Random thoughts on almost anything and everything, with an emphasis on defense, intelligence, politics and national security matters..providing insight for the non-cleared world since 2005.
Tuesday, June 30, 2009
What Supersonic Looks Like
An F-22 Raptor breaks the sound barrier during a fly-by of the carrier USS John Stennis last week (U.S. Navy photo)
If we had a prize for the shot of the week, we'd give to it Navy photojournalist Ron Dejarnett. He took the photo you see above last week, during Exercise Northern Edge in the Gulf of Alaska. Dejarnett captured an Air Force F-22 passing through the sound barrier, as it flew over the USS Stennis.
It's hardly the first time a fighter aircraft has been photographed at Mach 1. In fact, one of our favorite images shows a Navy F/A-18 breaking the sound barrier during a fly-by of the carrier Constellation in 1999.
Ensign John Gay's famous photo of a Hornet hitting Mach 1 near the USS Constellation. He captured the shot with a Nikon 90S, using a shutter speed of 1/1000th of a second. Gay's iconic image took first place in a 2000 world photography contest.
For the physics-and-engineering crowd, LiveScience.com offers this explanation of the effect depicted in the photographs:
A layer of water droplets gets trapped between two high-pressure surfaces of air. In humid conditions, condensation can gather in the trough between two crests of the sound waves produced by the jet. This effect does not necessarily coincide with the breaking of the sound barrier, although it can.
Indeed, it can.
Labels: sound barrier; F-22
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'In Pyongyang's crosshairs', by Edwin Black.
Might be of interest.
Pictures like this crop up regularly, usually with comments about "breaking the sound barrier."
The aircraft may or may not be supersonic, usually it is not. What you witness is transonic flight--that band of airspeed in which shock waves begin to form on the aircraft. The phenomenon is what causes the "barrier" that was so difficult to breach.
Air moving over a curved surface accelerates. As it approaches supersonic it forms a "normal" or perpendicular shock wave over the areas of highest curvature. That perpendicular shock wave drastically increases the drag and made it difficult with early powerplants to push through.
As you go faster, the shock wave moves back until it trails in a V like the wake of a boat. When that occurs and the whole airframe is ahead of the aerodynamic wave, you are supersonic and the drag is reduced.
When humidity is high, the perpendicular trans-sonic shock wave creates that condensation wall.
It looks a lot cooler from inside the cockpit! BTDT. Many times.
Although I read a lot about early supersonic flight as a boy I never heard or saw pictures of this water vapor side effect. Wow!
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