CFM to finish Leap core testing by mid-May

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CFM has logged more than 30h of testing in the second demonstration phase of its first Leap-X core demonstrator, the first of three engineering cores being built and tested in advance of its next generation Leap-X turbofan engine. Testing of eCore 1 is to be complete by mid-May, with the second developmental core expected to begin testing by mid-year 2011.

The company plans to certify the first engine in the new line, the Leap-1XC for the Comac 919, in 2014. Entry into service for the 150-passenger single-aisle aircraft is slated for 2016.

Phase one of eCore 1 testing ended in June 2009 after 27h of runs focused primarily on combustor and high pressure turbine (HPT) operation, while phase two is designed to check the high pressure compressor (HPC) over an expected 100h of run time. During a visit to CFM's Cincinnati headquarters on 26 April, engineers were running a HPC variable stator vane optimization test, checking engine performance with various customer bleed air demands.

eCore 2 will include the Leap-X1C's two-stage HPT, a fundamental change in the design architecture for the family that to date has used a single-stage HPT. The core's HPC will have 10 stages.

CFM to date has built more than 20,000 engines powering the Boeing 737NG family, Airbus A320 family, Airbus A340 and a variety of military aircraft.

For the Leap-X series, CFM has doubled both the bypass ratio (to approximately 10) and core pressure ratio (to approximately 20) to achieve an increase in specific fuel consumption by 15% above the latest CFM56-5B and -7B "tech insertion" models. Other gains include a 50% reduction in nitrogen oxides with respect to CAEP 6, largely through design changes to the combustor, and 10-15dB reduction in noise compared to ICAO Stage 4 limits, achieved in large part by the higher bypass ratio.

The increase in bypass ratio, which results in better propulsive efficiency, accounts for 45% of the SFC gain, as does an increase in thermal efficiency of the core, which will result in higher internal air temperatures, says CFM Leap programme director Ron Klapproth.

Though air temperatures are higher, CFM will maintain blade HPT blade temperatures to current levels by modifying the shape and cooling design of the blades. The Leap-X blades use the same nickel-based, single-crystal super alloy material with Yttria-stabilised zirconium (YSZ) thermal barrier coatings as existing blades.

In order to help recover some of the weight increase associated with increasing the bypass ratio of a turbofan engine, CFM plans to transition to a 50/50 titanium-aluminium (TiAl) alloy cast blade for the LPT. Klapproth says the company will test the new design -- which results in a blade that is half the density of nickel super alloy blades on today's CFM56 LPTs -- on a on CFM56-7B engine in the second and fourth quarters of this year.

Later this decade, the company plans to offer further weight savings and fuel efficiency increases by introducing ceramic matrix composite (CMC) blades for the core, some of which may not need bleed air for cooling. The initial Leap-X engines will use CMC materials for the HPT shroud.