.

Dispersion Analysis of the XM881

Armor-Piercing, Fin-Stabilized,

Discarding Sabot (APFSDS) Projectile

by Thomas F. Erhe

and Man IF. Hathaway

,

Approved for public release,; distribution is unlimited.
The findings in this report are not to be construed as an official

Department of the Army position unless so designated by other

authorized documents.

Citation of manufacturer’s or trade names does not constitute an

official endorsement or approval of the use thereof.

Destroy this report when it is no longer needed. Do not return

it to the originator.
Army Research Laboratory

Aberdeen Proving Ground, MD 21005-5066

ARL-MR-433 January 1999

Dispersion Analysis of the XM881

Armor-Piercing, Fin-Stabilized,

Discarding Sabot (APFSDS) Projectile

Thomas F. Erline

Weapons and Materials Research Directorate, ARL

Alan F. Hathaway

Arrow Tech Associates

Approved for public release; distriiyXion is unlimited.
- .

Abstract

This study compares the results of a dispersion test with mathematical modeling. A 1 Q-round

group of modified 25mm XM881 armor-piercing, fin-stabilized, discarding sabot (APFSDS)

projectiles was fired from the M242 chain gun into a designated target. The mathematical

modeling results come from BALANS, a product of Arrow Tech Associates. BALANS is a

finite-element lumped parameter code that has the capability to model a flexible projectile being

fired from a flexible gun. It also has the unique feature of an automated statistical evaluation of

dispersion. This study represents an effort to establish a combined experiment and simulation

approach to reduce system error.

ii
Acknowledgments

.

Mr. T. Marrs of the U.S. Army Aberdeen Test Center (ATC) performed centerline

measurements. Mr. B. Hudler, from the U.S. Army Research Laboratory (ARL), performed

projectile measurements. Mr. B. Patton (ARL) performed testing with Mr. D. McClelland of

Defense Services, Inc. Mr. B. Guidos (ARL) performed the jump analysis and provided the

authors with constructive guidance. Mr. K. Soencksen (ARL), Dr. P. Plostins (ARL), and

Mr. R. Whyte of Arrow Tech contributed to the yaw analysis.

. . . ill
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Table of Contents

1.

2.

2.1

2.2

2.3

2.4

3,

3.1

3.2

3.3

3.4

4.

5.

Acknowledgments....................................................................................................

List of Figures..........................................................................................................

List of Tables ...........................................................................................................

Introduction .............................................................................................................

Experimental Approach .........................................................................................

Overview of the Experiment ...............................................................................

Description of the XM881 ...................................................................................

Bore Straightness.................................................................................................

Experimental Results ..........................................................................................

Analytical Approach ...............................................................................................

Overview of BALANS ........................................................................................

BALANS Model of tRe XM88 4. ..........................................................................

Deterministic Analysis ........................................................................................

Stochastic Analysis .............................................................................................

Comparison Between Experimental and Analytical Results...............................

Summary and Conclusions.....................................................................................

References ................................................................................................................

Distribution List ......................................................................................................

Report Documentation Page ..................................................................................

I+Jg

..a

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vii

1

2

2

2

4

4

6

6

8

10

11

14

15

17

19

23

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vi
List of Figures

Figure

1. Jump Test Instrumentation ........................................................................................

2. XM881 Flight Vehicle at Mach 4.0 ..........................................................................

3. M242 Barrel SN 273 for the 25-mm Chain Gun.......................................................

4. The 25-mm XM881 Means of Jump Components....................................................

5. The 25-mm XM881 Dispersion of Jump Components .............................................

6. Analytical Approach to Predicting Dispersion ..........................................................

7. Graphical Representation of the XM88 1 Lumped Parameter Model .......................

8. Interaction Forces: (a) Straight Centerline, (b) SN 273 ...........................................

List. of Tables

Table

&

3

3

4

5

5

7

9

11

1. XM88 1 Sensitivity Data ............................................................................................ 12

2. Manufacturing Tolerance Information ...................................................................... 13

3. Simulated TJD Results of 10 Simulations of lo-Round Tests .................................. 13

4. Components of Dispersion (From Simulation No. 3) ............................................... 14

5. Total Dispersion Comparison.................................................................................... 15

vii
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. . .

