When aircraft are struck by lightning, the aircraft’s structural fuselage and components are stressed by electrical and thermo-mechanical constraints, which imposes a need for reliable experimental test benches to design accurate and enhanced lightning protection. In order to reproduce the in-flight conditions of an aircraft in a laboratory, the aim of this work is to design and implement launch equipment able to propel aeronautical test samples at speeds characteristic of an aircraft— from 10 m/s for ultra-light gliders to 100 m/s for airliners—before striking it with an electric arc within the laboratory dimensions of several meters. After a comparison of several propulsion techniques, the selected solution is an augmented electromagnetic railgun launcher. Since it requires the injection of a high current to be efficient and a low voltage operative point for safety considerations, specific and original electric generator and rail structures have been designed and experimentally implemented. Particular attention has been paid to the experimental problems encountered and mainly the sliding contact, since almost no literature references are available for railgun equipment at this level of performance. Then, based on different experimental implementations, a dynamic and ballistic model of the projectile has been developed to evaluate and characterize friction forces with the aim of predicting launcher performances with different inputs. This serves to control the speed of the material test sample during the lightning strike. Finally, the railgun equipment has been coupled to a lightning generator to reproduce the lightning strike of an aircraft respecting in-flight conditions.

When aircraft are impacted by lightning strikes, structural fuselage and components are stressed by electric and thermo-mechanical constraints, which impose a need for reliable experimental test benches to design accurate and enhanced lightning protections. The aim of this work is to investigate, design and compare different topologies of DC high-current generators in order to experimentally reproduce the continuous lightning current waveform component applied to produce an electric arc up to 1 meter long. An electrical model of a standard lightning C*-waveform for 1 m long arc is set, leading to an equivalent resistor varying from 4 to 8 Ω. This model enables a theoretical comparison between the DC/DC converters Buck and Buck-boost topologies to generate such a current-regulated waveform through a load using a capacitor bank and applying a minimum initial stored energy criterion. The experimental implementations of Buck and Buck-boost configurations are designed and tested. Optimizations about the accuracy of the current regulation through feedback loop and the respect of components operating electrical and power parameters are presented. In particular, the implementation of a snubber filter and a frequency control of the switching operations, which are mandatory elements in the operation of DC converters, are described to prevent the circuit from damaging initiated by transient overvoltage peaks. Both Buck and Buck-boost configurations are experimentally implemented to perform a standard C*waveform through a 4 Ω resistor and the Buck configuration proves ability to generate electric arcs up to 1.5 m respecting the standard aeronautic waveform of lightning.

During an in-flight lightning strike, the relative motion between the arc channel and the aircraft causes a sweeping of the attachment point on the aircraft skin. To predict the behaviour of the arc channel and therefore the potential locations for further restrikes, this study aims at investigating the phenomenon with an innovative method for producing sweeping arcs based on a stationary arc and an electromagnetic launcher propelling aeronautical samples. This article focuses on characterisation of the arc channel, aiming at establishing the evolution of its physical properties during swept-stroke for various experimental conditions. Firstly, the experimental coupling of the lightning generator with the electromagnetic launcher and with a wind tunnel is described with a discussion on the representativeness of the experiment. Then, high-speed cameras and voltage and current probes are used to measure the electrical and geometrical behaviour of the electric arc channel during a swept-stroke. The shape, the length, the voltage and the power evolution of the arc channel are evaluated for different input parameters such as speed, polarity, arc current and sample length. Furthermore, the influence of these parameters on the temperature of the arc channel is studied, resorting to an optical emission spectroscopy technique. The results are presented and discussed with the objective of providing a physical insight into arc elongation phenomenology during a swept-stroke.