Abstract
Projectile launch apparatus (20) for use in a fluid environment. The apparatus (20) comprises a launch tube (21) having a supercavitating projectile (24) with cavitator (29) received within the launch tube (21). A means for generating expulsion gas (not visible) is arranged to provide expulsion gas to propel the projectile (24) from the launch tube (21), with means for bleeding expulsion gas (31, 32) being provided to bleed a portion of expulsion gas around the projectile (24). This allows expulsion gases to contribute to the formation of the gas cavity around the supercavitating projectile (24) as the projectile (24) is launched from the launch tube (21). Particularly suited to the deployment of supercavitating projectiles underwater, such as in underwater mine disposal applications.
Claims
1. Projectile launch apparatus for use in a fluid environment, comprising a launch tube having a closed end and an open end, a supercavitating projectile received between the ends separating the launch tube into a forward section comprising the open end and a rear section comprising the closed end, and gas generation means arranged to provide expulsion gas into the rear section of the launch tube, such that in-use trapped expulsion gases within the rear section generate a pressure increase that acts on the supercavitating projectile to propel the projectile through the open end, wherein the supercavitating projectile comprises a nose section and a tail section, the nose section having a cavitator for generating a gas cavity around the supercavitating projectile when the projectile is launched, wherein the projectile launch apparatus further comprises means for bleeding expulsion gas around the projectile from the rear section of the launch tube into the forward section and thereby to the open end, such that in-use, expulsion gases can contribute to a formation of the gas cavity around the supercavitating projectile as the projectile is launched through the open end.
2. The projectile launch apparatus of claim 1, wherein the supercavitating projectile is banded with at least one discrete band to form a bore riding projectile, the at least one discrete band being conformal to an interior surface of the launch tube.
3. The projectile launch apparatus of claim 2, wherein the supercavitating projectile is banded with at least two discrete bands.
4. The projectile launch apparatus of claim 2, wherein the bands are formed from Nylon or PTFE.
5. The projectile launch apparatus of claim 2, wherein the means for bleeding expulsion gas comprises conduits extending through the discrete bands for a flow of expulsion gases from the rear section to the forward section of the launch tube.
6. The projectile launch apparatus of claim 2, wherein the means for bleeding expulsion gas comprises a clearance gap between an exterior surface of the supercavitating projectile and the interior surface of the launch tube.
7. The projectile launch apparatus of claim 6, wherein the clearance gap is less than 2 mm.
8. The projectile launch apparatus of claim 6, wherein the clearance gap is less than or equal to 100 m between the at least one discrete band and interior surface of the launch tube.
9. The projectile launch apparatus of claim 1, wherein the means for bleeding expulsion gas comprises a groove in an exterior surface of the supercavitating projectile and/or an interior surface of the launch tube, the groove extending between the rear section and the forward section such that the exterior surface of the supercavitating projectile and interior surface of the launch tube define a channel through which expulsion gases can flow.
10. The projectile launch apparatus of claim 1, wherein the supercavitating projectile comprises an internal conduit connecting the rear section of the launch tube with the forward section, through which expulsion gases can flow.
11. The projectile launch apparatus of claim 10, wherein the internal conduit takes the form of a spiral about the major axis of the supercavitating projectile.
12. The projectile launch apparatus of claim 1, further comprising initiation means for initiating the means for bleeding expulsion gas when the pressure in the rear section of the launch tube exceeds a predetermined threshold pressure value.
13. The projectile launch apparatus of claim 12, wherein the initiation means comprises a shear band attached to the tail section of the supercavitating projectile.
14. The projectile launch apparatus of claim 12, wherein the initiation means comprises an internal tapering of the rear section of the launch tube and a conformal tapering of the tail section of the supercavitating projectile.
15. The projectile launch apparatus of claim 1, wherein the cavitator comprises a plurality of stacked sections increasing in diameter in a nose-to-tail direction.
16. The projectile launch apparatus of claim 15, wherein each stacked section in the plurality of stacked sections is a cylindrical stacked section.
