SAE ARP 5637A-2017 Design and Maintenance Considerations for Aircraft Exterior Lighting Plastic Lenses.pdf

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1、 _ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising ther

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4、70 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/standards.sae.org/ARP5637A AEROSPACE RECOMMENDED PRACTICE ARP5637 REV. A Issued 2005-03 Revised 2017-09 Supersed

5、ing ARP5637 Design and Maintenance Considerations for Aircraft Exterior Lighting Plastic Lenses RATIONALE This document is to provide a design guide for plastic exterior lenses along with maintenance considerations. The most recent update is to provide additional references and more technical consid

6、erations in the design and maintenance of this type of exterior lighting system. TABLE OF CONTENTS 1. SCOPE . 2 1.1 Purpose 2 2. REFERENCES . 2 2.1 Applicable Documents . 2 2.1.1 SAE Publications 2 2.1.2 U.S. Military Specifications and Standards 2 2.1.2 RTCA Publications . 2 2.2 Definitions 2 3. PL

7、ASTIC LENSES . 3 3.1 The Desire for Plastic Lenses 3 3.2 Plastic Lens Issues 3 3.3 Design Guidance 4 4. MAINTENANCE . 5 4.1 Purpose 5 4.2 Action Required 5 4.3 Inspection Interval 5 4.4 Inspection . 5 4.5 Maintenance Action 6 5. NOTES . 6 5.1 Revision Indicator . 6 Figure 1 Plastic lens light transm

8、ission loss for wing tip exterior light assembly . 4 SAE INTERNATIONAL ARP5367A Page 2 of 6 1. SCOPE The information in this document is intended to apply to commercial jet transport category airplanes that incorporate plastic (polycarbonate or acrylic) lenses on exterior light assemblies, or are be

9、ing considered for such an application as opposed to glass lens designs. Exterior lighting applications include position light assemblies, anticollision light asemblies, and landing light assemblies. However, much of the material provided herein is general in nature and is directly applicable to man

10、y aircraft categories including, but not limited to, helicopters, general aviation aircraft, and military aircraft. 1.1 Purpose The purpose of this document is to provide guidance pertaining to the use of plastic (polycarbonate or acrylic) lenses on commercial jet transport aircraft to aircraft desi

11、gners, regulatory certification agents, and maintenance personnel. It is not intended to serve as design instructions for the creation of plastic or acrylic lenses. This document identifies significant performance aspects of plastic exterior light lenses that should be carefully managed for each len

12、s application. Additionally, this document provides basic inspection and maintenance procedures for plastic exterior light lenses. 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall

13、 apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applica

14、ble laws and regulations unless a specific exemption has been obtained. 2.1.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. AIR5689 Light Transmitting Glas

15、s Covers for Exterior Aircraft Lighting 2.1.2 U.S. Military Specifications and Standards Copies of these documents are available at http:/quicksearch.dla.mil. MIL-DTL-7989 Cover, Light-Transmitting for Aeronautical Lights, General Specification MIL-STD-810 Environmental Engineering Considerations an

16、d Laboratory Tests 2.1.2 RTCA Publications Available from RTCA, Inc., 1150 18th Street, NW, Suite 910, Washington, DC 20036, Tel: 202-833-9339, www.rtca.org. RTCA DO-160 Environmental Conditions and Test Procedures for Airborne Equipment 2.2 Definitions APPEARANCE: The aspect of visual experience by

17、 which things are recognized. CLARITY: The characteristic of a transparent body whereby distinct high-contrast images or high-contrast objects are easily (or) readily observable through the body. CRAZING: Network of apparent fine cracks on or beneath the surface of materials such as in transparent p

18、lastics, glazed ceramics, glass, or clear coatings. TRANSLUCENT: Transmitting light diffusely, but not permitting a clear view of objects beyond the specimen and not in contact with it. SAE INTERNATIONAL ARP5367A Page 3 of 6 DISTORTION: Defect in an image forming system whereby the image is not the

