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

Abstract

Fixed-wing Unmanned Aerial Vehicles are increasingly being utilized in maritime Search and Rescue (SAR) operations due to their superior flight endurance and aerodynamic efficiency compared to a multi-rotor system like a quadcopter. However, unlike rotary-wing UAVs, a fixed-wing aircraft cannot effectively hover over a target area without suffering to stall, since the requirement of maintaining sufficient forward airspeed to generate lift. Loitering maneuvers prove effective in weak winds but significantly worse in stronger wind conditions. The steep bank angles required to maintain the flight path do result in partial obstruction of the onboard camera by the drones own airframe. This in practice does reduce the effectiveness of aerial surveillance during critical rescue missions.

The purpose and goal of this thesis was to investigate whether an alternative flight pattern could improve the overall camera visibility while still maintaining the operational advantages that fixed-wing UAVs do provide. The work focused on the development and evaluation of a structured figure-eight based flight pattern which was intended to minimize camera blockage and reduce the spatial footprint of the maneuver during maritime SAR missions.

The research was conducted entirely within the ArduPilot Software-in-the-Loop simulation environment using ArduPlane. Along with custom Python scripts that were created to automatically generate way point missions and process the captured telemetry data extracted from MAVLink logs. The experiments evaluated how the wind speed, wind direction, pattern scale, and maximum allowed roll angle do affect the outcome on flight stability and also camera visibility. The visibility was analyzed using a geometric field-of-view and line-of-sight model combined with an occlusion criterion based on aircraft bank angle.

The study concludes that carefully configured figure-eight flight paths can enable a fixed-wing UAV to achieve similar surveillance behavior to a hovering multi-rotor UAV while also retaining the advantages that comes with the design choice of a fixed-wing. The findings do provide a technical foundation for future development for UAV flight strategies for maritime SAR missions and also demonstrates how flight-path optimization can help to improve aerial observation capabilities under challenging environmental conditions.