UNCLASSIFIED AD NUMBER ADB087370 NEW LIMITATION CHANGE TO Approved for public release, distribution unlimited FROM Distribution limited to U.S. Gov't. agencies only; Test and Evaluation; Oct 84. Other requests must be referred to ARDC, Attn: SMCAR-TSS, Dover, NJ 07801-5001. AUTHORITY DTIC Form 55, Control No. 1127009, dtd May 15, 2001. THIS PAGE IS UNCLASSIFIED
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UNCLASSIFIED
AD NUMBER
ADB087370
NEW LIMITATION CHANGE
TOApproved for public release, distributionunlimited
FROMDistribution limited to U.S. Gov't.agencies only; Test and Evaluation; Oct84. Other requests must be referred toARDC, Attn: SMCAR-TSS, Dover, NJ07801-5001.
AUTHORITY
DTIC Form 55, Control No. 1127009, dtd May15, 2001.
THIS PAGE IS UNCLASSIFIED
:-AD
AD-E401 243
0
TECHNICAL REPORT ARSCD-TR464022
CC00
30-MM TUBULAR PROJECTILE
* LUCIAN M. SADOWSKIK EDWARD T. MALATESTA
JOSEPH HUERTA
OCTOBER 1984
U..ARMY ARMAMENT RESEARCH AND DEVELOPMENT CENTERU FIRE CONTROL AND SMALL CWER WEAPON SYSTEM LARATORY'DOER, Mw wRE
Distribution fimrited to U.S. Government agencies only; test and evaluation; OctoberI19F4. Other requests for this document must be referred to ARDC, ATTN: SMCAR-TSS, LDover, NJ 07801-5001.
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.~84 210 2601-..
T" I-1l ' .I V% --- 7 W
The views, opinions, and/or findings contained inthis report are those of the author(s) and shouldnot be construed as an official Departmert of theArmy position, policy, or decision, unless sodesignated by other documentation.The citation in this report of the names ofcommercial firms or commercially availableproducts or services does not constitute officialendorsem-rent by or approval of the U.S.Government.Destroy this report when no longer needed. Donot return to the originator.
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UNCLASSIFIEDL:u qITY CLASS!ICICA'TICN OF THIS PAGE "Ihie, Pats Knfered)
REPORT DOCUMENTATION PAGE RI 'AD INSTtIrFioNsIAEPOX c tIII'LlTINC I'ORM
I REPORT NUMBER 2,
GOVT ACCESSION NL. k t'CIPIrNT'2 CATA,) NLJMHFP
Technical Report ARSCD-TR-84022 ____ -/
4. TITLE (and 'i,;httIe) "vPE OF RF,'.RT & PERI('O) C " ErF"
II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE
ARDC, TSD October 1984STINFO Division (SMCAR-TSS) 13. NIIMBER or PAGLE
Dover, NJ 07801-5001 9614. MONITORING AGENCY NAME & ADDRESS(II different fro;m Caontrolling Office) I5 SECURITY CLASS. I th s rop,,tn)
UnclassifiedI507DECLASSIF ICATIUN DOWNGRADING
SCHEJULEI
16. DISTRIBUTION STATEMENT (of this Report)
Distribution limited to US Government agencies only; test and evaluation;October 1984. Other requests for this document must be referred toARDC, ATTN: (SMCAR-TSS) Dover, NJ 07801-5001.
17. DISTRIBUTiON STATEMENT (of the abstract entered In Block 20, It different fron Report)
I8. SUPPLEMENTARY NOTES
19. KEY WORDS (Continue on reverse aide If necesiry ind Identify by block number)
Tubular projectile Aircraft weapon§Tubular ammunition Welded overlay band
Plastic bandsSTUP ammo30-mm ammunition
20. ABSTRACT (Catiue sa reve stil It necseary eau IdentIfy by block number)The feasibility of tubular ammunition (sometimes referred to as STUP ammo) hasbeen examined for both air-defense and air-to-air applications. The reducedtime of flight, high kinetic energy at the target, low manufacturing costs andincreased effectiveness have enticed weapon systems managers for half a decade.As a result, the Armament Division of the Fire Control and Small Caliber WeaponSystems Laboratory was asked to initiate the development of a 30-mm tubularcartridge for use in a weapon system feasibility demonstration called highimpulse airborne demonstration (HIGAD). (cont)DDFORM
DO , A 1473 EDITION OF I NOV 65 I5 OBSOLETE UNCLASSIFIEDL SECURITY CLASSIFICATION OF T; IS PA',E (Wh Vets EnteiII
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UNCLASSIFIEDSECURITY CLASSIFICATION Otw THIS PAGE(tWo Des Eloed)
20. ABSTRACT (cont)
The effort consisted of: an analytical study to determine the optimumdesign for the tubular projectile, fabrication of tubular projectiles(both copper and plastic rotating bands were investigated), ballistictesting and reduction of the data.
