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Smooth Surface Composite Insulation Wiring
Abstract:
The two primary wire construction types being used in military aircraft today are cross-linked Ethylene Tetrafluoroethylene (XL-ETFE) and composite fluoropolymer / polyimide tape wrap with an outer Polytetrafluoroethylene (PTFE) tape wrap. These insulations offer significant improvements over earlier polyimide (MIL-DTL-81381) and polyvinyl chloride (PVC) constructions but are not without drawbacks. XL-ETFE provides a low smoke, high fluid resistant, non-arc tracking insulation that is durable during installation and ground repair operations. However, durability and abrasion resistance are reduced at elevated temperatures, and maximum operating temperature peaks at 200 degrees Celsius. Composite insulation provides a more abrasion resistant solution with the inclusion of polyimide tape for hard surface chafe conditions and a PTFE outer layer that improves wear life during wire to wire contact. However, taped wrapped constructions create seams between insulation layers and aromatic polyimide can undergo hydrolysis under high moisture conditions.
To meet the rigors of the maritime environment of Naval aircraft a new wire type and specification set was developed. It addresses the non-suitable characteristics of tape wrapped composite while providing superior performance at elevated temperature to extruded materials. The smooth surface variant was evaluated along with existing composite and extruded insulations to determine performance improvements and maritime aviation suitability.
The smooth surface composite wire family provides a more robust outer jacket that provides install durability of extruded insulation through reduced tape edge thickness and improved sealing processes. Arc track resistance is improved and hydrolysis resistance doubled. The smooth surface composite variant is approved for Navy use without restriction.
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