At the conclusion of the tests in 2007, Gulfstream proclaimed the Quiet Spike trials a success, even going as far as to say that the demonstrations moved the company “one step closer” to the development of an SSBJ. But the trials proved only that the Quiet Spike could successfully extend and retract as the engineers hoped, not that they made any difference in the supersonic noise signature. That’s because Gulfstream and NASA didn’t specifically test whether the apparatus mitigated the sonic boom — and, in fact, NASA scientists say it couldn’t have done so because an otherwise stock F-15 is in no way designed to be quiet at supersonic speeds.
Today, a small number of startup firms and government research projects are seeking to advance the SSBJ discussion. One of the most well-known is Aerion, the Reno, Nevada-based technology company founded by Texas billionaire Robert Bass. Aerion has been doing research into the design for a 12-passenger SSBJ that would be capable of flying at nearly twice the speed of sound. But rather than building an airplane on its own, Aerion’s goal is to partner with one or more established OEMs, which would be tasked with certifying and producing the airplane.
Aerion has never focused specifically on quiet supersonic technology, preferring instead to refine its patented natural laminar flow wing technology, which it says can significantly reduce drag. Because of the performance gains, Aerion foresees its SSBJ being powered to Mach 1.6 by a pair of off-the-shelf Pratt & Whitney JT8D turbofans, the same engines that have powered commercial airliners, including the Boeing 727 and the McDonnell Douglas DC-9.
The company is now conducting flight tests with NASA at Dryden on an F-15 test airplane, with a goal of determining future required airfoil manufacturing standards.
Far more ambitious plans have been revealed by HyperMach Aerospace, which announced at last year’s Paris Air Show its plans for a 20-seat SSBJ dubbed the SonicStar. The company claims the airplane will be capable of flying at Mach 4 from New York to Sydney in four hours with a “minimal” sonic boom. How might this be possible? Well, when you’re a company with the word “hype” in its name, you can pretty much make any claims you want to, but here’s what HyperMach says: The sonic boom of the SonicStar jet will be minimized by an electromagnetically induced plasma wave that “absorbs” supersonic pressure waves (don’t laugh too hard — it’s theoretically possible, and NASA is looking into this technology). The airplane itself would be constructed of alloyed titanium, “nano-carbon” composites and thermoplastics — all required materials because of the extreme heat any flight at Mach 4 would generate.
The other key enabling technology of the SonicStar is its H-Magjet 4000-X series engines, under development by Portland, Maine-based SonicBlue, a sister company. Not a lot of information about this particular engine is available, although we uncovered this interesting nugget: Oil capacity of the engines will be zero because they will employ “magnetic levitation turbine technology” — and therefore will be totally frictionless.
HyperMach says the SonicStar is scheduled to fly in 2021, with certification possible by 2025. Price has been set at $180 million in 2011 dollars.
Boeing and Lockheed Martin both are participants in NASA’s N+3 supersonic research program, intended to field a commercially viable replacement for Concorde. Two competing proposals are currently under study. Boeing’s Icon II design would carry 120 passengers in a two-class, single-aisle configuration and be capable of cruising between Mach 1.6 and Mach 1.8, with a range of about 5,000 nautical miles.
Lockheed Martin’s Supersonic Green Machine is focusing on the possibility for achieving overland flight with dramatically reduced sonic boom through the use of an “inverted-V” engine-under-wing configuration. Lockheed Martin says it also is investigating other “revolutionary” technologies to help it achieve range, payload and environmental goals.
Clearly, bringing any of the proposed cutting-edge technologies to the design of a future SSBJ will be a challenge. Still, if a future supersonic transport can incorporate even a fraction of the technologies that are being dreamed up in labs and flight testing today, the world of tomorrow could become a much smaller place.