Paris Air Show

Paris 2011: Crunch time approaches for narrowbodied engine choices

 - June 19, 2011, 9:20 AM

Almost three full decades ago a battle was raging over the powerplant options for what was then the all-new Airbus A320. The competitors–CFM International and International Aero Engines (IAE)–were making claim and counter-claim as to the potential advantages their respective engines would bring to the aircraft, which had been developed to grab a slice of the huge single-aisle market until then dominated by the ubiquitous Boeing 737. 

Today, the fight to power the much-anticipated son-of-the-A320 is no less intense. But this time it is the re-engined, “sharklet” wing-tipped version: the A320neo. CFM International is still there in its original 50/50, transatlantic partnership between GE Aviation and Snecma, but this time only one of the original five IAE partners is present: Pratt & Whitney, which at the time of writing had taken all of the 332 orders and options for the aircraft with its all-new PW1100G geared fan engine. Rolls-Royce, the other major IAE partner, is absent from the competition, its future single-aisle strategy depending entirely on powering all-new single-aisle aircraft.

The intensity of the A320neo engine fight was highlighted a few weeks before this year’s Le Bourget show, when CFM quietly revealed it had decided to increase the fan diameter of its Leap-X engine by two inches. The move resulted from Airbus’ concerns that the existing engine’s 71-inch fan would result in a significant fuel burn disadvantage compared to the PW1100G. Airbus wanted to offer potential customers a choice of engines with similar performance because the resulting A320neo order book would be more likely to be split 50/50 between the competing engines–forcing the engine manufacturers to keep their prices down and helping the aircraft itself to be more competitive. 

The fan diameter increase means the engine will have a bypass ratio closer to the 12:1 figure set by the PW1100G, with its 81-inch fan. The late decision means extra work for France’s Snecma, however, which is responsible for the all-composite fan, adding to the workload as Leap-X development continues toward its early 2016 entry-into-service date.

Improved Fuel Burn

Tom Brisken, general manager, customer strategies at GE Aviation, claims the larger fan will bring improved fuel burn performance without requiring major work on the core, which is approaching its first major test. “We continue to develop the core as is usual in engine development programs,” he told AIN. “I am convinced that if we can nail the core, we will have, by far, the best engine for the A320neo.”

Paul Adams, Pratt & Whitney’s senior engineering vice president, disputes this. He reckons that in order to achieve the higher bypass ratio, CFM will “possibly” have had no choice but to reduce the core size of the Leap-X, in turn increasing core temperature. “The downside is that would be very negative from the maintenance point of view,” he told AIN. CFM denies it has had to do this, but the argument highlights the PW1100G versus Leap-X battleground: reliability and maintenance costs.

GE’s Brisken remains adamant that reliability, besides fuel burn performance, is central to airline decision making and that an engine based on an existing highly reliably design dating back to the GE90 powering the Boeing 777 will prove its worth. “There have got to be some concerns about bringing a brand-new engine to market,” he said.

Pratt & Whitney, only too aware that the gearbox reliability issue was central to sales of its engine, came under intense pressure from the airlines to provide strong maintenance guarantees. Testing of the geared fan engines already in development for the Bombardier CRJ and Mitsubishi MRJ has revealed no problems. “We also have a more conservative core [than P&W’s],” said Adams. “I have no worries with this engine at all.”

The Leap-X program was launched in July 2008 as a response to the dramatic surge in fuel prices. The biggest investment in CFM’s history, the engine now represents the company’s stake in a potentially vast market for more fuel-efficient aircraft. The engine combines the best technologies of the new GEnx which powers the Boeing 787 with the proven assets of the CFM56, designed for high-cycle operations typically flown by single-aisle aircraft. “It is evolutionary, not revolutionary,” said Brisken. “At entry into service we’re aiming for dispatch reliability levels in the same league as the CFM56-5 today–99.98 percent. It’s a big challenge but that’s our target.”

Several A320neo order decisions are thought to be in the pipeline, including from Virgin America and Air Asia, both potentially major customers. Both Brisken and Adams reckon there is a market will run for around 10 years and be worth potentially “several thousand” aircraft.

