GRAHAM WARWICK / WASHINGTON DC
A year after news of Boeing's Sonic Cruiser was first leaked, the US manufacturer is working hard to firm up the programme and bring the dream closer to reality
Almost a year after news of Boeing's Sonic Cruiser concept first leaked out, the company is working hard to match the technical and marketing reality with the public relations spin. The unveiling of the Sonic Cruiser, or "Project Glacier" as it was originally dubbed, was at least a year earlier than planned. This move was widely perceived as being in deliberate response to Airbus and its massive A380 public-relations campaign throughout 2000 and early 2001, but Boeing denies any such intent.
"If we had been given a choice we would not have said anything about the Sonic Cruiser until we were ready. It is still a product-development study, but enough information came out about it that it was impossible to keep it quiet," says Boeing. Nonetheless, the US giant has garnered huge amounts of publicity from the project, while quietly shelving its 747X growth plans.
However, as a result of the premature "birth" of the Sonic Cruiser, the company finds itself in an unusual position - it wants to keep to keep the marketing momentum rolling without losing long-term credibility should the concept founder on unforeseen technical or cost difficulties.
Although not yet a firm programme, the Sonic Cruiser project is already taking on a life of its own.
Walt Gillette, a veteran of the 777 programme is Sonic Cruiser vice-president and programme manager, while John Roundhill is marketing vice-president. Gillette, not surprisingly, has a highly positive vision of the future, and he wants the 103rd or possibly 104th anniversary of the Wright Brother's first flight to be marked by the maiden flight of the Sonic Cruiser. "It will take its first flight on 17 December of some year. That would be fitting for an aircraft that has the potential to radically change the way the world flies," he says.
Much of Boeing's Sonic focus is on establishing a platform for the fast-jet market, and convincing their customers of the intrinsic value of speed. "There's no point in Boeing creating the aircraft we think they needed," says Gillette. "That's why we've started the journey by asking the airlines what they want - but this time it's a different paradigm. You now have a new thoroughbred in your stable, and you have to rethink your race team. Airlines now need to think about three speed regimes - the 767, the 777 and the Sonic Cruiser."
Boeing's detailed audit with the airlines on the question was getting under way when the events of 11 September occurred. Since then, Boeing has been forced to revert to in-house analysis while the airlines tend to more immediate priorities. The long-term effect of the September attacks, and the subsequent airline crisis, has been to prompt the development of a more advanced Cruiser for later introduction in 2008, rather than a more basic variant in 2006.
Boeing Commercial Airplanes president Alan Mulally is still voicing strong support for the concept, saying it remains the "number-one" development consideration.
Boeing's basic argument is that airlines and their customers will want the Sonic Cruiser because speed saves time. Although quantifying this presents unique challenges, Boeing says the fundamental operations of a transonic-capable airliner offer instant money-making opportunities on long- and even medium-haul routes.
According to Gillette, "even a 15% increase in speed can mean an extra 20% to 30% utilisation per year." Giving the London-Singapore route as an example, he says: "The aircraft saves about 5h on that kind of sector [round-trip]. Not only does it go faster, but it doesn't need to refuel.
"Imagine having an aircraft that you can fly 25% more per year, as well as at 15% greater speeds. That allows a much higher utilisation and really moves the economics. It will also climb in and out of congested space quicker. We estimate 2.5min to 10,000ft [3,000m] versus 5.5min on a 777, and 16min to 41,000ft against 19.5min to 35,000ft on a 777," he adds. Gillette says the Cruiser will "punch out of airspace and come back and drop back in like a space shuttle. When there are around 500 Sonic Cruisers in service they will operate above the rest of the traffic in what we call 'cruiser space'."
Against this optimistic view the sceptics are finding an attentive audience. Even assuming that passengers are willing to pay a premium for a slightly shorter flight time, most argue that Boeing's cost arguments simply do not add up. The most frequent criticisms include the argument that the higher unit-cost basis of the aircraft is likely to negate any benefits from increased use.
Given the practicalities of slot usage and curfew limitations, the true increase in utilisation could be significantly less than Boeing predicts. Additionally, critics point out that even the crew-savings argument could be flawed should aircrew demand a Concorde-style premium for operating the Sonic Cruiser.
Another area is the overall operating economics. To reach the ambitious direct-operating-cost (DOC) levels predicted by Boeing, most say the technical advances planned for the project will need to be performing to the limit of their efficiency. Preliminary analysis performed by one potential supplier to the programme suggests, for example, that if a heavier 777-style aluminium-based structure (cheaper to build but more expensive to operate) is used instead of the lighter, largely composite material make-up currently planned, DOC could be increased by as much as 12%.
Environmental concerns also remain at the forefront of the studies. Keenly aware of the sensitivity of the subject after an angry open letter from European Commissioner Margot Wallstrom (Flight International, 3 July) over remarks made by Boeing's Harry Stonecipher at the Paris air show in June, the company is working hard to ensure the Sonic Cruiser is as environmentally friendly as possible.
However, even assuming emissions of smoke, carbon dioxide and nitrous oxides can be reduced by advanced combustor designs, Boeing acknowledges that higher speeds will mean higher fuel-burn rates per seat.
Technology focus
The success of the Sonic Cruiser is therefore more dependent on technical achievement than any Boeing commercial programme since the 707. Although many details of the proposed concept are still to be defined, and many more remain confidential, a few are gradually emerging.
Boeing appears to be happy with the basic shape of the Sonic Cruiser, the unusual cranked delta configuration which forms the key to the entire transonic concept. "It's all a question of how we arrange the pieces to allow area rule," says Gillette, who adds that the final shape is "more drawn by evolving up from a subsonic aircraft with a constant cross-section, than coming down from a supersonic design."
