Linearized Inflow and Interference Models from High Fidelity Free Wake Analysis for Modern Rotorcraft Configurations

Linearized inflow models have been used to represent dynamic wake effects for control law development and flight dynamics simulation of conventional main rotor / tail rotor helicopters. With the current focus in the industry toward high-speed concepts and electric vertical take-off and landing (eVTOL) aircraft, modern rotorcraft designs are trending away from the conventional main rotor / tail rotor configuration for which low-order dynamic inflow models have been applied and validated. Configurations currently in design and flight testing stages include coaxial, coaxial compound, tiltrotor, multi-rotor, and augmented lift concepts that involve strong rotor-rotor and rotor-airframe aerodynamic interactions. To support current trends in rotorcraft designs, it is necessary to revisit the low-order inflow model structure and application with respect to modern rotorcraft analysis and flight simulation methods. Research and development in recent years has focused on methods to extract equivalent linearized inflow / interference models from high-fidelity nonlinear rotorcraft aeromechanics models. This paper describes continuing work to develop an automated method for linearized inflow model extraction from high-fidelity rotorcraft aerodynamic / wake models. Emphasis is placed on the formulation of generic inflow model structures for single and coaxial rotor systems that capture relevant physical phenomena without over-parameterizing the low-order state-space inflow model.