Design of a Symmetrical Quad-rotor Biplane Tail-Sitter Aircraft without Control Surfaces and Experimental Verification

This paper presents the design of a symmetrical quad-rotor biplane tail-sitter VTOL UAV (Vertical Take-off and Landing Unmanned Aerial Vehicle) which is composed of four rotors and two symmetrically mounted fixed wings. This aircraft achieves high accuracy in the attitude control and smooth flight mode transition with four rotors rather than the conventional VTOL UAVs using control surfaces. The proposal of angled rotor mounting is adopted to address the issue of insufficient yaw control authority. The layout of symmetrically mounted fixed wings makes the aircraft have capability of rapid bidirectional flight mode transition to improve maneuverability. To validate the performance of the aircraft, simulation and flight experiments are both implemented. These results show that the aircraft has a rapid yaw response under condition of the stable attitude control. In comparative experiment, it is shown that the aircraft is more flexible than other similar configuration of aircrafts. This symmetrical quad-rotor biplane tail-sitter VTOL UAV will have a wide range of potential applications in the military and civilian areas due to its superior performance.

Design of a Symmetrical Quad-rotor Biplane Tail-Sitter Aircraft without Control Surfaces and Experimental Verification

This paper presents the design of a symmetrical quad-rotor biplane tail-sitter VTOL UAV (Vertical Take-off and Landing Unmanned Aerial Vehicle) which is composed of four rotors and two symmetrically mounted fixed wings. This aircraft achieves high accuracy in the attitude control and smooth flight mode transition with four rotors rather than the conventional VTOL UAVs using control surfaces. The proposal of angled rotor mounting is adopted to address the issue of insufficient yaw control authority. The layout of symmetrically mounted fixed wings makes the aircraft have capability of rapid bidirectional flight mode transition to improve maneuverability. To validate the performance of the aircraft, simulation and flight experiments are both implemented. These results show that the aircraft has a rapid yaw response under condition of the stable attitude control. In comparative experiment, it is shown that the aircraft is more flexible than other similar configuration of aircrafts. This symmetrical quad-rotor biplane tail-sitter VTOL UAV will have a wide range of potential applications in the military and civilian areas due to its superior performance.

In-Situ Immobilization of H₅PMo₁₀V₂O₄₀ on Protonated Graphitic Carbon Nitride under Hydrothermal Conditions: A Highly Efficient and Reusable Catalyst for Hydroxylation of Benzene

A novel heterogeneous catalyst was prepared by in situ immobilization of H₅PMo₁₀V₂O₄₀ (PMo₁₀V₂) on protonated g-C₃N₄ (pg-C₃N₄) under hydrothermal conditions. The results of ζ potential, PL, FT-IR, XRD, and XPS indicated that PMo₁₀V₂ was immobilized on the protonated CNC of CN heterocycles. XPS and EPR confirmed the presence of V⁴⁺ in the catalyst due to electronic interaction between PMo₁₀V₂ and pg-C₃N₄. The textural and morphology properties of the catalyst were characterized by N₂ adsorption–desorption, SEM, and TEM. PMo₁₀V₂/pg-C₃N₄ showed excellent catalytic performance with 25.8% benzene conversion and 99.7% selectivity to phenol in the hydroxylation of benzene to phenol. The excellent catalytic performance of PMo₁₀V₂/pg-C₃N₄ could be attributed to high dispersion of PMo₁₀V₂ on pg-C₃N₄, the presence of V⁵⁺/V⁴⁺ redox pairs, and the cooperative benzene-activation capability of g-C₃N₄. The PMo₁₀V₂/pg-C₃N₄ catalyst can be easily recycled without loss of activity

Does Farmland Transfer Lead to Non-Grain Production in Agriculture?—An Empirical Analysis Based on the Differentiation of Farmland Renting-In Objects

The study aims to estimate different land leasing entities’ intentions and drivers to grow non-grain crops. In 2021, following a multistage sampling technique based on non-grain farmland, 264 farmers from the Zengcheng District of China were interviewed using a well-structured questionnaire based on the theory of planned behavior and transaction cost. The structural equation model was used to quantitatively reveal the influence mechanism of the non-grain use of the transferred farmland. The difference in the non-grain use of the transferred farmland was analyzed from the perspective of the differentiation of the renting entities. The results showed that the profit margin of non-grain and food crops, and the follow-up behavior of business entities, all promote the non-grain utilization of transferred farmland; however, the transaction costs of non-grain utilization and the endowment constraints of agricultural businesses inhibit the non-grain utilization of farmland. The non-grain crops in the suburbs are more profitable, and the transaction costs of the farmland leasing entities are low, so they tend to be grain-free; the rents of the farmland in the outer suburbs are low and can be operated on a large scale, and the leasing entities tend to be grain-oriented. Large-scale leasing entities tend to grow grain, while small-scale leasing entities tend to grow non-grain crops. In general, large-scale leasing entities in the outer suburbs have high transaction costs and low land rents and tend to be grain-oriented. The small-scale leasing entities in the suburbs are close to the market, the transaction costs are low, the rental price of farmland is high, and they are more inclined to grow non-grain crops. The non-grain utilization of the leased farmland should be treated separately, the supervision of the grain production capacity of the leased farmland should be carried out, and the rotation of grain and non-grain crops should be encouraged; the moderate scale operation in outer suburbs should be encouraged, and the construction of high-standard basic farmland for grain-growing farmland should be promoted