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Boeing’s NMA Poses Propulsion Puzzle For Engine Makers
02 June 2017

Guy Norris

How will engine makers approach Boeing’s NMA—with a big small engine or a small big engine?

Power Posturing

There will be plenty of traffic between the chalets at this year’s Paris Air Show as engine makers jockey for position in the early contest to power Boeing’s New Midsize Airplane (NMA).

The stakes are high for all concerned. The embryonic Boeing project, unofficially dubbed the 797, is targeted at entry into service around 2025 and almost certainly will be the biggest «must-win» new development airliner program of the first half of the next decade. Strategically speaking, the NMA engine selection campaign is on a par with those for industry-defining propulsion deciders such as the Boeing 737 and 777-300ER. While it is too early to be sure, engine makers also know the winners will be in pole position to power an Airbus response.

History shows there is a long and complicated route to selection and, given the usual 5-6-year gestation period for new propulsion systems, now is the time to begin. Boeing is tipped to follow the 787’s market-driven dual-source model for the NMA rather than go sole-source as it did for the 777X. However, there are uncanny similarities between the present-day race for the NMA and 1999, when Boeing was in the final phases of what became a sole-source engine selection for the proposed 777-200X/300X longer-range variants, which became the 777-200LR/300ER.

Power Points

- NMA thrust requirement estimated in the 45,000-lb. range.
- Boeing’s power requirement is within thrust bracket of existing GE/Safran CFM joint-venture agreement
- Pratt & Whitney sees NMA as opportunity for its first growth GTF application
- Rolls-Royceis likely to offer engine based on the new geared UltraFan architecture
- NMA 2025 entry-into-service target will require new engine testing in 2022–23

The contest for the 777-200X/300X was fierce. Financially hit by the recent costly development of engines for the baseline 777 and Airbus A380, the cash-strapped engine makers were in no mood for another three-way market split. General Electric bid a growth version of the GE90, but only on the condition it was selected as the exclusive engine. Pratt & Whitney, which argued for a downselect to two options, proposed an all-new design based on a scaled-up version of the PW6000. Rolls-Royce, which had built a growth demonstrator called the Trent 8104, was confident of matching Boeing’s growing thrust needs but wary of another expensive market battle.

In the end, GE famously won with the performance promises of the GE90-115 Band a hefty financial package backed by pledges of 777 orders from GE Capital Aviation Services. Yet the engine selection events that came to a head at the Paris Air Show 18 years ago ultimately went far beyond the latest 777. They reshaped the industry, paving the way for today’s widebody teaming of Airbus and Rolls in Europe, and Boeing and GE in theU. S. GE’s selection also further alienated Pratt from the big-engine market and fired its determination to reenter the single-aisle sector by developing the geared turbofan (GTF).

Fast forward to today, and the distant echoes of this long-gone contest are still reverberating as the engine makers begin to shape their campaigns. There is one crucial difference, however, which only adds to the conundrum. The NMA’s outline thrust requirement is in the quirky 45,000-lb. range. In the 1960s, this was prime territory for the first generation of high-bypass-ratio engines such as GE’s CF6-6, the powerplant derived from the Lockheed C-5’s engine that equipped the first McDonnell Douglas DC-10, the Rolls RB211-22B for the initial Lockheed L–1011 and Pratt’s first JT9D-3 for the Boeing 747–100.

But as engine power grew, so did the aircraft, and the thrust sector was largely left behind until a decade later, when a second-generation turbofan series emerged to power the Boeing 757. One of these, the Rolls RB.211–535, was discontinued with the final delivery of the 757 in 2005, while Pratt’s PW2000 turbofan remained in production until relatively recently for the Boeing C-17 military airlifter. In neither case would the technology come anywhere near meeting the tough performance goals required for the NMA, the entire premise for which is anchored in the ability to fly widebody missions at single-aisle costs. The NMA engine specification likely will require high-bypass ratios of 10:1 and above and overall pressure ratios of at least 50:1 at top of climb.

As a result, the new NMA engine is above the current thrust range of the latest single-aisle power plants-CFM’s Leap or Pratt’s PW1000 GGTF-and well below the present generation of widebody production engines such as the PW4000, Trent and GEnx. For GE, the company’s response therefore will be framed within the original CFM joint-venture agreement with Safran Aircraft Engines, which extends up to 50,000 lb. thrust.

