Guy Norris/LOS ANGELES
CFM International (CFMI) is starting a series of multimillion dollar technology studies to support the development of a new baseline engine in the 89-178kN (20,000-40,000lb)-thrust range early next century.
The drive is aimed at maintaining the current market dominance of the joint General Electric/Snecma company, and fending off potential competition from Inter- national Aero Engines (IAE) and Pratt & Whitney. Although a partner in IAE, the latter recently began studies of a geared turbofan for next generation narrowbodies (Flight International, 24 December, 1997-6 January).
"We are the leader and we want to remain the leader. We don't want to be caught like Pratt & Whitney was with the JT8D," says CFMI president Gerard Laviec. Key drivers for the next generation CFM engine include a 15-20% lower cost of ownership compared to current models and cumulative noise levels 20dB below Stage 3. CFMI is also aiming for up to 7% lower fuel consumption compared to the CFM56-5B/P, as much as 50% lower emissions than current regulation limits and up to 20% lower maintenance costs.
"There will be no change before 2004/5," says CFMI executive vice-president Bill Clapper. "We see a period of a couple of years where we need to invest in this technology; to demonstrate its feasibility and get it ready for us to move." Clapper says that the targets are ambitious and adds that "the technology to do this is a very big step".
Major development studies are focused on a high stage loading high pressure (HP) compressor incorporating advanced three dimensional (3D) computational fluid dynamic (CFD) aerodynamics. Clapper says that the aim is to cut the HP compressor stages from the present nine to six. Another major departure from current engines is a planned close coupled, counter rotating, four stage, low pressure (LP) turbine. This development, using technology pioneered on programmes such as the GE36 propfan and YF120 advanced fighter engine, will also require studies of counter rotating differential bearings.
Other planned study areas include:
a one piece aluminium case containment design; low noise, high speed, wide chord fan; corrosion resistant bearings; booster case treatment, plenum for increased stall margin; cooled full authority digital engine control ; integral aluminium outlet guide vane and hub; short stiff core for enhanced performance retention; low emissions/low cost combustor with aerodynamic optimisation of combustor dome and elimination of hot spots; high loading single stage HP turbine with 3D aerodynamics; retention of two main frames, no mid frame; low noise exhaust, which could possibly incorporate a variable area design.Any future engine could also include a fan decoupler. The Snecma-developed innovation is designed to sever instantly the link between the LP system and the rest of the airframe in the event of a fan blade detaching.
The system works by using bolts in the number 1 and 2 bearing support assembly, which are designed to shear when loads exceed preset limits. These would be reached almost instantly following a blade failure as the fan assembly decelerates, digging into the abradable fan-case lining.
CFMI says that the feature will save more than 90kg in weight by resulting in a simpler, lighter fan case and pylon design.
"It is a totally new approach to the blade out problem," adds Clapper, who says that the feature is part of the CFM56-9 design now being proposed for the Airbus/ Chinese AE31X and IPTN N2130 regional jet projects.
Source: Flight International
