GUY NORRIS / EAST HARTFORD
PW-EXX powerplant has a two-spool, counter-rotating design, aimed at meeting Boeing's fuel consumption target
Pratt & Whitney has revealed details of its proposed PW-EXX engine for the 7E7 project in the run-up to Boeing's year-end decisions on powerplant partners and the formal launch of the programme.
P&W PW-EXX programme director Peter Smith says the outline configuration is a two-spool, counter-rotating design with a direct drive fan made of 24 "dual arc" wide-chord, hollow blades. Chasing Boeing's fuel consumption target of a 15% improvement over the 767-300ER, P&W's optimisation studies have covered over 23 fan pressure ratio/jet velocity ratio combinations, nine overall pressure ratio/turbine exit temperature cycles and four pressure ratio split cycles.
Thrust range is likely to be around 68,000-69,000lb (302-307kN) says Smith. "We're looking at whatever we have to do to meet the "book ends" around both 8,000nm and 500nm, which is a huge range to meet with one engine. We are all looking at innovative ideas to solve this equation."
Latest projections suggest a fan diameter of around 2.84m (112in) and a high pressure compressor (HPC) pressure ratio of 20:1 versus 17:1 on the General Electric/P&W Engine Alliance GP7000 and 11:1 on the PW4000. The fan, which is based on the GP7000 design, will be surrounded with an aluminium isogrid containment case, and downstream will feature integrated fan exit guide vanes leading into a four-stage low pressure compressor.
The HPC is a 10-stage unit based on the military F119 design, and will be made up of integrally bladed rotors to save weight and eliminate a potential failure mode. "We're planning to kick-off tests of this compressor by the end of 2004," says Smith, who adds the unit will have the same average compression ratio as the F119. The diffuser/combustor design will include a two-piece diffuser case and the next generation Talon X burner.
To meet the "more-electric" needs of the 7E7, it will be fitted with a core mounted gearbox and will have reduced bleed air offtakes for improved efficiency.
Assuming selection over either a GE or Rolls-Royce bid in what it expects will be a two-horse race, P&W plans to formally start the PW-EXX effort in the third quarter of 2004. To ensure a fully mature propulsion system at service entry, it plans to alter its development timescale by shortening the detailed design phase while lengthening the test phase by three months.
Compared with the 777 programme, the result will be a 10- month saving in bringing the first engine to test, a 21-month saving on the 747SP testbed programme, an 18-month saving on the fan blade out test, and 17 months on completing the 3,000 cycle ETOPS/service ready test.
Source: Flight International
