EP0338879B1 - Stabilizing means for projectile to be fired from a rifled barrel - Google Patents

Abstract

The technical sector of the invention is that of stabilising devices for projectiles with a low longitudinal moment of inertia. The stabilising device comprises a skirt (31) of substantially conical general shape, the axis of the cone coinciding with the axis of the projectile (1), this skirt (31) being fixed to the projectile (1) in the region of its rear part and being maintained by a connection means in a folded position when the projectile is in the barrel of the firearm, and unfolding at the exit of said barrel. The invention is used for stabilising self-propelled projectiles of the ramjet type. <IMAGE>

Description

The present invention relates to a stabilization device for a projectile, intended to be fired from a rifled tube, and having a small longitudinal moment of inertia, for example a self-propelled projectile comprising a penetrator of heavy material, such as tungsten, and an envelope of light material, of the composite type.

Self-propelled projectiles have been known for a few years already. We can distinguish two modes of self-propulsion:

Rocket propulsion, in which the projectile carries a propellant charge, of the solid or homogeneous solid propellant type, generating a gas pressure at its rear. This first mode of self-propulsion is used for example for rockets and also in certain artillery shells (see patent FR2522134); it then significantly increases the range.

The propulsion by ramjet uses a propellant load of the solid propellant type ablatable or autopyrolisable arranged inside an envelope comprising an air intake opening at the front of the projectile and an outlet nozzle. The air admitted at high flight speeds is slowed down in an inlet diffuser and enters the combustion chamber in the form of compressed air. The combustion of the mixture of air (oxidant) with the gas (reducing agent) obtained by autopyrolysis or ablation of the propellant block provides energy which is transformed into propelling force in the thrust nozzle.

This type of self-propulsion has a certain number of advantages compared to the rocket self-propulsion mode.

In particular, it allows (at equal reach) to minimize the weight of on-board propellant; in effect the oxidant will be constituted by the air admitted into the combustion chamber.

At equal performance, the pressures developed in the combustion chamber are lower (3.10⁶ to 6.10⁶ Pa for the ramjet versus 7.10⁶ to 25.10⁶ Pa for the rocket propellant), which simplifies the mechanical design of the projectile.

The fuel consumption of the ramjet at supersonic speeds is reduced, which allows long flight times.

The patent US2989922 describes a ramjet projectile intended to be fired by a cannon. This projectile comprises a military charge surrounded by a propellant composition, itself arranged inside a tubular envelope carrying a belt. This projectile is gyrostabilized in a conventional manner, the belt taking the scratches from the barrel of the weapon. Such a stabilization mode is possible because of the large longitudinal moments of inertia of the military load and the envelope.

As modern armor can be acquired by kinetic energy projectiles (such as arrow projectiles), it would be particularly advantageous to equip such projectiles with self-propulsion in order to increase their range and their terminal efficiency while reducing flight time.

The patent US4573412 shows such a projectile comprising a penetrator held in an envelope made of composite material of the fiberglass type.

This projectile is intended to be fired from a light tube and at reduced initial speed. In order to limit the quantity of propellant required and therefore the dimensions of the projectile, the mass of the penetrator is here less than that of the arrow type penetrators used in artillery, a reduction in perforation performance is ensured.

It would be tempting to be able to fire such a projectile from an artillery cannon; thus, the mass of propellant charge could be reduced due to the high initial speed communicated by the gun. Unfortunately, if the combination of a composite casing and a reduced diameter penetrator makes it possible to provide a projectile whose total mass corresponds substantially to the useful mass of the perforator, the longitudinal moment of inertia of such a projectile becomes too weak so that it is possible to gyrostabilize it (stabilization by rapid rotation speed of the order of 450 revolutions / second obtained by a shot in a rifled tube).

The stabilization mode proposed by patent US Pat. per second) necessary for the stability of the trajectory.

