OPTICAL CHARACTERISTICS OF AIRCRAFT TRANSPARENCIES bible part2.pdf

1
OPTICAL CHARACTERISTICS OF
AIRCRAFT TRANSPARENCIES
Bible
Dec 2021
GUIDE OF OPTICAL CHARACTERISTICS OF AIRCRAFT
TRANSPARENCIES
Part2
‫دليل‬
‫الخصائص‬
‫البصرية‬
‫الكبائن‬ (‫الشفافة‬ ‫لالجزاء‬
–
) ‫الريح‬ ‫واقى‬
‫لل‬
‫طائرات‬
‫الثانى‬ ‫الجزء‬
‫الهندسية‬ ‫المصطلحات‬ ‫تعديل‬ ‫مع‬ ‫ترجمة‬ ‫جوجل‬ ‫باستخدام‬ ‫الترجمة‬ ‫تم‬

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6.2.1 OPTICAL EFFECTS
For example windscreen , canopies optical parameters :
a. Optical Distortion
b. Angular Deviation
c. Luminous Transmittance
d. Haze
e. Major and Minor Optical Defects
f. Miscellaneous Effects
g. Acceptable limits have been derived over time for the parameters listed above
‫البصرية‬ ‫المؤثرات‬
) ‫الشفاف‬ ‫الزجاج‬ ‫خالل‬ ‫من‬ ‫النظر‬ ‫نتيجة‬ (
‫الكابين‬ ‫المثال‬ ‫سبيل‬ ‫على‬
‫الريح‬ ‫واقى‬ ‫او‬ ‫الشفافة‬ ‫الزجاجية‬ ‫ة‬
‫المحددات‬ ‫هى‬ ‫و‬
:
•
‫بصري‬ ‫تشويه‬ .
‫للصورة‬
•
‫الزاوي‬ ‫االنحراف‬ .
‫االشياء‬ ‫اماكن‬ ‫و‬ ‫للصورة‬
•
.
‫مدى‬
‫نفاذية‬
‫الضوء‬
•
‫ضباب‬ .
‫الرؤية‬ ‫ية‬
•
‫محددات‬.
‫والصغرى‬ ‫الكبرى‬ ‫العيوب‬
•
.
‫متنوعة‬ ‫تأثيرات‬
‫المقبولة‬ ‫البصرية‬ ‫الحدود‬
‫لل‬
‫الريح‬ ‫واقى‬ ‫او‬ ‫الشفافة‬ ‫الزجاجية‬ ‫كابينة‬
‫السابقة‬ ‫العناصر‬ ‫من‬ ‫لكل‬
6.2.1.1 OPTICAL DISTORTION
6.2.1.1.1 general
• Definition: The rate of change of angular deviation resulting from an irregularity in a
transparent part. This may be expressed as the angular bending of the light ray per unit of
length of the part (i.e., milliradians per centimeter).
• slope of the angle of localized grid line bending (i.e., 1 in 5).
• If the effects of refraction across a windscreen are varied, objects can be magnified,
minified, lengthened, foreshortened, misshaped, widened, narrowed, etc
• Optical distortion is caused by :
❖ changes in thickness,
❖ changes in curvature,
❖ changes in shape,
❖ heat induced stress,
❖ physical stress, etc.

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• Optical distortion can also cause moving objects to appear to vary in shape and motion in an
irregular way as they are seen passing through different viewing areas of the windscreen.
• Bending, discontinuity (see 5.1.5) or shadowing of screen (4.1) lines when seen through the
acrylic transparency.
• NOTE.
The slight curvature of lines which follow the transparency average curvature is not
considered as an optical distortion.