Vlll
1. Introduction

The U.S. Army has a need to improve its understanding of the effectiveness of

medium-caliber cannon systems. One of the methods for advancement toward this

understanding is to perform experirnental aerodynamic jump tests and mathematical modeling

that simulates the jump tests. One fielded system of major interest is the 25-mm M242

Autocannon, which is found on the Bradley Fighting Vehicle. This gun system was selected for

study by the U.S. and German Defense Exchange Agreement No. 1132. This system is ideal for

setup in a small-caliber range, such as the Aerodynamics Range Facility at the U.S. Army

Research Laboratory (ARLJ at Aberdeen Proving Ground (APG), MD.

The current service round, used with the 25-mm M242 Autocannon, is the M919

armor-piercing, fin-stabilized, discarding sabot (APFSDS) projectile used for armor penetration.

This round has a depleted uranium penetrator that would contaminate the experimental facility.

Therefore, the XM881, which has a tungsten penetrator and was a precursor of the M919,

presents itself as a suitable substitute. The XM881 has a flight vehicle that is geometrically

similar to the M919, including matching threads for fitting the sabot; however, the discarding

sabot of the XM88 1 was totally different from the M919. To better emulate the M919, it was

decided to replace XM881 sabots with the sabots used on the M919.

The dynamic state of a projectile at shot exit is determined in part by the in-bore launch

disturbances experienced by the projectile as it traverses the length of the barrel. A contributing

factor is the initial misalignment of the projectile’s principal axis and center-of-gravity (CG)

offset with respect to the bore centerline, As the projectile is driven axially downbore by the

propellant gas pressure, it is also forced to travel a lateral path that is determined by static and

dynamic curvatures. Tube droop in the vertical plane is a gravity-induced static curve, and the

bore straightness profile is a static curve due to the manufacturing processes’ inability to produce

a perfectly straight bore. The firing of the gun produces an array of complex interdependent

events. Axial travel of the projectile and propellant gas pressure will impart forces on the gun

for recoil and slight bending in the barrel. The projectile reacts in flexure to the massive barrel,

a
and the barrel responds to the projectile loads. The dynamic lateral path then becomes a

boundary condition of projectile balloting.

The balloting analysis program, BALANS, from Arrow Tech Associates, Inc., was chosen

for this study because of its multifunctional abilities, It has the capability to perform a single

shot deterministic case in either two or three dimensions and target impact dispersion analysis

using a stochastic approach.

Under this mission for investigating the experimental performance of the XM881, it is

believed that good agreement between the experimental results and modeling results with the

BALANS program will allow modeling to point to areas that need improvement. This is

especially true in the area of gun tube straightness and interactions between the projectile and the

gun tube. In this study, for example, both experiment and modeling show the in-bore balloting

reactions to be a significant contribution to dispersion.

2. Experimental Approach

2.1 Overview of the ExpertienL The M242 chain gun was setup at the Aerodynamics

Range of ARL, APG. A schematic of the test setup is shown in Figure 1. Two eddy probe

stations that measure lateral displacements were positioned about the muzzle brake of the gun to

capture the muzzle motion. A pressure probe trigger was located just outside of the muzzle to

start the experimental equipment. A sabot catcher plate was positioned several meters from the

muzzle. Six orthogonal x-ray stations were positioned within 2 ms of the muzzle to capture

velocity, yaw, and yaw rates. There were 25 orthogonal shadowgraph stations to measure the

flight vehicle motion (see Figure 2). At 100 m from the muzzle, a target setup recorded shot fall.

The muzzle displacements, pointing angles, transverse velocity, and angular velocity were

determined using data reduction analysis techniques found in Haug and Bornstein [l].

