CFM to finish Leap core testing by mid-May

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CFM International has logged more than 30h of testing in the second demonstration phase of its first Leap X core demonstrator as it prepares the ground for production of its advanced turbofan.

This unit is 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 the middle of 2011.

The company plans to certificate in 2014 the first engine in the new line, the Leap X1C for China's 150-seat Comac C919 twinjet. The aircraft is due to enter service in 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.

cfm leap x demonstrator, cfm international 
 © CFM International

Included in eCore 2 will be 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.

For the Leap X series, CFM has doubled both the bypass ratio (to roughly 10) and core pressure ratio (to around 20) to achieve a decrease in specific fuel consumption by 15% above the latest CFM56-5B and -7B "tech insertion" models.

The increase in bypass ratio, which results in better propulsive efficiency, accounts for 45% of the engine's lower fuel burn, 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.

Although air temperatures are higher, CFM will maintain 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 zirconate (YSZ) thermal barrier coatings as existing blades.

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 an CFM56-7B engine during this quarter and towards the end 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.