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‫البصري‬ ‫التشويه‬
‫عام‬
•
‫الزاوي‬ ‫االنحناء‬ ‫أنه‬ ‫على‬ ‫هذا‬ ‫عن‬ ‫التعبير‬ ‫يمكن‬ .‫شفاف‬ ‫جزء‬ ‫انتظام‬ ‫عدم‬ ‫عن‬ ‫الناتج‬ ‫الزاوي‬ ‫االنحراف‬ ‫تغير‬ ‫معدل‬ :‫التعريف‬
‫ميلي‬ ‫(أي‬ ‫الجزء‬ ‫طول‬ ‫وحدة‬ ‫لكل‬ ‫الضوء‬ ‫لشعاع‬
‫بال‬ ‫الزاوية‬
‫سنتيمتر‬ ‫لكل‬ ‫راديان‬
)
•
‫الموضعي‬ ‫الشبكة‬ ‫خط‬ ‫انحناء‬ ‫زاوية‬ ‫ميل‬
‫كمثال‬
‫(أي‬
1
‫في‬
5
)
•
‫كانت‬ ‫إذا‬
‫فيمكن‬ ، ‫متنوعة‬ ‫األمامي‬ ‫الزجاج‬ ‫عبر‬ ‫االنكسار‬ ‫تأثيرات‬
‫يحدث‬ ‫ان‬
‫وتصغيرها‬ ‫األشياء‬ ‫تكبير‬
‫وإطال‬
‫ت‬
‫وتقليلها‬ ‫ها‬
‫ذلك‬ ‫إلى‬ ‫وما‬ ، ‫وتضييقها‬ ‫وتوسيعها‬ ‫وتشوهها‬
•
‫بسبب‬ ‫البصري‬ ‫التشوه‬ ‫يحدث‬
:
‫في‬ ‫تغيرات‬
‫الزجاج‬ ‫لوح‬ ‫سمك‬
،
‫تغيرات‬
( ‫للزجاج‬ ‫الكروى‬ ‫الشكل‬ ‫نتيجة‬
‫االنحناء‬
.
)
‫ف‬ ‫تغيرات‬
‫الشكل‬ ‫ي‬
‫جدا‬ ‫صغير‬ ‫لو‬ ‫حتى‬ ‫مفاجى‬ ‫انحناء‬ ‫الهندسى‬
،
، ‫الحرارة‬ ‫عن‬ ‫الناجم‬ ‫اإلجهاد‬
‫ضغوط‬
‫احمال‬ ‫نتيجة‬
‫إلخ‬ ،
.
•
‫يتم‬ ‫حيث‬ ‫منتظمة‬ ‫غير‬ ‫بطريقة‬ ‫والحركة‬ ‫الشكل‬ ‫في‬ ‫متغيرة‬ ‫المتحركة‬ ‫األجسام‬ ‫ظهور‬ ‫في‬ ‫ا‬ً‫ض‬‫أي‬ ‫البصري‬ ‫التشوه‬ ‫يتسبب‬ ‫أن‬ ‫يمكن‬
‫عرض‬ ‫مناطق‬ ‫عبر‬ ‫تمر‬ ‫وهي‬ ‫رؤيتها‬
‫األمامي‬ ‫الزجاج‬ ‫من‬ ‫مختلفة‬
.
•
‫(انظر‬ ‫واالنقطاع‬ ‫االنحناء‬
‫الرسم‬
‫الشاشة‬ ‫خطوط‬ ‫تظليل‬ ‫أو‬ )
)‫البيضاء‬ ‫الخطوط‬ ‫ذات‬ ‫السوداء‬ ‫الشبكة‬ (
‫خالل‬ ‫من‬ ‫رؤيتها‬ ‫عند‬
‫الريح‬ ‫واقى‬ ‫او‬ ‫الشفافة‬ ‫الزجاجية‬ ‫الكابينة‬
‫ال‬
‫شفاف‬
‫لزجاج‬
‫األكريليك‬
.
•
‫مالحظة‬
.
‫ت‬ ‫التي‬ ‫للخطوط‬ ‫الطفيف‬ ‫االنحناء‬ ‫يعتبر‬ ‫ال‬
‫متوسط‬ ‫انحناء‬ ‫تبع‬
‫ًا‬‫ي‬‫بصر‬ ‫ا‬ً‫ه‬‫تشوي‬ ‫الشفافية‬
.
‫المتفق‬ ‫الحيود‬ ‫خارج‬ ‫الشديد‬ ‫االنحناء‬ ‫بل‬
‫عليها‬

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/* Every visibility zone have different acceptable optical defects */
/ *
‫كل‬
‫منطقة‬
‫رؤية‬
‫بها‬
‫عيوب‬
‫بصرية‬
‫مقبولة‬
‫مختلفة‬
‫االخرى‬ ‫عن‬
* /
‫الشاشة‬
‫البيضاء‬ ‫الخطوط‬ ‫ذات‬ ‫السوداء‬

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/* Some defects and the grid line distortion shape */
/ * ‫بعض‬
‫العيوب‬
‫وشكل‬
‫تشويه‬
‫خط‬
‫الشبكة‬ * /

