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Shaped Sonic Boom Demonstrator (SSBD)

NASA partnered with others to conduct an innovative flight research program using what was named the Shaped Sonic Boom Demonstrator (SSBD), a Northrop Grumman F-5E Tiger fighter jet modified with a larger nose. This modification, which made the front of the F-5E somewhat resemble a pelican's beak, was carefully shaped to change the pattern of shock waves it would generate while flying faster than the speed of sound. The theory behind the nose job was that the increased airplane volume at the front of the SSBD would result in less intense sonic booms heard or felt on the ground below.

The earliest efforts on sonic boom minimization through aircraft shaping began decades ago with the work of Jones [Lower Bounds for Sonic Bangs. Journal of the Royal Aeronautical Society, Vol. 65, June 1961, pp. 433-436] and Carlson whose studies of the effects of airplane-configuration effects using the Whitham far-field solutions of sonic-boom theory led to the definition of an equivalent-body shape that would produce an N-wave signature having a lower-bound overpressure and impulse. Continuing efforts by Carlson4 pointed out some important effects of configuration arrangement on sonic boom characteristics. Follow-on sonic boom minimization investigations by McLean indicated that for large slender airplanes during the climb-to-cruise phase of flight, non- N-wave near-field sonic boom signatures exist which depend on the detailed geometry of the airplane and that these non-asymptotic effects could be very important compared to the asymptotic far-field N-wave solutions.

Both McLean and Shrout, Ferri and Ismail and later Ferri suggested that changes in the airplane configuration relative to its volume and lift distribution could be used to provide for a signatures of greatly reduced overpressure as compared to an N-wave. Further evidence of this concept was provided by Hayes et al, who showed that in a real atmosphere the signature shape will freeze well before it reaches the ground from high altitudes. George and Seebass [Sonic Boom Minimization Including Both Front and Rear Shocks, AIAA Journal, Vol. 9, No. 10, Oct. 1971, pp. 2091-2093] provided a mathematical foundation for many of these ideas and developed a theory for an isothermal atmosphere that yielded an optimum near-field signature that minimizes maximum overpressure of flat-top and ramp-type signatures on the ground. Although mitigation of the sonic boom via specialized shaping techniques was theorized decades ago, until now, this theory had never been tested with a flight vehicle subjected to actual flight conditions in a real atmosphere. In July 2001, as mentioned above, DARPA awarded the NGC-led team a cooperative agreement to design, modify and fly an F-5E aircraft with the goal of providing the first-ever in-flight demonstration of an aircraft that has been modified to produce a shaped sonic boom pressure signature that persists through the real atmosphere to the ground.

The F-5E aircraft was made available by the U.S. Navy under a Cooperative Research and Development Agreement (CRADA) with Northrop Grumman [NGC]. The new components required for the specially shaped structure were designed, fabricated, and partially assembled at NGCs El Segundo, California facility. Final assembly and installation of the hardware took place at NGCs St. Augustine, Florida facility where the company performs F-5 depot work for the U.S. Navy. The modifications consisted of a new longer nose and the addition of aluminum frames, bulkheads and composite skin panels attached to the underside of the fuselage to create the required shape

The demonstrative success, which occurred on 27 August 2003 with repeat flights in the supersonic corridor at Edwards Air Force Base, was a critical milestone in the development of next generation supersonic aircraft that could one day fly unrestricted over land and help usher in a new era of time-critical air transport.

During a series of some 30 tests flown in August 2003 and January 2004, data gathered by airborne and ground sensors of the SSBD in flight proved the theory was well sound, and that additional research in the future could enable the long-sought realization of commercial supersonic flight across the United States. Indeed, that research continues as NASA and its research partners explore fresh ideas and design new tools for making supersonic flight quieter.

The SSBE (Shaped Sonic Boom Experiment) was formerly known as the Shaped Sonic Boom Demonstration, or SSBD, and is part of DARPA's Quiet Supersonic Platform (QSP) program. On August 27, 2003, a Northrop Grumman - modified U.S. Navy F-5E aircraft demonstrated a method to reduce the intensity of sonic booms. NASA's F-15B research testbed jet from Dryden flew in the supersonic shockwave of the F-5E in support of the test.

The project was an effort to lessen sonic booms. During the recent demonstration, an F-15B flew behind the modified F-5E sonic boom demonstrator aircraft in order to measure the aircraft's sonic boom characteristics. Flying behind and below the F-5E, and using its specially-instrumented nose boom, the F-15B recorded many shockwave patterns from the F-5E at various distances and orientations from the aircraft.

Pressure measurements obtained on the ground and in the air confirmed that the specific modifications made to a Northrop Grumman F-5E aircraft not only changed the shape of the shock wave signature emanating from the aircraft, but also produced a flat-top signature whose shape persisted, as predicted, as the pressure waves propagated through the atmosphere to the ground. This accomplishment represents a major advance towards reducing the startling and potentially damaging noise of a sonic boom.



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Page last modified: 29-01-2017 17:00:02 ZULU