Boeing's sonic cruiser could provide the 777 engine makers with a valuable new market outlet
Guy Norris / Los Angeles
For most of the past decade, the "big three" engine makers have asked themselves if they will ever make money on the remarkable powerplants each has developed for the Boeing 777. Now, in an ironic twist, Boeing is dangling the carrot of a new project which has only been made feasible by the leap in engine thrust size achieved with the 777.
Not only is Boeing saying that its sonic cruiser concept could be a best-seller, but that it may use virtually unchanged 777 engines. As Boeing Commercial Airplanes president Alan Mulally says: "Until we had 777 engines and an innovative design, we couldn't do the sonic cruiser." The company's former vice-president for business strategy and development, Mike Bair adds: "We do not have to change the bypass ratio. It works fine and does not necessarily need new engines."
The impression being created is therefore one of a relatively low-cost derivative being developed, though the true picture is more complicated and, potentially, a lot more expensive. Much depends on the level of technology airlines demand. "Conversations with airlines will revolve around timing versus technology - the payoff for new engines is the time taken to develop them," cautions Bair. The bottom line for General Electric, Pratt & Whitney and Rolls-Royce is, however, a new spin-off market for their costly big fans at a time when nothing else new is on the horizon.
Boeing is actually soliciting engine manufacturer input on three future airline concepts under the umbrella of its "20XX" project. While the sonic cruiser appears to be the leading contender, the other two would still be based around 777-style engine cores. GE says little about the project or its proposals, which it treats as a "commercial black programme". Its sonic cruiser team is sworn to secrecy, but it is known the company's study proposals are all based on the 10-stage high pressure compressor (HPC) of the GE90, or a higher thrust option, the nine-stage derivative HPC of the GE90-115B. The GE90 core has an unprecedented 26:1 pressure ratio, and forms the basis for the newly launched GP7000 family being developed in partnership with P&W.
Elements of the Tech56 "technology stocking" development programme, although aimed at the GE-Snecma CFM56 family, are also expected to feature in the studies, as will advanced technology from the NASA-led Ultra Efficient Engine Technology programme in which GE is a major player. Spin-off Tech56 technology, such as the low-noise chevron nozzle, is already being applied to the latest versions of the CF34 turbofans, and is being proposed for potential CF6 upgrade packages.
Although details remain sketchy, Boeing's three main studies include: the sonic cruiser, a high subsonic transport capable of Mach 0.95 to 0.98; a conventional 200-250-seat replacement for the 767; and a more unusual transonic transport aimed at a Mach 1.2 cruise speed.
With the higher compression ratio core capability for higher thrust requirements in mind, P&W executive vice president Bob Leduc says one study option is "an advanced turbofan, which would be a brand new centreline engine. There is a concept we are also pursuing that we think is novel and may have an application on a higher Mach number aircraft." An initial study is also being proposed which is a relatively simple derivative engine based around the core of the PW4098 developed for the 777-300.
R-R is again relying strongly on its well-honed three-shaft architecture - but with some major innovations, hints Phil Hopton, R-R's director of Boeing programmes. The three main studies include a "777-based offering in Trent 800 style which doesn't quite do it in terms of thrust", a more advanced concept aimed at an entry-into-service around 2008 and what Hopton describes as "the ultimate sort of engine we could do".
Size conundrum
Like the others, R-R faces the conundrum of how to adequately size the engine to meet high take-off thrust without making it too large for the relatively high cruise thrust requirement. At the same time, it must also come up with a concept that allows the same engine to perform as close as it can to a low bypass ratio turbojet in cruise, and yet transform to a Stage 4 capable high bypass ratio turbofan for take-off and landing. "The big issue really is installation," says Hopton, who adds that the large diameter of the 777-style engines and the large high Mach drag these could create are "major issues". At high Mach cruise speeds the engines would be "drinking from a fire hose", he adds.
One of the cleverest and most critical design aspects of the sonic cruiser is the semi-recessed engine installation, and the long duct inlet that feeds it. The resulting installation is thought to borrow design features taken from an amalgam of Boeing combat aircraft including the F/A-18E/F, F-22 and X-32 Joint Strike Fighter demonstrator. The long duct provides a mechanism for controlling the flow to the engine, and also hides the fan face. In a military guise this provides low-observability but, in sonic cruiser mode, it cuts down fan noise making it "extremely quiet", says Mike Bair. The integrated engine installation and nacelle would also be extended aft to allow the fan and core exhaust to be mixed before exiting, further reducing engine noise.
R-R says it is also looking at blow-in and blow-out doors to help control inlet flow at high Mach speeds, and is exploring "more novel ideas like a two-stage fan or even a tandem fan", says Hopton who adds that these are among a "whole host of possibilities". To tailor the engine for higher speeds, R-R is studying variable area nozzles to help optimise the engine cycle for best cruise performance. It also plans studies involving advanced technology being developed for the affordable near term low emissions (ANTLE) engine project. Launched by the European Commission in March 2000 under the auspices of the Efficient and Environmentally Friendly Aero Engine project, the ANTLE engine will be based on a Trent 500.
The advanced version will incorporate a new HPC plus intermediate and low pressure turbines, a low cost turbine rear frame, revised lubrication system and distributed engine controls. The engine will also use a new HP turbine and a dual annular combustor under development at R-R. "We will run a demonstrator engine based on the Trent 500 in 2003, so the timing is about right," says Hopton.
Under the ANTLE arrangement, R-R Deutschland is responsible for the HPC, FiatAvio will develop the intermediate pressure compressor, and Industria de Turbo Propulsores of Spain the low pressure turbine. Other contributors include Eldim, Hispano-Suiza, Howmet, TRW Lucas Aerospace, Calidus and Spain's INTA Institute. Techspace Aero and Volvo Aero are also involved as are the universities of Florence, Italy, and Lulea, Sweden.
Engine exclusivity
Overall targets include cuts in carbon dioxide emissions of at least 10% and in nitrous oxide of 60%, by 2008.
The sonic cruiser, or whatever new platform emerges from Boeing's studies, will create an interesting new dynamic in the tightly contested engine market. There have been no hint of demands for exclusivity on any side, though the recent experience of the 777-200LR and -300ER is bound to haunt both P&W and R-R as they make their pitches to Boeing.
As it stands, the impact of exclusivity on the longer range 777 models has been dramatic for GE. Without this business, GE has 31% of the 777-200/300 market with around 320 engines delivered or on order, compared to a similar number for P&W. R-R holds a 38% of the standard 777 market, and has almost 390 engines ordered or delivered. GE's business on the former 777X models, accounts for a further 98 engines, or 100% of the long-range market.
Perhaps the most important point about the 777 market, from the engine maker's perspective, is its relatively restricted size - just over 1,120 engines so far, not including spares. Although this will undoubtedly grow as the 777 matures, the prospect of another market outlet for the same generation of engines is a welcome prospect.
Source: Flight International
