GB2232647A

GB2232647A - Float for air-launched sonobuoy

Info

Publication number: GB2232647A
Application number: GB9013299A
Authority: GB
Inventors: Jeremy Spencer Harris
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1989-06-16
Filing date: 1990-06-14
Publication date: 1990-12-19
Also published as: GB9013299D0; GB8913961D0

Abstract

The invention provides a float/parachute for an aircraft-launch sonobuoy comprising a parachute 10 provided at its crown 13 with a vent and an inflatable fabric float 12 connected to the crown of the parachute such that the high air pressure inside the parachute during descent inflates the float. The parachute 10 is made from zero porosity nylon in cruciform shape. The floatation section 12 is made from polyurethane coated nylon, however, it may be integrally formed with the parachute. A fabric non-return valve is provided at the vent connected between the crown of the parachute and the floatation section to prevent loss of air from the floatation section in use. The inflatable float is conical, disposed such that in operation the apex of the cone is upright to give good stability in water, sufficient support for an internal antenna and low windage to reduce drift. During parachute descent the combination of parachute and inflated float provides improved air flight characteristics over the parachute on its own. <IMAGE>

Description

Mr-Launched Eqnobuoy The e invention relates to non-bucyant sonobuoys and in particular to their associated buays needed to deploy telemetry antennas above the water surface.

Sonobuoys, which may be ship or aircraft launched, consist of acoustic sensors which are suspended underwater fran floats to which antennas are attached. Acoustic readings can thus be transmitted via the floating antenna to a ship or aircraft. Existing non-buoyant sonobuoys use a gas bottle inflated float or buoyancy chamber to enable the telemetry antenna to remain above the sea or water surface during operation. This results in the inclusion within the sonobuoy of a gas bottle, an initiation device (often containing pyrotechnics) and a float or expanding floatation chamber. In the conventional arrangement when the sonobuoy contacts the water, a sea battery is activated which fires a gas bottle. This inflates the float which supports an antenna vertically above the surface of the sea.These additional items are heavy and bulky and in the case of the gas bottle and initiation device can present an explosion hazard under certain circumstances. Furthermore, because of volume restrictions imposed by the limited size of a sonobuoy, the parachute system used is often not particularly effective in controlling oscillation of the sonobuoy during airflightr after delivery fran an aircraft. This results in high aspect angles at water entry which impart very high rotational forces to the sonobuoy, resulting in damage to the internal sensors or electronic systems.

The object of the present invention is to provide a sonobuoy float which overcomes problems experienced with prior art arrangements.

The invention provides a float/parachute for an aircraft-launch sonobuoy comprising: a parachute for retarding the descent of the sonobuoy and provided at its crown with a vent; and an inflatable float connected to the parachute in air-tight manner over the vent such that the high air pressure inside the parachute during descent inflates the float.

This design of integrated float and retarder eliminates the requirement for a gas bottle and its associated initiation device, resulting in a safety improvement and a substantial reduction in mass and volume.

Preferably the parachute is made from a zero porosity material such as nylon and it may be a conventional cruciform shape. Advantageously there is provided an air-tight fabric floatation section connected to the crown of the parachute by a fabric non-return valve.

In the preferred arrangement the float/parachute combination is deployed by an attached drogue.

Advantageously the floatation section is conical, disposed such that in operation the apex of the cone is upright. This arrangement has been found to give good stability in water, sufficient support for an internal antenna and low windage to reduce drift. In addition this combination of parachute and float has improved air flight characteristics over the parachute on its own, due perhaps to a reduction in turbulence behind the float. Preferably the float is made of polyurethane coated ripstop nylon.

The e invention will now be described by way of example with reference to the accompeny Drawings of which: Figure 1 shows a sonobuoy with a float/parachute in air flight following deployment from an aircraft; and Figure 2 shows the sonobuoy floating in water.

As with conventional aircraft-launched sonobuoys a drogue parachute is used to deploy a cruciform parachute 10 attached to a sonobuoy 11 (Figure 1). The parachute material is made of non-porous nylon material and at the crown of the parachute 10 there is provided a float section 12 with a one-way fabric valve provided in the region 13 where the float section 12 connects to the crown of the parachute 10. The float section is manufactured from polyurethane coated ripstop nylon, consisting of a single piece of fabric glued together on one edge to form a cone approximately 0.8m high. This float section is then stitched to the crown of the parachute over a vent and sealed using a clear polyurethane adhesive.

The high pressure air inside the parachute inflates the float section by a ram-air effect and the one-way valve ensures that high pressure air is not lost from the float section 12. At the water entry the parachute 10 effectively caps the cavity formed by the sonobuoy entering the water and converts some of the kinetic energy of the assembly into a pressure rise which further increases the pressure in the float 12. After water entry (Figure 2) the hydrophone assembly is deployed from a cable 14 but the remainder of the sonobuoy casing, electronics pack and batteries remains attached to the parachute 10 which collapses and tends to close the mouth of the float section 12. This action further improves the sea keeping performance of the sonobuoy.The float 12 serves to support an aerial (not shown) for transmission of data from the sonobuoy.

The float arrangement, in which the floatation section can be an integral part of the nylon parachute, is simple, smaller and lighter than previous arrangements. Surprisingly also the airflight characteristic of the float/parachute of the present invention has been found to be better than that of a cruciform parachute alone, due possibly to reduced air turbulence behind the float. In addition the conical float has been shown to have good stability in the water and low windage to reduce drift. The e presence of the non-return valve prevents air loss fram the float when the float tips due to the action of waves. Trials have shown, however, that the arrangement works well without a valve; the partial seal provided by the collapsed parachute being sufficient to retain air in the float in moderate seas. As the valve is relatively inexpensive it is preferable, however, that one should be included.

Claims

1. A float/parachute for an aircraft-launch sonobuoy comprising: a fabric parachute for retarding the descent of the sonobuoy and provided at its crown with a vent; and an inflatable faric float connected to the parachute in air-tight manner over the vent such that the high air pressure inside the parachute during descent inflates the float.

2. A float/parachute for an aircraft-launch sonobuoy as claimed in claim 1 wherein the floatation section is conical, disposed such that in operation the apex of the cone is upright.

3. A float/parachute for an aircraft-launch sonobuoy as claimed in claim 1 or 2 wherein the float is made from polyurethane coated zero porosity nylon material.

4. A float/parachute for an aircraft-launch sonobuoy as claimed in any one of claims 1 to 3 wherein the parachute is made fram zero porosity nylon material.

5. A float/parachute for an aircraft-launch sonobuoy as claimed in any one preceding claim wherein the parachute is a cruciform shape.

6. A float/parachute for an aircraft-launch sonobuoy as claimed in any one preceding claim wherein a fabric non-return valve is provided between the floatation section and the crown of the parachute.

7. A float/parachute for an aircraft-launch sonobuoy as claimed in any one preceding claim wherein the floatation section is integrally formed with the parachute.

8. A float/parachute for an aircraft-launch sonobuoy as claimed in any one preceding claimwherein there is provided mans for connection of a drogue for deployment of the parachute.