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Fleet Week 2011: F-15 with shock collar

Conditions were exactly right this weekend (high humidity, fast aircraft) to produce a few shock collars (sometimes known as Prandtl–Glauert singularities (only a theoretical result), shock eggs or vapor cones). at the Fleet Week airshow in San Francisco.

 

This is not the aircraft breaking the sound barrier, but traveling close to it at transonic speed. Around the plane air is compressed into higher- and lower-pressure regions which cause instability in the flow. This builds up into a shockwave, and as the plane passes through it causes moisture to precipitate out of the air producing the beautiful but transient shock collar, as seen above.

 

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Rest of the 2011 Blue Angels pics are here. Also see 2010, 2009 and 2008.

 

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For other San Francisco fun, also see: SF Pride 2011, Carnaval SF 2011, Bay to Breakers 2011, and the How Weird Street Faire 2011 and other San Francisco Madness.

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Taken on October 8, 2011