Static Charge Protection
Static charge is imparted to a material through friction. An airplane becomes charged simply by passing through the air. Flight through precipitation (clouds or rain) increases charge accumulation, as there is more material contact. Static charge is routinely discharged in air at sea level, which is slightly conductive, and also in air with higher humidity. However, air with humidity below 20 percent and/or at higher altitudes is a poor conductor. The latter permits static charge to build up on aircraft surfaces, especially those of composite aircraft, where charge does not readily move.
The build-up of charge on a structure creates a voltage potential that increases with the amount of charge. On metal structures, this voltage potential is the same everywhere because metal conducts electricity. On composite structures, however, the voltage will vary. This voltage potential, in turn, generates an electric field which is most intense at areas of acute curvature - wing tips, propeller tips, trailing edges, tips and edges of wind turbine blades, etc. Built-up charge wants to travel - like charges repel and unlike charges attract. Eventually, the difference in charge between the air and structure becomes so great that the need to discharge the voltage potential takes over, resulting in a mass "dumping" of the excess charge into the atmosphere. Static charge build-up can trigger lightning within clouds or in charged atmospheric conditions. The electromagnetic wave created in the process can result in radio static - the reason static wicks are bonded at the trailing edges and outboard ends of aircraft flight control surfaces: to create multiple paths conduits for electrons to travel from the airframe to the surrounding air. This flow of electrons is enhanced by connecting the aircraft end of the wicks to the aircraft ground system, enabling the charge to dissipate before radio interference develops.
Contrary to popular belief within the general aviation community, static wicks are not merely useful in metal aircraft. Aero Options Inc. (Mattawa, Mass.) supplies AOI Static Wicks, which are frequently used by owners of Lancair IV kit planes, but are also recommended for other Lancair models, as well as Glasair, LongEze, Cirrus, Legend, and any other complex composite aircraft, which operate at higher altitudes and require unhindered communications.