Static discharger

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A portion of a static discharger on an aircraft. Note the two sharp metal micropoints and the protective yellow plastic.

Static dischargers, commonly known as static wicks or static discharge wicks, are installed on the trailing edges of aircraft including (electrically grounded) ailerons, elevators, rudder, wing, horizontal and vertical stabilizer tips. Fitted on almost all civilian aircraft today, they are high electrical resistance (6-200 Megaohm) devices with a lower corona voltage than the surrounding aircraft structure. They control the corona discharge into the atmosphere, isolating noise and preventing it from interfering with aircraft communication equipment. They are used on aircraft to allow the continuous satisfactory operation of onboard navigation and radio communication systems during precipitation (p-static) conditions. Precipitation static is an electrical charge on an airplane caused by flying through rain, snow, ice, or dust particles. When the aircraft charge is great enough, it discharges into the surrounding air. The discharge path is through pointed aircraft extremities, such as antennas, wing tips, vertical and horizontal stabilizers, and other protrusions. The discharge creates a broad-band radio frequency noise from DC to 1000 MHz. This RF noise can affect aircraft communication. During adverse charging conditions (air friction), static dischargers limit the potential static buildup on the aircraft and control interference generated by static charge. Static dischargers are not lightning arrestors and do not reduce or increase the likelihood of an aircraft being struck by lightning. Static dischargers are subject to damage as a result of lightning strike to the aircraft, and should be inspected after a lightning strike to ensure proper static discharge operation. Static dischargers will not function if they are not properly bonded to the aircraft. There must be a conductive path from all parts of the airplane to the dischargers, otherwise they will be useless. Access panels, doors, cowls, navigation lights, antenna mounting hardware, control surfaces, etc., can create static noise if they cannot discharge through the static wick.

Static dischargers on the winglet and aileron of an EasyJet Airbus A319-100

The first static dischargers were developed by a joint Army-Navy team lead by Dr. Ross Gunn of the Naval Research Laboratory and fitted onto military aircraft during World War II. They were shown to be effective even in extreme weather conditions in 1946 by a United States Army Air Corps team lead by Capt. Ernest Lynn Cleveland.

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