# How are aircraft protected from lightning strikes by conductive skin?

I've read this question and this one, but they don't really answer my question.

How or why are aircraft protected (from lightning) by a conducting skin, such as aluminum? Conductors allow current to flow through you! Wouldn't it be better to have an insulating shell?

I realize its not possible to have an ideal bubble completely protecting you, because the engines need to breathe air. Presumably these metal engines would then take the brunt of the lightning strike.

So let me try an example with a glider. Let's say we have a glider completely surrounded by an insulating skin. Just for the sake of ideal example, let's say this skin is the best material insulator known: diamond. (Okay, it's not solid diamond. It's just a diamond coating. Yes, they can build that via chemical vapour deposition. I know it's not economical, it's just for the sake of an ideal example.)

What would happen if this craft gets struck by lightning? Please don't say "it explodes" without some kind of citation or explanation or I will be suspicious of hollywood falsehood.

• I'm voting to close this question as off-topic because it is a question for physics.se (Faraday's cage) – Federico Jan 30 '16 at 23:13
• @Federico When you think about it, questions about lift, drag, and engine efficiency can also be asked on physics.SE. They are permissible here because they relate to aviation. I hope we can agree that lightning also relates to aviation. – DrZ214 Jan 30 '16 at 23:40
• Conductors allow current to flow through you! this is where your question falls down. This is an incorrect assertion. – Simon Jan 31 '16 at 8:06
• The question is based on a wrong understanding of electrostatics which states a metallic cabin protects the passengers from field (hence current) exactly like a lightning conductor protects a building. Actually today's issue in aircraft design is to recreate this protection where the cabin is not metallic (aluminum replaced by composites). Convincing demonstration on Youtube. Theory of equipotential closed surface. – mins Jan 31 '16 at 12:55
• @DrZ214, English.SE would be useless for this. The problem with "through" is that it depends on where the conductor is. If the conductor is around you, then the current will predominantly flow through the conductor and therefore around you, not through you. – Jan Hudec Feb 1 '16 at 8:53

Lightning striking a metal aircraft

A commercial aircraft [...] is struck several times during its whole service life.
In such a case, the airplane acts like a lightning rod. Its metal structure provides the lowest resistance for the electrical discharge on its way between the clouds and the ground. It is not uncommon that the airplane is thereby struck by a complete series of discharges, mostly between three and five, in exceptional cases up to 25.
Since an airplane in flight has no form of grounding, the lightning first enters the structure and leaves it again a split second later. The principle behind this occurrence is known by most people from physics lessons in school. The airframe acts as a so called "Faraday Cage". Like an automobile body the aluminium structure, when struck by a lightning, passes the electric energy around the interior and keeps the passengers safe.
The crucial technical equipment is thereby also kept safe from the high voltage and the aircraft can, in most cases, proceed normally with its flight. But to play it safe every lightning strike is documented by the cockpit crew and the aircraft is treated with a special inspection routine on its next check.

Source: "Lightning Strikes During Flight", Lufthansa Technik

Lightning striking modern aircraft with composite structures (as noted by this comment)

Composite parts that are in lightning-strike prone areas must have appropriate lightning protection. [...] Composite structures are less conductive than metal, causing higher voltages.
Lightning protection on airplanes may include wire bundle shields, ground straps, composite structure expanded foils, wire mesh, aluminum flame spray coating, embedded metallic wire, metallic picture frames, diverter strips, metallic foil liners, coated glass fabric, and bonded aluminum foil.
Lightning can also damage composite airplane structures if protection finish is not applied, properly designed, or adequate. This damage is often in the form of burnt paint, damaged fiber, and composite layer removal.

Source: "Lightning Strikes: Protection, Inspection, and Repair", Boeing, 2012

New technology improving the lightning protection of modern aircraft

Traditional methods to protect composite aircraft from lightning strike damage rely on a conductive layer embedded on or within the surface of the aircraft composite skin. This method is effective at preventing major direct effect damage and minimizes indirect effects to aircraft systems from lightning strike attachment, but provides no additional benefit for the added parasitic weight from the conductive layer.
A new multi-functional lightning strike protection (LSP) method has been developed to provide aircraft lightning strike protection, damage detection and diagnosis for composite aircraft surfaces. The method incorporates a SansEC sensor array on the aircraft exterior surfaces forming a "Smart skin" surface for aircraft lightning zones certified to withstand strikes up to 100 kiloamperes peak current.

Source: Szatkowski, G. N. at al.: "Open Circuit Resonant (SansEC) Sensor Technology for Lightning Mitigation and Damage Detection and Diagnosis for Composite Aircraft Applications", NASA, 2014

Further information can be found on the internet, see for example "Playing with Lightning in the Name of Aircraft Safety", NASA.

For the science behind the Faraday Cage and lightning striking insulators, please refer to Physics.SE.