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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.

This paper describes the design and operation of the pumping system used to remove boundary layer air from the wing surfaces of the X-21A Laminar Flow Control airplanes. Included are comments on pumping system requirements and design characteristics for future applications. Part 1 includes a discussion of the initial problem statement, system selection, and system operation. Part 2 covers the pumping design and development.