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Vol. 9 No 4 August 2001 

Lightning Protection for LCA

The LCA employs composite materials to realise better strength-to-weight ratio and avionics systems, such as full authority digital engine control and digital fly-by-wire flight control systems to perform functions which are critical from flight safety considerations. Further, the aircraft with improved instrument fit aims at operating in adverse weather to match the user requirements. All these desirable features from the performance point of view make the aircraft more vulnerable to lightning strike.

Based on these considerations, a comprehensive lightning protection plan was evolved to ensure that the lightning hardness of LCA  is adequately addressed and demonstrated. Vulnerable structures and systems in it, such as radome, wing, fin, and rudder were identified from direct effects point-of-view and have been lightning qualified. Flight control systems and engine control unit are being qualified against indirect effects of lightning.

LCA Radome

The nose cone radome houses the radar antenna. The antenna inside the dielectricLightning strike test on LCA model radome is a major electric field stress raiser at the front of the aircraft and will always be a potential lightning attachment point. Unless suitable protection scheme is in place, the lightning strike will puncture the radome wall and attach to the radar antenna,with the risk of severe damage to the radar antenna equipment as well as the radome. The protection scheme for the radome to protect it against the direct effects of lightning has been evolved through design studies and detailed experimentation. An optimum scheme has been worked out considering both radar performance and lightning protection .

The radome with the evolved scheme has successfully withstood high voltage and high current tests carried out as a part of qualification testing.

The high voltage tests proved the adequacy of protection scheme in preventing attachment to the radar antenna structure inside by puncturing the radome.

The high current tests carried out have verified the adequacy and efficiency of the scheme while ensuring the structural integrity of the radome.

LCA Wing

The wings of modern combat aircraft also serve as integral fuel tanks. In case of lightningLCA wing model undr current test strike to the wing, there could be sparks inside the wing that may trigger fuel ignition and cause explosion of the aircraft. Carbon fiber composite (CFC) spars, CFC top and bottom skins are used for wing construction.This results in a large number of CFC-to-CFC joints and CFC-to-metal joints. The chances of sparking due to lightning currents across joints involving CFC are more, as its conductivity is three orders of magnitude less than that of aluminium.

The lightning protection for wings was evolved through detailed studies and experimentation and considering the critical spars and zones. Towards this, current distribution in the wing was also evaluated by carrying out high current tests on an electrical equivalent engineering model of the wing.

As a part of the design of protection scheme, techniques were evolved for realising good electrical joints of CFC-CFC,CFC-metal and metal-metal.

The protection scheme has been implemented exhaustively in the actual wing based on the studies as detailed above.

LCA Fin/Rudder

LCA fin and rudder is of co-cured co-bonded composite construction. Lightning protection Lightning strikes test on LCA fin/rudderscheme was evolved through detailed design studies and experimentation and include metal foils, strips and mesh to establish good electrical continuity. High voltage attachments test and High Current tests were carried out as a part of qualification exercise from direct effects of lightning.