Development of an icing-resilient autopilot for automated egress of small UAVs from dangerous icing conditions

Abstract

Small fixed-wing unmanned air vehicles (UAVs) weighting under 20 kg are typically not protected against icing. Yet, commercial and military users find interest in operating this class of platform under cold climates where encounters with icing conditions are likely. This paper introduces a new concept named sense-and-egress that aims at safeguarding small UAVs in case of an inadvertent icing encounter. A short overview of the system’s operating principles and a plausible architecture candidate are given. Then, the benefits and drawbacks of the proposed solution are assessed with respect to both unprotected (no ice detection or deicing devices active) and fully ice-protected vehicles. Enabling technologies and knowledge gaps are briefly explored in order to gauge the maturity of the concept. The non-linear 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 manoeuvre. The selected control system structure and the tuning procedures for both the attitude controller and the total energy control system are detailed. The ability of the baseline autopilot to perform a simple egress manoeuvre with both clean and iced airframes is assessed in simulation. Simple yet effective solutions are implemented to improve the autopilot performance in icing while preserving its gust resistance capabilities.