Aerodynamic Analysis of Stopped and Stopping Rotors in Lift+Cruise eVTOL Configurations

This study investigates the aerodynamic behavior of lift rotors in a representative lift+cruise electric vertical takeoff and landing (eVTOL) configuration using high-fidelity Computational Fluid Dynamics (CFD) simulations. As lift+cruise concepts gain prominence for Urban Air Mobility (UAM) applications due to their operational simplicity, flight performance, and reduced cruise noise, a detailed understanding of rotor aerodynamics during transition and cruise is critical. CFD analysis was conducted for both slowed rotors at high advance ratios and fully stopped rotors, where traditional predictive tools become inaccurate. Results show that lift rotors operating at advance ratios approaching three exhibit quasi-steady behavior similar to stopped rotors. The influence of rotor lock orientation on aerodynamic loads was characterized, with a freestream-aligned lock angle minimizing drag and asymmetry. A rotor hub fairing was found to reduce blade root separation and drag, though at the cost of slightly increased hub moments. The sensitivity of axial loads to vehicle pitch angle was quantified, highlighting the need to account for effective angle of attack in cruise load predictions. These findings inform future modeling strategies, control system design, and airframe integration for advanced eVTOL vehicles concepts.