Reducing in-flight lightning strikes

Every commercial airplane is struck by lightning at least once per year, on average. The aircraft likely trigger 90% of those – a plane’s electrically conductive exterior acts as a lightning rod, attracting a strike that could damage the plane’s structure and compromise onboard electronics.

To reduce a plane’s lightning risk, Massachusetts Institute of Technology (MIT) engineers propose an electrical charging system.

To test their ideas, the MIT team – including Emeritus Professor Manuel Martinez-Sanchez and Assistant Professor Carmen Guerra-Garcia – developed a model of an aircraft-triggered lightning strike. As a plane flies through a thunderstorm or electrically charged environment, the outside of the plane becomes polarized, forming leaders, or channels of highly conductive plasma, flowing from opposite ends of the plane and eventually out toward oppositely charged regions of the atmosphere.

“These leaders carry current, but not very much,” Martinez-Sanchez says. “But in the worst cases, once they establish a circuit, you can get 100,000A, and that is when damage happens.”

The researchers developed a mathematical model to describe the electric field conditions under which leaders would develop, and how they would evolve to trigger a lightning strike. They applied this model to a representative aircraft geometry to see whether negatively charging the aircraft would prevent leader formation that would trigger a lightning strike.

Charging the plane to the right level significantly reduces the likelihood of it being struck by lightning, the team found – it took 50% higher ambient electric field to initiate a leader on a charged plane than an uncharged one.

Future planes could be outfitted with an automated control system of sensors and actuators fitted with small power supplies. The sensors would monitor the surrounding electric field for signs of possible leader formation, to which the actuators would respond by emitting a counteracting current to charge the aircraft. Such charging would require power levels lower than that for a standard lightbulb.

To make the charging system practical, Martinez-Sanchez says researchers will have to speed up response time. Based on their modeling, he and his colleagues have found that such a system could charge and protect a plane within fractions of a second, but this may still not be enough to protect against some forms of triggered lightning.

Massachusetts Institute of Technology
www.mit.edu