**6. Conclusions and Future Work**

In this study, a new metaheuristic path planning and tracking algorithm for payload hold–release mission is proposed to avoid obstacles. A hybrid HHO–GWO algorithm is proposed by combining the HHO algorithm, with high convergence speed, and the GWO algorithm, which has a high performance in avoiding local optima, so that the quadcopter can both avoid obstacles and track the planned path with minimum error. The performance of the proposed path-planning algorithm is compared with PSO and GWO. The minimum path distance and maximum convergence rate have been obtained with the newly proposed hybrid HHO–GWO metaheuristic optimization algorithm. The waypoints that the quadcopter desires to track are generated with the optimization algorithm not only minimizing distance but also energy. The path tracking has been carried out by these generated waypoints. The payload hold-and-release mission has been realized with a path-tracking controller. The mass component in the quadcopter model is changed during

payload holding and releasing. The position errors occur in path tracking with the sudden mass change of the quadcopter in this payload holding and releasing task. The results of path tracking are indicated by the minimum total path, mean square error, total time and consumed energy have been obtained for the newly proposed hybrid HHO–GWO. The most important contribution of this study is that the proposed control strategy and the position error caused by this mass uncertainty can be minimized. It is planned to perform environmental tests of the proposed metaheuristic-based approach by embedding it on a single UAV in the future. By comparing the results obtained with the results of our current study, studies will be focused on the optimum solution of path generation and tracking problems with the cooperation of multiple UAVs.

**Author Contributions:** Conceptualization, E.B., A.A. and R.H.; methodology, E.B., A.A. and R.H.; software, E.B., A.A. and R.H.; writing—original draft preparation, E.B. and A.A.; writing—review and editing, E.B., A.A. and R.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
