Thomas K. Harkins Howard K. Steves Jacques E. Goeller NOTICE

Transcription

1 Se rial Number Filing Date Inventr January 1998 Thmas K. Harkins Hward K. Steves Jacques E. Geller NOTICE The abve identified patent applicatin is available fr licensing. Requests fr infrmatin shuld be addressed t: OFFICE OF NAVAL RESEARCH DEPARTMENT OF THE NAVY CODE OOCC ARLINGTON VA ^^^r^m^mr «TIC QUALITY BTSPECTED*

2 NAVY CASE PATENT 5 SUPERCAVITATING WATER-ENTRY PROJECTILE 10 Origin f the Inventin The inventin described herein was made in the perfrmance f fficial duties by an emplyee f the Department f the Navy and.may be manufactured, used, 15 licensed by r fr the Gvernment fr any gvernment purpse withut payment f ryalties theren. Field f the Inventin 20 The inventin described herein relates t underwater prjectiles and in particular t lng-rd prjectiles used fr destrying underwater bjects such as bstacles, trpedes, and mines. 25 Backgrund f the Inventin Develpment f penetrating prjectiles as currently used in anti-armr applicatins has addressed numerus technlgical difficulties in rder t prduce effective weapns. The basic requirements f a lng-rd penetratr includes the use f high density prjectiles having a lng length-t-diameter rati and 0 having very high impact velcities. The presently available prjectiles are generally used fr maximum target penetratin f a hardened structure. The inventin adapts lng-rd penetratrs with the capability f traveling bth in air and water where the bject is t achieve lw-drag water penetratin fr the purpse f delivering high kinetic energy t underwater targets'. This requires that the hydrballistic prjectile maintain stability and

3 NAVY CASE PATENT 5 lw drag bth in air and water s that sufficient kinetic energy can be delivered t the underwater target t assure its destructin. Current prjectiles d nt exhibit the capability t travel in bth air and water and deliver high kinetic energy t defeat targets at any significant depth belw the water surface. An peratinal need exists fr a prjectile having the capability f launch abve 10 the water surface and prviding effective water travel after impact with the water surface. Summary f the Inventin It is an bject f the inventin t prvide an air-launchable, penetrating prjectile which is ballistically stable bth aerdynamically and hydrdynamically. 15 It is anther bject f the inventin t prvide a prjectile having a supercavitating nse which prvides a cavitatin bubble f sufficient size t encmpass the bdy f the prj ectile which reduces hydrdynamic drag. It is a yet anther bject f the inventin t prvide a prjectile launchable by existing gun systems and having sufficient strength t withstand high speed water impact 20 lads while maintaining sufficient strength and ductility t withstand gun launch and hydrdynamic lads during water travel. In accrdance with these and ther bjects, the inventin is a supercavitating water entry prjectile having aft munted empennage which prvides stabilizatin in bth air and water and a supercavitating nse sectin. The prjectile is a subcaliber, gun 25 launched, munitin using an apprpriate sabt assembly t prvide full caliber integrity. The prjectile has circumferential grves arund its center sectin t match

4 NAVY CASE PATENT 5 grves in the sabt assembly. Ä key feature in the inventin is the size and shape f the nse sectin. The prjectile has a nvel high strength extended blunt nse sectin fllwed by a truncated cnical sectin which angles twards the bdy f the prjectile in the range f five degrees. During underwater trajectry, the entire prjectile is cntained within the cavitatin bubble frmed by the blunt nse tip. The prjectile's empennage, 10 which prvides bth aerdynamic and hydrdynamic stability, fits within the bre f the weapn. Brief Descriptin f the Drawings The freging bjects and ther advantages f the present inventin will 15 be mre fully understd frm the fllwing detailed descriptin f representative cmpnents f a representative 25mm prjectile and reference t the appended drawings wherein: FIG. 1 is a side view f the prjectile with a partial cutaway f the aft end. FIG. 2 is a partial side view f the supercavitating nse sectin f the 20 prjectile. FIG. is a partial side view f a cutaway depicting a variatin f the supercavitating nse sectin f the prjectile. FIG. 4 is a side view f the prjectile with the sabt installed. FIG. 5 is a graphical representatin f the cavitatin bubble with a prfile 25 f the prjectile included.

