The Secret Life of Contrails

Ever wondered about contrails -- the cloud tails left hanging in the sky by airplanes?

They are created by airplanes flying at high altitudes, where the air is below –38 degrees Fahrenheit. Exhaust from airplane engines contains water vapor as well as other gases and particles of soot and metal. When the exhaust is expelled into and mixes with the cold air, the water vapor condenses into droplets, which instantly freeze into tiny ice crystals. What you see from the ground is a dense white stream of ice crystals behind an airplane.

Historically, contrails were a factor in World War II, when the skies sometimes became so clouded that fighter craft used the trails as cover
-- but they've also blown the cover of other airplanes:

In the early 1990s, after the U.S. military developed the B-2 stealth bomber, it again became interested in contrails. Steve Weaver, a senior meteorologist at Wright-Patterson Air Force Base, Ohio, points out:
“They spent all this money to develop a billion-dollar bomber that’s invisible to radar, but you can see its contrail with your naked eye.”
The original B-2 design included a tank outboard of the main landing gear that would store a chemical to mix with the exhaust and suppress contrail formation.

Flight Lines [Air & Space]

Image: Jason*

Thanks, Boing Boing!