Aircraft-triggered lightning

Some of our present and recent efforts are listed in what follows:

Flight testing of Active Aircraft Charging using RC aircraft 

A typical aircraft gets struck by lightning at least once per year. The damages arising from these phenomena cost the airline industry billions of dollars annually. Our group has theoretically and experimentally shown that charging an aircraft to a negative potential can reduce the likelihood of aircraft-initiated lightning. In this project we investigate a novel charge control system for lightning risk-reduction on airplanes. We have developed a small model RC aircraft flight platform, which is used to test the concept in the realistic conditions of flight. We control the potential difference between a thin corona discharge wire, suspended above the wings, and the airframe using an onboard high voltage power supply. The emission of positive ions from the corona wire charges the airframe negatively. The net charge of the aircraft is measured using a calibrated small field mill fitted on the plane. We want to demonstrate the ability to control the charge of the aircraft by remotely controlling the potential difference between the wire and the airframe. The corona discharge wire has proven to be an effective method of controlling the charge of an airplane in flight, up to a certain saturation value. 

   Related publications: Controlled electric charging of an aircraft in flight using corona discharge

 


Leader Attachment Testing to a Charged Model Aircraft

In collaboration with the Lightning Group of the Polytechnic University of Catalonia, we performed laboratory experiments to study the effect of vehicle net charge on the inception of a positive leader from an aircraft exposed to high atmospheric electric fields. The experiment models the first stage of aircraft-triggered lightning in which a positive leader typically develops from the vehicle and is shortly afterwards followed by a negative leader. This mechanism of lightning initiation amounts to around 90% of strikes to aircraft. Aircraft can acquire net charge levels of the order of a millicoulomb from a number of sources including corona emission, charged particles in the engine exhaust, and charge transfer by collisions with particles in the atmosphere. In addition, aircraft could potentially be artificially charged through controlled charge emission from the surface. Experiments were performed on a model aircraft with a 1m wingspan, which was suspended between two parallel electrodes in a 1.45m gap with voltage difference of a few hundred kilovolts applied across it. In this configuration, we found that the breakdown field can vary by as much as 30% for the range of charging levels tested. The experimental results show agreement with our electrostatic model of leader initiation from aircraft, and the model indicates that the effect can be substantially stronger if additional negative charge is added to the aircraft. The results from this work suggest that flying uncharged is not optimal in terms of lightning avoidance and open up the possibility of developing risk-reduction strategies based on net charge control.

Related publications: Aircraft charging and its influence on triggered lightning 

 

Electrostatic models of aircraft-triggered lightning
 

Current design and dimensioning of lightning protection measures for aircraft are primarily guided by testing and historical information. Developing an alternative approach to the design of lightning protection measures is particularly important when considering new vehicle configurations (drones, blended-wing-bodies), new materials (composites) or new concepts (more electric and all electric aircraft). An electrostatics perspective to the problem can aid the development of analysis tools based on the well-accepted bidirectional leader process of lightning initiation from aircraft. These methods were first proposed in the 1990s (Lalande et al., 1999; Lalande and Delannoy 2012) and couple an electrostatic simulation of realistic aircraft geometries to semi-empirical leader inception criteria. Viewed from this electrostatic perspective, to first order, the probability of aircraft-triggered lightning will only depend on the geometry of the vehicle, the ambient electric field, the atmospheric conditions (which will modify the leader inception thresholds) and the net vehicle charge. We have developed a model of lightning initiation that makes no assumption on the polarity of the first leader to be incepted. Such models can not only enable design by analysis, but also be exploited to devise new methods for protection and risk-reduction.

Lalande, P., Bondiou-Clergerie, A., Laroche, P. (1999). Proceedings of the 1999 International Conference on Lightning and Static Electricity (ICOLSE), Toulouse, France.

Lalande, P., Delannoy, A. (2012). Journal Aerospace Lab Issue 5, pp. AL05-08.

Related publications: Charge control strategy for aircraft-triggered lightning strike risk reduction