GB2339172A - Sonobuoy - Google Patents

Description

2339172 P/61283.GBA/TMST SONOBUO This invention relates to sonobuoys.

Sonobuoys are placed in the sea to receive underwater signals and to transmit them to a remote point such as an aircraft. The underwater signals may be indicative of the presence and location of submarines.

A typical sonobuoy comprises a parachute to assist in deployment from an aircraft, a float which expands on deployment and which includes at least one aerial for the transmission and/or reception of signals and a sonar unit which submerges on deployment. A cable is provided which provides power from a battery pack in the float to the sonar unit, and which also transmits signals detected by the sonar unit to the aerial.

It is desirable to be able to control the depth to which the sonar unit submerges so that a desired underwater region may be monitored. For this purpose, the sonobuoy is provided with depth control means.

Conventional depth control means employs at least one bum resistor and a depth control cord which is tied to the cable at a specific point, and which prevents the cable from unwinding beyond a predetermined length during deployment. Hence, the sonar unit submerges to a first predetermined depth. A second cord is provided and arranged 2 P/61283.GBA/TMST to release the depth control cord so that the sonar unit can sink to a lower depth. If the first predetermined depth is required the bum resistor, around which the second cord is wound, is energised until the second cord is burnt through so that it does not release the depth control cord on deployment. If the lower depth is required, the bum resistor is not energised so that the second cord remains intact and releases the depth control cord on deployment.

The invention provides a sonobuoy having a portion arranged to submerge on deployment and depth control means arranged so that, the portion submerges to a selected one of a plurality of predetermined depths, the depth control means comprising a depth control cord attached to a mount and corresponding to a first predetermined depth of submersion and selectively operable mechanical means arranged to release the cord so that the portion submerges to a second predetermined depth.

The provision of mechanical means permits the depth to be controlled whilst utilising little of the battery power for the sonobuoy. The depletion of battery power reduces the lifetime of the sonobuoy.

Preferably, the mount is an elongate fastener. Alternatively, a fastener may be interposed between the cord and the mount, Advantageously, the mechanical means is arranged to release the cord by releasing the mount. Alternative arrangements for releasing the cord include breaking the mount, 3 P/61283.GBA/TMST releasing the fastener, breaking the fastener and breaking the cord.

The mechanical means advantageously includes a moveable member, which may have a blunt region, sharp edge or sharp point, for releasing the cord.

The mechanical means may comprise a piston having a gas-filled cylinder. If the second predetermined depth is selected, the gas is caused to expand and move the piston so that the cord is released.

The gas may be caused to expand by activating a detonator in the cylinder, preferably by means of an electrical signal. Such a signal would be a short pulse which would use just a small amount of battery power.

The predetermined depth may be selectable before deployment, for instance by an operator onboard an aircraft.

The sonobuoy may further include a system arranged to detect that the sonobuoy has entered the sea, and consequently to initiate operation of the mechanical means if the second predeterTnined depth has been selected.

Of course, further depth control cords corresponding to further depths of submersion may be provided, with mechanical means for each depth control cord being arranged to operate in dependence on whatever depth is selected.

4 P/61283.GBA/TMST The mount may be of plastics material, and preferably includes glass so that the mount may be broken easily by the mechanical means.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic sectional view of a sonobuoy constructed according to the invention; Figures 2a-e and 3a-e illustrate a deployment sequence for the sonobuoy of Figure 1; Figure 4 is a schematic diagram of the depth control means of the sonobuoy of Figure is Figure 5 is a schematic diagram of altemative depth control means; and Figures 6a-c illustrate alternative mounting arrangements for the depth control cord of the sonobuoy of Figure 1.

Like reference numerals have been given to like parts throughout the specification.

Referring to Figure 1, the sonobuoy is shown in section, its main components being visible. These components include a parachute 1, an inflatable float 2, an aerial 3, P/61283.GBA/TMST depth control means shown within the broken line indicated by the reference numeral 4, cable pack 5, compliance 6, deployable drogue assembly 7 and sonar unit 8. These components are arranged within a canister 9. The compliance 6 is a thick elastic rope which, before the sonobuoy is deployed, is wound around the drogue assembly 7.

Hence, Figure 1 shows cross-sections of the compliance wound around the drogue.

The purpose of the compliance is to resist motion of subsea currents and tides, as does the drogue which, when deployed, takes on a parachute-like configuration and provides drag in both vertical and horizontal directions. One end portion 5' of cable from the cable pack 5 is visible, this end portion being attached to a unit 10 associated with an upper region of the sonobuoy, above the broken line running transverse to the length of the sonobuoy. The depth control means 4 includes a depth control cord 11, one end portion of which is tied to the cable 5' by means of a knot which will not slip or become untied during the lifetime of the sonobuoy. The other end portion of the depth control cord 11 is attached to a mount, shown here in the form of fastener 12 on a lower portion of the sonobuoy, within canister 9. The function of the depth control cord 11 during deployment of the sonobuoy is described below with reference to Figures 2 and 3.

