AD—A0’i6 ‘+90 SCHOOL. OF AEROSPACE MEDICINE 8ROOKS AFB VEX F.’6 13/6OPTICAL. EVALUATION OF F/Fe—ill FIELD—SERVICE—TEST W INDSHIELDS.(LJ)SEP 77 w F PROVINES, B KISLIN. T J TREDICI

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.]N CLASSI FlEDSECU RI” CLASSI FICAT IO N OF THIS PAGE ~‘WI,.., o at. Ent.r.d)

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READ INSTRU CTION SREPORT DOCUMENTATION PAGE BEFORE COMPLETING FORMTT RE PCR T NUMBER 2. GOVT ACCESS ION PlO 3 RECIPIENT ’S C A T A L O G NJ M B E R

- • SAM—TR —77 —l 9 ______________________________

4. T I T L E (a~d SubIItl.) / S T ,QLRE~~O~~T -&.P~~RIOD C O VE R E D

~ Progress Repor t. • -

• OPTICAL ~VALUATION OF F/FB—lll FIELD—SERVICE,- 17 Apr 7~~ — 18 Nov 76 ,~, _.

TEST WINDSHIELDS , • 6 PERFORMING G~~~~~~~’öR~ NUMBER

7 AUT PIOR(.) - B- CO NT RAC T O R G R A P 4 T N uMe ER(aI

Wayne F. Provines , ‘Major , USAF , BSC- Benjamin:Kislin1 Colonel , USAF , BSCThomas J. /Tredic i1 Colonel, USAF , MC ____________________________

9 PERFORu u~t O RGAN IZ~~TIO N NAM E AND ADDRESS 10. PROGRAM ELEMEN T . T A S K

USAF School of Aerospace Med icine (NGOP )Aerospace Medical Division (AFSC) , 62202F

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Brooks Air Force Base, Texas 78235 ~

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II . CONTROLL ING OFFIC E NAME AND ADDRESS — .~~~ EPO~~t . DATE 4

USAF School of Aerospace Medic ine (NGOP) Sep~~~~~— . ~~~77Aerospace Medical Division (AFSC) / / IS . NUMB ER Dc P A G E S ‘

Brooks Air Force Base, Texas 78235 12IT M C N ’ T O R I N G AGENCY NAME & A DDRESS(II dill,o.nl ft om Conl,o llt ng OVIice ) 15. S E C U R I T Y CLASS. (of th Ia r.po,~

UN CLASSIFIED

15. D E C L A S S I F I C A T I O N D O W N G R A D I N GSCHEDULE

IS D~ ST R I B U T I CCN S T A T E M E N T (of h i . R.port)

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17. D ISTRIBUTION S T A T E M E N T (of IS. .bat,.cc .nte,cd In Block 20 . ‘ I diul.,. nI fro ,o R.po,f )

Approved for public release; distribu t ion unlimited .

ii ~ S U P P L E M E N T A R Y NOT I S

19 0 EV WORDS ( Co.,tino. on too.,, . aid. If no .... ,, wd Id .nlIfy by block npmb.’ ,

Wi ndsh ie ldsF /FB—l l lO p t i c sDistort ion

2 0 A B S T R A C T (Coc’ In-~. on ,.v .r,. aid. If n•c.aaary and Id .nhify by block nwr b.,) Ten shipsets (pairs) ofF / F B — l l l b i rd— .~ p i ~-resistant windshields plus four shipsets of spares wereopticall y evaluated in the USAF School of Aerospace Medicine (USAFS AM) wind-shield laboratory before installation into aircraft. This was in support of afield-test program directed by the Air Force Flight Dynamics Laboratory . Toelicit distortion characteristics , the tTSAFSAM effort included the determthationof li. ’ht-transmissivity properties and haze values , pr ism—deviation mapping , andgrid-hoard photography. Seven of these windshields were opticall y evaluated alsoafter the test, for pre— versus post—field—service direct comparison. *--‘

