A new MIT study suggests that electrically charging planes could reduce their risk of being struck by lightning.
Experts estimate that every commercial airplane in the world is struck by lightning at least once a year. Although strikes pose little danger to passengers, they cost airlines time and money. Around 90% of these strikes are probably triggered by the aircraft itself.
When a plane flies through an ambient electric field, its external electrical state, which is normally in balance, shifts. As an external electric field polarises the aircraft, one end of the plane becomes more positively charged and the other more negatively charged. This polarisation can set off a highly conductive flow of plasma, called a positive leader – the stage that proceeds a lightning strike.
Their electrically conductive exterior can act as a lightning rod, sparking a strike that could damage the plane’s outer structures and compromise its onboard electronics.
To avoid lightning strikes, flights tend to be rerouted round storms, but MIT engineers say a new way to reduce a plane’s lightning risk is through an onboard system to electrically charge it.
The team found that if the plane is charged to the right level, its likelihood of being struck by lightning would be significantly reduced.
The dangers of polarisation
Researchers suggest that if the plane were temporarily charged to a negative level to dampen the more highly charged positive end, it would stop it initiating a lightning strike.
The team, which includes Emeritus Professor Manuel Martinez-Sanchez and Assistant Professor Carmen Guerra-Garcia, envisions fitting a plane with an automated control system consisting of sensors and actuators fitted with small power supplies. The sensors would monitor the surrounding electric field for signs of possible leader formation. If detected, the actuators would emit a current to charge the aircraft in the appropriate direction. The researchers say such charging would require power levels lower than that for a standard lightbulb.
Delays and repairs
Although lightning itself poses very little danger to passengers inside an aircraft, as a plane’s cabin is well-insulated against any external electrical activity, an aircraft that has been hit by lightning often requires follow-up inspections and safety checks that may delay its next flight. If there is physical damage to the plane, it may be taken out of service – something airlines would rather avoid.
Newer aircraft, made partly from nonmetallic composite structures such as carbon fibre, may be more vulnerable to lightning-related damage, compared with their older, all-metal counterparts. That’s because charge may accumulate on poorly conducting panels and create potential differences from panel to panel, which may cause certain regions of a panel to spark. A standard protective measure is to cover the outside of the aircraft with a light metallic mesh.
The researchers have shown how this would work at a conceptual level by modelling and have reported their results in the American Institute of Aeronautics and Astronautics Journal. The paper’s other co-author is Ngoc Cuong Nguyen, a research scientist in the aeronautics and astronautics department. The research was sponsored by Boeing.