The sonobuoy is shown before deployment and occupies a minimum volume, for storage until required. Deployment of the sonobuoy may be effected by dropping from an aircraft flying above the stretch of water to be monitored, the deployment sequence being shown schematically in Figures 2 and 3.

6 P/61283.GBA/TMST Figure 2a shows the sonobuoy as it descends towards a body of water 13. The parachute I is open and slows the descent of the sonobuoy. The sonobuoy impacts the surface of the water 13 (Figure 2b) and begins to submerge (Figure 2c). A detection system (not shown) detects that the sonobuoy is under seawater and, together with a switch, causes the sonobuoy electronics to be powered up and a gas bottle (not shown) in the canister to be pierced so that the float 2 begins to inflate, as can be seen in Figures 2d and 2e.

At this point, certain deployment components are jettisoned from the sonobuoy and cable 5' from the cable pack 5 begins to unreel as the lower portion of the sonobuoy, including the canister 9, the suspension-components 5, 6, 7 and the sonar unit 8 submerge further. The float 2, together with the upper unit 10, ascends towards the surface of the water. This is shown in Figure 2e.

As the lower portion of the sonobuoy sinks into the water and the cable 5' unreels from the cable pack 5, the depth control cord 11, being attached to both the cable pack 5 and the cable 5', comes into operation. Eventually, the depth control cord 11 supports the in-water weight of the cable pack 5 and the remainder of the lower portion so that the cable pack ceases to pay out. Thus, the lower portion, and hence the sonar unit 8, can submerge to a first predetermined depth.

Referring now to Figure 3a, the cable 5' has been fully deployed to a predetermined length associated with the first predetermined depth and the compliance 6, which is 7 P/61283.GBA/TMST elasticated, begins to pay out. Figure 3b shows the compliance 6 fully deployed. As the compliance 6 stretches, the drogue assembly 7 and sonar unit 8, which are strapped together, are pulled from the canister 9, as shown in Figure 3c. Figure 3d shows that, when the sonar unit has fully emerged from the canister, a retaining plug 14 is pulled out, which releases a strap 15 holding the drogue 7 to the sonar unit 8. The drogue 7, which is arranged to resist motion of the sonar unit 8 by subsea currents, completely unfold and the canister 9 jettisons. The sonobuoy is now completely deployed and ready to detect underwater acoustic signals.

It may be desirable that the sonar unit 8, when deployed, is at a different, lower depth from that shown in Figure 3e. Hence, the sonobuoy is provided with the depth control means 4 of Figure 1, shown in greater detail in Figure 4.

As well as the depth control cord I I and fastener 12, which is attached to a support 16, there is also provided a piston 17 having an expansion chamber 18. A fuse head 19 is located in the chamber 18. The piston 17 has a protrusion 20 arranged close to the fastener 12.

If the second predetermined depth, lower than the first depth, is desired, the depth control cord 11 has to be rendered inoperable to permit cable 5 to unwind further. This is accomplished by transmitting an electrical signal to the fuse head 19. This causes the fuse head 19 to create a small explosion. The explosion creates gas, which moves the piston 17. The moveable protrusion 20 on the piston 17 is driven against the 8 P/61283.GBA/TMST fastener 12.

Preferably, the fastener 12 is a pin of a brittle material, such as plastics material loaded with glass. A suitable composition would be 30% glass-loaded ABS. Tberefore, because the pin is brittle, it fractures easily when the protrusion 20 impacts on it. The fastener 12 may also be arranged to have a smaller diameter, or be thinner, in the region against which protrusion 20 is driven, to further facilitate breakage. Breaking the pin 12 in this manner effects release of the depth control cord 11. Thus, during deployment the cable 5' pays out beyond the first predetermined depth as the sonar unit 8 submerges, because the depth control cord 11 has been rendered ineffective by its release.

Ideally, the sonobuoy is arranged so that the depth of submersion is selectable before deployment by an operator, by means of a switch. However, if the second depth is selected, activation of the piston 17 is not effected until the sonobuoy has been deployed, in case of an aborted mission. A detection system (not shown) on the sonobuoy is arranged to detect that the sonobuoy has landed in the sea (that is to say has been successfully deployed) so that a signal can be transmitted to the fuse head if the second depth was previously selected by the operator before deployment.

