USAARL Report By Wun C. Chiou, Ph.D. SP5 Chun K. Park, M.S. SP5 Chris E. Moser, B.S. June Final Report

Transcription

1 USAARL Report ATTENUATION OF LIGHT TRANSMISSION IN ARMY AIRCRAFT TRANSPARENCIES DUE TO SLANTING By Wun C. Chiou, Ph.D. SP5 Chun K. Park, M.S. SP5 Chris E. Moser, B.S. June 1976 Final Report US Army Aeromedical Research Laboratory Fort Rucker, Alabama This document has been approved for public release and sale; its distribution is unlimited.

2 NOTICE Qualified requesters may obtain copies from the Defense Documentation Center (DOC), Cameron Station, Alexandria, Virginia. Orders will be expedited if placed through the librarian or other person designated to request documents from DOC (Formerly ASTIA). Change of Address Organiation receiving reports from the US Army Aeromedical Research Laboratory on automatic mailing lists should confirm correct address when corresponding about laboratory reports. Disposition Destroy this report when it is no longer needed. to the originator. Do not return it Disclaimer The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authoried documents.

3 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (IPIIen Data Entered) I. REPORT NUMBER r REPORT DOCUMENTATION PAGE : GOVT READ INSTRUCTIONS BEFORE COMPLETING FORM ACCESSION NO. 3. RECIPIENT'S CATALOG.NUMBER 4. TITLE (and Subtitle) 5. TYPE OF REPORT ll PERIOD COVERED TTENUATION OF LIGHT TRANSMISSION IN ARMY AIRCRAFT. RANSPARENCIES DUE TO SLANTING Final 6. PERFORMING ORG. REPORT NUMBER. 7. AUTHOR( ) B. CONTRACT OR GRANT NUMBER( ) un C. Chiou, Ph.D. P5 Chun K. Park, M.S. :PI> rhri c; I= Mnc;>r R C:: 9. PERFORMING ORGANIZATION NAME AND ADDRESS 1. PROGRAM ELEMENT, PROJECT, TASK io-optics Division (SGRD-UAO) AREA ll WORK UNIT NUMBERS S Army Aeromedical Research Laboratory DA 1498 ;nrt Rlu k>r AI 1n1n? II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE US Army Aeromedical REsearch Laboratory June 1976 GRD-UAC 13. NUMBER OF PAGES Fort Rucker. AL MONITORING AGENCY NAME ll ADDRESS(lf different from Controlllnll Olllce) 15. SECURITY CLASS. (of thle report) US Army Medical R & D Command ashington, DC Unclassified I Sa. DECL ASS I Fl CATION/ DOWNGRADING SCHEDULE 16. DISTRIBUTION STATEMENT (of thle Report) This document has been approved for public release and sale; its distribution is unlimited. 17. DISTRIBUTION STATEMENT (of the abatract entered In Blocll: 2, It different from Report) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (ContJnue on reverae side II necessary and Identify by block number) Transmission Reduction Slanting Transparencies 2. ABSTRACT (Continue..,..,..,._ elo II naceee..,. end Identify by l>locll: number) The rates of light transmission reduction due to the slanting in eight fixe< wing and fourteen rotary wing aircraft transparencies have been examined. We found that the optical quality at various portions of the UH-1 transparencies and all the fixed wing samples possess similar characteristics of transmission reduction. The windscreen and the armor glass of CH-54 samples are similar too. But the tinted versus the clear AH-lG transparencies are quite different. The tinted sample generally has 27% spectral transmission loss compared to that of DD FOAM I JAN 7) 1473 EDITION OF I NOV U IS O.BSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE(.,_ Data Entered)

4 UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGIE(IWI., Del... lend) the clear sample This reduction could constitute a dangerous loss of VlSlbility for the aviator, especially during periods of reduced illumintion and at night. The results presented in this study enable the potential users of the optical as well as the electro-optical devices to compute the amount of transmission reduction in most of the current Army aircraft. UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE(WIIen Data Entered)

5 SUMMARY The rates of light transmission reduction due to the slanting in eight fixed wing and fourteen rotary wing aircraft transparencies have been examined. We found that the optical quality at various portions of the UH-1 transparencies and all the fixed wing samples possess similar characteristics of transmission reduction. The windscreen and the armor glass of CH-54 samples are similar too. But the tinted versus the clear AH-lG transparencies are quite different. The tinted sample generally has 27% spectral transmission loss compared to that of the clear sample. This reduction could r:onstitute a dangerous loss of visibility for the aviator, especially during periods of reduced illumination and at night. The results presented in this study enable the potential users of the optical as well as the electro-optical devices to compute the amount of transmission reduction in most of the current Army aircraft. va/ COL, MSC Afi:.EYLJ Commanding