Then there is the question of where the engine size fits within the various families of the companies and the CFM joint venture. «You are actually talking about pulling demand down from a Rolls and GE perspective [in terms of the Trent and GEnx families]," says Richard Aboulafia, vice president of analysis at the Teal Group. «However, I don’t see it migrating upward either. So is it a big small engine or a small big engine?»

Boeing’s sole-source engine selection plan worked well for longer-range 777s but is unlikely to be repeated for the NMA. Credit: Joe Walker

For Pratt, the NMA is within reach of growth versions of the geared turbofan, the highest rated of which is the 33,000-lb.-thrust PW1133G for the Airbus A321neo. As for Rolls, the company recently made it clear that its route to the NMA could well include the all-new UltraFan development, a geared-fan engine based on the all-new Advance core. The news, which emerged in April, came as something of a surprise to industry watchers, as Rolls previously had indicated the prime target for the UltraFan would be larger widebodies requiring engines in the 100,000-lb.-thrust range (AW&ST April 17–30, p. 58). However, just as in 1999, all the engine makers come to the NMA contest on the back of very costly developments for other projects. In reality, none has much of an appetite for massive spending on yet another all-new centerline engine. CFM is over the hump on most of its certification work for the Leap family for the Airbus A320neo, Boeing 737 MAX and Comac C919 but still faces huge outlays as it ramps up production. As part of CFM, GE is still in the midst of GE9X development for the 777X, having only relatively recently switched to a focus on production ramp-up and follow-on upgrades for the 787’s GEnx engine.

Pratt’s $10 billion-plus development of the GTF continues to be costly, largely due to a handful of nagging mechanical and production issues. However, the PW1100G-powered A320neo and PW1500G-powered Bombardier C Series fleet is growing, and the user group is expanding as flight tests of the Embraer E 2 and Mitsubishi MRJ regional jets accelerate. Rolls similarly is reducing development spending on its TrentXWB-97 as flight tests of the Airbus A350-1000 accelerate and is seeing a slowing cost trajectory on the Trent 7000 for the Airbus A330neo and closely related Trent 1000 TEN, now in flight-test on the 787–10.

However, a concern for Rolls remains the longer-term impact of the UK’s Brexit decision on the fundamental research and development underpinning much of the Advance core and UltraFan technology. A large element of this has come through involvement in the pan-European Clean Sky aeronautics research program, the current phase of which is the €4 billion ($4.5 billion) Clean Sky 2. The program began in 2014 and will run through 2020. For its funding, €1.8 billion is coming from the European Commission and the rest from partners. The UK is expected to stay in Clean Sky 2 through its completion in 2020 because the budgets are already committed, but European officials are concerned a «hard» Brexit could derail a Clean Sky 3 joint undertaking if the UK cannot participate.

So while CFM studies its options, including potentially scaling the advanced GE9X core to fit an advanced new low-pressure system, one big question is whether the specter of further costly engine development could force Rolls and Pratt back into each other’s arms to bid for the NMA. Could, or should, the arch-rivals bury the hatchet for a second attempt at forming a joint «son-of-IAE» approach to the NMA? This has been tried once before, even after Rolls sold its 32.5% stake in International Aero Engines, in 2011 to Pratt’s parent company, United Technologies, when it became clear that the two founders could not agree to make Pratt’s GTF the basis for future developments.

Even though Pratt and Rolls later discussed a potential new venture aimed again at the future midsize market, this was abandoned in 2013 as Pratt focused on the GTF and Rolls directed its energies at the bigger turbofan market. So given the ironic about-face by Rolls, with its subsequent acceptance of the geared fan as the basis for its own new UltraFan engine architecture, could this be the moment to rekindle the alliance between the reluctant partners?

Not likely, says Aboulafia: «I’m not sure how you put Humpty Dumpty back together again." Although the notion of a Pratt-Rolls merger on a large scale «makes sense," the prospect of this or a more limited partnership over the NMA seems more remote than ever. Lurking in the background, like a bad dream that will not quite go away, is the ghost of SuperFan-ageared turbofan proposed by IAE for the Airbus A340 before being promptly abandoned in 1987. The premature attempt to launch the SuperFan opened the door for CFM to gain exclusivity on the A340 with the CFM56-5 °C and is a persistent reminder for all NMA contenders of the need to tread carefully.

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