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 µs rise time and 50 µs 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
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