5 NAVY CASE PATENT 5 FIG. 6 is a graphical representatin depicting decreasing underwater velcity fr increasing underwater range. While the afrementined figures apply t the 25mm prjectile, the inventin can be scaled t any caliber weapn. 10 Detailed Descriptin f the Inventin Referring nw t FIG. 1, the prjectile 10 f the present inventin is shwn with its majr sectins depicted. The prjectile has a cylindrical bdy cmprising three majr sectins, the cylindrical aft sectin 12, the cylindrical center sectin 22, and the nse sectin 2. The steel aft sectin 12 is cnfigured with suitable stabilizing empennage. 15 This empennage is in the frm f a plurality f fins 14. In the preferred embdiment, fur equally spaced fins are circumferentially lcated arund the aft sectin 12 and are sized t fit within the gun bre f a selected existing weapn. Fr aerdynamic stability, the center f gravity f the prjectile 10 must be lcated frward f the center f pressure. The lng bdy design f the prjectile 10 with fins 14 as stabilizing empennage n the aft 20 sectin 12 prduces restring frce sufficient t prvide gd stability in bth air and water. Gyrscpic-induced stability, such as used by spinning bullets in air, cannt be achieved because f the difference in the medium density f water versus air. A pay lad cavity 16 is lcated inside the aft sectin 12 f the prjectile 10 suitable fr cntaining tracer material r ther desired paylad. A threaded aperture prvides an attachment pint fr fixing the aft sectin 12 t the main bdy 24 f the prjectile 10. The main bdy 24 is a tungsten r similar heavy metal rd cmprising the

6 NAVY CASE " PATENT 5 center sectin 22 and the nse sectin 2 f prjectile 10. On the center sectin 22, circumferential grves 26 are machined t prvide a matching interface fr a sabt assembly (hereinafter described). The frward r nse sectin 2 f the prjectile 10 includes the tapered prtin 4 and the supercavitating blunt nse tip 6. The nse taper angle 8 f the 10 tapered prtin 4 frms a shulder 42 integral with the center sectin 22. As previusly described, it is necessary t generate a water cavity such that the entire prjectile 10 travels within the cavity. This cavity is prduced by the supercavitating blunt nse tip 6. The supercavitating blunt nse tip 6 is cylindrical abut the axis f the prjectile 10 and has a flat circular face 40 which generates the water cavity as the 15 prj ectile 10 travels thrugh water. It is imperative t the hydrdynamic stability f the prjectile 10 and, thus t success f the inventin, that the diametrical size f the flat circular face 40, the nse taper angle 8, and the length f the supercavitating blunt nse tip 6 be designed such that the shulder 42 des nt tuch the water cavity wall befre the fins 14 f the 20 stabilizing empennage tuch the water cavity wall. It is als imprtant t minimize the hydrdynamic drag f the prjectile 10 by reducing the diametrical size f flat circular face 40 as much as pssible withut prducing a resultant increase in hydrdynamic drag as a result f the fins 14 f the stabilizing empennage cntacting the water cavity wall in an excessive manner beynd what is necessary t prvide hydrdynamic stabilizatin. 25 Referring nw t FIG. 2, a detailed view f the nse sectin 2 is shwn. The afrementined supercavitating blunt nse tip 6 is illustrated in mre detail. Fr the

7 NAVY CASE " PATENT 5 subcaliber 25mm design having a nminal center sectin 22 (the center sectin 22 is depicted in FIG. 1) diameter f 0.27 inches, the preferred diameter f the flat circular face 40 is in the range f 0.10 inches in diameter. The preferred length f the supercavitating blunt nse tip 6 is 0.07 inches. The preferred nse taper angle 8 is five degrees. 10 A variatin n the supercavitating blunt nse tip 6 is depicted in FIG.. In sme applicatins where the water impact lads are higher than the strength f the material f the prjectile 10 (the prjectile 10 is depicted in FIG. 1), the supercavitating blunt nse tip 6 (as shwn in FIGS. 1 and 2) is replaced by a very high strength supercavitating insert 46. The supercavitating insert 46 is made frm very high strength material 15 sufficient t withstand the lads generated by the cmbinatin f high speed water impact and impact bliquities appraching perpendicular t the water surface. The supercavitating insert 46 is cylindrical with a flat circular face 50 which generates the water cavity. The supercavitating insert 46 is placed in the insert bre 47 f the prjectile 10. In this variatin f the supercavitating inventin, the alternative nse sectin f 20 the prjectile 10 includes the tapered prtin 44 having a nse taper angle 48 and frms a shulder 52 with the center sectin 22 (the center sectin 22 is depicted in FIG. 1). The tapered prtin 44 is terminated n the end by the lip 45. The means f securing the supercavitating insert 46 int the insert bre 47 may be secured by an interference fit, taper fit, threaded fit, r suitable bnding material.

