Lightning strike protection system for aircraft fuel tanks made of low electrical conductivity composite material

A system for protecting a structure against electrical discharges,

• the structure comprising an outer skin (I) of composite having an exterior surface and opposite surface, an internal part (II) of either composite or metallic material having one side facing the outer skin and another side, and a row of metallic fasteners (III) each having a nut (T) fastening the outer skin (I) with the internal part (II), and
• the system comprising a first metallic mesh (1) having a first side and an opposite side on substantially all of the exterior surface of the outer skin (I), a second metallic mesh (2) on at least part of the first side of the first metallic mesh (1), a washer (A) between the nut (T) and the other side of the internal part (II), and an organic finish (A.O.) that covers entirely the exterior surface, the system characterized in that:
• the first metallic mesh (1) is a thin metallic wire mesh laid up and cured simultaneously with the outer skin (I) of composite;
• the second metallic mesh (2) is a metallic wire mesh thicker than the thin metallic wire mesh that overlaps the first metallic mesh (1) a minimum of 50 mm from the row of the fasteners (III), and has been put by simultaneously with the curing of the outer skin (I) and subsequently drilled and countersunk for installation of the fastener (III);
• and
• metallic countersunk washers (3) in a subset of the row of the fasteners (III) so that there is at least one of the metallic countersunk washers (3) every 200 mm, each of the metallic countersunk washers (3) being installed at a gap existing between each of the fasteners (III) and a corresponding hole in the outer skin (I) and the internal part (II).