Small Gas Turbine Engine Technology

Performance of small gas turbine engines in the 250 to 1000 hp size range is significantly lower than that of large engines. Engines of this size are typically used in rotorcraft, commutercraft, general aviation, and cruise missile applications. Principal reasons for lower efficiencies of smaller engines are well known Component efficiencies are lower by as much as 8 to 10 percentage points because of size effects. Small engines are designed for lower cycle pressures and temperatures because of smaller blading and cooling limitations. The highly developed analytical and manufacturing techniques evolved for large engines are not directly transferrable to small engines. Thus, it has been recognized that a focused effort addressing technologies for small engines was needed and could significantly impact their performance. Recently, in-house and contract studies were undertaken to identify advanced engine cycle and component requirements for substantial performance improvement of small gas turbines for projected year 2000 applications. This paper presents results of both in-house research and contract studies, conducted with Allison, AVCO lycoming, Garrett, Teledyne CAE, and Williams International Rotorcraft results are emphasized. Projected fuel savings of 22-42 could be attained. Accompanying direct operating cost reductions of 11-17, depending on fuel cost, were also estimated. High payoff technologies are identified for all engine applications, and recent results of experimental research to evolve the high payoff technologies are described.