CFM International partners General Electric and Snecma have extended their successful 34-year partnership until 2040 and revealed plans to develop an all-new engine, provisionally called the Leap-X. The engine will provide 16 percent more fuel efficiency than today’s CFM56; however, it will not be offered for retrofit to existing aircraft.

In parallel, the company is working on an open-rotor design that could be ready in 2020, burning 26 percent less fuel. “We must pursue open-rotor technology and understand the challenges,” said CFM’s executive vice president, Bill Clapper.

The announcement adds to speculation on how the engine manufacturers will power the replacements for their current single-aisle offerings. While the airframers have shown little interest in offering a new generation of aircraft before the 2017 to 2020 time frame, the rocketing price of oil means the timescale is constantly under review. All of the engine companies have advanced engines in development–either open rotor or geared turbofan–but retain fallback solutions based on conventional turbofans.

Clapper vouched for the validity of the two-track approach to developing a new narrowbody engine. “We’ll run a Leap-X demonstrator in 2012. By then we’ll have a much better view of whether we can beat the challenge of open-rotor technology,” he said. “There’s another 10 percent to be had if open rotor is successful, but with fuel prices the way they are, we can certify an engine in 2016 if that’s what the airframers want.”  

The Leap-X “is a new engine from back to front,” said Clapper. “A year ago we would have said we could do 12.5 to 13 percent. We accelerated our technology program and now we can go to 16 percent.” He insisted the Leap-X won’t serve as an upgrade for the current CFM56 on the existing A320–an option sought by Pratt & Whitney for its geared turbofan. “Our path to market is clear,” said Clapper. “This is how we transition from one airframe to another.” 

CFM president and CEO Eric Bachelet stressed the need to address changes in economic imperatives caused by fuel price increases over the past three years. “We have to address the fact that fuel costs as a proportion of aircraft direct operating costs have gone from 43 percent to 60 percent since we launched the Leap 56 technology program in 2005,” he said. “We also have to meet much tougher noise and emissions regulations. This engine will emit 60 percent lower oxides of nitrogen against CAEP 6 and be 10 to 15 decibels quieter than Stage 4.”

 Clapper said almost half of the 16 percent fuel burn improvement comes from an all-new 18-blade fan (compared with  24 for the latest CFM56), increasing the bypass ratio from 5:1 to around 9:1–similar to the new GEnx powering the Boeing 787. The fan is made from a “breakthrough technology” three-dimensional woven resin transfer molding providing a 1,000-pound weight benefit per aircraft. “It is stronger and lighter than anything we’ve done before,” he added.

A new core is to run in June 2009, featuring an eight-stage high-pressure compressor (compared with nine in the CFM56), raising pressure ratio by 50 percent, from 11:1 to at least 16:1. A new HP turbine with ceramic matrix stator blades drives the compressor, while the combustor is an advanced version of the TAPS II design developed in the Leap 56 program.

Leap-X technologies are relevant to the open rotor now under development, said CFM executive vice president Olivier Savin. “We must have a strong core for this engine.” He identified three technologies key to the success of open rotors: fan aerodynamics and acoustics, maintenance costs and installation. The diameter of the engine under study would measure 14 feet–wider than the fuselage of an Airbus A320–with two rows of contrarotating blades. The 11-foot diameter GE Unducted Fan (UDF) open-rotor engine tested in the late 1980s demonstrated “tremendous potential for fuel burn improvement,” he added, “but we must be able to install the engine on the airframe in an efficient way so that we don’t lose the benefits.”

Low- and high-speed wind tunnel testing of an open-rotor design are due to begin later this year at NASA in the U.S., Moscow’s TsAGI and France’s HERA. One of the biggest challenges will center on a need to design a certifiable pitch change mechanism for the blades, each row of which is attached to its own low-pressure turbine stage. “We have 20 designs under study and we’re running an extensive rig test program to see if we can solve the problem,” said Clapper. The UDF pitch change mechanism was not commercially workable, he added. “This engine has to have the functionality and reliability for short-haul operations.”

The renewal of the marriage vows originally signed between Snecma and GE in 1974 continues a relationship that has produced arguably the most successful commercial powerplant of all time, with 18,500 CFM56 engines delivered so far to almost 500 operators. The relationship, under which the partners each produce 50 percent of the engine, remains unchanged, except that CFM International instead of GE and Snecma will provide maintenance, repair and overhaul services.     
    

⡱