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6.2.1.1.2 ACCEPTABLE OPTICAL DISTORTIONS (BENDING-TYPE)
6.2.1.1.2.1 ACCEPTABLE OPTICAL DISTORTIONS (BENDING-TYPE)
ON THE CRITICAL VISIBILITY ZONE
‫االنحرافات‬
‫المقبولة‬
(
‫نوع‬
)
‫الحقا‬ ‫التفصيلية‬ ‫الخطوات‬ ‫و‬ ‫الريح‬ ‫واقى‬ ‫على‬ ‫كمثال‬ ‫القياس‬ ‫كيفية‬

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1
-
(
‫نوع‬ ‫من‬
-
)
‫للكابينة‬
‫في‬
‫منطقة‬
‫الرؤية‬
‫الحرجة‬
NOTE: ALL DIMENSIONS ARE IN MILLIMETERS
‫مالحظة‬
:
‫جميع‬
‫األبعاد‬
‫بالمليمترات‬
6.2.1.1.2.2 ACCEPTABLE OPTICAL DISTORTIONS (BENDING-TYPE) ON THE SEMI
CRITICAL VISIBILITY ZONE AND NON CRITICAL VISIBILITY ZONE
2
-
(
‫نوع‬ ‫من‬
-
)
‫في‬
‫منطقة‬
‫الرؤية‬
‫شبه‬
‫الحرجة‬
‫منطقة‬ ‫و‬
‫الرؤية‬
‫غير‬
‫الحرجة‬

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6.2.1.2 DISCONTINUITIES
Optical distortion characterized by a sudden bending or an interruption of the screen
(fig 4.1) lines, when seen through the acrylic transparency. The discontinuities may
present in the following conditions:
‫التوقفات‬
‫الشبكة‬ ‫لخطوط‬
‫تشوه‬
‫بصري‬
‫يتميز‬
‫بانحناء‬
‫مفاجئ‬
‫أو‬
‫انقطاع‬
‫خطوط‬
‫الشاشة‬
،
‫عند‬
‫رؤيته‬
‫من‬
‫خالل‬
‫او‬ ‫الشفافة‬ ‫الزجاجية‬ ‫الكابينة‬
‫الريح‬ ‫واقى‬
‫الشفاف‬
‫زجاج‬ ‫من‬
‫األكريليك‬
.
‫قد‬
‫تظهر‬
‫االنقطاعات‬
‫في‬
‫الحاالت‬
‫التالية‬
:
/* types of discontinuities of the screen line */
/ * ‫أنواع‬
‫االنقطاعات‬
‫في‬
‫خط‬
‫الشاشة‬ * /

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optical characteristics common to aircraft transparencies
Name of characteristic / Explanation:/ Inspection:/ Measurement:/ Visual effect:/ Illustrations:
1- Angular Deviation (prismatic deviation, deviation)
Explanation: Angular deviation is the angular change that occurs when a light ray passes through a transparency (see figure )
The change is usually due to non -parallel surfaces in the transparency.
The amount of angular deviation depends on :
• index of refraction of the material,
• the angle of incidence,
• and the shape of the material.
It is especially important to characterize angular deviation in aircraft equipped with a head- up display (HUD). When the pilot places the 1H1UD
aiming reticle (pipper) on the target, he is aiming his weapon at the locating w here hie visually perceives the target . If the transparency causes
angular deviation, tale target will actually displaced from where the pilot sees it,
/* fish object under water school subject */
inspection: In general, angular deviation can not easily detected in the field by optical or visual means.
More often the derivative of angular deviation (rate of change of angular deviation) is noticed which is the distortion
Measurements : of angular deviation is performed with an angular deviation device (ASTM Standard Method F801) or a collimated light
source and theodolite. These measurements are done in a laboratory with the windscreen removed from the aircraft. At present there are no
methods of measuring angular deviation in the field.
Visual Effect: There is no obvious visual effect of angular deviation; the only effect is an indirect one due to weapons system inaccuracies
caused by the angular deviation as discussed above.

