• News
  • Engine makers under pressure to be more efficient

Engine makers under pressure to be more efficient

And Stephen Trimble in Washington

Airlines are turning up the heat on engine makers to develop new, more efficient powerplants to drive the development of the next generation of narrowbody aircraft

Open rotor engines look futuristic, and even slightly improbable, but there is a very real possibility that aircraft powered by this radical technology could be replacing Airbus A320s and Boeing 737s as the industry's narrowbody workhorses in the coming 10-15 years.

"It may well be that somebody, while flight testing prototypes, comes up with a reason why open rotor technology can't work, but starting here and working forwards, it really should be plan A," says Hal Calamvokis, ­strategic planning manager at UK-based ­low-cost carrier easyJet.

Jan Witsenboer

"The issue is that when you're over-asking you will get no new aircraft"

Jan Witsenboer

Senior vice-president corporate fleet development, KLM

As the picture to the right shows, open rotors basically look like fancy propellor-type engines. There are, however, design challenges. For instance, the classic ­underwing mounting position of today's turbofans may not be possible with the large-diameter blades of the open rotor. This points towards mounting the engines on the sides of the aft fuselage or ­beneath a high wing. If the potential can be realised, however, the introduction of open rotor engines would usher in the first all-new propulsion architecture since the late-1960s, when GE's introduction of the CF6 turbofan offered a game-changing improvement in fuel efficiency over turbojets.

The issue of new engine technology has come to prominence as several major European and US airlines step up the pressure on airframers to commit to next generation ­narrowbodies to facilitate their domestic fleet replacement and growth. The ideal successor, they say, would provide a quantum leap in economics improvement and emissions reduction as fuel costs continue to slice deep into their bottom lines and regulatory bodies demand greater cuts in ­carbon dioxide and nitrous oxide emissions.

Even as the call for next-generation narrowbodies grows louder, Airbus and Boeing do not yet see the incentive to quickly introduce replacements for their A320 and 737 families. They favour entry-into-service dates in the latter part of the next decade, as certification of widebody successors continues to be a keen focus in the nearer-term, and orderbooks for current-generation narrowbodies remain robust.

Substantially adding to this consideration, however, is a lack of maturity on new engine technology. Questions also linger about whether the industry's standard package of improvements for a generational upgrade - a 15% decline in fuel burn along with iterative reductions in other environmental emissions - will satisfy airline demands, or if as much as a 30% improvement in these metrics must be achieved.

The role that engine architecture plays in the development of breakthrough aircraft cannot be overstated. Even with the creation of all-new, composite-rich airframes, engines will contribute "roughly two thirds" of the ­efficiency gains, says IATA technical and operations specialist Juergen Haacker. "In terms of fuel efficiency, that is only achievable with a new type of engine."

Unified message

Hoping to spur a firm commitment for next-generation narrowbody development, IATA is working to deliver a unified message on powerplant preference. Understanding what engine technology is on the table is crucial for IATA to ensure that one voice is heard. "What we are currently doing, as asked by airline chief executives in our board meeting last December, is to provide them with a clear picture of what is going on in the industry," says Haacker. For most airlines, he adds, it is "difficult to understand the technologies in virgin type of development" and to determine whether they are "really so far down the road so that they can reasonably be expected to be available for certification in an aircraft for 2015", when IATA would like to see next-generation short- and medium-range aircraft emerge.

An initial engine assessment will be presented to members at IATA's annual general meeting in June. The association's intention is to begin working with airlines "in the latter part of the year" to align behind one view. However, IATA would like to see airlines go one step further, and formally tell airframers that their fleet renewal plans are dependent on the introduction of a new, more efficient narrowbody. That push from the customer base may be necessary, says Haacker, especially since narrowbody sales are now so strong.

Under study by airframers are two vastly different types of narrowbody aircraft engine designs. The first consists of a new class of conventional turbofans delivering the next - and perhaps the last - generational improvement for that forty-year-old technology. The announced competitors in this category include Pratt & Whitney, which is introducing the Geared Turbofan (GTF) in 2013, and the General Electric/Snecma joint venture CFM ­International, which aims to deliver the LEAP56 ­engine in 2015.