Alternative depth control means is shown in Figure 5. In this arrangement, there is no pin, instead the depth control cord 11 has been extended and has been attached to a mount 21. The protruding region 20 has been given a sharp edge, so that, if the 9 P/61283.GBA/TMST second predetermined depth is selected, the sharp edge is driven against the depth control cord 11, thereby cutting the cord. The cable pack 5 win pay out beyond the first predetermined depth because the depth control cord 11 has been rendered ineffective by its release by cutting.

The arrangement by which the depth control cord 11 is secured to the cable pack 5 is not limited to those shown in Figures 4 and 5. For instance, Figure 6a shows the depth control cord 11 attached to a mount 22. Release of the cord 11 may be carried out by cutting the cord, breaking the mount 22 or releasing the mount mechanically.

In the embodiment shown in Figure 6b, the depth control cord 11 is attached to fastener 12 which, in turn is attached to a mount 23. To release the cord 11, the mount 23 may be released or broken; the fastener 12, which may be the frangible pin of Figure 4, may be broken; or the cord itself may be cut.

A further variation is shown in Figure 6c, in which a fastener 12, which may also be the frangible pin of Figure 4, is interposed between the depth control cord 11 and another cord 24. In this case, release of the cord may be effected by cutting cord 11 or cord 24 or by breaking the fastener 12.

The invention is not limited to these embodiments and further variations may be apparent to those skilled in the art.

P/61283.GBAITMST Of course, the depth control means may have more than one depth control cord so that the sonobuoy can submerge to a selected one of any number of depths, in which case each depth control cord would have its own respective mechanical means for releasing the depth control cord.

P/61283.GBA/TMST

Claims (21)

CLAIM

1. A sonobuoy having a portion arranged to submerge on deployment and depth control means arranged so that the portion submerges to a selected one of a plurality of predetermined depths, the depth control means comprising a depth control cord attached to a mount and corresponding to a first predetermined depth of submersion and selectively operable mechanical means for releasing the cord so that the portion submerges to a second predetermined depth.

2. A sonobuoy as claimed in claim 1, wherein the mount is an elongate fastener.

3. A sonobuoy as claimed in claim 1, wherein a fastener is interposed between the cord and mount.

4. A sonobuoy as claimed in claim 1, 2 or 3, wherein the mechanical means is arranged to release the cord by releasing the mount.

5. A sonobuoy as claimed in claim 1, 2 or 3, wherein the mechanical means is arranged to release the cord by breaking the mount.

6. A sonobuoy as claimed in claim 3, wherein the mechanical means is arranged to release the cord by releasing the fastener.

12 P/61283.GBA/TMST

7. A sonobuoy as claimed in claim 3, wherein the mechanical means is arranged to release the cord by breaking the fastener.

8. A sonobuoy as claimed in claim 1, 2 or 3, wherein the mechanical means is arranged to release the cord by breaking the cord.

9. A sonobuoy as claimed in any preceding claim, wherein the mechanical means includes a moveable member arranged to release the cord.

10. A sonobuoy as claimed in claim 9, wherein the member includes a blunt region for releasing the cord.

11. A sonobuoy as claimed in claim 9 or 10, wherein the member includes a sharp edge for releasing the cord.

12. A sonobuoy as claimed in claim 9, 10 or 11, wherein the member includes a sharp point for releasing the cord.

13. A sonobuoy as claimed in any preceding claim, wherein the mechanical means comprises a piston in a cylinder arranged so that selective operation causes gas within the cylinder to expand and effect motion of the piston to release the cord.

14. A sonobuoy as claimed in claim 13, wherein the gas is caused to expand by 13 P/61283.GBA/TMST activation of a detonator located in the cylinder.

15. A sonobuoy as claimed in claim 14, wherein the detonator is activated by an electrical signal.

16. A sonobuoy as claimed in any preceding claim, arranged so that a predetermined depth is selectable before deployment.

17. A sonobuoy as claimed in any preceding claim, further comprising detection means arranged to detect submersion of the portion and to operate the mechanical means, if selected.

18. A sonobuoy as claimed in any preceding claim, further comprising a second depth control cord attached to a mount and corresponding to the second predetermined depth of submersion, and selectively operable mechanical means for releasing the second cord so that the portion submerges to a third predetermined depth.

19. A sonobuoy as claimed in any preceding claim, wherein the mount is of plastics material.

20. A sonobuoy as claimed in any preceding claim, wherein the mount is of a material including glass.

14 P/61283.GBA/TMST

21. A sonobuoy, substantially as hereinbefore described, with reference to, or as illustrated in, the accompanying drawings.

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