The results of the effort are:
0 The parametric analysis revealed that the benefit of the subcalibertubular projectile in terms of time of flight was outweighed by theincrease in kinetic energy which would be delivered to the target bythe full bore projectile;
* The projectiles with plastic rotating bands remained intact and obturated
well; and
* The projectile had reduced time of flight to a range of 2100 meters,where the projectile became high drag, causing the projectile to berange limited. This unique property makes a tubular projectile anideal training round.
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UNCLASSIFIEDSECURITY CLASSIFICATION OF THIS $PAGE 47,.n Oar. F,,Iad)
4.4 .~
IPAGE
Introduction 1
Parametric Analysis 1
Computation of Projectile Weights 2
Design Characteristics of the Tubular Projectiles 3
Flow Characteristics of the Tubular Projectiles 3Configuration Design Requirements 4Internal Ballistics 5Stress Analysis 6
Fabrication 6
Projectile 6Pusher Plate 7Obturator 7
Evaluation 8
Inspection 8Indoor Range Testing 8Exterior Ballistics 9
Conclusions 10
References 11
Appendixes
A. Copper Banded Projectile 57B. Plastic Banded Projectile 61C. Radar Test Results 65
Time of FlightVelocity Decay
D. Drag Coefficients 77
Distribution List 95on For
NTIS GRA&iDTIC TABUnannounoedJustflioati0o
By .. . .Distribution/Availability Codes
Dist Special
TABLES
Page
1. Constraints for parametric analysis 13
2. Steel 14
3. Tungsten 15
4. Internal ballistic sumary 16
5. Geoetric properties 17
6. Inspection of GAU-8 plastic banded tubular projectile 18
7. Inspection of GAU-8 copper banded tubular projectile 19
8. Inspection of Hispano Suiza tubular projectile 20
16. Modification of copper banded GAU-8 projectile 46
17. Zero degree impact of shot 2 on 2-in. armor 1.55 in. 47penetration
18. Back of armor of shot 2 48
19. zero degree impact of shot 4 on 2 in. armor 1.59 in. 49penetration
20. Side of armor from shot 4 50
21. Impact at 600 obliquity of shot 10 on 1.05 in. 51armor-complete penetration
ift
PAGE
22. Back of armor of shot 10 52
23. Impact at 560 obliquity of shot 9 on 1.5 in. 53armor 1.10 in. penetration
24. Pressure time curves GAU-8 tubular projectile 54
plastic banded and copper banded penetration
25. 30-ram GAU-8 projectiles CD vs Mach numbers 55
26. 30-m Hispano Suiza projectile CD vs Mach numbers 56
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INTlMDUCION
A tubular projectile is a cylindrical projectile with a large circular ductalong the longitudinal axis. When launched from a gun, the projectile uses a
4pusher plate and an obturator to seal the propelling gases behind the projectilewhile in the gun tube. When the projectile exits from the muzzle, the pusherplate and obturator are completely separated fron the projectile. The properlydesigned hollow projectile launched at or above the design Mach number willachieve the desired supersonic internal flow conditions. This flow conditionproduces the ideal low drag characteristics of the tubular projectile. As thevelocity of the projectile decreases, the internal flow urdergoes a change andbecomes choked. In the choked flow condition, air continues to flow internally,but at subsonic velocity. In this mode, the drag is similar to a streamlined
L, standard projectile.
Although, experimentation on tubular projectiles can be traced as far backas 1858 very little knowledge about supersonic flow, particularily in ducts, wasknown until after 1944. Use of this supersonic flow theory permitted a truescientific evaluation of tubular projectiles in the late 1960's by the CanadianDefense Research Establishment. During the early 1970's, the ARDC WeaponSystems Concept Team (WSCr) conducted experimentations on tubular shapes in avariable Mach number wind tunnel. Based on the findings from these experimentsthe WSCr developed a design methodology for tubular shapes for ballisticapplications. Limited investigations of several tubular applications wereconducted in several caliber sizes. The largest effort was the 20-mn programwhich resulted in the automatic firing of tubular projectiles from the vulcanair defense system. This firing yielded system dispersion for the tubularprojectile in the M61 automatic gun and a measurement of velocity as a functionof time which yielded drag coefficients as a function of Mach numbers.
The purpose of the effort described in this report is to determine singleshot dispersion of a tubular projectile when fired from a hard mount and toverify the existing value of drag coefficients as a function of Mach numbers.
PARAMETRIC ANALYSIS
The foundation of any parametric analysis is a good understanding of theconstraints placed on that analysis and the variables which are permitted. Thisprogram was funded by the Army Aviation Systems Command (AVSCXI) who directedthat this ammunition effort be on tubular ammunition for air-to-air (helicopter-to-helicopter) engagements. Since this ammunition effort was to be ccmpatiblewith the weapon for the high impulse gun airborne demonstration (HIGAD), theammunition was constrained to function in the 30-nun, GAU-B system. This
constraint defined the gun caliber, gun tube length, peak chamber pressure,ammunition impulse and available case volume. The Weapon Systems Concept Tham(WSCr) recommended the highest length to diameter ratio (L/D) possible withoutexceeding 3. The interior ballistics investigation was limited to conventionaltechnology by the available funding. The projectile material selection was alsolimited by available funding. The parametric analysis was conducted on bothsteel and tungsten projectiles but actual hardware fabrication was limited tothe steel projectiles only.
