DTIC S WL-TP A Multiple Armature Railgun Launcher WRIGHT LABORATORY, ARMAMENT DIRECTORATE

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1 "AD-A WL-TP A Multiple Armature Railgun Launcher Mark W. Heyse DTIC Wright Laboratory, Armament Directorate Analysis and Strategic.efense Division ELECTE Electromagnetic Launcher Technology Branch FEB W. Eglin Blvd., Ste 29 S ml Eglin Air Force Base FL W Antonlos Challita, Brian L. Maas, David P. Bauer lap Research, Inc Culver Avenue Dayton OH JANUARY 993 FINAL PAPER FOR PERIOD AUGUST APRIL 992 Approved for public release; distribution Is unlimited WRIGHT LABORATORY, ARMAMENT DIRECTORATE Air Force Materiel Command I United States Air Force I Eglin Air Force Base S2 069

2 NOTICE When Government drawings, specifications, or other data are used for any purpose other than in connection with a definitely Government-related procurement, the United States Government incurs no responsibility or any obligation whatsoever. The fact that the Government may have formulated or in any way supplied the said drawings, specifications, or other data, is not to be regarded by implication, or otherwise as in any manner construed, as licensing the holder, or any other person or corporation; or as conveying any rights or permission to manufacture, use, or sell any patented invention that may in any way be related thereto. This technical paper has been reviewed and is approved for publication. The Public Affairs Office has reviewed this paper, and it is releasable to the National Technical Information Service (NTIS), where it will be available to the general public, including foreign nationals. FOR THE COMMANDER Even though this paper may contain special release rights held by the controlling office, please do not request copies from the Wright Laboratory, Armament Directorate. If you qualify as a recipient, release approval will be obtained from the originating activity by DTIC. Address your request for additional copies to: Defense Technical Information Center Cameron Station Alexandria VA If your address has changed, if you wish to be removed from our mailing list, or if your organization no longer employs the addressee, please notify WIJMNSH, Eglin AFB FL , to help us maintain a current mailing list. Do not return copies of this paper unless contractual obligations or notice on a specific document requires that it be returned.

3 Form Approved REPORT DOCUMENTATION PAGE 0M No Public reporting burden for this collation of information is estimated to average I hour per response, including the time for reviewing Instructions, searching existing data sources. gatherng and maintaining the data needed, and completing and reviewing the collection of information. Send comments rerrding this burden estimat or any other apect of txis collcton of information, including suggestions for reducing this burden, to Washington HIeadquarters ServKies ctorate or Informnntion Operations and Reportls 25 Jefferson Davis Highway. Suite 204, Arlington. VA and to the Office of Management and Budget, Paperwork Reduction Project ( ). Washington. DC AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED I January 993 Technical Pa er. Aug 89 - Apr TITLE AND SUBTITLE 5. FUNDING NUMBERS A Multiple Armature Railgun Launcher C : F C-0285 PE': 65502F PR: AUTHOR(S) TA: 70 Mark W. Heyse, WL/HNSH WU: 7 Antonios Challita, Brian L. Haas, & David P. Bauer, IAP Research, Inc. WL Program Manager: Hark W. Heyse (WL/MNSH) 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) B. PERFORMING ORGANIZATION lap Research, Inc. REPORT NUMBER 2763 Culver Ave Dayton OH SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 0. SPONSORING/MONITORING Wright Laboratory, Armament Directorate AGENCY REPORT NUMBER Analysis & Strategic Defense Division Electromagnetic Launcher Technology Branch (WL/HNSH) 0 W Eglin Blvd Ste 29 WL-TR Eglin AFB FL the 6th Electro-. SUPPLEMENTARY NOTES Approved by PA for unlimited release in Apr 92, published in magnetic Launcher Conference proceedings. 2a. DISTRIBUTION / AVAILABILITY STATEMENT 2b. DISTRIBUTION CODE Approved for public release, distribution is unlimited. A 3. ABSTRACT (Maximum 200 words) As longer projectiles are accelerated, the efficiency (projectile' mass/launch mass) of the launch package decreases. The reduction in efficiency makes launching projectiles with a L/D (length-to-diameter ratio) greater than 20 undesirable. EN guns have several launch characteristics that differ from conventional guns. Higher launch velocities are achievable in EM guns because sonic gas velocities do not limit the projectile velocity. Acceleration profiles for EM guns are more constant. The acceleration forces can be distributed on the projectile easily because the accelerating force can be distributed with multiple armatures. These characteristics combine to make EM guns a very attractive approach for launching very long (i.e.. high L/D ratio) projectiles. Railgun launchers with multiple armatures can distribute the accelerating force. Each armature is supplied gun current for acceleration through its own set of rails. This multi-rail, multi-armature concept was tested at the railgum test facility. The results demonstrated feasibility. We were able to control current distribution to multiple armatures. This paper describes the theory and test results for multi-armature launch of high L/D projectiles. 4. SUBJECT TERMS IS. NUMBER OF PAGES Railguns, Electromagnetic Launcher, Electromagnetic Accelerators 2 6. PRICE CODE 7. SECURITY CLASSIFICATION 8. SECURITY CLASSIFICATION 9. SECURITY CLASSIFICATION OF REPORT OF THIS PAGE OF ABSTRACT 20. LIMITATION OF ABSTRACT UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED SAR NSN Standard Form 298 (Rev 2-89) Prescoibed by ANSI Std 3W

