## 3 Conclusions  
The execution of inspection and maintenance operations in illustrative scenarios such as power lines, bridges, viaducts and other civil infrastructures, consisting typically of the appropriate collocation of a sensor or device in the point of interest, presents considerable risk when conducted at high altitude by human operators, and becomes a technological challenge when it is intended to be performed by an aerial robot operating outdoors. Overcoming the gap between research in indoor laboratories and practical application in realistic outdoor conditions also introduces significant difficulties, particularly in terms of positioning accuracy and reliability, requiring the integration of additional systems that reduce the effective payload. New mechatronic designs, estimation and measurement methods, control frameworks and technological solutions emerge from demanding applications that have been shown increasing interest in terms of the application of aerial robots to reduce the time, cost and risk compared with traditional procedures. Since most of the inspection and maintenance devices currently employed in the realization of these operations are intended to be used by human operators, aerial robotics researchers and engineers face the problem of integrating or adapting these devices to aerial platforms, where the limited payload and flight time capacity are still the main constraints. It is foreseeable, however, that manufacturers will develop new inspection solutions adapted for aerial robots given the benefits and potential uses evidenced by multi-rotors. Author Contributions:Conceptualization, A.S., J.C. and M.O. ; investigation, A.S., J.C. and M.O. ; writing--original draft preparation, A.S.; writing--review and editing, A.S., J.C. and M.O. ; visualization, J.C. and M.O. ; supervision, J.C. and M.O. ; All authors have read and agreed to the published version of the manuscript. Funding:This research was partially funded by the European Commission grant number 871479 through the AERIAL-CORE H2020 project (AERIAL COgnitive integrated multi-task Robotic system with Extended operation range and safety). Acknowledgments:We want to thank [PERSON] from the University of Seville, coordinator of the AERIAL-CORE project, for his contribution in the dissemination of this Special Issue. Conflicts of Interest:The authors declare no conflict of interest. References  
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