FR2629584A1 - STABILIZATION DEVICE FOR LOW-LENGTH INERTIA PROJECTILE TIRED FROM A RAY-OUT TUBE - 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.

Description

The present invention relates to a stabilizing device for a

  projectile, intended to be fired from a striped tube, and having a weak moment

  of longitudinal inertia, for example an automatic projectile

  propellant comprising a penetrator of heavy material, such as tungsten, and an envelope of light material, composite type. Self-propelled projectiles have been known for some years now. Two types of self-propulsion can be distinguished: Rocket propulsion, in which the projectile carries a propellant charge, of composite solid propellant type or

  homogeneous, generating a gas pressure at its rear part.

  This first mode of self-propulsion is used for example for rockets and also in some artillery shells (see patent FR2522134), it then allows to significantly increase the range. * Ramjet propulsion uses - an ablatable or autopyrolisable solid propellant propellant charge disposed within an envelope having 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 as compressed air into the combustion chamber. The combustion of the mixture of air (oxidant) with the gas (reducer) obtained by autopyrolysis or ablation of the propellant block brings energy which is transformed.

  in propulsive force in the thrust nozzle.

  This type of self-propulsion has a number

  advantages over the rocket self-propulsion mode.

  It allows in particular (in equal range) to minimize the mass of embedded propellant, in fact the oxidant will be

  constituted by the air admitted into the combustion chamber.

  At equal performances, the pressures developed in the

  combustion chamber are lower (30 to 60 bar

  the ramjet against 70 to 250 bar for the rocket propeller), which simplifies the mechanical design

of the projectile.

  The fuel consumption of the ramjet at supersonic speeds is reduced which allows long flight times. US2989922 discloses a ramjet projectile to be fired by a gun. This projectile comprises a military load surrounded by a propulsive composition, itself arranged inside a tubular envelope carrying a belt. This projectile is gyrostabilized conventionally, the belt taking the stripes of the tube of the weapon. Such a stabilization mode is possible because of the important longitudinal moments of inertia of the

military charge and envelope.

  Modern armor can be acquired by kinetic energy projectiles (such as arrow projectiles), it would be particularly interesting to equip such projectiles self-propulsion to increase their range and their terminal efficiency while decreasing the flight time. US Pat. No. 4,537,312 shows such a projectile comprising an indenter held in an envelope of material

fiberglass type composite.

  This projectile is intended to be fired from a light tube and at reduced initial velocity. In order to limit the amount of propellant needed and thus the dimensions of the projectile, the mass of the indenter is here less than that of the penetrators of the arrow type used in artillery, it follows a decrease in perforation performance. It would be tempting to be able to fire such a projectile from an artillery gun, so the propellant charge mass could be reduced due to the high initial velocity imparted by the gun. Unfortunately, if the combination of a composite envelope and a reduced diameter indenter provides a projectile whose total mass substantially corresponds to the useful mass of the perforator, the longitudinal moment of inertia of such a projectile becomes too much. low to make it possible to gyrostabilize it (stabilization by fast rotation speed of the order of 450 revolutions / second obtained by

a shot in a striped tube).

  The stabilization mode proposed by the patent US4573412 comprises a conventional empennage including a leading edge

  is arranged opposite the output of the propellant gases, this.

  which makes it possible to give the projectile the speed of rotation reduced (of the order of a few turns per second)

  necessary for the stability of the trajectory.

  Such a projectile can not therefore be fired from an artillery weapon with a striped tube, the rotational speed that would be communicated to it would also risk

  to destroy the empennage as a result of inertia.

  Another solution for drawing a projectile with low longitudinal moment of inertia from a striped tube is to provide a slippery belt (such as that described by the patent FR8616066), the stabilization device then being constituted by a conventional empennage.

  Such a solution nevertheless has disadvantages.

  Indeed aerodynamic calculations show that the.

  stabilization of a projectile of caliber 105 mm and whose longitudinal inertia is of the order of 10-2 kg.m2 requires the presence of stabilizing fins, the total surface of all the fins being of the order of 3000 cm2 for an opening angle of 30e fins !!. Such a surface requires the design of a complex deployment device and requires to use a portion of the interior volume of the projectile to shelter fins and deployment device, this to the detriment of the total amount of propellant charge on board. Moreover, such a tail will have the effect of increasing the tratnée of the projectile and therefore of

decrease the range.

  It is the object of the invention to provide a stabilization device, compact and very simple design, which allows to shoot a projectile low longitudinal inertia, and in particular a projectile of the previous type, ie associating a penetrator in heavy material and a light envelope, from a weapon

  conventional artillery with a striped tube.