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Angular Deviation
• definition: The angular displacement of a light ray from its original path as it passes through a
transparent material, expressed as an angular measurement (degree, minutes of arc, milliradians).
• The amount of deviation is a function of
❖ the index of refraction of the transparent material
❖ and the angle between the observer's line of sight and the transparent surfaces
/*Recognize a distinction between angular deviation and another phenomenon called lateral displacement.*/
• lateral displacement,
the image shift .i.e
a light ray refracted by a transparency section that has parallel surfaces. The path of the ray is not
changed in angle with these parallel surfaces, because the refraction angles are equal and opposite.
The shift in location of an image due to lateral displacement is constant with distance
so the amount of error (d) is very small. /* see MISCELLANEOUS EFFECTS, */
lateral displacement errors are insignificant at great distances.
• Angular deviation. (angular displacements)
• The image shift with angle not parallel
• The surfaces of the material sides are not parallel.
• The unequal refraction angles result in a net angular change (alpha) in the path of the ray.

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• The shift in location of an image due to angular deviation can become very significant with
an increase in distance.
• Angular deviation can be caused by :
❖ changes in thickness
❖ curvature across a transparency
❖ ( also increase the thickness means more severely Angular deviation, )
contribute significantly to inaccurate target aiming
angular deviation. Test Method: ASTM F801-96.
• windscreen is set into place and then removed
• Virtually all of them measure the change in location of a point (image)
• A number of measurements may be required to verify that a given windscreen is optically
suitable because the angle between the pilot's line of sight and the transparent surface will
vary across the windscreen

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• The area of greatest concern is usually the gun sight area.

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• Although angular deviation errors are not usually large in this area, their effects can be
devastating.
• The slightest angular deviation here will lead to sighting errors unless accurately
compensated for this deviation.
• measure angular deviation in this critical zone should be carefully chosen for aircraft that
will have a Head-Up Display (HUD)
• Error data must reflect pure angular components and not be contaminated by lateral
displacement errors.
• /* lateral displacement errors are insignificant at great distances.*/ LAB test distances are
necessarily abbreviated and lateral displacement errors could be the cause of a significant
portion of the total image shift
• Only test set-ups that employ some means to measure image shift at optical infinity will
yield pure angular deviation error data.
• Accurately compiled error information can then be compensated for in the aircraft's weapon
delivery
• methods to measure angular deviation, including ones that give pure error data, is AMRL-
TR-82-43.
2- Binocular Disparity
Explanation: Binocular disparity exists when the image seen with the left eye is different from the image
seen by the right eye. Excessive binocular disparity may be caused by the transparency or the interaction of
the transparency with the HUD, leading to visual problems.
Inspection: Binocular disparity is sometimes difficult to notice by visual inspection. It may be detected by
alternately closing the left and right eyes and observing a shift in the position of an object.

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Measurement: Binocular deviation can be measured by taking angular deviation measurements from the left
and right eye position and subtracting the left eye result from the right eye result. This is done for both
horizontal and vertical angular deviation directions.
The horizontal data provides information on eye convergence or divergence and the vertical data provides
information on eye divergence (one eye having to rotate upward or downward compared to the other eye in
order to fuse the images). It may also be quantified by taking double exposure photographs through the
transparency, with one exposure made , with the camera in the left eye position and the other from the right
eye position (without
advancing the film). Separation of the grid lines indicates the presence of binocular deviation
(see figure ?????????? not clear black and white ). This latter method, however, does not distinguish between
lateral displacement effects and angular deviation effects. It is therefore only a good measure of
binocular disparity for the specific grid board distance used to obtain the double exposure photographs.
Visual Effect: Binocular disparity may be manifested in several ways: eye strain, headache, fatigue,
suppression of the image from one eye by the visual system, or doubling of vision. Sometimes these effects
may occur only over a period of extended viewing. Tolerances for binocular disparity vary among individuals,
so a certain amount of disparity may cause problems for one individual and not another
A high precision instrument to measure angular and binocular deviation introduced by aircraft
windscreens by using a shadow casting technique
• ABSTRACT
• Objects viewed through transparent sheets with residual non-parallelism and irregularity
appear shifted and distorted. This distortion is measured in terms of angular and binocular
deviation of an object viewed through the transparent sheet. The angular and binocular
deviations introduced are particularly important in the context of aircraft windscreens and

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canopies as they can interfere with decision making of pilots especially while landing,
leading to accidents. In this work, we have developed an instrument to measure both the
angular and binocular deviations introduced by transparent sheets. This instrument is
especially useful in the qualification of aircraft windscreens and canopies. It measures the
deviation in the geometrical shadow cast by a periodic dot pattern trans-illuminated by the
distorted light beam from the transparent test specimen compared to the reference pattern.
Accurate quantification of the shift in the pattern is obtained by cross-correlating the
reference shadow pattern with the specimen shadow pattern and measuring the location of
the correlation peak. The developed instrument is handy to use and computes both angular
and binocular deviation with an accuracy of less than ±0.1 mrad (≈0.036 mrad) and has an
excellent repeatability with an error of less than 2%.
•

