Gas turbine engines (GTEs) for aircraft GTE have undergone continual evolution and improvement since their introduction during World War II. As shown in Figure 3-1, fundamental engine performance parameters have been significantly advanced. However, there remains substantial potential for improvement beyond the current state of the art for fielded military engines, which must undergo further technological development to boost efficiency by increasing compressor inlet temperature (T3) and turbine inlet temperature (T4). For example, as shown in Figure 3-1, for large turbofan engines, fuel efficiency has improved only to the extent of closing 38 percent of the gap between the first jet engines and the theoretical Brayton cycle limit. An additional 15 percent fuel efficiency is expected to be realized in large gas turbines between now and the end of 2020 (planning horizon). Similarly, the specific horsepower of small turboshaft, turbojet, and expendable engines has increased, but only to 33 percent of the theoretical Brayton cycle limit. It is foreseen that between now and the end of the 2020 planning horizon, small gas turbine efficiency will be further improved by 30 percent. The committee believes that five technologies are critical for obtaining the improvements: (1) high-temperature compressor disk materials, (2) high-temperature turbine blade materials, (3) thermal management systems utilizing high-temperature, high-heat-sink fuels, (4) lightweight hot structures, and (5) signature controls.

FIGURE 3-1 Progress in turbine engine fuel efficiency. Note: The green boxes in the figure suggest some of many ways in which efficiency could be (or actually was) improved. SOURCE: AFRL (2005a).

Three nearly simultaneous cutbacks to major gas turbine S&T programs have reduced total U.S. funding to between one-half and one-third of pre-FY00 levels. This total comprises funding for the versatile, affordable, advanced turbine engines (VAATE) program, the Integrated High Performance Turbine Engine Technology (IHPTET) program (see Figure 3-2), and the manufacturing technology (ManTech) program and takes into account the National Aeronautics and Space Administration’s (NASA’s) decision to drastically reduce aeronautics funding. (NASA traditionally invested approximately $100 million per year in gas turbine S&T.)

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