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Experimental studies of the mechanisms of lightning strokes to radome have shown that the protection efficiency can be related to the ability of diverter strips to initiate stable leaders before inception of energetic discharges take place inside the radome. A model based on a 3D code for electric field calculation is used to compute the threshold of these different processes and deduce the optimum strip height for a given internal electrode configuration. The results of this model are successfully compared to experimental estimation of optimum protection.

The main purpose of the experiments described here is the analysis of the mechanisms of radome protection with lightning diverters of various types and sizes. A high voltage arrangement and associated diagnostics have been implemented to perform a quantitative study of the inception and propagation mechanisms of the corona and leader discharges that precede the final breakdown. It is shown that ambient humidity plays a significant role on the discharge process and that the nature of the discharge initiated from the strip is very different depending on the strip type. Segmented strips are more likely to allow energetic discharges to propagate from an internal antenna leading to radome puncture.

In the framework of an EC (European Community) project EM-HAZ (Electromagnetic Hazard), an Automatic Lightning System Detection And Recording (ALISDAR) has been developed. Electrical and magnetic field measurements are the best way to characterize the lightning strike to aircraft. A finite difference time domain (FDTD) method is used to estimate the lightning current from E and H field measurements. The severity and the location of the lightning strike could be used to optimize the maintenance operations. The best location in terms of cost for the ALISDAR sensors is a dummy window. The validation of the ALISDAR system is planned through two laboratory experiments.

In the European FULMEN program, a collection together with an analysis of available data on lightning have been collected in a public database produced by Aerospatiale. This database contains data on In-flight and ground measurements, on In-flight incidents and manufacturer transfer functions. In this paper, the data of the in-flight measurements are presented. The In-flight data have been extracted from the Convair and Transall campaigns performed during summer 1985 and 1988 respectively. The measurements have shown that a lightning strike to an aircraft can be decomposed into four main phases: (1) the pre-breakdown phase associated with the general electrostatic condition just before the lightning, (2) the leaders development phase, (3) the recoil streamers phase and (4) the continuous current phase. For each phase, the main physical parameters (current, number of impulse current, impulse period, impulse duration, electric field, …) have been collected.

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.

The definition of lightning attachment zone in the standard regulatory documents have been inferred from empirical approach. In the framework of the European FULMEN program, the actual physical processes involved in a lightning strike to aircraft or helicopter are studied to improve the determination of the initial lightning attachment. In flight experiments performed in the 80’s have shown that there are two main processes which lead to a lightning strike to aircraft. The first process occurs when an aircraft flies into a region of the thunderstorm where the electric field is intense. The result is the triggering from the aircraft of preliminary discharges which lead to lightning development. The second process is the interception by the aircraft of a natural lightning channel developing in the vicinity of the aircraft. The experiment, performed at the test center of CEAT in November 1997, has been designed to simulate the initial phases of both processes.