2.2 Description of the XM881. The XM88f is a 25-mm APFSDS experimental round that

has gone through a number of design iterations. The XM881 specimens available did not match

2
Eddy Probes

6 Orthogonal

X-rav Stations

25 Orthogonal

Shadowgraph

Stations

J \

Pressure

Probe

Trigger

100-m Target

1

iEl

Figure 1. Jump Test Instrumentation.

Figure 2. XMSSI Night Vehicle at Mach 4.0.

the particular versipn of the penetrator drawings found. Therefore, detailed measurements were

performed. The total length of the flight vehicle is 153.0 mm with the penetrator length of

82.8 mm and threaded length of 29.4 mm starting at 64.4 mm from the base of the flight vehicle.

(Refer to Figure 2 showing a print of a shadowgraph of the flight vehicle from the test.) The

original sabots were removed from the flight vehicle and replaced with those found on the M919.

3
2.3 Bore Straightness. The M242 chain gun was set up with barrel serial number (SN) 273,

which was measured for centerline straightness and bore gauged for service condition. The

vertical (without gravity droop) and horizontal centerline referencing the rear face of the tube

(RFT) of SN 273 is shown in Figure 3. The manufacturing irregularities noted in the centerline

are typical with positive up and to the gunner’s right.

0.2

0.15

0.1

0.05

0

-0.05

-0.1

-0.15

-0.2

-0.25

iv242 -SN273

-Horizontal

-Vertical -dro

Length (m m) RFT=O

Figure 3. M242 Barrel SN 273 for the 25-mm Chain Gun.

2.4 Experimental Results. The experimental results are utilized in jump and dispersion

models that are defined in Plostins et al. 121. The means of major angular components of jump

and dispersion are displayed in Figure 4 in milliradians. The muzzle pointing angle component

is noted as “PA.” The muzzle of the gun has transverse velocity noted as ‘TV,” which imposes

on the projectile at shot exit. The angular deviation ‘of the projectile center of gravity relative to

a coordinate system attached to the muzzle at shot exit is known as projectile “CC” jump. The

“CC” jump is caused by in-bore balloting, muzzle blast, projectile mechanical disengagement,

and sabot discard. The component noted as “AJ” is aerodynamic jump, which is the mean

angular deviation of the projectile swerve trajectory. There was no measurable evidence of

disturbance from sabot discard on the projectile “CC” jump. The sabot discard was completed

within 0.15 m from muzzle, which is too close to the muzzle to capture in the x-ray stations. In

Figure 4, positive is up and to the right.

4
0.6 7 1

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

-1

PA CV CG AJ TOTAL

HAzim uth

I E levation

Figure 4. The 25mm XMSSl Means of Jump Components.

The standard deviations of the components of jump are displayed in Figure 5. The dispersion

model may be simple if the total dispersion is the result of the sum of the independent individual

jumps. The square of the standard deviations of the individual jump components will sum to the

square of the impact dispersion. This empirical model appears to be best suited for this type of

experiment.

0.6

0.5

0.4

0 0.3

0.2

0.1

0

PA CV CG AJ TOTAL

=Azim uth

IE levation

1

Figure 5. The 25mm XM881 Dispersion of Jump Components.

5
3. Analytical Approach

3.1 Overview of BALANS. BALANS [3] simulates the dynamic response and interaction of

a flexible projectile and a flexible gun tube during in-bore travel. It also includes the effects of a

curved bore profile. The simulation utilizes individual models of the projectile and gun tube, in a

time step iterative solution Pertinent motion and load data are periodically saved during the

analysis to produce selective summary graphical displays. BALANS takes advantage of the

interior ballistics simulation and CG offset calculations of PRODAS [4] and an automatic

lumped parameter modeling capability to assist in building a BALANS model.

The analytical procedure utilized in BALANS presupposes that the projectile is initially

misaligned within the gun tube due to manufacturing tolerances. During firing, this

misalignment produces secondary forces, causing transverse displacement and yawing motion of

the projectile as it travels from breech to muzzle. The resulting yaw angle, angular rate, and

transverse velocity at muzzle exit are then analyzed for their effects on ‘dispersion. It should be

noted that BALANS calculates the projectile state (yaw, yaw rate, and transverse velocity) at

muzzle exit while the experimental setup determines the state of the tube and bore at the

projectile exit.

