A Quieter, Gentler Sonic Boom

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Flight tests last Wednesday proved that modifying the shape of an aircraft can reduce the intensity and noise of a sonic boom, Northrop Grumman has announced. The new technology could eventually make it possible for supersonic jets to fly from point to point over land, instead of being restricted to transoceanic hops, like the Concorde ... and to be much uglier. A team from NASA, Northrop Grumman, and the Pentagon flew an F-5E with a modified nose section at NASA's Dryden Flight Research Center at Edwards Air Force Base, in California. The test aircraft has a specially shaped "nose glove" and added aluminum substructure and a composite skin on the underside of the fuselage, and has designers dreaming of aircraft that may precipitate reworking the term "sonic boom." The project is part of DARPA's "Quiet Supersonic Platform (QSP)" program, an effort to develop technologies that could allow military and business aircraft to operate with reduced sonic boom. "This theory had been demonstrated only in laboratories and wind tunnels," said Charles Boccadoro, Northrop Grumman's QSP program manager. "It took a cooperative effort of government and industry to achieve this breakthrough." An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to waves created by the bow of a ship. When the aircraft exceeds the speed of sound (approximately 750 mph at sea level), the pressure waves combine to form shock waves, which are heard as a sonic boom when they reach the ground. The idea of modifying aircraft shape to reduce the sonic boom is not new -- in 1986, an engineering professor in Cambridge, England, was awarded a patent for a modified aircraft configuration that would address the problem. "You need an aeroplane that doesn't disturb the air very much because disturbances cause resistance to motion, which produces the sonic boom," said Prof. John Ffowcs Williams, winner of last year's prestigious Sir Frank Whittle Medal. "I envisaged an aeroplane making destructively interfering waves, a double flying wing in fact ... The upper and lower surfaces of the wing assembly would be formed so that the airflow over them is straight and smooth. It would create no waves as it travelled, eliminating or at least minimising the sonic boom." Sounds a bit like a supersonic LongEZ -- maybe Prof. Ffowcs Williams should get together with Burt Rutan.