DD ~~~~~~~ 1473 ED ITION OF I NOV 65 IS OBSOLETE ~ / • UNCLASSIFIEDSECUR ITY CLASSIFICATION OF THIS PA GE (WN.n Datli tnIii,p~~)

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OPTICAL EVALuATION OF F/FB—lll FIELD—SERVICE TEST—WINDSHIELDS

INTRODUCTION

This report describes the principal effort by the USAF School ofAerospace Medicine (USAFSAM) in support of the F/FB—lll bird—impact—resistant windshield field—service- test program (Air Force FlightDynamics Laboratory Project 1426-75—01 and Tactical Air CommandProject 75C—126W) .

The F/FB— 11l windshield design is rather atypical for flight air-craft in that it consists ‘~f two side—by— side windshields forming acone section installed at 68 degrees from vertical and viewed throughan obli que ang le by the aircrew (Fig. 1).

Figure 1. F—1IIF , 70—2390, front view .

Earl y in the aircraft ’s opera t ional h istory , windshinld—opticsproblems arose which included : nighttime multip le imag ing, roll orband distortion , and subtle but significant visual symp toms and head-ache comp laints from the aircrew . After an extensive investigativeprogram by General Dynam ics , the distortion and visual—symptomspr oblems were , w it h excep tions , resolved by imposing (implementing

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and fulfilling) complicated specifications pertaining to magnifica-tion (lensing) and prismatic changes (displacement grading). Themultiple images remained but were generally aircrew acceptable dueprimarily to adaptation.

A more serious windshield concern arose in the form of destructivebirdstrikes. Because of its high~-speed, low—level mission require-ments, the F/PB—Ill has a high probability in encountering birdstrikesof enormous impact force. When a number of strikes occurred on the0.85—cm (0.33—in) thick, 3.-ply, chemically tempered glass windshields,catastrophic windshield failure occurred with bird penetration; andaircraft loss resulted in some instances. Concerned about this losspotential, the U.S. Air Force requested the development of a wind-shield that would survive a high—speed birds trike at mission profileand velocity (TAC “Required for Operational Capability” (ROC) #26—71).Pittsburgh Plate Glass (PPG) Industries, under contract award, developeda windshield , approximately ,2.54 cm (1 in) thick, of a 10—ply designcomposed of acrylic, polycarbonate, and proprietary innerlayers. Thestructural propertie8 of this windshield will defeat penetration in ahigh—speed bird impact. The Air Force Flight Dynamics Laboratory (AFFDL)development program manager was directed to field—test ten shipsetsof the PPG windshields for approximately 1 year before recommendingfull—fleet retrofit. The purpose of the field test was to evals’stethe enviroomental effects upon the unproved plastic materials ai~ tomonitor aircrev acceptance of potential optical—error characteristicsimparted in the manufacturing process.

USAFSAiI’s contribution in response to the TAC ROC was multifaceted.A standard optical evaluation of all test windshields before aircraftinstallation was performed to establish an optical—properties databank for post—field—test comparison and for correlation with pilot—response data. Efforts were also made to obtain data not addressed bythe manufacturer; certain co on measurements technics were refined ;and additional evaluation technics and procedures were devised.

• More

detail on these additional USAFSPIN efforts will be presented in forth-coming reports.

STANDARD OPTIC AL EVALUATIONS CONDUCTED BY USAFSAMBEFORE AND AFTER FIELD TESTS

The initial USAFSAN windshield—optics evaluation included thefollowing determinations:

1. Light tranamissivity

a. Normal incidence

b. Designed pilot—eye—position incidence

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2. Haze (light scatter) value

3. Prism—deviation mapping

4. Grid—board photography

Instrumentation and Procedures Requiredto Generate Optical Data

The light—transmission quality of the F/FB—111 windshield wasdetermined in the normal and installed—angle positions. A Pritchardluminance meter and a Spectra standard light source (100—ft L, or29.19 cd/rn2) were the equ ipment employed . The Pritchard was alignedin the designed pilot—eye position for the installed—ang le measure-ments.

