« Back

Vol. 9áNo 4áAugustá2001á

Simulation of Lightning-Aircraft Interaction

Any assessment of the effects of lightning strokes on aircraft, involves: (i) tests to identify zones on the aircraft which preferentially attract lightning, (ii) tests simulating a direct lightning stroke to help assess the direct effects, and (iii) tests to simulate indirect effects to enable estimation of induced voltages. These tests are classified into high voltage and high current tests. High voltage tests simulate the high electric fields that exist around the aircraft just prior to lightning attachment and formation of the return stroke. On return stroke, high currents flow on the aircraft and are studied by conducting high current tests.

High Voltage Tests

High voltage tests are carried out using the impulse voltage generator. Two main high voltage tests, viz., corona/streamering test and attachment point test are conducted on the aircraft to simulate the effects of electric field prior to lightning attachment and after attachment, respectively.Corona/streamering test involves subjecting a model of the test object to an impulse electric field high enough to produce corona and streamers and identify their locations.

Attachment point tests are done on a component or a full-scale prototype of the aircraft by subjecting it to an impulse voltage discharge. These tests are useful in determining whether lightning will puncture the dielectric covers ( e.g., radome) and attach to the internal components or whether the stroke will flashover across the surface of the dielectric and attach harmlessly to metallic structures.

MIL-STD 1757A defines a 1.2 Ás rise time and 50 Ás fall time impulse voltage wave shape for the above tests.

High Current Tests

When an aircraft is struck by lightning, the aircraft forms a part of the total lightning path. The lightning, which is a pulse current, flows between the attachment point and the exit points on the aircraft.The total event may consist of many pulses of current, each having different parameters, such as peak current, rise time and duration of charge transfer.

To assess the effects of lightning, it is convenient to characterise the lightning flash into several current components each of which affects the aircraft in a somewhat different manner. For this purpose,the military standards have defined four lightning current components designated as A, B, C, and D for direct effect testing and one current component designated as E for indirect effect testing.

The four current components together represent a very severe flash and have therefore been utilised by manufacturers and regulatory authorities for lightning protection design and verification purposes.