Sole sourcing is being debated as the battle to power Boeing's 777-200X/300X moves into a decisive phase


It is time again for cards to be put on the table in the power battle between the industry's "big three"- General Electric, Pratt & Whitney and Rolls-Royce. Unlike previous tussles, the winner - or winners - must develop the most powerful commercial turbofan ever built - a huge engine capable of up to 115,000lb thrust (510kN), and possibly more.

The target for all three is Boeing's long-delayed family of 777-200X/300X ultra-long-range derivatives. All are working on solutions to Boeing's thrust requirements and, particularly in the case of GE, preferably on an exclusive basis. The three each submitted bids to Boeing in late May. Some sources suggest that the results could be announced as early as August. Plans call for work to start on the next generation turbofans as soon as January next year, in time to meet Boeing's service entry date of September 2003.

Deciding how, and what, to bid has not been easy. Faced with the heavy development costs and low returns in the fiercely contested market for the original 777 series, the powerplant makers have watched Boeing move the goalposts several times as it tried to understand the needs of the marketplace. The subsequent delay in committing to a final offering has had numerous repercussions - not all of them bad.

For the engine-makers, it initially provided much-needed breathing space. For R-R, which developed its Trent 8104, it meant frustration as the proposed aircraft grew in size beyond the big engine's design thrust limit. The Trent 8104 therefore became an orphan powerplant and a de facto technology demonstrator. Ironically, some of this technology is finding its way into the Trent 500, now in final development for the Airbus A340-500/600, arch rival to the 777X, as well as R-R's newest large Trent design.


Mixed blessing

For Boeing, the delay has been a mixed blessing. In one sense, the timing was good because the manufacturer was besieged with other, expensive, problems and could ill-afford the cost of another major derivative on top of several other new product development efforts, including the latter models of the 737 Next Generation family, as well as the 717-200, and stretched 757-300 and 767-400.

Added to this came the collapse of the Asian market, the key target for both the 777-200X and -300X. The bad side of the delay for the US manufacturer is the rapid launch and growing market share of the A340-500/600. Boeing's early lead has evaporated, and, in the current schedule, the earliest the 777X will enter service is mid-2003, or roughly the same time as its Airbus rivals.

As envisaged, both the 777-200X and -300X versions will be offered with a maximum take-off weight of up to 750,000lb (340t), requiring engines of at least 110,000lb thrust. Studies of a thrusting auxiliary power unit, which briefly preoccupied Boeing as an alternative to a new breed of main engines, have been dropped after airline concerns over complexity and higher maintenance costs.

The -200X will be capable of seating 301 in a typical tri-class layout. It is designed to have a range of 16,300km (8,800nm). The longer -300X, by contrast, will have three-class seating for up to 359 passengers and a range capability of around 13,400km. Boeing says: "At the moment, we don't know which one will launch first. But whichever it is, the first will be offered for entry into service by mid-2003, with the second version following four to six months later."

GE has come full circle with the GE90 and is vigorously pursuing the 777X market. The move, begun quietly in the middle of last year, dramatically reversed its earlier retrenchment on the GE90. In 1997, it had written off the engine's development costs and stopped all but background study work on significantly higher thrust versions.

Pushed at the highest corporate levels by GE chairman and president Jack Welch and GE Aircraft Engines president Jim McNerney, the GE90 programme is in the midst of an aggressive revival. Based partially on upgrades and improvements developed as performance improvements for the GE90-90B and forthcoming -94B engines, GE is preparing a raft of new technologies to support a growth engine which it has dubbed the GE90-11XB.

GE will be ready to "pull the trigger on the growth programme in the first quarter of 2000 if we have a business agreement with Boeing", says Dick Ostrom, manager of GE90 advanced programme integration. Launch would be followed by 24 months of development and testing, followed by a 12-month flight certification programme with Boeing prior to entry-into-service in mid-2003. The thrust range of the bigger engine will be between 110,000lb and 115,000lb, says Ostrom who adds that GE engineers are "on the edge of our seats because we are not sure what Boeing will do with the aircraft. It does appear to be certain it won't be less than 110,000, and maybe 112,000, but it will probably be somewhere between 110,000 and 115,000."