Such a projectile cannot therefore be fired from an artillery weapon comprising a rifled tube, the speed of rotation which would be communicated to it would moreover risk destroying the empennage as a result of inertia.

Another solution making it possible to fire a projectile at a low longitudinal moment of inertia from a striped tube consists in providing it with a slip belt (like that described by patent FR8616066), the stabilization device then being constituted by a conventional tailplane.

Such a solution nevertheless has drawbacks. Aerodynamic calculations show that the stabilization of a 105 mm caliber projectile whose longitudinal inertia is of the order of 10-² kg.m² requires the presence of stabilizing fins, the total surface of the assembly fins being of the order of 3000 cm² for a fin opening angle of 30 ° !!. Such a surface requires the design of a complex deployment device and requires the use of part of the interior volume of the projectile to house the fins and deployment device, to the detriment of the total amount of propellant charge on board. In addition, such a tail will have the effect of increasing the drag of the projectile and therefore of reducing the range.

Also known is US-A-3 081 703 describing a stabilization device for a rotating projectile, comprising a cone held in the folded position when the projectile is inside the launching tube and deploying at the exit of this tube. However, the projectile described is of the self-propelled rocket type, the rotation being obtained by means of gas deflectors. The launching tube is thus a smooth guide tube and the projectile is therefore not subjected to a canon environment. The fins include a means for holding in the folded position which is a combustible star; this star is burned by the gases ejected by the projectile. It is understandable that such a projectile cannot be fired from a cannon, since the propellant gases developed in the chamber of the latter would cause the almost instantaneous combustion of the retaining star and therefore the release and the deterioration of the skirt inside the barrel of the weapon. These propellant gases would also cause the anticipated combustion of the propellant charge carried by the projectile which would decrease its range.

The object of the present invention is to provide a projectile stabilization device associating a heavy material penetrator and a light casing fired from a conventional artillery weapon comprising a striped tube, in which the stabilization skirt is protected. folded position during the gun phase.

The subject of the invention is therefore a stabilization device for a self-propelled projectile with low longitudinal moment of inertia,
in particular for a projectile comprising a penetrator of heavy material, such as tungsten, and an envelope of light material of the composite type, device comprising a skirt of generally frustoconical shape, the axis of the truncated cone coinciding with the axis of the projectile , the skirt being integral with the envelope at the rear part of the projectile, characterized in that the skirt consists of a set of tongues maintained in a folded position by a connecting means when the projectile is in the tube the weapon, which deploys at the outlet of said tube, the connection means being constituted by a shoe linked in rotation to the casing and receiving the gas pressure at its rear part so as to push the projectile into the tube, the sabot separating from the envelope at the outlet of the barrel, the projectile being intended to be fired by a rifled tube.

Each tab can be connected to a locking means in position constituted by a centrifugal lock engaged in a radial housing formed in the envelope.

The centrifugal lock can be constituted by a shouldered rod.

The tongues each have an entanglement at their longitudinal edges so as to provide an overlap at their junction.

The shoe carries at least one hole communicating the internal part of the projectile with the outside.

The shoe carries opposite the holes and at the internal part of the projectile, a pyrotechnic ignition element.

The shoe is made integral with the projectile at the level of the indenter.

The half-angle at the top of the truncated cone of the skirt is between 5 ° and 15 ° when the latter is in the deployed position, and the ratio of the outside diameter of the envelope to the diameter (D) of the largest circle of base of the truncated cone of the skirt is greater than or equal to 70%. The tongues are secured at one end of the envelope at a circular generator of the envelope and are regularly distributed along this generator, the number N and the width of the tongues being such that in their deployed position their free ends cover at least 70% of the largest base circle of the trunk of the skirt cone.

An advantage of the present invention lies in the fact that the tongues are kept in the folded position during the entire barrel phase.

Another advantage lies in the isolation of the tongues by the shoe from the propellant gases in the barrel.

Another advantage lies in the automatic deployment of the tabs in the deployed position.