8 NAVY CASE PATENT 5 It is imperative t the hydrdynamic stability f the prjectile 10 (as shwn in FIG. 1), and thus t success f the inventin, that the diameter f the flat circular face 50, the length that the supercavitating insert 46 prtrudes frm the prjectile 10, and the nse taper angle 48 be designed such that the shulder 52 and the lip 45 d nt tuch the water cavity wall befre the fins 14 (the fins 14 are depicted in FIG. 1) tuch the water cavity 10 wall. Hwever, in rder t minimize the hydrdynamic drag f the prjectile 10, the diametrical size f flat circular face 50 must be reduced as much as pssible withut prducing a resultant increase in hydrdynamic drag which results when the fins 14 f the stabilizing empennage prtrude int the water cavity wall t an excessive depth beynd what is necessary t prvide hydrdynamic stabilizatin. 15 Fr the subcaliber 25mm design having a nminal center sectin 22 (the center sectin 22 is depicted in FIG. 1) diameter f 0.27 inches, the preferred diameter f the flat circular face 50 f the supercavitating insert 46 is n the rder f 0.10 inches in diameter. The preferred prtrusin distance f the supercavitating insert 46 frm the face f the lip 45 is 0.20 inches. The preferred diameter f the lip 45 is 0.16 inches. 20 The preferred nse taper angle 48 is five degrees. The verall cnfiguratin f the prjectile 10 with the three sabt petals 62 is shwn in FIG. 4. The sabt petal 62 is frmed in a 120 degree segment and the three sabt petals frm a cmplete 60 degree fit ver the center sectin 22 f prjectile 10. The circumferential grves 26 (as shwn in FIG. 1) f the prjectile 10 match with the 25 circumferential sabt grves 56. The sabts are held in place by the bturatin band 64. The bturatin band 64 prvides a gas seal during cartridge actuatin in the weapn.

9 NAVY CASE PATENT 5 During firing, the sabt petals 62 and the bturatin band 64 separate frm the prjectile 10 shrtly after muzzle exit frm the weapn. Stabilizing fins 14 are shwn fr reference. Qp^atijijailtheJnYentin FIG. 5 is a tw-dimensinal, graphical representatin f the cavitatin bubble 1 frmed by travel f the blunt nse thrugh the water. The cavity radius in units f inches, alng the rdinate f the graph, is shwn with respect t length f cavity in units f inches, alng the abscissa. The water cavity wall 72 stands ff frm the nse sectin 2 f the prjectile and ff the entire prjectile 10. By this means, the entire prjectile 10 travels inside f the cavitatin bubble as it travels thrugh the water. In this illustratin, 15 it can be seen that if the prjectile 10 is disturbed abut its lngitudinal axis, the tip f the fins 14 will cntact the water cavity wall prir t the shulder 42. One embdiment f the inventin is adapted t a subcaliber prjectile launched frm a 25mm caliber cannn. The cartridge used t launch the prjectile utilized existing parts frm the standard M919 cartridge, including the 25mm sabt assembly, the 20 bturatr, and the prpelling charge. The inventin, hwever, can be applied in similar fashin t ther lng-rd prjectiles. FIG. 6 illustrates the hydrballistic capabilities f several calibers f lng-rd prjectiles with the inventin incrprated int the rund. The prjectile velcity in units f feet per secnd, alng the rdinate f the graph, is shwn with respect t range f water travel in units f feet, alng the abscissa. The 25mm 25 hydrballistic ptential 81 shws the expnential decay typical f velcity degradatin

