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The AiResearch TFE731-2 Turbofan Engine Control system was created out of a recognition of engine and aircraft operating requirements in which a free weighting of candidate control components and logic was made. From this free design iteration process, which considered both conventional and advanced concepts of control, the control described in this paper has evolved and has fulfilled the in-flight operating requirements of the engine.

This paper presents the results of an altitude test evaluation of a variable-cycle turbofan engine. The test engine was a medium-bypass, two-spool turbofan engine modified to incorporate variable inlet guide vanes and first-stage stators in the low-pressure compressor, variable first-stage stator vanes in the low-pressure turbine, and variable area fan and primary exhaust nozzles. The results of the testing indicated that these variable-geometry components offer potential improvements to the following problem areas in multimission aircraft at off-design conditions: inlet spillage drag and exhaust-system boattail drag, compressor surge-margin control, airframe bleed-air extraction effects on engine performance, and performance limited by engine operating limits.

A program, under the sponsorship of the U.S. Air Force Aero Propulsion Laboratory, is now under way to provide the computational tools necessary to predict noise signatures for small turbopropulsion engines and to design attenuation equipment as required to meet specific low-noise goals. The 24 month program, scheduled for completion in August 1973, involves the analysis of turbine engine noise prediction and attenuation methods, as well as the experimental verification of these analyses with full-scale hardware. This paper reviews the methodology development phases and examines acoustical data from bare and attenuated engine tests.

Considerable operational experience has been acquired in South America, Africa, Europe, Southeast Asia, and in other remote areas in STOL type aircraft operating from extremely short, primitive, unimproved fields. This type operation not only makes certain special demands of the engine, but also exposes it to a rather hostile environment. The engine is subjected to all types of foreign object ingestion, as well as the fine sand and dust that is stirred up by propeller reversing. This paper describes this type of operation, emphasizing those aspects which make life difficult for the engine. Solutions to some of these special problems are described, as well as activities now in process seeking further improvement.