CFM starts ground tests for Leap engine family

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CFM International has commenced a series of ground tests on the first full Leap engine selected to power the Airbus A320neo family, with a close facsimile chosen by China's Comac for the C919 narrowbody.

The beginning of ground tests heralds the beginning of a nearly decade-long transition by the General Electric and Snecma joint venture from building the stalwart CFM56 turbofan engine to the Leap series.

The Leap engine ground tests began two days early and achieved full take-off thrust after a series of break-in runs, according to CFM.

"Everything we have seen tells us the Leap engine is going to deliver all we promised and much more," says CFM executive vice-president Chaker Chahrour.

Airbus is scheduled to begin flying the first Leap-1A engine on the A320neo in 2015, or one year ahead of planned airworthiness certification for the airframe and engine together. Boeing also selected the narrower Leap-1B to power the 737 Max family.

The Leap engine represents the first all-new centreline engine for the GE-Snecma joint venture in almost 40 years.

It breaks from the architecture of the CFM56 in several ways.

First, the Leap engine incorporates a two-stage high-pressure turbine, versus a single-stage for the CFM56. The additional stage makes the engine more fuel efficient, at the expense of fully optimising the weight and maintenance cost of a single-stage turbine system.

The Leap-1A engine also uses a 10:1 ratio of airflow that bypasses the engine core, almost double the 5.5:1 bypass ratio of the CFM56. The new engine achieves the higher bypass ratio by using a wider fan, measuring 2m (78.7in) across for the Leap-1A. To compensate for the extra weight of a wider fan, CFM switched to using lighter composite fan case and composite blades.

Internally, CFM is also making the engine burn fuel more efficiently by increasing the temperature of the combustion process. The hotter temperatures forced CFM to switch to a new material in one part of the engine. The Leap engine features a ceramic matrix composite material in the lining shrouds seated around the tips of the blades on the first stage of the high-pressure turbine.

The new design and materials used in the Leap engine allow CFM to claim that it will reduce fuel burn and noise by "double-digit" margins.

The Leap engine is competing for orders on the A320 family with the Pratt & Whitney PurePower PW1100G-JM geared turbofan, the successor of the International Aero Engines V2500 that has battled the CFM56 for orders over the past three decades.

CFM has committed to use 28 ground and flight test engines over the three-year certification programme for all three variants. The entire test engine fleet is expected to accumulate 40,000h of testing prior to entry into service.