  Thus, the subject of the invention is a stabilization device for a self-propelled projectile with a low moment of longitudinal inertia and intended to be drawn by a striped tube, and in particular for a projectile comprising a penetrator made of heavy material, such as tungsten, and an envelope of light material, of composite type, characterized in that it comprises a skirt, of substantially conical general shape, the axis of the cone coinciding with the axis of the projectile, skirt integral with the envelope at the level of the rear part of the projectile and held by a connecting means in a folded position when the projectile is in the barrel of the weapon, pt unfolding at the exit

said tube.

  Preferably, the half-angle at the apex of the cone of the skirt is between 5 and 15 when the latter is in the extended position, and the ratio of the outside diameter of the envelope to the diameter of the largest base circle of the skirt.

  cone of the skirt is greater than or equal to 70%.

  According to a particular embodiment, the connecting means is constituted by a shoe rotatably connected to the envelope, this shoe holding the skirt in the folded position and the skirt is constituted by a number N of tabs, made integral with the wrapped by one of their ends at a circular generatrix of the casing and regularly distributed along this generator, the number N and the width of the tongues being such that in their deployed position the free ends of the tongues cover at least 70 % of the largest circle of

base of the cone of the skirt.

  According to other characteristics: There is a locking means in the deployed position,

each tongue.

  The shoe carries a guide belt for sealing the propellant gases in the barrel of the weapon. The shoe has at least one hole communicating the

  internal part of the projectile with the outside.

  The shoe is facing the holes and at the inner part of the projectile, a pyrotechnic ignition element. The shoe is secured to the projectile at the penetrator. Of particular interest is a self-propelled projectile of the ramjet type of the device.

stabilization device according to the invention.

  The invention will be better understood on reading the

  following description of a particular mode of

  production. Description made with reference to the attached drawings

  in which: FIG. 1 is a representation in axial section 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

  following respectively the planes A-A, B-B, C-C, D-D.

  Figure 4a shows an enlarged detail of Figure 4.

  Figure 6 shows the part. rear of the projectile during the flight. Figure 1 shows the front part and the rear part of a self-propelled projectile 1 type ramjet. This projectile comprises a casing 2 made of a light material of composite type (for example a carbon-epoxy), and a

  penetrator 3 in heavy material such as tungsten.

  The indenter 3 is disposed coaxially with the casing 2, and is made integral with it by a tubular element 26 (see FIG. 2), also made of carbon-epoxy, and which

  extends over substantially the entire length of the envelope.

  This element comprises an outer tube 27, glued on the inner surface of the envelope, and an inner tube 28 bonded to the indenter, these two tubes being connected by ribs 7, here four in number (see FIG. 2), which thus delimit four chambers between the indenter and the envelope. A propellant charge 5 is disposed within the chambers. This load is of the ablatable propellant type. An annular space 25 is provided between the propellant charge and the indenter, in order to allow

  the flow of air inside the ramjet.

  The ribs have only one support function of the penetrator and they may include openings (not shown) communicating the chambers between them, in order to regulate the combustion of the load

propulsive 5.

  The front portion (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 integral with the

  front part of the indenter, (for example by gluing).

  The nose 4 and the hull 8 define an opening

annular 17 of admission of the air.

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

  pressure of air entering the annular opening 17.

  The inner rear part of the envelope 2 will constitute

a nozzle 16 for ejecting gases.

  The projectile 1 carries at its rear portion a shoe 6 which is secured to the indenter 3 by means of a connecting screw 14, a conical housing 23 ensuring correct positioning of the shoe and the indenter. The connecting screw is dimensioned so as to break when, at the exit of the projectile of the tube of the weapon, the pressure exerted on the shoe at the level of the nozzle 16, becomes

  superior to that exercised at the back of the hoof.

  The shoe 6 carries on its outer cylindrical surface a belt 11, which is intended to come to take the scratches of the barrel of the weapon and to thereby achieve sealing and rotation of the projectile in a completely conventional manner. The shoe 6 is pierced with two holes 12 which communicate the inner part of the projectile with the outside, it also carries, facing the holes 12, ignition elements 13, which include for example a pyrotechnic ignition composition associated to one

  delay composition (these compositions-being of known type).

  Here these ignition elements are screwed into countersinks 21 having the same axis as the holes 12. The function of these elements will be specified later. The shoe 6 carries out the rotation of the casing by means of four dogs 24 cooperating with notches 29 (see FIG. 6) having a complementary shape and made at the rear part.

of the shell 2 of the projectile.

  The rear portion of the envelope carries thirty tabs 9 (see Figure 4), which are secured to the side surface of the casing 2, by one of their ends, by means of screws 18. These tabs are fixed at the level of '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 shoe 6, and a deployed position at the exit of the barrel of the weapon after disconnection of the shoe and the projectile. In the deployed position each tongue makes with the axis of the projectile an angle a. As an indication, FIG. 1 shows a tongue in the folded position and a

tongue in the deployed position.

