Abstract:
A sabot for a projectile comprising at least two segments intended to surround and drive a sub-caliber penetrator, such sabot comprising a calibered thrust plate, wherein said sabot incorporates a body made of a light material, said body having at least one longitudinal insert made of a material having high mechanical properties, said insert having indentations cooperating with an external profile of said penetrator to allow it to be driven, said indentations extending those of said sabot body and which thus also cooperate with the external profile of said penetrator.

Description:
FIELD OF INVENTION 
   1) Field of Invention 
   The technical scope of the invention is that of sabots for sub-calibre projectiles. 
   2) Description of the Related Art 
   In a known manner, sub-calibre projectiles comprise a sub-calibre penetrator held by a calibred sabot. The sabot is formed of several segments (at least two and generally three) and releases the penetrator upon exiting the weapon. The sabot generally has a sealing band that is positioned in a groove arranged on one part of the calibred sabot, a part usually called the thrust plate since is it here that the pressure of the propellant gases is exerted. 
   The sabot allows the velocity of the sub-calibre penetrator to be increased. However, it constitutes a dead weight that consumes part of the available kinetic energy and it is thus desirable to reduce the mass of the sabot in order to improve the velocity, and consequently, the performances of the penetrator. 
   Furthermore, present day sub-calibre munitions have longer and longer penetrators so as to improve the piercing performances upon impact on a target. 
   Such penetrators have substantial longitudinal and transversal inertias and must be firmly held in place during firing by the front and rear parts of the sabot. 
   However, reinforcing these parts, for example by ribbing, makes the sabot heavier and thus causes the penetrator to lose velocity. 
   By way of example, patents U.S. Pat. No. 5,103,735 and U.S. Pat. No. 5,359,938 describe a sabot having ribbing that improves its transversal rigidity. 
   To make the sabot lighter, it is also proposed to use a composite material in its manufacture. Patent GB2251676 describes, for example, a sabot whose segments are constituted by laminated elements made of oriented fiber composite materials. 
   This solution is, however, costly to implement. 
   The aim of this invention is to propose a sabot that overcomes such drawbacks. 
   Thus, the sabot according to the invention has been made lighter whilst providing mechanical performances adapted to the firing constraints of a highly elongated penetrator (L/D&gt;30). 
   This sabot is, in addition, easy to manufacture and relatively inexpensive with respect to a sabot made entirely of composite material, for example. 
   SUMMARY OF THE INVENTION 
   Thus, the invention relates to a sabot for a projectile comprising at least two segments intended to surround and drive a sub-calibre penetrator, such sabot comprising a calibred thrust plate and wherein it incorporates a body made of a light material, such body having at least one longitudinal insert made of a material having high mechanical properties, such insert having indentations cooperating with an external profile of the penetrator to allow it to be driven, such indentations extending those of the body of the sabot and which thus also cooperate with the external profile of the penetrator. 
   The material of the insert or inserts will preferably have a longitudinal modulus of elasticity that is greater than or equal to 100 Giga Pascals and an elastic limit greater than of equal to 900 Mega Pascals. 
   The material of the insert or inserts may thus be selected from among the following materials: titanium or titanium alloy, steel, composite material. 
   According to one characteristic of the invention, the insert will be thinner at the thrust plate than on either side of it. 
   Each insert may extend on either side of the thrust plate, the body comprising at least two bearing surfaces level with the thrust plate for the insert, such surfaces arranged on either side of the thrust plate. 
   According to a first embodiment, the body of each segment may incorporate a longitudinal recess made in its plane of symmetry and intended to receive an insert. 
   The recess may pass radially through the body of the segment on either side of the thrust plate. 
   The insert may be made integral with the segment body by at least two screws arranged near to the front and rear ends of the insert. 
   According to a second embodiment, the body of each segment may incorporate at least two longitudinal recesses each made at a joint face intended to come into contact with another segment when the sabot is assembled, the inserts being thus positioned at the inter-segment joint faces of the sabot. 
