Collision-free paths Motion planning 2 Unmanned aerial vehicles (UAV) 2 3-D environments 1 3D path planning 1 Air navigation 1 Antennas 1 Avoid obstacles 1 Cluttered environments 1 Collision avoidance 1 Curve fitting 1 Dynamics 1 Elliptic tangent graph 1 Energy efficiency 1 Energy efficient 1 Fixed wings 1 Fixed-wing UAV 1 Flight paths 1 Free flight 1 Graph theory 1 Guidance strategy 1 Heuristic methods 1 High quality 1 Node-based 1 Node-based algorithm 1 Obstacles avoidance 1 Path planners 1 Path planning method 1 Tangent graph 1 Target guidance 1