Materials advancements promise next-gen engine energy efficiency
This year's Farnborough International Airshow was dominated by the headline-making announcements of huge orders for 's 737 MAX, along with more modest sales for 's rival . In both cases, the major selling point is double-digit fuel savings over current models, given the cutting-edge technology incorporated into the family and the new geared-turbofan Pratt & Whitney , offered as an option for the A320NEO, along with the Leap-1A.
The technology incorporated in these next-gen engines has little to no history in the airline world.
Mark Wibben, director of powerplants for, reports that, while the Leap-1B's high-temperature operation will employ more expensive materials, its maintenance cost per flight hour should be relatively flat compared to the engines now powering its fleet. The Leap-1B will power the 737 MAX, for which Southwest was the launch customer.
“Fuel burn is our biggest concern,” Wibben notes. “But, since the Leap-1B is a new—rather than a derivative—engine, we expect that new tooling and maintenance procedures will be developed to maintain the engine on-wing, and that durability will be at least the same as our current engines.”
Bill Tiffany, Southwest's senior director of supply-chain management, reports that Boeing is advertising a 14–15% improvement in fuel burn, using theseries as a baseline for comparison. Of that, 11% is attributable to the engine, with the remainder to airframe design changes. Tiffany says that the Leap-1B draws on technology that is already proving itself in service.
“Much of the material to be used in this engine is already flying on theand . For example, composites are used in the GEnx fan case, fan blades and twin-annular, pre-swirl (TAPS) combustor component,” says Tiffany. “There will be improved airflow around the blades and fewer piece parts, which means that there will be less to go wrong.”
The airline is not expecting premature line-replaceable-unit removals because of the engine's high heat operation, he says. “The large fan and high bypass ratio should provide better cooling.”
According to Ed Duran,'s general manager for customer service engineering, the research and development for the GEnx—used on the and —focused heavily on composites. “We use polymer composites in the GE90 fan blades, but for the GEnx we took that a step further by using composites in the fan case, which has resulted in a considerable weight savings,” he explains.
Duran also notes that the GEnx TAPS design enables the engine to exceed nitrogen oxide emission standards, thanks to a lean-burn approach that still maintains the combustor's durability requirements. The lean-burn process, he notes, was achieved using new manufacturing methods in the fuel-injector components.
The Leap family, he says, will benefit not only from the advanced parts technology derived from the GEnx and the GE90, but also from the CFM56 family, which was used as the design baseline. One example he cites is the Leap's high-pressure turbine blades that have been designed to run at the same metal temperature as those on the CFM56-5B. “They will have the same durability, even though the Leap will achieve 15% better fuel consumption.”
In tandem with durability,paid particular attention to component repairs. “During the design phase, there was a requirement for components—the combustor, the frames, the cases and the turbine and compressor airfoils—to be repairable. We think that those components will be more repairable, more of the time, as a result of the design requirements,” he states.
Users of the Leap engine will benefit from the electronic-trending technology incorporated into the GEnx, says Duran. “The GEnx diagnostics have the capability to provide more information on more systems in the engine because of better interrogation of events, which provides earlier warnings of potential issues. We will be extending that technology to the Leap family.”
Developments in trend monitoring have, in fact, resulted in an increasing amount of inflow data, revealing how an engine is operating in the field, reports Jacques Juneau, vice president of engine services for Abu Dhabi Aircraft Technologies (ADAT) in the United Arab Emirates. “Electronic data-generation capability has increased to the point where the information provided can determine the optimal time for engine removal without disrupting an airline's operations. Now we can determine the reason for an event, in less time, and know better where to troubleshoot, minimizing repair costs and those pertaining to spare engine fleet maintenance,” he says.
John McKirdy, vice president and global account executive for Chromalloy, notes that the new engines also are being designed for greater durability and repairability.
“That will mean more acceptance by the airlines of DER [designated engineering representative] repairs, since it's less costly to repair a part than to replace it. With industry requirements for greater on-wing life, increased fuel efficiency, decreased emissions and decreased maintenance costs, that often means developing parts that are less prone to deterioration under higher heat conditions, but at the same time, present more salvage or repair opportunities,” says McKirdy. “At Chromalloy, we have looked at parts considered to be non-repairable by the existing repair manuals and developed repair schemes we can certify for those parts,” he says.
The development of emerging nanotechnology coatings, which provide an enhanced thermal barrier, is helping to extend on-wing component life, says Juneau. “We see significant progress made in the coatings world. This should lead to longer on-wing time, although it is still too early to know for sure.”
Airlines appear to be taking somewhat of a wait-and-see attitude with respect to the new engine technology, especially where performance and life-cycle support agreements are concerned.
“The maintenance contracts being negotiated with GE for the Leap-1B are similar to those for our CFM56,” says Southwest's Tiffany. “But we are including provisions in our agreements with both GE and Boeing that will guarantee the advertised fuel-burn and exhaust-gas-temperature (EGT) performance—after overhaul.”
Because of the engine's new trending technology, it will be possible to track the variables that influence fuel-burn and EGT performance more accurately than in the past, he notes. “This is the first time, at Southwest, that we have included this in a maintenance service contract.”
Interestingly, Tiffany says that there has been less discussion about engine on-wing time, than fuel burn. “We expect that the time on wing will be comparable to, if not better, than what we are experiencing with the CFM56-7.”
