Parameterized Design of a 

Supersonic Radome 

Michael S.L. Hollis 

20010501 133 

Approved for public release; distribution is unlimited. 
Celazole@ is a registered trademark of Celanese Acetate. 

I-DEAS@ is a registered trademark of Structural Dynamics Research Corporation. 

MACOR@ is a registered trademark of Dow Corning. 

PEEK” is a trademark of Victrex. 

Pentium@ isa registered trademark of Intel Corporation. 

Torlon@ is a registered trademark of Amoco Performance Products. 

Ultem@ is a registered trademark of GE Plastics. 

Vespel@ isa registered trademark of E.I. DuPont de Nemours. 

Victrex@ is a registered trademark of Victrex PLC Corporation -United Kingdom. 

The findings in this report are not to be construed as an offkial Department of the Army position 

unless so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an offkial 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 2 1005-5066 

ARL-TR-24 18 April 2001 

I . 

. 

Parameterized Design of a Supersonic 

Radome 

Michael S.L. Hollis 

Weapons and Materials Research Directorate 

Approved for public release; distribution is unlimited. 

i 
Abstract 

ii 

With the new requirements of the future combat systems (FCS), gunlaunched projectiles will most likely be decreasing in diameter and 

increasing in muzzle velocity. In addition, these projectiles will be carrying 

entire electronic systems, specifically, global positioning system 

(GPS)/inertial guidance and terminal homing. These systems will sense 

during the flight and terminal environments of the projectile and will 

provide data links (probably two-way telemetry) for system diagnostics 

and dynamic re-targeting. Most of these sensing elements involve various 

antennae operating at a variety of frequencies ranging from GPS (1.5 GHz) 

to millimeter wave seekers (94 GHz) to optical seekers (1 PHz). Because 

of packaging constraints, these systems are likely to be placed forward on 

the projectile body. All these antennae require a protective “window” for 

transmitting and/or receiving signals. Based on the location of these 

systems, that window is usually described as the projectile radome. 

The radome must withstand the cannon launch and ballistic environment. 

The intense aero-heating of supersonic flight softens polymers, thus 

reducing the structural integrity. Of course, it is obvious that the radome 

must perform well electronically across a possible wide band of radio 

frequencies. 

This report studies the use of several (polymer types) materials, which 

can be machined to create a radome of a desired shape. These polymers, 

which are either extruded or molded into stock shapes, were chosen 

based on the dielectric constant (relative to air, between 3 and 4) and 

thermal and structural properties. A generic radome geometry was 

selected to perform the thermal and structural analyses. An older 

yawsonde geometry, which was flight tested, was also analyzed. 

In addition to suggesting a quick solution, it is also suggested that a more 

intensive effort be performed to find higher performance material 

solutions for the design of radomes for FCS-like projectile launch/flight 

conditions. The aerothermal, convective, conductive and structural 

analyses are a skeleton of a study that needs to be performed. Other 

materials such as ceramics, composites, and other polymers also need to 

be studied. 
ACKNOWLEDGMENTS 

, 

3 

The author would like to thank the following people for their expertise and guidance 

in various areas. Mr. Bernard Guidos of the U.S. Army Research Laboratory (ARL) 

is acknowledged for his continuing guidance in performing aerothermal analyses. Mr. 

Guidos also provided technical assistance in the application of the ABRES shape 

change code (ASCC) on various UNIX computing platforms. Dr. Steve M&night and 

Dr. William Spurgeon of ARL are also commended for their expertise in polymers 

and how the mechanics change with time and, temperature. Drs. Jerry LaSalvia and 

Paramel Pate1 of ARL are also thanked for their knowledge of ceramics, including 

MACOR@. Bradford Davis and David Hepner of ARL are acknowledged for 

processing data from a flight test that occurred in August 1999 at Yuma Proving 

Ground, Arizona. The flight profile was used to create the verification model for this 

report. Finally, the author would like to thank Ms. Andie Over-field of DSM’ 

Engineering Plastic Products for her technical expertise and knowledge of polymers. 

She was able to answer technical questions and provide material property data in a 

timely and professional manner. 

1 not an acronym 

. . . 

111 
INTENTIONALLY LEFT Bum 

. 

iv 
Contents 

C 

i - 

. 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

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

Problem Description. ............................... 

Temperature-Dependent Properties of Polymer Materials ... 

In-Flight Surface Heat Transfer ........................ 

4.1 In-depth Thermal Response of the Radome ............... 

4.2 Materials ...................................... 

4.3 Results ........................................ 

4.4 Model Verification. ............................... 

4.5 In-Flight Surface Heat Transfer ....................... 

4.6 In-depth Thermal Response of the Yawsonde ............. 

Results ........................................... 

Conclusion ....................................... 

Future Work ...................................... 

