Automatic landing for fixed-wing unmanned aerial vehicles with optical sensors

An autopilot for the landing of fixed-wing mini unmanned aerial vehicles is presented in this work. The objective is to realize a landing autopilot which allows a coordinated landing along a predefined approach path without any map data or previously measured landing coordinates as well as in the absence of global positioning system measurements. Optical sensors for the perception of the landing site and the true ground onboard the MAV are utilized in a direct feedback scheme based on the MAVs basic controllers, rather than fusing the sensor information to a navigation filter. This ensures a minimum implementation effort for the landing autopilot. The landing control is separated in two parts, the landing approach and the touchdown phase. For the landing approach, a visual servoing controller has been developed. It uses direct feedback from, at minimum, an inertial navigation system, an airspeed sensor and a camera. The landing site has to be marked with three artificial visual markers placed by the operator in a defined triangular shape. During the final stage of the landing, the base markers of the marker triangle leave the camera's field of view. In addition to the inertial navigation system and airspeed sensor, the remaining single optical marker at the top of the triangle and two additional optical flow sensors are applied to control the touchdown phase. Finally, the implementation of the automatic landing system on a real mini unmanned aerial vehicle system is outlined. The presented flight tests demonstrate the fully automatic landing of a fixed-wing mini unmanned aerial vehicle along a predefined path relative to an artificially marked landing site and a coordinated touchdown relative to the true ground based on optical sensors.