19、shape of an ideal image of the object. For example, a straight pole viewed through a window having non-planar surfaces may appear to have bends in it. MATTE: Lacking luster or gloss. Synonymous with “flat” in paint terminology. OUTGAS: To remove embedded gas from (a solid), as by heating or reducing

20、 the pressure. 3. PLASTIC LENSES 3.1 The Desire for Plastic Lenses Traditionally, glass has been the material used for exterior light assembly lenses. Glass offers excellent optical performance, durability (even when exposed to the airstream), and can withstand high operating temperatures. Glass is

21、more dense, costly, can be brittle, and is susceptible to foreign object impact damage. Plastic lenses offer some relief from the drawbacks of glass. Plastic provides a significant reduction in lens weight (low weight is a key performance attribute for all aircraft). Plastic can be simpler to mold a

22、nd work with and the tooling required could be less expensive. This can contribute to a lower lens cost as well as a shorter lead time for procurement. Plastic also offers good resistance to foreign object impact damage. Careful consideration must be given to the total cost of ownership of both type

23、s of materials over the life of the aircraft, which is another key consideration for the owners of commercial aircraft. 3.2 Plastic Lens Issues The most significant shortcoming of plastic lenses is optical performance. When plastic lenses are exposed to the airstream, particulate (ice and rain) and

24、abrasives in the airstream damage the lenses exposed surfaces. This is referred to as “lens erosion” damage and it appears as cloudy or opaque areas on the lenses much like sandblasting would produce. The effect of this degradation is reduced light transmission and light being scattered in unwanted

25、directions. The light reduction can be significant. Figure 1 show actual transmission rates that have resulted from this condition. The amount of light loss resulting from this condition will vary according to the exact material and its exposure to the airstream. With prolonged exposure, the transmi

26、ssion rates will stabilize after a significant reduction in transmission. Plastics are sensitive to chemical attack and fluid exposure. Some plastics (such as polycarbonate) are extremely sensitive. In some instances, the plastic wrap that covered polycarbonate lenses for shipment cause lens crazing

27、 due to a chemical reaction between the two materials. Refer to section 11.0 of DO-160 for test methods to validate fluids susceptibility of the plastic lens. Plastics are heat sensitive. If high heat loads are applied to the plastic lenses, they may distort, blister, discolor, and become brittle. E

28、xposure to ultraviolet light from solar radiation will also damage the material over time resulting in discoloration and brittleness. Plastics lenses have a coefficient of thermal expansion (CTE) that is different than that of other materials used to construct the light assembly housings or installa

29、tions. Standard methods of attaching the lenses can allow the different expansion rates to cause mechanical stress in the lenses thereby producing cracks (especially in the areas of fastener mounting holes). There have been some attempts to prevent or reduce lens erosion by adding a protective hardc

30、oat (spray on and brush on). Industry experience shows that hardcoated lenses do not hold up to the many flight hours at high speeds that a commercial jet transport airplane is exposed to. The plastic material is a soft substrate that flexes when subjected to airloads and vibration causing the coati

31、ng material to flake and break off. While automobiles have had success with plastic lenses, and some business jets have had limited success with plastic lenses, neither of these applications are exposed to the speeds and/or number of exposure hours (flight hours) that a commercial jet is exposed to.

32、 SAE INTERNATIONAL ARP5367A Page 4 of 6 There have been some attempts to prevent or reduce lens erosion by adding a protective laminate (urethane tape) to the outer lens surface. Tests have shown that the adhesives blister and melt when exposed to high heat loading from the light assemblies combined

33、 with heat from solar loading while the airplane is static on the ground. Many of the laminates depart the airplane during flight operations. Therefore, this method is not yet reliable. Mil-Std-810 section 505.4 detailed guidance on solar radiation testing as a possible test method for validating th

34、e solar loading capacity for the plastic lens. The loss of light intensity from discoloration, lens cracks, or transmission loss may result in light levels that are below the required regulatory levels. The change in light distribution because of lens distortion, lens blisters, or lens cracks may re