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

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

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

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

Figures 

1. An Example of a Yawsonde . . . . . . . . . . . . . . . . . . . . . . . . 

2. Experimental Velocity Profile. . . . . . . . . . . . . . . . . . . . . . . . 

3. Hemispherical Radome Geometry . . . . . . . . . . . . . . . . . . . . . 

4. Comparison of Heat Transfer Coefficients at Various Mach 

Numbers for Turbulent and Laminar Flow Conditions . . . . . . . . . 

5. 

6. 

7. 

8. 

Steady State Adiabatic Wall Temperatures at Various Mach 

Numbers for Turbulent and Larninar Flow Conditions . . . . . . . . . 

Axisyrnrnetric Finite Element Mesh of General Radome Geometry . . 

Computed Temperature Response at Radome Monitor Points for 

MACOR@ With a Laminar to Turbulent Transition . . . . . . . . . . . 

Computed Temperature Response at Radome Monitor Points for 

Ultem@ 1000 With a Laminar to Turbulent Transition . . . . . . . . . 

1 

2 

3 

4 

6 

7 

7 

11 

13 

13 

15 

16 

16 

19 

21 

23 

29 

2 

4 

5 

5 

6 

7 

9 

9 

V 
9. 

10. 

11. 

12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

Computed Temperature Response at Radome Monitor Points for 

Torlon@ 4.203 With a Laminar to Turbulent Transition . . . . . . . . . 

Computed Temperature Response at Radome Monitor Points for 

PEEKTM 30% Glass Fiber Reinforced With a Larninar to Turbulent 

Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Computed Temperature Response at Radome Monitor Points for 

Celazole@ With a Laminar to Turbulent Transition . . . . . . . . . . . 

Computed Temperature Response at Radome Monitor Points for 

Vespel@ With a Laminar to Turbulent Transition . . . . . . . . . . . . 

Yawsonde About to be Launched From a Gun on an M831 

Projectile.................................... 

Weibel Velocity Versus Weibel Time From YPG Flight Test . . . . . . 

Comparison of Heat Transfer Coefficients at Various Mach Numbers 

for Turbulent and Laminar Flow Conditions for a Yawsonde . . . . . 

Steady State Adiabatic Wall Temperatures at Various Mach Numbers 

for the Yawsonde Geometry . . . . . . . . . . . . . . . . . . . . . . . . 

Axisymmetrical Layout of the Yawsonde Model . . . . . . . . . . . . 

Axisymmetrical Finite Element Model of the Yawsonde . . . . . . . . 

Computed Temperature Response of a Yawsonde With a Mach 3 

Launch and a Laminar to Turbulent Transition Boundary Layer 

Scheme..................................... 

10 

10 

11 

12 

12 

12 

13 

14 

14 

15 

16 

Tables 

1. Physical Properties of Studied Materials . . . . . . . . . . . . . . . . . 

2. Material Properties Used for the Thermal Analysis. . . . . . . . . . . 

8 

15 

. 
PARAMETERIZED DESIGN OF A SUPERSONIC RADOME 

1. Introduction 

With the new requirements of the future combat systems, gun-launched 

projectiles will most likely be decreasing in diameter and increasing in muzzle 

velocity. In addition, these projectiles will be carrying electronic systems for 

global positioning system (GPS)/inertial guidance and terminal homing. These 

subsystems will require the projectile to sense the flight and terminal 

environments and to provide data links (probably two-way telemetry) for system 

diagnostics and dynamic re-targeting. Most of these “sensing” elements involve 

various antennae operating at a variety of frequencies. Examples range from GPS 

(1.5 GHz) to millimeter wave seekers (94 GHz) to optical seekers (1 PHz). 

Because of packaging constraints, these systems will probably be placed forward 

on the projectile body. All these antennae require a protective “window” for 

transmitting and/or receiving signals. Based on the location of these systems, 

that window is usually described as the projectile radome. 

The radome must withstand the cannon launch and ballistic environment. The 

intense aero-heating of supersonic flight softens polymers, thus reducing the 

structural integrity. Of course, it is obvious that the radome must perform well 

electronically across a possible wide band of radio frequencies. 

Since telemetry and inertial sensors have become more affordable, a diagnostic 

fuze can be built, based upon a yawsonde (Hepner et al. 2000) (see Figure 1). 

Originally configured for artillery projectiles, this device is built in other 

geometries, depending upon the munition requirement. Even this simple device 

that uses a telemetry antenna under the radome is being examined for possible 

melting or softening at high launch velocities. The protective radome has been 

made of polymers such as nylon and polycarbonate because of the materials’ 

strength and radio frequency (RF) transparency. 

This report studies the use of several (polymer types) materials, which can be 

machined to create a radome of a desired shape. These polymers, which are 

either extruded or molded into stock shapes, were chosen on the basis of the 

dielectric constant (relative to air, between 3 and 4) and thermal and structural 

properties. 

