Lightning Current Shared Between Two Concentric Ellipsoids for First Order Estimation of Current Distribution on Aircraft

Abstract:
Suitable protective measures must be incorporated to safeguard the aircraft and the personnel from the harmful effects of a lightning strike. Composite aircraft experience much more damaging effects compared to metallic aircraft. Covering the composite aircraft skin with a highly conducting thin foil or wire mesh is a commonly employed measure for lightning protection. As the skin of the aircraft is supported by the airframe, the current shared between them depends on various factors, such as the rise-time of lightning current and the relative thickness and proximity of the skin and airframe. To assess the extent of current sharing between the skin and airframe in metallic as well as composite aircraft, a concentric ellipsoidal model (replicating the fuselage and air-frame in highly simplified form) is considered for the study. A frequency domain analysis is carried out using the impedance network method to find the current distribution in the ellipsoidal model, by injecting the current at the frequency corresponding to the rise time of standard component A and experimental waveform, as well as the low frequency which corresponds to the tail of lightning current. The analysis is also carried out using ANSYS Maxwell3D eddy current solver to account for the current distribution in thick shells. The dependency of current sharing on the gap between the ellipsoids and the length of the model is analysed further for the sake of comprehension.