Hal Calamvokis    
EasyJet's Hal Calamvokis: "Working forwards, open rotor really should be plan A"

The former has been selected by ­Bombardier for its proposed 110/130-seat CSeries airliner and by Japan's 70/90-seat Mitsubishi Regional Jet. Both engine projects seek to offer a 15% fuel burn improvement. For the 150-seat-class narrowbody engine offering, P&W's favoured route is as part of the International Aero Engines consortium that includes Rolls-Royce, MTU Engines and Japanese Aero Engines, with a proposal based on the GTF architecture. "We're in dialogue right now but nobody knows when the ­Boeing and Airbus aircraft are going to come along," says P&W senior vice-president ­marketing and sales Bob Keady.

Game changer

The second type of engine design under close scrutiny is based on the open rotor concept, which aims to provide a 20% to 30% fuel burn improvement. Two of the three largest narrowbody engine makers - CFM and Rolls-Royce - are actively pursuing this technology for introduction after 2017. So ­advanced is the proposition that P&W ­executives believe it will not be viable for the airliner market until 2020 or 2022.

GE's open rotor concept leverages the improved turbofan core from LEAP56, but replaces the ducted fan with two sets of unshrouded, counter-rotating blades. This dramatically increases fuel efficiency by maximising the amount of airflow bypassing the engine core. Narrowbody engines in service today achieve a bypass ratio of 5:1. The advanced turbofans, including LEAP56 and GTF, raise that figure to 9:1. The bypass ratio for an open rotor, however, increases to 15:1.

Hoping to drive innovation by challenging engineers to get out of a "comfort zone" that in the last 50 years has made it easy to predict how the next transport aircraft would look and perform, easyJet in 2007 revealed a concept aircraft design that featured two rear-mounted open rotor engines and promised as much as 50% improvement in fuel efficiency and carbon dioxide emissions. The future aircraft could look very different from easyJet's concept, says Calamvokis. However, the ­carrier wants powerplant manufacturers to pursue open-rotor architecture as the prime engine technology for next-generation ­narrowbody airliners as it promises to offer the most significant efficiency and ­environmental gains.

One of the issues that may be driving the current timeline discussion for new-technology aircraft, he notes, is that airframers would prefer to have two engine suppliers from the beginning for risk management purposes. The question remains, he says: "Do we have to wait for the laggard manufacturer whereas the first manufacturer might be ready by 2015 and the second by 2018?"

There are other drawbacks to open rotor engines. For instance, the technology may disrupt flight schedules due to speed limitations. Most turbofan-powered narrowbodies are designed for maximum efficiency at 0.8-Mach speed. Open rotor engines, however, are expected to be most efficient at 0.7-Mach speed. On short routes, the difference may be difficult to notice, but the sums change for transcontinental or long-haul flights.

Additionally, while open rotor engines promise higher fuel savings, there could be a severe penalty on noise, a hot-button issue for regulatory bodies. Engine makers, which face the challenge of reducing higher noise levels mainly generated by the counter-rotating blades, say there are a number of prerequisites that must be met, including a "predictability of the future political environment for new engines", says Haacker. "If the government, especially local green activists, also push on the noise element locally, then the open rotor concept may not have the same chances. That is where IATA could step in and work with them."

Meeting every efficiency demand may be an impossible task. "Some of these goals like super-low emissions and super-low noise and super-low NOx and super-low CO2 are diametrically opposed to each other when you get down to the basic chemistry and physics of it," says Southwest Airlines senior director of engineering and maintenance programmes Dale Stolzer, noting that "you can design an engine that's fuel efficient, and lower NOx" but you will have to compromise elsewhere, such as on noise.

Unlike other airlines that have shown preference for open rotor engine technology, Southwest has been relatively quiet on this point. Stolzer says that while open rotor architecture "promises the most fuel burn efficiency", there are other issues "that nobody has their arms wrapped around" yet, including whether the powerplant will pass regulatory standards for blade-out and whether it will be the most cost-efficient in terms of maintenance. As such, the world's largest 737 operator continues to study the market. "Have we sent a message to Boeing that this is what we want? No we have not. We're looking at every option that's on the table and trying to come up with a long-term plan," ­explains Stolzer.


