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Quiet Supersonic Platform (QSP)

The Quiet Supersonic Platform (QSP) program was directed towards development and validation of critical technology for long-range advanced supersonic aircraft with substantially reduced sonic boom, reduced takeoff and landing noise, and increased efficiency relative to current technology supersonic aircraft. DARPA initially identified three potential military roles for quiet, efficient supersonic aircraft: a reconnaissance vehicle, a medium bomber, and a high-speed transport that could quickly deliver vital spares and other equip-ment to forward-operating locations (the function most related to an SSBJ).

Improved capabilities include supersonic flight over land without adverse sonic boom consequences with boom overpressure rise less than 0.3 pounds per square foot, increased unrefueled range approaching 6,000 nmi, gross take-off weight approaching 100,000 pounds, increased area coverage and lower overall operational cost.

The vision of the DARPA QSP program was to foster the development of new technologies sufficient to mitigate sonic boom to the point that unrestricted supersonic flight over land was possible. The program was designed to motivate approaches to sonic boom reduction that bypass incremental "business as usual" approach and was focused on the validation of multiple new and innovative "breakthrough" technologies for noise reduction that can ultimately be integrated into an efficient quiet supersonic vehicle.

Highly integrated vehicle concepts will be explored to simultaneously meet the cruise range and noise level goals. It may be possible to meet DARPA's target for the sonic boom by changing the shape of the aircraft, and without using exotic technologies such as plasmas. The idea was not to eliminate the pressure wave but to change the normal 'N-wave' profile of the boom to a smooth hump, removing the rapid pressure rises at the nose and tail of the aircraft. Advanced airframe technologies will be explored to minimize sonic boom and vehicle drag including natural laminar flow, aircraft shaping, plasma, heat and particle injection, and low weight structures.

Although QSP's origins were linked to plans for a supersonic corporate transport, DARPA regards it as a dual-role program. The QSP technology could lead to an efficient, heavy-payload, long-range supersonic bomber.

The initial Quiet Supersonic Platform (QSP) constracts were awarded to Northrop Grumman, McDonnell Douglas and Lockheed Martin Corp. on 09 November 2000.

On November 7, 2000, Northrop Grumman Corporation's Integrated Systems Sector (ISS) was awarded a contract by the U.S. Defense Advanced Research Projects Agency (DARPA) for Phase I system integration studies and technology development for the Quiet Supersonic Platform (QSP) program. The one-year contract was worth up to $2.5 million. This win builds upon the results of the future strike aircraft study completed for the Air Force. The future strike aircraft study helped refine requirements for the type of aircraft platform, weapons and technologies for future strike capability. Northrop Grumman will work with government laboratories, universities and other industry participants to explore breakthrough technologies, unconventional design approaches and unique systems solutions.

DARPA selected GE as the engine contractor for QSP, with work focused on a variable-cycle engine. Compared with existing propulsion technology, it was 20 per cent more efficient in the cruise and weighs one-third less because of its simpler nozzle. Using Euler codes, Eagle Aeronautics completed a detailed study in early March 2001 defining the shape of the equiva-lent area distribution for modifying the front portion of an F-5E (while staying within the overall length and width of an F-5Fs forebody). CFD analysis indicated this loft would generate a flattop signature from 30,000 feet at Mach 1.4.

In September 2002 Northrop Grumman Corporation's Integrated Systems sector unveiled a design for an efficient and capable long-range supersonic cruise aircraft that would operate with a less intense sonic boom. The design, or "preferred system concept," which includes variants for a long-range military strike aircraft and a civil business jet, was part of Northrop Grumman's work under the Defense Advanced Research Projects Agency's (DARPA) Quiet Supersonic Platform (QSP) program. QSP was focused on the validation of multiple breakthrough technologies to enable such aircraft.

On August 27, 2003, the Northrop Grumman-led sonic boom team demonstrated for the first time in flight that modifying the aircraft's shape can lower the intensity of its sonic boom. The tests were conducted on the same supersonic test range where Chuck Yeager first broke the sound barrier nearly 56 years earlier. The flight tests validated a technology that could lead to unrestricted supersonic flight over land.

Northrop Grumman conducted the Shaped Sonic Boom Demonstration at NASA's 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 while sensors on the ground and in other aircraft measured intensity of the shock waves created by the plane. Shortly thereafter, an unmodified F-5E flew supersonically through the same airspace. The data comparison of the two aircraft signatures clearly showed a reduction in the intensity of the sonic boom produced by the modified F-5E. An identical test performed later that day confirmed the original results.

Northrop Grumman's QSP preferred concept, which culminated the company's work in Phase I of the QSP program, incorporates dual-use technologies in a design relevant to the military strike and business jet applications. In Phase II, Northrop Grumman was focused on maturing the military design and validating the key integration technologies.

QSP targets include a low sonic boom signature of 0.14 millibar (0.3lb/ft2), a range of 11,100km (6,000nm), and a maximum cruise speed of Mach 2.4. The vehicle, weighing around 45,400kg (100,000lb), would also have a payload of around 9,080kg, and 7.5 thrust-to-weight ratio engines with a thrust specific fuel consumption (TSFC)of 1.05. Target cruise lift/ drag ratio was 11. The dual relevant approach meant the design can accommodate either two side-by-side, 8.3m (27.3ft) long weapons bays, or a 6.9m long passenger cabin.

The design called for a joined-wing aircraft that was 156 feet long with a wingspan of 58 feet. It features a top-mounted, active isentropic air inlet, extensive laminar aerodynamics and wings with an adaptive leading edge. The preferred concept met DARPA's QSP goals of 0.3-psf initial boom overpressure (approximately seven times lower than that of current commercial supersonic jets), a speed greater than Mach 2 (twice the speed of sound) and a range of 6,000 nautical miles.

Northrop Grumman worked with Raytheon Aircraft Company, Wichita, Kan., its principal subcontractor during Phase I, to explore synergies with the civil sector. To evaluare the dual relevance of these technologies, Raytheon Aircraft designed the variant for the civil business jet, while Northrop Grumman designed the military long-range strike variant.

In addition, under a shaped sonic boom demonstration project of the QSP program, Northrop Grumman Integrated Systems has successfully completed a critical design review with DARPA, an important milestone in preparation for the first-ever flight demonstration of a sonic boom mitigated by airframe shaping.

If the project continued, an X-plane could fly as early as 2006, and technology would be ready for a full-scale development program to start in 2008. Of corse, none of this happened. Even so, the QSP participants had learned much and documented a great deal of data that could be of potential value in the future. The program had explored and evaluated a wide range of cutting-edge technologies, advancing the state of the art in aeronautics, propulsion, and related fields.

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