4 PREFACE This paper documents research conducted on multiple aruature/rail railguns for accelerating long rod penetrators. It was presented at the6th Electromagnetic Launcher Conference in Austin TX on 28 April to I May 992. This work was funded by WL/MNSH of the Armament Directorate at Eglin AFB FL under the Kinetic Energy Weapons Program of the Strategic Defense Initiative. Mr. Mark W. Heyse, Mr. James B. Cornette. and Mr. Nolan E. Taconi from WL/MNSH and personnel from UAP Research, Inc. in Dayton OH performed the work during the period of August 989 to April 992 at IAP in Dayton OH. A vhloa For~ -ueat I U iii/iv (Blank) iv A-: qab~jity Codes "'vf ll and/or tipeciaj

5 A MULTIPLE ARMATURE RAILGUN LAUNCHER Antonios Challita, Brian L. Maas, and David P. Bauer WAP Research, Inc., 2763 Culver Avenue, Dayton OH USA and Mark Heyse United States Air Force, WLJMNSH, Building 3, Eglin AFB FL Ahwtraw-As longer projectiles are accelerated, the Sabots are used to transfer accelerating forces to the efficiency (projectile mass/launch mass) of the projectile during launch. As the launch package exits launch package decreases. The reduction in the gun, the sabot separates from the projectile. The efficiency makes launching projectiles with a L/D sabot kinetic energy is wasted since it separates from (length-to-diameter ratio) greater than 20 the projectile at shot exit from the gun. Ideally, the undesirable. sabot mass should be zero to minimize this wasted EM guns have several launch characteristics energy. Longer, higher aspect ratio projectiles which differ from conventional guns. Higher require more sabot support to maintain acceptable launch velocities are achievable in EM guns projectile stresses. As projectile length increases the because sonic gas velocities do not limit the sabot size become so massive that a great deal of projectile velocity. Acceleration profiles for EM energy is wasted. It becomes inefficient to launch the guns are more constant. The acceleration forces package. Fig. I illustrates this point. The efficiency can be distributed on the projectile easily because of the launch package mass decreases with an the accelerating force can be distributed with increase in projectile L/D ratio. This reduction in multiple armatures. These characteristics combine launch efficiency reduces the desirability to launch to make EM guns a very attractive approach for long projectiles. The key to launching long launching very long (i.e., high L/D ratio) projectiles is to reduce sabot mass. projectiles. Railgun launchers with multiple armatures can distribute the accelerating force. Each armature. is supplied gun current for acceleration through its..., own set of rails. We tested this multi-rail, multiarmature concept at our railgun test facility. Our results demonstrated feasibility. We were able to control current distribution to multiple armatures. This paper describes the theory and test results for - multi-armature launch of high L/D projectiles. INTRODUCTION " High acceleration stresses make long, high aspect ratio projectiles difficult to gun launch. As longer projectiles are accelerated, the efficiency (projectile a I L 3 is 34 mass/launch mass) of the launch package gets worse. Prijctih Ltngth/ Di i lulr This work was sponsored by the US Air Force under Fig.. The efficiency of single sabot launch packages decreases with an increase in contract F C-O. projectile length.

