Northrop Grumman’s Integrated Systems sector, in co-operation with the Defense Advanced Research Projects Agency (DARPA) and NASA, has made aviation history by demonstrating a method to reduce the bone-jarring impact of sonic booms. The technology could usher in a new era of supersonic flight.
In flights conducted on August 27 the government and industry team showed that modifying an aircraft’s shape can reduce the intensity of its sonic boom. This theory had never been demonstrated in actual flight.
The technology, being developed as part of DARPA’s Quiet Supersonic Platform (QSP) program, could eventually lead to unrestricted supersonic flight over land.
‘This theory had been demonstrated only in laboratories and wind tunnels,’ said Charles Boccadoro, Northrop Grumman’s QSP program manager. ‘It took a co-operative effort of government and industry to achieve this breakthrough.’
An aircraft travelling 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 flights were conducted at the NASA Dryden Flight Research Center at Edwards Air Force Base, California. An F-5E aircraft with a specially modified nose section flew supersonically through the test range, and sensors on the ground and in other aircraft measured the sonic boom overpressure. Shortly afterwards, an unmodified F-5E flew supersonically through the same airspace. The data comparison of the two aircraft signatures showed a reduction in intensity of the sonic boom produced by the F-5E with a modified fuselage. An identical test later in the day confirmed these results.
‘The demonstration has proven the theory that you can reduce sonic boom intensity by changing aircraft shape, and engineers will be able to study the data to learn more about the effects of aircraft shaping on sonic overpressure,’ said Boccadoro. ‘Based on those studies, an experimental aircraft could eventually be built that will produce a noticeably quieter sonic boom.’
The Shaped Sonic Boom Demonstration (SSBD) program is a $7 million co-operative agreement with Northrop Grumman, DARPA and NASA’s Langley Research Center and Dryden Flight Research Center. Other government and industry entities are participating in the program.
The F-5E’s modifications, which were designed and installed by Northrop Grumman, include a specially shaped ‘nose glove’ and the addition of aluminium substructure and a composite skin to the underside of the fuselage. The US Navy’s Naval Air Systems Command provided the F-5E aircraft.