  The set of tabs forms a substantially conical skirt 31, the half-angle at the apex of this cone being equal to a 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, circle

  whose diameter is D (see Figure 6).

  The tongues are held in the folded position by an inner cylindrical surface 15 of the shoe 6 (see figure), they are not protruding relative to the outer surface of the envelope. They are not likely to be damaged by a possible contact with the tube of

the weapon during the gun phase.

  Each tongue has two recesses 30 (see Figure 4a) whose shapes and relative provisions are such that there is a partial overlap of each tongue by one of its neighbors, and that as well in the folded position in the deployed position. In addition, one tongue out of two carries a latch 10, constituted by a shoulder pin 19 adapted to slide in a radial housing 20, arranged on the envelope, up to

  contact with a countersink made in this housing.

  Thus in the deployed position the tongues provided with locks are immobilized by the latter, and they themselves immobilize the tongues without locks

  through the recesses 30.

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

neighboring tongue.

  It would have been possible to provide each tongue with a lock, but the arrangement adopted here makes it possible to reduce the size of the stabilization device according to the invention. Tongues and bolts are made for example of steel and are dimensioned so as to ensure good mechanical strength and the maintenance of the angular position deployed during the flight (speed of the projectile of the order

  1500 m / s, accelerations of the order of 34000 g).

  After their release, centrifugal forces of inertia

  make them take their deployed position (see Figure 6).

  All the tongues then make with the axis of the projectile 1 an angle has of the order of 10 '. * As the inertial forces tend to move them further away from the lateral surface of the casing, all the shouldered rods 19 then abut in their radial housing 20, which ensures symmetry of all the tabs, (symmetry of

  order 30 rotation 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 sabot 6 grows. the projectile in the tube, the belt 11 takes the scratches, realizes the seal and communicates a rotational speed which will be of the order of 500 revolutions / second at the exit of the tube of the weapon. During all this gun phase, the pressure exerted on the back of the shoe 6 is greater than that exerted on it at the inner part of the projectile. At the exit of the tube, it is the internal pressure which becomes predominant, causing the rupture of the connecting screw 14. It will be dimensioned in such a way that this rupture occurs in the first 100

  meters traveled by the projectile.

  During the barrel phase the gases could penetrate through the holes 12 inside the casing and cause the initiation of the pyrotechnic ignition elements 13, these elements will make it possible to ignite the charge

  propulsive 5. By playing on the characteristics of the-

  delay composition and ignition composition it is

  possible to achieve this ignition at a time totally.

  controlled (preferably in the next tenth of a second

the shot).

  After the separation of the hoof and the projectile, the

  tongues take their deployed position.

  The inertia of such a projectile relative to its axis is of the order of 102 kg.m2 (for a caliber of 105 mm, Tungsten penetrator, carbon-epoxy envelope), and it is too weak to ensure a gyrostabilization (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 empennage is made impossible because of the very high speed of rotation communicated by the tube of the barrel (of

  the order of 500 revolutions / second), which would cause its break.

  The thirty tabs of the stabilization device according to the invention are aerodynamically equivalent to a conical skirt disposed at the rear of the envelope, 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 make it possible to obtain a trajectory

stable.

  Remember that the static margin is the distance between

  the center of gravity of the projectile and the focus of the

  aerodynamics acting on it.

  A projectile that does not rotate will be all the more stable as the focus of the aerodynamic forces will be further away from the center of gravity and behind it (significant static margin, at least equal to the caliber). On the other hand, a gyrostabilized projectile will be all the more stable as its static margin will be smaller 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 appreciated by means of a coefficient, said coefficient of essential stability, which depends on the speed of rotation and 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 including the skirt proposed by the invention can not be gyro-stabilized. Indeed, the focus of the aerodynamic forces is then too far from the

center of gravity.

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

0.5 and the projectile is unstable.

  By arranging a substantially conical skirt, the axis of the cone coinciding with the axis of the projectile, at the rear part of the latter, the focus is brought closer to the aerodynamic forces of the center of gravity of the projectile while maintaining it in front of it. here and we reduce the margin

static in absolute value.

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

the back of the envelope.

  Thus, for a projectile of caliber 105 mm, with a skirt constituted by thirty tongues whose length is 50 mm, and making with the axis of the projectile an angle of the order of 10, the focus of the forces aerodynamics is approximately 20 mm forward of the center of gravity, the essential stability coefficient is

  then 1.6 and the projectile is gyrostabilized.

  It should be noted that, all the dimensional characteristics being equal, this projectile equipped with such a skirt and pulled from a smooth tube would not be stabilized because the focus of the aerodynamic forces

  is in front of the center of gravity.

