vapor cone cray-cray

The Prandtl–Glauert Singularity, a.k.a. "vapor cone"

Many of you have ben asking how the vapor cone pictured in the sound barrier post forms.  This vapor cone is known as the Prandtl–Glauert Singularity or P.G. Singularity.  It is sometimes also referred to as a shock collar or shock egg.

This effect can be seen anytime air is forced to rapidly expand and contract, such as during supersonic flight, and even during bomb explosions.

Apollo 11

Operation Crossroads

F-18

The cause of the PGS is complicated & still being studied, but in general what occurs is that rapid air pressure changes in the wake of the aircraft traveling at or above the speed of sound cause a temperature drop.  If the tempertaure drops below the dew point, water vapor in the area condenses into water droplets.  So the cone-shaped shock wave is, in simple terms, a cloud that forms in the region of the shock wave, much like the cloud-in-a-jar that you saw in 7th grade.

Source: Wikipedia.org

Cool.

This widely circulated new photo shows a Air Force F-22 Raptor aircraft participating in an exercise in the Gulf of Alaska June 22, 2009 as it executes a supersonic flyby over the flight deck of the aircraft carrier USS John C. Stennis.

The visual phenomenon, which sometimes but not always accompanies the breaking of the sound barrier, has also been seen with nuclear blasts and just after space shuttles launches, too. A vapor cone was photographed as the Apollo 11 moon-landing mission rocketed skyward in 1969.

Robert Roy Britt, Editorial Director
LiveScience.com
robert Roy Britt, editorial Director
livescience.com – Tue Jun 30, 9:35 am ET

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