Path Planning for Unmanned Fixed-Wing Aircraft in Uncertain Wind Conditions Using Trochoids

On-board path planning is a key capability for safe autonomous unmanned flight. Recently, it has been shown that using trochoids for turn segments allows for run-time efficient path planning under consideration of the prevailing wind. However, with varying wind conditions and uncertainty in the estimation of wind speed and direction, paths optimized for a reference wind condition may become infeasible to track for the aircraft. In this work, we discuss how to calculate conservative turn rate limits and we present a novel approach to calculate safety distances along trochoidal turn segments in order to account for an unknown wind speed and airspeed component of bounded magnitude. This allows to plan flight paths that are optimized for the currently expected wind condition but are still safe in case the aircraft experiences different wind conditions. We present results from simulation and flight tests which demonstrate the impact of uncertain and varying wind conditions on the tracking performance of paths with circular and trochoidal turn segments. The results show that trochoids can be used to reduce path tracking errors even if the prevailing wind changes significantly. Furthermore, the proposed method to calculate safety distances conservatively over-approximates path deviations in all considered cases. Thus, it can be used to plan safe paths in the presence of uncertain wind conditions without solely relying on conservative performance limits