A generic radome geometry has been selected to perform the thermal and 

structural analyses. Various polymers, capable of being machined into the 

1 
radome geometry, are studied. An older yawsonde geometry, which was flight 

tested, will also be analyzed. 

Figure 1. An Example of a Yawsonde. 

2. Problem Description 

Future gun-launched projectiles will have higher muzzle velocities. There 

currently exists a need for RF transparent radome solutions with muzzle 

velocities near Mach numbers equal to 3 (M=3). FCS requirements may push 

these velocities as high as M=5. Assessments of aerothermal heating 

requirements for specific radome geometries need to be studied. Trade-off 

studies involving aerodynamic shape, antenna location, materials, and RF 

characteristics also need to be made. 

This report studies one specific radome geometry and analyzes the aerothermal 

implications from M=3 to 1.8. Turbulent and laminar boundary conditions are 

studied in addition to a laminar to turbulent transition scheme. The results from 

the aerothermal analyses are then entered into a convection-conduction thermal 

model to determine temperatures throughout the radome geometry. The thermal 

model is also used to perform linear, quasi-static, finite element structural 

analyses at launch and at appropriate times in the flight when the computed 

temperatures reach the polymer softening temperatures. 

The final product of this report is twofold. The first is a short-term solution using 

the extruded/molded plastics to manufacture a radome. The other is a guideline 

for a more extensive study to find several solutions for high speed, RF 

transparent radomes for ballistic projectiles. 
3. Temperature-Dependent Properties of Polymer Materials 

Polymer materials are characterized into two types of plastics: thermoplastics 

and thermosets. Thermoplastics are broken into two main groups: amorphous 

and semi-crystalline. Amorphous and semi-crystalline plastics have a glass 

transition temperature. “Glass transition is a phase change of amorphous solids, 

such as glasses, metals, and polymers. A non-crystalline material is converted to 

a relatively hard, elastic and glassy state from a soft, elastic plastic and rubbery 

state when being cooled through its glass transition temperature Tg” (Li 1999). If 

Young’s Modulus were plotted versus temperature for almost any thermoplastic 

on a logarithmic scale, then Tg would occur as a step function when the high 

strength of the polymer changes to a softer state. Thermosets do not have a Tg, 

but they do soften with temperature. 

The materials that were studied in this report are 

l Nylon 66, which is unfilled. This semi-crystalline material is very 

common with a variety of manufacturers. 

l Ulteme 1600, an unfilled amorphous polyetherimide, which is 

manufactured by General Electric Plastics. 

l Victrexe polyetheretherketone (PEEKTM) 450GL30, which is a general 

purpose 30% glass fiber-reinforced grade of used for injection molding and 

extrusion. This semi-crystalline, polymer is manufactured by Vi&exe. 

l TorIon@ 4203L, which is an unfilled polyamideimide semi-crystalline 

resin, manufactured by British Petroleum (BP) Amoco Chemicals. 

l Hoechst Celanese Celazole@ polybenzimidazole (PBI), which is an 

unfilled compression-molded amorphous thermoplastic, manufactured by DSM 

Engineering Plastics. 

l Vespele P-1, which is an unfilled high performance polyimide resin, 

manufactured by DuPont. 

l MACORe, which is a machinable glass ceramic (MGC). This is the only 

ceramic that was studied. MACORe has a continuous use temperature of 800” C. 

3 
4. In-Flight Surface Heat Transfer 

The in-flight (i.e., aerodynamic) heat transfer coefficient distributions were 

obtained from separate analyses involving the ABRES’ shape change code 

(ASCC). ABRES is a computational procedure for predicting the aerodynamic 

heat environment, shape change, and thermal response of axisymmetrical reentry bodies (Acurex Corporation 1981). In this report, ASCC was used to predict 

the computed heat transfer coefficient, h, and the adiabatic wall temperature, TaW, 

acting along the geometry. ASCC was chosen for the ease of use, speed, and 

accuracy. 

A velocity profile, depicted in Figure 2, is the desired flight profile, for which the 

heat transfer coefficients are calculated. The flight starts with an M=3 launch and 

linearly declines to M=1.8 in 4.5 seconds. Figure 3 depicts the hemispherical 

radome geometry that was used for the analyses. 

Figure 4 shows the heat transfer coefficients for the radome at various Mach 

numbers, and Figure 5 shows T,,. The coefficients were calculated with laminar 

and turbulent flow conditions. Initially, the convection-conduction thermal 

model was run with turbulent-only conditions, and the results indicated that the 

radome, made of Ultem@, would melt very early in the flight. Running the same 

problem with laminar-only conditions indicated that the same radome would 

survive. The correct boundary layer case involves a laminar transition; thus, a 

laminar-turbulent scheme was adapted. 