Figure 6 contains a flow diagram of this stochastic method for predicting dispersion.

Whether trying to predict dispersion on a new design or solve a dispersion-related problem on a

current design the approach is very similar. It begins with gathering basic technical information

such as manufacturing dimensional data, assembly drawings and/or specifications, and analytical

results from other analyses or tests such as finite element analyses or experimental results of the

sabot front borerider. This information is critical to building the accurate analytical model of the

projectile to be used during all analyses within this approach. From this

study can also be performed for input into the in-bore balloting analysis.

information, a tolerance

6
Production History

. CG Offset Analysis

+ +

Physical Properties Interior Ballistics

+ +

BA’ ANS

*

Muzzle Exit Condition Sensitivities

I

Target Impact Dispersion Analysis

. Statistically determine exit. transition, 4

and free flight conditions.

. 10 tests of 20 rounds

+

Stochastic Dispersion Prediction

Figure 6. Analytical Approach to Predicting Dispersion.

The second piece of information required is production history information suclh as Statistical

Process Control (SPC) information. Even if working with a new projectile design for which

there is no production history, it is valuable to obtain this information for a similar design or a

projectile with similar characteristics.

Because some of the inputs to this approach are statistical in nature, the historical data

provide a foundation from which to derive the statistical information.

The last type of information required is test and/or measurement that is important to

predicting dispersion but is not derived from analysis. This includes bore centerline

7
measurements, boresight errors inherent within a test fixture or boresight tool, known sabot

discard issues from tests of similar sabots, etc.

As can be seen in Figure 6, the drawings, production history, and results from previous

analyses are used for physical modehng of the projectile, which in turn is the basis for several

analyses to be described in the following sections, Each of the analyses results in dispersion

component sensitivities that are then used in predicting dispersion.

3.2 BALANS Model of the XM88f. The basic inputs for the BALANS in-bore balloting

analysis are a lumped parameter model of the projectile that properly 6hara6teIkZeS its mass

properties and flexibility, a forcing function, and several distances and runouts that are used to

orient the projectile within the gun tube. The lumped parameter model is generated

automatically from the PRODAS geometric model.

Figure 7 is an example of the XM881 as a lumped parameter model automatically generated

from PRODAS. As shown, the upper half of the model is the actual projectile as generated from

PRODAS. The lower half attempts to mirror the upper half by reflecting the hrmped parameter

node/element model.

The forcing function required for the balloting analysis is provided direcay from the

PRODAS interior ballistics analysis module0 PRODAS uses the Baer-Frankl methodology to

simulate combustion of propellant grains and calculate the time-dependent parameters of base

pressure (which is applied to the projectile aft of the obturator during the balloting analysis), spin

velocity and acceleration (which is used to cal6ulate centrifugal forces during in-bore travel), and

axial acceleration (which is used to calculate axial forces during in-bore travel). Transverse

forces are calculated from the induced balloting motion.

In addition to the lumped parameter model, the dispersion analysis requires manufa6turing

dimensional and tolerance information and transition and free-flight sensitivity information. The

8
.

.

Figure 7. Graphical Representation of the XM881 Lumped Parameter Model.

manufacturing information consists of several critical dimensions and tolerances necessary for

in-bore balloting. These define the locations ‘of the projectile/gun tube interfaces and some of the

critical projectile dimensions which affect dispersion. The statistical in-bore balloting analysis

uses these dimensions and their tolerances to randomly orient the projectile in the gun tube.

Several hundred m-bore balloting analyses are generally required to obtain statistically valid

muzzle exit yaw, yaw rate, and transverse velocity predictions [5].