6 INTRODUCTION Most aircraft windscreens are designed to match the cont6ur of the 111Aihrrrne beellu!; or af!!1"1:ld.ym!ftit t:bfisiderations. A slat1tiftg Wihdshield not only possesses its inherent optical distortions, but also causes prismatic displacement as well as a loss in light transmission. Investigators in US Air Force Laboratories ' ' have quite extensively conducted research in these areas. For example, Grether 1 has studied the effect of slope and windscreen upon the optical degradation of pilot vision in the forward direction. In surveying the literature, one notices that most distortion and transmission reduction studies were done on high-speed aircraft windshields. Recently, several optical and spectral transmission studies on low-speed fixed and rotary wing Army aircraft windshields have been reported by us 4 5 ' Furthermore, we also 1 measured several samples for attenuation of light transmission due to slanting 6 This study continues the same subject with eight fixed ing and fourteen rotary wing aircraft windshield samples. The transparencies from one of the rotary wing aircraft (UH-1) have been studied in detail. The samples have been prepared from the center, the corner, the side portions of the windshield as well as from the crew door, the sl idinrj door and the fixed portion of the door. Results from these particular cross-sectional analyses enable potential users of optical and the electrooptical devices to compute the amount of transmission reduction from almost all the transparent ortions Of the UH-1 aircraft. METHODOLOGY a. Samples Eight fixed wing and fourteen rotary wing aircraft windscreen samples are labeled in Tables A and B respctively. All the samples were cut into 2 11 X 2 11 squares except the sample of U-8D/U"'"8F where the whole windshield was used. b. Apparatus: Model 198, Spectra Pritchard Photometer was used to measure the light transmission. A supporting device, calibrated in one degree increments in both the horiontal and vertical planes, was used to position and rotate the test samples through an angular range of oo - 9. A Macbeth Quantalog Transmission Densitometer was employed to read the transmission of some samples at oo angle only. The light source was a Spectra Regulated Brightness Source (9 ft.l).

7 c. Procedure The equipment was aligned along a horiontal axis running from the centfal aperture opening in the photometer detector head and through the centers of the sample and brightness source screen. After this alignment procedure was completed, and after the photometric equipment was internally calibrated, the transmission measurements were then taken. d. Design The 1 ight source 11 the jack was placed in front of the photometer detector head., Te sample held by the supporting device was centered between the light source and the photometer; In this case, the supporting device was designed to allow us to accurately simulate any angle of inclination likely to be encountered in the aircraft. RESULTS AND DISCUSSION Results are shown in Tables Fl to F8 and Rl to Rl4 and their respective figures. The average values for an incident angle normal to the vetical position of the sample varied from 6% to 95%. The light transmissions.due to slanting of the samples were expectd to decrease. The rate of loss gradually increases up to approximately 5 within 5% at each level while the increases of the rate of loss is comparatively less up to 5. Generally we find that the rate does not exceed 25% for any of the test samples at 6 except CH-47 and AH-lG. At the range beyond 6, the rate of attenuation is increasing rapidly. This may be beyond the aviator s concern because incident angles of an aviator s vision relative to the position of the windscreen would rarely exceed 6 during the actual course of flying. The attenuation is caused by light scattering, reflection, and refraction from the front and the back surface of the windscreen material. Furthermore, the degree of polariation affects the amplitude of the electric field. When the angle reaches the Brewster angle, the light is totally plane polaried. Thus one of its electric field component vanishes. The light transmission thus reduces. The Brewster angle is dependent upon the refra,ctive indices of the material.: CONCLUSION In conclusion, we have examined the rates of the transmission reduction of eight fixed wing and fourteen rotary wing aircraft transparencies. The results are summaried in Tables A and B respectively for fixed wing and rotary wing aircraft transparencies. The transmission reduction occurs gradually as the slanting angle approaches 6. 2

8 From various portions of UH-1 samples, the transmission reduction throughout the measuring range possesses more or less common characteristics. In other words, the optical quality of the windshield transparencies are almost the same for all the UH-1 samples and for all the fixed wing samples. The same is true for the CH-54 windshield transparency with respect to its armor glass sample. However, in AH-lG transpar- encies, the tinted sample has an average 25% transmission reduction with respect to its clear transparency. The problem of this unnecessary reduction has been pointed out by Crosley7 and by one of ust previously. This reduction could constitute a dangerous loss of visibility for the aviator, especially during periods of reduced illumination and at night. In summary, the results presented in. this report enable the potential users of the optical and the electro-opticl dvices to 6ompute the amount of transmission reduction due to slanting. 3

