C-Rate Constrained Path Planning for Battery Pack Health Management in Long-Term eVTOL Operations

This paper develops a battery-aware trajectory optimization framework for a tilt-rotor electric vertical takeoff and landing (eVTOL) aircraft operating within advanced air mobility (AAM) systems. Although eVTOL vehicles enable zero-emission flight and flexible routing, their heavy reliance on lithium-ion batteries imposes critical operational constraints, particularly during vertical takeoff and landing, transition, and other high-power maneuvers that could accelerate battery degradation and reduce long-term mission reliability. To address these challenges, we formulate a multi-phase optimal control problem (OCP) that explicitly regulates the battery discharge rate (C-rate) throughout the flight mission. The proposed approach integrates multi-phase tilt-rotor eVTOL dynamics with the Rint battery equivalent circuit model (ECM), enabling trajectory decisions that account for long-term capacity fade. The optimization jointly minimizes mission time and energy consumption, while enforcing constraints on state-of-charge (SOC) evolution, C-rate limits, and actuator capabilities. We solve the proposed multi-phase OCP using the GPOPS-II optimal control solver. The OCP problem considers an eVTOL powertrain system and battery pack in addition to the eVTOL dynamics. Simulation results demonstrate that the C-rate-constrained trajectory generated by the optimizer yields safer and more sustainable operation without compromising mission performance, thereby supporting long-term reliability of eVTOL operations.