6 Normally, one sabot is used to accelerate a one sabot. An electromagnetic (EM) railgun is not projectile. The sabot is designed to support most of subject to the same limitations. EM forces can be the rod length. It transfers accelerating force via distributed on multiple sabots by distributing current shear, all along the supporting interface. This between sabots. interface is illustrated in Fig. 2(a). Here, portions of the rod are shown unsupported. The unsupported rod MULTIPLE ARMATURE/SABOT LAUNCH must be strong enough to withstand the tensile and PACKAGE AND BARREL compressive stresses due to acceleration. These stresses are highest at each end of the sabot, as Design Fig. 2(a) shows. For stronger rods or lower accelerations, the length of unsupported rod can be There is an optimum number of sabot/armatures increased. With an increase in unsupported length, for a specified long rod projectile []. However, in sabot size and mass shrinks. this paper we will focus on the two sabot configur- A multiple sabot launch package improves launch ations. We also assume that equal acceleration forces package efficiency by reducing sabot mass. A on the two sabots is desired. What is needed is an multiple sabot package allows an increase in the EM gun which provides controlled acceleration forces length of unsupported rod. This is shown in Fig. to multiple sabot/armatures (the armature is meant as 2(b). The multiple sabot package not only has both the current carrying part of the sabot). ends of the rod unsupported, it also enables In an EM gun, the acceleration force (the Lorentz unsupported length in the middle of the rod. Each force) is due to the interaction of the current flowing segment of unsupported rod is sized to not exceed in the armature with the magnetic flux density tensile and compression strength limit. The multiple imposed on the armature [2]. This force may be sabot launch package allows us to reduce the total expressed by: sabot mass compared to single sabot packages. Less energy is therefore lost due to sabot mass. F = hx B, () The use of multiple (two or more) sabots as shown in Fig. 2(b), can reduce sabot mass for long where B f magnetic flux density, rods launched from any type gun. In conventional I = armature current, and propellant guns however, it is difficult to adequately (a armature width. distribute the propellant gas pressure on more than SABOTSABOT SABOT - I - 0 roact Ion PreJoe: I I * reocilon I " F gh a I Fig. 2(a) A long rod, launched with a conventional single sabot, has high stresses as each end of the sabot. Fig. 2(b). Two sabots distribute launch loads causing high projectile stresses at four locations on the projectile. 2

7 Armature acceleration force is clearly controlled the total current is about 70% to the leading and 30% by magnetic flux density and armature current. to the trailing. This result is derived from the fact Fig. 3 is a sketch of a two armature launch packages that the magnetic flux B, is about twice B, for teh in a two-rail pairs railgun. This sketch identifies the 70%-30% current split. current in each armature and the magnetic field imposed on each armature. The leading armature is CURRENT DISTRIBUTION CONTROL similar to the normal EM gun. The magnetic field is due to the current flowing through the leading Achieving the necessary leading and trailing armature. The leading armature acceleration force is current distribution cannot be accomplished in a expressed by: normal railgun consisting of two conducting rails and similar armatures. Current will share depending on Ft = It ca x Bt, (2) the resistance of the two paths. Most of the current would flow through the trailing armature. The where B, = magnetic flux density imposed by required current distribution can be achieved by current to the leading armature, on properly selecting the electrical impedance of the the leading armature, and components in each circuit. These components are: Ii = leading armature current. ) armatures, 2) rails, and 3) power supply. We evaluated all three methods for current control and determined that current distribution control by using separate power supplies is the most advantageous. F =ItxB Controlling current distributionby connecting each rail segment to a separate power supply is the.,,simplest and most flexible method. With this method, the armature impedance is unimportant. Both metal and hybrid armatures can be used, and Z. transition of one armature does not affect the current distribution. The disadvantage is that two separate power supplies are required. Modular power supplies T"IUM ~"-t are ideal for this application. This is the method that Fig. 3. Magnetic flux on leading and trailing we selected to use for demonstrating the multiarmature is not equal (arrow size indicates armature launch technique. current magnitude). TESTING THE MULTI-ARMATURE AND MULTI-RAIL DESIGN The magnetic field imposed on the trailing armature is due to the current to the trailing armature We constructed a barrel and the required power plus the magnetic field due to current to the leading supply interfaces and tested the launcher by launching armature. The force on the trailing armature is long rod projectiles to high velocities. A description expressed as: of the launcher, launch packages, and test results follows. Ft =i I, (. x ['B, + B30], (3) Launch Package where B, = magnetic flux density imposed by current to the trailing armature, A photograph of a typical launch package is on the trailing armature, shown in Fig. 4. The projectile was a tungsten rod B,, = magnetic flux density imposed by the with an L/D ranging from 20 to 40. The armature current to the leading armature, on and sabot functions were integrated into one the trailing armature, and component. We elected to use metal armatures for I, = trailing armature current. this application. The launch package had two armatures (a leading and a trailing). The leading Examination of (2) and (3) reveals that to obtain armature was composed of two halves; a top leading equal forces on the leading and trailing armatures, the and bottom leading. Each half was powered by a currents in the leading and trailing armatures must be separate rail pair. The trailing armature was powered unequal. In fact, to obtain equal forces the split of by the current from the center rail. Current in each 3