Velocity Profile 

2.6 

P 

5 2.4 

9 

2.2 

2.0 

1.8 

0 I 2 3 4 

Time (s) 

Figure 2. Experimental Velocity Profile. 

1 

not an acronym 

4 
Figure 3. Hemispherical Radome Geometry (units in inches). 

- h3 

Input for thermal analysis, M3 . . . . . . h2.5 

--- h2 

- h3lam 

.*.*** h2.51am ) 

. -analysis, M2.5 

input for thermal 

OS!, , , , , , , ( I,, , , I,, , , , , , , , , , , , , , , , , , , , , , , r 

0 10 20 30x1 o-3 

Axial Location (m) 

Figure 4. Comparison of Heat Transfer Coefficients at Various Mach Numbers 

for Turbulent and Laminar Flow Conditions. 

5 
- taw-turbulent BC 3 

- Taw-turbulent BC 2.5 

- - - Taw-turbulent BC 2 

taw-laminar BC 3 

l ** taw-laminar BC 2.5 

l l *** taw-laminar BC 2 

- geometry 

800 

-3 

I 

10 2; 

Axial Location (m) 

30x; o-3 

Figure 5. Steady State Adiabatic Wall Temperatures at Various Mach Numbers 

for Turbulent and Laminar Flow Conditions. 

A heat transfer coefficient transition region was imposed. in a calculation by 

Guidos for a nose cap of a 120~mm XM797 (Guidos 1995). Guidos imposed a 

knurled region on the nose to initiate a transition from laminar flow to turbulent. 

A similar approach was used for this report. Figure 4 shows the heat transfer 

coefficients with the transition curves. A linear curve between the laminar curve 

at 11 mm and the turbulent curve at 21 mm was imposed. However, it was 

decided to be more conservative and create a step function as depicted in the 

plot. For instance, for M=3, the initial laminar heat transfer coefficient would be 

approximately 2500 W/m’/K, with a step transition to a turbulent 3900 W/m’/K 

for the rest of the geometry. Heat transfer coefficient and Taw for M=1.8 were 

calculated via linear interpolation. 

4.1 In-depth Thermal Response of the Radome 

The author used the same radome geometry to conduct several transient, twodimensional (2D) analyses for different materials. The software used to create the 

models was Structural Dynamics Research Corporation (SDRC) Integrated 

Design and Analysis Software (I-DEASe). I-DEAS@ uses a finite volume 

formulation to model heat conduction with a general geometry. The onedimensional (1D) numerical and analytical results for steel rod convective 

heating, presented by Guidos (1995), were used to validate the I-DEAS@ software 

before the analyses were completed. The computational time for each material is 

6 
a matter of minutes on a Silicon Graphics, Incorporated (SGI) 320 NT with a 

single Pentium@ processor. 

The 2D axisymmetric model is described in Figure 6, along with the monitoring 

points. The unstructured mesh contains 5,261 quadrilateral elements and 4,989 

nodes with a mesh refinement of 0.09 mm at the surface. An initial temperature 

of 25” C was prescribed for the entire model, with a constant heat sink 

temperature load of 25” C on the bottom of the geometry. 

x 

Figure 6. Axisymmetric Finite Element Mesh of General Radome Geometry. 

I-DEAS@ software is not capable of physical state changes such as melting. When 

the temperature of a monitoring point reached above the Tg or softening 

temperature, the material was declared inadequate for aero-heating. Material 

properties were also kept constant throughout the transient analysis. 

4.2 Materials 

Table 1 lists all the materials that were analyzed in this report. These materials 

were selected on the basis of a low dielectric constant, high heat capacity, and 

tensile strength. 

4.3 Results 

Using the various materials, the author computed temperatures for the radome 

geometry. Figures 7 through 12 show plots of the temperature history at 

monitoring points throughout the flight of the projectile. Figure 7 shows the 

temperature response of the radome if it were made of MACORe. Since 

7 
MACORe is capable of temperatures as great as 1000” C, the aerothermal heating 

was not considered a problem. However, the high dielectric constant disqualifies 

the material for use as a radome. Figure 8 depicts the temperature response of 

Ulteme 1000. Within a second, portions of the radome reach temperatures above 

the softening temperature and the Tp. Temperature response for Torlone 4203 is 

displayed in Figure 9. Within 1.5 seconds, portions of the radome have 

temperatures that exceed both the softening and the Tp temperatures. Figure 10 

shows the plots for 450GL30,30% glass-reinforced PEEK@. 