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•
3. Birefringence (rainbowing)
Explanation: The term birefringence means the material in question has two indices of
refraction. Polycarbonate under stress becomes birefringent and thus exhibits two indices
of refraction that align with the directions of the stress. These two indices of refraction cause
polarized light to travel at different velocities through the material. The incoming linearly
polarized light is converted to elliptically polarized light due to the birefringence. The
degree of rotation of the electric field vector of the light further depends on the wavelength
(color) of the light since the material also has a certain amount of chromatic dispersion.When
the light exits the windscreen, the angle of exit acts like a partial analyzer (polarizer) which
results in some wavelengths being attenuated more than others. Thus the exiting light
exhibits a color effect depending on the degree of birefringence and the extent of the
polarization. These color patterns, or rainbowing, can be relatively strong for clear blue sky
days (blue sky can be about 80% polarized). The pattern of these colors on the windscreen
remains constant as a result of built in residual stress in the windscreen (during the
manufacturing process), but the actual colors making up the pattern will vary depending on
the orientation of the windscreen with respect to the polarization vector of the exterior light.
Inspection: Birefringence is visible to the unaided eye when observing the transparency with
a polarized light source, such as a clear blue sky. The birefringence pattern can be enhanced
by observing it through a second polarizer, such as a pair of polarized sun glasses. (This is
why USAF pilots are not allowed to fly with polarized sun glasses.)
Measurement: There is as yet no accepted method of measuring birefringence in terms of
its effects on vision.

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Visual Effect: Birefriagence has been noted as a concern but has not been labeled as a
problem. Anecdotal information gathered on F- 111 and B-I windscreens indicates that the
primary visual effect is one of annoyance or minor distraction.
(see figure ?????????? not clear black and white ).: Birefringence patterns of F- Ill
windscreens produced by two different manufacturing techniques.
4 Crazing
5.1.6 CRAZING
Explanation: Crazing is the occurrence of very small "micro cracks" In a transparency or
coating. These cracks usually are localized and are oriented in the same direction. In bright
light conditions and at certain sun geometries, the cracks will act like many tiny mirrors and
reflect light into the pilot's line of sight (see figure ?????????????? black white ). Crazing
may be induced by chemicals, age, or other causes.
❖ Both basic forms of acrylics used in aircraft transparencies are affected by crazing. Crazing is
a network of fine cracks that extend over the surface of the plastic sheet (it is not confined/*
not only*/ to acrylic materials) and are often difficult to discern/* inspect */. These fine
cracks tend to be perpendicular to the surface, very narrow, and are usually less than 0.025mm
(.001 inches) in depth. Crazing is induced by prolonged exposure to surface tensile stresses
above a critical level or by exposure to organic fluids and vapors.
❖ (a) Stress crazing may be derived from residual stresses caused by poor forming practice,
relatively high tensile stresses at a surface induced by prolonged loading,/* long time loading
*/ and residual surface stresses induced by machining, polishing, or gouging.
/* gouging make (a groove, hole, or indentation) with or as with a sharp tool or blade.*/
❖ (b) Stress crazing has a severe effect on the mechanical properties of acrylics; however, the
effects are reduced in stretched materials.

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❖ (c) Stress crazing affects the transparency of acrylics. Generally, stretched acrylic panels will
be replaced due to loss of transparency from stress crazing before significant structural
degradation occurs.
❖ (d) Some detrimental compounds can induce crazing; others may dissolve the acrylic or be
absorbed in the material. Crazing induced by solvent and other organic compounds has more
severe effects on the mechanical properties than stress crazing. Dissolution of the acrylic and
chemical absorption into the acrylic degrades the mechanical properties.
/* Concentration of multiple small cracks in a surface area or in an acrylic transparency */
/* (the appearance of numerous tiny cracks in the material) */
in the internal area due to internal stresses
summery (i.e. it is Caused by:)
• impact,
• flexure,
• temperature changes,
• machining,
• and solvent action
• or molding shrinkage.
Inspection: Visual examination of the transparency under bright light conditions is a good
way to observe crazing.
However, the appearance of crazing is dependent upon the relative positions of the light
source, transparency, and observer, so it may be difficult to observe if the geometry is not
right.

