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Aviation History
2004
2004-09 - 1138.PDF
UK: engines more torque to drive the considerably increased electrical requirement of 'all-elec tric' aircraft; and a hotter, more efficient core," says Morgan. Lower noise is an increasing priority, as was shown recently in Singapore Airlines' requirement that its newly ordered A380s should meet the London Heathrow airport QC4 noise limits due to be introduced in 2006. This meant that the Trent 900 fan diameter had to be increased, to provide a higher bypass ratio - leaving it 101mm wider than the optimum. "It's the first time environment has been a factor in engine design," says Morgan. He says the contra-rotating high-pressure (HP) and intermediate-pressure (IP) spools introduced on the Trent 900 were made possible through improvements in bearing technology, which can handle much higher rotational speeds between the two shafts. "The spools used to spin the same way to keep bearing speeds down," he says. "Contra-rotation means you get a higher net swirl out of the HP compressor, which puts it more or less in the right orientation for the IP stage. We save about 1% in fuel." According to Morgan, capability and cost have increased about equally in the past 30 years. "We believe we need to be more imag inative on increasing capability while keep ing cost at the same, or lower, levels," he says. This is particularly true of the fastest- growing segment of aviation - unmanned air vehicles. R-R, through its North American operation, powers Northrop Grumman Global Hawk and Fire Scout UAVs. These use existing engines, but the emphasis in future will be to develop "clusters" of powerplants suitable for different applications. R-R is involved in the US Versatile Affordable Advanced Turbine Engine (VAATE) programme, one focus of which is UAV power. "The emphasis on UAVs has shifted since the Iraq campaign started," says Morgan. "We have moved away from short- to medium-range subsonic UAVs towards providing a long-range supersonic strike capability. We're looking at com bined-cycle gas turbines to meet that requirement, and with our Concorde her itage we're uniquely placed to do so." R-R's latest civil engine, the Trent 1000, was chosen along with General Electric's GENX to power the Boeing 7E7, a relief for the company, which had to wait a long time to power the 7E7's predecessor, the 767. Robert Nuttal, vice-president, marketing, for R-R's airlines division, says the 7E7 requirement was met with an engine that is aerodynamically based on the Trent 900. The major difference in the 7E7 design is the "dramatically" higher electrical power needed for the aircraft's pressurisation sys tem, which is now supplied by electrically powered compressors instead of using air ANTLE: TRENT 500 BASELINE INCORPORATING NEW TECHNOLOGY Controls Distributed systems Fuel pump High-pressure compressor Five stages Blisks Combustor Lean burn Staged compressor Entire engine Increased temperatures and pressures High-pressure turbine Reduced blade numbers Increased temperature Contra-rotating FLIGHT Low-pressure turbine Four stages Novel construction Intermediate-pressure turbine Cooled structural NGV Variable capacity Oil system Oil pump Air riding carbon seals Accessory gearbox Brush seals Bearings seals Electric breather Health monitoring Intelligent sensors Advanced electronic health monitoring bled directly from the HP compressor. For R-R, this provided an unexpected benefit. Analysis showed that taking the generator drive from the intermediate instead of the HP shaft improved compres sor aerodynamics and resulted in signifi cantly lower idle speeds, reducing noise while taxiing, as well as delivering a 50% reduction in fuel burn - and therefore pol lution - during descent. Higher ratio The Trent 1000 also brings a significantly higher bypass ratio compared with the Trent 900 - 11:1 against 9:1. This is done by increasing the hub-to-tip ratio of the 2.8m-diameter fan with a smaller-diameter core and improved three-dimensional computer-designed aerodynamics at the fan root. All modern aeroengines now fea ture 3D designs, which has resulted in improved prediction of airflow and com pressor and turbine performance. "The inhibitor is computer power," says Morgan. "Today we can do stresses on sin gle blades and the fan, but we need an order of magnitude improvement in com puter power to develop a complete physi cal understanding of the engine." Under the Vision programme, technolo gies are spun into new engine designs as they become available. The Trent three- shaft family has benefited most to date because of the common basis for its respec tive models, but R-R wants to repeat the process in its two-shaft line-up, which includes engines from R-R North America, International Aero Engines and R-R Deutschland. "We're trying to bring to the small end what we've done with the Trent and develop a single, scaleable engine cov ering the 7,0001b to 30,0001b-thrust [30- 135KN] range," says Morgan. Elements on the drawing board include a new nine-stage boosterless HP compressor, under develop ment at R-R Deutschland, and a new fan, which R-R NA is studying. "The next two years will see rig testing of major compo nents," he adds. The demonstrator programme covers two- and three-shaft designs, with the goal of improving efficiencies, reducing the size of the engine and pushing up pressure ratios. "We want to do more with less," says Morgan. "We're currently achieving pres sure ratios of around 4.5:1 in six stages and we're aiming at 5.5:1 in five stages. That's a 20% increase in loading per stage." The same applies to turbine develop ment, where "excellent" results have been obtained from a new soluble ceramic man ufacturing process, which means that cool ing air can be directed more accurately at turbine-blade hot spots, improving cooling and enabling the blades to run at higher temperatures without affecting life. Opti mising the process in this way halves the amount of cooling air needed and results in lower NOx production. Stage numbers will be reduced, the goal being to halve the number of nozzle guide vanes, while reduc ing the number of turbine blades by 30%. Nuttal says the approach to engine design has changed to reflect the particular operational specifications of modern com mercial aircraft. "Every engine in the last 15 years has been a bespoke design. No one engine is suitable for another aircraft - we have to take into account subtleties of design to give Airbus and Boeing the best life-cycle costs with respect to the way the aircraft is operated." • www.flightinternational.com FLIGHT INTERNATIONAL 6-12 JULY 2004 47
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