ARMY RESEARCH LABORATORY 

Development of a Plastic Stabilizer 

for the M865 Training Projectile 

by James Garner, 

Mark Bundy, and James Newill 

i 19990708 160 1 

Approved for public release; distribution is unlimited. 

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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5066 

filtT_d-MR-445 May 1999 

Development of a Plastic Stabilizer 

for the MS65 Training Projectile 

James Garner, Mark Bundy, and James Newill 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
Abstract 

The U.S. Army Research Laboratory (ARL) has fabricated and tested a preliminary version 

of an injection-moldable plastic M865 training round stabilizer assembly. This preliminary 

stabilizer (flare) is made from polyetheretherketone (PEEK) and is expected to handle the m-bore 

and out-of-bore aerothermal environments sufficiently to conform to the performance of the 

present M865 flare. A more refined flare assembly that matches physical properties of center-ofgravity location and weight, as compared to the present aluminum flare, can be engineered. A 

refined flare assembly will use a steel insert with the plastic flare section molded around it. 

Injection-molding a plastic flare promises several potential advantages. An entirely, or 

predominantly, plastic flare assembly can be produced at a significantly reduced cost. 

Injection-molding the flare should also reduce the variability typically associated with machined 

parts. The flares could also be manufactured more quickly. 

ii 
Table of Contents 

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1. 

2. 

3. 

4. 

5. 

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

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

Design Philosophy and Requirements ................................................................... 

Testing and Analysis ............................................................................................... 

Conclusions .............................................................................................................. 

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

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

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

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List of Figures 

Figure 

1. A Simplified Schematic of a Proposed M865 Flare Assembly ................................. 

2. High-Speed Photograph of the Initial M865 Plastic Flare Design ............................ 

3. Hypothesized Failure Lines on the Initial M865 Plastic Flare Design ..................... 

4. Views of Recovered Piece and Original ................................................................... 

5. Flare Stress Analysis Results (psi) Under Acceleration and Hydrostatic Loading ... 

6. Schematic of Improved Plastic MS65 Flare Design .................................................. 

7. In-Flight Photo of M865 With a Plastic Flare ........................................................... 

F&g 

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1. Introduction 

Defense budget cuts mandate that the U.S. Army train more efficiently. Efficiency, in most 

cases, is measured in “bang for the buck.” Systems that meet U.S. Army requirements at 

reduced cost are prime candidates for product-improvement programs. This philosophy extends 

down to the component level. 

The current aluminum stabilizer (flare) for the M865 training projectile, fired from the Ml 

Abrams M256 cannon, costs approximately $15 when purchased in quantity. Much of this cost 

is due to machining while meeting the tolerances given for the part. The flare provides the 

aerodynamic stabilization for the round and must withstand gun launch and flight loads. In 

addition, the flare must also be chemically compatible with the propellant bed. Producing a flare 

that meets these requirements and is less expensive could result in large peace-time dollar 

savings to the U.S. Army. The cost estimate to produce an injection-molded plastic flare appears 

to be conservatively $lO-and potentially less. The U.S. Army Research Laboratory (ARL), 

with support from the Close Combat Armaments Center, Picatinny Arsenal, NJ, has undertaken 

this effort. 

2. Design Philosophy and Requirements 

The present M865 flare is basically conical with slots milled at the rear to induce roll 

consistent with stable and accurate flight. A hollowed rear section reduces stabilizer weight and 

assists with tracer visibility. As the round slows during its flight, the high-drag characteristics of 

the flare take effect and thus limit the maximum range of the training projectile. To mimic this 

performance, a replacement flare for the M865 requires the same exterior geometry and weight. 

The proposed plastic flare appears is an ideal candidate to meet these 

configuration is more accurately described as a combination of an extended 

injection-molded plastic flare. Figure 1 shows a simplified schematic section 

needs. The flare 

metal stud and an 

of the first design. 

1 
Figure 1. A Simplified Schematic of a Proposed MS65 Flare Assembly. 

The metal stud is used to provide a strong connection to the flight body. A metal stud with an 

injection-molded plastic flare surrounding it is far less complicated to fabricate, more 

consistently produced, and less expensive. Much of the expense in the production of the current 

aluminum flare is machining to part tolerances. A modified stud, not shown in Figure 1, uses a 

hollowed rear to serve as a tracer well and is planned for a future improved design. The stud 

mass of metal provides a ready heat sink for the heat generated by the tracer. The final, and 

perhaps most obvious, purpose of the metal stud is to increase the flare weight to bring it back to 

standard aluminum part weight. 