   Each recess may thus incorporate a profile that cooperates with a matching profile carried by the insert. 
   According to one variant, each joint face may have two recesses: one placed to the fore of the thrust plate and the other to its rear, each recess being intended to receive a specific insert. 
   Alternatively, the recesses arranged in the body of each segment may extend on either side of the thrust plate, the body comprising at least two bearing surfaces for the insert at the thrust plate, such surfaces being arranged on either side of the thrust plate. 
   Each insert may be made integral with a segment body by at least one screw arranged at the thrust plate part of the segment in question. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more apparent from the following description of the different embodiments, such description being made with reference to the appended drawings, in which: 
       FIG. 1  shows a longitudinal section view of a sub-calibre projectile equipped with a sabot according to a first embodiment of the invention, 
       FIGS. 2   a  and  2   b  are two views of the same sabot according to the first embodiment, views in which the penetrator has been removed, view  2   a  being a section view and view  2   b  being a non-sectioned view. 
       FIGS. 3   a  and  3   b  are cross sections of this sabot, such sections being made along the planes references respectively AA, BB and CC in  FIG. 2   a,    
       FIGS. 4   a  and  4   b  are two views of a sabot according to a second embodiment, views in which the penetrator has been removed, view  4   a  being a longitudinal section and view  4   b  being a non-sectioned view. 
       FIG. 4   c  is a detailed view of the link being the insert and a sabot segment, 
       FIGS. 5   a  and  5   b  are cross sections of this sabot, sections made along the planes reference respectively DD and EE in  FIG. 4   a.    
       FIGS. 6   a  and  6   b  show a variant of the sabot according to this second embodiment, view  6   a  being a longitudinal section and view  6   b  being a non-sectioned view. 
       FIGS. 7   a  and  7   b  show a variant of the sabot according to this second embodiment, view  7   a  being a longitudinal section and view  7   b  being a non-sectioned view. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   With reference to  FIG. 1 , a sub-calibre projectile  1  (or discarding-sabot projectile) comprises a sabot  2  surrounding a penetrator  3  fitted with a tailpiece  4 . This projectile  1  is intended to be fastened to a combustible case, not shown. 
   The sabot classically comprises three segments  2   a ,  2   b ,  2   c  that are made integral with one another by a band  5 , which also ensures the sealing against the propellant gases within the gun barrel (not shown), and by two retaining rings  12  and  13 , one at the front and the other at the rear of the sabot (such rings being optional). 
   The segments are in contact with one another at their joint faces. The penetrator has threading (or grooves) that cooperate with matching threading (or grooves) on the sabot. Such an arrangement ensures that the penetrator is driven in translation by the sabot. 
   A silicon seal  6  is placed between the band  5  and the rear part of the sabot  2 . 
   Classically, the sabot  2  incorporates a calibred thrust plate  7  arranged substantially level with the penetrator&#39;s  3  center of gravity. The sabot is prolonged on either side of the thrust plate  7  by a rear part  8  and a front part  9 . The diameter of the front  9  and rear  8  parts decreases regularly between the thrust plate  7  and the front or rear end of the sabot  2 . 
   The front part  9  of the sabot has calibred arms  10  evenly spaced angularly. There is one arm per segment, therefore here there are three arms for the sabot. 
   These arms form a seat ensuring the guidance of the front part of the sabot inside the gun barrel. 
   In accordance with the invention, the sabot comprises a body made of a light material, for example an aluminum alloy, such body incorporating at least one longitudinal insert  11  made of a material having high mechanical properties. 
   By light material, we mean a material having a density of less than 3. The segment body will preferably be made of an aluminum alloy, or perhaps a composite material. 
   By material having high mechanical properties, we mean a material having a longitudinal modulus of elasticity greater than or equal to 100 Giga Pascals and an upper elastic limit greater than or equal to 900 Mega Pascals. 
   These mechanical performances are well over those of aluminum. The following may, for example, be selected as the material for the inserts: titanium or a titanium alloy, high performance steel (for example, maraging steel) or a composite material (for example, a material based on oriented carbon fibers). 
