aircraft transparency testing - airtificial birds

7/29/2019 Aircraft Transparency Testing - Airtificial Birds

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AEOC-TR-86-2

Aircraft TransparencyTesting - Artificial Birds

C. J. WeI~hCalspan Corporation

andIst k Vincent Centoizc, USA.'040o April 1986

Final Report for Period July 1, 1984 - May 1, 1985

DTIC~~ELECTE

S APR2 3 1986

BARNOLD ENGINEERING DEVELOPMENT CENTER

ARNOLD AIR FORCE STATION, TENNESSEEAIR FORCE SYSTEMS COMMAND


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NOTICESWhen U. S. Govertnent drawiap, specifications, or other data are used for any purpose other than adtfinitely related Government procurement operation, the Government thereby incurs no responsibilityno r any obligation whatsoever, and the fact that the government may have formulated, futnished. or inny way supplied the said drawings. bpecificatlons. or other data, isno t to be regarded by implicaiion orotherwisc, or in any marmer liccn-iL4 the holder or any other person or corporation, or conveying anytights or permission to manufacture, use, or se l any patented invention that ma y in any way be relatcdthereto.Qualified users may obtain copies of this report from the Defense Technical Information Center.References to named commercial products in this report are not to be oa.dcrcd in any scrise as aui

" xs.J ,e,.ntm of the Iodxut by thc Unitel S.wats Aix Force or the Go.ernnint.

1wa t to-, be,i ,ciwed by the Offwc of Publi,7 Affaus (PA) and m rcleasable to the NationalTchrual hlfotmAtion .cr ice (N i IS) At NTIS. it -ill be available to the general public, includingforeig' nations.

APPROV AL STA1 IMIFNT-

1h q..rt hab bcn reviewed and approvtd.

N |N(T N I ('I-NTONZI. 1,t 1.t, USAFHt-ei;'y h%trins DivisionI . ,. c, ;: ol Acrspiac Iight lliianiics Testti~u!) fo'r Otpeiat ionsV7E

Appioved for publication:l(K I MI: COMMANIER

LOA El. L C KEEL, Lt Colonel, USAFiDirecor of Technologyieputy Ior Operations

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2b ECA LASSIICATIONONRONSEULSERVRE OF THIS PAGE.4 PEFORINGORGAIZAION REPORT DOCU(SMNITONG OAGANZTOEEOR UBRS

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RArnIAIO Argnoldrng Ierin ~ ppticohbeDevelopment Cente DOF_______________________6c. ADDRESS (City.Staep nd ZlIPCae 1b. SOURCESWiy StF tU ND ISCde

Air Force Systems Conmmand EEET~O ON OArnold Air Force Station, TN 37389-5000

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'Welsh. C. J., asa op/ECDvsond Centonze, Vincent, 1st t,SAF

17 COSATI CODIES 18, SUBJECT TERMS ,Ceint n mw ,iiri f .cuwa ansd Identify by block numbed#FIEL CiROUP SUB GR transparency testing144bird impacts

_Jartificial birds,. '~~.19 ABSTRACT IC-fltnir .i. everse if necesmsa nd identify by blink nuinberi

An analysis was made concerning the use of artificial birds in ird impact testingof aircraft transparencies. Results of this analysis, includirui impact measurementsat a nominal velocity of 500 fos, indicate that the use of artificial birds for impacttesting at these conditions is mpractical. This follows from the importance anddifficulty of simulating the shear strength chracteristics of real birds in ransparency

20 OIST041BUTIONIAVAILABILITY (IF AIISTRACT 21 ABSTRIACT SECURIrY CLASSIF-ICATIONUNC!_AS~lFIFflUNtIMITED f SAME AS RP T fOTIC USERS Uj UNCLASSIFIED22. '4AME OF RLILUIONSIRLt INDIVIDUAL 221, TELEPIINF. NUMBER 7-, noFFIC! s"YI

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U)NCLASS IF EDSECURITY CLASSIFICATION OF TOI-1 PAGE

3. DISTRIBUTION/AVAILABILITY OF REPORTApproved for public release; distribution unlimited.

11. TITLEAircraft Transparency Testing - Artificial Birds

141

1INCLASSIEIEDSECURITY CLASSIFICATION OF THIS PAGE

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PREFACE

The work reported herein was performed by the Arnold Engineering Development Center(AEDC), Air Force Systems Command (AFSC). The results were obtained by Calspan

'Corporation, AEDC Division, operating contractor for the aerospace flight dynamics testing" facilities at the AEDC, AFSC, Arnold Air Force Station, Tennessee under Project NumberCC60VK. The Project Monitor was 1st Lt Vincent Centonze. The research was performedfrom July 1, 1984 through May 1, 1985, and the manuscript was submitted for publicationon November 27, 1985.

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AEDC-TR-8

CONTENTS

Pa1.0 INTRODUCTION ......................................................2.0 APPARATUS .................................................

2.i Test Facility ................................................. ......2.2 Projectiles and Sabots ..............................................2.3 Test Instrum entation .................................................

3.0 DISCUSSION .........................................................3.1 Types of Im pacts ....................................................3.2 Experim ental Tests ...................................................