What, then, of Boeing’s answer to the A320neo? Perhaps all will be revealed here at Paris, but the general opinion is that it has abandoned any plans for another re-engined version of the 737 and is concentrating on an all-new aircraft. Boeing has said only that it intends to address the single-aisle market with a 145- to 185-seat offering.

All-new Engine

This is where Rolls-Royce comes in. At the 2010 Farnborough airshow Rolls’s head of strategic marketing, Robert Nuttal, insisted that an all-new engine for an all-new aircraft was the only solution that made business sense to the UK company. “First, we don’t think a re-engined aircraft offers any significant net financial benefit to the industry,” he told AIN. “Second, at manufacturing level the program will be only half as long as a new engine program, so the returns are far less, and third, if re-engining occurs it delays an all-new aircraft which would bring real benefits in terms of fuel economy and emissions.”

With the A320neo, the third option has now happened, so does Rolls-Royce still believe in its strategy of a year ago? Speaking exclusively to AIN before the show, Nuttal confirmed that the company remained “unable to see a business case” for powering a derivative aircraft and was pressing ahead with an aggressive technology readiness program aimed at providing an advanced engine for an all-new aircraft. “We believe that a bespoke engine provides a viable, strong business case,” he said.

The company is running two engine demonstrator programs as well as an open-rotor research effort, all aimed at providing a “range of concepts to suit the timing and size of aircraft when they appear.” The three-shaft Advance 3 program and two-shaft Advance 2 are each running core technology demonstrators, the Advance 2 core having already demonstrated, said Nuttal, a “world-leading 22:1 pressure ratio high-pressure compressor.” This core goes to its next altitude test in June and will continue testing to 2014. Testing of the first Advance 3 core is complete and the second core is on track for the third quarter of this year.

“We are the only company to have three potential candidates for a future new aircraft,” said Nuttal. “Our strategy is to ensure we are in a position of technical readiness with programs that are applicable across the board. There is a tremendous amount going on at Rolls-Royce.” He is “emphatic” that the UK company will be aboard any new single-aisle aircraft.

GE and P&W both claim that development versions of their respective engines will also be suitable for an all-new aircraft. Brisken said GE has been “very engaged” with Boeing developments of the Leap-X. “We have to make the right decision at the right time,” he stated. “We will not be surprised if Boeing launches this year. They like our technology and they like what we’re doing. Boeing will want the best.”

Adams said the Boeing issue is “really interesting from our point of view. I think they will come out with an all-new aircraft. They are very interested in our geared fan engine, which has considerable development capability.” He said that the development process would produce a PW1100G offshoot with a further 5-percent fuel burn advantage over the A320neo engine by the expected 2019-2020 in-service date. “We’re looking at a range of possibilities with Boeing,” he added. 

Open Rotors

Open rotors remain potential future powerplants only for Rolls-Royce and GE/Snecma. Brisken said it is still “too early for such an engine and the airframers recognize that. We don’t see an open rotor before 2030 from the technology point of view and we still question if it is the right approach.”

Rolls-Royce puts the airframe requirement slightly earlier, at “mid to late decade.” Nuttal said the airframers are taking open rotors seriously and that both Boeing and Airbus have been involved in simulations of potential engine configurations. “We’re working on both pusher and tractor layouts. A rear location is more complex than an underwing tractor, but we’re looking at all the airframe issues,” he explained.

Rolls-Royce has completed the first three open-rotor test sets and is about to embark on the fourth, which will concentrate on blade optimization. Nuttal said trials to-date have shown that an open rotor could yield up to a 10-percent fuel burn advantage over a conventional engine designed at the same time, but it would be 10dB noisier. “That means it would still be quieter than anything flying today, so we’re confident that with continuing development we will have a very viable product,” he concluded.

With the battle lines drawn between CFM and Pratt & Whitney on the A320neo and with Rolls-Royce putting all of its single-aisle cards on a future all-new aircraft, this year’s Paris Air Show promises to be as interesting as ever for engine industry-watchers.