Aerodynamics of a 0.60 Caliber Electromagnetic Projectile

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AD-A234 660MEMORANDUM REPORT BRL-MR-3907BRL

AERODYNAMICS OF A 0.60 CALIBERELECTROMAGNETIC PROJECTILE

JAMES M. GARNER 3T105 ~MAYO02 1991APRIL 1991

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED.

BESTAVAILABLE COPYU.S. ARMY LABORATORY COMMAND

BALLISTIC RESEARCH LABORATORYABERDEEN PROVING GROUND, MARYLAND

9.1 5 01 01.5


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Aerodynamics cf a 0.60 Caliber Electromr-gnetic Projectile6. AUTHOR(S) 1L 62618AH80

James M.Garner7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATIONREPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRES.Ik 5) 10. SPONSORING, MONITORINGAGENCY REPORT NUMBERBallistic Research LaboratoryATTN: SLCBR-DD-T BRL-HR-3907Aberdeen Proving Ground, MD 21005-506611. SUPPLEMENTARY NOTES

12a. DISTRIBUTION AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution is unlimited.13. ABSTRACT (Maximum 200 words)

Spark photography range tests of a 0.60 caliber electromagnetic projectile were conducted todetermine the aerodynamic characteristics at supersonic velocities. The design demonstratedadequate stability and typical drag characteristics. The effect of an asymmetric base geometryon the location of the aerodynamic center of pressure is also shown.

14. SUBJECi fERMS 15. NUMBER OF PAGESRail Guns 20Armatures 16. PRICE CODE17. SECURITY CLASSIFICATION 18. SECURITY LLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACTOF REPORT OF THIS PAGE OF ABSTRACTUNCLASSIFIED UNCLASSIFIED UNCLASSIFIED SAR

7S 0 550S29F1ED Slaroard o r ,98 Rev 289)

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AcknowledgementsThis work is supported by the Close Combat Armament Center, Armament ResearchDevelopment and Engineering Center, Dover, NJ through the Joint Services Small ArmsProgram. Thanks are extended to Mr. Michael Nusca, of BRL, for assistance in computingthe aerodynamic center of pressure locations for different projectile orientations, and toDavid Hepner, also of BRL, for graphics help. Consultation with James Bradley, of BRL,concerning aeroballistic coefficient determination is also appreciated.

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Table of ContentsPage

ACKNOWLEDGE MENTS .. . . .. . . . .. . . . .. . 1lLIST OF FIGURES.........................................1viLIST OF TABLES.......................................... ixINTRODUCTION...........................................1BACKGROUND.............................................1TEST RESULTS............................................1I

Drag Coefficient................................ ..... 2Lift Coefficient....................................... 2Static MXomnent Coefficient................................ 2Center of Pressure of Normal Force..........................3Pitch Damping Coefficient .. .. .. .. ... ... ... ... ... ..... 3Modal Damping Rates. .. .. .. ... ... ... ... ... ... ..... 3Electromagnetic Considerations .. .. .. .. ... ... ... ... ..... 4

CONCLUSIONS .. .. .. ... ... ... ... ... .... ... ... ... .... 4LIST OF SYMBOLS .. .. .. .. ... ... ... ... .... ... ... ... .. 13DISTRIBUTION LIS r.. .. .. .... ... ... ... ... ... ... ...... 13


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List of FiguresFigare Page

1 Projectile Configuration ........ .............................. 52 Zero Yaw Drag Coefficient versus Mach Number ..................... 63 Zero Yaw Lift Coefficient versus Mach Number ......................4 Zero Yaw Static Moment Coefficient versus Mach Number .............. 85 Center of Pressure versus Mach Number ........ ................... 96 Zero Yaw Pitch Damping Moment Coefficient versus Mach Number... . . .. 107 Damping Rate Exponents versus Mach Number ..... ................ 11

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INTRODUCTiONIn December 1989 a meeting between Armament Research Development and Engi-

neering Center and Ballistic Research Laboratory (BRL) personnel reviewed the progressof the 0.60 caliber electromagnetic (EM) projectile. The conclusion of the meeting wasthat a spark range test should precede EM firings to be conducted at the University ofTexas (UT) in June of 1990. Since the modest small caliber range facilities bordered themachine snop area at UT. it was considered important to determine the behavior of theprojectile beforehand. This report details the aeroballistic behavior of the EM projectileas determined from the spark range test at the BRL Aerodynamics Range.

BACKGROUNDA sketch of the 0.60 caliber projectile tested is shown in Figure 1. The tungsten nose

of the projectile is a Sears-Haack shape. This nose section threads into the aluminumafterbody. The afterbody, flare, and armature are one piece and form the remainder of theprojectile. The exterior grooves, shown near the nose afterbody joint, allow the afterbodyto support a torlon bore-rider (not shown). Small fins, dubbed "finlets", are shown on thearmature portion of the projectile. The finlets are roughly an eighth of a centimeter highand two and one half centimeters long. Their purpose is to add pitch-plane stability. Aslot extending from the rear of the projectile to the rear of the flare is also shown. Theslot's purpose is electromagnetic in nature. Finally, the rear view shows a noncircular basethat attempts to maximize the conductivity to armature weight ratio.

TEST RESULTSTable 1 contains salient projectile physical characteristics. The two transverse mo-

ments (I., and I, in the pitch and yaw planes respectively) and axial rr ment of inertiadiffer widely due to the projectile's mass distribution. The ratios of the transverse mo-ments to the axial are roughly five times larger than a typical round. The following table.Table 2, is a tabulation of the aeroballistic coefficient values obtained from the test.

Interior ballistic modelling indicated that the projectile survived acceleration loadsgreater than 100,000 g's. This information indicated UT's standard safety measures wouldbe appropriate when testing.

