Design and evaluation of wind-resistant UAV loitering patterns for sea rescue missions

Sammanfattning

Fixed-wing Unmanned Aerial Vehicles are increasingly being utilized in maritimeSearch and Rescue (SAR) operations due to their superior flight endurance andaerodynamic efficiency compared to a multi-rotor system like a quadcopter. However,unlike rotary-wing UAVs, a fixed-wing aircraft cannot effectively hover over atarget area without suffering to stall, since the requirement of maintaining sufficientforward airspeed to generate lift. Loitering maneuvers prove effective in weak windsbut significantly worse in stronger wind conditions. The steep bank angles requiredto maintain the flight path do result in partial obstruction of the onboard cameraby the drones own airframe. This in practice does reduce the effectiveness of aerialsurveillance during critical rescue missions.The purpose and goal of this thesis was to investigate whether an alternative flightpattern could improve the overall camera visibility while still maintaining the operationaladvantages that fixed-wing UAVs do provide. The work focused on thedevelopment and evaluation of a structured figure-eight based flight pattern whichwas intended to minimize camera blockage and reduce the spatial footprint of themaneuver during maritime SAR missions.The research was conducted entirely within the ArduPilot Software-in-the-Loopsimulation environment using ArduPlane. Along with custom Python scripts thatwere created to automatically generate way point missions and process the capturedtelemetry data extracted from MAVLink logs. The experiments evaluated how thewind speed, wind direction, pattern scale, and maximum allowed roll angle do affectthe outcome on flight stability and also camera visibility. The visibility was analyzedusing a geometric field-of-view and line-of-sight model combined with an occlusioncriterion based on aircraft bank angle. The study concludes that carefully configured figure-eight flight paths can enable afixed-wing UAV to achieve similar surveillance behavior to a hovering multi-rotorUAV while also retaining the advantages that comes with the design choice of afixed-wing. The findings do provide a technical foundation for future developmentfor UAV flight strategies for maritime SAR missions and also demonstrates howflight-path optimization can help to improve aerial observation capabilities underchallenging environmental conditions.