Mechanism for Lightning Protection of CFC Structures Using Interwoven Wires

Small diameter aluminum wires interwoven with the outermost graphite ply on carbon fiber composite (CFC) structures have been successfully used on aircraft such as the Learfan and the Beech Starship to protect the aircraft structure from lightning direct effects. Previous testing on the Beech Starship indicated that the ability of the aluminum wires to remove the surface finish was essential to minimizing structural damage. A test program was established on behalf of the Advanced General Aviation Transport Experiment Program (AGATE) and Raytheon Aircraft to determine which material properties of the interwoven wires promote removal of the surface finish. The test program examined the ability of aluminum, brass, copper, and Monel^® wire fabric, applied on a fiberglass laminate, to remove a typical aircraft surface finish while conducting low-level simulated lightning current. Current and action integral levels at which each wire material began to remove surface finish were measured and used to identify wire material properties conducive to surface finish removal. Post-test visual inspections of the test samples were made to identify surface finish removal mechanisms. Calculations are presented that predict the ability of the tested wire materials to remove surface finish when interwoven in a graphite ply.