• La Figure 1 est une représentation en coupe axiale d'un projectile comprenant un mode particulier de réalisation du dispositif de stabilisation selon l'invention.
• Les Figures 2, 3, 4, 5 sont des coupes de la précédente suivant respectivement les plans A-A, B-B, C-C, D-D.
• La Figure 4a montre un détail agrandi de la Figure 4.
• La Figure 6 représente la partie arrière du projectile pendant le vol.

The invention will be better understood on reading the description which follows of a particular embodiment, description made with reference to the appended drawings in which:

• Figure 1 is an axial sectional representation of a projectile comprising a particular embodiment of the stabilization device according to the invention.
• Figures 2, 3, 4, 5 are sections of the previous one respectively on the planes AA, BB, CC, DD.
• Figure 4a shows an enlarged detail of Figure 4.
• Figure 6 shows the rear part of the projectile during the flight.

FIG. 1 shows the front part and the rear part of a projectile 1 of the self-propelled type with ramjet. This projectile comprises an envelope 2, made of a light material of the composite type (for example a carbon-epoxy), and a penetrator 3 made of heavy material such as tungsten.

The penetrator 3 is arranged coaxially with the casing 2, and it is made integral by a tubular element 26, (see Figure 2), also made of carbon-epoxy, and which extends over substantially the entire length of the envelope. This element comprises an external tube 27, glued to the internal surface of the envelope, and an internal tube 28 glued to the indenter, these two tubes being connected by ribs 7, here four in number (see Figure 2), which thus delimit four chambers between the indenter and the envelope. A propellant charge 5 is placed inside the chambers. This charge is of the propellant type ablatable. An annular space 25 is provided between the propellant charge and the penetrator, this in order to allow the flow of air inside the ramjet.

The ribs have only a support function for the penetrator and they may include openings (not shown) making the chambers communicate with each other, this in order to regulate the combustion of the propellant charge 5.

The front part (or hull) 8 of the casing 2, (which is made of carbon-epoxy), is supported by four other ribs (see Figure 3), on a nose 4 secured to the front part of the indenter (by example by collage).

The nose 4 and the hull 8 define an annular opening 17 for air intake.

The particular shape of the nose 4 ending in a point 22 is designed (in a known manner) so that the shock wave coming from the point during the flight of the projectile at a supersonic speed has the effect of increasing the pressure air entering the annular opening 17.

The internal rear part of the casing 2 will constitute a nozzle 16 for ejecting the gases.

The projectile 1 carries at its rear part a shoe 6 which is made integral with the penetrator 3 by means of a connecting screw 14, a conical housing 23 ensuring correct positioning of the shoe and the penetrator. The connecting screw is dimensioned so as to break when, at the exit of the projectile from the barrel, the pressure exerted on the sabot at the level of the nozzle 16, becomes greater than that which is exerted on the back of the hoof.

The shoe 6 carries on its external cylindrical surface a belt 11, which is intended to take the scratches from the barrel of the weapon and thus to achieve the sealing and the rotation of the projectile in a completely conventional manner.

The shoe 6 is pierced with two holes 12 which make the internal part of the projectile communicate with the outside; it also carries, opposite the holes 12, ignition elements 13, which will for example include a ignition pyrotechnic composition associated with a delay composition (these compositions being of known type). Here these ignition elements are screwed into counterbores 21 having the same axis as the holes 12. The function of these elements will be specified below.

The shoe 6 carries out the rotation of the envelope by means of four dogs 24 coming to cooperate with notches 29 (see FIG. 6) having a complementary shape and produced at the rear part of the envelope 2 of the projectile.

The rear part of the envelope carries thirty tabs 9 (see Figure 4), which are made integral with the lateral surface of the envelope 2, by one of their ends, by means of screws 18. These tabs are fixed at level d 'a circular generator of the envelope and are regularly distributed on this generator.