To determine its haze value , the windshield was positioned adja-cent to the beam port of a Gardner haze meter and the meter value wasrecorded . Due to the haze meter design, readings were restricted tothe periphery of the windshields ; i.e., 12.5 cm (5 in) in from theedge—attachment borders .

To generate the prism—deviation map , the windshield was verticallysuspended from a hoist , fore—arch area up. A template placed over thewindshield divided it into approximately 10— X 10—cm (4— X 4—in) squares(Fig. 2). A HeNe laser beam was posed normally through each square ,and the beam divergence was read from a target vectored and calibratedin minutes of arc. These deviation maps are used to determine if thewindshield meets boresight specifications. With technic refinement ,these data have afforded accurate information in predicting multiple—image locations through the windshield .

Distortion effects were obtained by evaluating a grid hoard photo—graphed through the windshield (Fig. 3). Lensing and displacementgrading values were determined by the procedure described in GeneralDynamics Report FZM—12—10952A , “Optical Evaluation of the F—ill Wind-shield ,” 20 May 1970. This procedure was successful, for the mostpart , in resolving aircrew visual complaints in the glass windshields.

Table 1 provides the optical specifications required and themeasurements made for the field—test windshields . An instrumentcalibration error invalidated some haze measurements. Table 2 identi-fies each windshield and the aircraft in which it was installed .Multip le serial numbers associated with an ‘tvidual aircraft indi-cate changes in windshields during the pr

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Figure 2. Prism-deviation overlay pattern

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~~~I~C 1 f ’ t i - ~ fl~~ ( ~~c i~~i ’ o t u d v t ;~r .~ rep lac-: ;~L~~s-- L. : . l L e l d s exceededd i ap lact•i ro . r t — a r a d ing . ; p o i i c a t i on s) . Tho t~lo- o r i g i na l s rac h ib i tedslii -z h~~l y ;i~~hci --t h a n - - a ’ - - : ’ :~t a h l e ‘ l e ’ ? l O t Lon va~~u - ~, . nca r t he t o r e — a r c h area .and one d i i l o . ’ isL 1 a ; . t h e t i ;~~~~ r l~ f t ar e a - ~r the opt ica lfr e e ~ont ’ , as see n in ~ i p ; . e ‘~~ . Th ~.-se ; ‘r o p e r t i e a w er ’ act c ’nsider ed ac a n p r l i m i s e t~ i...lit sn~~e~ v~ and t h e ; i i l - . -~p 1c ~t ~~~~ ion w i n t ah i e ld s wereinclud ed ft t oe r ~e l d t~~.-;~ . Qu€-atic ~nnai rcs ~‘ & ‘ t e d i s t r i ~~i i t c d tO t i eu s i n g s i t i a rons • it . r~ -~ w ~, i s I ~ie d~ w er e ro t ~ar t i c i i —l n r L v d i t f ~’’ - : ’ ; rov~ t h e I l - .- r t ea( t ~~~~~~~~ on the l :t 0 1 J o win d s h ie ld~ - .Ro l l or ban dist f t i o n , a l I t i r o n t ft . 1 w i n d s h ie l d s . ~;as ‘os t pronouncednear th~ ed pea and towa rd t i e I ~“er - - - t h i r d l t . ~~~wLr ,d - t i e l d , i . e . ,to’Jar I the t o r ar c h . ~~b t d o t u i ’ 1 d s i l a t er pr t i I ! c t i ’ it n i n a tow ed leoc

r v ~ re d i s t o r t i o n lei rtda .