The transition and free-flight sensitivity information is used to determine those components

of dispersion after the projectile has left the gun tube. Transition sensitivities are separated into

sabot discard and boresight sensitivities, Errors induced by sabot discard may have significant

variation from one projectile configuration to another. They have both a physical component

that can occur due to asymmetric loads applied to the core during discard and an aerodynamic

interference component. Sabot discard is the least well understood of the major contributors to

dispersion and therefore is generally determined from test, observation, and/or experience.

9
Boresight errors are the errors associated with pointing the gun at the target. Boresight errors

vary between calibers, gun crews, and instrumentation

The free-flight dispersion component sensitivities include muzzle velocity, aerodynamic

jump, aerodynamic trim angle, crosswinds, and aerodynamic/mass asymmetries. All of these

parameters are determined via trajectory analysis within PRODAS as follows:

The muzzle velocity sensitivity factor is the drop variation due to muzzle velocity

variation and can be calculated by comparing the drop of trajectory simulations made by

perturbating muzzle velocities.

The aerodynamic jump sensitivity relates dispersion to the muzzle exit yaw rate of the

projectile. This factor is dependent upon the physical and aerodynamic characteristics of

the projectile as well as the projectile spin and velocity.

The crosswind sensitivity of the projectile is determined by trajectory simulations of the

projectile flight to the range of interest both with and without a nominal crosswind

applied.

The aerodynamic trim angle of a projectile configuration (due to manufacturing

tolerances) may be calculated from PRODAS predictions of the body (alone) and fm

(alone) center of pressure and normal force coeffkients, and from the expected one-sigma

vahre of the angular misalignments of the nose and tail sections.

The aerodynamic/mass asymmetries factor is determined by simulating trajectories with a

trim angle assumed to be oriented at orthogonal and diametrically opposed orientations.

3.3 Deterministic Analysis. Once the lumped parameter model of the projectile and gun

system is finished, one needs to run test cases, starting with the most basic analysis before

proceeding to more complex simulations. First, run the simplest case-for example, a

two-dimensional single-shot simulation using a straight centerline including gravity droop.

10
When the results appear reasonable, then move on to a simulation that includes the measured

centerline from SN 273. Now, one simple way of obtaining insight from the modeling results is

to compare the results from the straight centerline to the measured centerline of SN 273. In

Figure 8(a), the projectile lateral forces resulting from interaction with a smooth, straight

centerline are shown. Though the loads are low, it is immediately apparent that balloting causes

high-frequency disturbance. In Figure 8(b), the projectile lateral forces resulting from interaction

with a centerline that includes manufacturing irregularities are shown The loads are only

slightly higher except for some higher forces noted near shot exit delivered to the rear contact of

the projectile.

interactton Forces - Straight CenterlIne

8000

2

s

f 4000

E

8

t

0

0.000 0.001 0.002 0.003 0.004

Time (set)

lnteractlon Forces - St&?73

8000

s

g

5 4000

d

8 0

8

IL

p 4000

‘E

6

-8000

0.000 0.001 0.002 0.003 0.004

Time (set)

(a) 00)

Figure 8. Interaction Forces: (a) Straight Centerline, (b) SN 273.

The deterministic analysis provides a detailed analysis at each node in the lumped parameter

model in terms of bending moments, shear forces, nodal displacements, projectile shape at each

time step, and exit conditions. It is equivalent to performing a single-shot experiment to

investigate issues other than dispersion. Since the analysis presupposes an initial projectile

orientation in the gun tube, which is difficult to determine experimentally, the deterministic

analysis has limited usefulness when trying to evaluate overall projectile performance parameters

such as dispersion.

11
3.4 Stochastic Analysis. Since production history information such as SPC information

does not exist for the XM881 specimens in our inventory, the parameters required for input had

to come from either measurements or estimates based on M919 data. For the sensitivity values

found in Table 2, the muzzle velocity data come frozln the experiment. Aerodynamic jump, yaw

factor, and spin rate come from the PRODAS segment, Boresight, sabot discard, and

miscellaneous error numbers are engineering best guess values based on experience with similar

projectiles. For simplicity, values that were assumed to be zero, such as wind factors,

aerodynamic, and mass asymmetries, are not shown in the table.