17. The projectile launch apparatus of claim 16, wherein the cavitator comprises an annular recess extending around a periphery of an interface between each stacked section.
18. The projectile launch apparatus of claim 1, further comprising an inflatable bladder having an opening for receiving a gas, the inflatable bladder being releasably mounted to the launch tube and arranged to receive through the opening a portion of the expulsion gas from the gas generation means when the projectile launch apparatus is in-use, such that the inflatable bladder can be deployed as a marker buoy.
19. The projectile launch apparatus of claim 18, wherein the opening of the inflatable bladder is arranged to collect expulsion gas exiting the open end of the launch tube when the projectile launch apparatus is in use.
20. The projectile launch apparatus of claim 18, wherein the buoy is attached to the launch tube or supercavitating projectile using rope or wire means.
21. The projectile launch apparatus of claim 1, wherein the supercavitating projectile further comprises decoupling means for rotationally decoupling the nose section from the tail section.
22. A torpedo comprising the projectile launch apparatus of claim 1.
23. The torpedo of claim 22 comprising a plurality of projectile launch apparatuses.
24. A method of launching a supercavitating projectile in a fluid environment, the method comprising: (a) Locating the projectile launch apparatus of claim 1 in a fluid environment; (b) Initiating the gas generation means to provide expulsion gas into the rear section of the launch tube; (c) Bleeding expulsion gas around the projectile from the rear section of the launch tube into the forward section of the launch tube and thereby to the open end; and then (d) Launching the supercavitating projectile through the open end of the launch tube, such that expulsion gases can contribute to formation of the gas cavity around the supercavitating projectile as the projectile is launched through the open end.
25. Use of means for bleeding expulsion gases to bleed expulsion gases from a gas generation means of a projectile launch apparatus around a supercavitating projectile received within a launch tube of the projectile launch apparatus in order to reduce friction and drag effects acting on the supercavitating projectile when the supercavitating projectile is launched from the launch tube into a fluid environment.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:
[0040] FIG. 1 provides an illustration in perspective view of an embodiment of a projectile launching apparatus for use in an underwater environment;
[0041] FIG. 2 provides an illustration in cutaway side view of an embodiment of a projectile launching apparatus for use in an underwater environment;
[0042] FIG. 3 provides an illustration in perspective view of an embodiment of a supercavitating projectile for use in a projectile launching apparatus;
[0043] FIG. 4 provides an illustration in side view of an embodiment of a supercavitating projectile for use in projectile launching apparatus; and
[0044] FIGS. 5a, 5b, and 5c, provide an illustration in cutaway side view of an embodiment of a supercavitating projectile at various stages during launch from a launch tube in a projectile launching apparatus.
DETAILED DESCRIPTION
[0045] FIG. 1 provides an illustration in perspective view of an embodiment of a projectile launching apparatus 1 for use in an underwater environment. The apparatus 1 comprises a cylindrical launch tube 2 having a closed end (not visible) and an open end 3. A cylindrical bore is evident at the open end 3 of the launch tube 2 into which a supercavitating projectile 4 has been received. The supercavitating projectile 4 has a circular cross section substantially conformal to the interior surface of the launch tube 2. The supercavitating projectile 4 further comprises a cavitator 5 on a nose section of the projectile 4 and visible through the open end 3 of the launch tube. The cavitator 5 itself comprises a plurality of stacked cylindrical sections. The tail end of the projectile 4 is not visible. The launch tube 2 is approximately 30 cm in length, has an internal diameter of approximately 4 cm, and is formed from stainless steel. The supercavitating projectile is formed from aluminium.