A tricyclic reduction was employed in determining the projectile characteristics. 2 Thetricyclic reduction is normally used when a projectile asymmetry exists. For the reductiona third, constant magnitude, modal arm, K 3 , is assumed in addition to the two modalarms of the epicyclic motion. The size of this arm depends on the reduction data, but it

'Braun, W.F. "The Free Flight Aerodynamics Range, I .S Army Ballistic Research Laboratory, Aberdeen Proving (Ground.MD, F RL Report No. 1048, A'igust 1958. AD 202249)2 Mtirphy, C.I.. Free Flight Motion of Symmetric Missiles" I'S. Army Ballistic Research Laboratorv, Aberdeen Proving(round, MD. BRI, Report No. 1216 July 1963. (AD 142757)


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is typically smaller than the other two epicyclic modal arms.Some criteria and general engineering rules-of-thumb are applied when examining the

data in the reduction process. Firstly, the data from the rounds with the fewest numberof range stations are examined closely. Another standard is that the K, arm must begreater than 3 times the fitting error,' The C~iqv + CNM1 0 value in Table for Round 19437did not pass this criterion, and is therefore absent. Absolute errors as a percentage of thecoefficient values are listed in the reduction printout.

Drag CoefficientThe drag coefficient for the 0.60 caliber projectile is assumed to be of the form:

CD = CD 0 + CD 62 62 + ...... (1)

where CD is the range value of the drag coefficient, CD0 the zero yaw drag coefficient. othe quartic yaw drag coefficient, and 62, the yaw squared.4 The zero yaw drag coefficientdat a it by a least squares curve, displayed in Figure 2 how a typical supersonic declinewith increasing Mach M) number (the quartic yaw drag (ontribution is small comparedto CD0o). The curve fit is done for rounds with similar values of CD, 2 and excludes rounds19452 and 19453

The 0.60 caliber EM projectile drag coefficient is roughly 10% smaller in comparisonto INTERACT predictions for a projectile with a full flare and circular base at I = 4 to5 The effect of the finlets on the drag coefficient is probably on the order of 5-10%. 6

Lift CoefficientSimilarly the lift coefficient for zero yaw, CL . 0 , as a function of Mach number is shownin Figure 3 The graph illustrates a small variation from approximately M= to 5.

Static Moment CoefficientThe variation in static moment coefficient for zero yaw, CN1 0 with respect to Machnumber is shown in Figure 4. This graph indicates that the projectile has adequate stabilityin the Mach range depicted.

3 bid'Murphy, C H.,"Data Reduction for the Free Flight Spark Ranges," U S. Army Ballistic Research Laboratory. Aberdeen

Proving GroundMD, BRIL Report No 900 February 1954. (AD 035833)'Nusca, M J."Superonic/Hypersoruc Aerodynamics and Heat Transfer for Projectile Design using Viscous-Inviscid Inter.action" BRL-.TR-3119, June 1990. (ADA 224354)'Celmjns, l. Drag and Stability Tradeoffs for Flare-Stabilized Projectiles, U.S Army Ballistic Research Laboratory Ab-erdeen Proving Ground MD, Paper presented at the 28th Aerospace Sciences meeting, Reno, NV AIAA Report txO-K6s,January 1,990.

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Electromagnetic ConsiderationsMany of the projectile attributes are driven by EM factors. These factors must beaddressed if a successful design is to be achieved, They are:

1. The armature must make good electrical contact with the railsanid condtict the required current.

2. The projectile should eliminate or at least minimize arcing.

3. The projectile support mechanism must not interfere with current path.

Other considerations such as transient launch stresses due to rapid current rise times areimportant. This may be primary in the material selection for future afterbody sections.It is hoped a two jointed projectile design, with a tungsten nose and a high strength.lighi weight afterbody material, rmay permit higher launch acceleration, further improvestability, and enhance terminal ballistic effects.

CONCLUSIONSThe aerodynamic characteristics of the 0.60 caliber F.M round are well behaved inthe Mach number range from 1.2 to 5. In addition the projectile survived accelerations inexcess of 100,000 g's, and is suitable for testing at the University of Texas range.The noncircular base has lessened the drag without sacrificing projectile stability.The projectile design represents an efficient combination of aerodynamics and armature

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Table 1. Projectile PhysicaI Cl arawt rReference Diameter 1 524 cmCenter of Gravity 4.31S ciniLength Overall 8 S0 c'iiNose Length 2.408 ciiiSlot Width .(*)S c'i,Weight 31.4S grmiisPitch Plane .Moment of Inertia 238 46 graili-cin'Yaw Plane Moment of Inertia 237. T2 gram-cii-Axialt Moment of Inertia 4.58 grIlT -('11i

'Table 2. AerodynamI (oeffi('intsRound Mach No. CDo CL, C Cx , + C, A.I0 i19452 1.196 .617 2.34 -1,97 -40.2 -1SO : 39519453 1 312 .521 2.29 -1 85 -25.7 -171 -.363)19454 2.237 .395 2.09 -1.33 -20.8 -. 131 -.23719457 3.9,42 .270 1.96 -1.01 -. 107 119458 4.500 .215 1-94 -0.96 -10.8 -.1)3 -. 14519459 4.884 .197 1.93 1-0.93 -10.2 W .01 ,

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LIST OF SYMI3(LS

CD Drag coethicioiitC1 . Lift coeticienitCM1 Static mon11ilt CoefficienitCM + M . Pitch (lalflilg" Moment coefficb mi1tC PN Ceniter )f Jpre-.siire of normal )forc ill calibers from the

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Aerodynamics of a 0.60 Caliber Electromagnetic Projectile