They are likely to occupy two positions: a folded position when the projectile is in the barrel of the weapon and carries the sabot 6, and a deployed position at the exit of the barrel of the weapon after separation of the sabot and the projectile. In the deployed position, each tongue makes an angle α with the axis of the projectile. As an indication, Figure 1 shows a tongue in the folded position and a tongue in the deployed position.

The set of tongues forms a substantially conical skirt 31, the half-angle at the top of this cone being equal to α and the axis of the cone coinciding with that of the projectile. The free ends of the tongues are regularly distributed over the large base circle of this cone, a circle whose diameter is D (see Figure 6).

The tongues are held in the folded position by an internal cylindrical surface 15 of the shoe 6 (see FIG. 5), they are therefore not projecting relative to the external surface of the envelope. They do not then risk being damaged by possible contact with the barrel of the weapon during the barrel phase.

Each tongue carries two recesses 30 (see Figure 4a) whose shapes and relative arrangements are such that there is total covering of each tongue by one of its neighbors in the folded position and partial covering in the deployed position.

In addition, one tongue out of two carries a lock 10, constituted by a shouldered rod 19 capable of sliding in a radial housing 20, arranged on the envelope, until contact with a counterbore made in this housing.

Thus, in the deployed position, the tongues provided with latches are immobilized by the latter, and they immobilize themselves the tongues devoid of latches by means of the recesses 30.

It can thus be said that each tongue is immobilized in the deployed position by a locking means which is here either the bolt 10, or the recess 30 carried by the neighboring tongue.

It would have been possible to provide each tab with a lock, but the arrangement adopted here makes it possible to reduce the size of the stabilization device according to the invention.

Tabs and latches are made for example of steel and are dimensioned so as to guarantee good mechanical strength as well as the maintenance of the angular position deployed during the flight (speed of the projectile of the order of 1500 m / s, accelerations of l 34000 g).

After their release, the centrifugal inertia forces make them take their deployed position (see Figure 6). All the tongues then form an angle α of the order of 10 ° with the axis of the projectile 1. The inertial forces tending to separate them further from the lateral surface of the envelope, all the shouldered rods 19 are then in abutment in their radial housing 20, which ensures symmetry of all the tongues, (symmetry of rotation of order thirty around the axis of the projectile).

The different phases of the operation of such a projectile are as follows:

The projectile is placed in the chamber of a weapon and is fired in a conventional manner, the gas pressure exerted on the rear part of the shoe 6 pushes the projectile into the tube; the belt 11 takes the scratches, performs the seal and communicates a speed of rotation which will be of the order of 500 revolutions / second at the outlet of the barrel of the weapon. During this entire cannon phase, the pressure exerted at the rear of the shoe 6 is greater than that exerted on it at the level of the internal part of the projectile. At the outlet of the tube, it is the internal pressure which becomes preponderant, causing the rupture of the connecting screw 14. The latter will be dimensioned in such a way that this rupture occurs in the first 100 meters traveled by the projectile.

During the cannon phase, the gases could penetrate through the holes 12 inside the envelope and cause the initiation of the pyrotechnic ignition elements 13, these elements will make it possible to ignite the propellant charge 5. By playing on the characteristics of the delay composition and of the ignition composition it is possible to carry out this ignition at a completely controlled instant (preferably in the tenth of a second following the firing).

After separation of the shoe and the projectile, the tabs take their deployed position.

The inertia of such a projectile relative to its axis is of the order of 10-² kg.m² (for a caliber of 105 mm, Tungsten penetrator, carbon-epoxy casing), and it is too low to ensure gyro-stabilization (for comparison, an explosive shell of the same caliber has an inertia of the order of 0.25 kg.m²). The use of a conventional tail unit is made impossible because of the very high speed of rotation communicated by the barrel tube (of the order of 500 revolutions / second), which would cause it to break.

