Although it may be music to the ears of aviation aficionados, the sudden and startling double-boom one hears when a nearby aircraft flies faster than the speed of sound can be a first-class annoyance to the uninitiated. So much so that most supersonic flight over land is prohibited in the United States and many other countries, except in controlled military testing airspace.
For several years, NASA has been researching means to reducing not only the strength of the shockwave produced when a high-performance aircraft exceeds the speed of sound, but also the perceived intensity of those shockwaves – or sonic booms – heard by persons on the ground. NASA Dryden's current Sonic Booms On Big Structures – or "SonicBOBS" – project is part of that effort.
NASA's Dryden Flight Research Center has planned a series of research flights by two F/A-18 aircraft on the mornings of Thursday, Oct 14 and Saturday, Oct 16, 2010 that will result in multiple sonic booms being heard in the local area of Edwards Air Force Base. The experiments will examine the structural response of large office buildings to low-amplitude sonic booms. Offsite visitors that are influential in the development of supersonic cruise vehicles will also experience these quieter sonic booms.
Worth noting is that the flights scheduled for Oct. 14 will be on the 63rd anniversary of the first manned supersonic flight flown by Air Force Capt. Chuck Yeager in the Bell X-1 rocket plane – and the first sonic booms over the high desert.
Portions of the flights by two NASA F/A-18 aircraft in restricted airspace over Edwards will be at supersonic speeds, and are expected to generate numerous sonic booms about two or three minutes apart during the tests. Perceived loudness of the booms will vary, and depend greatly on local atmospheric conditions, including temperature and wind profile, at the time of the flights. The flight profiles are designed to keep focused sonic booms away from surrounding communities.
The Sonic Booms On Big Structures – or SonicBOBS – study is a follow-on research to tests in 2006 that measured the perceived intensity of sonic booms on an old house, further tests in 2007 on a house of modern construction, both located in the base housing areas, and more recent tests in 2009 that instrumented the Consolidated Support Facility, the Edwards AFB Museum, and the Environmental Management Building.
For the current studies, the Consolidated Support Facility has again be instrumented with transducers to measure the momentary overpressure from sonic booms, ranging from inaudible to about 0.8 psf. The two F/A-18 aircraft will fly unique flight profiles in the high altitude supersonic corridor above the base at altitudes of 30,000 to 49,000 feet.
The first sonic booms on Oct. 14 will occur over a half-hour period beginning about 9:30 a.m. and focus on the Consolidated Support Facility building. The second series of flights on Oct. 16, scheduled on Saturday to minimize noise, are slated for about 8 a.m. and 10 a.m. The resulting sonic booms will be targeted on the sensors installed in and near the Consolidated Support Facility building.
Project officials have reserved Friday, Oct. 15 as a backup flight date if Thursday's flights cannot be completed on Oct. 14, and Saturday, Oct. 23 as a backup flight date for those scheduled for Oct. 16.
While potentially loud, these sonic booms should not cause any structural damage and Edwards' residents will only hear booms that are at or below levels normally heard on the base.
SonicBOBS is a joint effort of NASA's Langley Research and Dryden Flight Research Centers, with the cooperation of Gulfstream Aerospace Corporation, Pennsylvania State University, and Seismic Warning Systems, Inc. The research is sponsored by the Supersonics Project of NASA's Aeronautics Research Mission Directorate.
NASA Dryden Flight Research Center