"Son of CFM56" -- TECH56

"Son of CFM56" is becoming a reality as component testing for the successor to the world's best-selling airline turbofan engine proceeds apace around the world.

Not that there will necessarily be a successor. But GE and Snecma, joint partners in CFM International, aim to be ready with new technology should it be required, either as a new engine or as improvements to the current CFM56 engine line.

"We really don't need a new engine yet, but if we do, we will be ready," TECH56 project manager Bill Clapper told Show News. "The CFM story has been to continuously provide value to customers through evolution, and there's no question we will infuse new technology into our multi-generation family plan for the CFM56-but right now the technology cupboard is bare."

It is time to restock it with new technology that could also be applicable to other engines; hence TECH56.

This project aims to develop sufficient new technologies to build a new engine, or to incorporate them as needed. The three-year TECH56 program will be complete halfway through 2001.

Current highlights are the second-build six-stage high-pressure compressor going to test this month, and the new low emissions Twin Annular Pre-Swirl combustor about to begin testing on a full annular rig-which will evaluate a complete combustor rather than its individual components. The TAPS combustor will then be run in a demonstration CFM56-7 engine in October to see how it performs in a proper engine environment in regard to hail ingestion, endurance and emissions.

"In combustor technology TAPS is probably the biggest change in the state of the art were trying to do, and we have a lot of work there to demonstrate and validate its feasibility," said Clapper.

The first complete contra-rotating dual spool high pressure turbine-low pressure turbine is due to go to test this month. Clapper is looking for improved efficiency in the LPT through a reduction in blade downstream shock stress. The LPT incorporates new airfoil technology and 20% fewer airfoils. CFM is the only manufacturer with more than 145 million hours of operating experience with a single high pressure turbine.

Several designs of new brush seals have completed running in Russia, and CFM intends to test them in an engine in the first quarter of next year.
The 61-inch swept-blade fan has completed blade-out tests, and similar tests will begin on the larger 68-inch hollow-blade fan early next year.

The new compressor, which runs at the same efficiency but with three fewer stages than the current design, could form the basis for a new CFM56 in the future. It ran in its first-build configuration for 100 hours earlier this year, leaving Clapper "excited" with the results.

"It had excellent aerodynamic behavior, and stresses were mostly within 30% of limits," he said. "We had a little bit of an efficiency miss and we're looking at tweaking the front stages to get that back. But overall the results look awfully good."

If assembled into a single new engine, the TECH56 could provide 15-20% lower cost of ownership, noise levels as much as 20% below current Stage III requirements, a 40-50% reduction in emissions, and maintenance costs some 15-20% better than current CFM56 engines. Fuel consumption could be reduced by as much as 5%, although infusion of the technology into derivatives of current CFM engines would probably result in a lesser benefit of anywhere between 2% and 4%.

By John Morris