This class is a base model for building a custom propulsion system that would not be possible with the ConventionalPropulsion model, and this class extends the PropulsionBase partial model. An example of such a propulsion system is modeled in this library for the Hawker Siddeley HS-121 Trident 3B aircraft. Currently, the only constraint for building a custom propulsion system is that no electric and combustion engines can be combined.

The parameter describing the engine type of all engines in the propulsion system, namely the engineType parameter, is usually not to be set by the user as its value is set correctly in the complete propulsion models that extend the ConventionalPropulsion model. However, when building a custom propulsion model with this class, the user must set its value such that it best represents the propulsion system. Its value will be used in the Body model for estimating the center of mass location of the fuselage.

Additionally, as required for the AircraftBase model to work properly, equations for solving the variables for mass properties and drag force of the entire propulsion system, which are declared in the PropulsionBase partial model, need to be written by the user when using this model to build a custom propulsion system. The AircraftBase model also requires either a TankSystem or BatterySystem model to be included in the custom propulsion system as their variables are also used by the AircraftBase model in the calculations to solve for the mass properties of the entire aircraft model and for the energy flows.