Tables 1 and 2 contain sensitivity data and manufacturing information required for the

simulation. Generally, these data are obtained from previous simulations, testing, drawings,

and/or SPC data collected by the manufacturer. For this simulation, the source of the data was

either through measurements (meas.) or from engineering estimates (est.) that are based on

previous experience in simulating and testing of similar rounds.

Table 1. XM881 Sensitivity Data

II Characteristic Data Source

Aerodynamic Jump Factor (dimensionless) est.

a

Muzzle Velocity Standard Deviation (m/s) 8.419

Muzzle Velocity Factor (dimensionless) 0.005

est.

est.

. Boresight Error (dimensionless) 0.050 est.

Sabot Discard Error (dimensionless) 0.050 est.

I Miscellaneous Errors (dimensionless) 0.100 est.

Muzzle Velocity (m/s) 1398.4 meas.

I Initial Yaw Factor (rails) I 0.010 I est. II

II Muzzle Spin Rate (r-ad/s) 2900.0 est. II

The BALANS dispersion results presented here in Table 3 are the result of 10 different

simulations of 10 rounds each stochastically determinin g projectile orientations and other key

12
Table 2. Manufacturing Tolerance Information

Characteristic

Distance to Obturator

Distance to Forward Spring

Distance to Bore Rider

Value Data Source

(mm> 1

63.0941 meas.

101.143 meas.

110.236 meas.

Bore Diameter 1 25.100 1 meas. 11

Forward Bourrelet Mean Diameter 1 24.970 1 est. I I

Forward Bourrelet Standard Deviation

Forward Bourrelet Runout (Mean to Penetrator)

Forward Bourrelet Runout Standard Deviation

Rear Bourrelet Runout (Mean to Penetrator)

Rear Bourrelet Runout Standard Deviation

Sabot Inside Diameter at Forward Bourrelet

0.015 est.

0.025 est.

0.010 est.

0.025 est.

0.010 est.

I 8.273 I meas. 1

Sabot Inside Diameter at Forward Bourrelet Standard Deviation 1 0.000 ] est. II

Table 3. Simulated TID Results of 10 Simulations of lo-Round Tests

II 2 I 0.384 I 0.469

3 0.377 0.463

4 0.350 0.441

5 0.402 0.484

6 0.321 0.419

7 0.460 0.533

II 8 I 0.292 I 0.397
dimensions as described earlier to develop the muzzle exit conditions of yaw, yaw rate, and

center of gravity velocities. To perform the target impact dispersion analysis, the muzzle exit

sensitivities are combined with the transition sensitivities and free-flight sensitivities. Table 4

shows the components of dispersion for one of the simulations.

Table 4. Components of Dispersion (From Simulation No. 3)

Dispersion Component

Windage 0.000 0.000

Boresight 0.050 0.050

Sabot Discard 0.050 0.050

Aero/Mass Asymmetries ~0.000 0.000

Yaw Angle 0.001 0.001

Transverse Velocity 0.058 0.058

Muzzle Suin 0.204 0.204

In-Bore Total (Yaw Rate + Yaw Angle + Transverse Velocity + Muzzle Spin) = 0.371 II

4. Comparison Between Experimental and Analytical

Results

This project is still a work in progress. The Aerodynamics Branch of ARL and Arrow Tech

Associates are continuing the dialog necessary to resolve all the parameters deftitions and

understand ah the translations that may be required to make BALANS output results correlate to

the similar quantities that are used in the experimental arena. At the present time, the two parties

believe the bottom line quantities of horizontal and vertical standard deviations (sigmas) for total

dispersion can be compared directly (see Table 5).

14
Table 5. Total Dispersion Comparison

From a strict comparison point of view, the differences between the experimental values and

the mean of the simulation values appear to be quite large. However, the difference between the

minimum and maximum values of the ten simulations is also significant. This implies that there

is some variability in a lo-round sample size, Another source for the differences is in the

number of simulation parameters that had to be estimated.

