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electrical bonding of composite materials 2
- Thread starter ombarba
- Start date
Huh? fiberglass/epoxy is nonconductive, usually, so bonding in the EMI sense makes no sense.
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Ombarba...
Usually the problem with secondary structural composites [like fairings, tips, etc] is precipitation-static ['P-static'] charge build-up. This problem can be mitigated by anti-static coatings that also ground thru attachments fasteners and active static diverters such as trailing-edge static wicks. For components that cannot tolerate conductive coatings [such as antenna radomes, antenna covers, etc], and are subject to lightning strikes [primary lightning zone locations], then discretely placed metal straps [plain or segmented lightning diverter strips] bleed-off P-static and absorb/direct lightning pulses exterior surface of the composite, and lead directly to an aluminum airframe bond-point. These external straps are often sacrificial for aircraft safety [IE; absorb/redirect destructive lightning energy, one-time] and can be readily replaced.
For large area primary composite structure, methods are in-place to mitigate P-static build-up and to absorb/conduct-away lightning strikes. These ‘processes’ use conductive coating mechanisms [such as metallic/metalized coating; or conductive erosion coatings]; or wire-mesh or conductive filaments embedded into the entire outer composite layers, etc… using materials and methods which are highly proprietary. Electrical wire grounding paths [separate of conventional airframe ground/bonding paths] for aircraft systems components are mandatory. Extreme care [design, testing, fabrication, maintenance] is required for composite airframe structures, that also serve as integral fuel tanks, to eliminate all potential for static-arc, electrical-arc, lightning-arc/hot-spot ignition, etc, that could initiate fuel-fed fire/explosion.
Regards, Wil Taylor
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Usually the problem with secondary structural composites [like fairings, tips, etc] is precipitation-static ['P-static'] charge build-up. This problem can be mitigated by anti-static coatings that also ground thru attachments fasteners and active static diverters such as trailing-edge static wicks. For components that cannot tolerate conductive coatings [such as antenna radomes, antenna covers, etc], and are subject to lightning strikes [primary lightning zone locations], then discretely placed metal straps [plain or segmented lightning diverter strips] bleed-off P-static and absorb/direct lightning pulses exterior surface of the composite, and lead directly to an aluminum airframe bond-point. These external straps are often sacrificial for aircraft safety [IE; absorb/redirect destructive lightning energy, one-time] and can be readily replaced.
For large area primary composite structure, methods are in-place to mitigate P-static build-up and to absorb/conduct-away lightning strikes. These ‘processes’ use conductive coating mechanisms [such as metallic/metalized coating; or conductive erosion coatings]; or wire-mesh or conductive filaments embedded into the entire outer composite layers, etc… using materials and methods which are highly proprietary. Electrical wire grounding paths [separate of conventional airframe ground/bonding paths] for aircraft systems components are mandatory. Extreme care [design, testing, fabrication, maintenance] is required for composite airframe structures, that also serve as integral fuel tanks, to eliminate all potential for static-arc, electrical-arc, lightning-arc/hot-spot ignition, etc, that could initiate fuel-fed fire/explosion.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]
Electrical bonding in composite structures presents some challenges. But things are also not easy with metal airframes. Remember the horrible situation with electrical ground circuit faults causing an explosion in the center body fuel tanks of a 747?
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