Dynamic characteristics analysis and fuzzy control in the full conversion of a small tiltrotor unmanned aerial vehicle

Abstract

Dynamic characteristics analysis and fuzzy control of a tiltrotor UAV are presented. In order to design a full-conversion flight controller for a tiltrotor UAV, the dynamic characteristics of a small tiltrotor UAV during helicopter-to-airplane conversion is investigated. In conversion mode, the longitudinal dynamic characteristics of a target model shows nonlinearity. A six-degree-of-freedom nonlinear equation of motion using computational fluid dynamic data and wind tunnel test data is developed based on a Bell Model 301 tiltrotor research aircraft. It reflects the flight test information and realistic aerodynamic data as accurate as possible, and uses the full equations of motion of real flight vehicle excluding the irrelevant equation blocks in the UAVs. The eigenvectors is utilized to investigate the stability of uncontrolled motion of a small tiltrotor UAV to apply the center speed line of the conversion corridor during conversion flight. New center speed lines are defined on the parameters that were set through the eigenvectors and flight test results. The time-varying characteristics of the conversion maneuver, over which system dynamics change rapidly, are handled by a T-S fuzzy control approach in both longitudinal and lateral axes. This method provides more robust control during forward and backward nacelle conversions. Simulation results indicate that a small tiltrotor UAV exhibits a salient feature nacelle tilt during the backward conversion flight from airplane to helicopter mode. The performance of the proposed controller is verified via simulations of applying the rapid reference inputs, aggressive maneuvers and the center speed lines under various tiltrate conditions.