5. Summary and Conclusions

The full scope of correlating the experimental work with the modeling efforts is incomplete at

this time. However, despite the lack of closure on this project, this work has brought the

following insights:

e

. .

Use of this combined experimental and analytical approach can lead to more effective

test plans by providing engineers with the relative magnitude of dispersion improvement

to be expected by changes in a configuration.

The experimental approach complements the analytical approach by providing accurate

aerodynamic coefficients, a necessary ingredient to determining the free-flight

sensitivities for the analytical approach.

15
. The BALANS analytical approach is useful in the investigation of piece-part dimensional

tolerances and their effect on dispersion,

. Since dispersion is a combination of random independent and interdependent events,

statistics becomes an important issue. The most important issue is whether one can

experimentally predict an overall projectile performance parameter such as dispersion

from a lo-round group.

. When combining the experimental approach with the mathematical simulation approach,

the modeler should be involved in the experimental methodologies to allow for more

understanding of detailed comparisons.

6
6. References

.

1. Haug, B. T., and J. A. Bornstein. “Gun Dynamics Measurements for Tank Gun Systems.”

Proceedings of the Fifth U.S. Army Symposium on Gun Dynamics, edited by T. E. Simpkins

and C. G. Homan, U.S. Army Armament Research, Development, and Engineering Center,

Benet Weapons Laboratories, Watervliet, NY, 1987.

2. Plostins, P., I. Celmins, J. Bornstein, and J. E. Diebler (Battelle Pacific). “The Effects of

Sabot Front Borerider Stiffness on the Launch Dynamics of Fin-Stabilized Kinetic Energy

Ammunition.” BRGTR-3047, U.S. Army Ballistic Research Laboratory, Aberdeen Proving

Ground, MD, October 1989.

3. &TOW Tech Associates. “BALANS Version 2. User’s/Technical Manual.” South

Burlington, VT, August 1998.

4. Arrow Tech Associates. “PRODAS Version 3.9. User’dTechnicd Manual.” South

Burlington, VT, January 1998.

5. Hathaway, A. F., and J. R. Burnett, Jr. “Stochstic Approach to Predicting Dispersion.”

Proceedings of the 49th Aeroballistic Range Association Meeting, The Hague, Netherlands,

October 1998.

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22
OMB No. 0704-0188

of the XM881 Armor-Piercing, Fin-Stabilized, Discarding

lL162618AH80

I’homas F. Erline and Alan F. Hathaway*

U.S. Army Research Laboratory

4Tl-N AMSRL-WM-BC

4berdeen Proving Ground, MD 21005-5066

Il. SUPPLEMENTARY NOTES

@Arrow Tech Associates, Inc., 1233 Shelbume oaRd, Suite D-8, South Burlington, VT 05403

IZa. DlSTRlBUTlON/AVAllABlLlTY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution is unlimited.

13. ABSTRACT(hfaximum 200 words)

This study compares the results of a dispersion test with mathematical modeling. A lo-round group of modified

25-mm XM881 armor-piercing, fin-stabilized, discarding sabot (APFSDS) projectiles was fired from the M242 chair

gun into a designated target. The mathematical modeling results come from BALANS, a product of Arrow Tech

Associates. BALANS is a finite-element lumped parameter code that has the capability to model a flexible projectile

being fired from a flexible gun. It also has the unique feature of an automated statistical evaluation of dispersion. This

study represents an effort to establish a combined experiment and simulation approach to reduce system error.

14. SUBJECT TERMS

lispersion, gun dynamics, projectile dynamics, modeling, experimentation

15. NUMBER OF PAGES

25

16. PRICE CODE

17. SECURITY CLASSIFICATION 18. SECURlTY CLASSlFlCATlON 19. SECURITY CLASSlFlCATlON 20. LIMITATION OF ABSTRACT

OF REPORT OF THIS PAGE OF ABSTRACT

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

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