GB2181823A - Projectiles - Google Patents

Abstract

A deployable surface 9 is disclosed herein which unfolds and extends along a narrow rearward section 3 of a mortar bomb after launch to improve the aerodynamic characteristics of the bomb. An artillery shell (Figs. 7 and 8 not shown) may be similarly provided. <IMAGE>

Description

SPECIFICATION Projectiles This invention relates to projectiles, more particularly but not exclusively to mortar bombs.

A mortar bomb may comprise a forward section from the rear of which there extends a column. Fins are mounted at the rear end of the column and, between the fins and the forward section, a series of propellant charge wafers are suspended on the column, these being ignited to propel the bomb from its launch tube. The sudden reduction in crosssectional area at the interface between the forward section of the bomb and the column produces airflow turbulence during flight and hence drag. The forward section may be tapered down to the charge suspension column but clearly this taper has to be quite short so as to leave room for the charges.For the best aerodynamic characteristics, the taper should extend as far along the column as possible (ideally, of course, it should extend right along the column to its rear end) and one object of the invention is to provide a means of achieving this, with the minimum increase in size and mass.

According to one aspect of the invention, there is provided a mortar bomb comprising a forward section, a propellant charge mounting column extending rearwardly from the forward section, and deployable bomb surface defining means operable, upon launch of the bomb, for becoming extended along said column from an initial stowed position to a deployed position in which it defines a tapered surface extending from the forward section along the column.

Advantageously, the deployable bomb surface defining means comprises a series of portions encircling the column, for example, a series of conical members or the coils of a helical leaf spring, the portions having respective diameters such that, initially they can be nested one within another and on deployment, can telescope out from one another along the column to form a stepwise tapering surface.

The use of deployable surface defining means which extends, following launch, to provide a turbulence-reducting interface, say between two parts of differing cross-sectional area or shape, may be applicable for projectiles other than that of the aforementioned mortar bomb.

Thus, according to a second, more general aspect of the invention, there is provided a projectile of which the surface comprises a turbulence-inducing region and deployable surface defining means operable to extend over said region following launch of the projectile and which then defines, over that region, a surface less likely than the region itself to induce turbulence.

According to a third aspect of the present invention, there is provided a device for improving the range of a projectile, the device including extendable means for reducing turbulence in the air flowing over the projectile and hence the effects of drag, and which becomes operable for reducing said turbulence at a given instant after launch of the projectile by extending from a retracted position to an extended position to provide a gradual reduction in cross-sectional area towards the tail end of the projectile.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a sectional side elevation of a tail section of a mortar bomb before launch; Figure 2 is a sectional side elevation of a tail section of a mortar embodying the invention before launch; Figure 3 is a sectional side elevation of the Fig. 2 mortar after launch; Figure 4 is a side elevation of a taper formed by a coiled spring; and Figures 5 and 6 are two arrangements for locking the cones of Fig. 3 in position; and Figures 7 and 8 illustrate a taper fitted to an artillery shell before and after launch respectively.

The mortar 1 of Fig. 1 comprises a forward section 2 (only part of which is shown) from the rear of which there extends an axial column 3 supporting a tail fin assembly 4 at its rear end. The column 3 interfaces with section 2 by way of a short tapered region 5. The tail fin assembly 4 comprises a number of fins 6, for example, six or eight, but only two are shown in the figure. Prior to firing of the mortar, the operator suspends a number of horseshoe shaped propellant charges 7 on one column 3. Four charges 7 are shown in position on the column 3 but, of course the actual number used is dependent on the desired range through which the mortar is to be fired.

The mortar is then place in its firing tube (not shown), the charges 7 are ignited by the detonation of a primary charge (not shown) positioned in the column 3 and the gas pressure resulting from the combustion of the charges propels the mortar from the tube. Despite the amelioration afforded by the taper 5, the relatively sudden reduction in diameter of the mortar from the section 2 to column 3 becomes a source of turbulence and hence drag during flight.

The Fig. 2 mortar is like that of Fig. 1 except that it includes an extendable taper 9 which is held in a closed position against the region 5 before launch by a pin or latch 10.

