As yet, there is no known reliable method for directly measuring the thrust of a turbofan in flight. Manufacturers of civil turbofans use various indirect thrust measurements to indicate performance of an engine to the flight deck. Included among these are: Engine Pressure Ratio (EPR), Integrated Engine Pressure Ratio (IEPR), Fan mechanical speed (N1), and various Turbine Gas Temperatures such as ITT or EGT. Of key concern is whether these thrust indicators give an accurate account of the actual engine thrust. The accuracy of these methods, which is crucial at take-off, may be compromised by various types of common engine deterioration, to the point where a thrust indicator may give a false indication of the health and thrust of the engine. A study was done to determine the effect of advanced engine cycles on typical values of these parameters. A preliminary investigation of the effects of common kinds of turbofan deterioration was conducted to see how these faults can affect both actual engine performance and the indirect thrust indicators.

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