In a previous work, the author presented a simplified thrust model to be used in predicting the performance of high-speed aircraft. That model contained an ad hoc estimate of the stagnation pressure loss in the inlet/diffuser of the engine. The current analysis attempts to capture some of the actual physics of the flow, modeling the incoming flow as a single oblique shock followed by a single normal shock, and including frictional losses in the subsonic portion of the diffuser. The result is a polynomial function of Mach number that captures much of the actual physics of the flow. Results using the new model are compared to the previous model and the data on which that model was based. A sample calculation of cruise Mach number for a jet aircraft is also included.