Engine Technology

Aircraft engine manufacturers, by nature a highly conservative group that steers on the side of risk reduction, are making calculated gambles. To stay competitive, they must make business and technology decisions they hope will keep them ahead of ever-increasing airline demands. Reduced maintenance, lower emissions, better fuel burn, greater reliability and operating costs—all for a better price—are the minimum criteria merely to stay in the game.

This tough competitive environment goes a long way to explaining the announcement in October by Pratt & Whitney and Rolls-Royce that they will restructure their long-standing joint venture company International Aero Engines (IAE) and start a new company dedicated to developing engines for new mid-size aircraft in the 120-230 seat size.

The surprise decision—which sees Rolls do an about-turn on geared turbofan technology as it now aligns with Pratt on GTF development—is seen as a bold, but necessary strategic maneuver to combine technological and marketing forces against rivals GE Aviation and CFM International.

The Pratt/Rolls deal has a certain karma about it. Thirty years ago, the companies put aside competitive differences to join forces via IAE and create the V2500 engine, a successful venture that took away CFM’s monopoly on the Airbus A320-family with its CFM56 engine. Fast forward to the present, however, and CFM’s Leap engine is now similarly poised to lead the competition to power the next generation of narrowbodies, the Boeing 737 Max and the A320neo. IAE became an awkward obstacle to Pratt promoting the GTF over the V2500 because Rolls would not let that happen. So what started as an innovative business venture that kept Pratt and Rolls in the narrowbody sector has evolved with a changing market place into a potential block against securing a share of the Max and neo markets as well as the future mid-size aircraft market. Neither engine company could afford to be locked out of such a significant sector.

The ultimate solution was a business deal as elegant as it was shrewd. By buying out Rolls’ 32.5% share of IAE—a deal it hopes to complete by mid-2012—Pratt sets itself free to pursue the future mid-size market with the technology offerings it feels will best compete against the Leap. Rolls, meanwhile, gets a $1.5 billion cash injection under the buy-out terms as well as undisclosed fees for each hour flown by the current V2500-powered fleet for 15 years. The value of the fees, it is thought, could ultimately match or outstrip the $1.5 billion cash payment.

Rolls also gets “in” on GTF technology development. And as the IAE venture gradually gives way to a new 50:50 Pratt/Rolls program, both companies are better positioned to take on CFM. “This is good news for the A320 and the neo. It gives IAE customers the assurance of seamless service and a single point of contact for potential fleet transitions from V2500 fleets to geared turbofan-powered A320neo fleets,” Rolls said.

In today’s world, it’s no longer good enough to have the best technologies; business savvy is also critical.

Technology remains vital, however. And so there has been a surge of activity by all players aimed at ensuring they have the right blend of technologies in place to mesh with airlines’ most pressing business needs and the in-service introductions of new aircraft types.

Top of the list of most sought-after technologies is fuel economy.

“Fuel burn is absolutely the number one issue—it’s the most expensive item. It used to be personnel costs, but now a one or two percent fuel burn advantage represents big money, perhaps almost $200,000 per year savings from a one percent fuel burn saving. It easily saves $2 million on the nose of the airplane,” said Tom Brisken, GE Aviation GM, commercial customer strategies.

At Pratt, meanwhile, the technology thinking seems firmly fixed on GTFs being the way of the future. The deal forged with Rolls on IAE, and which begins a new joint venture to pursue GTF development, confirms this. So the new relationship starts a fresh phase in which Rolls no longer nay-says Pratt’s GTF-technology-based PW1000G engine—a previous source of much friction between the two companies—but instead gets a slice of GTF action and, ultimately, sales.

Pratt and some other industry insiders are convinced that the GTF route may prove to be the smart bet. GTFs are considered by many industry observers a key technology enabler to achieving the greater fuel burn savings that airlines are demanding; a trend likely to continue with the uncertainty on the economy and oil prices. The future, therefore, could be bigger GTFs; or GTFs with the same thrust, but bigger fans and shorter engines.

 ATW understands that as Pratt engineers work with Airbus and Boeing, they are discovering they can install larger-diameter fans than originally believed because the GTF’s smaller-diameter low-pressure turbine means it can be mounted closer to the wing to increase ground clearance.

 The A320neo has an 81 in. fan—until recently, any fan bigger than mid-70 in. was considered giant—and Pratt has done studies on the potential for putting a 94 in. fan on a future new narrowbody.

Over time, the core will continue to get smaller. For the 2025 timeframe, Pratt is believed to be looking at 30,000 lb. thrust GTFs, the same size as the current neo engine, with cores as small as some turboprops. 