  In fact for there to be stability in this case it would be necessary, as already stated in the preamble, to have an empennage of large dimensions that can reject the aerodynamic focus at least one caliber behind the center of gravity, penalizing solution from the clutter point of view and which in addition will cause an increase in the projectile drag, and therefore a

decrease in scope.

  Provided that the focus of the aerodynamic forces is in front of the center of gravity and at a sufficiently small distance for stability, the height of the skirt may be arbitrary, but it may be noted that for a value of constant angle, skirts whose height is too high will have a base diameter much greater than the diameter of the projectile-which will cause an increase in the drag and therefore a decrease in the

scope of the projectile.

  Conveniently, the skirt will be dimensioned such that, in its deployed position, the ratio of the diameter of the shell of the projectile to that of the largest circle of

  base of the cone of the skirt (D) is not less than 70%.

  Similarly, a value between 5 'and - for the half-angle at the top of the cone of the skirt will be chosen in order to

  reduce the drag caused by this last.

  This shows the main advantage of the invention, which is to provide a stabilization device that makes it possible to fire a projectile of low inertia.

longitudinal 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 that can be fired from a striped tube. The ramjet thus makes it possible to obtain a projectile whose range or terminal efficiency is notably increased compared to projectiles of the type

conventional arrow.

  The device according to the invention also makes it possible to lighten the envelope, which makes it possible, for an equal mass, to use a heavier indenter and increases even further.

  the terminal efficiency of the projectile.

  An advantage of the embodiment described above is that it simplifies the production of the skirt according to the invention by discretizing it. The conical shape is thus approximated by a set of tongues. Wind tunnel tests have shown that a number N of tabs 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 a good aerodynamic approximation of this-last under the usual firing conditions of a

  large caliber projectile from a striped tube.

  Other variants are also possible.

  The tongues may be smaller in number, it will be possible for example to provide four tabs having a substantially cylindrical profile so as to adopt a folded position along the envelope, but having a cut such that their free end is wider that their end attached to the envelope. There will still be overlap of the tongues in the folded and unfolded 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 stem 19 and the radial housing 20 may be conical, the conicity ensuring the locking in position

dépioyée.

  Finally, it is possible to use the stabilization device proposed by the invention with a rocket type self-propelled projectile such as that described in US Pat. No. 4,537,312 cited in the preamble, the invention then allowing this projectile to be fired from a conventional striped tube. But the use of the stabilization device according to the invention for a ramjet type projectile will make it possible to obtain (as noted in FIG.

  preamble), the best cost-effectiveness compromise.

Claims (8)

  1-Stabilization device for a projectile (1) self-propelled with a low longitudinal moment of inertia and intended to be pulled by a striped tube, and in particular for a projectile comprising a penetrator (3) of heavy material, such as tungsten, and an envelope (2) of light material, of composite type, characterized in that it comprises a skirt (31) of generally conical general shape, the axis of the cone coinciding with the axis of the projectile (1), skirt secured to the casing (2) at the rear part of the projectile and held by a connecting means in a folded position when the projectile is in the barrel of the weapon, and deploying at the outlet of said tube.  2-stabilizing device according to claim 1, characterized in that the half-angle at the top of the cone of the skirt is between 5 and 15 when the latter is in the deployed position, and in that the ratio of the outside diameter of the casing (2) on the diameter (D) of the largest base circle of the cone of the skirt (31) is greater or equal to 70%.   3-Stabilizing device according to one of the   1 or 2, characterized in that the connecting means   is constituted by a shoe (6) rotatably connected to the enve-   loppe (2), this shoe now the skirt in the folded position.   4-stabilization device according to one of the   cations 1 to 3, characterized in that the skirt is constituted by a number N of tabs (9), made integral with the casing (2) by one of their ends at a circular generatrix of the envelope and regularly distributed along this generator, the number N and the width of the tongues being 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 (31).   -Stabilization device according to claim 4, characterized in that it comprises a locking means in   deployed position of each tongue.   6-stabilization device according to one of the   cations 3 to 5, characterized in that the shoe (6) bears a   guide belt (11) intended to come to realize.   Sealing propulsive gases in the barrel of the weapon.   7-stabilization device according to one of the claims   3 to 6, characterized in that the shoe (6) carries at least one hole (12) communicating the inner part of the projectile with the outside.   8-Stabilizing device according to claim 7, characterized in that the shoe (6) bears against holes (12) and at the inner part of the projectile, a   - pyrotechnic ignition element (13).   9-stabilization device according to one of the claims   cations 3 to 8, characterized in that the shoe (6) is rendered   secured to the projectile (1) at the penetrator (3).   Self-propelled projectile of the type equipped ramjet   of a stabilizing device according to one of the cations 1 to 9.