:i r - r e t - ‘~ l i e a ro t h at_ nc~’ - ‘ m d - I t i e l d s :, ir i cd . T h i s r epor t doesadd ross the r e~.pon ic 1 i n u l v s is . ied - ‘ r r e l t I I ; iO \ .’ t 0 :1 • th e a i rc re~

c n meiit s c e nt t r ’ li c ii d I - - t o r t ion . r e ’. i n g . t i l t ip l i i ;ii ,~~~ in g , and a ra in—i-low i n ’-~ e f f i - - t o a r t h e w I n d s h i ~ld td 1 e~ . 0) th e t f l or ig inal wind shields h i pr i -’t s ( f i v e g o t d — e L i !, f i v e fli fil I l a t i t , on ! ’ ’ one ~~~~~~ ( a i r c r a f tF7 0—2 5h ) Wa s r t ~~cc t ed h ’, , i ~~c rews J t er m u l t i p l e f l i h i t s as unaccep tab lew i t h r e ;p eet t - ~ f l i g h t saf t v . h r n p l . i i t t s on t h i - wind - l i i & l d set includedd e p t h — p i r c € p t ion d i t f i c u l t y i n land i ng , ex t ens ive h a z i n g , excess ive dis-t o r t ion , and w i d i m u l t ip le— i m - I g e sI~~i-- Irnt i n n . S ince t h i s w n dshie ld so thad m i t t h oj r n t i \ r ~ i - i l a p e i f i c a t i o n s , L L was i .i~~~~ad t hat somed p r , I d ing pr ip rtv 1 - l i ) c i c- i p i d d e t - c t on . Thi; set w - s r : l o V c d f rom

he a i r c r a f t m d a n t I ’ ! ISAF SAM f o r a t u d v . Ex ept t o a w i d e m u ] t ip I- - a p I f l t ion and a d y n a m i c d e p t h — pi- r I , i on i i t r at ion (which

is5

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TABLE 2. CHART OF BIRD-RESISTANT-TR .ANSPARZNCY INSTALLATION

LH RN LH REAircraft Windshield Windshield Canopy Canopy

S/N S/N S/N S/N

F70—2389 502915 502911 502907 502904Mountain Home

F70—2390 504969 504006 503948 503947Mountaim Home 509107 509125

605290 605286

E68—062 503931 503955 503962 503966Upper Heyford 605270 605217

E68—064 503932 503930 503926 502923Upper Heyford

A67—098 502912 503929 503935 503934Nellie

A67—058 504995 505014 504971 504973Nellis 606304 605292

P8—243 504972 504005 504975 504974Plattsburgh

P8—244 502914 503965 504989 504996Plat t sbur gh

C—l25 503933 505023 504999 505012Australia

C—l26 504990 504976 504997 505020Australia

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not statistically significant), the origin of the aircrew visual com-plaints is unresolved on an optical basis. Two additional windshieldsets wh ich met optical specifications wer e installed on this aircraft;again , sever e a ircrew comp laints resulted in their subsequent removal.Factors other than degraded optics are suspected in the windshieldrejections on this aircraft.

Postservjce evaluations of seven windshields are included in thedata section (see Table 1). As had been forecasted , haze values ofthese sets increased due to exterior surface erosion caused by thef l ight environment and improper cleaning procedures. Surface scratchingis presumed to be the primary causative factor , since hand pol ish ing ofwindshields 503929 and 504995 reduced the haze. Comparisons of prism—dev iation maps of three windshields (504990, 504995 , 503931) befo reand after field use are within instrument—error tolerance , indicatingno change in optics due to aging or environmental factors. Figures4 and 5 are pre— and postservice maps of one typ ical windshield (504995).Distortion pho tographs before and after field use of the three wind-shields also show no changes.

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Figure 5. Post—service—test deviation map .

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Two unforeseen visual problems arose h’ring the field—service test.Airerews reported colored fringes or “rainbowing ” in the windshields ,especially near the edges when f l y ing i.nto a clear daytime sky . Thesepatterns were not particularly annoying with the rarly shipsets , hutcomplaints became more serious when replacement windshields wore lrtstalled .The rainbow patterns are attributed to the birefriit~ ent properties cf thepolycarbonate layers that become manifest when looking t h r n ’r g h them . ntothe partially polarized sky . Later prod ;ct~ on runs of the replacementwindshields diffused and displaced the fr ;nge patterns toward the ed geof the windshields and to some extent al!eviated the pilot dissatisfac-tion associated with the rainbowing .