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Measurement: There is no quantitative method to measure crazing as of this writing. Extent
of crazing is left to subjective judgment.
Visual Effect: Crazing can be almost invisible and have essentially no effect on vision until
the sun angle is just right and the micro-cracks (acting like little mirrors) reflect the sunlight
directly into the pilot's eyes. Under this reflection condition the visual effect is significant
loss of contrast in the exterior world scene which can cause severe visual impairment during
the time the reflection geometry is satisfied.
5 Delamination
Explanation: Delamination is a separation of the layers of a laminated transparency which
may be due to residual or induced stress in the transparency. There are several events that
may enhance the occurrence of delamination, such as overheating the transparency, thermal
cycling, and defective manufacturing.
Inspection: Delamination is detected by looking for bubble areas within the transparency; it
often occurs near an edge.
Measurement: There is no specified method to measure delamination, although the width
(distance from the edge of the windscreen) of the delamination area is commonly measured
using a ruler.
Visual Effect: Delamination is easily noticed but is usually confined to the edges of a
transparency (at least in its early stages). This reduces any effect on vision. The area that is
Delaminated has a lower transmissivity and higher reflectivity due to the extra air- plastic/
glass interface that is created at the delamination. This also enhances the effect of multiple
imaging.
6 Diffraction (streaking, starburst patterns, bowtie effect, arcing)
Explanation: Diffraction is one of the three basic means by which light rays change their
direction of tra'cl (the other two are refraction and reflection). Diffraction is a rather complex
subject, but tile effect essentially occurs as a scattering of light from the edges of some
obstacle. This scattering can occur from objects too small to see or from easily visible
scratches on the surface of a transparency. Diffraction of light from very tiny objects (at the
molecular level) is what gives rise to haze. This type of effect is evident in even new
materials since it is a characteristic of the material itself (see also haze or halation).
Diffraction also occurs from inclusions (meshes) and micro scratches on the surface of the
windscreen. Sometimes these scratches are not in random orientations but are in uniform
directions, which give rise to an easily noticeable diffraction pattern. If the scratches are all
in one direction or arch, the resulting diffraction pattern will appear as streaks emanating
from point sources of light. These patterns are usually only evident at night when viewing
point sources of light.

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This is because in the daytime the daylight scene washes out the pattern effects making them
invisible to the naked eye
Inspection: Diffraction is detected by looking through the transparency at a light source at
night or in a (dark environment.)
Measurement: There is no measurement for diffraction other than a subjective assessment.
Visual Effect: Diffraction patterns are usually only distracting; they are observed primarily
at night.
(see figure ?????????????? black white ). Diffraction patterns of the lights of a multiple
imaging light array as viewed through a defective B-lB windscreen.
7 Distortion
Explanation: Distortion is the rate of change of angular deviation across the transparency. It
can be caused by non-parallelisms in the surfaces of a transparency or localized changes in
the index of refraction of the transparent material. There are several types of distortion which
have specific names within the transparency industry. Some of the more common types are
Listed here:
1. bullseye - caused by a localized depression or bulge in the transparency, creating a circular
lens-like distortion; hence, the name "bullseye."
2. band distortion - distortion occurring in a narrow, elongated region across an area of the
transparency.
3. edge distortion - distortion occurring at or near the edge of a transparency. Often the most
severe distortion within the transparency will occur along an edge. deletion line distortion --
a thermally induced distortion occurring around the heater coating deletion line. A large
temperature gradient between the heated and unheated portions of the windscreen may cause
localized distortion in some transparencies where the index of refraction varies with
temperature.

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Inspection: Distortion is readily identified visually by viewing objects through the
transparency and noting waviness in lines and changes in the shapes and relative sizes of
objects, particularly near the edges of a transparency and in areas where the viewing angle is
very acuteeee.
Measurement: Currently three methods for measuring distortion are used within the
transparency industry: grid line slope, displacement grade, and lens factor. The most widely
used method is grid line slope (ASTM Standard Method F 733 or variations). Grid line slope
measurements are made by taking a photograph of a grid board through the windscreen. The
maximum slope of a horizontal grid line is the grid line slope value of the transparency.
Visual Effect: The visual effects of distortion depend upon the severity of distort ion. 1)ist or
tion may be distracting, give false motion cues by changing the perceived relative velocity of
out-of- the-cockpit objects, or in some cases cause headache and nausea. Minor distortions,
while aestlietically unoappealing, have showni no significant degradation on the performance
of visual tasks.
Figure ?????? Distortion of a grid board as viewed throtigh a traflspamlic N. Figure ????
Distortion of a field-portable string board through a B-B windscreen. Note the edge
distortion. Figure ?????????: Distortion of an aircraft when viewed through the heater coating
deletion line of a B-IB windscreen.
8 Halation (haze, scatter, glare)
Explanation: Halation is the scattering of light by the windscreen into the line of sight -f
the pilot. It is caused by the diffraction of light by particles within the transparency or by
fine scratches and/or dirt on the surface. It is most significant when flying towards the sun

