Electrical interaction between atmospheric volcanic ash and aircraft in flight:mechanisms and application for hazard detection

The charging of aircraft surfaces in flight by ice and other particulates has been studied since the 1940’s, and volcanic ash suspended within dispersed plumes has been a hazard to aviation since the advent of commercial jet airliners in the 1960s. This study examines the interaction of volcanic ash particles with metallic surfaces likely to be found on an aircraft, and its ability to charge those surfaces by impact. We do this by directing a high-pressure jet of mixed air and volcanic ash, sieved to <63 μm dia., at fixed 50 mm x 50 mm target. The charging is quantified as the charge generated on the target surface per unit mass of particulate impacted. By testing volcanic ash alongside a control material (Ballotini™) which is not expected to fracture the study provides evidence that fracto-emission is the dominant charging process. It is demonstrated that volcanic ash impacting a metallic target at mass delivery rates of approximately 5 mg s-1 can generate charge to mass ratios of 0.5 to 0.8 C kg-1 at impact speeds in the range of 60 to 70 ms-1. It is also found that the charging behaviour is non-linear with respect to velocity of impact and that charging behaviour varies dependant upon the materials of the particle and the impacting surface. The study includes the investigation of two types of volcanic ash, sand and some qualitative work to investigate the impact of ice on the targets. From this we conclude that the measurement of particulate mass concentration is possible, and discrimination of particulate type is possible by exposing multiple target materials in parallel. We therefore hypothesise that the observed behaviours could form the basis for an on-board volcanic ash detection sensor system for pilot warning and guidance