In this study, a modified Block A* algorithm is applied to the path planning of hybrid-driven underwater gliders, which combine the buoyancy-driven mode of underwater gliders and the propeller-driven mode of autonomous underwater vehicles, in the ocean environment characterized by strong currents. The objective is to predict a sequence of steering directions and the appropriate driving mode, such that vehicles can minimize their energy consumption to reach the goal region. In this work, we modify the path generation approach of the original Block A* algorithm to gain more realistic paths for hybrid-driven underwater gliders and apply an effective energy consumption model in the heap value calculation to find energy-cost optimal paths. Zermelo's function is also incorporated to select the driving mode. The performance of the presented method is then discussed by conducting simulations in three different ocean environments. The results indicate that compared to other methods, the modified Block A* method avoids local turbulent flow and gains feasible paths for hybrid-driven underwater gliders at a lower energy cost.

With the rapid development of vertical takeoff and landing (VTOL) aircraft, the blade design of a propeller suitable for VTOL aircraft with a wide range of operating conditions has become a challenging and popular task. This paper proposes a multi-objective optimization framework for a VTOL propeller using an inverse design method at the cruising stage, which is developed from the Betz optimum theory and blade element momentum theory (BEMT). Different from passing studies, the maximum thrust-to-weight ratio at hover (MTWRH) is taken as one of the two objectives in this paper, which is closely related to the wind-resistance capability and maneuverability during takeoff and landing. The other objective is the energy consumption of the whole mission profile. A fixed pitch propeller (FPP) and a variable pitch propeller (VPP) are both optimized using the proposed framework for the Vahana A³ tilt-wing aircraft and validated by the computational fluid dynamics (CFD) method. The influences of the level flight energy ratio, hover disk loading and cruising speed toward the optimization result are analyzed, respectively. The results show that the MTWRH has a significant impact on the optimization result both for the FPP and VPP. A comparison between the two propeller forms validates the advantages of the VPP both in energy saving and takeoff maneuverability. The quantitative rules of this advantage with the level flight energy ratio are calculated to provide a reference for choosing the appropriate form. Overall, the methodology and general rules presented in this paper support the propeller optimization and form selection for VTOL aircraft.

This article studies the model, control and simulation on transition flight of a novel tail-sitter with vertical takeoff and landing capability. The proposed tail-sitter adopts an innovative varying fuselage shape design to break the technical bottleneck in the balance of efficient horizontal flight and agile vertical flight. Overset grids and computational fluid dynamic methods are used to explore the vehicle’s prestall aerodynamics, which are relative to not only the angle of attack and sideslip angle but also to the varying angle between two rear fuselage’s parts. High angle of attack aerodynamics based on the improved Viterna and Corrigan stall model is also established for this novel tail-sitter. Meanwhile, an accurate model of the propeller is tested in a wind tunnel. Combining the forces and moments generated by propellers, aerodynamics and gravity, a 6DoF nonlinear time-varying dynamic model is built. A robust controller based on incremental dynamic inversion method is designed for this tail-sitter, which is good at dealing with uncertainties and external forces. Nominal and model mismatch conditions are simulated to verify the controller’s performance. Different varying strategies for the mechanism are analyzed during the transition flight. Simulation results show that this novel tail-sitter can transform between vertical and horizontal flight mode easily and the varying strategy related to pitch angle is a prior choice for transition flight.