GB2091856A

GB2091856A - Training projectile

Info

Publication number: GB2091856A
Application number: GB8201428A
Authority: GB
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1981-01-23
Filing date: 1982-01-19
Publication date: 1982-08-04
Also published as: FR2498749B1; NO150095B; NL8200213A; IT1149306B; SE8100385L; ES271926Y; NO820195L; IN157560B; IL64791A; NO150095C; IT8247608A0; CA1192443A; GB2091856B; SE442445B; BE891866A; CH656218A5; ES271926U; FR2498749A1; DE3201629A1; DE3201629C2

Abstract

A training projectile which is stabilized by its own rotation during flight is described and comprises a conical nose section (1), a cylindrical intermediate portion (2) and a tail section. The projectile is provided with aerodynamic surfaces in the form of fins (4) or grooves (8) (not shown) on the cylindrical intermediate portion (2). The fins and grooves, respectively, extend substantially radial and parallel to the symmetrical axis (5) of the projectile. The arrangement of said fins or grooves imparts a braking effect on the projectile to reduce its rotational velocity after launching so that the projectile at a specific, critical rotational speed becomes unstable and tips or tilts. This means a substantial increase of air resistance and a corresponding reduction of the projectile velocity forwards. By an appropriate adjustment of the fins (4) and grooves (8) respectively, it is possible to locate the instability just behind the target distance when training. The ballistic properties of the training projectile are maintained up to the target distance but the maximum firing range is reduced compared with the normal live ammunition. <IMAGE>

Description

SPECIFICATION Training projectile This invention relates to a training projectile which is stabilized by its own rotational velocity during flight For military training purposes, normal live ammunition is commonly replaced by specific training ammunition for economic reasons. Such training ammunition is often of more simple design than normal live ammunition in order to reduce the firing costs. In order to enable military personnel to be trained under substantially normal firing conditions, it is important that the ballistic properties of the training ammunition substantially correspond to those of the live ammunition it replaces. As a result, the maximum firing range of the training ammunition then corresponds to the maximum firing range of the live ammunition in question.This also means, however, that military training sessions using the training ammunition must take place on the few very large proving grounds and that comparatively large areas must be closed in order to allow firing to take place.

As a consequencea new type of training projectile has recently been proposed which, up to a predetermined firing distanc, has substantially the same ballistic properties as the live ammunition in question, but which has a substantially reduced maximum firing range compared with normal live ammunition. The advantage of using this type of training ammunition is that such ammunition allows realistic military training sessions to be held on substantially smaller proving grounds than previously.

One example of such a training projectile is described in the Specification of German Patent No.

1678 197, the training projectile being formed with a number of channels on its nose section which channels are made in such a way that an air stream is formed in the channels and gives the projectile an impulse in a direction opposite to its direction of rotation. In one alternative embodiment, these channels may be replaced by a number of shovels but also in this case it is the axial air stream which is utilized to impart to the projectile an impulse in a direction which is opposite to the direction of rotation of the projectile.

By forming the projectile with such means for deflecting the axial air stream, it is then possible to reduce the rotational velocity of the projectile so much that finally a critical value for the rotational velocity is reached where the projectile is no longer stable in its trajectory but tips or tilts. When this happens the air resistance is increased considerably with the result that the firing range is reduced.

One disadvantage with this type of projectile is that the deflecting channels as well as the shovels make the projectile comparatively complicated and expensive. Furthermore, it is difficult to modify the projectile for different firing distances. By making such arrangements in the front section of the projectile there is also a risk that the ballistic properties of the projectile even up to the actual firing distance are changed.

According to the present invention there is provided a training projectile which is stabilized by its own rotation during flight, wherein the projectile comprises a conical nose section, a cylindrical intermediate portion and a tail section, and wherein the projectile is provided with braking means for reducing the rotational velocity of the projectile after launching, the braking means comprising a plurality of aerodynamic surfaces located on the cylindrical intermediate portion and extending radially of and parallel to the symmetrical axis of the projectile.

The present training projectile is simple to manufacture and can be modified for different firing distances.

In the present projectile, the aerodynamic surfaces may be made in the form of fins, which is appropriate for a sub-calibre projectile, or formed by grooves or notches made directly in the cylindrical surface, for instance in case of a full-calibre projectile. A common feature of both types ofsurface is that the air resistance is increased in the direction of rotation which means that the rotational velocity of the projectile is reduced after launching. At a specific rotational speed the projectile becomes unstable and tips. By adjusting the location, size and/or number of the aerodynamic surfaces it is possible to make this critical speed occur at a specific distance from the launch, preferably just behind the targer distance for the practice firing.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of Example some embodi mentsthereof, and in which Figures la, lb and ic show three different training projectiles with aerodynamic surfaces in the form of fins, and Figure 2 shows an alternative embodiment in which the aerodynamic surfaces are formed by grooves.

