Navigation and Control of Unconventional VTOL UAVs in Forward-Flight With Explicit Wind Velocity Estimation

This paper presents a solution for the state estimation and control problems\nfor a class of unconventional vertical takeoff and landing (VTOL) UAVs\noperating in forward-flight conditions. A tightly-coupled state estimation\napproach is used to estimate the aircraft navigation states, sensor biases, and\nthe wind velocity. State estimation is done within a matrix Lie group framework\nusing the Invariant Extended Kalman Filter (IEKF), which offers several\nadvantages compared to standard multiplicative EKFs traditionally used in\naerospace and robotics problems. An SO(3)- based attitude controller is\nemployed, leading to a single attitude control law without a separate sideslip\ncontrol loop. A control allocator is used to determine how to use multiple,\npossibly redundant, actuators to produce the desired control moments. The wind\nvelocity estimates are used in the attitude controller and the control\nallocator to improve performance. A numerical example is considered using a\nsample VTOL tailsitter-type UAV with four control surfaces. Monte-Carlo\nsimulations demonstrate robustness of the proposed control and estimation\nscheme to various initial conditions, noise levels, and flight trajectories.\n