Last updated March 14, 2018 at 2:46 pm
A new system may reduce the chance of your flight being struck.
After months of work you’re finally on holidays, sitting in 32A, catching up on the latest Marvel film and wondering just how much training you’d need to do to match Chris Hemsworth’s physique.
Suddenly there is a flash through the window next to you, and did you hear a thud or was it your seatmate’s jaw hitting the floor as the camera pans across Hemsworth’s abs for the fourteenth time?
Unperturbed, you keep watching the film and consider another plastic cup of wine.
Aviation experts estimate that every commercial airplane in the world is struck by lightning at least once per year.
Many are complete non-events, with passengers and sometimes even pilots not realising what had happened. Other times a loud bang shakes up the passengers. The vast majority of the time the flight continues as normal, with no damage to the plane or its systems beyond maybe a black smudge on the paintwork.
Very rarely, however, a lightning strike could damage the plane’s outer structures and compromise its onboard electronics. For this reason planes which are struck by lightning are inspected by engineers after landing, and only returned to service if all given the ok.
Now, researchers from the Massachusetts Institute of Technology are working on an onboard system which can help protect the planes from being struck by lightning by taking an unexpected approach – electrically charging the exterior of the plane.
Flying lightning rods
Around 90 percent of the lightning that causes these strikes are triggered by the aircraft itself: In thunderstorm environments, a plane’s electrically conductive exterior can act as a lightning rod, sparking a strike.
To minimise the risk, flights are typically rerouted around stormy regions of the sky. However, most are unavoidable, occurring during take-off or landing at lower altitudes.
The idea of charging the plane’s skin stems from the fact that, when a plane flies through an electric field such as a storm, its external electrical state shifts away from its normal balance.
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. As the plane becomes increasingly polarized, it can set off a highly conductive flow of plasma, called a positive leader. These flowing from opposite ends of the plane and eventually out toward oppositely charged regions of the atmosphere, potentially creating a circuit and leading to a lightning strike.
In this finely balanced situation, the researchers think that creating an electric charge of their own to dampen the more highly charged positive end will reduce the chances of a lightning strike. By reducing the positive charge, it will prevent the charge from reaching a critical point where it causes the lighting.
Lightning laboratory test on model aircraft. Credit: Joan Montanya/Polytechnic University of Catalonia
Their idea also seems technically doable, with the power required to create their charge less than what is needed for a standard lightbulb.
“We’re trying to make the aircraft as invisible to lightning as possible,” said one of the MIT researchers, Jaime Peraire. “Aside from this technological solution, we are working on modelling 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.”
The researchers developed a mathematical model that described the electric field conditions which would develop leaders, and how they trigger a lightning strike. Using this model, they found that slightly negatively charging the plan would prevent the leaders from forming and triggering a lightning strike.
They found that using the system, the electric field the place was flying through, such as a storm, would need to be 50% stronger to initiate a leader. Needless to say, the plane’s risk of being struck by lightning would be significantly reduced.
The team is now testing the charging system in MIT’s wind tunnel to see if the mathematical model matches real life.
The risk to future aircraft
The research was sponsored by Boeing, which makes sense given the potential cost and risk to the manufacturer and airlines.
New aircraft such as the Boeing 787 Dreamliner are partially built from non-metallic composite materials such as carbon fibre. While super light and strong, these could conversely be more vulnerable to damage caused by lightning compared to all-metal models.
Carbon fibre is a poor conductor, meaning charge may accumulate on panels and create potential differences from panel to panel, causing regions of the panels to spark.
To prevent this localised accumulation of charge, a standard protective measure is to cover the outside of the aircraft with a light metallic mesh which allows the charge to move freely.
“Modern aircraft are about 50 percent composites, which changes the picture very significantly,” said lead researcher Professor Carmen 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.”
The research has been published in American Institute of Aeronautics and Astronautics Journal
