not limited to the embodiments shown above as examples, but can be subjected to modifications within the scope of the following claims. For instance, the invention is not limited to the number of flaps on the flare. The design of the flaps and their location are not essential for the concept of the invention, and it has no significance whether or not there are one or several flaps on the same bearing. It is also conceivable that the bearing should consist of a clamping recess in the carrying member from which the sheetformed parts extend as described above, which flaps will then be turned or folded out. Nor need the sheetformed parts extending from the bearing cover each other entirely; the essential point is that said conditions for a possible difference between the centrifugal loads between the parts are fulfilled. In addition to flares, the invention can also be used for smoke or gas developing compositions.

I claim:

1. A parachute-supported device containing a combustible composition and constituting part of a projectile to which projectile is imparted a high spin velocity about its lengthwise axis when fired from a gun barrel and from which the device is separated when the spin velocity of the projectile is reduced below a predetermined value, in combination with a braking device, said braking device comprising:

a cylindrical body member;

a plurality of flaps each of which being composed of two superimposed and secured to each other layers of form-retaining sheet material having a curvature substantially matching the circumferential curvature of said body member; and

a pivot means for pivotally mounting each of said flaps on said body member, each of said pivot means including a pivot pin extending transversely of the lengthwise axis of said body member, the two layers of each flap straddling at one end the respective pin and envelope the same, said pins constituting pivot axes for pivotal movements of the flaps between an inactive position in which the flaps are folded upon the circumferential surface of the body member and a spread-apart braking position in which the flaps define an angle with said surface, the flaps being in said inactive position prior to the application of a spin velocity to the projectile and in said braking position when the projectile is in flight due to the centrifugal force then acting upon the flaps;

the aerodynamic configuration of said flaps being such that the differential between the centrifugal forces acting upon opposite sides of the flaps does not exceed the inherent bending resistance of the material of which the flaps are made.

2. The parachute-supported device according to claim 1 wherein the said pivot means limit pivoting of the flaps to a predetermined maximal angle relative to the circumferential surface of the body member.

3. The parachute-supported device according to claim 1 wherein said two layers of sheet material have substantial equal peripheral outlines.

4. The parachute-supported device according to claim 1 wherein the lengths of said flaps is such that the free end portion of each flap overlies the pivot means for the circumferentially adjacent flap when said flaps are in the folded position.

5. The parachute-supported device according to claim 1 when the length of one of the flap layers is longer than that of the other, the length of each longer layer being such that the protruding end portion of the longer layer overlies the pivot means for the circumferentially adjacent flap when the flaps are in the folded position.

6. The parachute-supported device according to claim 1 wherein said body member includes a tubular extension, said pivot means being mounted on said ex- 9. The parachute-supported device according to claim 1 wherein each of said pivot means comprises a lengthwise elongate groove in the circumferential surface of said body member, each of said grooves having a substantially circular cross-sectional outline con- 5 structed at the surface of the body member, the respective end of the flaps terminating in an enlarged edge fitted in said grooves for retention therein.

k l I I

Claims

1. A parachute-supported device containing a combustible composition and constituting part of a projectile to which projectile is imparted a high spin velocity about its lengthwise axis when fired from a gun barrel and from which the device is separated when the spin velocity of the projectile is reduced below a predetermined value, in combination with a braking device, said braking device comprising: a cylindrical body member; a plurality of flaps each of which being composed of two superimposed and secured to each other layers of form-retaining sheet material having a curvature substantially matching the circumferential curvature of said body member; and a pivot means for pivotally mounting each of said flaps on said body member, each of said pivot means including a pivot pin extending transversely of the lengthwise axis of said body member, the two layers of each flap straddling at one end the respective pin and envelope the same, said pins constituting pivot axes for pivotal movements of the flaps between an inactive position in which the flaps are folded upon the circumferential surface of the body member and a spread-apart braking position in which the flaps define an angle with said surface, the flaps being in said inactive position prior to the application of a spin velocity to the projectile and in said braking position when the projectile is in flight due to the centrifugal force then acting upon the flaps; the aerodynamic configuration of said flaps being such that the differential between the centrifugal forces acting upon opposite sides of the flaps does not exceed the inherent bending resistance of the material of which the flaps are made.

6. The parachute-supported device according to claim 1 wherein said body member includes a tubular extension, said pivot means being mounted on said extension.

7. The parachute-supported device according to claim 6 wherein said extension includes in its outer surface a peripheral groove, said pivot means being mounted within said groove, the radial depth of said groove being such that the outer surfaces of the flaps in the folded position thereof are substantially flush with the circumferential outline of said extension.

8. The parachute-supported device according to claim 1 wherein each of said flaps is formed of one strip of sheet material folded back upon itself about the respective pivot pin.

9. The parachute-supported device according to claim 1 wherein each of said pivot means comprises a lengthwise elongate groove in the circumferential surface of said body member, each of said grooves having a substantially circular cross-sectional outline constructed at the surface of the body member, the respective end of the flaps terminating in an enlarged edge fitted in said grooves for retention therein.