Six main enabling and risk-reduction technologies are in development to support the growth plan. The first and foremost of these is the three dimensional (3D) aerodynamic high pressure (HP) compressor. Developed relatively recently for the -94B engine, on which it will first enter service, the advanced HPC design uses 3D aerodynamics and advanced clearance control optimisation to produce up to 20íC additional exhaust gas temperature margin, and the bulk of a 1.7% improvement in fuel consumption. "Advanced 3D aero is one of those technologies that we need to enable growth to 110,000lb thrust and beyond," says Ostrom. "It is an enabling technology and it is a fully committed programme."

key enablers

Other key enablers include a toughened composite for the fan blades, which themselves are expected to increase in diameter from 3.1m to as much as 3.3m. The toughened composite brings a higher fan speed capability, says Ostrom. The company is studying the use of "Z-pins" to reinforce the blades in a similar way to the reinforcement of concrete with metal bars. The Z-pins, or reinforcing pins, will be driven through the blade material perpendicular to the layers of composite ply. "The pins could be carbonfibre or titanium," says Ostrom, who adds that tests on sample blades begins this June at Wright Patterson AFB, Ohio. The Z-pin concept is an extension of the stitch-like reinforcing technique used for the leading edges of the titanium-sheathed blades.

The fan mid-shaft is also being strengthened with stronger material to handle higher torque loads. "It will allow us to get the torque for the low pressure [LP] turbine transmitted to the fan and booster. We identified the chemistry for this stronger steel in late 1996 and we are working through a series of machining trials. We are in the process of testing the material from a full-scale melt. So the bottom line is that we will have checked the manufacturability and will have it all established by January 2000," says Ostrom.

A load reduction device (LRD), being investigated for the CMF56 as part of the TECH56 technology initiative, is being examined as a major weight-saving option for the GE90-11XB. A rig test "confirmed that it did reduce dynamic loads that were transmitted to the engine frames and case". The LRD reduced loads by 50%. It acts similarly to the fuse pin in an aircraft pylon by shearing at a pre-set stress level. The shear point is at a flange aft of the number one bearing support housing. It effectively disengages the fan from the rest of the engine in the event of a blade-off, or other severe vibratory condition.

Maturing technology

The LRD technology is expected to be mature at the completion of tests in the third quarter of this year. Another advance due to become ready for use by the same time is dubbed the 'low solidity aerofoil" LP turbine (LPT). This advanced design reduces the blades and vanes in the LPT by 20% to 25%, but without reducing efficiency. "The LPT module is therefore smaller and weighs less, and has lower maintenance costs," says Ostrom. "We are in the process of running a rig test at the Evendale LPT research site and should complete performance verification in the third quarter of this year." Three-dimensional aerodynamic design techniques are also being applied to the HPT, and tests to confirm the performance of these changes will be completed by this year's end.

This August, Korean Airlines will accept the first of three 777-300s powered by the 98,000lb-thrust PW4098 engine, the most powerful commercial engine yet to enter service. Flight tests are "on schedule", says Bob Leduc, P&W executive vice-president engine programmes. "The engine has been put through some very tortuous manoeuvres and it hasn't hiccupped once. Hopefully, we will get aircraft certification in the July timeframe."

Leduc admits that the programme is running about a year behind schedule. This, together with the engine company's apparent fixation on the PW6000 at the lower end of the thrust range, was enough to convince many that P&W was not in the running for the higher-thrust 777X engine competition. According to Leduc, this is "misinformation". P&W submitted a bid to Boeing on around 26 May.

The biggest shock is what sort of engine it has submitted for Boeing's consideration, departing from the standard PW4000 derivative path and branching out with a virtually all-new engine based on core technology scaled up from the PW6000. "It is time to come out with a whole new generation of engine. You've got to remember that every engine out there is around 15 years old," says Leduc, who adds that "everybody expected us to come out with another PW4000 derivative".