35、sult in light distribution that does not comply with the required regulatory patterns. Figure 1 - Plastic lens light transmission loss for wing tip exterior light assembly 3.3 Design Guidance As can be seen from the information in 4.2, the decision to use plastic lenses instead of glass lenses shoul

36、d be carefully contemplated. Once the decision to use plastic lenses has been made, the following design recommendations are offered: Clear polycarbonate, when used to make exterior lighting lenes, offers excellent initial transparency, durability, and a higher index of refraction than glass. Materi

37、als with higher indexes of refraction bend light to a greater degree than materials with lower indexes of refraction. Understand the transmission loss of the plastic lens material due to flight exposure. Design the exterior lights such that they satisfy all of the intensity and distribution performa

38、nce requirements with the lens degraded. Design the exterior light assemblies with low heat generating light sources. Keep all heat producing light sources as far away from the lenses as possible. Keep the lens away from external heat sources such as jet exhaust areas This will help minimize discolo

39、ration and lens deformation. L e n s T r a n s m i s s i o n L o s s(Po l y c a r b o n a te )- 4 0- 3 5- 3 0- 2 5- 2 0- 1 5- 1 0-50- 1 0 0 - 5 0 0 50 100V e r t i c a l A n g l e ( d e g r e e s ) M e a s u r e dR e l a t i v e t o A i r c r a f t F o r w a r d D i r e c t i o nLightIntensityLoss(%

40、)SAE INTERNATIONAL ARP5367A Page 5 of 6 Choose plastic materials that resist fluid exposure and chemical attack. There is no plastic that resists damage from all fluids, but some plastics are better than others. Fluids such as de-icing fluid, mineral/lube oil, hydraulic fluid, solvents, cleaning flu

41、ids, detergents, and jet fuel that are typically found in aircraft operational environments should be of primary consideration. Avoid the introduction of chemicals onto the surfaces of plastic lenses. The light design should utilize materials that will not outgas and produce chemical deposits on the

42、 lens surfaces. If lens deposits from outgassing can not be avoided, then understand the materials incorporated in the light assembly to ensure that the plastic lens material used will be resistant to the chemical deposits that may result from the outgassing process. Keep the lens away from sources

43、of external chemical deposits such as jet exhaust areas. Design lens attachment methods that avoid CTE related cracking. This usually involves allowing for expansion (float) and using clamping attachments instead of fasteners in fastener holes. Institute a maintenance inspection program to evaluate

44、the condition of each plastic lens and accomplish the appropriate action to keep the exterior lights performing correctly. A basic maintenance process is provided in Section 5. 4. MAINTENANCE 4.1 Purpose The purpose of an exterior light lens maintenance inspection is to maintain the illumination per

45、formance of the lighting equipment being assessed. For lighting systems that have performance levels that are required by a regulatory agency, the inspection may be the means to maintain a certification compliant system. 4.2 Action Required Perform a visual inspection of the plastic lens on each ext

46、erior light assembly. Evaluate the appearance of each lens with respect to the criteria listed in 5.4. Perform maintenance if required. NOTE: Ensure that the applicable lighting systems are deactivated per the airplane maintenance manual instructions. 4.3 Inspection Interval The inspection interval

47、is discretionary. It is desireable to base the interval on actual in-service performance data, however, such data is not available in many instances. For these situations, it is recommended to apply very conservative (short) intervals and extend the intervals as the cumulative inspection data indica

48、tes it is reasonable to do so. 4.4 Inspection Visually inspect each lens for the following: Dirt and/or deposits. Crazing (Lens should not exhibit a network of fine cracks on or beneath the surface). Clarity (Lens should be transparent and clear, i.e., clearly see light source and reflectors. Lens s

49、hould not be translucent, cloudy, or opaque in appearance). Cracking (Lens should not have cracks) Blistering or Bubbling (Lens should not contain air pockets, lumps, or voids) SAE INTERNATIONAL ARP5367A Page 6 of 6 Peeling or Flaking (Lens surface or coating should not peel or flake) Discoloration (lens should not exhibit signs of yellowing, darkening, etc.) Surface deterioration (Lens should be smooth and have a gloss