[0046] FIG. 2 provides an illustration in cutaway side view of an embodiment of a projectile launching apparatus 20 for use in an underwater environment. A launch tube 21 is shown having an open end 22 and a closed end 23. A supercavitating projectile 24 is shown received into the launch tube 21, the launch tube comprising a breakable seal 25 over the open end. The breakable seal 25 is formed from a frangible plastic and seals the launch tube from water ingress prior to launch of the projectile 24. The seal 25 is breakable by action of the projectile 24 urging against it during launch. The supercavitating projectile 24 divides the launch tube into a forward section 26 comprising the open end 22 of the launch tube 21, and a rear section 27 comprising the closed end 23 of the launch tube 21. The supercavitating projectile 24 is conformal to the interior surface of the launch tube 21 and provides a close fit. The tail section 28 of the projectile 24 comprises a taper that interfaces with a cooperating taper of the launch tube 21. This seals the rear section 27 of the launch tube 21 from the forward section 26. The supercavitating projectile 24 also comprises a cavitator 29 at the nose section 30 proximate the open end 22 of the launch tube 21. The cavitator 29 comprises a plurality of stacked circular sections of increasing diameter in the nose section 30 to tail section 28 direction. The supercavitating projectile 24 is formed from metal and has a lower caliber than the launch tube 21. The projectile 24 further comprises three peripheral Nylon bands 31 encircling the projectile 24 at three distinct locations along its length. The bands 31 increase the diameter of the projectile 24 to substantially the bore diameter of the launch tube 21. A small clearance gap 32 of 1 mm is provided between the surface of the supercavitating projectile 24 and the interior surface of the launch tube 21. The clearance gap 32 extends along the long of the projectile 24, but does not extend to the tail section 28 of the projectile which provides a Luer fit to the launch tube 21. The propulsion means is not visible but comprises a high pressure gas cylinder located in the tail section 28 of the projectile 24. The high pressure gas cylinder is able to vent high pressure gas into the rear section 27 of the launch tube 21 in order to propel the projectile 24 from the tube 21. The supercavitating projectile 24 is shown as a single unitary mass of aluminium approximately 30 cm in length and with a diameter of 4 cm. The launch tube 21 is also made of metal with dimensions configured to suit the projectile.
[0047] FIG. 3 provides an illustration in perspective view of an embodiment of a supercavitating projectile 33 for use in a projectile launching apparatus. The projectile 33 is shown without a launch tube to illustrate the construction and geometry. The projectile 33 is formed from metal as a cylindrical unitary mass. It comprises a nose section 34 that gradually tapers in an ogive geometry towards a cavitator 35 at the front of the projectile 33. The cavitator 33 comprises four cylindrical stacked sections approximating plates of increasing diameter in the nose-section 34 to tail-section 36 direction. At the interface of each stacked section there is a recess to encourage improved supercavitating flow. The cavitator 33 impacts the fluid through which the projectile 33 is propagating and generates a supercavitating flow around the projectile 33. The tail section 36 is shown comprising a taper in the nose section 34 to tail section 36 direction. This is a Luer taper for interfacing with a compatible launch tube. Three discrete peripheral bands 37 of Nylon are shown encircling the projectile 33 at discrete points along its length. The bands 37 are attached to the projectile 33 and provide an increased projectile diameter such that the projectile 33 can effectively ride the bore of a launch tube. The bands 37 are shown comprising a split 38 to enable easier fitment onto the projectile.
[0048] FIG. 4 provides an illustration in side view of an embodiment of a supercavitating projectile 40 for use in a projectile launching apparatus. The side view illustration is provided to aid the explanation of the geometry of the projectile 40. The projectile 40 has a circular cross section and forms an elongate cylinder of unitary mass comprising a nose section 41 and a tail section 42, the latter comprising a Luer taper. The unitary mass is formed from metal. Three distinct bands 43 are shown encircling the projectile 40 at different points along its length. The bands 43 are glued to the projectile 40. The bands 43 minimally increase the overall diameter of the projectile 40, in this embodiment the bands 43 increase the diameter by up to 1 mm. The bands 43 are formed of Nylon which exerts less wear onto a launch tube from which the projectile 40 is launched. At the nose section 41 there is also a tapering towards the front of the projectile 40, the tapering being ogive. Attached to the front of the nose section 41 is a cavitator 44 comprising four cylindrical stacked sections of increasing diameter in the nose section 41 to tail section 42 direction. The overall diameter of the cavitator 44 is less than the overall diameter of the projectile 40. At the interface of each stacked section in the cavitator there is a recess 45. The recess 45 encourages toroidal flow of fluid, such that laminar flow can be achieved over the toroidal flow, thereby improving overall skin drag for the projectile 40.