The STF, or study turbofan, as it has been unofficially known, is also a departure from P&W's new engine development strategy for the next century. Although this is also based on the PW6000, the strategy soon diverges with thrust growth. The original plan was to develop the geared fan PW8000 from the PW6000. To follow was a series of geared fan engines which would eventually become the modern successors to the PW2000 and PW4000 family. This overall strategy appears to still be in place, however as far as the 777X was concerned, time was critical and P&W did not have enough to allow the geared fan concept to play out at the very highest thrust ranges.

On the other hand, it has recognised the need for something radically new and expects to spin other new generation powerplants off the back of the STF. "I can't afford to look at a singular investment with the 777X," says Leduc.

The new engine will be dominated by a large, 3.2m-diameter fan. Like the current 2.8m-diameter unit on the PW4084/98, the new fan will consist of hollow titanium blades. Aft of the fan will be a four-stage LP compressor, in place of the seven-stage unit on the PW4098, or six-stage LP compressor on the PW4084/90. The core will be made up of an eight-stage HP compressor, instead of the standard 11-stage unit, and a two-stage HP turbine. The LP turbine module in the engine's aft will consist of a six-stage unit, rather than the seven-stage unit in the PW4084.

Like GE, Leduc believes Boeing will be "driving for a conclusion sooner, not later". He adds: "We have to pull the trigger around next January to meet the entry into service target of mid-2003." As for exclusivity, Leduc's attitude appear similar to that of R-R - due partly to P&W's large market share and partly because of lessons learned with the A340-500/600 experience two years ago. "We had the same discussions about exclusivity on the A340 and looked what happened there. The guys who demanded exclusivity lost, and the ones that didn't got exclusivity de facto."

R-R pins its hopes on a natural progression of its successful Trent derivative strategy to win it a place on the 777X. It is using the Trent 8104 to provide technology for the proposed Trent 8115 model. A key new technology is the swept fan which enables more airflow to be pumped through the engine without a huge increase in drag-creating diameter.

Trent Strategy

If nothing else, the 8104 experience appears to have infused R-R with high confidence in its ability to develop a low-risk solution for the 777X's higher thrust needs. The first 8104 ran in December and the second engine is due to run in July. The initial engine was given a "clean bill of health" after tests and, in terms of performance, the company says it is "pretty damn pleased with the outcome. Core capacity was effectively higher than anticipated. That is good news in that Boeing has moved on in their aspirations from 320t and 334t take-off weight, to 340t and maybe more.

"Inevitably, that has forced us to increase the thrust of our engine, which was particularly driven by the 777-300X. That's why we have come up with the 8115," R-R says.

R-R has taken the core of the 8104 and scaled it 2.5% geometrically and by around 5% aerodynamically. It has also increased the diameter of the fan from 2.8m to 3m, while also introducing the swept blade. The reasons for the size increase are "both thrust and noise", says R-R, particularly as Boeing is expected to aim the 777X at more stringent levels. "The engine looks very good, and gives the aircraft performance as good as anything else," says the company. R-R says the new engine is also expected to give good take off performance at critical limited runways, such as Los Angeles International.

The engine will otherwise retain the overall configuration of the Trent 800 family with an eight-stage intermediate pressure (IP) compressor, a six-stage HP compressor, and a single-stage HP turbine and IP turbine. The engine will also retain the five-stage LP turbine of the Trent 800, but it will have fewer aerofoils.

The 8115 test programme will incorporate a 2,000-cycle extended range twin operations (ETOPS ) phase. "We must have 207min ETOPS clearance 'out of the box'. With a current 12-month rolling average of zero in-flight shut downs on the current engine we are well placed in the ETOPS arena," says the company.

As far as exclusivity is concerned, R-R says it is "happy to compete on traditional terms and we've made that very clear to Boeing. With our customer base, they want an opportunity to select a Rolls-Royce engine. It could be quite dangerous to set off on an exclusive solution just to suit one or two customers in the near term, and compromise the longer term" it adds.

With the bids in, it seems the 20th century's final power struggle is truly under way.

Source: Flight International