Lightning protection system for aircraft composite structure

A lightning protected composite fuel tank on board an aircraft, the fuel tank comprising:

• a composite fuel tank shell, the composite fuel tank shell comprising a layered composite material forming an internal volume configured to contain fuel;
• tank structure comprising a tank support member within the fuel tank;
• a fastener extending through the tank support member and into the layered composite material of the composite fuel tank shell such that a first end of the fastener is below a coextensive outer surface of the fuel tank;
• a nonconductive or dielectric material plug filling a gap between the first end of the fastener in the layered composite material of the composite fuel tank shell and the coextensive outer surface of the fuel tank;
• and
• an electrically conductive layer on the coextensive outer surface of the fuel tank and surrounding the nonconductive or dielectric material plug, the electrically conductive layer not in electrical contact with the fastener.

A method of fabricating a lightning protected aircraft fuel tank, the method comprising:

• selecting a fuel tank comprising an electrically conductive fuel tank shell comprised of electrically conductive composite material, and having locations for fastener centerlines, and an electrically conductive layer on an outer surface of the fuel tank shell along the locations for fastener centerlines;
• creating holes in the fuel tank shell at fastener points in the fastener centerlines, the holes having countersunk portions to receive fastener head portions of fasteners;
• attaching the fuel tank to an aircraft substructure with the fasteners in the holes so that the fastener head portions in the countersunk portions are not in electrical contact with the electrically conductive layer;
• and
• filling spaces between the fastener head portions and the outer surface of the fuel tank shell with a nonconductive or dielectric material.