ANALYSIS: CFM aims for smooth Leap into service

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Design freeze of the CFM Leap-1B for the Boeing 737 Max means that all three versions of the single-aisle powerplant have formally entered the assembly stage.

CFM's latest schedule indicates that 12 Leap-1B test engines will form part of the development programme, complementing 13 Leap-1As for the Airbus A320neo and three Leap-1Cs. Testing of the -1C, for Comac's C919, will benefit from -1A commonality.

Over the next six months the manufacturer will release detailed engineering schematics which will allow the production of components in time for the first full -1B for testing to emerge in mid-2014.

It will be the exclusive powerplant for the 737 Max which enters service in 2017. Flight testing will begin in 2015 ahead of certification in 2016.

The test programme for Leap will cover some 40,000 cycles and involve 30 flight-test engines across the three variants.

"It's definitely our objective to have a service-ready product and not just meet the regulation," says Leap programme manager Gareth Richards. "Experience has taught us that, the more testing we do before the first engine goes into service, the smoother that entry will be."

Leap uses an 18-blade fan. CFM has been testing its woven composite blades, using its engine blade demonstrator known as MASCOT, since 2009 and the company is undertaking a second phase of testing designated MASCOT 2.

"The fan module of Leap, if [made of] metal, would be twice as heavy," says Snecma's Leap programme manager François Bastin. He says the company is performing endurance testing to 5,000 cycles, which is "only required by us".

Leap technology includes a fan case 30% lighter than its aluminium equivalent, 10-stage high-pressure compressor, two-stage high-pressure turbine, and a five- to seven-stage low-pressure turbine.

Bastin says the low-pressure turbine has been "tested inside-out" and will undergo dual-spool rig testing in late 2013, which will help "remove all question marks about interaction and balance of the turbines".

Testing of the third version of the core has moved to an altitude facility. "The core is really a technology programme," says Richards. "It will continue as a technology vehicle for future engines and derivatives."

CFM is underscoring its use of ceramic matrix composites for the high-pressure turbine's first-stage shroud.

"We're convinced this is the beginning of a new material revolution," says Richards. Fuel nozzles on the Leap engines, he adds, will be made exclusively through the process of additive manufacturing. "We think the use of that technology is going to explode."

Bastin says the extensive testing and gradual evolution of the technical advancements makes the Leap a "low risk" option. CFM says it wanted to achieve the same level of efficiency as rival engines "without the complexity". Richards insists that the company is "guaranteeing" costs of maintenance "equivalent to the CFM56".

The manufacturer will start ground testing of the Leap-1A - design of which was frozen in June 2012 - in autumn this year. Multiple engines will perform ground-test runs before flight testing starts in 2014.

CFM expects that, by 2020, it will have "completely transferred" its CFM56 commercial production to Leap. Richards believes it will be producing "almost no CFM56s" by that date, beyond a few spare engines and certain powerplants for military applications.

Richards says that the company has started running Leap technology in a version of the General Electric GEnx engine for the Boeing 787 and 747-8, and that this will go to test later in May.