CompositesWorld
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35 CompositesWorld.com NEWS N E W S N S N E W S E N W S W drive the front fan and compressor and then provides propulsive force as it exits the exhaust jet. Te majority of a turbofan's thrust, however, is the result of incoming air that is diverted around the compressor and turbine. Te difer- ence in the volume of air that bypasses the compressor vs. the air delivered to it is expressed as the "bypass ratio." Bypass thrust does not require direct fuel burn. In the quest to improve operating costs, there- fore, engine manufac- turers have steadily increased bypass ratios, particularly in the engine families that support large transport aircraft (see Fig. 3, p. 34). In general, the greater the bypass ratio, the better the fuel efciency, especially at subsonic speeds. Larger bypass ratios, however, result in larger fan sections and, in turn, heavier turbofans. Te GE Aviation (Cincinnati, OH, US) CF6 engine family, for example, entered service in 1973 with a bypass ratio of 5:1. Te CF6's fan section accounts for 20% of total engine weight (~4,090 kg). GE's new GEnx turbofan, which produces about the same amount of thrust, has a bypass ratio of 10:1. Its fan accounts for 30% of the engine's 5,807-kg weight. Each kilogram added to the fan section necessitates 2.25 kg of extra support structure in the engine and the aircraft wing. Design drives composites To mitigate weight increases, aeroengine manu- facturers have replaced metal with compos- ites (see Fig. 4). Troughout the 1980s and 1990s, the application of composites in aircraft engines was relatively limited. More than half of the total composite volume was directly associ- ated with nacelle components, such as thrust reversers, acoustic liners, cascades, blocker doors, radial drive fairings and cowlings. On some models, aramid fbers (often in the form of dry-fber belts) were used to reinforce aluminum fan cases. Composite nose cones, a variety of air ducts and engine air-oil seals were fairly common as well (see Fig. 5). When it entered service in 1995, GE's GE90 engine applied many more advanced materials and resin transfer molding (RTM) processing to introduce a number of new composite compo- nents — most notably, large fan blades made from hundreds of plies of intermediate-modulus carbon fber prepreg. Since then, FIG. 4: Turbofan Engine Composite Usage vs. Engine Dry Weight Composites will continue to account for an increasing share of total turbofan dry weight with a commensurate reduction in that total. Source | Composites Forecasts & Consulting 1960 1970 1980 1990 2000 2010 2020 40% 35% 30% 25% 20% 15% 10% 5% 0 LEFT: The composite fan blades and inlet guide vanes, as shown here on a GE GEnx-2B engine, represent some of the most impor- tant applications of advanced materials on turbofan engines. Source | Olivier Cleynen composite blades, fan containment cases, bypass ducts, stator vanes and a host of less glamorous detail components and brackets have become common not only in commercial jets but also in business and military aircraft. Composites fyaway outlook Based on fgures compiled by Composites Forecasts and Consulting (Mesa, AZ, US) in support of a recent production forecast for jets, turboprops and piston-powered planes during 2014-2023, we estimate that 67,710 turbofan-type jet engines will be needed to support expected global aircraft production (see Fig. 6). FIG. 5: Common Aeroengine Applications Composites are making incursions into an ever-larger number of turbofan components. Source | Composites Forecasts & Consulting Turbofan Engine Section Typical Applications Fan Section Spinner cones, fan blades, fan spacers, fan platforms, fan containment cases, bypass ducts, stator vanes, outlet guide vanes, various mounting brackets, cable trays Low-pressure Compressor Air-oil seals High-pressure Compressor Turbine shrouds Combustor (none found) High-pressure Turbine Fan exit cases Low-pressure Turbine (none found) Exhaust/Exit Exhaust nozzles Nacelle Inlet lips, fan cowls, access doors, acoustic liners, pylon fairings, blocker doors, thrust reversers and cowlings, support barrels Aeroengines, 2014-2023