Contact Modeling and Experimental Validation for Start and Landing of VTOL UAVs

Kurzfassung

The Chair of Helicopter Technology at the Technische Universität München (TUM) together with the Institute of Robotics and Mechatronics of the Deutsches Zentrum für Luft-und Raumfahrt (DLR) are developing an Autonomous Rotorcraft for Extreme Altitudes (AREA). The Flying Robots group as part of the DLR-Institute of Robotics and Mechatronics is especially interested in Un- manned Aerial Vehicles (UAVs) with Vertical Take-Off and Landing (VTOL) capabilities. VTOL UAVs are often operated in harsh environments where landing becomes a challenging maneuver. To provide save landing procedures, a realistic contact model of the physical interaction between the VTOL UAV’s landing skids and the landing surface is elaborated in this thesis. This contact model is integrated into a complete simulation model to provide a representation of the helicopter dynam- ics for the process of landing and analysis of ground resonance phenomena. Therefore, helicopter dynamics are elaborated in Maple, a software from Maplesoft for symbolic computing. The result- ing equations of motion are exported to MATLAB code which is implemented into Simulink using embedded MATLAB blocks to provide time histories of the dynamic system. The resulting Simulink model is then adjusted using experimental data from a vibration test, where natural frequencies and mode damping are determined. In order to investigate the phenomenon of ground resonance, Coleman plots are elaborated. A simple model used for the Coleman analysis, is compared to the elaborated simulation model. Due to the rotor configuration, gravity and aerodynamics are succes- sively implemented in the model and its effects on ground resonance are examined. No significant effects are found as ground resonance is mainly driven by inertial forces. Due to the stiff-in-plane rotor blades of the AREA prototype and hinge damping in the rotor hub, ground resonance is found unlikely to occur. Finally, a landing approach is simulated and verified with recorded flight data of four flights where a good accordance is found.