Design & SimulationOctober 17, 2019

How Simulation Helps Keep Aircraft Safe From Lightning Strikes

Flying in an airplane is an experience that makes many people uneasy.…
Avatar Clare Scott

Flying in an airplane is an experience that makes many people uneasy. Although flying is one of the safest ways to travel, it’s hard not to think about what could potentially go wrong when you’re sitting thousands of feet above the Earth and trusting the skills of pilots, mechanics and engineers to keep you safe. Flying can feel particularly scary during turbulence or rough weather, and if a storm approaches, one question may worry the mind of a nervous traveler: What if the plane gets struck by lightning?

Lightning strikes do happen to planes occasionally, but thankfully there are plenty of safety measures in place to prevent damage to the aircraft or harm to the passengers inside. The airframe and panels are made from conductive aluminum materials that allow the lightning current to transfer from an attachment point to an exit point, while remaining on the surface of the aircraft. This critically keeps very high currents away from cables and electrical systems on the interior and ensures the aircraft is safe in a storm. Passengers may not even be aware that a lightning strike has occurred.

Over the past few years, due to their high strength and low weight, composite materials have started to be used for major parts of commercial airframes. In contrast to aluminum ones, composite materials have much lower electrical conductivity and are more vulnerable to lightning strikes, with current diffusion possible through the surface of the aircraft to vulnerable systems inside. The good news is that metallic foil or wire mesh can be added in between the composite layers, however, to provide an effective current path that can match the aluminum airframe.

Despite these protections, there are certain externally exposed parts of the aircraft that may be vulnerable to lightning strike. The radome, or radar cover, for example at the front of the aircraft is made from a nonmetallic material which could allow current ingress, particularly as it’s a common lightning attachment and exit point. To overcome this problem, metallic lightning diverters are employed. Similarly, there may also be additional lightning protection close to antennas to channel energy to a preferred ground, away from sensitive electronics near the surface. As an additional measure, surge protection is also typically built into antenna circuits and equipment interfaces that includes high transient current suppression or filtering.

Without all these built-in protections, lightning currents could diffuse into or penetrate the airframe and use cable systems as a convenient current path or conductor, leading to catastrophic results: transient currents or voltages would interfere with flight systems, and if current levels were high enough, cables and avionic systems could be destroyed.

The potentially disastrous consequences  make it critically important that all lightning protection systems are in place, working properly and effective. The use of electromagnetic simulation helps ensure that sufficient shielding and preferred lightning channels are built into the airframe, with static computation used to determine the most likely lightning attachment points. Cable bundle layout is simulated to help minimize nearby lightning current effects, and cable shielding effectiveness can be verified. Simulation can demonstrate that the correct design of an aircraft will keep induced currents at equipment interfaces to levels below certification thresholds. Engineers are also able to compute lightning return stroke transients, visualizing current distribution and generating insight into where extra shielding might be required. Finally, engineers can ensure through simulation that field levels will be within certified limits around fuel tanks – all before the aircraft is actually built and physically tested.

As safe as aircraft are now, research is still being conducted into how they can be made even more resistant to lightning strikes. Simulation is being used to assess the performance of new lightweight materials. There is also interest in the increased use of optical fiber networks, which are non-conducting, to mitigate resonance problems due to the long length of certain metal cables. Research is exploring multiphysics aspects such as induced currents, heat sources, mechanical deformation of composite panels, and stringers, which are the axial bars behind composite panels that bond to the skin of the frame. In addition, fastener technology is changing to reduce arcing, particularly around fuel tanks.

Airplane travel has plenty of stressors associated with it, including airport crowds and security, so the less a traveler has to worry about, the better. Thanks to the highly effective systems in place to protect aircraft from lightning strikes – and the extensive simulation and testing used during the design and manufacturing process – travelers can rest easy once on board, even during rough weather.

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