Well actually, a plane must not allow the buildup of static electricity, because it can totally disable radio communications and navigation. And this means they must not permit the build up of static electricity.
Static is made simply when an electrically insulating material rubs with another material, either conductive or not.
A build up of static electricity depends on 4 things
- a constant source, like flying through the air, and this grows exponentially through particles of smoke, dust, cloud, snow and rain.
- an electrical “capacity” to collect the electricity, like the aircraft’s large metal surface – an electrical capacitance of about 2000 picofarads.
- being insulated from ground and other electrical conductors, so as not to discharge the electricity.
- that the voltage not reach the “corona” voltage, at which point the air ionizes and begins allowing electricity to discharge into the air.
The only control possible is discharge. So aircraft have bonded onto the outer edges of the wings, stabilizer and fin, as many “static wicks” as are required, typically 20+ wicks.
These function by having a very small geometry such as needles so that ionization and discharge begins at only 300 volts rather than starting to spark at 10,000 volts or so. The reason for so many is to keep simple balance, to have as many wicks as required when the aircraft flys through the most severe weather. Because elsewise, the rising voltage exceeds the general atmospheric ionization of 10,000 volts, and the radios all fail.
Author – Jock McTavish
