1 EXTENDABLE LIFTING TAIL DEVICE FOR SHELL The present invention relates to a deployable lift-generating tail assembly device for artillery rounds. At the present time, most tail assemblies do not generate lift but perform a stabilizing function. Most present-day solutions are in the form of folding fins in the form of shell sections that espouse the external cylindrical shape of the shell case. The space taken up by these known devices is small, but this shape of fin is not at all conducive to gliding and, what is more, their deployment is restricted by the caliber of the round. A subject of the present invention is a deployable lift-generating tail assembly device for artillery rounds that can increase the length of the gliding flight of the round on its trajectory. The tail assembly device according to the invention is characterized in that it comprises a tail assembly with one or more pairs of fins (a condition necessary in order to have a good gliding wing structure), each fin comprising at least two flat leaves, that are folded at the start of the shot and protected by a cup, these fins becoming deployed during flight, once the cup has been discarded, through the effect of the spinning of the round, their leaves then becoming coplanar. The present invention will be better understood from reading the detailed description of one embodiment, taken by way of nonlimiting example and illustrated by the attached drawing, in which: - figure 1 is a perspective view of a cup of a shell with cutaway showing part of the folded tail assembly of the invention, - figure 2 is a perspective view of the folded tail assembly of figure 1, with the cup removed, - figures 3 and 4 are other perspective views showing the folded fins of the invention from different angles, - figure 5 is a perspective view of one exemplary embodiment of an unfolded fin of the device of the invention, and - figure 6 is a perspective view of the fin of figure 5 deployed and 2 fixed to the shell. The present invention is described hereinbelow with reference to a shell fitted with a tail assembly consisting of four folding fins each having two flat leaves, but it can of course be applied to other types of artillery round and is not restricted to the embodiment in which there are four folding fins each comprising two flat leaves, and may comprise a different number of fins, and the fins may comprise more than two flat leaves. The case of the shell 1, on which only the posterior end 2 has been depicted in the drawing, is extended by a spar 3 which supports the cup 10. The spar 3 is connected to the end 2 of the case of the shell by a substantially flat ring-shaped wall 4, and this central spar supports the flange 3a. A tail assembly 5 with four identical deployable fins 6 to 9 is fixed to the wall 4 and the flange 3A and is capped, before the shell is fired, with a cylindrical cup 10 the outside diameter of which is substantially equal to that of the case 2. The fins 6 to 9 are each made up of two flat leaves in the overall shape of rectangular parallelepipeds of slender thickness (a few millimeters), respectively referenced 6A and 6B to 9A and 9B. The "plane" of these leaves will hereinafter be the name given to the plane parallel to their large faces and passing through their center. Leaves 6A to 9A (here known as "supporting leaves") are articulated by one of their short sides to respective pivot axles 6C to 9C, these axles being fixed by one of their ends to the wall 4 and the flange 3A, parallel to the longitudinal axis of the shell, and uniformly spaced (arranged 900 apart) on a common circle centered on the longitudinal axis of the shell and situated between the central spar and the inside diameter of the shell cup. A plate 3A is fixed to the other end of the axles 6C to 9C, perpendicular to the longitudinal axis of the spar 3. The length of the leaves 6A to 9A, measured at right angles to their corresponding pivot axle, is greater than the distance separating two successive pivot axles. The rotation of the leaves 6A to 9A about their respective pivot axles is limited to approximately 270' by means which have not been depicted in the drawing. The first extreme position in terms of rotation that these leaves can occupy, and which is known here as the "rest position" of the fins 6 to 9 (see figures 1, 3 and 4) is a position in which each of them is in contact with the articulated end of the next leaf (considered in the clockwise direction in this instance, with the shell viewed from the rear), this first extreme position being the position in which the fins 6 to 9 3 can be capped with their protective cup, which prevents any movement of the leaves when in position. The tail assembly 5 thus folded into the rest position forms a polyhedron of which the outline, considered in a plane perpendicular to the longitudinal axis of the shell, is approximately square. Of course, if each of the four fins comprises more than two leaves, their length and the way in which they are folded are such that said contour remains a square. Of course likewise, if the tail assembly comprises more than four fins, said contour of the polygon comprises a corresponding number of sides. The second extreme position in terms of rotation of these leaves 6A to 9A (see figure 6) is the position in which their plane coincides with a radius passing through the longitudinal axis of the spar 3 and through the corresponding pivot axle (6C to 9C). It will be noted that, in figure 2, fin 6 is slightly shifted from its rest position. The leaves 6B to 9B (here referred to as "end leaves") are articulated to the respective ends of the supporting leaves 6A to 9A which are the opposite ends to those which are articulated the axles 6C to 9C. The rotation of the end leaves, once the fins 6 to 9 have been mounted on the pivot axles 6C to 9C, is limited to about 900. The first extreme position in terms of rotation of the end leaves, as depicted in figures 1, 3 and 4, and corresponding to the aforementioned rest position, is the one in which these end leaves are substantially perpendicular to the respective supporting leaves and are practically parallel to the next supporting leaves (the leaf 6B is practically parallel to the leaf 7A, and so on) and in fact, each end leaf then rests against the articulated tubular end of the next supporting leaf, the length of the supporting leaves being determined accordingly. The second extreme position in terms of rotation of the end leaves 6B to 9B (see figures 5 and 6) is the position in which they are in the extension of the corresponding supporting leaves, thus in each instance forming a flat straight fin. This second extreme position of the end leaves is determined by end stops 6E to 9E, of which there are two in the present example, and which are formed on their articulated ends and rest against the end of the corresponding supporting leaf. Of course, if the fins comprise more than two leaves, each of the leaves other than the supporting leaf comprises such end stops which rest against the corresponding supporting leaf (preceding leaf). Advantageously, the articulations of the end leaves and the supporting leaves each comprise a non-return device 6E, not depicted on the supporting leaves, locking each of the leaves in the deployed position.
4 The fins described hereinabove deploy as follows. The shell 1 is fired with the cup 10 capping the folded fins 5, as depicted in figure 1. The shell is fired in such as way as to impart to it a rotational movement about its longitudinal axis (a rolling movement). After a defined length of time, the cup 10 which was capping the fins is discarded, causing the fins to deploy simply under the effect of spinning of the shell and the leaves catching the wind. The direction in which the fins are folded is, of course, such, that the spinning of the shell forces them to unfold: thus for the example depicted in the drawing, the rotation of the shell, as viewed from the rear, is in the clockwise direction. In conclusion, the solution of the invention allows the opening of true aerodynamically lift-generating fins of straight shapes needed for optimal gliding flight of the round. These fins are folded in the cup of the round into two or more leaves, while at the same time taking up a minimal amount of space compatible with the diameter of the round, the cup being discardable during flight. They deploy under the effect of the spinning of the round. Deployment of the fins is halted by the end stops situated on the axle at the base of the fins with the possibility of some non-return device. The invention thus makes it possible to have substantial fin deployment.