The purpose of this report is to introduce the concept of a modular propulsion system architecture, suitable to cover a wide set of implementations on different hybrid-electric aircraft. The core components identified allow for modularity of power creation, power routing and power delivery from an arbitrary number of power generation modules (technology agnostic) to an arbitrary number of electric drive motors. In this novel approach to conceptual design of hybrid-electric powertrains, two research achievements are particularly worth mentioning.