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An effective analysis would strive to obtain the highest possibleprobability of kill. Such an analysis would be very complex and would requirevulnerability testing and scenerio definition. It was decided to simplify theanalysis by assuming that time-of-flight to the target would be the parameter tominimize. Time-of-flight would be ccmputed for various projectiles as thecaliber was varied from a subcaliber size of 12am through the full bore size of30nm. Once the caliber of the projectile was defined, the length was determinedby the maximum length to diameter ratio of 3. To preclude exotic advances inthe state of the art of internal ballistic technology the authors limitedthemselves to real and achievable muzzle velocities which were obtained usingthe projectile internal ballistics analysis (PIBA) program. This ccmputer codein FORTAN uses the ballistic curves developed by Dr. H. P. Manning for
N% calculating the velocity performance of smnall arms weapon systems.
SCMTATION OF P1WJCTILE WIGHTS
In order to calculate the total launch weight of the tubular projectileassembly, the dimensions of two existing tubular projectile designs (20-nrn and30-rim) were analyzed. Three analytical equations to determine the weights ofthe projectile, the pusher plate and the obturator were generated. Theseequations listed below required only the outer diameter of the flight projectileand the density of the material being considered.
1 T = D FR30 1) T (2.541)
Wp =1 R30D Pp (0.4)
Wo=8 R P0 ROD 10.348-R2oo]
Where:
Wr = Weight of tubular flight projectile (grains)
ROD = Radius of tubular flight projectile (inches)
PT = Density of tubular flight projectile material (grains/inch3)
Wp = Weight of pusher plate (grains)
P = Density of pusher plate material (grains/inch3)
WO = Weight of obturator (grains)
Po-- Density of obturator material (grains/inch3)
Using the above equations both the launch and flight weights of the tubularprojectile in steel and tungsten were computed in 2-mm increments from 12-nmthrough 30-m. The flight weights for the steel tubular projectiles are showngraphically as a function of diameter (see figure 1).
2
Those weights and the GAU-8 system constraints (see table 1) were then usedas input to the interior ballistics program (PIBA) to cunpute both muzzlevelocity and single shot impulse to the gun. The muzzle velocities of the steelprojectiles are depicted as a function of subcaliber diameter in figure 2.Figure 3 shows single shot impulse for the steel tubular projectiles as afunction of the subcaliber projectile diameter. Table 2 lists launch weight,flight weight, muzzle velocity and impulse for all of the steel subcaliberprojectiles and table 3 lists the same parameters for all of the tungsten sub-caliber projectiles. It is noted that all cases meet the impulse constraintwhich was 150 lb sec.
The flight weights and muzzle velocities of the various subcaliber tubularprojectiles of tables 2 and 3 were then used as input to a two degree of freedomcomputer program to compute the time of flight to various ranges of interest.The program uses Newtonian mechanics to calculate the trajectory of projectiles.This program also requires the input of a drag coefficient vs Mach number curveto compute the time of flight. The best available drag coefficient which wasdetermined from the 20-mn tests conducted at Ft. Bliss, TX was used. Thecomputed data for the subcaliber steel tubular projectiles summarized in figure4 graphically shows the time-of-flight to various ranges as a function of thediameter of the subcaliber steel tubular projectile. Examination of this dataindicates that the optimum steel tubular projectile is somewhere in the range of22-m to 24-qm in diameter and that is only markedly noticeable at the longerranges of 2500 meters to 3000 meters. At the more probable ranges of engagmentbelow 1500 meters, the time-of-flight curve is almost flat, fielding adifference in time of-flight at 1500 meters between the 22-um subcaliberprojectile and the 30-nn full bore projectile of approximately 0.12 seconds.This modest gain in time of flight to 1500 meters is insignificant when comparedto the decrease in kinetic energy delivered to the target at 1500 meters. Thefull bore 30-mn delivers more than 52,000 ft pounds as compared to the 24,000 ftpounds delivered by the subcaliber 22-m. In addition, the full bore 30-num willaffect an area on the target that is 87 percent greater than the area affectedby the subcaliber 22-mn tubular projectile. Using engineering logic in lieu ofa detailed analysis one can see that the most effective projectile choice wuldbe the full bore 30-mn tubular projectile.
