Abstract
When an aircraft is struck by lightning damage of external structural elements is primarily caused by mechanical electrical impact of discharge on the aircraft, which results in the formation of dents on the skin, bends of panel elements (there have been cases of bending turbofan blades) and other deformations. Firstly, the mechanism of such lightning effect is caused by the action of ponderomotive forces generated by the interaction of the current in the lightning channel with currents flowing through the metal structures of the aircraft. Secondly, the shockwave of lightning has a physical impact on the elements of construction. The presence of condensation (moisture, ice) on the surface of the aircraft can significantly increase the damage of fuselage skin resulting from the electromechanical impact of lightning, which was confirmed by the results of the experimental research conducted at the Chair of Physics of the Moscow State Technical University of Civil Aviation. The water depth (as far as it is known, thunderstorm in most cases is accompanied by rain precipitation) can be large enough especially on the ground during parking and taxiing, as well as at takeoff operation and landing. Sheet samples of aluminum alloy skin D16AT with electrical discharge parameters (current amplitude 50–60 kA, duration of the first half-wave 30 microseconds) which were relatively equal to average parameters of natural lightning strike were tested. With water depth of not over 8 mm the indentations up to 2 mm deep and 30 mm in diameter were formed on samples up to 1,5 mm thick, with a sample thickness of 0,8 mm – over 10 mm in depth and up to 60–70 mm in diameter. Educated estimates indicated that presence of water increases the electrodynamic pressure on the skin several times. Firstly, having in consideration the elastic component such deformation can bring a danger to control mechanisms and surfaces located proximately under the skin when subjected to lightning strike. Secondly, electromechanical pressure amplification coupled with the striking acoustic wave generated by lightning can result in supercritical pressures in the mounting hardware of the skin. All of this should be taken into account both at the design stage of the aircraft and during aircraft operation including in particular post-flight inspection of the aircraft struck by lightning.
Highlights
When an aircraft is struck by lightning damage of external structural elements is primarily caused by mechanical electrical impact of discharge on the aircraft, which results in the formation of dents on the skin, bends of panel elements and other deformations
The mechanism of such lightning effect is caused by the action of ponderomotive forces generated by the interaction of the current in the lightning channel with currents flowing through the metal structures of the aircraft
The presence of condensation on the surface of the aircraft can significantly increase the damage of fuselage skin resulting from the electromechanical impact of lightning, which was confirmed by the results of the experimental research conducted at the Chair of Physics of the Moscow State Technical University of Civil Aviation
Summary
В данной работе будет экспериментально показано, как наличие воды на поверхности металлической обшивки самолета может усилить ее повреждение при поражении молнией. Электромеханическое воздействие молнии на воздушное судно (ВС), следствием которого является образование вмятин на обшивке, загибов консольных элементов (известны случаи загиба лопастей винтов ТВД) и подобных деформаций, обусловлено, во-первых, действием пондеромоторных сил, рождаемых взаимодействием тока в канале молниевого разряда с токами, растекающимися по металлическим конструкциям ВС [1]. В случае же нормальной ориентации канала молнии к поверхности обшивки, как показывают расчеты [1], при амплитуде тока 100 кА и длительности разряда 50 мкс максимальные напряжения в обшивке могут достигать 100 МПа, что соизмеримо со штатными нагрузками в спокойном режиме полета. Наличие на поверхности воздушного судна конденсата (влаги, льда) может существенно усилить повреждение обшивки (как металлической, так и композитной с проводящим покрытием) в результате электромеханического воздействия молнии. В данной работе будет экспериментально доказано, что этому же, хотя и в меньшей степени, способствует влага на поверхности, в первую очередь в результате дождя (как известно, гроза в подавляющем большинстве случаев сопровождается осадками)
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