Nonlinear Aero-Propulsive Modeling for Fixed-Wing eVTOL UAV from Flight Test Data

This paper presents a methodology for constructing an aero-propulsive system identification model for a fixed-wing propeller-driven aircraft with limited flight data. Developing a flight dynamics model is an iterative process involving costly and time-consuming flight testing to collect relevant data. To maximize the utilization of available data, this study employs a time-domain system identification procedure on flight data from various maneuvers and flights. The methodology incorporates multivariate orthogonal functions to capture the nonlinear terms representing the coupled effects of the propeller and airframe dynamics. A stepwise regression is then employed to identify the most pertinent model parameters. Estimation of variables associated with the propulsive contribution is accomplished through an electrical propulsive model, identified using command and battery data from static thrust and flight tests. Aero-propulsive derivatives are determined using the output-error method, where the accuracy is assessed based on a colored noise correction. To validate the predictability of the flight dynamics model, out-of-sample data are employed. The construction of the electrical propulsive model and identification of aerodynamic derivatives from flight data were specifically carried out for a particular eVTOL flight test vehicle; however, the techniques employed are generalizable and applicable to other aircraft models.