DESIGN CHAXTERISTICS OF TE "UUAR PRWCrILES
* Flow Characteristics of the Tubular Projectiles
0With increasing demand for high performance in projectiles, various meanshave been used to minimize the total drag of a shape. ibis decrease in drag hasbeen brought about to a certain degree by streamlining the nose, boattailing theaft section, or by emission of gases at the base. These methods appear to be
'* reaching an asymptotic limit on drag reduction for conventional shapes. Theproperly designed unconventional tubular shape shows excellent promise ofperformance superior to that of existing low drag conventional shapes.
To obtain an appreciation of the low drag potential of tubular shapes, theelements contributing to the total drag at supersonic speeds should bedescribed. The major contributors to drag for conventional shapes are the
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frontal area (forebcxy) and the base. A tubular shape, correctly designedexternally and internally will show an appreciable decrease in both frontal andbase drag because of the presence of the internal passage and minimal losses dueto the internal flow. The skin friction drag is higher than that of theconventional configuration, because in addition to external skin friction, thereis internal skin friction present due to the internal flow. But the overalldrag coefficient is decreased by a factor of two when compared to mostconventional projectiles available to date.
Proper internal supersonic flow conditions must exist to allow the low dragperformance of the tubular configuration. The internal flow becumes supersoniconly when it is said to be swallowed. This is generally indicated when a lip ornose shock wave is generated externally as shown in figure 5. A choked flowcondition which indicates a high drag mode is characterized by detached or bowshockwave as indicated in the same figure. It should be noted that the chokedflow condition can result in one of two ways. Improper internal design of thetubular projectile will cause a choked flow condition at all velocities. Aproperly designed tubular projectile will experience a choked flow conditiononly when the projectile decelerates to a Mach number too low to sustaininternal supersonic flow. The change from low drag condition to a high dragcondition is instantaneous at this critical Mach number.
Configurational Design Requirements
The Aerodynamics Research and Concepts Assistance Section (ARCAS) ChemicalSystem Laboratory, has been doing developmental wrk on tubular projectileshapes of various sizes since 1974. Experience has shown that there mst betrade-offs in the design approach in order to obtain reasonable projectileweight and low drag characteristics.
The internal geometry was selected to allow the tubular projectile todecelerate to a Mach number of 1.8 before the high drag mode was reached. Theinternal portion of the projectile (see figure 6) consists of the .nvergence
section, constant area section, and the divergence section. The length todiameter ratio of three has been considered a practical ratio.
The 30-mm tubular projectile shape used in these tests has the followingdesign characteristics:
o Nose lip angle of 100
o Boattail angle of 100
o Internal divergence angle of 30 15'
o A length to diameter ratio of three.
o Welded overlay rotating band or plastic rotating band.
Figure 6 shows the general contour and pertinent dimensions of the 30-mm tubularprojectile tested in the program.
4
KInternal BallisticsThe selection of an optimum propellant for the 30-rm tubular cartridges
consisted of two steps. The first step entailed using analytical methods toselect the propellant for the cartridge. The second step involved ballisticfirings in order to verify that the propellant yielded the predicted muzzlevelocity within the pressure constraints of the barrel.
The tubular projectile with sabot was predicted to be 250 grams. Thelength of projectile travel is 2.25 meters (88.58 inches), the barrel cross-sectional area is 7.35 square centimeters (1.139 square inches). The casevolume available for propellant was estimated to be 162 cubic centimeters (9.9cubic inches). Using the computer code, PIBA and propellant masses of 154 and162 grams, the code predicted muzzle velocities of 1280 meters per E73cond (nips)and 1310 meters per second (rps), respectively. Therefore, a minimum muzzlevelocity of 1280 naps (4200 feet per second) will be obtainable.
Due to limited funding, conventional propellants were selected which would9 yield the greatest muzzle velocity but also conform to the operating pressures
of the weapon. Three single base extruded propellants were selected, IMR 6962,CR8325, and IMR4996. The relative quickness values based on IMR4350 as astandard are 64, 58, and 51 respectively.
With propellants selected, internal ballistic testing was conducted onFebruary 26, 1979. A 30-rm Hispano Suiza barrel and cartridge case were used asthe test vehicle due to availability of components. The barrel was attached toa hydrorecoil bond mount. A lumiline screen was placed at a distance of 7.62meters from the muzzle and another lumiline screen was placed at a distance of3.05 meters beyond the first screen. A counter was attached to the lumilinescreens to record the time interval for determination of velocity. Peak chamberpressure was recorded using a copper crusher gage. A total of 15 rounds ofammunition was fired during the test. Table 4 summarizes the results.
Three propellants were tested in order of increasing relative quickness.Propellants IMR4996 and IMR6962 were eliminated due to excess pressure. Duringtesting, a graphical prediction showed that for IMR4996 a loading density of 100percent would yield a peak pressure of 434 mega pascals (MPa) (63 kpsi). Thispressure is above the 393MPa nominal operating pressure for the system. The 581
MPa reading for IMR6962 clearly eliminated this propellant, as well. Theloading density of CR8325 --is increased based on a revised prediction of tubularintrusion into the cartri..e case. At a loading density of 105 percent,repeated firings yielded a velocity of 1277 meters per second (m/s) with astandard deviation of 6 m/s. The calculated muzzle velocity was 1286 m/s, whichwas satisfactory. The mean peak pressure of 430 MPa with a standard deviationof 1OMPa was higher than the nominal pressure, but was within the maximumallowable pressure for the barrel. Since this effort was to demonstrate aconcept, propellant CR8325 was used for ballistic testing.
