Technology Update: Little noise from supersonic camps
After a whole lot of fanfare two years ago, when the Aerion and Supersonic Aerospace International (SAI) quiet supersonic business jet (SSBJ) concepts were first announced at the 2004 NBAA Convention, work continues on the development of these and other supersonic business jet designs, albeit more quietly.
Very little has been heard from the Aerion and SAI camps over the last year. SAI, in fact, is not exibiting here at NBAA. Both companies continue to work on refining their designs and seeking commercial partners, they say. Aerion hopes to have something to announce on that front before year-end, according to co-chairman Brian Barents.
Dassault is building on its 1990s design via participation in the pan-European/Russian High Speed Industrial Aircraft Project (HiSAC), a 37-member, four-year consortium of industry, academic and governmental organizations, funded in part by a $17.8 million grant from the European Commission, which is looking into SSBJ development.
While much SSBJ work remains in the camps of the theoretical or wishful thinking, there are recent concrete developments concerning the science involved.
Gulfstream began flying a key component of its potential SSBJ over the summer. Following successful ground and wind-tunnel testing, a Gulfstream “quiet spike” sonic boom mitigator made several successful test flights at NASA’s Dryden base in Mojave, Calif., in July and August, while mounted to the nose of an F-15B testbed. The composite, telescoping spike weighs 470 pounds. The device measures 14 feet during subsonic flight but extends to 24 feet during supersonic cruise.
The patented device is designed to break up the initial “N” wave of a traditional sonic boom into a series of very weak shocks, thus transforming what was once a sharp boom crack into a much quieter sound. The spike produces a boom with smoother and more rounded pressure waves shaped roughly like a sine wave or a sideways “S.” Gulfstream claims the device will enable a Mach 1.8 supersonic business jet to have a boom signature that is only 0.0001 that of the retired Anglo-French Concorde supersonic airliner.
“From the outset it has been understood that the sonic boom must be reduced to acceptable levels before consideration could be given to developing a prototype quiet supersonic jet,” said Pres Henne, Gulfstream’s senior vice president of programs, engineering and test. “These tests are just a few in a series of activities that must be undertaken to prove to numerous regulatory agencies and environmental groups, both at home and abroad, that supersonic flight over land is achievable in a way that will significantly reduce the impact of the sonic boom on people and on the environment.”
Apart from continuing its research projects, Gulfstream has also constructed a supersonic acoustic signature simulator that audibly demonstrates the benefits of its boom mitigation technology. The simulator made its first NBAA appearance last year.
In March, Gulfstream hired Gerard Schkolnik from NASA Dryden to direct its sonic boom suppression research. The quiet spike is part of Gulfstream’s working design for a Quiet Supersonic Jet (QSJ) that features a variable-geometry swept wing (similar to that on the recently retired U.S. Navy F-14) and a pair of center-line engines. The theory is that as the wings sweep back through transonic and into supersonic flight, the spike will extend to disrupt and quiet the attendant sonic boom. It remains to be seen whether a second spike is needed on the aircraft’s tailcone to provide additional boom mitigation.
Gulfstream’s baseline for a $70 million to $100 million QSJ calls for an aircraft that has a range of 4,800 nm, can achieve speeds of up to Mach 1.8 over land, has a balanced field length of less than 6,500 feet, seats eight passengers in a cabin comparable to that of a GII, and weighs less than 100,000 pounds.
Europeans Test SSBJ Concept
While Gulfstream flight tests its supersonic technology, the European HiSAC consortium has broken into project teams to study and evaluate differing designs and technologies even while three of its leading members–Alenia, Dassault and Sukhoi–look to form a more formal alliance and recruit a major U.S. partner. In June, after Alenia Aeronautica made a major investment in the development of Sukhoi’s former Russian Regional Jet, rebranded the Superjet 100, Alenia CEO Giovanni Bertolone said, “We are going to start negotiations on building a supersonic business jet in a few days.”
Sukhoi’s director general, Mikhail Pogosian, was part of the aborted S-21 Sukhoi-Gulfstream supersonic business jet program during the 1980s.
While the Alenia-Sukhoi alliance is concerned primarily with building the Superjet 100 regional airliner, the companies are further studying a joint SSBJ.
The study phase is also where HiSAC appears to be loitering. The consortium has split into three working teams that are evaluating technologies in terms of low noise, long range and low boom. Those three working groups are being led by Dassault, Alenia and Sukhoi, respectively. The baseline HiSAC aircraft borrows liberally from the original Dassault design in that it evolved from a Falcon 50-size, eight-passenger cabin and features the company’s signature three-engine design.
HiSAC is studying a panoply of technologies and designs including synthetic- and periscope-vision systems, variable-cycle engines and various wing designs. Among the latter are delta, high-sweep, high-dihedral, swing-wing and laminar shapes. The initial evaluations are expected to conclude next summer.
The “multidisciplinary optimization” evaluations are being conducted against the initial goal of developing an aircraft that is compliant with ICAO Chapter 4 (Stage 4) anti-noise requirements, meets NOx emission reduction targets and has a reduced overland boom signature, transatlantic range and a cabin that seats eight to 16 passengers.
Over the course of its four-year funding cycle, HiSAC is expected to “provide achievable specifications for an environmentally compliant and economically viable small-size supersonic aircraft.” They would include a roadmap for enabling technologies and continued development, while at the same time recommending changes in related environmental regulations.
As currently constructed, HiSAC will not produce an actual aircraft. Its work is expected to stop just short of the proof-of-concept stage. Proof-of-concept aircraft currently are not in the cards for any of the other supersonic players, either. While flights of the Gulfstream quiet spike are seen as a major development on the road to an SSBJ, the FAA remains reluctant to relax its decades-old ban on civilian supersonic flight over land unless and until an actual aircraft is built.