Advanced modeling and simulation techniques are becoming more important in today's industrial design processes and for aircraft energy systems in specific. They enable early and integrated design as well as validation of finalized system and component designs. This paper describes the main methods and tools that can be applied for different phases of the energy design process.For demonstration, the object-oriented modeling language Modelica was chosen, since it enables convenient modeling of multi-physical systems. Based on this standard, common modeling guidelines, a modeling library template, and common interfaces have been provided. A common modeling infrastructure is proposed with considerations on additional libraries needed for local tasks in the energy design process.The developed methods and tools have been tested by means of some predefined use cases, which are performed in cooperation with diverse aircraft industrial partners. Each use case represents a specific modeling, simulation, or design task. This use case approach covers a wide range of the overall energy system design process.