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Fixing What Yeager Broke: Reducing Sonic Booms
1.28.04

U.S. Navy F-5E in flight
  Northrop-Grumman Corporation's modified U.S.
  Navy F-5E Shaped Sonic Boom Demonstration
  (SSBD) aircraft.
  NASA Photo by Carla Thomas.
When Chuck Yeager first broke the sound barrier more than 50 years ago, the world's first sonic boom thundered across the Mojave desert, undoubtedly causing even the local gecko population to perk-up and take notice.

Even as that historical event ushered in a new era, supersonic flight over land has remained restricted to military aircraft flying over specially designated desert ranges in order to avoid disturbing population centers.

Last year, during the successful Shaped Sonic Boom Demonstration project, a team including the NASA Langley Research Center, NASA's Dryden Flight Research Center at Edwards Air Force Base, Calif., and Northrop Grumman Corp., proved the theory that by carefully altering the contours of a supersonic aircraft, the shockwave and its accompanying sonic boom can be shaped.

Did you know?
Mach number was named after the Austrian physicist Ernst Mach. Mach 1 is the speed of sound which is approximately 740 miles per hour. An airplane flying less than Mach 1 is traveling at subsonic speeds, faster than Mach 1 would be supersonic speeds and Mach 2 would be twice the speed of sound.
Recently, the work continued as the team gathered and refined higher Mach number and higher altitude sonic boom data in the quest to reduce the intensity of sonic booms.

This effort is identifying and maturing technologies that could eventually enable unrestricted supersonic flight over land by future military and business aircraft, possibly ushering in a new era of supersonic flight.

"We now have over 1,300 high-quality recordings of sonic booms," said Ed Haering, NASA Dryden's principle investigator for sonic boom research. "In all these flights the SSBD aircraft had shaped sonic booms, with interesting differences in the shapes with variations of Mach number and altitude," Haering said.

microphones under F-5E SSBD record sonic booms.
  One of many microphones arrayed   under the path of the F-5E SSBD aircraft   to record sonic booms.
  NASA photo by Tony Landis.
Using a specially-modified F-5E, the renamed Shaped Sonic Boom Experiment team started the second round of experiments, flying many supersonic flights, most at the primary test point speed of Mach 1.4.

Several of the flights included NASA Dryden's F-15B research testbed aircraft following in order to measure the F-5E's shockwave signature close-up. During the flights, many shockwave patterns were measured by the F-15B at various distances and orientations from the F-5E.

An unmodified F-5E flew a few seconds behind the demonstration aircraft to provide a baseline sonic boom measurement to validate the reduced boom produced by the demonstrator.

A USAF Test Pilot School Blanik L-23 glider carrying a microphone on the left wingtip, and a pressure transducer on the side of the fuselage, flew at a lower altitude of 10,000 feet under the path of the F-5E, which flew at 32,000 feet, in order to record sonic booms in the air.

Did you know?
Aircraft passing Mach 1 produce a loud sound referred to as a sonic boom and sometimes even a double sonic boom. Thunderlike sonic booms are cuased by the air molecules being crowded into shockwaves by an aircraft. The sonic boom is the "wake" of the plane's shockwaves combined together. Double booms are produced first by shockwaves from the plane's nose and then from its tail.
In addition, sonic boom data was gathered on the ground by an array of 42 sensors and recording devices stretched out over two and a half miles under the flight path of the F-5E. Dryden-developed Boom Amplitude and Direction Sensors recorded ground-level sonic boom signature data.

The Vehicle Systems division of NASA's Office of Aeronautics funded the project, which was formerly part of the DARPA's Quiet Supersonic Platform program. Northrop-Grumman Corporation's Integrated Systems Sector in El Segundo, Calif., modified the U.S. Navy F-5E aircraft into the SSBD aircraft.


Gray Creech
NASA's Dryden Flight Research Center




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