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In recent years, the design and development of military propulsion systems have greatly benefited from advancements in analytical modeling and prediction tools. However, flight testing continues to play an integral role in the maturation of fighter engines. The severity of the fighter mission role dictates the need for capabilities beyond those normally attributed to commercial propulsion systems. While comprehensive static and simulated in-flight engine testing are key elements in developing these capabilities, flight testing provides the avenue for verification that all engine and control functions operate as intended in an integrated environment and that the propulsion system meets with customer, and specifically, pilot approval. In addition to the role that flight testing plays in introducing new propulsion technology into operational service, an equally critical function is served by providing the opportunity for component improvement verification.

The key commercial aircraft propulsion requirements toward ensuring flight safety, operational efficiency, reduced CO2 footprint, and community acceptability include high installed thrust, low specific fuel consumption, and reduced noise. The objective of this paper is to highlight the various ways turbofan performance can be enhanced. First the advantage of high bypass ratio (BPR) configurations will be explained with the help of clean sheet cycle designs with the corresponding off-design performance. The achievement of hot day performance and improved durability with high BPR designs, and the benefit from core supercharging has been presented. Next, the use of on-line control effector modulations, including variable bypass exhaust nozzle, for further improvement in cruise SFC (up to an indicated 2.6%) is shown. This is followed by a discussion of medium BPR mixed exhaust designs which have a performance advantage compared to the same BPR separate exhaust configurations.