Made available by the 1st Brigade Combat Team, 82nd Airborne Division on Facebook, the following image is one of the most beautiful night shots I’ve ever seen.
It depicts a U.S. Army CH-47 Chinook helicopter loading troops at Ab Band, in Afghanistan.
Among the other things that make this picture so beautiful is the so called Kopp-Etchell’s effect. As the image title “Dust in the rotors” suggests, the seemingly solid rotor disks are caused by the sand hitting the metal blades and eroding their surface. Since the peripheral speed increases from the blades’ root to the tips, the erosion hence the visual corona effect is more visible near the blades’ tips.
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The halo effect, caused by the oxidation of eroded particles, was dubbed “Kopp-Etchells effect“, by war correspondent Michael Yon to honor Cpl. Benjamin Kopp, and Cpl. Joseph Etchells, two fallen American and British soldiers.
Although much beautiful, the visual corona is also dangerous for the helicopter, because it makes a low flying or landing chopper not only clearly audible, but also clearly visible from distance.
Image credit: U.S. Army / 1st Brigade Combat Team, 82nd Airborne Division
