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To expand the application prospects of quadrotors in challenging scenes such as those with dense obstacles and narrow corridors, task-driven reconfigurable quadrotors are highly desirable. Aiming to address hazard missions, in this paper, translational reconfigurable quadrotors and rotational reconfigurable quadrotors are proposed with their assumptions and mathematical models. Related motion control laws were designed using model reference adaptive control (MRAC) theory based on Lyapunov stability theory, whose validity was demonstrated by sufficient numerical simulations. The simulation results verify the feasibility of the proposed control laws and reveal the important effect of time delay on the stability of the motion control system. Additionally, the dependence of motion control's stability on the time constant of reference system was discussed. [ABSTRACT FROM AUTHOR]

In this paper, the aerodynamic performance of an orthogonal octorotor UAV considering horizontal wind disturbances is investigated with numerical simulations and experiments. To obtian the effect of horizontal wind on the flight efficiency of the orthogonal octorotor UAV, the power consumption and thrust with different wind speeds (0–4 m/s) and rotational speeds (1500–2300 RPM) are measured in a low-speed wind tunnel. Also, the velocity distribution of downwash flow, blade tip vortex distribution, streamline distribution and rotor blade tip pressure distribution of the orthogonal octorotor UAV were simulated by the computational fluid dynamics (CFD). The test results show that the thrust is increased at lower wind speed compared with 0 m/s. Specifically, it increased by 8.1% at 2 m/s and 8.8% at 4 m/s, respectively. It is interesting to note that the increased power consumption caused by the interference of horizontal wind at a higher rotor speed leads to a decrease in power loading (PL). Additionally, the thrust increased with a higher PL at low speed, where the PL achieved the maximum for the wind of 2.5 m/s and obtained a better aerodynamic performance. Compared with traditional octorotor UAVs and eight equivalent isolated rotors, the orthogonal octorotor UAV has also been proven to obtain good wind resistance. Simulation results show that the increase in wind speed and rotor speed will make the flow field more complex and the airflow interference between rotors more intense, which leads to changes in rotor thrust and power consumption. [ABSTRACT FROM AUTHOR]

Micro aerial vehicles (MAVs) usually suffer from several challenges, not least of which are unsatisfactory hover efficiency and limited fly time. This paper discusses the aerodynamic characteristics of a novel Hex-rotor MAV with a coaxial rotor capable of providing higher thrust in a compact structure. To extend the endurance during hover, flow field analysis and aerodynamic performance optimization are conducted by both experiments and numerical simulations with different rotor spacing ratios (i = 0.56, 0.59, 0.63, 0.67, 0.71, 0.77, 0.83, 0.91). The measured parameters are thrust, power, and hover efficiency during the experiments. Retip ranged from 0.7 × 105 to 1.3 × 105 is also studied by Spalart–Allmaras simulations. The test results show that the MAV has the optimum aerodynamic performance at i = 0.56 with Retip = 0.85 × 105. Compared to the MAV with i = 0.98 for Retip = 0.85 × 105, thrust is increased by 5.18% with a reduced power of 3.8%, and hover efficiency is also improved by 12.14%. The simulated results indicate a weakness in inter-rotor interference with the increased rotor spacing. Additionally, the enlarged pressure difference, reduced turbulence, and weakened vortices are responsible for the aerodynamic improvement. This provides an alternative method for increasing the MAV fly time and offers inspiration for future structural design. [ABSTRACT FROM AUTHOR]