ASTM F1165-98
(Test Method)Standard Test Method for Measuring Angular Displacement of Multiple Images in Transparent Parts
Standard Test Method for Measuring Angular Displacement of Multiple Images in Transparent Parts
SCOPE
1.1 This test method covers measuring the angular separation of secondary images from their respective primary images as viewed from the design eye position of an aircraft transparency. Angular separation is measured at 49 points within a 20 by 20° field of view. This procedure may be performed on any aircraft transparency in a laboratory or in the field. However, the procedure is limited to a dark environment. Laboratory measurements are done in a darkened room and field measurements are done at night.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.3 The values stated in acceptable metric units are to be regarded as the standard. The values in parentheses are for information only.
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Designation: F 1165 – 98
Standard Test Method for
Measuring Angular Displacement of Multiple Images in
Transparent Parts
This standard is issued under the fixed designation F 1165; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers measuring the angular separa-
tion of secondary images from their respective primary images
as viewed from the design eye position of an aircraft transpar-
ency. Angular separation is measured at 49 points within a 20
by 20° field of view. This procedure may be performed on any
aircraft transparency in a laboratory or in the field. However,
FIG. 1
the procedure is limited to a dark environment. Laboratory
measurements are done in a darkened room and field measure-
3.4 installed angle—the part attitude as installed in the
ments are done at night.
aircraft; the angle between the surface of the windscreen and
1.2 This standard may involve hazardous materials, opera-
the pilot’s 0° azimuth, 0° elevation line of sight.
tions, and equipment. This standard does not purport to
address all of the safety concerns, associated with its use. It is
4. Summary of Test Method
the responsibility of the user of this standard to establish
4.1 The procedure for determining the angular displacement
appropriate safety and health practices and determine the
of secondary images entails photographing a light array of
applicability of regulatory limitations prior to use.
known size and distance from the transparency. The photo-
1.3 The values stated in acceptable metric units are to be
graph is then used to make linear measurements of the image
regarded as the standard. The values in parentheses are for
separation, which can be converted to angular separation using
information only.
a scale factor based on the known geometry.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards:
5.1 With the advent of thick, highly angled aircraft trans-
E 177 Practice for Use of the Terms Precision and Bias in
parencies, multiple imaging has been more frequently cited as
ASTM Test Methods
an optical problem by pilots. Secondary images (of outside
E 691 Practice for Conducting an Interlaboratory Study to
lights), often varying in intensity and displacement across the
Determine the Precision of a Test Method
windscreen, can give the pilot deceptive optical cues of his
altitude, velocity, and approach angle, increasing his visual
3. Terminology (see Fig. 1)
workload. Current specifications for multiple imaging in trans-
3.1 primary image—the image formed by the rays transmit-
parencies are vague and not quantitative. Typical specifications
ted through the transparency without being reflected (solid
state “multiple imaging shall not be objectionable.”
lines).
5.2 The angular separation of the secondary and primary
3.2 secondary image—the image resulting from internal
images has been shown to relate to the pilot’s acceptability of
reflections of light rays at the surfaces of the transparency
the windscreen. This procedure provides a way to quantify
(dashed lines).
angular separation so a more objective evaluation of the
3.3 angular displacement—the apparent angular separation
transparency can be made. It may be used for research of
of the secondary image from the primary image as measured
multiple imaging, quantifying aircrew complaints, or as the
from the design eye position (u).
basis for windscreen specifications .
5.3 It should be noted that the basic multiple imaging
characteristics of a windscreen are determined early in the
This test method is under the jurisdiction of ASTM Committee F-7 on
Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on
design phase and are virtually impossible to change after the
Transparent Enclosures and Materials.
windscreen has been manufactured. In fact, a perfectly manu-
Current edition approved April 10, 1998. Published July 1998. Originally
factured windscreen has some multiple imaging. For a particu-
published as F 1165 – 88. Last previous edition F 1165 – 88.
Annual Book of ASTM Standards, Vol 14.02. lar windscreen, caution should be taken in the selection of
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F1165–98
aircraft when moving the elevated array. If wind conditions
present a hazard, do not attempt to measure.
8.3 Turn the array board on.
8.4 Place the camera in the design eye position and adjust
the camera such that the array is centered in the field of view;
focus the lens on the center light of the array.
8.5 Set the camera aperture to f/16 and the shutter speed to
an appropriate setting.
8.6 Take the picture(s) and develop 8 by 10 prints or a
suitable enlargement.
FIG. 2
8.7 On the photograph, measure the distance (L) from the
second light to the sixth light on the middle row. To ensure
specification criteria for multiple imaging, as the inherent
accuracy, use a precision measuring device, such as a digital
multiple imaging characteristics may vary significantly de-
caliper.
pending upon windscreen thickness, material, or installation
8.8 For each light in the 8 by 10 print, measure the linear
angle. Any tolerances that might be established should allow
separation (r) of the secondary image from the primary image
for inherent multiple imaging characteristics.
using the calipers. Measure from the center of both spots when
taking the measurement.
6. Apparatus
9. Calculation
6.1 Light Array—The light array isa7by7 matrix of small
incandescent lights (flashlight bulbs) mounted on a metal 9.1 To obtain the scale factor F, which relates the linear
frame. The separation of the lights is 406.4 mm (16 in.) on distances on the photograph to actual angular distances as
center making the overall dimensions of the array 2.44 by 2.44 measured from the design eye position, use the equation as
m (8 by 8 ft). A suitable power supply, such as a rechargable follows:
12-V d-c gel cell, is also required. A backdrop of nonreflective
229.2
F 5 mrads/mm (1)
material (such as black velvet) should be placed several inches
L
behind the array to block out background lights and prevent
reflections.
9.2 Compute the angular separation u for each light of the
6.2 Camera/film—No special camera or modification is
array using the equation:
needed for this process. The lens should have a focal length of
u5 r 3 F (2)
about 50 mm or as is necessary to permit the light array to fill
most of the field of view of the camera. The film should be
9.3 Enter the angular separation data intoa7by7 table so
black and white.
the rows and columns correspond to the location of lights on
7. Test Specimen
the array.
7.1 Position the part to be measured in the installed angle
10. Precision and Bias
(or installed in the aircraft for a field measurement) such that
10.1 Precision—An interlaboratory study (ASTM RR-
the camera is located in the pilot’s design eye position. No
F07 – 1003) was conducted to determine the precision of this
special conditioning other than cleaning is required.
standard. Twenty
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