Modeling of lightning effects on simple structures and helicopter airframes using FDTD

One critical problem that as aircraft may encounter during a flight is lightning. The effects of lightning can be roughly distinguished as direct and indirect. The direct effects are closely related to the points where the lightning arc enters and exits the aircraft. Examples of different effects include melting of the aircraft skin, puncture of nonconducting externally mounted parts and sparks in the fuel system. The indirect effects have to do with the magnetic and electric fields coupled to the interior of the aircraft. These can cause temporary upset or even permanent damage to the electronic equipment of the aircraft. The mechanisms through which this coupling can happen are resistive voltage drop on the airframe structure and through apertures, such as windows. Even with no apertures, the lightning current flowing in the metal wall of the airframe produces a non-zero magnetic field at the interior. This field together with the resistive voltage drop form the diffusion mechanism. In this paper the lightning current on a structure is modeled using FDTD. Then the diffusion mechanism is described for simple cylindrical structures and simulation results are shown. Finally, results on a Blackhawk helicopter structure excited with a lightning pulse are presented.