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and may occlude significant portions of the field of view. (See figures 2.14 and 2.15.)
Inspection: Halation is observed by looking through the transparency with a bright light
source (or the sun) shining on it. Any veiling glare or s~attered light by the transparency
that interferes with your view is known as halation, or haze. The amrount of haze depends
on the intensity and location of the light source and the view angle.
Measurement: Hialation may be measured by ASTM Standard Method F 943 in the field
and in the laboratory or by D 1003 in the laboratory only. Ihaze may be quantiiied as the
haze index value (by ASTM F 943) or as percent haze (ASTM D 1003).
Visual Effect: Ilalation reduces the contrast of objects viewed through the transparency,
which makes out-of-the-cockpit objects less visible and decreases the detection range of
air-to-air targets
.
Figure ?????????: An example of halation.
9 Multiple Imaging (ghost images)
Explanation: Multiple imaging is ob~servedl only at night or in very (dark ambient light
conditions. It is the appearance of two or more images of a single object or light source. It
is caused by light rays reflecting off the inner and outer surfaces of the transparency and
back into the pilot's eye. Secondary images may vary in location and intensity with respect
to the primary image. (See figures 2.16 - 2.19.)
Inspection: Multiple images are observed by looking through the transparency at night (or

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in a dark environment) at bright light sources. They appear as fainter images of the lights
around the primary image.
measurement: The angular displacement of the secondary images from the primary image
may be measured following ASTM F 1165. The intensity ratio of the images may also be
measured, although a formal procedure does not yet exist.
Visual Effect: In most cases multiple images are simply distracting. In extreme cases, they
may give the pilot false motion cues, such as an inaccurate perception of approach velocity
or rate of descent during nighttime landing.
F'igure??????: Muliitiple linagitig (if a 7 X 7 light array
10 Reflections (cockpit reflections)
Explanation: Reflections from transparency surfaces of cockpit objects (glare sn, .1. flight
suit, helmet, etc.) or instrument lights interfere with the aircrew's out-of-the cockpit visiou.
The reflections are most significant at night or in bright sunlight conditions.

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Inspection: Reflections are easily observed visually under a variety of conditions.
Measurement: The reflectivity of a transparency may be measured photometrically. A
new ASTM, standard method is currently being published which details the measurement
procedure.
Visual Effect: Reflections on the transparency reduce the contrast of out-of-the-cockpit
objects and may even obscure these objects.
Figure ????????: Reflections 4f the glare shield.
A. Haze
• Definition: Spatial attribute of smokiness or dustiness that interferes with clear vision.
• The ratio of diffuse to total transmittance of a beam of light.
• As light enters or passes through a transparency, some of the light may be scattered or diffused,
and may appear as haze or fog in the transparency.
• Haze is defined in terms of light scattered and, therefore,
lost in passage through the transparency.
• The scattered light creates a veiling luminance that reduces the contrast of objects viewed through
the windscreen.
• The most predominant cause of haze is tiny surface scratches that usually come about as a result
of the cleaning process.
• The haze effect is increased as the angle of incidence is increased.
Test Method: A rather sophisticated test set-up is required to accurately measure haze in the
laboratory.
• A collimated light source(parallel light ray )/* A typical collimator, namely, one that is a parabolic reflector,
has a focal point on which a light source should be placed. The light source approximates a point source, which
enables light rays reflected by the reflector to form a collimated beam with a narrow light distribution angle.*/
is used in conjunction with a device to determine the amount of scattered light.

OPTICAL CHARACTERISTICS OF AIRCRAFT TRANSPARENCIES bible part2.pdf

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OPTICAL CHARACTERISTICS OF AIRCRAFT TRANSPARENCIES bible part2.pdf