VPM-Derived State Space Inflow Model for Multi-Rotor Air Vehicle Modeling and Simulation

To achieve increased speed, range, and payloads of existing rotorcraft, Future Vertical Lift (FVL) considers compound configurations that have multiple rotors, ducted fans, auxiliary wings, etc. The FVL configurations introduce more aerodynamic lifting devices/surfaces that make aerodynamic interaction a dominant phenomenon to address. Recent development of eVTOL air vehicle for urban commuting also involves multiple rotors in order to provide sufficient lift and controls to meet the VTOL requirement within limited landing/takeoff space. There is a strong need for developing a state space inflow model that supports flight dynamics modeling and simulation of Future Vertical Lift (FVL) with multi-rotor systems. This paper discusses a systematic approach that is effectively used to derive a finite state induced inflow model from first-principle based viscous Vortex Particle Method (VPM) using the CIFER R system identification tool. The paper presents an inflow model framework that accommodates both the rotor self-induced and mutual interference between an arbitrary number of rotors in one unified formulation. The off-rotor wake interference on aerodynamic surfaces and fuselage is also addressed by the unified formulation. The first-principle based VPM captures the fundamental interactional rotor wake dynamics and provides the accuracy for the inflow model parameters identified from the VPM simulation. The model formulation and model parameter identification method were verified for both single main rotor and co-axial rotor configurations. The verifications were performed by comparing the inflow response of the identified finite state inflow model with first-principle based VPM simulation at various flight conditions in both frequency and time domains. The approach was also validated using measured helicopter frequency response data and excellent agreement between the predicted and the measured response data was obtained.