     FIGS. 2   a ,  2   b  show the sabot  2  without the penetrator  3 , the band  5  and rings  12  and  13 . 
   In accordance with this first embodiment of the invention, each segment  2   a ,  2   b  or  2   c  of the sabot incorporates a longitudinal recess  14  made in its plane of symmetry  15   a ,  15   b  or  15   c  and which is intended to receive an insert  11  (see more specifically  FIGS. 3   a ,  3   b  and  3   c ). 
   The recess  14  passes through the segment body on either side of the thrust plate  7  (see  FIGS. 2   a ,  2   b  and section  3   b ). Such an arrangement facilitates the machining of the recess  14  of the sabot. 
   Each insert  11  is in contact with the penetrator  3  and incorporates indentations (not shown, for example, threading or circular grooves) that cooperate with an external profile of the penetrator  3  to allow it to be driven. 
   The body  2  of the sabot also has analogous indentations (not shown) that prolong those in the inserts  11  and which cooperate with the external profile of the penetrator. 
   In practical terms, each insert  11  will be made integral with its sabot segment (here by means of screws  16  placed at each end of the insert). The indentations will then be made in a single simultaneous machining operation of the body of the sabot  2  and the inserts  11 . The perfect continuity of the indentations is thus ensured between the different materials, thereby facilitating the assembly of the penetrator  3 . 
   The front and rear ends of each insert incorporate tabs  28  housed in matching depressions made in the sabot body. These tabs carry the female threading receiving the fastening screw  16  and ensure the radial retention of the insert with respect to the sabot. 
   The hybrid sabot according to the invention is thus formed of the assembling of an aluminum body (light material but with low mechanical properties) with inserts of a generally denser material (titanium or steel) but with high mechanical properties. 
   The materials are distributed in the sabot in correlation with the mechanical stresses to which they are to be subjected. 
   The most mechanically stressed zones of the sabot are the front  9  and rear  8  median zones since they must withstand substantial longitudinal and transversal inertial loads generated by the penetrator  3 . The thickness of these zones in reduced and the insert material predominates in these zones. 
   The thrust plate  7  is less mechanically stressed. It is thus unnecessary to implement a material that has high mechanical strength at the thrust plate. The material must, however, be light since the sabot is voluminous at this point. 
   The material of the sabot body will thus be predominant at the thrust plate. 
   As may be more particularly seen in the sections ( FIGS. 3   b  and  3   c ) the insert is thus thinner at the thrust plate  7  ( FIG. 3   c ) than on either side of it ( FIG. 3   b ). Such an arrangement also allows the aluminum surface (sabot body), which is in contact with the penetrator at the thrust plate  7 , to be increased. Resistance to shearing of the sabot body  2  in the zone of the sabot where the shearing stresses are the strongest is thus improved. 
   Furthermore, at the thrust plate  7 , the sabot body  2  comprises two bearing surfaces  17  and  18  for the insert. These surfaces are positioned on either side of the thrust plate  7 . The front  18  and rear  17  bearing surfaces ensure that the front and rear parts of the insert  11 , to which the inertial loads of the penetrator are applied, are driven by the sabot body  2 . 
   Bearing surfaces  17  and  18  are plane and inclined with respect to the sabot axis  19 . 
   The insert  11  is of a length selected such that it only covers the most mechanically stressed front and rear parts. It is thus pointless to prolong the insert to the front and rear ends of the sabot, which are less mechanically stressed than the median parts of these front  9  and rear  8  parts. 
   Thus, as may be seen in  FIG. 2   b , the rear length L R  of the insert  11  between the rear bearing surface  17  and its rear end is between 50% and 70% of the length L 1  of all the rear part  8  of the sabot (length between the rear bearing surface  17  and the rear end of the sabot). 
   Similarly, the front length L F  of the insert  11  between the bearing surface  18  and its front end is between 40% and 70% of the length L 2  of the front part  9  of the sabot (length between the front bearing surface  18  and the front end of the sabot). 