[0049] FIGS. 5a, 5b and 5c provide an illustration in cutaway side view of an embodiment of a supercavitating projectile 51 being launched from a launch tube 52 in a projectile launching apparatus 50. With regard to FIG. 5a, a supercavitating projectile 51 is shown within a launch tube 52. The launch tube 52 lacks a breakable seal and so prior to launch the launch tube 52 is flooded by fluid from the fluid environment of use. The supercavitating projectile 51 is therefore immersed in the fluid in the launch tube 52. The supercavitating projectile 51 substantially conforms to the interior surface of the launch tube 52. The tail section 55 of the projectile 51 comprises a Luer taper and cooperates with a corresponding tapering of the launch tube 52 to provide a seal and prevent fluid ingress behind the projectile 51. This separates the launch tube 52 into a forward section 53 and a rear section 54. The nose section 57 of the projectile 51 comprises a cavitator 58 for generating supercavitating flow around the projectile 51 once launched. The projectile 51 also comprises banding 56 to ride along the interior surface of the launch tube 52. Apart from the Luer taper of the tail section 55 of the projectile 51, there is a clearance gap 59 of approximately 1 mm between the the main body of projectile 51 and launch tube 52, and a smaller gap of 100 micrometres between the banding 56 and the launch tube 52. In FIG. 5a the projectile 55 is in a pre-launch configuration, with the apparatus 50 itself being within an underwater environment.
[0050] FIG. 5b illustrates a later stage during launch of the projectile 51 from launch tube 52. High pressure gas from a gas canister within the tail section 55 of the projectile 51 has been expelled into the originally sealed rear section 54 of the launch tube. The build up of high pressure gases has urged the projectile 51 partially through the open end of the launch tube 52. This has separated the seal between the tail section 55 of the projectile and rear section 54 of the launch tube 52 originally formed by the Luer taper. As a result, a portion of expulsion gases controllably bleed past the tail section 55 of the projectile 51, past the bands 56, and out of the launch tube 52 at the open end. This gas flow is indicated by the bold arrows in the figure. These gases force fluid from the launch tube 52 and form a gas bubble 60 at the open end of the launch tube 52 through which the projectile 51 transits. At the same time, supercavitating flow 61 is forming at the cavitator 58 of the projectile 51. Expulsion gases within the rear section 54 of the launch tube 52 continue to urge the projectile 51 from the launch tube 52.
[0051] Now observing FIG. 5c illustrating the projectile 51 at an even later time during launch, expulsion gases in the rear section 54 of the launch tube continue to urge the projectile 51 from the launch tube 52. However the gas bubbles 60 and 61 from FIG. 5b have now coalesced providing a single gas bubble 62 within which the projectile 51 is propagating. This gas bubble 62 has formed prior to the projectile 51 entirely exiting the launch tube 52. As such skin drag is significantly reduced, and friction effects within the launch tube have been reduced owing to the air flow around the projectile 51. The cavitator 58 continues to generate supercavitating flow as the projectile 51 fully exits the launch tube and continues towards a target. Overall the projectile experiences reduced transit time and improved stability.
[0052] Whilst the embodiments shown are intended for use underwater, the advantages of the invention may be achievable in other fluids such as air. The cavitator described is an example of a supercavitating structure and other geometries may be used in other embodiments of the invention, provided that such geometries generate supercavitating flow within the chosen fluid of deployment. The projectile has been described as a single unitary mass, however the projectile may in other embodiments be a vessel for transporting other objects. For instance the projectile may comprise a shell within which a dart can be transported to an intended target, the shell breaking upon impact with the intended target to reveal the dart for penetrating the target. Additionally, grooves may be provided on an external surface of the projectile interfacing with the interior surface of a launch tube to define channels for gas flow. Angling may be applied to the grooves at approximately 45 degrees or other angle to the major axis of the projectile such that in use a degree of rifling is imparted to the projectile during launch by virtue of the flow of high pressure gas.
