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Supersonic aircraft would be much quieter than before

     Washington: NASA is concluding a series of flight tests to measure shock waves generated by an F-15 jet in an effort to validate computer models that could be used in designing quieter supersonic aircraft. The project, known as Lancets (Lift and Nozzle Change Effects on Tail Shock), embodies research aimed at enabling the development of commercial aircraft that can fly faster than the speed of sound without generating annoying sonic booms over land. Supersonic flight over land generally is prohibited because of annoyances caused by their noise. A sonic boom is created by shock waves that form on the front and rear of an aircraft. The boom loudness is related to the strength of the shock waves. The formation of the shock waves is dependent on the aircraft geometry and the way in which the wing generates lift. During the flight tests at NASA's Dryden Flight Research Center in Edwards, California, one of two F-15s generally followed 100 feet to 500 feet below and behind the other, measuring the strength of the leading aircraft's shock waves at various distances using special instruments. Global Positioning System relative positioning was used to guide the pilot of the probing aircraft to a test position and for accurate reporting of measurement locations. Lancets is the latest in a series of NASA projects investigating the effects of aircraft geometry and lift on the strength of shock waves.
-Jan 23, 2009