   The sabot according to the invention thus has a mass of 20 to 30% less than homogenous sabots made of aluminum, whilst having adequate mechanical strength. 
   This results in an increase in the velocity of the penetrator of around 5% to 8%, thus an increase in its performances. 
   A second embodiment is shown in  FIGS. 4   a ,  4   b ,  4   c ,  5   a  and  5   b.    
   For the sake of clarity, the sabot is shown on the Figures alone, without the penetrator, the band and the retention rings. 
   This embodiment differs from the previous one in that the inserts  11  are placed at the joint faces  20   a ,  20   b  and  20   c  that separate the different segments  2   a ,  2   b  and  2   c.    
   Furthermore, and classically, this sabot incorporates a calibred conical part  21  at its front part and in place of the arms  10 . 
   This conical part incorporates a front pocket  22  intended to receive the external aerodynamic drag upon exiting the gun barrel so as to facilitate the opening of the sabot. 
   So as to receive the inserts, the body of each segment  2   a ,  2   b  and  2   c  incorporates two longitudinal recesses  23  each made in a joint face ( 20   a ,  20   b  or  20   c ). These recesses  23  can be more particularly seen in  FIGS. 5   a  and  5   b.    
   The recesses  23  extend on either side of the thrust plate  7 . 
   Once again, the sabot body  2  comprises at least two bearing surfaces  17  and  18  at the thrust plate  7  for the insert  11 . These bearing surfaces are arranged on either side on the thrust plate  7 . 
   Each insert  11  is made integral with a single sabot segment by a screw  24  placed level with the thrust plate  7  of the segment in question. 
   This screw is housed in a counter-sink  25  in the insert  11  such that does not hinder the assembly of the segments (see  FIG. 4   c ). 
   The shaft of the screw  24  is perpendicular to the joint face  20  in question, in which a threaded bore is made to receive the screw. 
   Once again, the front and rear ends of each insert incorporate tabs  28  housed in matching depressions in the sabot body. These tabs ensure the radial retention of the insert with respect to the sabot. 
     FIGS. 6   a  and  6   b  show a variant of this second embodiment. 
     FIG. 6   a  shows two inserts  11  that are not sectioned. 
   In accordance with this variant, each recess  23  has a profile  26 , formed here by a succession of teeth oriented perpendicularly to the sabot axis  19 . This toothed profile  26  cooperates with a matching profile  27  on the insert  11 . 
   Such an arrangement allows the loads between the sabot body  2  and the insert  11  to be distributed over a larger surface. It also prevents any relative axial movement of the inserts with respect to the sabot segments during firing. 
   Once again, the inserts  11  extend on either side of the thrust plate  7  and the body  2  comprises two bearing surface  17  and  18  at the thrust plate  7  for the insert. Each insert is fastened to a sabot segment by a screw  24 . The front and rear ends of the inserts incorporate tabs  28  that are housed in matching depressions in the sabot body and that ensure the radial retention of the insert with respect to the sabot. 
     FIGS. 7   a  and  7   b  show another variant of this embodiment. 
   This variant differs from the previous one in that each joint face  20   a ,  20   b  and  20   c  has two recesses  23   a  and  23   b . Recess  23   a  is arranged to the fore of the thrust plate  7  and recess  23   b  is arranged to the rear of the thrust plate. 
   Each recess  23   a  or  23   b  receives a specific insert  11   a  or  11   b.    
   Once again, each recess has a profile  26  that cooperates with a matching profile  27  on the insert. 
   The profiles are formed by a succession of teeth oriented perpendicularly to the sabot axis  19 . 
   These profiles ensure the transmission of the inertial load of the penetrator between the insert and the sabot body. 
   The front and rear ends of each insert incorporate tabs  28  housed in matching depressions in the sabot body and that ensure the radial retention of the insert with respect to the sabot. 
   In this variant, there is no insert at the thrust plate, the sabot&#39;s mass is thus reduced. 
   Each insert is fastened to a sabot segment, for example by bonding.