WO2000066968A1

WO2000066968A1 - Projectile with controlled ballistics

Info

Publication number: WO2000066968A1
Application number: PCT/FR2000/001154
Authority: WO
Inventors: Jean Baricos; Nicolas Villedieu; Jean-Pierre Siegler; Pascal Gendre
Original assignee: Etienne Lacroix Tous Artifices S.A.
Priority date: 1999-04-30
Filing date: 2000-04-28
Publication date: 2000-11-09
Also published as: DE60011723T2; FR2793017B1; ATE269967T1; DE60011723D1; ES2222204T3; EP1090265B1; EP1090265A1; AU4573700A; FR2793017A1; CA2335919A1

Abstract

The invention concerns a projectile, in particular to be used in the field of fireworks, characterised in that it comprises a leading front face (10) a peripheral envelope (30) separated by a transitional ridge (20) located in a plane (P) perpendicular to the axis (O-O) of the projectile, said front face (10) not extending upstream of said plane (P).

Description

PROJECTILE WITH CONTROLLED BALLISTICS

The present invention relates to the field of projectiles.

It applies to all types of projectiles or rockets, self-propelled or not, in particular ballistic. The present invention relates in particular, but not limited to, projectiles having applications in the field of fireworks.

The object of the present invention is to propose, with simple technical means, a projectile which is stable relative to its ballistic axis and without rotation or roll.

The present invention can in particular find application in the field of fireworks, for the generation, in the air, of figures, symbols, or even letters or the like having a controlled geometry and orientation. Many works have already been carried out in this area.

The method generally proposed for producing patterns such as a circle, triangle, number or other shapes, consists in arranging stars in a bomb body in the same arrangement as the pattern itself.

These stars are agglomerates made from a pyrotechnic composition which burns with a flame color characteristic of the formulation used.

At the time of the explosion of the bomb, the stars are lit and dispersed in the atmosphere and will represent the desired pattern by several light points, each point being made by a star. The fineness of the pattern in this case depends on the number of stars loaded in the bomb.

Another solution has been described in documents FR-A-2764687 and FR-A-2764688 in the form of a pyrotechnic projectile comprising a body containing a burst charge and a combustible charge, the ignition and dispersion of which are ensured by the explosion of the burst charge, in which the combustible charge is formed by a combustible metallic powder with oxygen from the air, disposed within the bursting charge according to a pattern corresponding to the shape of the firework pattern to be obtained in the sky.

As for controlling the orientation of the projectiles, it is generally proposed to search for it using fins arranged on the outer periphery of the projectile.

However, to the knowledge of the Applicant, none of the devices hitherto proposed are fully satisfactory, in particular in terms of stability, except for embedding complex control means, which the present invention seeks to avoid. The study of the parameters governing the stability of a projectile is indeed very complex.

One can find for example a theoretical approach to the aerodynamics of cylinders in the work "Theories of fluid dynamics" A. Bonnet, J. Luneau (Cépadues éditions). Being recalled that one calls "slender", a body whose longitudinal dimension measured parallel to the speed vector is much larger than its transverse dimensions (Rockets and missiles are characteristic examples of slender bodies) and that the method of singularities is a method for solving the Laplace equation (ΔΦ = 0) in order to determine the flow around an obstacle, the basis of the theory is as follows.

The slender body theory is a linearized version of the singularity method. It is therefore only applicable for obstacles whose local slope of the walls, relative to the speed vector at infinity remains sufficiently low. It allows for example to approach the calculation of aerodynamic forces on the body of a missile or fuselage of revolution at low incidences.

As part of the slender body theory, expression of the pitching moment with respect to an arbitrary point A is: Mz = ^_1/2 pco V S ^ _re fL EFCM _r _{/ t}

with v the volume of the body considered, L the total length of the machine, XA the distance between the nose is the point A, S _q the surface of the base of the machine, V _œ the speed at infinity upstream, p _∞ the density of fluid at infinity upstream, Sref the reference surface, Lr _ef the reference length, α the incidence.

In the case where A is the instantaneous center of rotation, for example of gravity G of a body in free flight, the preceding formula, giving the coefficient of pitching moment compared to G, allows, according to the geometrical data of the body , to define its stability conditions.

The body is stable if, at a variation of incidence Δα, negative or positive, the moment of the forces which act on the body tends to eliminate this variation of incidence.

The stability condition is therefore:

> 0 da hence (L - X _g ) S _q - V> 0 x either, since -> 0:

0 <^ <1

E ES,

We deduce that the main parameter to control to obtain a stable projectile would be the position of its center of gravity.

However, the Applicant has found that this parameter was far from sufficient and departing from the prejudices accepted by those skilled in the art, a developed a new structure which is distinguished from known prior projectiles, in particular by the geometry of its attack face.