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Stress Analysis
, The structural integrity of any new concept should be analyzed beforefabrication. A finite element scress analysis was conducted at ARDC on theinitial design (see figure 7). 'he results indicated a substantial amount ofplastic deformation in the base of the projectile from the base to a distance ofapproximately 3.81mm from the base. This deformation can alter theconfiguration of the boattail of the projectile and could lead to in-bore
"- problems with the projectile. In addition, the stresses in the bottom of thecrimp groove were near the yield point. The stresses in the remainder of theprojectile including the rotating band and its interface with the body were lowand provided a large margin of safety.
With these results, several design modifications were made. After a fewiterations, a final design emerged (see figure 8). The boattail angle waschanged from 100 to 80. The exit/diverging angle was changed from 3 degrees, 15minutes to 3 degrees. This change increased the surface area on the base of the
* projectile, which in turn decreased the stress in the base of the projectile.The plastic deformation in the base of the projectile was eliminated.
The above changes in the projectile configuration changed the geometricproperties of the projectile. Table 5 compares the initial design to themodified design. These slight differences in the geomatric properties of theprojectile designs were not expected to affect the flight characteristics.Therefore, the hardware was fabricated in accordance with the modified design.
FABRICATION
The tubular projectile consists of three parts: projectile, pusher plate,and obturator. Three different projectiles were fabricated for this effort:two configurations for air to air applications and one configuration for airdefense application (see figure 9). A different procedure was used to fabricateII each projectile component. The details of the processes are presented below.
.' Project ile
The projectile was machined from AISI-4340 steel bar stock. The bar stockwas sectioned and machined for application of a copper rotating band, or aplastic rotating band. The details of the procedure for a copper bandedprojectile will be presented first, followed by the plastic banded projectile.For the copper banded projectile, a blank was sectioned from bar stock andmachined (see figure 10) so as to be compatible for use in a copper overlaywelding machine. A hole through the blank along its axis was required so watercould be circulated for cooling of the blank during banding using the weldedoverlay machine. An iterative approach was required in order to define theproper wire thickness, current settings, rotating rates and number ofrevolutions required to band the projectile. The details of the bandingprocedure are discussed in appendix A. A total of 100 blanks were banded.
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Forty of the 100 banded blanks were machined to the original tubular design.The remaining blanks were machined to the modified design. The banded blankswere machined close to final dimensions, then heat treated to obtain a hardnessof 52 and 54 on the Rockwell C scale. Upon completion of heat treatment, theblanks were polished to final dimensions (see figure 11), yielding a tubularprojectile.
With the recent advances made in the field of plastic rotating bands, 39steel projectiles were machined from AISI 4340 steel bar stock. In order toaccommadate a nylon rotating band, a slight band seat of 0.5 millimeters wasmachined into the projectile before heat treatment. The projectiles werepolished to final dimensions. Two techniques investigated by the Air Force wereconsidered for application of the rotating band onto the projectile.
The first technique consists of applying a coating of plasma sprayedmaterial onto the band seat and then injection molding plastic onto thisundercoating creating a rotating band (ref 1). The Air Force projectiles werefired in a GAJU-8 barrel. Muzzle velocities of 1280 to 1370 ups were recorded.In flight photographs showed that the band obturated well, imparted spin to theprojectile and remained in tact after launch. The second technique consisted ofapplying an adhesive to the band area and then injection molding the band to atubular projectile body. The Air Force tubular projectile resembled the ARDCdesign. For this technique, no band seat is required. The results of thetesting revealed that the rotating bands remained intact after launch, obturatedwell and imparted spin to the projectile. Muzzle velocities in excess of 1219raps were recorded.
The second technique was chosen for application to the ARDC tubular
projectiles. The banding process is described in Appendix B. Figure 12 showsthe projectile at various steps in the fabrication process from bar stockthrough completion using the plastic injection molding technique.
Pusher Plate
The pusher plate was machined from AISI-4340 steel bar stock. The plateswere heat treated to a hardness on the Rockwell C scale of 52 to 55. The plateswere then machined to final dimensions.
cbturator
The obturator was machined from 31.75 millimeter bar stock. The materialwas nylon 6/12.
The next section of the report deals with the inspection, assembly andtesting of the projectiles.
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EVALUATION
The evaluation of the tubular projectiles consisted of three phases.First, an inspection of the cczponents; second, indoor range testing to evaluatechamber pressure, muzzle velocity, sabot discard and integrity of theprojectile; and third exterior ballistic testing to determine dispersionparameters, time of flight, velocity decay and a drag curve for each of theprojectile designs.
