Disturbance observer based control for gust alleviation of a small fixed-wing UAS

This paper outlines a method of applying a linear disturbance observer to a small Unmanned Aerial System (UAS) to reduce the influence of unpredictable gusts on the non-linear aircraft dynamics. This work aims to show that by using a linear state-space model it is possible to estimate external disturbances and use the available control surfaces to alleviate the influence of gusts on aircraft dynamics accordingly. This paper focuses on the longitudinal channel of a small UAS to demonstrate the strategy. A baseline Linear Quadratic Regulator with Integral Action (LQI) is first developed; the disturbance observer based control strategy is then patched into this baseline controller to demonstrate the performance improvement. Simulations are conducted using the designed linear observer to alleviate various disturbance sources on a fully non-linear simulation of the UAS. This aims to demonstrate performance of an observer in a realistic situation where uncertainties between the linear observer and non-linear plant to be controlled are present.