Thus, the above object is achieved in the context of the present invention by means of a projectile comprising a front attack face and a peripheral envelope separated by a transition edge situated in a plane perpendicular to the axis of the projectile, and in which the front face of attack does not extend upstream of this plane.

In other words, the present invention recommends using a projectile without warhead. However in the case of such a cylinder without warhead, the volume v of the cylinder is equal to the quantity LS _q . It would therefore theoretically be necessary for the center of gravity to be on the front face so that the cylinder is stable at zero incidence in order to comply with the established criteria recalled above. Thus, the theory suggested that such a cylinder is unstable at low incidences.

However, the Applicant has demonstrated that, a priori very surprisingly, a projectile which meets the characteristics indicated above, makes it possible to meet the objective sought.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawings, given by way of nonlimiting examples and in which:

- Figure 1 shows a schematic side view of a projectile according to the present invention, - Figures 2 and 3 show views in axial section of two alternative embodiments of the front attack face of a projectile according to the present invention, and

- Figure 4 shows an axial sectional view of the rear part of a projectile according to an alternative embodiment of the present invention. After long studies and research and numerous trials, the

Applicant has determined that in order to obtain a projectile which is stable relative to its ballistic axis and this without rotation or roll, it is desirable to control in particular the following parameters: a) the geometry of the face of attack before 10, b) the length (L1) / transverse dimension (D1) ratio, c) the nature of the transition 20 between the front face 10 and the peripheral surface 30 and d) the position of the center of gravity of the projectile .

Concerning the geometry of the front attack face 10, the Applicant has determined, as indicated above that it is desirable that the transition edge 20 between the front attack face 10 and the peripheral surface 30, be located in a plane P perpendicular to the axis

O-O of the projectile.

Furthermore, the Applicant has determined that, unlike known projectiles which have a forward tapered attack face, this attack face 10 should preferably not extend upstream of this plane P, in order to obtain a projectile high stability.

Thus preferably, the front face 10 is planar and situated in this plane P. However, if necessary, the front face 10 can be of the concave type recessed with respect to this plane P, from the edge 20, as illustrated for example in Figures 2 and 3.

A variant of concave attack face 10 with continuous curvature, for example generally spherical, has thus been illustrated in FIG. 2, while the attack face 10 illustrated in FIG. 3 is stepped (here it has a central cavity 12, bordered by a crown 11 located in the plane P, and delimited by a cylindrical skirt of revolution 13 and a flat bottom 14 parallel to the plane P.

The foregoing characteristics have been highlighted by the Applicant essentially after numerous tests.

Indeed, they go against generally accepted theories which require, as recalled previously, an attack face tapered forward.

Concerning the relationship between the length L1 and the dimension D1 transverse to the axis OO of the projectile, the Applicant has determined that preferably this ratio L1 / D1 is between 0.25 and 20, very preferably between 0.5 and 12, and even between 1 and 3 and advantageously of the order of 2.5. Regarding the transition 20 between the front face and the peripheral surface 30, the Applicant has determined that the latter is preferably formed of a sharp edge, without pronounced chamfer or rounding.

Regarding the position of the center of gravity of the projectile, the Applicant has determined that preferably, for the ammunition to be stable at zero incidence, the center of gravity must be located approximately two-thirds before the ammunition, preferably in the front half of the munition, and even very advantageously to have good stability in the first third. Furthermore, the Applicant has found that the projectile, and consequently its peripheral surface 30, is preferably included in a straight cylinder resting on the transition edge 20.

The aforementioned peripheral surface 30 can be cylindrical, that is to say defined by a rectilinear generator parallel to the longitudinal axis O-O. However, this last characteristic is not absolutely mandatory. The peripheral surface 30 may in fact have, at least over a part of the length of the projectile, areas set back with respect to the right cylinder bearing on the transition edge 20.

It is thus possible, for example, to envisage that the peripheral surface 30 is delimited by a curved generator which is concave towards the outside of the munition.

According to another alternative embodiment, the peripheral surface 30 is delimited by a section which converges towards the rear of the projectile. Preferably, the projectile has symmetry with respect to its longitudinal axis O-O.

It may have a circular cross section, the peripheral surface 30 then being for example cylindrical of revolution. As a variant, the cross section of the projectile can be of the polygon type or else have flats.

On this point the Applicant has indeed found that a cylindrical projectile provided with flats behaves in substantially the same way in flight as a cylinder of revolution. By way of nonlimiting example, the peripheral surface 30 of the projectile can comprise three flat parts equi-distributed around the longitudinal axis OO, each flat part having for example a cord with a length of the order of 10 mm for a projectile having a diameter of 45mm.