Inspection
The plastic banded, copper banded, GAU-8 and Hispano Suiza tubularprojectiles were inspected for critical dimensions. An extensive examination ofthe GAU-8 plastic banded tubular projectiles revealed dimensional uniformitywithin the manufactured lot (table 6). The copper banded projectiles (table 7)and the Hispano Suiza tubular projectiles (table 8) were inspected to a lesserdegree; however, uniformity was met for these rounds as well. The pusher plateand the obturator (table 9) for the GAU-8 tubular projectiles were inspected forkey dimensions. Only the mass was provided on the Hispano Suiza obturators andpusher plates (table 10). Examination of all data reveals uniformity throughoutthe lots.
Indoor Range Testing
The tubular projectiles were tested in the following order, Hispano Suiza,GAU-8 plastic banded; and, lastly, the GAU-8 copper banded tubular projectiles.Lumiline screens were placed at 8.5, 23.8, 39.0 meters fran the muzzle of thegun. A micro-flash photography apparatus was placed at 8.5 meters fram themuzzle of the gun. Armor plate was placed at 45.7 meters fram the muzzle of thegun.
A total of 21 rounds was tested in an indoor range. The Hispano Suizaprojectiles were fired from a Hispano Suiza field barrel. Plastic banded GAU-8projectiles were fired from a GAU-8 Mann Barrel. The in-flight photographs (seefigures 13 and 14) revealed that the rotating bands produced a good gas seal andthat the projectiles are structurally sound. The chamber pressure and muzzlevelocities (tables 11 and 12) for the Hispano Suiza and plastic banded GAU-8projectiles confirmed the results that were obtained fran the internal ballisticportion of the program. However, the high chamber pressures that wereencountered during the initial testing of the GAU-8 tubular copper bandedprojectiles (see figure 15 and table 13) lead to a redesign of the copperrotating band. After several iterations, a relieved rotating band (figure 16)yielded a moderate pressure and muzzle velocity.
The penetration data gathered against the armor plate which was placed at 45.7meters (150 feet) fran the muzzle of the gun is shown in tables 11, 12 and 13.The projectile would not penetrate 5.08 centimeters of armor at 0 degreesobliquity (see figure 17, 18, 19, and 20) but will penetrate 5.08 centimeters ofarmor at 60 degrees obliquity (see figures 21 and 22). (Depth of penetrationwas measured normal to armor plate surface). At large angles of obliquity, the
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projectile digs itself into the armor plate (see figure 23). Due to itshardness, the projectile fragments upon impact. Further testing will berequired to determine the ballistic limit of the tubular round of ammunition.
Examination of yaw cards which were used for the first two rounds firedreveal that the pusher plate will depart from the projectile flight path withina 4 degree cone angle. The obturator will depart from the projectile flightpath within a 2 degree cone angle.
Exterior Ballistics
The external ballistic testing of the three different projectiles consistedof two phases. The first phase conducted in March 1980 pertained to measuringthe dispersion parameters of the projectiles and obtaining determination of thechamber pressure and muzzle velocity. The second phase conducted in May 1980pertained to the Hawk radar tracking of the projectiles in order to determinethe drag coefficients for the tubular projectile.
During the first phase, an accuracy target was placed at 1000 meters fromthe muzzle of the barrel. Chamber pressure (see figure 24) muzzle velocity, andthe velocity of each round was recorded (table 14). The dispersion for the GAU-8 target practice projectiles manufactured by Aerojet, had a mean radius of 0.7mils. The plastic banded GAU-8 tubular projectiles and copper banded GAU-8tubular projectiles had a mean radius of 0.4 and 0.9 mils, respectively.
The dispersion is not available for the Hispano Suiza tubular projectiles.After several attempts to walk the projectiles onto the target, the test wasconcluded (ref 2). The problem did not lie with the ammunition but with thebarrel. The Hispano Suiza barrel was not clamped in the proper places during
- the test firings. This was not discovered until after the test. The test was'4 concluded in order to save the remaining projectiles for the Hawk Radar Test.
The Hawk Radar Test was conducted in May 1980. A total of 22 rounds ofammunition was tested (table 15). Of the 22 rounds of ammunition tested, 8 ofthe projectiles were target practice rounds, which were fired for reference.The Hawk Radar data was reduced to generate range and velocity as a function oftime of flight. Appendix C contains time of flight and velocity decay data f-reach round of ammunition. The time of flight values were reduced to generate adrag curve for each of the rounds of ammunition presented in Appendix D. Foreach of the different types of projectiles, a mean drag table was generated.This mean table is simply the arithmetic mean of the individual rounds ofammunition. The mean values were then plotted to generate drag curves for eachdifferent type of projectile. Figure 25 ccmpares the GAU-8 plastic banded andcopper banded tubular projectiles with the 30-nm GAU-8 Aerojet target plasticprojectiles. Figure 26 compares the Hispano Suiza tubular projectiles with theHispano Suiza target practice projectiles. It is interesting to note that thedrag curve for the Hispano Suiza tubular projectile fits between the drag curvesfor the two GAU-8 tubular projectiles.