The thirty tongues of the stabilization device according to the invention are aerodynamically equivalent to a conical skirt disposed at the rear of the casing, the axis of the cone coinciding with the axis of the projectile. This skirt will cause a modification of the projectile drag and a decrease in absolute value of the static margin which will allow to obtain a stable trajectory.

Recall that the static margin is the distance between the center of gravity of the projectile and the focus of the aerodynamic forces acting on it.

A projectile which does not rotate will be all the more stable as the focus of the aerodynamic forces will be further from the center of gravity and behind it (large static margin, at least equal to the caliber). On the other hand, a gyro-stabilized projectile will be all the more stable as its static margin will be lower in absolute value (the focus of the aerodynamic forces being in front of the center of gravity of the projectile).

For a gyrostabilized projectile, this stability is usually assessed by means of a coefficient, called the essential stability coefficient, which depends on the speed of rotation and on the geometry of the projectile. A projectile is gyrostabilized when this coefficient is greater than 1.5.

A projectile with low longitudinal inertia (of the order of 10 -² kg / m²) and not comprising the skirt proposed by the invention cannot be gyrostabilized. Indeed, the focus of aerodynamic forces is then too far from the center of gravity.

By way of example, the projectile of FIG. 1 (105 mm caliber), without the skirt according to the invention, has its aerodynamic focus situated on the axis of the projectile and substantially at the mid-height of the hull 8, c '' is to say approximately 240 mm in front of the center of gravity of the projectile, the essential coefficient of stability is then of the order of 0.5 and the projectile is unstable.

By having a substantially conical skirt, the axis of the cone coinciding with the axis of the projectile, at the rear part of the latter, the focal point of the forces is brought closer aerodynamics of the projectile's center of gravity while keeping it in front of it and the static margin is therefore reduced in absolute value.

This skirt will be positioned so as to ensure an essential coefficient of stability greater than 1.5. In practice, it will suffice to position it so that the base circle of the cone practically coincides with the rear of the envelope.

It can thus be seen, for a 105 mm caliber projectile, that with a skirt constituted by thirty tabs the length of which is 50 mm, and making an angle with the axis of the projectile of the order of 10 °, the focus of the aerodynamic forces is approximately 20 mm in front of the center of gravity, the essential stability coefficient is then 1.6 and the projectile is gyro-stabilized.

It should be noted that, all the dimensional characteristics being equal, this projectile equipped with such a skirt and fired from a smooth tube would not be stabilized because the focus of the aerodynamic forces is located in front of the center of gravity .

In fact for there to be stability in this case it would be necessary, as has already been specified in the preamble, to have a tail unit of large dimensions which can reject the aerodynamic focus at least one gauge behind the center of gravity, penalizing solution from the point of view of congestion and which will furthermore cause an increase in the drag of the projectile, and therefore a reduction in the range.

Provided that the focus of the aerodynamic forces is located in front of the center of gravity and at a sufficiently reduced distance so that there is stability, the height of the skirt can be arbitrary, but it can however be noted that, for a value of constant angle, skirts whose height is too large will have a base diameter much greater than the diameter of the projectile which will cause an increase in drag and therefore a decrease in the range of the projectile.

In practice, the skirt will be dimensioned so that, in its deployed position, the ratio of the diameter of the projectile envelope to that of the largest base circle of the cone of the skirt (D) is not less than 70% .

Similarly, a value between 5 ° and 15 ° will be chosen for the half-angle at the top of the cone of the skirt in order to reduce the drag caused by the latter.

We thus see the main advantage of the invention which is to provide a stabilization device which makes it possible to fire a projectile of low longitudinal inertia in a striped tube.

It thus becomes possible to design a ramjet projectile comprising a penetrator made of heavy material, such as tungsten, a projectile which can be fired from a striped tube. The ramjet thus makes it possible to obtain a projectile whose range or terminal efficiency is significantly increased compared to conventional arrow type projectiles.

