Vortex Ring State Susceptibility Prediction Model for Vertical Takeoff and Landing Configurations

Kurzfassung

The vortex ring state (VRS) is a hazardous aerodynamic condition that occurs in rotorcraft propulsors during descent, leading to severe thrust fluctuations and potential loss of control. Whereas the phenomenon has been extensively studied for conventional helicopters, the susceptibility of emerging electric vertical takeoff and landing (EVTOL) aircraft remains insufficiently understood. These vehicles differ in design and operation, featuring diverse configurations with multiple propulsors, high disk loading, a variety of proposed landing profiles, and rotor tilting - all of which influence VRS behavior. Therefore, assessing VRS susceptibility across various EVTOL configurations and flight conditions is critical to ensure safe and reliable operations. This study presents a robust assessment framework by adapting an existing VRS onset prediction model to account for EVTOL-specific dynamics, especially rotor tilt. A VRS margin metric is proposed to provide a consistent and scalable measure of VRS susceptibility across vehicle types and operating scenarios. The proposed method is validated through high-fidelity simulations using the vorticity transport model, confirming that the model predictions are consistent with wake evolution toward VRS onset. Using this framework, a sensitivity analysis is conducted to examine the effects of landing trajectory, EVTOL configuration, propulsor disk loading, and airframe drag. Although landing trajectory is the dominant factor, susceptibility to the VRS is also influenced by vehicle design and control strategy, highlighting the importance of tailored assessment for EVTOL VRS susceptibility.