Furthermore, the Applicant has determined that preferably, the propulsion means associated with the projectile are calculated so that the speed of the projectile in ballistic phase external to the launcher is between 25 and 250 m / s, advantageously of the order of 60 to 120m / s and very preferably around 10Om / s.

The Applicant has in fact determined that these ranges of value are necessary to allow the projectile according to the invention to fly correctly, despite its geometry which deviates from that generally accepted by those skilled in the art. The above elements mainly concern the external ballistics of the projectile.

The Applicant has also determined that preferably, it is desirable to take care of the elements of internal ballistics in order to obtain a projectile which is stable relative to its ballistic axis and without rotation or roll. In this area, the Applicant has determined that if necessary, as illustrated in FIG. 4, the projectile can be equipped at its rear part with a skirt 40, for example cylindrical, or even cylindrical of revolution centered on the OO axis.

Of course the present invention is not limited to the particular embodiments which have just been described, but extends to all variants in accordance with its spirit.

Claims

1. Projectile, characterized in that it comprises a front attack face (10) and a peripheral envelope (30) separated by a transition edge (20) situated in a plane (P) perpendicular to the axis (OO ) of the projectile, said front face (10) not extending upstream of this plane (P).

2. Projectile according to claim 1, characterized in that the peripheral surface (30) is included in a straight cylinder resting on the transition edge (20).

3. Projectile according to one of claims 1 or 2, characterized in that the front face (10) is planar and located in the plane (P) containing the transition edge (20).

4. Projectile according to one of claims 1 or 2, characterized in that the front face (10) is concave and recessed relative to the plane (P) containing the transition edge (20).

5. Projectile according to claim 4, characterized in that the front attack face (10) is concave with continuous curvature, for example generally spherical.

6. Projectile according to claim 4, characterized in that the front attack face (10) is stepped.

7. Projectile according to one of claims 1 to 6, characterized in that the ratio (L1 / D1) between the length and the transverse dimension of the projectile is between 0.25 and 20.

8. Projectile according to one of claims 1 to 7, characterized in that the ratio (L1 / D1) between the length and the transverse dimension of the projectile is between 0.5 and 12.

9. Projectile according to one of claims 1 to 8, characterized in that the ratio (L1 / D1) between the length and the transverse dimension of the projectile is between 1 and 3.

10. Projectile according to one of claims 1 to 9, characterized in that the ratio (L1 / D1) between the length and the transverse dimension of the projectile is of the order of 2.5.

11. Projectile according to one of claims 1 to 10, characterized in that the transition (20) between the front face (10) and the peripheral surface (30) is clear, without chamfer or pronounced rounding.

12. Projectile according to one of claims 1 to 11, characterized in that the center of gravity of the projectile is included in the 2/3 before it.

13. Projectile according to one of claims 1 to 12, characterized in that the center of gravity of the projectile is included in the front half thereof.

14. Projectile according to one of claims 1 to 13, characterized in that the center of gravity of the projectile is included in the first third before it.

15. Projectile according to one of claims 1 to 14, characterized in that the peripheral surface (30) is cylindrical.

16. Projectile according to one of claims 1 to 14, characterized in that the section of the peripheral surface (30) converges towards the rear of the projectile.

17. Projectile according to one of claims 1 to 16, characterized in that the peripheral surface (30) has a symmetry with respect to the longitudinal axis (O-O).

18. Projectile according to one of claims 1 to 17, characterized in that the peripheral surface (30) has a symmetrical cross section of revolution around the longitudinal axis (O-O).

19. Projectile according to one of claims 1 to 17, characterized in that the cross section of the peripheral surface (30) is of polygon type.

20. Projectile according to one of claims 1 to 17, characterized in that the peripheral surface (30) has at least one flat.

21. Projectile according to one of claims 1 to 17 and 20, characterized in that the peripheral surface (30) has three equi-distributed flats.

22. Projectile according to one of claims 1 to 21, characterized in that the propulsion means are adapted to generate a projectile speed in external ballistics between 25 and 250m / s.

23. Projectile according to one of claims 1 to 22, characterized in that the propulsion means are adapted to generate a projectile speed in external ballistics between 60 and 120m / s.

24. Projectile according to one of claims 1 to 23, characterized in that the propulsion means are adapted to generate a speed in the external ballistic phase of the order of 100m / s.

25. Projectile according to one of claims 1 to 24, characterized in that the projectile comprises in its rear part an annular skirt

(40).

26. Projectile according to one of claims 1 to 25, characterized in that it comprises a payload capable of forming fireworks.

27. Projectile according to one of claims 1 to 26, characterized in that it comprises a payload capable of forming a symbol of controlled geometry in the air.