10 NAVY CASE PATENT 5 while traveling thrugh a fluid medium. The 0mm hydrballistic ptential 82, the 5mm hydrballistic ptential 8, the 40mm hydrballistic ptential 84, the 76mm hydrballistic ptential 85, and the 105mm hydrballistic ptential 86 are als shwn in this graph. The water entry velcities f each caliber represented in the graph are decayed frm the muzzle velcity by 1000 feet f air flight. The velcity ptential f 10 each caliber cartridge is driven by the particular design. The features and advantages f the present inventin are numerus. The inventin's unique supercavitating nse sectin allws current lng-rd ammunitin designs t have hydrballistic ptential. The supercavitating nse, which is designed t be incrprated as part f a subcaliber prjectile such as the M919's subcaliber prjectile, 15 is based upn a truncated cne with an extended tip whse diameter in this particular prjectile is 0.10 inch. The base diameter f the truncated cne is the diameter f the cylindrical center sectin f the subcaliber prjectile bdy. The angle f the truncated cne determines the majrity f the length f the supercavitating nse. The length f the extended tip, expressed in terms f the diameter f the tip, can be as shrt as 0.2 times 20 the diameter t as lng as 2.0 times the diameter. The extended tip diameter, the length f the extended tip, and the cne angle are critical t the stability during water entry and subsequent travel t the underwater target. The nse diameter als cntrls the diameter f the water cavity such that the water cavity wall clears the shulder f the nse cne at the jint with the prjectile's cylindrical center sectin. Hwever, the stabilizing 25 empennage n the aft end f the prjectile can cntact the water cavity wall prviding

11 NAVY CASE PATENT 5 stability befre the unstable situatin f the cne shulder cntacting the water cavity wall can ccur. The supercavitating nse tip diameter is made as small as pssible t reduce the hydrdynamic drag which results in high kinetic energy delivered t the target. The supercavitating nse tip diameter and cne angle are designed t ptimize drag reductin 10 while maintaining the required shape and mass distributin t prmte stability nt nly in water but als in air. The material chsen fr the prjectile has a number f prperties critical t the design. The tungsten ally r heavy metal equivalent must withstand the high impact lads due t high velcity water impact, particularly fr the nse tip. The prjectile 15 material must als maintain strength and ductility t withstand gun launch and hydrdynamic lads during underwater travel. T achieve high kinetic energy at the target, the density f the material must be high. The materials f the present inventin achieved but are nt limited t water entry velcities up t 400 feet per secnd. The use f the aft empennage fr stabilizatin in bth air and water gives further 20 advantage t the inventin. Using the empennage fr bth fluid mediums gives the inventin rbustness with simplicity. The empennage is preferably in the frm f fins, but it may be f a flared nature (flared designs have strength and mass prperty disadvantages). The prjectile's basic cnstructin is based n a lng-rd prjectile design which 25 incrprates empennage n the aft end f the prjectile that prvides bth aerdynamic and hydrdynamic stability. The frnt end, r nse, f the prjectile is shaped in such a 10

12 NAVY CASE PATENT 5 way that the water is displaced by the nse tip, creating a cavitatin bubble which is large enugh fr the rest f the prjectile t travel in. The 25mm M919 cartridge was chsen as the basis fr prf f the inventin, but wuld apply t ther calibers as well. The shape f the existing M919 prjectile was mdified t incrprate the supercavitating nse. 10 Althugh the inventin has been described relative t a specific embdiment theref, there are numerus variatins and mdificatins that will be readily apparent t thse skilled in the art in the light f the abve teachings. Variatins in nse tip design may imprve the capability slightly. T achieve underwater stability, the water cavity frmed by the tip must clear the frward part f the bdy such that the fins can 15 stabilize the prjectile. Nse tip designs including smaller diameter flats, flared, cnical, and pwer law shapes can be adapted t the prjectile t ptimize drag. It is therefre t be understd that ' the inventin may be practiced ther that as specifically described

13 NAVY CASE PATENT 5 ABSTRACT A supercavitating water-entry prjectile having empennage n the aft end which prvides bth aerdynamic and hydrdynamic stability and a supercavitating nse sectin is prvided. A representative prjectile is a subcaliber munitin adapted fr use in a 25mm weapn using a sabt currently in use with the M919 rund. The prjectile 10 has circumferential grves arund its center sectin t match these sabts. A key feature in the inventin is the size and shape f the nse sectin. The prjectile has a nvel high strength extended blunt nse sectin fllwed by a truncated cnical sectin which angles twards the bdy f the prjectile in the range f five degrees. During underwater trajectry, the entire prjectile is cntained within the cavitatin bubble frmed by the 15 blunt nse tip. The prjectile's aft empennage, which prvides bth aerdynamic and hydrdynamic stability, fits within the bre f the weapn. IX

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