The design is designated as a near sonic transport, which uses a classic Sears-Haack distribution to achieve area-ruling below Mach 1.
Although the aircraft will be tested at speeds slightly in excess of Mach 1 as part of certification requirements for its intended cruise speed of Mach 0.98, Gillette insists the Sonic Cruiser is not a would-be Concorde in disguise. "We are looking at Mach 1 and not any faster, but we think in 10 to 12 years the time will come when we believe the technology will be there for a variable supersonic transport [SST]. Frankly, the maturity of the technology is not yet there for a modern Mach 1.4 to Mach 2 SST," he says.
Project Glacier pinpointed Mach 0.98 and Mach 1.02 as the apparent "sweet spots" for a transonic design. Project Yellowstone, another project definition effort grouped under the Project 20XX umbrella set up by Boeing to explore next-generation jet technologies, is meanwhile continuing to focus on an environmentally optimised conventional design in the Mach 0.80 to 0.82 speed range. A further study continues to evaluate a potential Mach 1.2 to 1.4 SST.
"The baseline focus is near the speed of sound, and that was selected based on environmental requirements, particularly sonic boom and other criteria. We did look at faster aircraft, and the data indicates so far that a Mach 1.2 or 1.6 would have a much higher fuel burn. With a twin-engined aircraft you just can't get the non-stop design range we're looking for on this project," says Roundhill.
The Mach 1.02 option "doesn't make a big difference in terms of time. The aircraft is clearly stable at that higher speed, but it would require a bigger engine because the increase in drag is dramatic. We will continue to think about it, however," he adds.
Tests at the University of Washington's low-speed tunnel and Boeing's transonic tunnel confirmed good stability and performance characteristics to Mach 1.08. "It turns out to be longitudinally statically stable. When we looked at the first data we said: 'Wow'. The canard-configured aircraft showed no indication of 'Mach tuck', and pitch characteristics were 'steady and level'. The strain gauges on the wing showed no buffet onset," says Gillette.
As a result of the tests, the canard has moved aft slightly, and the vertical tails have moved outboard and forward. "We looked at the control needs and the interference effect of the canard wake," says Roundhill, who adds that this phase of high-speed windtunnel tests is focused on defining "exact wing-sweep, thickness, canard location and tail location".
As Boeing continues to drive towards finalising definition by the end of March, it has also become increasingly obvious that simple derivatives of 777 engines will not work. "This aircraft has a different relationship of climb thrust to take-off thrust and we found the optimal core size was smaller than the 777," says Roundhill. The findings "argue for a major change, if not a brand new engine", he adds.
Core size is traditionally set by top-of-climb thrust requirements, while noise limits generally govern fan pressure ratio (PR) and bypass ratio, and hence the configuration of the low-pressure spool. Under the standard relationship between these factors, the Sonic Cruiser engine would have a sea-level thrust of more than 100,000lb (445kN). However, the integrated engine configuration of the Sonic Cruiser, added to the 2.8m- (9.2ft-) diameter restrictions of the "semi s-duct" inlet and Boeing's exhaust velocity requirements, means the take-off thrust target is actually nearer 90,000lb.
As a result, all three engine makers are studying new powerplants using core technology derived from their respective 777 engine families. So far, only General Electric has shown its hand by revealing initial details of a "Gen X" study engine using an 80% scaled version of the GE90-115B high-pressure compressor. Tests are due to begin on this core, a nine-stage derivative of the original energy-efficiency engine design developed in association with NASA, around late 2003. To achieve the thrust targets with a smaller diameter fan, GE is increasing fan PR, but believes the shrouding effect of the long-duct nacelle will compensate for the higher noise levels which usually result from such design changes.
Two basic family members are being studied, a 200-seater aimed mainly at transpacific airlines, and a larger version seating between 240 and 250 for transatlantic carriers. Although precise dimensions have not been released, the larger capacity version is estimated to be around 68m long, with a maximum take-off weight of about 281,480kg (620,000lb). The 200-seater will have a range of roughly 13,875km (7,500nm), while the 250-seater will be capable of 12,000km-plus. Boeing's original plan to offer a range of more than 9,000nm was dropped after discussions with the 15 prime airlines involved in helping shape the aircraft.
"We are assuming both baseline versions will grow in range just like the 777. In the past we've always had to work fuel capacity, but we haven't run into that limit yet," Roundhill says.
The all-important question of cross-section is also being narrowed down to a configuration, "which provides room for LD3 (cargo containers) downstairs and 777 comfort upstairs. As it is a longish aircraft we can have a seven-abreast layout in premium economy, and a 777 or 747 business arrangement up front," he adds. This complex cross-section issue has been made even more crucial vis-a-vis the Sonic Cruiser because of the impact of frontal area and finesse ratio on high-speed drag. Boeing's initial findings appear to be a cabin cross-section of about 5.3m in diameter.
Sample fuselage sections are being constructed from composite materials, which Boeing proposes to use to an unprecedented degree on the new project. Roundhill says: "We have a much higher application of composites than the 777 (which was around 11% by weight), because of environmental and economic requirements. The baseline has composites in the primary structure of the tail and the wing, and we are looking at large amounts of composites in the fuselage as well." Gillette adds that "with the production rates we'll see for Sonic Cruiser we will need twice the manufacturing capacity for carbon-composite and resin manufacturing than we have today." Systems technology will place an emphasis on reliability and an increased use of electric power.
Against the backdrop of industry recession, the Sonic Cruiser programme is also providing much-needed inspiration to Boeing and many of its hard-pressed suppliers. Roundhill, recalling a childhood flight in a Pan Am 707 says: "It was majestic, and the magic is still there. With the Sonic Cruiser we're going to find it and bring it back."
Source: Flight International
