Northrop Grumman F-5E Modified For Sonic Boom Demonstration Completes First Flight

An F-5E fighter jet with a modified fuselage has completed its initial flight in preparation for a joint government-industry test program to demonstrate the relationship between the shape of a supersonic aircraft and the strength of the sonic boom it creates. The Shaped Sonic Boom Demonstration (SSBD) program is jointly sponsored by the Defense Advanced Research Projects Agency (DARPA), Northrop Grumman Corporation's Integrated Systems sector and NASA Langley Research Center. This program is scheduled to begin in several weeks at NASA's Dryden Flight Research Center, Edwards Air Force Base (CA).

The demonstrations are part of DARPA's Quiet Supersonic Platform (QSP) program, an ongoing effort to identify and mature technologies that could allow military and business aircraft to operate with reduced sonic boom. "Our objective is to show that by modifying the shape of an aircraft, the shape and behavior of shock waves -- and therefore the intensity of a sonic boom -- can be significantly altered," said Charles Boccadoro, Northrop Grumman's QSP program manager.  "This technology could eventually enable unrestricted supersonic flight over land." In the July 24 flight, an F-5E provided by the US Naval Air Systems Command  took to the air for the first time since it was modified for the SSBD. The modifications, performed at Northrop Grumman's St. Augustine, Fla., facility, include a specially shaped "nose glove" and the addition of aluminum substructure and composite "skin" to the underside of the fuselage.  Test pilot Roy Martin reported that performance matched the preflight simulation.

Northrop Grumman will move the aircraft to its facility in Palmdale (CA) for additional checkout flights before the SSBD data-collection flights begin.

An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the waves created by the bow of a ship as it moves through water.  When the aircraft exceeds the speed of sound (about 750 miles per hour at sea level), the pressure waves combine to form shock waves.  The noise heard on the ground as a sonic boom is the sudden onset and release of pressure after the buildup by the shock wave, also known as "peak overpressure." During the upcoming SSBD flight demonstrations, the modified F-5E will be flown through the supersonic corridor at the NASA Dryden Flight Research Center.  Sensors on the ground and in other aircraft will measure the sonic boom overpressure.  Shortly thereafter, an unmodified F-5E will be flown through the same air space, and its sonic boom will be measured. 

By comparing the signatures of the two aircraft, test engineers expect to be able to learn more about the effects of aircraft shaping on the sonic boom. Northrop Grumman has been under contract with DARPA's QSP program since 2000. As part of its work, the company has designed a long-range supersonic aircraft with military strike and business jet variants and validated key integration technologies associated with that design. "Our work on the QSP program builds upon our advanced development capabilities to identify solutions for future aircraft systems," said Boccadoro. "Demonstration of a shaped sonic boom could help usher in a new era of supersonic aircraft."

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