MIT engineers have proposed a new technique to reduce lightning strikes on aircraft, as part of a study sponsored by the Boeing Company.
Aviation experts estimate that around 90 percent of lightning strikes are triggered by a plane’s electrically conductive exterior itself.
The plane’s exterior acts like a lightning rod, sparking a strike that could potentially damage the aircraft’s outer structures and compromise its onboard electronics.
The current solution utilized by most aviation authorities worldwide is to have flights rerouted around stormy regions of the sky.
Now, MIT engineers led by Emeritus Professor Manuel Martinez-Sanchez and Assistant Professor Carmen Guerra-Garcia, have proposed an onboard system that could protect a plane by electrically charging it.
The idea stems from the fact that, when a plane flies through an ambient electric field, its external electrical state, normally in balance, shifts.
As an external electric field polarizes the aircraft, one end of the plane becomes more positively charged, while the other end swings towards a more negative charge.
Once the plane becomes increasingly polarized, it can set off a highly conductive flow of plasma, called a positive leader – the preceding stage to a lightning strike.
In such a precarious scenario, the researchers propose temporarily charging a plane to a negative level to dampen the more highly charged positive end, thus preventing that end from reaching a critical level and initiating a lightning strike.
Lightning itself poses very little danger to passengers inside an aircraft, as a plane’s cabin is well-insulated against any external electrical activity.
Nevertheless, an aircraft that has been hit by lightning often requires follow-up inspections and safety checks that may delay its next flight or even keep it grounded forever.
What’s more, newer aircraft made partly from nonmetallic composite structures such as carbon fiber may be more vulnerable to lightning-related damage, compared with their older, all-metal counterparts.
“Modern aircraft are about 50 percent composites, which changes the picture very significantly,” says Guerra-Garcia. “Lightning-related damage is very different, and repairs are much more costly for composite versus metallic aircraft. This is why research on lightning strikes is flourishing now.”
According to the researchers, a standard protective measure adopted by most airline companies is to cover the outside of the aircraft with a light metallic mesh.
To see whether the charging idea held up, the MIT team first developed a simple model of an aircraft-triggered lightning strike.
The researchers then 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.
Once applied on a representative aircraft, their results showed that, averaging over field directions and intensities, the charged scenario required a 50 percent higher ambient electric field to initiate a leader, compared with an uncharged scenario.
Image and content: Joan Montanya/Polytechnic University of Catalonia/MIT