9 REFERENCES 1. Grether, W., 11 ptical factors in aircraft windshield design as related to pilot visual performance, 11 AMRL-TR-73-57, Smith, R.N. and J.R. Me!yer, 11 EVluation of the split-line optical distortion test method, 11. WADG Technical Note, , Chapanis, A. and S. Scachter, 11 Distortion in glass and its effect on depth perception, 11 TSEAL , Chiou, W.C., 11 Visible and near infrared spectral transmission characteristics of windscreens in Army aircraft, 11 USAARL Report No 76-14, Chiou, W.C., F.F. Holly, C.K. Park, and A.A. Higdon, Jr., 11 The use of opaque louvres and shields to reduce reflections within the cockpit:' USAARL Report No 76-6, Moser, C., 11 The attenuation of light transmission in Army aircraft windscreens due to slanting, 11 USAARL-LR , Crosley, J.K., 11 Tinted windscreens in U.S. Army aircraft, 11 USAARU Report_ 68-7, 1968.

10 TABLE A RATE OF ATTENUATION IN LIGHT TRANSMISSION (%) OF FIXED WING AIRCRAFT Aircraft soo goo U-6A o U-8/U':"8F 1 1 ' T ;4 1. T-42/U CV CV ;] OV

11 TABLE B RATE OF ATTENUATION IN LIGHT TRANSMISSION (%) OF ROTARY WING AIRCRAFT Aircraft goo OH TH-55/H-6A CH CH CH-54 (Armor Glass) AH-lG AH-lG (Tinted) UH-lD UH-1 (Center) UH-1 (Corner) UH-1 (Back) UH-1 (Crew Door) UH-1 (Sliding Section) UH-1 Door (Fixed Portion)

12 TABLE Fl Aircraft: DeHavilland U-6A (Beaver) Angle of Transmission (%) Inclination (} Samele 1 Samele 2 Samele 3 Average l

13 TABLE F2 Aircraft: Beech U-8/U-8F Angle of Transmission (%) Inclination () Sample 1 Sample 2 Sample 3 Average NOTE: In this case, the whole windscreen had to be tested. However, due to the double curvature of the windscreen, angles greater than 7 could not be measured.

14 TABLE F3 Aircraft: Cessna T-41 Angle of Transmission (%) Inclination () Sample 1 Sample 2 Sample 3 Average

15 TABLE F4 Aircraft: Beech T-42/U-8 Angle of Transmi ss.i on (%) Inclination {} Samle 1 Samle 2 Samle 3 Average

16 TABLE F5 Aircraft: DeHavilland CV-2 (Caribou) Angle of Inclination ( ) Transmission (%) NOTE: Data were supplied by the manufacturer.

17 TABLE F6 Aircraft: DeHavilland CV-7 (Buffalo) Angle of Inclination ( ) Transmission (%} NOTE: Data were supplied by the manufacturer.

18 TABLE F7 Aircraft: -1 (Back) Angle of Inclination () Samle 1 Samle 2 Samle 3 Average Transmission (%)

19 TABLE F8 Aircraft: OV-1 Angle of Inclination (} SamE1e 1 SamE1e 2 SamE1e 3 Average Transmission (n

20 TABLE R1 Aircraft: 811 Ho.58 Angle of Transmission (%) Inclination b SamE1e 1 SamE1e 2 SamE1e -3- Average ' ] , ; ' < i

21 TABLE R2 Aircraft: Hughes TH-55/H-6A Angle of Transmission (%) Inclination ( ) Sample 1 Sample 2 Sample 3 Average C' ' '\