Table 1. Physical Properties of Studied Materials 

MACORe Nylon 66 Ulteme Torlone 4203 450GI.30 Celazolee Vespele 

Density (g/cc) 2.52 1.15 1.28 1.42 1.51 1.3 1.43 

Young’s 

modulus(Gpa) 

Compressive 

strength (Mpa) 

Poisson’s 

ratio 

Thermal 

conductivity 

(W/m/K) 

Softening 

temperature (“C) 

Tg or melting 

(“Cl 

Specific heat 

(KJ/kg/“C) 

Dielectric 

constant 

66.9 

94 

.29 

1.46 

N/A 93 200 278 232 427 360 

N/A 260 215 275 340 399 N/A 

.79 1.67 1.67 0.36 1.65 1.65 1.13 

6.03 3.6 3.15 3.9 3.7 3.2 3.55 

2.9 

86 

.4 

.24 

3.3 4.0 

152 220 

.35 0.45 

.13 0.26 

6.89 6.2 

179 

0.45 

.43 

345 

.3 

.4 

2.4 

86.2 

0.41 

.35 

Because the temperatures reached the softening temperature, quasi-static linear 

finite element structural analyses were conducted on the radomes made of 

Ultem@, Torlone 4203, and 450GL30. One analysis was performed with 20,000 g’s 

launching acceleration with the material temperature at room temperature. A 

second analysis was conducted at a time in flight when the softening 

temperature had been achieved at some of the monitor points. The material 

properties of the entire model were changed to those when the material 

properties soften. The boundary loads consisted of 60-psi static pressure over the 

geometry. This analysis indicated that the radome geometry would significantly 

deform, possibly placing the material into a nonlinear plastic region of stress and 

strain and possibly impacting aerodynamic performance. 

8 
.oo 1.00 2.00 3.00 4.00 4.50 

Time (S) 

Figure 7. Computed Temperature Response at Radome Monitor Points for 

MACOR@ With a Lank-tar to Turbulent Transition. 

220.14 

200.00 

150.00 

';; 

al 

; 

z 

L 

P 

2 100.00 

50.00 

20.24 - 

0.00 0.50 1.00 1'5o 2.00 2.50 

Time (!I) 

.j I. .j f...i ,,j.. .I., i ,...; ,,.. !“. 

;. ,_,._.,,_.,,,.... ;... 

: : : : 

. I . . . . . . . . . . . 

: 

Figure 8. Computed Temperature Response at Radome Monitor Points for 

Ultem@ 1000 With a Laminar to Turbulent Transition. 

9 
325.70 

0 .oo 1.00 2.00 3 .oo __ 4 ."O 4.50 

Time (S) 

Figure 9. Computed Temperature Response at Radome Monitor Points for 

Torlon@ 4203 With a Larninar to Turbulent Transition. 

310 

300 

100 

10 

.oo 

: : : 

,......~....~........ ;... 

: : : 

, :. 

.oo 1.00 2 .oo 3 .oo 4.00 4.5 

Tine (Sl 

Figure 10. Computed Temperature Response at Radome Monitor Points for 

PEEK@ 30% Glass Fiber Reinforced With a Laminar to Turbulent 

Transition. 
Although this analysis is conservative, the 450GL30 was considered to be too 

weak at the higher temperatures for use. The computed temperature responses 

for Celazole@ were very promising since the temperatures never exceeded the 

softening or the Tg temperatures. The temperature responses are displayed in 

Figure 11. Figure 12 displays the computed temperature responses of the 

monitoring points of a radome made from Vespel@. None of the temperatures 

reach the softening temperature; however, they do reach the Tg. Structural 

analyses indicated that the material would survive launching conditions and that 

the material structural properties did not decrease sufficiently to weaken the 

material during the supersonic flight profile. Nylon was not analyzed because of 

its low melting temperature. 

: .:. :. 

..:. ..: . . ., .I,., ,., _.,.. :.. . . . . i.. ..: . . . . . . . . . . .; i 

^^ __ 

Figure 11. Computed Temperature Response at Radome Monitor Points for 

Celazole@ With a Laminar to Turbulent Transition. 

4.4 Model Verification 

Analyses must be tempered with some data to validate the predictions. For the 

case of a yawsonde, flight experiences do exist, based upon flights conducted at 

Yuma Proving Ground (YPG), Arizona. A yawsonde was installed onto a 

modified M831 high explosive antitank tracer projectile (HEAT-TP), as seen in 

Figure 13. The projectile was launched at about 1060 m/s (M=3.1) and achieved a 

flight profile as seen in Figure 14. The projectile, with the large flat face 

immediately after the aerodynamic fuze body, decelerated quickly. This flight 

configuration survived the launch and flight, while telemetering data until it hit 

the desert floor. Although the aerothermal analysis had been conducted, the 

thermal analysis had never been performed. Instead, the yawsonde was designed 

with Nylon 66 because of its strength, thermal properties, and dielectric constant 

11 
(Hollis & Brandon 1999). To handle the high temperature stagnation region 

temperatures, however, the nylon windshield was fitted with a button screw 

made of MACOR@. 

