Hover-Informed Equivalent Lifting-Line Model for Predicting Aerodynamic Interference in eVTOL Multi-Rotor System

Aerodynamic interference among multiple rotors significantly affects the performance and efficiency of electric Vertical TakeOff and Landing (eVTOL) aircraft, particularly in complex configurations such as coaxial or tandem layouts. High-fidelity computational methods can accurately capture these interactions but are computationally expensive, while conventional analytical models often neglect hover and low-speed regimes, reducing prediction accuracy. To address these limitations, this paper develops a hover-informed equivalent lifting-line model that integrates experimental hover data with analytical expressions to predict rotor-rotor aerodynamic interference across the full flight envelope. The proposed method is evaluated against both tandem and coaxial rotor configurations, showing good agreement with experimental and computational results. Application to a coaxial octo-rotor eVTOL demonstrates that at hover and low speeds, the upper front rotor mainly interferes with its corresponding lower rotor and at low-to-medium speeds it primarily affects the rear rotors. Aerodynamic interaction also significantly alters the power distribution of the rear rotors, causing an increase in power with forward speed under hover and low-speed conditions. The lower rear rotor experiences the strongest interference, contributes least to total thrust, and underperforms compared with the other rotors. These findings indicate that the hover-informed equivalent lifting-line model effectively captures rotor-rotor aerodynamic coupling across the full flight envelope and provides a computationally efficient tool for eVTOL design and optimization.