From Guy Inchbald
Gary Streeter worries that the new generation of airliners with composite airframes might be at risk from lightning strikes (11 June, p 22). Yes, lightning does present a potential hazard. I spent some years as an electromagnetic pulse test engineeer – including 1999, the year of the glider accident Streeter mentions.
Modern high-performance composites tend to be based on carbon fibre, which conducts preferentially along the individual fibres. These are embedded in a non-conductive resin matrix. The net result of a strike on unprotected material is not wholly unlike the fragmentation and delamination seen when metal control lines are carried within an insulating fibreglass structure, as in the incident mentioned in the letter.
The Lear company once developed an all-carbon airframe that did not pay sufficient attention to the novel failure modes of such a material, and the design had trouble achieving certification. Nobody is going to miss that trick again.
The aviation industry has been aware of the problem for a long time, and continues to devote a great deal of effort to making its products safe. Designs have been tried and tested in the military arena and are now ready for commercial airliners.
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One solution is to design in a safe path that the discharge current will prefer, to divert it away from any critical areas. My successors then get to test whether the job has been done properly. Which is good fun.
Upton-upon-Severn, Worcestershire, UK