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CCNCLUS IONS
The 30-u tubular projectile program was a success. The results of theprogram worth noting are summarized below:
1. The parametric analysis revealed that the difference between the full boreand subcaliber tubular projectile in terms of time of flight was outweighed bythe increase in kinetic energy which would be delivered to the target by thefull bore projectile. Therefore, the full bore projectile was selected for theprogram.
• 2. The stress analysis conducted on the design of the projectile revealedpossible structural problems could occur in the base of the projectile.Ballistic testing of the original design, Hispano Suiza tubular projectile,showed that the concern expressed was unnecessary.
l 3. The plastic rotating bands on the tubular projectiles remained intact andobturated well. The muzzle velocity and peak chamber pressure prediction were
*. verified by the ballistic tests.
4. The tubular projectile has significant reduced drag coefficient as comparedto conventional projectiles at high Mach number. This property of the tubularprojectile yields reduced time of flight to a range of 2100 meters. Then, theprojectile becomes high drag, causing the projecitle to be range limited. Thisunique property makes a tubular projectile an ideal training round.
5. The amount of reduction in the time of flight of a tubular projectile ascompared to a conventional projectile at a distance of 2,000 meters isapproximately 25%. The percent difference in the drag coefficient at Mach 2.5between the tubular projectile as compared to the conventional projectile isapproximately 50%. The dispersion of the tubular projectile is approximatelyof the dispersion for the conventional projectile.
6. The purpose of the program did not entail determining the ballistic limit ofthe tubular projectile; therefore, no comment will be made on this point.
10
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References
1. Stephen J. Price, Rotating Band for High Velocity Thin-Walled Projectiles,Report Number AFATL-TR-79-7, Florida, January 1979.
2. George B. Niewenhous, Feasibility Test of 20n Tubular Projectile, MaterialTesting Directorate, Maryland, 1978.
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pAPPENDIX A
I.9 CliPPER BANDED PLEJDZTILE
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I'I
II
I.9
I
5 57
I
The banding of the steel projectiles was a manual procedure. The equipmentrequired for the process consisted of a tungsten inert gas (TIG) welder,rotating table, and CDA-189 copper wire of various diameters. A total of 10 barstock sections, blanks, (see figure 10 in body of report) from the 100 blank lotwas used to determine the procedure for applying the bands to the blanks. Theprocedure consisted of placing a blank into the rotating table, and applying aweld bead in a tightly wound helix onto the band seat area. Initially, wire of2.38-mm diameter was selected. Eleven revolutions were required of the blank toapply sufficient copper to the bank seat area for the rotating band. (No waterwas circulated through the projectile using this manual procedure.)
Examination of the band seat after chemically etching the copper from thesteel body revealed a smooth surface, indicating little absorption of thesubstrate material into the band. It was determined that only 0.25 percent ofthe steel diffused into the copper band. The time required to perform the taskwas approximately 30 minutes per blank. The amount of copper applied to theblank exceeded the maximum dimension for the rotating band. In order to reducethe time required to band the projectile, the wire was changed to a diameter of3.18 millimeters. Four revolutions were required, for a total of eight minutes.However, etching revealed cracks in the band indicating an unacceptable weld.After numerous attempts to weld the band onto the blanks failed, a decision wasmade to return to the 2.38 millimeter diameter wire for the banding of thestock.
The process requires a considerable period of time to apply the copper toeach bar stock section, but this procedure resulted in an acceptable copperrotating band. The TIG weld process using 2.38-wm wire was used to apply thecopper to the bar stock sections.
59
APPENDIX B
PLASTIC BANDED PFCJECILE
pEVIOUS PAOE
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The procedure used to prepare the projectiles for banding and the materialsused are described in this section.
The tubular projectiles were placed in a bath of trichlorethylene andsoaked until the surfaces were free from oil. The projectiles were thencentered in a lathe and rotated. The hand seat was cleaned with emery paper toremove the oxidized surface. The outside surfaces were wiped and lint wasremoved by ccpressed air. After all the projectiles were prepared, theprojectiles were placed in a lathe for the second time. Using a small paintbrush, a coating of 253-P adhesive was aplied to the band seat area, from thecrimp groove to the boattail. The projectiles were air dried overnight. Thefollowing day, the projectiles were placed in a 2320 oven for 45 minutes. Thetemperature of the projectile, the nylon 12 and the 3 piece insert for thesingle cavity mold (see figure B-1.) were checked periodically until all threeitems were the same temperature. The projectiles were inserted one by one intothe mold. In a period of 45 minutes the 42 projectiles were banded. During thebanding process, a projectile was tested for structural integrity of therotating band. The projectile was placed into a fixture to simulate the landsand grooves of a barrel. A 9 kilogram mass was dropped 1.8 meters aito theband. This simulated the approximately 81 joules the projectile wouldexperience in the launch environment. No cracking or separation of the bandfrom the projectile body was observed.