And although Pratt says its main focus is on the narrowbody market, the United Technologies company is believed to be actively talking with Airbus and Boeing about the potential to scale up GTF to A380-size engines as the technology develops and is demonstrated.

Lighter and More Efficient 

Boeing’s decision to go for a composite airframe with the 787 Dreamliner was based predominantly on the estimated 20% fuel burn savings that the lighter weight of composites would help achieve. This decision, combined with Boeing’s all-electric aircraft approach, was a key driver in how GE and Rolls approached their engine designs for the 787. Rolls developed the Trent 1000, a 74,000 lb. thrust engine with a fan over nine feet across and with fuel efficiency built in from design start. Airlines that have selected the Trent 1000 for their 787s include launch customer All Nippon Airways (ANA), which took delivery of its first 787 in late September and in October flew its first passenger service from Tokyo to Hong Kong.

GE developed the GEnx-1B engine from its GE90 core architecture for the 787. It also developed the GEnx-2B variant for the Boeing 747-8, for which it was selected by launch customer Cargolux. The first Cargolux 747-8F was delivered Oct. 12.

“When you do something big and something that stretches the technology in the regulatory environment that we are in now, it is a huge achievement. The 787 is a real step forward in technology and when we started the GEnx program in 2003, we drained the swamp of all the technology we had. For the most part, these technologies have come through as reliable and efficient,” GE’s Brisken said.

“Boeing was very clear that they were going out for a composite plane because of the 20% savings on fuel burn. A lighter aircraft adds to the fuel efficiency. That was the big one; and an all-electric airplane made a huge impact on the engine and how we configured it. The challenge Boeing presented us was to be 15% better than predecessors, so we scratched our heads about what would be the overall architecture for the engine—GE90 or CF6? The architectures have similar thrusts, but it did not take long for us to decide that the GE90 was the way to go and we are glad with that decision.”

Among the factors that steered the decision was the GE90’s 8.5 bypass ratio, which has been taken to about 10 for the GEnx. GE believes high bypass ratios will grow in importance over the next couple of decades and that the next set of new airframe designs will create different- looking aircraft that can accommodate very high bypass ratio engines.

Other improvements with GEnx include its seven-stage low pressure turbine with fewer fan blades compared to further reduce weight. Composite fan blades and case and titanium Aluminide low-pressure turbine blades were also important, GE says. “If you stay with metal on high bypass, it gets very heavy because it gets very large,” Brisken said. Composites also add durability and reduce maintenance costs: GE believes that there will effectively be no life limit on the GEnx’s blades and that the engine will never need to be pulled from the 787 wing.

Lighter engines also mean the wing can be thinner—another weight saving. GE says the weight savings are about 400 lb. per engine—or a total of around 1,000 lb. with the wing savings. That equates to carrying four or more extra passengers. “The revenue savings for the airlines are huge,” Brisken said.

There are around 250 787s for which the engine selection has still to be made and that will be a fierce battleground between the GEnX and the Trent 1000. Fuel burn, weight savings, maintenance costs will be touted by both manufacturers, as will the “green” factor and emissions numbers. For now, carbon dioxide emissions are the prime focus of airlines wanting to minimize their CO2 footprint and regulatory taxes. But engine manufacturers believe the reduction of smog-causing Nitrogen Oxide will also grow in importance with regulators, so they are planning for that in their designs now rather than be forced to redesign combustors down the road. The GEnx was the first GE engine to use the low emission combustion system known as TAPS, which was further extended with a development called eTAPS that led to the lowest NOx combustor.

In the narrowbody field, the jump that CFM’s Leap has enjoyed on the A320neo and the737 Max is likely to have nudged Pratt and Rolls into their V2500 solution.

“We have already demonstrated Max performance levels; our competitors have to improve by 20%, but we are there. It’s a smaller core and higher bypass ratio [than the GEnx], but the architecture is identical. Those differences are all modeled very well. It’s been the right approach to understanding what we have learned and build on what you learn and make refinements. We think for the Leap, for that particular application on the A320, it’s the right architecture and customers are beginning to see that now for the neo re-engined A320,” Brisken said.

Using what GE refers to as “baby GEnx architecture,” the Leap engine will go through its certification program next year, a process expected to be completed by the end of 2014 ready for entry into service in 2015/2016.

A restructured IAE, however, leaves Pratt free to directly challenge the Leap, and with Rolls now happy to acknowledge that, the competition to power mid-size aircraft is set to heat up.