When an aircraft is struck by lightning it is generally the result of a plane’s electrically conductive exterior acting as a lightning rod that could potentially damage the planes outer structures and compromise its onboard electronics.

To avoid lightning strikes, flights are usually rerouted around storms but this is not foolproof. MIT engineers are looking to reduce a plane’s risk of getting hit by lightning in an onboard system that would protect a plane by electrically charging it.

The MIT idea stems from the fact that when a plane flies through an electric field, its external electrical state shifts. As an external electric field polarizes the aircraft, one end of the plane becomes more positively charged while the other swings more negative. As the plane becomes increasingly polarized, it can set off a highly conductive flow of plasma—the preceding stage of a lightning strike.

The engineers propose temporally changing a plane to a negative level to dampen the more highly charged positive end, preventing that end from ever reaching a critical level. The team tested the idea in modeling showing that such a method could work, at least conceptually.

MIT envisions a plane with an automated control system consisting of sensors and actuators fitted with small power supplies. The sensors monitor the surrounding electric field for signs of a shift in polarization and the actuators would emit a current to charge the aircraft in the appropriate direction. This system would only require power equal to that of a standard lightbulb, MIT says.

"We're trying to make the aircraft as invisible to lightning as possible," said Jaime Peraire, head of MIT's Department of Aeronautics and Astronautics and the H.N. Slater Professor of Aeronautics and Astronautics. "Aside from this technological solution, we are working on modeling the physics behind the process. This is a field where there was little understanding, and this is really an attempt at creating some understanding of aircraft-triggered lightning strikes, from the ground up."

Reducing Risk

MIT developed a model of an aircraft that triggers a lightning strike. As a plane flies through a thunderstorm or other electrically charged environment, the outside of the plane beings to be polarized upping the possibility of a lightning strike. Mathematical models were developed to describe the electric field conditions under which a lightning strike would be triggered. Then the team used the same models with this system to ward off strikes.

The results show the charged scenario required at 50 percent higher ambient electric field to generate a critical situation where lightning would strike, compared to an uncharged scenario. By charging the plane, its risk of being struck by lightning is significantly reduced.

"Numerically, one can see that if you could implement this charge strategy, you would have a significant reduction in the incidents of lightning strikes," said Manuel Martinez-Sanchez, MIT emeritus professor. "There's a big if: Can you implement it? And that's where we're working now."

To make the system practical, MIT is working to speed up the response time in order to protect a plane within fractions of a second. However, researchers warn this is still not enough to protect against all forms of triggered lightning.

"The scenario we can take care of is flying into an area where there are storm clouds, and the storm clouds produce an intensification of the electric field in the atmosphere," Martinez-Sanchez said. "That can be sensed and measured on board, and we can claim that for such relatively slow-developing events, you can charge a plane and adapt in real time. That is quite feasible."

The full research can be found in the journal American Institute of Aeronautics and Astronautics Journal.