Lightning Test Facility

With the increasing use of modern sensitive electronics and also of non-metallic composites, modern aircraft are highly vulnerable to lightning.  The effects of lightning on aircraft are broadly classified into Direct effects and Indirect effects.  The Direct effects are the physical damages caused at the lightning attachment and hang-on locations.  These include local burn-throughs, tufting of non-metallic composites, splintering/shattering, fuel ignition, puncture of electrical insulation, etc.  The Indirect Effects are those caused by the electric and/or magnetic fields of lightning.  they include temporary upset/malfunction and/or permanent damage to the various electronic/electric circuitry.  An aircraft especially the military aircraft, should be lightning-proof for both strategic as well as economic reasons.  A Lightning Test Facility helps in achieving the lightning-worthiness of aircraft through well designed experiments.`

Test Facilities

To assess the effects of lightning strokes to aircraft, the procedure involves

		Tests to identify zones on the aircraft which preferentially attract lightning
		Tests simulating a direct lightning stroke and help assess the direct effects
		Tests to simulate indirect effects and enable estimation of induced voltages.

 

The lightning Test Facility is equipped for conducting all the high voltage and high current test as per MIL specification of modified versions.

Impulse Voltage Generator
for identification of lightning attachment zones

The impulse voltage generator has nominal ratings of 4000 kV and 126 kJ.  It can generate the standard 1.2/50 µs waveshape and other waveshapes as well.  This is used for identifying zones most vulnerable from the point of lightning-attachment.  This test is conducted on scaled-down models.

Equipment for assessing "Direct Effects"
High Current generators for current waveforms A, B, C and D

The A Generator can deliver current pulses of 200 kA, duration less than 500 µs and action integral of 2 * 106 A2 through an inductive load of upto 5 µH.

The B generator can deliver near-rectangular current pulses of magnitude more than 2kA (max voltage 5 kV), duration 5000 µs, the charge transferred being 10 C.

The C generator can deliver rectangular current pulses of 200A to 400A (max voltage 1000V) and adjustable duration upto one second, so that charge transfer is 200 C.

The D generator can deliver current pulses of 100 kA, duration less than 500 µs and action integral 0.25 * 106 A2 through an inductive load of 6 µH.

The above current pulses can be applied in the desired sequence and combination using an output switch which in turn comprises of a set of adjustable spark gaps.

The facility is suitable to test a full aircraft as well as to test small samples.  A double walled dark chamber measuring 8ft * 8ft *8ft permits photography of any sparks during tests on small samples. 

Equipment for assessing Indirect Effects -
Generator for current waveform E

This generator works on the Marx principle, and has four stages, rated 100kV/stage.  Each stage has a capacitance of 4 * 0.36 µF.  It can deliver a current of 50kA with a rate of rise of current of about 35 kA/µs through an inductance of upto about 6 µH i.e., a full aircraft.  Here also, the current is returned through a cage to achieve low inductance.

Fuel Ignition test

A special flame proof for conducting fuel ignition test is also available.

Diagnostics

The following instrumentation is available at present

		Digital Impulsive Analysis System (DIAS) model 730, made by M/s.  Haefely Test System of Switzerland.
		Nicolet 490-E Digital C R O system with mass storage option.
		Tekhind model 2430A Digital Storage Oscilloscopes
		Nikon F3HP cameras.