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The past 15 years of concept development leading to today s aircraft regenerative turbine engine are broadly reviewed. With this as background, current regenerative turboprop engine technology is discussed. Comparisons are made of the range and endurance capabilities of aircraft equipped with simple and regenerative cycle engines; projections of further development potential are made. The application of regeneration in turbofans, particularly in the moderate to high bypass engines, is considered. Performance characteristics are shown for various flight conditions and bypass ratios to illustrate the potential gains from regeneration. The question is one of determining whether the associated weight and drag penalties offset the reduction in fuel consumption. The problem offers a major challenge to the ingenuity of the engine designer.

The mission capability of some gas turbine powered vehicles can be greatly enhanced by the application of regeneration to the engine thermodynamic cycle. The application of regeneration to aircraft propulsion presents many unique design problems to the designer as a result of the need for very lightweight components and high performance. The many design parameters that must be evaluated, and the many tradeoff studies that must be accomplished to arrive at the best regenerator and gas turbine design are discussed. Also, the results of a series of studies are presented to graphically portray the fuel economy which results from the use of regenerative engines.

A rotor-shaft system supported at one end by a spline coupling, and at the other end by a flexible bearing support having asymmetric and nonlinear characteristics is analyzed. The effects of nonlinearity and asymmetry in the flexible support, on the response to excitation from sliding friction in the spline coupling and rotor unbalance are investigated. The spline friction is represented as coulomb friction. As a result of the sliding friction excitation, a bounded nonsynchronous whirl is shown to occur at rotational speeds above the undamped natural frequency of the system.

The Allison 250 turboprop program is reviewed including engine characteristics, the development program, FAA certification, and development to higher power ratings. Market and installation programs are reviewed including general aircraft turbine engine trends, turbine engine market potential, and a discussion of the justification and merits of small turboprop aircraft. Various 250 turboprop installations are discussed.

Allison has developed and obtained FAA type certificate for the Model 250 turboprop engine rated at 317 shaft horsepower. This engine has been flight tested in several experimental installations. Development of the engine to 400 shp is continuing. Weight savings from the lighter turboprop engine result in increased aircraft useful load; the reduced drag of the smaller turbine engine coupled with ram recovery and higher continuous ratings provide higher performance at comparable reciprocating engine power levels. These factors result in increased aircraft productivity and net worth to offset the higher price associated with the turbine engine.