100 

17 

Computed Temperature Response at Radome Monitor Points 

for VLSPEL Using a Laminar to Turbulent Transition 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..~.. 

.*o 

13 

j..;...i...; .,,( : ..; ., 

k--b 1: 

.i : .I. 

: 

..I.. .j. I 

: i: f j : : : : : : : j: : : : : : : : : : 

,. :. .;. .I. _;. : ,....: i . . . .._.........i..... . . . . . 

: (... . j... :.. : ..:. . ..I_. . . .._ (... : : : : : : : y.. ,:. 

I....: . .. . . . . . . . . . . . . . . . i i I I. _j.. : ! , I . . : ;I ._. 

li 

: : : 

. ...’ . . . . . . I . . . ..I I I : : : : : : : i . ..“...‘~.......‘....‘.....‘j I . ...; I 

: : .; .,......... :.._ .: : : . . . . ,....,.., : I : :I 

... ........ .:. ......... .. ..I....i....l....l..........i. ..: .. ..i . ..i : : ...................................... 

-. .-- 

0.00 1.00 2 .oo 3.00 4.00 4.50 

Time (S) 

Figure 12. Computed Temperature Response at Radome Monitor Points for 

Vespel@ With a Laminar to Turbulent Transition. 

400 

, I I I 1 

0.0 0.5 1.0 1.5 2.1 

WeiklRADARTime(s) 

Figure 13. Yawsonde About to be 

Launched From a Gun on 

an M831 Projectile. 

Figure 14. Weibel Velocity Versus Weibel 

Time From YPG Flight Test. 

12 
4.5 In-Flight Surface Heat Transfer 

The aerodynamic heat transfer coefficient distributions were also obtained from 

separate analyses via ASCC. For validation of this report, an exterior 

axisymmetric geometry was modeled and solved for the initial part of the flight 

at the proper Mach numbers. Heat transfer coefficient, h, and the adiabatic wall 

temperature, Til,, are the results of these models, acting along the geometry. 

Figures 15 and 16 show the laminar and turbulent heat transfer coefficients and 

TaW, respectively. Also shown is a laminar-turbulent transition scheme for the 

heat transfer coefficients. 

._--._-. h2525 

_.-...-.. ,,2,2 

.._..... .._..... ,,s,a,,, h3lam 

‘hpj1am’ ‘hpj1am’ 

-.-‘. h2lam 

- radial1 

, , , , , , , , I , , , , , , , , , , , , , , , , , , , I / ( , , , , , , I , , , , , 

0 20 40 60 60x1 o-3 

Axial Location (m) 

Figure 15. Comparison of Heat Transfer Coefficients at Various Mach Numbers 

for Turbulent and Laminar Flow Conditions for a Yawsonde. 

4.6 In-depth Thermal Response of the Yawsonde 

A 2D transient analysis was conducted for the multiple material yawsonde 

configuration. The analysis was also performed with the I-DEAS@ code. The 2D 

geometry is described in Figure 17 with the transition points. The analysis used 

the laminar-to-turbulent boundary condition scheme developed with the ASCC. 

The multi-material model consists of aluminum, Stycast 1090-Si epoxy, which is 

used for encapsulating electronics, nylon 66, MACOR@, and air. Figure 18 

displays the mesh and the monitor points: high heat transfer coefficient 

laminar(l), high-to-low heat transfer coefficient laminar(2), laminar-to-turbulent 

transition(3), monitor points 4 and 5, and a monitor point on the aluminum. 

Because of the differences in aerothermal heating between the hemispherical 

radome and the cone shape radome, the heat transfer coefficients were broken 

13 
into a few more regions for the cone shape. The mesh, which consists of 7,744 

elements and 7,490 noses, is on the order of 0.14 mm in size near the surface of 

the yawsonde. Material properties used for the thermal analysis are displayed in 

Table 2. Nylon and MACOR@ properties are given in Table 1. 

,i: .*; .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

. 

- -~~*~**.==.~.~*~..=.~~*.****.***...*~*................................................ 

700- 

I 

. . . . . . . . . tam 

s 

---- taw25 

iii 

-a-. taw2 

i 660- 

m**** taw3lam 

l l 9 l ‘taw25lam’ 

E 

s! -. 

0.1 taw2lam 

* - radial2 

._._._._._._._._._._.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. 

1 

. . . . . . . . . . . ..-...-...-...-.-...-...-.....-.-...-.- 

I I I I 

0 20 40 60 80x10” 

Axial Location (m) 

Figure 16. Steady State Adiabatic Wall Temperatures for Various Mach Numbers 

for the Yawsonde Geometry. 

Figure 17. Axisymmetrical Layout of the Yawsonde Model. 

14 
X 

Figure 18. Axisymmetrical Finite Element Model of the Yawsonde. 

