Definition of a numerical methodology for the evaluation of Lightning Indirect Effects (LIE) on Aircraft during the design and certification phases

Lightning is a high current and high voltage phenomenon that can statistically struck an aircraft during the flight once a year. It has been categorized by the organs of certification three different lightning effects on the aircraft : Lightning Direct Effects (LDE), Lightning Indirect Effects (LIE) and Fuel System. In particular, the Indirect Effects are the result of interaction of the electromagnetic fields that accompany lightning flash toward the aircraft causing dysfunctions or some damages in the internal electrical/electronic wiring equipments. This thesis focuses on the Lightning Indirect Effects (LIE) on a simplified 3D Digital Aircraft Mock-up model of C-27J in order to calculate the Transient Control Levels (TCL) in correspondence of a reduced to a minimum network wiring . These measurements have been done by the use of tool CST Studio Suite in which there was respectively used two software packages : CST MICROWAVE STUDIO, dedicate to the design and modification of the 3D Aircraft Mock-up model of C-27J imported by a CATIA file and CST CABLE STUDIO, utilized to generate and investigate on the equivalent circuit from the cable harness based on the classical transmission line theory. The simulation approach for the analysis of the indirect effects of lightning strike on aircraft where based on : - Time-domain method TLM (Transmission Line Matrix), for the return stroke current and to predict transient fields coupling on the surface of the aircraft, - 3D EM solver for currents (on the cable harness) and electromagnetic fields (around the cable harness). Relying on certifications, several and different models where tested, following the definition of entry and exit points for the zones of major probability of lightning strike on the aircraft.