FAQs
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Possibly, but the source of trouble may be with may components other than the radome. All external plastic parts should be suspected. All hinged assemblies, chock mounted boxes and instrument panels should be checked to see that they have a good electrical ground to the airframe. This also applies to the aircraft’s static dissipating devices attached to the trailing edge of wings and empennage.
Other forms of electrical interference can result from improper shielding of the aircraft’s electrical system interaction between radio antennas, engine ignition systems and power sources. When troubleshooting an aircraft with static problems, a unit-by-unit check should be made to eliminate all possibilities.
When checking the radome lighting diverter strips should be checked with special care to ensure they are properly grounded to the aircraft. There may be hidden problems. If your anti-by-unit troubleshooting does not eliminate the static problem, measure the electrical conductivity between the strip and air frame. If this is poor, remove the radome and inspect the hidden connections for breaks, weak spots or corrosion. Worn diverter strips should be replaced and corroded terminals cleaned before reassembly.
- The radome should be included as a part of the regular line mechanic’s inspection. Its surface should be checked for pits cracks chipped paint or other physical damage. Small pits can be cleaned well and sealed with a good dielectric coating.
- Lightning diverter strips should be inspected to determine that they make good electrical contact and are not abraded or broken.
- The life of a good anti-static / anti-erosion coating is generally about two years. As it erodes away the color will gradually change from black to brown. When this occurs it is wise to re-coat the frontal area.
First a good anti static/anti-erosion coating should be applied to the frontal area of the radome. This balance of the radome surface then should be painted with a product having a composition that promotes static bleed-off. The anti-static/anti-erosion coating should not be over coated with the second material.
Lighting diverter strips extending from the frontal area of the radome to the airframe should be part of every radome installation on high speed aircraft. These diverter strips continuously collect static build-up from the surface of the radome and conduct it to the airframe without severe sparking or arcing.
Under conditions of low humidity the static electric charge on a radome surface can build up to a very high potential. Severe spark discharging as a result of this condition will create radio interference over a wide band of frequencies. Physical charge may lso occur. The electrical discharges chip the paint and often burn small pits or pinholes n the radome. These small surface punctures created by the arcing rapidly increase in size as carbon deposits resulting from the charring encourage further strikes. If this condition is left unchecked, eventual damage to the radome will result from water penetrating through the radome surface into the radome core.
The material most susceptible to static build up are insulators (dielectrics) Their poor conductivity prevents the electrical charge from readily flowing to surrounding areas of lower voltage potential, thus helping to maintain a state of equilibrium. Instead the chare remains on the surface of the material where it will gradually build up as a result of continuing frictional contact until it reaches a high enough potential to form streamers. These streamers are the path taken as the static electricity discharges in the form of an electric arc.
Unfortunately, from a functional stand point it is necessary to manufacture radomes from the dilectric materials, thus making them a prime source of static generation.
As the speed of the aircraft increases, so does the friction of the air passing over the radome surface. This increases the voltage of the charge that builds up. Aircraft cruising at low speeds are less likely to be affected. Radome shape is also a factor. Small pointed radomes will build charge faster than large blunt radomes.
The first account of static electricity is believed to date back to 600 BC when a Greek philosopher Thales of Miletus rubbed amber with silk and produced a static charge. The Greek word for amber was elekron and it is from this that we derive our word electricity.
Static is an electric charge that can build up when to electrically dis-similar materials are rubbed together. Initially the materials show no tendency to either attract or repel each other. However, after being rubbed briskly together and quickly separated it will be found that they tend to attract one another. This attraction has been created by the friction of contact between the materials in describing the process we say the materials have become electrified or charged.
This process of electrification separates some quality or substance associated with the materials. This quality or substance can be regarded as two distinct types designated positive (=) or negative (-). Initially both types ( + and -) are considered to be present in each of the electrically dissimilar materials in equal amounts. However during the process the electrical properties of the materials become unbalanced. One retaining an excess of positive charge, and the other retaining an excess of negative charge. We have all experienced this phenomenon when we walk briskly across carpeting and then are shocked as the built up electrical charge in our body is suddenly discharged to the electric switch or some other object we are about to touch.