After the projectiles cooled to roam temperature, they were placed in thelathe for the third time. The band was turned to a diameter of 31.14 + 0.05n.n.The diameter is based on the groove diameter of the barrel of 31.19 + 0.05m. Aleading and trailing angle of 15 + 2 degrees was placed on the band to eliminateplastic filaments as the band is engraved. It was thought that these filamentsincrease drag during flight.
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APPENDIX C
PADAR TEST RESULTS
TIME OF FLIGi~rVELOCITY DCY
I6
A total of 22 projectiles were tracked by the Hawk Radar. Target practiceprojectiles were fired as well as the tubular projectiles. The key parametersfor the projectiles are presented in Table C-i. The meterological data which isrequired to reduce the radar data is contained in Table C-2. Tables C-3 throughC-7 contain the time of flight and the velocity of the projectiles as a functionof range.
The numbering of the projectiles 1 through 22 in the tables in appendix Ccorrespond to the values presented in Table 15 of the report. Target practiceprojectiles were fired before and after the GAI-8 tubular projectiles and theHispano Suiza tubular projectile . The target practice projectiles serve as areference round so that comparison can be made between a conventional projectileand the tubular projectile. The radar data was reduced at 0.02 seconds time offlight intervals. Tables C-3 through C-7 summarize the reduction of the radardata.
The choking of the air flow through the tubular projectile is evident inthe velocity decay plot for the tubular projectile. For example, figure C-l isthe velocity decay plot for the GAJU-8 target practice projectile. The curve hasa gradual change in slope. Figure C-2 is the velocity decay plot for theplastic banded GAUl-B tubular projectile. The velocity decay curve has a sharpdiscontinuity at 2.5 seconds of flight. This discontinuity represents theunique property of the tubular projectile.
To the left of the discontinuity, the air flows through the center of theprojectile. To the right of the discontinuity the flow is choked. Thisdiscontinuity is observed for each of the tubular projectiles.
The time of flight values were used to generate by computer methods thedrag coefficients, CD as a function of the projectile velocity. Tables D-1through D-10 contain the drag coefficients for each of the 5 different types ofprojectiles. The numbers in the column headings of the tables refer to thefiring sequence of the projectiles.
For each of the different projectile types, a mean drag table wasgenerated. Tables D-2, D-4, D-6, D-8, D-10, refer to the GAU-8 target practice,GAU-8 plastic banded tubular projectiles, GAU-8 copper banded tubularprojectiles, Hispano Suiza target practice, and Hispano Suiza tubularprojectiles respectively. The CD values in the above tables are the arithmeticmean of the individual values for each projectile. The mean values are plottedas Figures 22 and 23 in the report. The mean values of CD should be used togenerate ballistic trajectories.
CommanderU.S. Army Armament Research and Development CenterArmy Armament, Munitions and Chemical ComandATr : SW.AR-TSS (5)
SMCAR-SCSMCAR-SCASM'AR-SCA-U, (6)
SMCAR-SCSSMCAR-SCM-PSWEA&-LCA-0PS'I~cAR-SCA,-,O
S .AR-SE-IADover, NJ 07801-5001
ComanderU.S. Army Armament, Munitions and Chemical CcammndATTW: AMEb-GCL (D)Dover, W1 07801-5001
AdministratorDefense Technical Information CenterATIN: Accessions Division (2)Cameron StationAlexandria, VA 22314
DirectorU.S Army Material Systems Analysis ActivityATTN: RXSY-MAberdeen Proving Ground, MD 21005
Cnander/DirectorChemical Research and Development CenterU.S. Army Armament, Munitions and Chemical CenarATTN= SMCAR-SP-I
SIEAR-RSP-A (5)APG, Edgewod Area, MD 21010
DirectorBallistics Research LaboratoryATTN: tRXBR-OD-STAberdeen Prcting Ground, MD) 21005
ChiefBenet Weapons Laboratory, LCLArmament Research and Development CenterU.S. Army Armament Research and Development ComandAT7N: DRSC-ICB-JMWatervliet, NY 12189
95
CommanderU.S. Army Armament Munitions and Chemical CommandATTN: AMSMC-LEP-LRock Island, IL 61299
DirectorU.S Army TRADOC Systems Analysis ActivityATIN: ATAA-SLWhite Sands Missile Range, i4 88002
CammanderU.S. Army Aviation Research and Development CaziandATN: DRDAV-NSt. Louis, MO 63166
DirectorApplied Technology LaboratoryU.S. Army Research and Technology LaboratoriesATI: DAVDL-ASL-ASWFort Eustis, VA 23604