MICHAEL PHELAN / DERBY
Revised contra-rotational philosophy and fan improvements should enhance performance
Rolls-Royce wants to incorporate fan improvements and a revised contra-rotation philosophy into its proposed Boeing 7E7 engine, as it aims for a 2005 launch of the advanced Trent variant.
Boeing is targeting a 20% per seat performance improvement for the 7E7, to which the 60,000-70,000lb-thrust (267-311kN) engines will contribute significantly. R-R plans a scaled version of the Airbus A380's Trent 900 as the baseline design.
Mike Howse, R-R director engineering and technology, says a narrower fan hub could be used, while contra-rotating the intermediate pressure (IP) spool rather than the high-pressure (HP) spool would further improve efficiency.
"Alower hub/tip fan ratio allows an increased mass flow without increasing fan diameter, and gives more mid-span fan blade region," says Howse. "Contra-rotating the IP makes more sense in terms of reducing work, but we avoided it in the Trent 900 because it's hard to ensure the quality of airflow from the fan root."
Howse says Boeing's no-bleed-air concept for the 7E7 will have benefits for the core section. "We can reduce the core flow, which helps us obtain the 10.5:1 bypass ratio we want, and it will allow us to extract electrical power from the IP spool. This allows us to have lower stage loading in the IP."
R-R is also experimenting with different combustor configurations to achieve Boeing's 50% oxides of nitrogen NOx reduction target, and trials on its ANTLE (affordable near-term low emissions) Trent 500 demonstrator rig next year should aid the selection.
R-R intends to transfer 7E7 technology to its other engines, and does not see the no-bleed philosophy preventing the engine being used on other platforms. "If we want to bleed from this engine, we could do it by changing the core a bit, but some would call that a different engine anyway," says Howse.
Pratt & Whitney is offering a clean sheet design, dubbed the PW-EXX, for the 7E7, while GE Aircraft Engines is proposing a scaled-down version of its GE90. Boeing aims to use 7E7 technology engines to offer an upgraded 747 from 2009.
Source: Flight International
