All About Aircraft Static Dischargers

Airplanes propelling through the atmosphere create friction against the solid particles of precipitation, liquids, and more that are present in the air, which create electrical charges on the exterior of the aircraft. This is also called static electricity, which can be seen when a person rubs a balloon on their hair, for example. These charges have the potential to create radio interference, which is dangerous because pilots cannot communicate properly with those on the ground and the navigation equipment cannot work properly. More specifically, the radio frequency spectrum is disturbed during a moment of radio interference, which impacts electrical circuits by something called electromagnetic induction. This can interfere with the circuit’s performance, perhaps even causing it to stop working. The static and excess electrons that would accumulate on the thin edges of the plane could cause a spark, which is incredibly dangerous.

There are three types of static discharge that typically cause radio interference on aircraft: corona, streamering, and arcing. First, corona discharges create light and produce sound. They are formed as a result of electrical discharge that ionizes the air in a powerful electric field. By the time an aircraft gets to 100,000 to 200,000 volts, these electric fields concentrate on the sharp ends of the plane, including the wing tips, tail, and nose. The result is radio interference that appears as a hissing noise on the aircraft’s radio. Next, streamering is a type of electrical discharge that moves from composite materials to metal on the aircraft; another way a charge can develop is on a painted part of the plane before it jumps to an unpainted piece of metal like a screw. In order to avoid streamering discharges, people apply resistant paint which dissipates the charge. Finally, there is arcing, a type of electrical discharge that creates an often barely visible glow and looks like an arc. This type of electrical discharge is caused by a certain area of the plane being insulated so that when a charge arrives, it creates that arc. In general, arcing usually occurs because something like the bonding straps have broken.

Bonding is what connects different metal pieces on an aircraft so that any applied static charge is equalized, which helps avoid a spark.They come in the form of jumpers, leads, and clamps. Bonding jumpers in particular need to be very short, metal needs to be touching metal, and the resistance can’t exceed .003 ohm.

Issues associated with static electricity on airplanes can be solved by the placement of small discharge wicks, which are attached to the wingtips, the aircraft’s tail, and control surfaces. They are made of hundreds of cotton fibers and graphite wrapped into a cylinder shape similar in size to a drinking straw. Additionally, they become smaller at the ends and have sharp, conductive carbon at their tip. The entire exterior ‘skin’ of the airplane is connected to these wicks, except for the airplane windshields. When the aircraft is traveling through ice crystals, large amounts of rain, or snow at high altitudes, these wicks dissipate static charges that come into contact with the plane. Static wicks even protect aircraft against lightning. They lower the needed voltage for corona discharge as well. When the plane moves through the air, the static discharge wicks put the built up static electricity back into the atmosphere. This is how radio interruptions are avoided on aircraft.

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