The lightning strike to aircraft starts with the development of a positive discharge from the aircraft, followed few milliseconds later, by the inception of a negative discharge propagating in the opposite direction. The location of the inception points of both discharges are important in order to identify the most threatened zones of the aircraft in the initial lightning phase.
In the 90’s Onera and the University of Padova have developed a set of physical models which simulate the inception and development of long sparks in laboratory. These models have been adapted to the case of lightning discharges introducing the appropriate E-field distributions and specific physical processes due to high currents flowing into the channels. These models can also provide an evaluation of the minimum ambient field necessary to sustain stable propagation of lightning leaders over long distances.
In the framework of the European FULMEN program, these models have been applied to determine the initial attachment zone of the lightning on aircrafts and helicopters. From a given aircraft geometry and ambient field direction, we compute (1) the location of the entry point (starting point of the positive discharge) and the exit point (point associated with the negative one), (2) the minimum ambient field which allows a stable propagation of the discharges. The computation has been repeated for an equiprobable distribution of the direction of the ambient field. The calculated zones of entry and exit points are presented and commented in the case of a Airbus A319 and a Super Puma helicopter.