KLM senior vice-president of corporate fleet development and aircraft trading, Jan Witsenboer, agrees that a trade-off may be necessary: "We need to get the trade-off on the table before we decide 'let's go for this or this.'" He warns airlines against making too-hefty requests for fuel and emissions improvements, however. "The issue is that when you're over-asking you will get no new aircraft. It's always important to stretch goals, but when a goal becomes unrealistic, let's say 30%...I think 15% direct operating costs improvement is maybe a little bit more of a realistic figure, based on technology know-how, and it should be attainable. Of course we would like to say 40% or 50%, but that only gives [original equipment manufacturers] a reason to do nothing because in that case the ­technology is not so far along."

PW Geared Turbofan
Pratt & Whitney's geared turbofan demonstrator engine - planned for entry into service in 2013
If open rotor engines can be successfully brought to market as soon as 2017, any new narrowbody airframe introduced after 2013 could see itself out-classed. Keen to insulate itself from this possibility, Bombardier aims to carve out a position in the 100/149-seat segment with its proposed GTF-powered CSeries rather than tackling the 150-plus seat arena. For the CSeries to really succeed, however, Bombardier's ability to secure orders from North American carriers appears key.

American Airlines is considering ­replacements for its 425-strong fleet of Boeing ­­MD-80s and 757s Delta Air Lines for its MD-80s and Northwest for its McDonnell Douglas DC-9s. To support near-term growth, American has been adding 737-800s. The carrier also has options to add more -800s to the fleet. These airframes "can provide some interim replacement for our MD-80s as we really pursue hopefully finding the next breakthrough technology for an engine that provides substantial benefits", says American executive vice-president ­operations Bob ­Reding. "We're looking at an engine that can beat that from 12% to 30%, but clearly 30% would really get our attention."

American is "very supportive" of new technology efforts, including the GTF that has been selected for the CSeries. However, it is really looking for a next-generation narrowbody with an average of 150 seats. "We could operate 130 seats in several of our markets but we look at what we really need that makes the most sense for us and it's really the 150-seat aircraft," says Reding. "It doesn't mean if we had an absolutely wonderful airplane with 140 seats that we wouldn't take a close look at that. But we are asking the OEMs to really take a close look at 150 seats."

GTF technology also "seems to be the most appropriate technology for the aircraft size below the one we're looking at", says easyJet's Calamvokis. EasyJet operates a mixed fleet of A319s and 737-700s and has over 200 A319s on order and option. It would prefer the potential benefit that an open rotor would bring even if the performance guarantee in the beginning might not be as tight.

Replacement time

United Airlines has made known its strong interest in replacement aircraft. "We are encouraging them because we think that is the right way to replace what is a pretty large narrowbody fleet for us," says Jake Brace, chief financial officer at United Airlines. He adds, however, that the carrier would not seek a replacement aircraft until well into the next decade. Aircraft lessors have also contributed to the debate. ILFC chief Steven Udvar-Hazy says a successor for the A320 and 737 will ­require a 15% improvement in economic performance.

LCAL chief executive Steve Clarke says the Dubai-based leasing company plans to diversify its portfolio, which currently consists of 21 787s, with "the next green aircraft", and that this will most likely be a next-generation narrowbody. He says LCAL wants Airbus and or Boeing to launch a next-generation narrowbody this year and place the aircraft into service in 2010, but acknowledges neither manufacturer seems interested in launching a new narrowbody programme in the short-term.

The current generation of 737s are exclusively powered by the CFM56. "The real issue is GE's dominance on the 737. There's no real onus on them to kill their cash cow," Clarke says.

It remains very important, however, for engine manufacturers to offer retrofit packages of improvements for their existing engine families. "We are always pushing the OEMs for that. So that applies with effect to all the families, CFM56 up to the GE90 and of course that is also driven by the fuel price and environmental pressure nowadays," says KLM's Witsenboer, adding that Air France-KLM would like to see upgrade packages "as soon as possible".

Last year we polled over 20 carriers to gauge their thoughts on a new-generation narrowbody. Visit

Related Content