A practical method for predicting the windmilling performance of simple turbojet engines in flight has been developed. The method incorporates the available loss correlations and analyses to estimate the major engine component performance and requires only basic geometric data. For a given flight Mach number and ambient conditions the steady-state windmilling performance is obtained by equating the compressor input torque to the turbine output torque. The transient performance is obtained from the excess turbine output torque. The present method’s predictions are compared to the available windmilling test data from a typical small simple turbojet engine. They show good agreement over a wide range of flight conditions. Thus, this method can be used during the preliminary design stage of an engine development when the detailed hardware geometry and the component performance data are not yet available.

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