This model shows how a simple representation of a turbojet can be built using custom Simscape™ library blocks. The model predicts the total engine thrust given the Mach number, altitude and temperature at the inlet to the turbine. Normally an engine controller would control fuel rate by measurement of fuel flow and limit the demand if temperature limits are exceeded. Here the controller is inverted as this results in a simpler set of equations suitable for system-level performance studies. The simplification that the compressor and turbine pressure ratios and efficiencies are constant can be removed by using Simscape™ language lookup tables to make these parameters dependent on mass flow.