What Are Those Metal Rods On The Aircraft Wing?

Ever wondered what those rods sticking out of the trailing edge of an airplane wing are? Some might think they are ariels or sensors, but actually, they are a lot simpler than that. These are called static wicks, and are fundamental to safe flying – here’s what you need to know.

static wicks
What are those little rods for? Photo: Till Niermann via Wikimedia

What’s that thing on the wing?

If you’re a window gazer like most flying fans are, you might have noticed some little metal rods sticking out of the back of the wings of the plane. Depending on the plane type, there might be five, ten, or even more of them visible, so what are they for?

These small structures are called static wicks, and perform an important task for the safety of flight. Also known as static dischargers, these small devices help to dissipate static charge that might be encountered during the course of the flight.

The most obvious source of such static electricity would be lightning. Modern aircraft are designed to cope with this, and the static wicks are one element that provides lightning protection for the plane.

However, the plane itself can sometimes create a static charge, a result of flying through the atmosphere and ‘rubbing’ against it. This is particularly the case when flying through cloud or precipitation. This friction can cause static to build up, with the excess electrons often accumulating in the thinnest edges of the airframe, such as the ends of the ailerons and flaps.

static wicks
 Static wicks protect the plane from a buildup of static charge. Photo: Adrian Pingstone via Wikimedia

The problem with this sort of buildup of charge is that, if it is not equal across the airframe, it could cause a spark. Sparks near to the engine and fuel tanks is not a desirable situation, for obvious reasons. Added to this, excess static can sometimes cause interference with radios and other sensitive equipment onboard.

How static wicks work

If you look closely at the static wick, you’ll see it’s made from a cord-like structure riveted to the skin of the trailing edge. This ensures it makes metal contact with the aircraft surface. The device is made up of hundreds of cotton fibers which are impregnated with graphite, wrapped into a cylinder about the thickness of a soda straw.

Often, static wicks will be tapered towards the end, with a sharp carbon point at their tip. This gradient attracts the static charge, allowing electrons to flow off the aircraft and back into the atmosphere. This effectively discharges static from the aircraft, preventing interference with radio equipment and avoiding a buildup of charge on the plane’s surfaces.

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Static wicks can be used on tail empennage too. Photo: Getty Images

These innocuous devices can also be fundamental in the rare event of a lightning strike. Occupants of the aircraft are protected from lighting as the aircraft’s surface conducts the electricity through its skin. The wicks allow these huge voltages to be safely discharged.

However, such an extreme event can sometimes lead to the static wicks becoming burned or melted. Thankfully, they are easy and cheap to replace, and ground crew will regularly inspect aircraft to ensure all the static wicks are in good shape.

Static wicks have been in use since the Second World War, and today are mandated by regulators like the FAA for all civil aircraft.