Acting on impulse

Aircraft made of a higher proportion of carbon-fibre composite (CFC) materials could be more vulnerable to damage from lightning strikes.

The composite components of the A350 use a copper foil to dissipate electricity

Researchers from Cardiff University’s School of Engineering and EADS Innovation Works are beginning a study into the electrical discharge phenomena in CFC materials and components used for aircraft.

Modern aircraft made of aluminium are considered highly capable of resisting lighting. When struck, the fuselage dissipates the electricity with lightning discharge wicks on the wingtips.

Future aircraft such as the Boeing 787 or Airbus A350, which are being readied for commercial deployment, will rely more on CFC materials and feature a nearly all-composite fuselage.

This will create new challenges for dissipating electricity. Engineers at Cardiff are claiming that these challenges can be most efficiently met with a greater understanding of how discharges created by CFC differ to those from materials such as aluminium.

The difference in charges is largely due to CFC’s structure. Principal investigator A Manu Haddad, of Cardiff’s High Voltage Energy SystemsResearch Group, explained CFC panels consist of several carbon-fibre layers embedded in special resins. A metallic mesh is inserted between the carbon-fibre layers. This is unlike a metal, whose structure is uniform.

’The conduction and charging processes of [CFC] structures are different and more complex than that of single metal panels,’ he said.

Researchers in Cardiff’s ’lightning laboratory’ will attempt to visualise this phenomena using high-voltage tests, computer modelling and simulations.

Haddad added that the group will use generators capable of delivering current up to 250,000A and 400,000V to simulate the ’worst-case scenario’ direct lightning strikes.

Matthew Cole, technical lead for the Lightning Direct Effects Group at EADS Innovation Works UK, said that a direct hit from a lightning bolt with that current and voltage could create electrical discharge in composites that generate temperatures high enough to melt resins and weaken structures.

The current method for mitigating this problem, he said, is using a metallic layer on the surface of the composite. For example, Cole said the composite components of the A380 are layered with a bronze mesh, while the A400M and A350 will use a copper foil to dissipate electricity.

Ian Risk, head of EADS Innovation Works, said the information gained could result in new solutions for dissipating electricity. Future solutions, he said, could include coating composites with paints that contain carbon nanotubes to increase conductivity.