An important part of future air vehicle design will be the development of a transient integrated aircraft system model. DC electric power system modeling poses particular challenges because they are highly dynamic and employ short time constant line replaceable units [1, 2, 3]. This paper describes an approach to modeling an aircraft's electric power system that uses simplified non-physics based models of the line replaceable units that are part of future 270VDC aircraft power systems. The model is an alternative to physics based models and is particularly useful for the initial phases of aircraft development before hardware development has occurred. A 270VDC aircraft power system model is constructed as an example using the unit models. Selected results will be presented.