Alain Delannoy

The lightning swept stroke along an aircraft in flight. Part I: thermodynamic and electric properties of lightning arc channels

During a lightning strike to an aircraft in flight, the lightning channel becomes deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. The main part of the lightning current is a continuous current with a magnitude of hundreds of amperes and a duration of hundreds of milliseconds. The objective of this article is to analyse the properties of the lightning channel during this continuous current phase in order to parametrize them; this parametrization is used in a companion paper (Larsson et al J. Phys. D: Appl. Phys. 33 1876-83) for complete swept-stroke simulations. A model of the thermodynamic evolution of a lightning channel during its continuous current phase is developed and numerically solved. In this model, the channel is assumed to have axial symmetry. A quantitative analysis of the influence of failing axial symmetry is also included. The main conclusions are that the steady-state conditions are rapidly reached and that the channel can be considered to be a free-burning arc subjected to increased thermal losses due to transverse aerodynamic flow.

New Investigations of the Mechanisms of Lightning Strike to Radomes Part I : Experimental Study in High Voltage Laboratory

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.

New investigations of the mechanisms of lightning strokes to radomes. Part II : Modeling of the protection efficiency

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.

Comparison of experimental and numerical results for transient electromagnetic fields induced on a scale model aircraft by current-injection technique

A scale model of the Transall C160 military aircraft, 1/10 of the actual, was installed above a large copper ground plate and connected to it. The entry point at the nose was hard-wire connected to a 12- mu F/5-kV capacitor bank, and the current pulse launch was made using a triggered atmospheric-pressure spark gap. The exit point at the tail or at the left wing tip, depending on the configuration, was connected to the ground plate via an 80- Omega waveshaping resistor. The transient electromagnetic fields on the outer skin of the model were measured using D-dot and B-dot sensors. Three D-dot sensors were mounted on the forward upper fuselage, on the top and the bottom of the left wing. Two B-dot sensors were mounted on the forward upper fuselage and on the top of the left wing. The current was also measured using three i-dot sensors mounted on the nose boom, on the left wing tip, and on the tail boom. A comparison of experimental and computed electromagnetic fields on the scale model was performed for two experimental configurations of current injection: nose to tail and nose to left wing. As shown for one typical case, all the data were predicted with excellent frequency agreement and very good amplitude agreement.<<ETX>>

Décharges diélectriques et perturbations électromagnétiques sur satellites géostationnaires

RésuméDe nombreuses anomalies de fonctionnement ont été observées sur satellites géosynchrones. Elles sont attribuées à des décharges électrostatiques survenant sur les revêtements isolants à la surface du satellite, en particulier lors des périodes d’orages magnétiques. Le satellite est un corps électriquement flottant qui se décharge en émettant dans l’espace un nuage d’électrons. Ce phénomène d’expansion électronique constitue la spécificité du problème électromagnétique sur satellite. Celui-ci se pose en termes nouveaux nécessitant une description précise du processus de décharge.AbstractVarious operational anomalies on satellites in geosynchronous orbit, chiefly occurring during magnetic storms are attributed to spacecraft charging. The build up of static charges on the surfaces of the spacecraft leads to various breakdown processes. Self-sustained discharges, characterized by a strong electrons emission out of the material, may occur on negatively charged films of polymer used, for example, as thermal blankets. The so-called blowoff emission is an important source of perturbation through a complex interaction of the electromagnetic field with the spacecraft, the description of which needs a precise knowledge of the breakdown mechanism.