A friend sent me pictures of the Kopp-Etchells Effect. From Wikipedia:
Abrasion strips on helicopter rotor blades are made of metal, often titanium or nickel, which are very hard, but less hard than sand. When a helicopter flies low to the ground in desert environments, sand striking the rotor blade can cause erosion. At night, sand hitting the metal abrasion strip causes a visible corona or halo around the rotor blades. The effect is caused by the pyrophoric oxidation of eroded particles and is known as the Kopp-Etchells Effect.
The combat photographer and journalist Michael Yon observed the effect while accompanying U.S. soldiers in Afghanistan. When he discovered the effect had no name he coined the name “Kopp-Etchells Effect” after two soldiers who had died in the war, one American and one British.
The pictures are uncredited, so I will just send a thank you out in the ether for sharing these beautiful pictures of events in an awful time.
One final picture.
(h/t Jeff Norman)
