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Aviation History
2004
2004-09 - 2001.PDF
M1.8. In comparison, Gulfstream's sub sonic G550 weighs in at 41,300kg and with the same 1,830m take-off run can carry eight passengers 12,500km at M0.8. The QSJ is a big aircraft - 42.7m long, with a span of 30.5m wings forward and 18.3m wings aft. The G550 is 29.4m long with a 28.5m span. The cabin is Gulfstream II size, and therefore substan tially shorter than the G550's. The QSJ needs 38,0001b (170kN) of take-off thrust - compared with the G550's 30,8001b - 18,0001b of transonic acceleration thrust and 12,5001b of cruise thrust at M1.8. Gulfstream is aiming for airport noise per formance lOdB below Stage 4, and an engine overhaul interval of better than 2,000h, compared with 7,000h for the G550's Rolls-Royce BR710s. High sticker price The QSJ price goal is $70-100 million, or roughly twice the cost of a G550. Despite this high sticker price, two Gulfstream market assessments have identified a "con servative" market for 180-350 aircraft. Independent market surveys have esti mated the market at 300-400 aircraft. A big driver of SSBJ market optimism, given the likely pricetag, is the perceived demand for fractional ownership. Fractional operator Netjets makes no secret of its enthusiasm for an SSBJ, citing the popularity of its M0.92 Cessna Citation Xs. Netjets feels a non-stop trans-Pacific range of at least 8,800km is a must for a supersonic business jet. The company believes a Citation X-size cabin, although smaller than the Gil size assumed by Gulfstream, would be acceptable for flights of less than 5h and would make a trans- Pacific aircraft more feasible. Netjets says several long-time share owners have indi cated "extreme interest" in paying $10 mil lion for an eighth share in a Ml .8 SSBJ with 9.250km range and Citation X-size cabin. At the 200h/year an eighth share would buy, cost/hour would be under $25,000 for factional versus $55,000 for full ownership, Netjets estimates. This would make owning an eighth share in an SSBJ about as expen- Variable sive as a quarter share in a Gulfstream G200 geometry super mid-size business jet, Netjets points provides out. This helps explain the attraction of flexibility but fractional ownership to SSBJ proponents, adds but again supersonic cruise over land is complexity required for the market to materialise. to the QSJ In addition to Gulfstream, Boeing, Cessna, Dassault, Raytheon and Sukhoi have expressed interest in developing a supersonic business jet - although most talk in terms of co-operating with other manufacturers as development costs are likely to exceed $1 billion. Lockheed Martin's Skunk Works says it has already "closed the design" on a low- boom supersonic business jet, but the com pany shows little intention of proceeding with commercial development. Asked about its plans, Lockheed Martin says "the government is our customer" and points to the lack of a current military requirement for a low-boom supersonic aircraft. Despite this, the company has competed consider able design work, including windtunnel testing, on an SSBJ. Lockheed Martin's SSBJ is a joined-wing Lockheed aircraft, with a bracing tail allowing use of Martin's a long-chord, highly swept wing with joined-wing underslung engines. The bracing tail, design which connects the tip of the fin to the distributes wing at mid-span and supports the engine lift and area nacelles, allows a configuration that dis- to minimise tributes lift and area so as to minimise sonic boom sonic boom, but which would otherwise be-too flexible and prone to flutter. The design also features supersonic natural laminar flow, to reduce drag, and wing shaping to recover nacelle pressure drag. The Skunk Works' SSBJ is 39.6m long, with a maximum take-off weight of around 65,000kg. Construction is conven tional, and the engine inlets simple, for low cost. The boom signature is designed to resemble a sine-wave. Lockheed Martin believes it can reduce boom pressure at audible frequencies by 30 to 100 times, and that the perceived boom loudness will be well within acceptable limits at one SBJ flight a day and still within the region of acceptability at 10 flights a day. Pros and cons A 2003 study by Raytheon Aircraft for NASA Langley highlighted the advantages and disadvantages of low-boom design. Two aircraft were designed for the same mission, to carry six passengers 9,250km at Ml.8 from a 1,830m take-off. One was con strained to have a boom initial overpressure of just 1.95kg/m2. Whereas the high-boom design came in at 46,000kg take-off weight, and was 40.7m long with a 19.2m span, the low-boom design weighed in at 54,000kg, with a 50.4m length and 21m wingspan. As weight usually equals cost in aircraft, the high-boom design looks to have an advantage until the restriction on super sonic overland flight is factored in. Forced to fly subsonically over part of its route, the aircraft's range and average speed decrease while its mission duration and operating costs increase, limiting its useful ness and challenging the business case. Raytheon concluded that a supersonic business jet is technically achievable given reasonable progress on key technologies over the next decade, and that the size and weight consequences of a low-boom design are small relative to the utility gained by being able to fly supersonically over land. But, the study warned, the definition of regulatory requirements allowing super sonic overland flight is "imperative". • 34 12-18 OCTOBER 2004 FLIGHT INTERNATIONAL www.flightinternational.com
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