A quantum leap forward


Performance. Execution. Technology. The LEAP high-bypass turbofan engine has it all. Mark Venables reports on the latest developments surrounding its entry into service.

The first LEAP-powered commercial flight happened on August 2, 2016 on a Pegasus Airlines flight from Istanbul to Antalya. Since then, more than 80 LEAP-powered aircraft have entered service with a total of 18 operators on four continents. Overall, this fleet has logged more than 200,000 flight hours and 100,000 flight cycles.

“The LEAP engine entry into service is the most successful in our history and has been exceptional by any measure,” said Gaël Méheust, president and CEO of CFM International. “Our customers are thrilled with the fuel efficiency the engines are providing, as well as the world-class utilisation level they are achieving with this very important asset. Aircraft powered by the LEAP engine are flying more than 95% of available days. This is simply unprecedented for a new engine.”

The LEAP is providing operators with a 15% improvement in fuel consumption and CO2 emissions compared to today's best CFM engine, along with dramatic reductions in engine noise and emissions.

The foundation of the LEAP engine is heavily rooted in fourth-generation aerodynamic design and environmental technology, but it is the advanced materials the company has introduced in this engine that is changing the way aviation looks at jet propulsion and laying a solid technology pathway for the future engine developments.

“The engine is the only one in commercial aviation to feature one-piece woven carbon fibre composite fan blades and fan case,” François Bastin, executive vice-president, CFM International explains. “This design provides a three-dimensional aerodynamic fan system that helps achieve lower fuel burn in a high flow/high bypass engine that is lighter weight and has lower noise. Building the fan required development of new resin transfer moulding production processes, a development that has been underway at CFM parent company Safran Aircraft Engines for more than 30 years.”

The blades and case are manufactured using a proprietary process that weaves the parts in three dimensions on a loom into their final shape. These preforms are then injected with resin and baked in an autoclave. The final step is adding a titanium leading edge for increased durability. This technology results in fan blades that are not only lightweight but so durable that each individual blade is strong enough to support the weight of a wide-body airplane like the Airbus A350 or Boeing 787.

“Because of the wide-chord blade design, the LEAP fan has just 18 blades, half the number on the CFM56-5B, 25% fewer than the CFM56-7B, and 10% fewer than its competitor,” Bastin adds. “The total fan system is virtually maintenance-free, reducing aircraft weight by 1,000lbs compared to the same size fan manufactured using all-metal materials. This lower weight, along with state-of-the-art blade aerodynamic design, contributes nearly half of the 15% fuel efficiency improvement the engine is providing.”

LEAP Engine
At Safran, engine assembly takes place on two pulse lines that stretch 60m

Putting it all together

LEAP-1B engines for the Boeing 737 MAX are assembled at GE Aviation’s facilities in Lafayette, Indiana, while the LEAP-1A engines for the Airbus A320neo family are assembled at Safran’s Villaroche facility, located 50km south east of Paris. The plant has 12 engine test rigs, including one for the GE90, which is one of the two largest closed test cells in Europe, and about 40 partial test facilities.

At Safran, assembly takes place on two pulse lines that stretch 60m; each line having a capacity of up to 500 engines per year. They have the capability to assemble all three versions of the LEAP engine: the LEAP-1A, the LEAP-1B, and the LEAP-1C for the COMAX C919. These two lines allow Safran to assemble up to 1,000 engines/year at Villaroche. A third LEAP assembly line could later be added to the first two, if deemed necessary to increase production capacity.

These two new lines incorporate several innovations. Engine movements will be managed by touch screens, and overhead handling by a swing cradle that enables the engine to be rotated around its horizontal axis so workers do not have to work at heights. Positioning of components and subassemblies on the engine uses laser projection and virtual reality assistance systems, while operators work on connected tools and other advanced devices. The design of these pulse lines calls on operator feedback and recommendations, and will significantly enhance user comfort and efficiency at workstations.

The LEAP is said to provide a 15% improvement in fuel consumption and CO2 emissions

Adding to performance

While additive manufacturing has been used for decades in engine development for rapid prototyping, as well as for non-critical stationary parts, the LEAP engine fuel nozzle is taking that technology to a whole new level. The twin-annular, pre-mixing swirler (TAPS) II combustor is providing a 50% margin to current CAEP/6 emissions regulations. In addition, CFM is the first in the industry to produce such a sophisticated part using additive manufacturing.

GE began work on the additive nozzle in 2001. In 2008, CFM determined that the technology was mature enough to be introduced in the LEAP engine.

“Additive manufacturing enables CFM to produce parts not possible with conventional equipment,” Bastin adds. “The use of the technique enables engineers to design the part the way it needs to be, rather than to accommodate traditional subtractive manufacturing.

“For example, the nozzle produced traditionally would have required more than 25 individual pieces to be brazed into the part; a time-consuming process that did not provide an optimised design. With additive manufacturing, that number has been reduced to less than five parts.”

Other advantages include time savings because design changes can be turned around very quickly and integrated into the product. In addition, additively manufactured parts have greater material strength, with powders available to cover a wide range of applications. And, while the parts are stronger, they are also lighter, which helps contribute to improved fuel efficiency.

The fuel nozzle is grown, layer by layer, using a process called Direct Metal Laser Melting (DMLM). The process uses a focused laser beam that generates the heat required to melt fine powder in a controlled environment. There are approximately 1,000 layers per inch on an additive manufactured part.

[caption id="attachment_14842" align="aligncenter" width="1024"] The LEAP-1A engines for the Airbus A320neo family are assembled at Safran’s Villaroche facility[/caption]

The heat is on

While the fan provides the propulsive efficiency needed to achieve half of the lower fuel consumption, the other half – thermal efficiency – comes from the engine core, specifically the high-pressure compressor and high-pressure turbine. The two-stage high pressure turbine (HPT) incorporates three-dimensional aerodynamic design, advanced coatings, and casting technology to improve cooling, the key to maximise the life of the blades. It is also the first commercial introduction of ceramic matrix composites (CMCs).

CMCs are made of silicon carbide ceramic fibres and ceramic resin, manufactured through a highly sophisticated process. This material, which has been in development for more than 30 years, is one-third the weight of a comparable metal part but with two times the strength, coupled with 20 times more temperature capability. Using this material means less cooling air is required in the turbine, which improves fuel efficiency.

“The high-pressure compressor makes a significant contribution to engine efficiency and achieves it with fourth-generation aerodynamic design techniques,” says Bastin. “The shape of the blades is highly contoured allowing them to compress air more efficiently while using fewer blades, just like the fan blades mentioned earlier.”

The LEAP compressor has a 22:1 compression ratio, meaning it reduces the volume of the air 22 times as it passes through the compressor. This is twice the compression ratio of the CFM56 and 30% more than the competing engine’s compressor.

Rounding out the material innovations in the LEAP engine is the low-pressure turbine. The blades improve performance with an advanced 3D aerodynamic design and these are manufactured from Titanium Aluminide (TiAl). This material provides a 50% weight savings compared to nickel-based alloys while its thermal capabilities reduce the requirement for cooling air. The weight savings can amount to 100lbs per LPT stage.


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