Recent lightning induced voltage test technique investigations

Lightning induced voltage testing techniques are discussed. The cause/effect relationships associated with technique procedures which generate a better understanding of test circuit behavior was investigated. The travelling waves propagate in a transverse electromagnetic (TEM) mode at the speed of light. However, due to reflections and refractions at the junctions of different impedance sections of the aircraft (i.e., wing and tail attachments) the bulk of the wave energy travels distances considerably farther than the nose to tail dimension. Consequently, the wave appears to take longer to reach the tail, which is interpreted as a slower propagation velocity. Travelling electromagnetic waves reflecting and refracting on the aircraft transmission lines control the response of the system during the initial few microseconds of the test. The system itself will govern the current risetime which can be injected due to the reflection/refractions and the low pass filter characteristics of the system. With configurations, current risetimes faster than 100ns do not appear possible.