Originally Posted by
tdracer
Disclaimer - I'm not a lightning/EMI expert, but I did have to deal with it for my engine systems - I know just enough to be dangerous
Yes, there is a copper mesh imbedded in the carbon fiber on the 787. While carbon has reasonable electrical conductivity, it's still considerably worse than aluminum (order of magnitude). That higher resistance means that the electrical current/voltages induced by a lightning strike are much higher than for aluminum structure. The copper mesh dramatically improves the conductivity of the carbon, but it's still a bit worse than aluminum. As a result, the lightning transient requirements for the 787 systems are somewhat higher than for aircraft with aluminum primary structure (I don't recall specifics, but IIRC the voltage requirements were about twice as high for carbon fiber aircraft).
Clear? Pop quiz in the morning
Right on tdracer. in the 1980s, Boeing did a LOT of work on lightning strike on carbon composites - for example A-6 rewing and B2. A major problem was to handle how to handle pass-throughs in wing tanks as in front and rear spars- while being sure there would be NO sparks. So methods were developed to be able to copper plate inner and outer carbon composite surfaces and provide connectivity to the internal ' mesh' or its equivalent. at about the same time the aborning 777 was considering using some fuel tankage in the empennage section-( horiz stab ) Some of the ensuing discussions within the constraints of military v commercial issues were quite interesting to say the least.
For but one example - the commercial boys wanted to use aluminum mesh for weight savings over copper. Thenit was pointed out that aluminum v carbon and a bit of moisture made a almost useable battery
