Hybrid unmanned aerial vehicles (UAVs) are gaining popularity in the defense sector. The introduction of a high-power electrical network provides new challenges in thermal management and safe vehicle operation. Existing efforts have focused on the modeling and control of thermal systems. However, the dynamic behavior of the electrical and mechanical components increases the complexity of the power management system. To enable model-based system design and real-time application tool development, this paper presents a graph-based modeling framework to represent the dynamic behavior of electrical and mechanical components onboard a UAV. An algorithm for composing a system-level graph model from component-level graph models is introduced. Cell and motor models are experimentally validated. A fault detection case is presented for a UAV model to demonstrate modeling capability for real-time applications.