4.0 CONCLUDING REMARKS ..............................................REFERENCES .........................................................

ILLUSTRATIONSFigure

1. AEDC Bird Impact Range, S3 .............................................2. Test Area Arrangement ...................................................3. Target Plate Installation ..................................................4. Projectiles Just Prior to Target Plate Impact ................................5. Debris Patterns Following Impact ..........................................6. Deformations of Aluminum Target Plates ...................................

TABLE1. Shot Su m m ary ........................................................... 1

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1.0 INTRODUCTIONOver the last several years a concerted effort has been directed toward improving the

bird impact resistance characteristics of aircraft transparencies. Ground testing is an impor-tant part of this effort in which carcasses of previously killed birds (normally 4-lb chickens)are used in the impact tests of the transparencies.-Because of the inhomogeneity of real birdsand their irregular geometry, investigators in the past, for example Ref. 1, have examinedthe use of artificial birds having more desirable features such as a homogeneous materialand a simple geometry. Recommendations listed in Ref. I include the use of a homogeneousgelatin material with 10-percent porosity as a substitute bird material that is molded in acylindrical shape having a fineness ratio of two; however, additional experimental tests relatedto the use of artificial birds were also included in the recommenations of Ref. 1.

A study, including six impact shots made at a nominal velocity of 500 fps, was recentlymade at AEDC concerning the use of artificial birds, and the purpose of this report is topresent the results of that study.

2.0 APPARATUS2.1 TEST FACILITY

The Range S3 test unit is comprised of a compressed-air-operated launcher, an X-raysystem for measuring bird velocity, and a test stand for placement of the test target. Thetest unit and test area arrangement are shown in Figs. I and 2, and detailed descriptionsof the test unit and its capabilities are contained in Ref. 2. The target configuration usedin the current test is shown in Fig. 3 and consisted of aluminum (T6-6061) plates bolted toa l-in.-thick steel support plate with a 16-in.-diam opening. The support plate was adjustedtransversely to the flight direction to position the center of the 16-in.-diam opening on thegun centerline.2.2 PROJECTILES AND SABOTS

Projectiles launched in the current tests were either 4-lb chicken carcasses or artificialbirds of a 4-in.-diam cylindrical shape with a nominal fineness ratio of two. The artificialbirds were fabricated of a gelatin material using a molding process consistent with the recom-mendations of Ref. I. The nominal density of the artificial birds was 0.92 gm/cm- , and thecorresponding longitudinal density gradient was within two percent of he mean density. The4-lb required weight was obtained by small adjustments to the length of the artificial birds.The chicken carcasses were of chickens previously asphyxiated, quick frozen, and stored at0F, Prior to testing, a carcass was thawed in still air at room temperature (75'F) for ap-proximately 24 hours or until the body cavity temperature was 70 + 101F. Small adjustments

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to the bird carcass weight were required to achieve the 4-lb weight requirement and wereaccomplished by clipping carcass appendages.

Th e real and artificial birds were mated to the launch tube using sabots fabricated ofeither polyethylene foam or balsa wood. Separation of the bird from the sabot after launchwas accomplished through use of the tapered and grooved conic sabot stripper attached directlyto the vent section of the launch tube (Fig. 2). As the launch package entered the sabot strip-per. the sabot velocity gradually decreased to zero by the shearing of the sabot material,permitting the biid to exit in free flight.

2.3 TEST INSTRUMENTATIONBird positio' and orientation prior to impact were monitored using three 105-kv X-ray

shadowgraph units mounted on an instrumentation cart positioned along the flight path (Fig.2). The X-ray stations were nominally 3.5 ft apart with the first station located approximately5 ft from the muzzle of the sabot stripper. Each X-ray station was activated when the birdsevered a 24-gage copper wire in an electrical breakwire system. Each X-ray pulser also trig-gered a chronograph system providing elapsed time measurements between stations. Birdvelocity was computed from displacement-time measurements obtained from the in-flightX-rays and the chronograph system.

Photographic documentation of an impact event and the resulting debris patterns wasrecorded using 16-mm motion picture cameras (Hycam Model No. 41-004) operating htapproximately 5000 frames/sec.

3.0 DISCUSSION3.1 TYPES OF IMPACTS

A basic relationship in impact testing is one in which the momentum of the projectileprior to impact with a target is equated to the total impulse required in stopping the projectile:

(mv)i F f Atwhere

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(my), projectile momentum prior to impactm = projectile massv = projectile velocity

and

Fer * At - total impulse required in stopping the projectile

Fef = effective force during the impact eventAt = time of the impact event

It is important to observe that in a transparency impact test the effective shear strengthof the projectile (real birds) is normally much less than the allowable shear stress of thetransparency; hence, in such a test, At can be defined approximately by the crush time ofthe projectile (the time between the impacts of its leading and trailing edges) and is propor-tional to the shear strength of the projectile material. In turn, Fee, the primary parameterin determining the extent of transparency damage, is inversely proportional to At for a giventotal impulse. It follows that the damage in a transparency impact is very dependent on theshear characteristics of the projectile material.

