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The efficiency of axial flow compressors is greatly affected by the amount of air that leaks past the blade tips. It is desirable, therefore, to reduce the clearance between the compressor case and the rotating compressor blades as much as possible. One solution to the problem is to utilize a clearance coating in the compressor case at the blade tip paths Two methods for accomplishing this on both new and overhaul cases are discussed in detail.

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.

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.