Altitude Evaluation of a Variable Cycle Turbofan 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.