Towards an Automated Sense-and-Egress Procedure for Small UAV in Icing Conditions: Development of a Baseline Path Following Autopilot

This paper introduces a new concept named Sense-and-Egress that aims at safeguarding small Unmanned Air Vehicles (UAV) in case of an encounter with icing conditions. A short overview of the system operating principles and a plausible architecture candidate are given. The benefits and drawbacks of the proposed solution are assessed with respect to both unprotected (no ice detection or deicing devices) and fully ice-protected vehicles. Enabling technologies and knowledge gaps are briefly explored in order to gauge the maturity of the concept. The nonlinear flight dynamics model of an existing UAV is built up using results from numerical aerodynamics software. The model is then improved and validated using system identification from existing flight test data. A bespoke path following autopilot is designed to control the UAV during the escape maneuver. The selected architecture and its tuning procedure are detailed, then the performance of the main controllers is analyzed in both frequency- and time-domain. A sample case is provided to assess the ability of the autopilot candidate to perform simple egress maneuvers with either a clean or an iced airframe. Suggestions are given for improving the robustness of the autopilot to the effects of ice accretion.