Table 2. Material Properties Used for the Therrnal Analysis 

Material P (g/cm31 WJ/kg/K) G (kJ/WW 

Aluminum 2.79 177.0 .875 

Stycast 1090 SI 0.72 0.19 .385 

Air (STP) 0.0013 26.3 1.007 

5. Results 

Figure 19 displays the temperature response for the laminar-to-turbulent flow 

scheme. Depicted are the temperature histories of the points from the previous 

figure. These temperature histories indicate that the windshield would survive 

the launch and flight. Since the yawsonde worked properly, even though the 

data report temperatures close to melting, one could assume that the analysis is 

quite conservative. A linear structural analysis with the material properties at 

room temperature was conducted and is discussed in Hollis and Brandon (1999). 

15 
/ I. ./ Monitor 4 2.OE+02 / ., _.. 

Aluminum 

Softening temperature: 92 C 

’ ’ ’ 

1 * I I , I I * 

O.OE+OO S.OE-01 nmecs. l.OE+OO l.SE+OO 1.9E+OO 

Figure 19. Computed Temperature Response of a Yawsonde With a Mach 3 

Launch and a Laminar to Turbulent Transition Boundary Layer 

Scheme. 

6. Conclusion 

A series of transient thermal analyses with conservative input assumptions has 

been conducted on two different radome geometries. A gross indicator of “it 

worked” provides some validation of the predictions for the yawsonde radome 

and its materials, based upon flights at YPG. In this case, the laminar-toturbulent flow scheme was used. Based on this method of analysis, one could 

choose from the previously mentioned polymers to manufacture a radome. The 

choices would be Celazole@ or Vespel@. Since this analysis was performed to find 

a quick solution and since Celazolee is a specially ordered product not readily 

available, Vespel@ is an appropriate choice for fabricating a radome because it is 

available in various extruded lengths. 

7. Future Work 

This report was aimed at finding a quick solution for a supersonic radome. The 

laminar-to-turbulent boundary condition imposed may not be accurate. During 

the revision phase of this report, the aerodynamic heat analyses were re-run for 

the hemispherical geometry and the yawsonde windshield. Inside the ASCC, a 

16 
switch was set for the computation to determine the transition point. This 

analysis yielded different results, which contained lower heat transfer 

coefficients than indicated in the imposed laminar-turbulent transition scheme. 

Future efforts should include refining the aerodynamic heat transfer analyses to 

improve accuracy. 

In addition to suggesting a quick solution, it is also suggested that a more 

intensive effort be performed to find higher performance material solutions for 

the design of radomes for FCS-like projectile launch/flight conditions. The 

aerothermal, convective, conductive, and structural analyses are a skeleton of a 

study that needs to be performed. Materials that have functional temperatures in 

the region of the adiabatic wall temperatures of super and hypersonic vehicles 

need to be studied. Some of these materials may be ceramics, composites, and 

other polymers. Antenna radiation patterns and intensity measurements of the 

material and the geometry also need to be made. The structural analyses will 

need to be improved by implementing proper material orientation of the 

properties and by using LAMPAT (Bogetti, Hoppel, & Bums 1995) for the 

composite materials. A linear solution for the structural analyses may be all that 

is necessary since the radome geometry should not deviate significantly so as not 

to affect aerodynamics. If the linear solution indicates nonlinear deformation, 

then the candidate material does not have sufficient strength. 

2 

not an acronym 

17 
18 

, 
References 

, 

Acurex corporation/Aerotherm, “Aerotherm Assessment of Projectiles Using the 

ABRES Shape Change code (ASCC),” ARBRL-CR-00462, Ballistic Research 

Laboratory, Aberdeen Proving Ground, Maryland, August 1981. 

s Bogetti, T.A., C.P.R. Hoppel, and BP. Burns, “LAMPAT: A Software Tool for 

Analyzing and Designing Thick Laminated Composite Structures,” ARL-TR890, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, 

September 1995. 

Guidos, B.J., and W.B. Sturek, “Computation of Hypersonic Nosetip Heat 

Transfer Rates for an M829-Like Projectile,” ARL-MR-52, U.S. Army Research 

Laboratory, Aberdeen Proving Ground, Maryland, April 1993. 

Guidos, B.J., “Computed In-flight Temperature Response of a 120~nun XM797 

Gas Generator Training Round Nose Cap,” ARL-MR-267, U.S. Army 

Research Laboratory, Aberdeen Proving Ground, Maryland, October 1995. 

Hepner, D.J., Muller, P.C., Hollis, M.S.L., Burke, L.W., D’Amico, W., Davis, B.S., 

Borgen, G., “An Aeroballistic Diagnostic Fuze,” ARL Patent No. 00-44, U.S. 

Army Research Laboratory, Aberdeen Proving Ground, Maryland, -patent 

pending. 