22 TABLE R3 Aircraft: CH-47 Angle of Inclination () Sample 1 Sample 2 Sample 3 Average Transmission (%)

23 TABLE R4 Aircraft: CH-54 Angle of Tnc1ination () Sample 1 Sample 2 Sample 3 Average Transmission (%)

24 TABLE R5 Aircaft! CH-54 (Atmor Glass) Angle of Inc1ination () Sample 1 Sample 2 Sample 3 Average Transmission (%) A '

25 TABLE R6 Aircraft: AH-lG Angle of Inc1iriation {) Sam2le 1 Sam2le 2 Sam21e 3 Average Transmission (%l

26 TABLE R7 Aircraft: AH-lG (Tinted) Angle of IncH nation () Samplel Sample 2 Sample 3 Average Transmission (%)

27 TABLE R8 Aircraft: Bell UH-1 (Iroquois) Angle of Transmission {%) Inclination ( ) Sample 1 Sample 2 Sample 3 Average

28 TABLE R9 Aircraft: UH-1 (Center) Angle of Inc1ination () Sample 1 Sample 2 Sample 3 Average Transmission (%)

29 TABLE RlO Aircraft: UH-1 (Corner) Angle of Inc1ination () Sample 1 Sample 2 Sample 3 Average Transmission (%)

30 TABLE Rll Aircraft: UH-1 (Back) Angle of I nc1i nation () Sample 1 Sample 2 Sample 3 Average Transmission (%)

31 TABLE Rl2 Aircraft: UH-1 (Crew Door) AnglEL..Qf. Inclination () Sample 1 Sample 2 Sample 3 Average Transmission.(%)

32 TABLE Rl3 Aircraft: UH-1 (Sliding Section) Angle of Inclination ( Sample 1 Sample 2 Sample 3 Average Transmission (%)

33 TABLE R14 Aircraft: UH-1 (Door Fixed Position) Angle of Inc1ination {} Sam(!le 1 SamEle 2 SamEle 3 Average Transmission {%} sa

34 "' -. 5 "'... c( 25 AIRCRAFT: DEHAVIlLAND U-6A (BEAVER) ANGLE Of. INCLINATION ( ) FIGURE Fl, 4

35 TRANSMISSION {%) Ul -,. Q m.,., - -n... G') <= ;;o rr1.,., N n, w Ul " l> -;a n ;a l> -n... Dl m n :I: c CD.C ' c CD -n

36 1' AIRCRAFT: CESSNA T-41 _ V) V) - V) 5 <( 25" ANGLE OF INCLINATION ( ) FIGURE F3

37 1 AIRCRAFT: BEECH T-42/U _ V) V) 5 "' <( ' \;. I I I I I I I I ANGLE OF INCLINATION ( ) FIGURE F4

38 1! AIRCRAFT : DeHAVILLAND CV-2 (CARIBOU).,..._,... -V) V) - V) <( 1-75 so, ANGLE OF INCLINATION ( ) FIGURE F5

39 DeHAVIlLAND AIRCRAFT:.DeHAVJLLAND CV-7 (BUFFALO) U') 5 U') - U') c( ANGLE OF INCLINATIO ( ) FIGURE F6

40 TRANSMISSION (%) - U'l -..., l> (,.) (i) r- m "T1.., - t-1 Ci) c: :;o rr1 - U'l "T1... n r- l> -4 - "'....._. CD )> -;a n )> """

41 1 AIRCRAFT: OV en en - en <( a.: ANGLE OF INCLINATION ( ) FIGURE F8

42 "' 5 - "' 25 "' c( 1- ANGLE OF INCLINATION ( ) FIGURE Rl AIRCRAFT: BELL OH-58.. ' ', I t

43 1.- _ V) V) - 5 V) <( 25 AIRCRAFT: HUGHES TH-SS/OH-6A ANGLE OF INCLINATION ( ) FIGURE R2

44 1 AIRCRAFT: CH en en - en <C ANGLE OF INCLINATION ( ) FIGURE R3

45 1 AIRCRAFT: CH _. - "' - 5 "' c( ANGLE OF INCLINATION ( ) FIGURE R4

46 1 AIRCRAFT: CH - 54 ( AMOR GlASS )... 7 SJ... - "' - 5 "' <C ANGLE OF INCLINATION ( ) FIGURE R5

47 1 AIRCRAFT: AH - lg J. COBRA ) - CLEAR , 5.,., - 25 <C... Clf: ANGLE OF INCLINATION f ) FIGURE R6

48 1 AIRCRAFT:,; AH - lg - JtNTED "' - 5 "' c( ANGLE OF INCLINATION. ( ) FIGURE R7

49 1 AIRCRAFT: BELL UH-ID IROQUOIS "' - "' "' 75 5 <( ANGLE OF INCLINATION ( ) FIGURE R8

50 AIRCRAFT: U H - 1 ( CENTER )...._,. - "' - "' "' <C ANGLE OF INCLINATION ( ) FIGURE R9

51 1 AIRCRAFT: UH - 1 ( CORNER ) _... - "' 5 i "' "' c( 25 t ANGLE OF INCLINATION ( ) FIGURE RlO

52 I -"' 5 "' - "' <C 25 a.: t- AIRCRAFT: i U H - 1 { BACK ) ( i ANGLE OF INCLINATION { ) FIGURE Rll

53 _, 5 "' - "'... c( 25 AIRCRAFT: U H - '1\ ( CREW DOOR ) I ANGLE OF INCLINATION ( ) FIGURE Rl2

54 1 AIRCRAFT:: UH - 1 ( SLIDING SECT ) ,_. - "' 5 "' - "' <( ANGLE OF INCLINATION ( ) FIGURE Rl3

55 AIRCRAFT:iUH - 1 ( DOOR FIXED 1-! PORTION ) _,.. -"' 5 "' - "' c( ANGLE OF INCLINATION ( ) FIGURE Rl4 r