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This paper describes the structural design of a composite material front housing for the T56 turboprop reduction gear case. The objective of the composite gear case is demonstration of the feasibility of composites for stiff, lightweight gear reduction cases and the advancement of structural and material technology. Turboprop reduction gear assemblies have typically used magnesium or aluminum for the case structure. Magnesium has reasonable strength properties and low density but the modulus is also low; furthermore, it exhibits poor corrosion resistance. Aluminum has sufficient strength but the specific stiffness, E/ρ, is similar to magnesium so the case is heavy for many applications. In addition to these disadvantages, the mounting requirements for propellers, engine, and transmissions dictate high loads on the gear case structure.

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.

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.

Recently there have been many new developments in aluminum-base diffusion coatings as well as with other coating materials for protection of metal parts in high temperature oxidizing environments. Evaluation is described of many of these coatings on three separate laboratory test devices, for determining (1) resistance to erosion in a high velocity high temperature oxidizing atmosphere, (2) resistance to cracking and oxidation in a thermal fatigue test, and (3) sensitivity to light impact damage at elevated temperatures. Experience with diffused aluminum base coatings on some turbine engine components is discussed, and limitations of the evaluated coatings are cited.