Hollis, M.S.L., B.J. Guidos, and P.J. Conroy, “Thermal Analysis of a Subminiature 

Telemetry Sensor Mounted in a Kinetic Energy Projectile Base,” ARL-TR1425, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, 

August 1997. 

Hollis, M.S.L., and F.J. Brandon, “Design and Analysis of a Fuze-Configurable 

Range Correction Device for an Artillery Projectile,” ARL-TR-2074, U.S. 

Army Research Laboratory, Aberdeen Proving Ground, Maryland, December 

1999. 

Li, R., “Time-temperature Superposition Method for Glass Transition 

Temperature of Plastic Materials, ” Materials Science and Engineering: A278 

(2000), pp. 36-45, Elsevier, 1999. 

19 
, 

20 
Bibliography 

Guidos, B.J., personal communications, U.S. Army Research Laboratory, 

Aberdeen Proving Ground, Maryland, May 2000. 

M&night, S., personal communications, U.S. Army Research Laboratory, 

Aberdeen Proving Ground, Maryland, June 2000. 

Overfield, A., personal communications, DSM Engineering Plastic Products, Inc. 

Technical Group, Reading, Pennsylvania, June 2000. 

Internet site, MatWeb, The Online Materials Information Resource, 

www.matweb.com. 

Internet site, BP Amoco Chemicals-Engineering Polymers, 

ww.bpamocaengpolymers.com. 

Internet site, GE Plastics-Ultem 1000, www.geplastics.com. 

Internet site, Accuratus Ceramic Corporation, MACOR, www.accuratus.com. 

Internet site, DSM Engineering Plastic Products, www.dsmepp.matweb.com. 

Internet site, www.Dupont.com/enggpolymers/Americas/vespel/docs/ 

233630a.pdf. 

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 

April 200 1 

4. TITLE AND SUBTITLE 

Parameterized Design of a Supersonic Radome 

3. REPORT TYPE AND DATES COVERED 

Final 

5. FUNDING NUMBERS 

PR: AH80 

6. AUTHOR(S) 

Hollis, M.S.L. (ARL) 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS 

U.S. Army Research Laboratory 

Weapons & Materials Research Directorate 

Aberdeen Proving Ground, MD 21005-5066 

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U.S. Army Research Laboratory 

Weapons & Materials Research Directorate 

Aberdeen Proving Ground, MD 21005-5066 

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AGENCY REPORT NUMBER 

ARL-TR-24 18 

2a. DISTRIBUTION/AVAILABILITY STATEMENT 

Approved for public release; distribution is unlimited. 

12b. DISTRIBUTION CODE 

3. ABSTRACT (Maximum 200 words) 

‘With the new requirements of the future combat systems (FCS), gun-launched projectiles will most likely be decreasing in diameter 

and increasing in muzzle velocity. In addition, these projectiles will be carrying entire electronic systems, specifically, global 

positioning system (GPS)/inertial guidance and terminal homing. These systems will sense during the flight and terminal environments 

of the projectile and will provide data links (probably two-way telemetry) for system diagnostics and dynamic re-targeting. Most of 

these sensing elements involve various antennae operating at a variety of frequencies ranging from GPS (1.5 GHz) to millimeter wave 

seekers (94 GHz) to optical seekers (1 PHz). Because of packaging constraints, these systems are likely to be placed forward on the 

projectile body. All these antennae require a protective “window” for transmitting and/or receiving signals. Based on the location of 

these systems, that window is usually described as the projectile radome. 

The radome must withstand the cannon launch and ballistic environment. The intense aero-heating of supersonic flight softens 

polymers, thus reducing the structural integrity. Of course, it is obvious that the radome must perform well electronically across a 

possible wide band of radio frequencies. 

This report studies the use of several (polymer types) materials, which can be machined to create a radome of a desired shape. These 

polymers, which are either extruded or molded into stock shapes, were chosen based on the dielectric constant (relative to air, between 

3 and 4) and thermal and structural properties. A generic radome geometry was selected to perform the thermal and structural analyses. 

An older yawsonde geometry, which was flight tested, was also analyzed. 

In addition to suggesting a quick solution, it is also suggested that a more intensive effort be performed to find higher performance 

material solutions for the design of radomes for F&-like projectile launch/flight conditions. The aerothermal, convective, conductive 

and structural analyses are a skeleton of a study that needs to be performed. Other materials such as ceramics, composites, and other 

polymers also need to be studied. 

4. SUBJECT TERMS 

microwaves radio waves thermophysical properties 

polymers thermal analysis 

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OF REPORT OF THIS PAGE OF ABSTRACT 

Unclassified Unclassified Unclassified 

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35 

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F.-_l-.> r--. ,.ne ,m.. ,. A,.\ 

NSN 7540-01-280-5500 sranoaro rorm LYE tnev. ~-out 

Prescribed by ANSI Std. 239-18 29 

298.102