After launch i.e. when the charges 7 have been consumed, the pin 10 is released by a pyrotechnic device (not shown)or by some other means, and the taper 9 is extended by some means to the tail fin assembly 4 along the central member 3 providing a gradual change in cross-sectional area in the tail sec tion 8. This gradual change reduces the effects of drag due to the turbulence of the airflow over the mortar.

Fig. 3 shows a construction which produces the taper 9 and comprises a series of nested conical elements 11 which are extended by the acceleration forces after the pin 10 has sheared during launch of the mortar, and may be locked in the extended position by the friction between adjacent elements i.e. a wedging action due to the conical shape of elements themselves. Alternatively, some form of detent arrangement may be utilised for this purpose, for example, a projection e.g. a latch area, formed on a portion of one element engaging with a groove formed on another portion of an adjacent element. Two such arrangements are illustrated in Figs. 5 and 6 and will be described in more detail later.

A second construction of the extendable taper 9, a coiled spring 12 is shown in Fig. 4 in its extended position. The spring 12 is initially coiled around the member 3 (not shown) with the outer coils 13 attached to the region 5.

When the pin 10 is released, the central coils 14 of the spring travel along the member 3 to the tail fin assembly 4. The coiled spring 12 is designed so that the pin 10 acts against the force of. the spring to hoid it in the closed position when the taper 9 is unextended, and when the pin is released the spring self-deploys i.e. the central coil 14 travels along the member 3 under the action of the force stored in the spring. The extended spring then forms the taper between the portion 2 and the tail fin assembly 4.

In Fig. 5 a portion of two elements 11 are shown. Each element has a 'notch' portion 15 formed at one end and a latching portion 16 formed at the other end. The 'notch' portion 15 is defined by a detent 17 on one side and a lip 18 on the other. The latching portion 16 is also defined by a lip 19, the lips 18 and 19 being formed by portions of the element 11 being folded back on themselves as shown.

Before the elements 11 are released, they lie against the region 5 as shown in Fig. 2 with the 'notch' portions 15 and latching portions 16 lying in lines parallel to the region 5. On release, the elements 11 extend and the latching portions 16 engage with the portions 15 to lock the elements 11 in the extended position as shown in Fig. 3. Similarly, in Fig. 6, each element 11 has a latching portion 20 and a hole 21 in which a portion 20 of an adjacent element engages in the extended position of Fig. 3.

The extendable taper may also be fitted to artillery shells to improve their range, as shown in Figs. 7 and 8. Before launch, the taper is retained against a portion 22 of a shell 23 in its unextended position. After launch, the taper extends as shown in Fig. 8 to provide a modified surface 24 which is less turbulence-inducing.

The nested conical elements 11 and the coiled spring 12 may be made from steel or phosphor bronze or any other suitable material.

Claims (8)

1. A mortar bomb comprising a forward section, a propellant charge mounting column extending rearwardly from the forward section, and deployable bomb surface defining means operable, upon launch of the bomb, for becoming extended along said column from an initial stowed position to a deployed position in which it defines a tapered surface extending from the forward section along the column.

2. A bomb according to claim 1, wherein the deployable bomb surface defining means comprises a series of portions encircling the column, having respective diameters such that, initially they can be nested one within another and on deployment, can telescope out from one another along the column to form a stepwise tapering surface.

3. A bomb according to claim 2, wherein the portions comprise a series of conical members.

4. A bomb according to claim 2, wherein the portions comprise the coils of a helical leaf spring.

5. A projectile of which the surface comprising a turbulence-inducing region and deployable surface defining means operable to extend over said region following launch of the projectile and which then defines, over that region, a surface less likely than the region itself to induce turbulence.

6. A device for improving the range of a projectile, the device including extendable means for reducing turbulence in the air flowing over the projectile and hence the effects of drag, and which becomes operable for reducing said turbulence at a given instant after launch of the projectile by extending from a retracted position to an extended position to provide a gradual reduction in cross-sectional area towards the tail end of the projectile.

7. A mortar bomb substantially as hereinbefore described with reference to Figs. 1 to 6 of the accompanying drawings.

8. An artillery shell substantially as hereinbefore described with reference to Figs. 7 and 8 of the accompanying drawings.