Oslo-basedASA, or Norwegian, has ordered 100 each of the 737 MAX and the A320NEO. The Pratt & Whitney PW1127G has been selected to power the A320NEOs, to be delivered starting in mid-decade. But Tore Jenssen, the airline's fleet manager, says that he is actually expecting less on-wing time than with the CFM56.
“When you compare the Leap-1B to the CFM56, you are looking at a larger engine which runs hotter, in order to achieve better fuel burn,” Jenssen notes. “You cannot have both fuel burn and maintenance efficiency, so the trade-off is better fuel burn for less time on wing.”
He adds that time on wing for the PW1127G should be at least as good as the Leap-1A, even though it's a bigger engine. “Because of its larger, slower-speed fan, it will run cooler and still be more fuel efficient.”
Pratt & Whitney Commercial Engines' marketing director, Paul Finklestein, points out that fuel savings will be achieved largely through the application of its geared technology, which was designed to permit a slower-speed fan to run, in combination with a higher-speed, low-pressure compressor and low-pressure turbine. “Using fewer stages to produce more power, the engine achieves the required thrust and better fuel efficiency, yet runs cooler than conventional engines,” he explains.
Finklestein emphasizes that low maintenance was integral to the design of the engine, which will be certified by year-end and enter service on thein the latter part of 2013. The CSeries will specifically use the PW1500G, while the PW1127G will enter service on the A320NEO in 2015.
“The Pratt & Whitney geared turbine engine uses six less stages in the compressor and turbine, and 2,000 less airfoils, in the hot section, than a conventional engine,” Finklestein says. “Maximum on-wing repair capability has been facilitated with 34 dedicated boroscope ports, enabling engine inspection from the front to the end of the low-pressure turbine. An additional 10 dedicated boroscope ports for on-wing compressor blade blending have been provided.”
The engine, reports Finklestein, also benefits from an advanced cooling system technology within the airfoils themselves, enabling greater cool-air flow.
The geared turbofan technology has Norwegian Air Shuttle's Jenssen taking a somewhat cautionary approach with respect to maintenance support. “We want to wait until we have a better understanding of how these engines will operate, before signing a maintenance service contract. At that time, we will look at either a power-by-the-hour or time-and-material contract.”
, which also selected PW1100G power for the 40 A320NEOs it has on order, for delivery beginning in 2018, sees minimal risk.
“Although the engine's geared turbofan technology has never had a commercial airline application, we believe there is little risk, since it has been used in the helicopter world for many years with no real problems,” says Larry Montreuil, director of corporate supply-chain management for JetBlue. “We're comfortable with the fact that the gearing system will help it run more efficiently, and, with the larger fan, it won't have to work as hard.”
He explains that initial concerns regarding spares support were alleviated by assurances from the original equipment manufacturer (OEM) that it is dual-sourcing components. “We are confident they have protected their supply chains, and have a high degree of comfort with that.”
Montreuil adds that the OEM is also under contractual obligation to provide technology insertion as the engine matures, particularly in such areas as thermal protection and advertised fuel burn.
JetBlue, explains Montreuil, has structured a “bifurcated maintenance agreement” with Pratt & Whitney on the new engine. Under the contract, JetBlue will pay a monthly fee to cover nonscheduled removals and minor engine maintenance. For major shop visits, the airline will pay a flight-hour rate for the hours flown for the specific engine that is in the shop. The airline, he reports, has a similar agreement with GE on the CF34s that power its190s. In that case, JetBlue pays a flat fee at the shop visit.
Joe Maloy, director of propulsion engineering for, reports that one of the most important concerns that airlines have about new-technology powerplants is “engine performance retention,” which, he says, relates mostly to any changes with fuel-burn and EGT margins. (He says that, at this time, US Airways has neither the 737 MAX nor A320NEO on order.)
“When you start seeing fuel-burn increases, that's a sign that the engine's performance is deteriorating faster than expected. That, and narrowing EGT margins, need to be mitigated by the maintenance service contract with the OEM,” Maloy explains. “Performance retention is a much bigger concern than the risk of an inflight shutdown with the new-technology engines coming along.”
For the NextGen Leap and PW1100G, the unanswered question is component durability, Maloy stresses.
“What drives an engine off-wing is any failure in the accessories or hardware that surround the engine, rather than the condition of the gas generator,” he says. “Both the CFM Leap and the Pratt & Whitney PW1100G are being advertised to achieve a 15% or better mission fuel burn, but pushing an airplane to do that means that the engine will operate at a higher speed and a higher internal temperature. Although the components should be able to withstand the higher temperatures, will they be able to do this over a significant period of time?”
Craig Harry, US Airways' supply-chain managing director, advises that as more new-technology engines are introduced, contractual flexibility in cost-per-hour maintenance plans will become even more important.
“When you deal with new technology, your knowledge of that engine, and the way it will perform, will be extremely limited at the start of the program, simply because there hasn't been any real experience with the engine,” Harry explains. “If the engine performs better than expected, adjustments in the cost per hour should be specified up front in the contract, rather than renegotiated during the life of the contract.”
The contracts also should guarantee availability of spare engines on a no-limit basis, he says.
“The performance and cost guarantees are the burden on the OEM,” Harry stresses.