A plastic flare must survive the high-temperature flight environment, as well as the 

high-pressure high-temperature gun launch. These two regimes present very different challenges 

for the flare. Prior test measurements have shown that in-flight temperatures on the aluminum 

flare are 500-550 K (Stumpfel 1996). A heat-resistant plastic must be chosen accordingly to 

meet this challenge. Some commercially available plastics have heat-distortion temperatures 

above this temperature (Ash and Ash 1992). The least-understood criterion is the in-bore 

requirement for the flare. In bore, the flare is subjected to intense heat (1,920 K) and pressures 

on the order of 330 Mpa. Fortunately, these conditions only last for a portion of the 6-ms-bore 

travel time. This time is insufficient for substantial pyrolization of the flare (Bundy 1996). The 

pressure and acceleration effects are more immediate and appear to dominate the material choice 

2 
for in-bore and transitional (just out of bore) conditions. The material must also survive severe 

acceleration loads. 

3. Testing and Analysis 

Firings were performed to attempt to evaluate polyetheretherketone (PEEK) as a flare 

material. This material was chosen since it had performed well in past tests as a fm material for 

an M735 projectile. Prior testing showed PEEK resin to be flexible enough, such that fins of this 

material bent but remained intact throughout the flight. One of the conclusions from this past 

test was that the plastic material chosen should be strong, but not too stiff, in order to avoid 

material fracture. Data were obtained only for short ranges (about 0.2 km). The flare test was 

designed to gather data in the same regimes (in-bore and transitional ballistic). The transitional 

ballistic environment muzzle blast produces large pressure gradients and must be considered in 

any stabilizer design. 

Four firings of the proposed design were conducted at the Transonic Experimental Facility 

(TEF) of Aberdeen Proving Ground (APG). After each firing, the flare broke off and fractured 

into several pieces near (approximately 10 m) the gun muzzle (see Figure 2). A photograph of 

the flare model before firing and a recovered piece of a fired flare indicate that it failed in shear 

along a conical surface from the base of the stud cavity to the hollowed flare base. Figure 3 

shows the hypothesized failure lines ‘on a section view of the flare. The small recovered core 

(shown in Figure 4) has a circular base that corresponds almost exactly to the diameter of the 

flare at the base of the hollowed area. 

A finite element model of the plastic flare was created to better understand why the design 

was failing and what changes were needed to halt this failure. An Ansys* finite element model 

* Version 5.4, Swanson Analysis Systems, PO Box 65, Johnson Rd., Houston, PA 15342. 

3 
Figure 2. High-Speed Photograph of the Initial MS65 Plastic Flare Design. 

Shear failure 

lines 

Figure 3. Hypothesized Failure Lines on the Initial MS65 Plastic Flare Design. 

calculated to match those occurring in bore. Figure 5 shows the Von Mises stress contours on 

the rear portion of the flare that result due to the in-bore pressure and acceleration conditions. 

One theory is that the flare failed in bore. 

The next flare model fired had modifications based on the examination of the recovered part 

geometry and the results of the stress analysis. The hollowed flare section was filled, and the 

4 
(a) Side View. 

(b) End View. 

Figure 4. Views of Recovered Piece and Original. 

aluminum connection stud was extended the entire length of the flare. Both of these 

modifications actually simplified the flare design and manufacture. Again, a simplified version 

of the design is shown in Figure 6. Filling the base creates a slight drag increase, but trajectory 

simulations indicate that the round will still be a ballistic match over the ranges of interest. The 

stud cavity was extended the length of the flare, but the aluminum stud was positioned just short 
. 

c 

Figure 5. Flare Stress Analysis Results (psi) Under Acceleration and Hydrostatic Loading. 

Figure 6. Schematic of Improved Plastic MS65 Flare Design. 

