Lightning and static charging tests were performed on one transport aircraft radome and one small aircraft nose radome at the NASA Icing Research Tunnel (IRT), Lewis Research Center, Cleveland, Ohio. The primary purpose of these tests was to evaluate the effects of rain and icing conditions on the lightning protection effectiveness of segmented-type diverters. A secondary purpose was to evaluate the effects of static electrical charges deposited by rain and ice particles. The tests were performed under Task 2.4 of the Joint Program on Improving Lightning and Static Protection of Radomes. Fifty-four lightning tests were performed on two radomes to evaluate the effect of icing, precipitation drop size, and temperature on the ability of segmented diverters to prevent puncture of a radome skin and attachment to the internal radar antenna. Five of the tests resulted in radome puncture under icing conditions. One of the punctures occurred under rain without radome icing. At the time this puncture occurred, twenty previous tests had been performed on the same radome with the high voltage electrode at the same position. As a result, the radome test section had been repeatedly stressed which probably resulted in the puncture.
Ice buildup, determined from measurement and observation, ranged from approximately 3 mm (.125 in.) to 25 mm (1 in.) on the large transport radome. The 25 mm (1 in.) ice buildup allowed two punctures to occur between diverters at their tip ends during a single test. The thinner, clear ice, allowed single punctures to occur during each of three tests on this radome.
A single puncture occurred on the small aircraft radome when rime ice buildup allowed a puncture to occur at the antenna edge even though the adjacent diverter appeared to ionize.
Measurements of static charge voltage and current yielded insignificant readings. Additional tests performed at the NASA IRT at a later date using a 305 mm × 305 mm (12 in. by 12 in.) plate showed that no appreciable charging occurred at wind velocities of 161 km/hr (100 mph), the approximate velocity in the diffuser section where the radomes had been located. Negligible charging occurred when the plate was in the 90 degree orientation (plate parallel to windstream) and also when the precipitation drop size was 14 μm. The highest charging current (1.15 μA) occurred at a velocity of 483 km/hr (300 mph) at −4 C (25 F), 40 μm drop size, and plate orientation of 0 degrees.