Van Bortel Blog

P-Static, Lightning & the Cessna Corvalis

Sunday, May 26, 2013

By Darryl J. Taylor

Precipitation Static, commonly referred to as P-Static, can be a major source of frustration for aircraft designers, engineers and pilots. P-Static can cause significant radio interference on VHF and UHF bands and aircraft damage if not properly discharged.

P-Static exists as a result of two atmospheric conditions. The first being an aircraft's presence in a thunderstorm. Since you shouldn't be flying in or near a thunderstorm, we'll focus on the second, the triboelectric charging caused by snow, rain or dust particles contacting the vehicle frontal surface. Triboelectricity is a charge of electricity generated by friction. Think static build up between your shoes and carpet.

Generally, the greatest effects of P-Static come from flying in icing conditions and heavy, dry snow. However, flying through any type of precipitation or cloud can cause static build up. One of the most common, and most noticeable, symptoms of P-Static is radio interference. Audible static can be heard through the headset and radio reception is diminished. In an early Eclipse Jet, I suffered P-Static strong enough to completely take out my VHF radios. In another Eclipse Jet, P-Static intermittently caused a complete shut down of the left Aircraft Computer System (ACS).

Causes of Interference

Every time we fly there is some sort of friction with dust and air particles, right? So what causes the radio interference and other negative effects? There are three methods of charge redistribution, corona discharges from sharp edged extremities, streamer discharges on dielectric surfaces and arc over between electrically isolated metallic sections.

The American Heritage Science Dictionary defines a Corona Discharge as:

"An electrical discharge characterized by a corona, occurring when one of two conducting surfaces of differing voltages has a pointed shape, resulting in a highly concentrated electric field at its tip that ionizes the air around it."

These corona discharges can have significant energy levels in the VHF bands. As most of you know, your aircraft radios operate in the VHF band. A corona discharge is most likely to occur at various sharp edges around your aircraft such as the wing tips.