The importance of the projectile material strength, i:cluding any artificial bird materialthat might be selected, tends to be unique to this type of impact testing. For example, inhypervelocity impacts, the impact stresses generated are normally many times larger thanthe allowable stresses of the projectile materials: hence, At tends to be insensitive to projec-tile material changes. Furthermore, in many low-speed impacts, in which the projectile materialallowable shear stress can be appreciably higher than that of the target material, At againtends to be insensitive to projectile material changes.

3.2 EXPERIMENTAL TESTSBecause of both the importance of the projectile material strength in transparency im-

pact tests, as discussed in Section 3.1, and the inhomogeneity of real birds, it was questionablethat an artificial biud material, as defined in Ref. 1, could adequately simulate the impactcharacteristics of a real bird. This is particularly true considering ihe wide range of test con-ditions normally associated with transparency tests. rhus, tests were designed to maximize

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AEOC-TR.86-2

the capability of detecting differences in projectile material characteristics. Th e tests used4-lb birds impacting high-strength aluminum plates (normal to bird flight direction) withthe impact events monitored through the use of high-speed movie cameras. Such tests per-mitted at (crush time of bird) and the resulting debris patterns to be obtained from an ex-amination of the movie film, and the maximum permanent deformation (flight direction)of the target plate to be obtained from posttest measurements.

All shots were made at velocities near 500 fps and are summarized in Table 1. The Atvalues, obtained from a frame-by-frame exani.-'ition of the movie film, indicate that thereal bird behaved as a near-zero-shear material; that is, At was appr')ximately equal to thelength of the bird divided by the impact velocity. Th e At of the gelatin bird was about 30percent larger than that of the real bird. The difference in the lengths of the gelatin birdand the real bird only accounts for about one third of the difference observed between theAt values. It follows that the At measurements indicate the shear strength of the gelatin birdwa s appreciably larger than the strength of a real bird. Photographs of an artificial bird anda real bird just prior to impact are shown in Fig. 4. Photographs of bird debris followingimpact of the leading edge of the birds are shown in Fig. 5. Th e large differences in the debrispatterns shown in Fig. 5 indicate, again, that the shear strength of the gelatin bird is ap-preciably larger than that of a real bird. A photograph showing representative differencesin the deformations of aluminum plates between real and artificial bird impacts is presentedin Fig. 6. Corresponding deformation measurements listed in Table 1for the 0.25-in.-thickaluminum target plates indicate that the maximum permanent deformation (ir. the flight direc-tion) of a target plate from a real bird impact was about 35 percent larger than that fromthe gelatin bird. It is important to observe that all three types of measurements, at, debrispatterns, and plate deformation, are consistent in indicating appreciable differences in theshear characteristics of the gelatin bird material from that of a real bird.

The present measurements, in conjunction with the importance of projectile materialstrength noted in Section 3.1, indicate that it is impractical to use current homogeneoussubstitute materials in impact testing of transparencies. F-t her, the detected differences inthe impact characteristics of real and artificial birds at 500 fps may not be representativeof differences that could occur at other test conditions. In addition, experience in impacttesting of transparencies at AEDC indicates that sanitation and cleanup concerns attributedto the use of real birds are insignificant.

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4.0 CONCLUDING REMARKSAn analysis was made concerning the use of artificial birds in impact testing of aircraft

transparencies, including impact tests made at a nominal velocity of 500 fps. Significant dif-ferences in the impact behavior between real and artificial birds were measured, and the resultsof the analysis indicate that the use of artificial birds for impact testing at these conditionsis impractical. This follows from the importance and the difficulty of simulating the shearstrength characteristics of real birds in this type of an impact.

REFERENCES

I. Challita, Antonios. "Validation of a Bird Substitute for Development and Qualificationof Aircraft Transparenci-s." AFWAL-TR-80-3098, (AD-A097 736), October 1980.

2. Sanders, E. J. "The von Klrm~n C;es Dynamics -acihit, Ranve S3 - Description andCapabilities." AEDC-TR-76-9. ,AD-B008983L) January 1976.

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Table 1. Shot SummaryLengtht Targettt Maximumttt

Shot Projectile of Projectile Velocity Plate Thickness, Deflection ofMaterial in. fps in. Target Plate, in.I Gelatin 8.34 471 0.25 1 3/162 Chicken 7.67 478 0.25 1 5/83 Gelatin 8.52 497 0.25 1 1/44 Chicken 7.75 494 0.25 1 11/165 Gelatin 8.52 499 0.25 1 5/166 Chicken 7.79 511 0.50 13/16

t As measured at third X-ray stationtt All target plates were of T6061-T6 aluminum alloy.tt t Measured in flight direction

NOTES: A detailed examination (frame-by-frame) of the movie film fo r the series of shots indicates aAt equivalent to 6-1/2 frames for the real chicken and to 8-1/2 frames for the gelatin bird. Frame timeinterval was nominally 0.2 msec.All projectiles, gelatin or chicken, were adjusted to 4 lb.Gelatin bird diameter was 4 in., and nominal maximum chicken diameter was 5-1/4 in.

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aircraft transparency testing - airtificial birds

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