ASTM_F_1165_-_15.pdf

Designation:F116515Standard Test Method forMeasuring Angular Displacement of Multiple Images inTransparent Parts1This standard is issued under the fixed designation F1165;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers measuring the angular separa-tion of secondary images from their respective primary imagesas viewed from the design eye position of an aircraft transpar-ency.Angular separation is measured at 49 points within a 20by 20 field of view.This procedure is designed for perfor-mance on any aircraft transparency in a laboratory or in thefield.However,the procedure is limited to a dark environment.Laboratory measurements are done in a darkened room andfield measurements are done at night.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.2.1 ExceptionThe values in parentheses are for informa-tion only.1.3 This standard possibly involves hazardous materials,operations,and equipment.This standard does not purport toaddress all of the safety concerns,associated with its use.It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicability of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology(see Fig.1)3.1 primary imagethe image formed by the rays transmit-ted through the transparency without being reflected(solidlines).3.2 secondary imagethe image resulting from internalreflections of light rays at the surfaces of the transparency(dashed lines).3.3 angular displacementthe apparent angular separationof the secondary image from the primary image as measuredfrom the design eye position().3.4 installed anglethe part attitude as installed in theaircraft;the angle between the surface of the windscreen andthe pilots 0 azimuth,0 elevation line of sight.4.Summary of Test Method4.1 The procedure for determining the angular displacementof secondary images entails photographing a light array ofknown size and distance from the transparency.The photo-graph is then used to make linear measurements of the imageseparation,which can be converted to angular separation usinga scale factor based on the known geometry.5.Significance and Use5.1 With the advent of thick,highly angled aircrafttransparencies,multiple imaging has been more frequentlycited as an optical problem by pilots.Secondary images(ofoutside lights),often varying in intensity and displacementacross the windscreen,can give the pilot deceptive optical cuesof his altitude,velocity,and approach angle,increasing hisvisual workload.Current specifications for multiple imaging intransparencies are vague and not quantitative.Typical specifi-cations state“multiple imaging shall not be objectionable.”5.2 The angular separation of the secondary and primaryimages has been shown to relate to the pilots acceptability ofthe windscreen.This procedure provides a way to quantifyangular separation so a more objective evaluation of thetransparency can be made.This procedure is of use for researchof multiple imaging,quantifying aircrew complaints,or as thebasis for windscreen specifications.5.3 It is of note that the basic multiple imaging character-istics of a windscreen are determined early in the design phaseand are virtually impossible to change after the windscreen hasbeen manufactured.In fact,a perfectly manufactured wind-screen has some multiple imaging.For a particular windscreen,caution is advised in the selection of specification criteria for1This test method is under the jurisdiction of ASTM Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved Nov.1,2015.Published November 2015.Originallyapproved in 1988.Last previous edition approved in 2010 as F1165 10.DOI:10.1520/F1165-15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 multiple imaging,as inherent multiple imaging characteristicshave the potential to vary significantly depending upon wind-screen thickness,material,or installation angle.Any tolerancesthat might be established are advised to allow for inherentmultiple imaging characteristics.6.Apparatus6.1 Light ArrayThe light array is a 7 by 7 matrix o