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This question already has an answer here:

Modern jetliners are protected from lightning by their metal skin. When they are struck by lightning, the electricity almost invariably travels through the skin and out the other side without damaging the internals or passengers.

While carbon fiber is electrically conductive, I have not been able to find any resources with a direct comparison between it and aluminum. This forum post would seem to suggest that it is less conductive, mentioning that

Although partially conductive, carbon fiber materials, and carbon fiber masts, are regarded as non-conductive (nonmetallic) for the purpose of this technical information report. For lightning protection, carbon fiber masts require the addition of an air terminal and primary conductor as described elsewhere in this technical information report.

Is carbon fiber as electrically conductive as aluminum, and if not, does this pose a problem in the event of a lightning strike?

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marked as duplicate by RedGrittyBrick, ymb1, Simon, fooot, J. Hougaard Feb 12 '17 at 17:16

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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From Boeing's AERO:

Areas that have the greatest likelihood of a direct lightning attachment incorporate some type of lightning protection. Boeing performs testing that ensures the adequacy of lightning protection. Composite parts that are in lightning-strike prone areas must have appropriate lightning protection.

Lightning protection on airplanes may include:

  • Wire bundle shields.
  • Ground straps.
  • Composite structure expanded foils, wire mesh, aluminum flame spray coating, embedded metallic wire, metallic picture frames, diverter strips, metallic foil liners, coated glass fabric, and bonded aluminum foil.

That suggests for composite areas that are vulnerable to lightning strikes, extra measures are taken to enhance the conductivity.

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I agree with the answer from ymb1, but I think that the underlying rationale would be useful to add as well. I've looked into lightning strike protection a little bit for a small helicopter design project I worked on and am drawing from that and a useful article from Composite World (http://www.compositesworld.com/articles/lightning-strike-protection-strategies-for-composite-aircraft).

Insofar as I understand it, lightning is always attempting to get to a ground (i.e., to the lowest potential state possible), and an airplane provides a possible location for leaders (some explanation here: http://www.srh.noaa.gov/srh/jetstream/lightning/lightning_max.html - the gist is that you get an electrical channel forming from both endpoints when you have a lightning strike) going from the ground to the cloud or vice versa to form -- and at a much closer distance to both, increasing the possibility for a strike to occur with the aircraft in the middle of it. This is especially true for airplanes with metal or otherwise conductive skin, such as carbon fiber.

With respect to the question asked, I think that the relative ability of carbon fiber to conduct electricity is a tricky one to answer and is, perhaps, too simplified. Composites are those wonderful materials that can be formulated just about any way you want to give whatever properties you want. For example, a representative sample of the carbon fiber material from the tail boom for my model airplane is going to behave incredibly differently when compared to a sample of the carbon fiber material on the leading edge of the space shuttle. Each has been weaved in the different way, fibers are in different orientations, different additives have been thrown in, perhaps even additional or different fibers have been added to obtain different desired structural or electrical properties, flame resistance, or corrosion resistance. Hence, saying whether or not a carbon fiber airframe is more conductive than aluminum is not really a straightforward question. The important thing, though, is that it DOES conduct electricity and that can be problematic.

Hence the importance of lightning strike protection (LSP) measures. If you don't have an LSP system, your skin becomes the route upon which the electricity can travel, causing damage ranging from burned off paint to scorched skin material to holes burned in the airframe to delaminated composite members. What LSP does is create an alternative, low-resistance path for the lightning to follow between entry and exit points in an effect to plan where your damage is going to be and mitigate it.

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