The other visual problem of considerable concern is that of a ve ’l i ngglare caused by sunlight reflected o f f a degraded glare—shie ld s u r fa c eand then mirrored into the aTircrew ’s eyes ay :he back su’.Ji~ of th e wind-shield . This glare effect , comb ined wi 0-i ~be inheren t haze cf the p l a s t i cma ter ials of toe windshie ld , car. c a t i s a a r a r e e t ’h a c k g r o u n d c r t r a s ttion and reduced visual performance capability . This is particularl;manifest under i~tazv atmospl-eri’: condi ions and/or when the sun is ~~catedat certain overhead angles. Diffftoltv in reod cg etters and nurtera son ground targets was a direct cause for : er ’oving a shirret from airer- aftC— l26 . A n o n r e fl e ct i v e c lo th ol:iced ~~‘er t i e g lare shie d greatlY redltcesthis problem. Whether or not a m at er I a L ; solut ion can be found to thisdegraded—g lare—shield problem remaIns unknown at this time .

ACKNOWLEDGMENT

Sincere appreciation is extended to Technical Sergeant Steven G. Kinel ,Sergeant Howard K. Saulsberry , and Senior .\irman Alberto Carrasquillo fortheir contributions in support of this study.

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GLOSSARY

SOME OPTICAL TERMS AS APPLIED TO AIRCRAFT WINDSHIELDS

TRANSMISSIVITY : The ;~c’-cencage of incident l ig h t n a s s in c t h r o u g h anopt i ca l mec .iim . All transparencies re:it~co - tadabsorb some i.ight , resulting in a viewed lraioc thatis less bright than the actual object.

DISTORTION : Light refracted or bent in various ways as it passesthroug h an op tical medium resul ts in a viewed imagenot being a true representation of the object——i.e.,straigh t lines appear crooked , wavy , etc. “anytypes of distortion occur. Three of these have beenpar ticularly no tewor thy on both the F—lu glas — andplastic—windscreen problems .

1. Lensing——A magnification or minification effectwh ich may vary in extent from one portion of a trans-parency to another . Lensing causes objects to beincreased or decreased in size and may have a de-grading effect on visual focusing; it also has thepotential for disrup ting the binocular visual system.

2. Displacement Grading——A gradual apparent slope ofa line away from its true horizontal or verticalor ien ta t ion when viewed across the transparency . Themagni tude of d isp lacement grading varies from onepor t ico of the F — i l l windshield to another bu t usu-ally is most pronounced approximately one— third thedistance d own the aft—arch area. The visual effectis toot of creating a slight rotation of the horizonand , if pr onounced , is suspected as causing a de-grad ing bir .ocular visual effect.

3. Roll or Band D i s t o r t i o n — — A wavy or rippl ingeffect usually toted at the fore one—third area ofthe F—ill w i n d ~~r f o l d . Viewed objects appear to undu-late as seen through the affected area.

MULTIPLE IMAGES: Internal interface reflection (ligh t reflecting backand forth within the transparent media surfaces)effects one or more additional visual images, oflesser intensity , of a sing le object——usually anexternal light source located in a dark background .The multip le— images ’ locations with respect to thep rimary (real) image depend upon the geometry , slope ,and prism deviation of the transparency . The imagesmay ap pear , disappear , and swirl , depending upon theinterrelation of the above factors .

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HAZE: A scattering effect of ligh t passing through anop tical medium. This scatter is caused by imperfec-.tions (such as scratches) on the surface and/oreffects within the medium itself . The visual effectis that of an object appearing cloud y , obscured , orless distinct from i ts background (reduction itcontrast).

RAINB~~JTNG : When light passes through a b i re f ringent medium,colors may appear due to diffraction . The resultantcolors and patterns depend on stresses within themedium. This effect is accentuated if the incidentligh t is polarized to some amount. Sky lIg ht Ic &

good example.

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