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DOI: 10.2514/1.32750 Since October 2005, the T-wing tail-sitter unmanned air vehicle has undergone an extensive program of flight tests, resulting in a total of more than 50 flights, many under autonomous control from takeoff to landing. Starting in August 2006, free flights with conversion between vertical and horizontal flight modes have also been undertaken. Although the latter flights have required some guidance-level ground-pilot input, significant portions of them were performed in autonomous mode, including the transitions between horizontal and vertical flight. This paper considers the overall control architecture of the vehicle, including the different control modes that the vehicle was flown under during the recent series of tests. Although the individual controllers for each flight mode are unremarkable in themselves, it is notable that the aggregate system allows the vehicle to fly throughout its entire flight envelope, which is considerably broader than that of conventional fixed- or rotary-wing vehicles. The performance of the controllers for the different flight modes will also be considered, with a particular focus on hover dispersion results, in differing wind conditions. The majority of these flights were performed on a tether test rig during autonomous control development, to ensure vehicle safety with minimal impact on vehicle dynamics. The demonstration of autonomous flight under the constraints imposed by the tether system in winds up to 18 kt is a significant achievement. Results from the more recent horizontal flight tests with conversions between vertical and horizontal flight are also presented. Most important, these results confirm the basic feasibility of tail-sitter vehicles that use control surfaces submerged in propeller wash for vertical flight control.

This paper considers the key aspects of the development of the T-Wing tail-sitter unmanned air vehicle (UAV), starting from a novel concept through to the current flight test vehicle. The T-Wing is a twin-engine UAV that relies on propeller wash over its elevons and rudders for control during low-speed vertical flight but performs the majority of its mission in wing-borne horizontal flight. The foundation for the successful development of the T-Wing to date is the integrated aerodynamic and propulsion analysis of the wing–propeller interaction. This is critical for the vehicle's vertical flight controllability and feeds directly into other key areas of the overall development process, including the use of multi-disciplinary optimization for preliminary vehicle design and the development of an extensive six-degree-of-freedom non-linear simulation of the vehicle to aid in control system design. This paper also presents some of the testing that has been used to support the analysis. This has allowed the T-Wing to progress from a paper concept to a flying research UAV. [ABSTRACT FROM AUTHOR]

ObjectiveIn order to reduce the wave-making resistance of high-speed ships, this paper proposes an innovative hydrofoil appendage with a drag reduction effect. MethodsAn NACA 0012 airfoil is selected for the hydrofoil appendage cross-section, and a series of studies on the drag reduction effects of bow-mounted hydrofoil appendages of different sizes and installation positions is carried out using the numerical calculation method verified by convergence and reliability tests. The drag reduction effect of adding a T-wing to the stern of a ship is further studied. ResultsThe results show that the maximum drag reduction is 7.38% and 6.82% at high speeds of Froude number 0.45 and 0.494 when the hydrofoil appendage is only installed at the bow. The drag is further reduced after adding the T-wing to the stern, and the total drag reduction is 9.35% and 11.13% at high speeds of Froude number 0.45 and 0.494. Conclusions The hydrofoil appendage with a drag reduction effect proposed in this paper greatly reduces the total drag of high-speed ships, improves their speed and provides new technical means for further improving their navigation performance.

Abstract Since the handover of the sovereignty of Hong Kong from Britain to China in 1997, convergence between Mainland China and Hong Kong has gradually emerged. During this process, young people have engaged in demonstrations to express their dissatisfaction with government policies and limited socio-economic progression. However, the underlying reasons for their dissatisfaction have not been fully investigated. This study investigates their perceived challenges and opportunities during the convergence, with the objective of identifying the factors affecting the Mainland China–Hong Kong convergence and examining young people’s perceived challenges and opportunities during the convergence. Mixed research methods of focus groups and a survey were adopted. Ten focus groups with 83 participants were conducted to collect qualitative data on the factors relating to convergence. Based on the qualitative data, a questionnaire was constructed to investigate young people’s perceived challenges and opportunities during the convergence, using a sample of 1253 young people. Ordinary least-squares regression was applied to analyse the relationships among identified factors. The study found that Hong Kong’s youth tended to regard the Mainland China–Hong Kong convergence as an opportunity for socio-economic progression, and they identified three challenges during the convergence. It also revealed that young people’s higher education, perceived housing challenges, and perceived socio-economic challenges are negatively related to the convergence, whereas their perceived challenges associated with entrepreneurship and innovation are positively related to the convergence. The development of more well-balanced and mutually beneficial policies that satisfy the needs of young people will lead to a higher acceptance of the convergence. As such, young people will be more willing to embrace the opportunities and face the challenges brought about by the convergence, resulting in a more harmonious society and socio-economic progression.