Some Observations Pertaining to the Adequacy of Lightning Current Injection Tests to Aircraft

Lightning strikes are responsible for some of the catastrophic airborne accidents. Design of suitable protection schemes requires prior knowledge of the current and field levels during a lightning strike. For assessing these quantities and for the validation of the design, lightning current injection tests are specified. Current tests are performed with components A to D which are specified in standards. Most of the tests are practical only at the component levels. For subjecting the whole aircraft to lightning tests, standards suggest a return conductor (RC) arrangement. The return conductor arrangement permits injection of current with magnitude and rise time specified in standards. However, in a natural environment, there is no such return path for current. Therefore, the lightning electromagnetic environment experienced by an aircraft during an actual lightning strike could be different from that simulated by laboratory tests. The present work aims to investigate this considering Standard Dynamics Model (SDM) aircraft. The impedance network method is employed for determining the current and voltage distribution for the current component A. It is shown that in the real environment, the voltage drop across the aircraft is much higher than that in a laboratory test. The inevitable use of the return conductor is responsible for the differences in the electromagnetic environment.