Boeing studies 'mini 777' as Sonic Cruiser alternative

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Boeing is pitching its ‘super efficient airplane’ concept to airlines as a long-range 200-250-seater that would be capable of matching the seat-mile operating costs of the larger 777 family.

The US manufacturer is studying the conventionally configured “reference aircraft” alongside three versions of the Sonic Cruiser and could make a decision on which aircraft to launch in 2003 if there is sufficient airline interest, Sonic Cruiser vice president and programme manager Walt Gillette said in a conference call with journalists in Asia today. Entry into service is tentatively targeted for 2008.

The super efficient aircraft would fly at approximately the same speed as today’s 777 but incorporate the advanced “enabling technologies” under study as part of the Sonic Cruiser project.

Boeing is currently trying to understand whether airlines want a 250-seater that could cruise at speeds of up to Mach 0.98 – saving approximately 1hr per 3,000nm (5,500km) flown – at approximately the same seat-mile cost as today’s 767, or the efficiency optimised aircraft that would be 17-20% cheaper to operate, says Gillette.

“We need to discuss the value of speed,” says Gillette. “What we are doing now is having a dialogue with the airlines about which way we should do this.”

The four key enabling technologies identified by Gillette are advanced computational fluid dynamics (CFD), composite and aluminium materials, systems and engines.

Contemporary CFD technology enables designers to predict aerodynamic performance with an accuracy in excess of 99%, he says. Meanwhile “very great competition” is developing between producers of aerospace composites and advanced aluminium alloys, offering much lighter materials than those available when the 767 was designed.

Thirdly it is now possible in principle to eliminate an aircraft’s engine-driven bleed air system altogether and rely solely on electrical and high-pressure (5,000psi) hydraulic power transmission. Electrical power would come from an engine shaft-mounted generator rather than via a step-aside gear box.

Finally all-new engines should provide further efficiency gains, says Gillette. The 767’s current powerplants are “one-and-a-half generations old”, with each generation typically yielding a “5-6%” improvement in efficiency, he believes.

The three Sonic Cruiser configurations under study include the now familiar canard-equipped configuration, and two “mid-wing” alternatives with no canard and conventional empennages that can cruise at the same high Mach 0.98 speed range.

One mid-wing design has aft-mounted engines similar to the original Sonic Cruiser design, while the alternative has forward-mounted engines on nacelle struts and significantly more area-ruling of the fuselage.

“All three of these will do the Sonic Cruiser mission,” says Gillette, which he defines as operating at Mach 0.95-0.98 over a range of 7,500nm.

The super efficient aircraft would meanwhile offer the same speed, range and passenger comfort as the 777, but at a 17-20% lower seat-mile operating cost compared with the 767 and comparable to that of the larger 777. “Obviously we would be looking at further enhancements over that design,” he says.

It is currently optimised for long-range missions but “would also do very well at the short ranges”, says Gillette. However it would not necessarily replace the existing 757 and 767 families.

Boeing last month hosted potential customer airlines in Seattle. “We are all thinking about what would be the best way to move forward,” he says. “All of the carriers expressed interest in both choices. I don’t believe anyone has made a firm decision.”