8 The barrel operated extremely well. The : : " : inductance gradient was about 0.4 micro-henry per meter. We were able to independently power each rail pair throughout the tests. The straightness of the 7 L rail was not as good as we would have liked. A better scheme to attach the middle rail is needed for future testing. The details of the barrel performance is described in another paper presented at this Fig. 4. The launch package had two conference by the authors (3]. armatures powered independently. Interface We modified our existing power supply-gun rail pair was about equal. interface to accommodate the need to power the armatures independently. We built an inteiface which Barrel allowed us to provide 5/8 of the total current to the leading armature and 3/8 of the current to the trailing We designed and constructed a 30 mm square armature. This was possible because of the bore EM gun barrel with three rail pairs. The EM modularity of the power supply. A photograph of the gun barrel is shown in Fig. 5. The rails were gun interface is shown in Fig. 6. This top view of insulated from each other with a /6 inch thick GIO the interface shows two plates, one feeding the insulator. The three rails were pinned together along trailing armature rail and one feeding the leading the length of the bore with nylon pins. The pins were armature rails. This interface performed extremely spaced about 8 inches apart. The rail spacing was well. We were able to maintain separate power to maintained with a 30 mm GlO insulator. We used a the armatures. 3 m gun for most of our tests. The rails were enclosed with a stainless steel laminated structure. three rail pair EM barrel, to each rail pair. /4

9 Launch Results We conducted a total of 8 tests during the development and demonstration testing of the multi- I ' armature, multi-rail launch system. The test para- I meters are presented in Table. The launches were CC conducted with tungsten rods with an L/d rangingt --- from 20 to 40. The total current levels ranged -. from 500 ka to I MA. The rod mass ranged from.4 60 to to g. g. The launch highest package successful mass launch ranged velocity from. N J8247 achieved was 200 m/s. Typical current, muzzle. * - voltage, and velocity traces are shown in Figs These are for a launch package of 75 g. Fig. 7 ' shows the total current as well as the leading and "in, (,s) trailing armature current during the shot. Fig. 8 illustrates the current split among the armatures. Fig. 8. Current split remains constant throughout Note that the current split remained constant throughout the launch. The muzzle voltage traces of each rail pair are shown in Figs. 9, 0, and.."'": Fig. 9 is for the top leading armature, Fig. 0 is the, muzzle voltage of the bottom leading armature, and l[ Fig. I is for the trailing armature. Note that all,,' three armatures contacts remained metal-to-metal., i contact throughout the launch. The average velocity I is shown in Fig. 2. The velocity was computed -" from the B-dot data. The post-test observation and B- 39 dot data indicated that the launch package remained intact throughout the launch.. X2 In this program, we successfully demonstrated the,. feasibility of using a multi-armatures and rails.3 L 2., concept to launch long rods to high velocities. This (P.) methodology has the potential of achieving high Fig. 9. Top leading muzzle voltage. velocity and high efficiency launches (low parasitic mass). Higher velocities could not be achieved with this present system because of in-bore balloting caused by rail misalignment and lack of sabot support L/E" of the rods.,, ' " '' 7"~a 7 Tl ".~~~~Total ;',.,, * "".- Il Lo". - I.e I Thi..d;W.~,,_ ~ 4.o~ ' *.. - l S.0-30O.. I It 4 m, -L~~ 3 S W. 84 Tir (PS) Fig.0. Bottom leading muzzle voltage. Fig. 7. Typical rail current traces for multi-armature railgun. W 5 AVAILABLE TO DTIC DOE8 NOT PERMIT FULLY LEGIBLE REPRODUCT-OY?

10 se - I To 847 o,.. t-l- g I fto i A Fig.. Trailing muzzle voltage. Fig. 2. B-dots are used to compute average velocity. TABLE. LONG ROD LAUNCH SUMM4ARY 263mm 8240 NIA N/26.0 bruti~ ccow 5ail mat.asingle brailen Rod broke unguts Trailing arm dug jeni rail So~uinurod launch t Predicted velocity was 00 ads ' Saadoinuy me. uouare B go trailing arm Repastof Ten09 uuing CJbank IS Rcpu&a(ofT 0 atower crrent only leading rails powered Only trailing rail$ powered S Rod broke 2 am frmbrooc S.9 64.S Socotard taumch Amontazise~d ad of rod S.3 Succpm raw L4 Rod hbrb early as CONCLUSION REFERENCES Based on our development work, we demonstrated ( Bauer, D. P., 'Anti-Armor Electric Rail Gun% Report No. that EM guns can be designed to launch very long ADE-4l lss. January 984. projectiles by distributing the launch force along the [2 Barber,. P.. -Me Acceleration of Macroparticles and a length of the rod via multiple amature-rail pairs. Hypervelocity Electronmagnetic Accelerator*, The Australian This method takes advantage of the unique features of National University. EP-Tl2, March 972. the railgun (controlling forces by controlling current), [)MsBinLBur ai. n hlis nois and can be exploited to achieve hypervelocity launch *3Mut-anBianl of long rods. Future work must incorporate sabots Muh-Ra-08 Banary which provide better external projectile support and.jaar9 improve rail construction to provide higher precision bore. Barrel Depavid P..forande elei.p~~o ader"ma Repilrt ANto.nio, (W" AvArILALL ~- W ES NOT PERMI FTJW LEU'b",LLE. " 6

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