Market research studies predict a worldwide demand for as many as 500 supersonic business jets (SBJ) that can cruise at Mach 1.5 and be bought for about $80 million. Major business-jet companies — including Dassault, Cessna, and Gulfstream — claim to be working on their versions of SBJs, but are reluctant to talk details. Only Bombardier, the Canadian business-jet builder, says it just doesn't see an SBJ in its future. In the meantime, two upstart startups — Aerion Corp. and Supersonic Aerospace International (SAI) — each say they will have an eight to 12-passenger SBJ with a 4,000-nautical-mile range FAA-certified and on the tarmac early in the next decade. Strangely, the two companies are taking almost diametrically opposed paths.
At Aerion, based in Reno, Nev. (aerion.com), engineers are using natural laminar-flow (NLF) wings, a proven engine, and standard airframe design to minimize complexity. This approach should keep the project on schedule and within budget because it presents no need for extensive testing and FAA certification.
The powerplant Aerion picked is Pratt & Whitney's JT8D-219, a jet engine with up to 21,700 lb of thrust. The engine will be modified to put out only 19,600 lb of thrust. It's a member of the JT8D family of engines, which are on nearly a third of the world's commercial airliners. It is also used on military aircraft, including the Joint Stars, Awacs, and KC-125 tankers. The engines are incredibly reliable and have racked up more than half a billion hours of service since introduced in 1964. They have been upgraded and refined for lower maintenance costs and economic performance over the years. Pratt & Whitney will also aid Aerion in designing inlets, nozzles, and nacelles.
The composite-fiber wings will be straight rather than a swept or delta configuration. They will be slightly tapered with a sharp leading edge made of titanium and have a thin, modified biconvex cross section. The wings will weigh 1,900 lb.
The NLF wing design keeps the air next to the wing flowing in smoothly shearing layers rather than letting it get turbulent. At supersonic cruise, for example, laminar flow covers up to 70% of the upperwing surface and up to 100% of the lower-wing surface. Laminar flow lowers viscous (skin friction) drag and improves range and fuel economy. NASA tested and proved laminar flow wing technology worked back in 2000 and Richard Tracy, Aerion's chief technology officer, was involved in that project. Aerion now holds several patents on the supersonic NLF wing.
The NLF wing has roughly the same drag qualities at subsonic speeds as current swept-wing jets, which will let Aerion's aircraft efficiently fly overland routes where supersonic flight is prohibited. In fact, its range is roughly the same — 4,000 nm — at super and subsonic speeds. This means it should profitably handle short and long-haul overland missions. Where legal, it will cruise at up to Mach 1.1 without generating a sonic boom on the ground ("boomless cruise"). If there are no speed restrictions, it will fly at Mach 1.6, a top speed that doesn't require exotic materials to handle high temperatures. The jet will also be set up for efficient cruise at 51,000 ft, the same altitude current business jets use. This simplifies certification and eliminates technical unknowns of flying above that height.
The straight wings will carry full-span flaps on their trailing edges, giving the aircraft an approach speed of 120 knots. This will let the plane operate from runways less than 6,000 ft long.
Current plans call for a 6-ft-tall cabin that accommodates up to 12 passengers in a high-tech style. Reclining seats can be heated or cooled; controls for entertainment and communications slide out of the armrests; and LCD thin-film devices bathe the cabin in soothing colors. The 30-ft-long cabin includes room for a full galley and a bathroom. This could change as engineers trade cabin size for a longer range.
PUSHING THE EDGE
SAI (saiqsst.com), working out of Las Vegas, is designing the Quiet Small Supersonic Transport (QSST) and relying on leading-edge technologies to bring it off. SAI hired Lockheed-Martin's famed Skunk Works to design the basic airframe and shape. Skunk Work plans include a patented inverted V-tail and aerodynamic shaping on the fuselage to minimize the jet's sonic signature. The inverted tail helps support the engines, which are set far back in the fuselage, and adds stiffness to the highly swept wing. Although the design is somewhat radical, SAI is confident it can be built using proven, reliable technologies with no breakthrough materials or manufacturing processes.
According to SAI engineers, the QSST should generate "imperceptible" sound levels when taking off or flying supersonically. The company believes the plane will be quiet enough to get government approvals for "environmentally responsible supersonic flight over populated areas." Studies indicate it will create overpressures of 0.3 to 0.5 lb/ft2. The Aerion design should generate overpressures in the 1.2 to 1.6 lb/ft2 range, almost half that of the Concorde SST.
The QSST will use a delta-canard wing configuration, which performs best at supersonic speeds. When flying at Mach 0.92 to 0.98, for example, the wing is less efficient and range drops by approximately 220 to 3,780 nm.
General Electric, Pratt & Whitney, and Rolls Royce, the leading jet-engine manufacturers, have all proposed engine designs that meet SAI's goals for performance, sound, and emissions. For example, all three say their engine will cruise supersonically without afterburners, be reliable enough to last 2,000 hr between overhauls, and put out the necessary 32,000 to 35,000 lb of thrust.
Both SAI and Aerion estimate their planes will cost about $80 million and be flying operationally early in the next decade.
AERION And OSST: A Head To Head Comparison
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