6 
of the flare base. A room-temperature-vulcanizing (RTV) sealant was 

recess to prevent gun gasses from penetrating between the stud and 

infiltration at this joint would likely produce severe damage. 

inserted into this slight 

the plastic flare. Gas 

, The fiig results were far more promising with the improved flare design Two projectiles 

using this flare were fired. The first round flare fractured, but the flare pieces were large as 

opposed to the small pieces of the flares from the initial test series. The second firing was a 

complete success, as shown in the high-speed photograph of Figure 7. A circular impact hole in 

a yaw card confinned that the entire flare was present and intact. It is believed that the first flare 

in the second series failed because there was no sealant at the stud/penetrator/plastic interface. A 

theory assumes that the rearward displacement of the PEEK flare due to acceleration caused a 

gap between the projectile and the flare front. This gap was immediately filled by high-pressure 

gas. Once the round exited the bore, the high-pressure gas escaped and caused the flare to fail. 

The sealant at this joint used on the second round is thought to be responsible for stopping the 

penetration of high-pressure gun gas. An epoxy seaknt was used at this interface. 

Figure 7. In-Flight Photo of MS65 With a Plastic Flare. 

. 4. Conclusions 

1 Injection-molding the flare around a metal stud is an inexpensive alternative solution to the 

current flare design. Both trapped high-pressure gasses at shot exit, and in-bore acceleration 

7 
forces pose severe threats to the success of a plastic flare. In-bore heating does not appear to be 

a challenge, as relatively little of the flare material is pyrolized in the relatively short in-bore 

exposure time. Adverse aerothermal heating effects are also expected to be negligible, since the 

temperatures measured in flight are at or below the distortion temperatures for some plastics. 

This has not been experimentally demonstrated for longer range flights (>2 km). A successful 

near-field firing of a second-generation design was achieved using PEEK as the flare material. 

Investigating other plastic material choices and refming the design are the next logical steps in 

the development of the plastic flare. This testing offers a preliminary validation for the use of 

polymer plastics as a flare material and suggests that their dynamic properties make them 

suitable for expanded use. 

8 
5. References 

. 

Ash, M., and I. Ash. Handbook of Plastic Compounds, Elastomers, and Resins. VCH 

Publishers, Inc., New York, NY, 1992. 

Bundy, M. “Plastic Fins for Minetic Energy (KE) Penetrators.” ARL-TR-1267, 

U.S. Army Research Laboratory, Aberdeen Proving Ground, MD, December 1996. 

Stumpfel, C. “In-Flight Projectile Imaging by Infrared Emission/Rotating Mirror Technique 

With Temperature Calibration.” AI&-TR-1148, U.S. Army Research Laboratory, Aberdeen 

Proving Ground, MD, July 1996. 
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REPORT DOCUMENTATION PAGE Form Approved 

OhlE No. 0704.0188 

Development of a Plastic Stabilizer for the M865 Training Projectile 

lL162618AH80 

U.S. Army Research Laboratory 

ATTNI AMSRL-WM-BC 

Aberdeen Proving Ground, MD 21005-5066 

REPORT NUMBER 

ARL-MR-445 

a. SPON.~~R~N~~~ON~TORING AGENCY NAMES(S) AND ADDRESS 10.SPONSORINWMONITORlNG 

AGENCY REPORT NUMBER 

11. SUPPLEMENTARY NOTES 

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 

Approved for public release; distribution is unlimited. 

13. ABSTRACT(Maxmum 200 words) 

The U.S. Army Research Laboratory (ARL) has fabricated and tested a preliminary version of an injection-moldable 

plastic M865 training round stabilizer assembly. This preliminary stabilizer (flare) is made from polyetheretherketone 

(PEEK) and is expected to handle the in-bore and out-of-bore aerothermal environments sufficiently to conform to the 

performance of the present M865 flare. A more refined flare assembly that matches physical properties of 

center-of-gravity location and weight, as compared to the present ahmrin~ flare, can be engineered. A refined flare 

assembly will use a steel insert with the plastic flare section molded around it. Injection-molding a plastic flare promises 

several potential advantages. An entirely, or predominantly, plastic flare assembly can be produced at a significantly 

reduced cost. Injection-molding the flare should also reduce the variability typically associated with machined parts 

The flares could also be manufactured more quickly. 

14. SUBJECT TERMS 

plastic fins, mantiacturing, cost savings 

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