Weatherwatch: how aircraft protect themselves against rain and dust
If you travel on an airliner this summer, you may notice a series of metal prongs projecting from the trailing edge of the wings. These are often misidentified as lightning rods; in fact, they provide protection against static electricity.
Anyone who regularly walks on a nylon carpet knows that you can pick up static charge by a process of frictional charging. This can give you an unpleasant electric shock when you touch a metal door handle. Something similar happens to an aircraft flying through rain or dust particles, as it picks up a tiny amount of charge from contact with each one.
This effect is known as precipitation static. Because the aircraft is not earthed, the charge has nowhere to go, so it keeps building up. When the charge becomes sufficiently powerful, it will spontaneously discharge through aerials and other extremities in a series of giant sparks – technically known as “corona discharge”. The sparks cause radio interference, which may affect the aircraft’s navigation and communication equipment.
Hence those metal prongs on the wings. Known as static discharge wicks, they provide a path for electric charge to leak away gradually back into the atmosphere, without any sparks or radio interference.
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