The body of the projectile shown in the drawings is an example of an appropriate projectile design and is basically identical for the different embodiments. The projectile comprises a conical nose section 1, a cylindrical intermediate portion ("waist") 2 and a tail section 3. In this case the projectile is intended to be launched by means of a separate propellant charge (not shown) and is therefore provided with a tail section with grooves for the charge. For a full-calibre projectile the tail section may have another design.

Four fins 4 are distributed symmetrically over the periphery of the cylindrical intermediate portion 2 of the projectile body but in three different axial positions: at the front (Figure 1a), in the middle (Figure 1b) and at the back (Figure 1c) of the cylindrical portion 2. The fins are directed axially, parallel to the symmetrical axis 5 of the projectile, and extend radially out from the surface of the cylindrical portion 2. In the axial direction, the fins extend for about one third of the length of the cylindrical portion 2 and in the radial direction extend to about one fifth of the radius of the cylindrical portion 2.For aerodynamic reasons, the front end surface 6 of each fin has been cut so that if forms an angle of approximately 45" with the symmetrical axis 5 of the projectile and furthermore the edges of this end surface has been machined approximately 45" so that the fin has a forwardly directed sharp edge.

The rotational velocity which is given to the projectile on leaving a gun barrel is reduced by the braking effect of the side surfaces of the fins due to the air resistance. When the rotation has been reduced so much that the rotational speed has reached a specific critical value, the projectile is no longer stable but tips or tilts, which means a significant and sudden increase of air resistance for the projectile so that its forward movement in its trajectory is also braked. This in turns means a significant reduction ofthe maximum firing range compared with normal live ammunition. By varying the size of the fins, i.e. their radial and axial extents, as well as their axial positions it is possible to make said instability occur just behind the present target distance.

Compared with the previous type of projectiles with channels or surfaces for deflecting an air stream axially, the present projectile has a more simple construction, while the basic form of the projectile body is maintained. Each of the fins may be arranted on the cylindrical intermediate portion 2 but as an alternative they may also be arranged on a replaceable ring which is threaded on the cylindrical portion 2. This last-mentioned alternative is preferred because a plurality of replaceable rings with different fin configurations adapted to different firing ranges may be used. Such a ring 7 has been indicated in Figure la and in this case the ring is arranged in a corresponding recess on the cylindrical surface of the intermediate portion 2.

Figure 2 shows an embodiment of the present projectile in which the aerodynamic surfaces for braking the rotational velocity of the projectile are formed by grooves 8 in the cylindrical intermediate portion 2. In conformity with the corresponding fins in Figure 1 the grooves 8 are distributed symmetrically over the periphery of the projectile body and their location, depth and axial extension may be easily adjusted to the desired braking effect. If the grooves 8 are not extended over the entire axial length of the cylindrical intermediate poertion, the rear end 9 of the groove is preferably cut to form an angle of 45" with the symmetrical axis of the projectile for aerodynamic reasons.

The embodiment illustrated in Figure 2 may be used for sub-calibre as well as full-calibre projectiles, but the embodiment of Figure 1 with fins can be used for sub-calibre projectiles only. Sub-calibre projectiles are provided with separate propellant charges and then the fins and grooves, respectively, of the intermediate portion may be used as a support for the propellant charge.

It is to be appreciated that many modifications of the projectiles just described are possible. For example, four symmetrically distributed fins have been illustrated. However, other numbers of fins may be used, if appropriate. Furthermore, the fins and the grooves, respectively, may have an axial extension which corresponds to the full length of the cylindrical intermediate portion 2.

Claims

1. A training projectile which is stabilized by its own rotation during flight, wherein the projectile comprises a conical nose section, a cylindrical intermediate portion and a tail section, and wherein the projectile is provided with braking means for reducing the rotational velocity of the projectile after launching, the braking means comprising a plurality of aerodynamic surfaces located on the cylindrical intermediate portion and extending radially of and parallel to the symmetrical axis of the projectile.

2. A projectile as claimed in Claim 1, wherein the aerodynamic surfaces are formed by fins arranged on the cylindrical surface of said intermediate portion.

3. A projectile as claimed in Claim 1, wherein the aerodynamic surfaces are formed by grooves on the cylindrical surface of said intermediate portion.

4. A projectile as claimed in Claim 2 or 3, wheren said fins or grooves are distributed symmetrically aboutthe periphery of said intermediate portion.

5. A projectile as claimed in Claim 2, wherein the fins are arranged on a replaceable ring which ring is arranged on said cylindrical intermediate portion.

6. A training projectile which is stabilized by its own rotation during flight substantially as hereinbefore described with reference to any one of Figures la to ic and 2 of the accompanying drawings.