The device according to the invention also makes it possible to lighten the envelope which authorizes, at equal mass, the use of a heavier penetrator and further increases the terminal efficiency of the projectile.

An advantage of the embodiment described above is that it makes it possible to simplify the production of the skirt according to the invention by approximating the continuous shape by a limited number of tongues. Wind tunnel tests have shown that a number N of tongues whose dimensions are such that, in their deployed position, the free ends of the tongues cover at least 70% of the largest base circle of the cone of the skirt, gives good aerodynamic approximation of the latter in the usual conditions for firing a large caliber projectile from a rifled tube.

Other variations are also possible.

The tongues may be of a smaller number, it will be possible for example to provide four tongues having a substantially cylindrical profile so as to be able to adopt a folded position along the envelope, but having a cut such that their free end is wider than their end fixed to the envelope. There will still be an overlap of the tongues in the folded and deployed positions, the shape of the skirt obtained being substantially conical.

It is possible to provide other locking means in the deployed position for the tabs. Thus the shouldered rod 19 and the radial housing 20 may be conical, the conicity ensuring locking in the deployed position.

It is finally possible to use the stabilization device proposed by the invention with a self-propelled rocket-type projectile such as that described in patent US4573412 cited in the preamble, the invention then authorizing the firing of this projectile from a conventional striped tube.

However, the use of the stabilization device according to the invention for a ramjet-type projectile will make it possible to obtain (as noted in the preamble) the best cost-effectiveness compromise.

Claims (9)

1. Stabilisation device for a self-propelled projectile (1) with a low longitudinal moment of inertia, particularly for a projectile comprising a penetrator (3) in heavy material, such as tungsten, and a casing (2) in a lightweight material such as a composite, the said device comprising a skirt (31) whose general shape is substantially that of a truncated cone, the axis of the cone coinciding with the axis of the projectile (1), the skirt being integral with the casing (2) at the rear of the projectile, characterised by the fact that the skirt consists of a series of strips, maintained in the folded position by a retaining device while the projectile is in the gun barrel, which deploy after leaving the said barrel, the retaining device being a sabot (6) which rotates with the casing (2) and is subjected to the pressure of the gases at its rear end so as to push the projectile along the barrel, the sabot separating from the casing on leaving the gun barrel, the projectile being designed to be fired from a rifled barrel.
2. Stabilisation device according to claim 1, characterised by the fact that each strip is linked to a means of position locking consisting of a centrifugal locking pin (10) engaging in a radial recess (20) in the casing (2).
3. Stabilisation device according to claim 2, characterised by the fact that the centrifugal locking pin (10) consists of a stepped-section rod (19).
4. Stabilisation device according to any of claims 1 to 3, characterised by the fact that all the strips (9) have tongues (30) along their longitudinal edges so that they overlap where they join.
5. Stabilisation device according to any of claims 1 to 4, characterised by the fact that the sabot (6) has at least one hole (12) connecting the inside of the projectile with the outside.
6. Stabilisation device according to claim 5, characterised by the fact that the sabot (6) carries a pyrotechnic detonator (13) opposite the holes (12) and on the inside of the projectile.
7. Stabilisation device according to claim 5 or 6, characterised by the fact that the sabot (6) is joined to the projectile (1) on the penetrator (3).
8. Stabilisation device according to any of claims 1 to 7, characterised by the fact that the half-angle of the apex of the truncated cone skirt (31) is between 5° and 15° when the skirt is in the deployed position, and that the ratio of the outside diameter of the casing (2) to the diameter (D) of the largest base circle of the truncated cone skirt (31) is not less than 70%.
9. Stabilisation device according to any of claims 1 to 8, characterised by the fact that the strips (9) are attached to one end of the casing along a circular generator of the casing (2) at regular intervals, the number N and the width of the strips being such that in the deployed position their outer ends cover at least 70% of the largest base circle of the truncated cone skirt (31).

Images