Research On Conceptual Design Of VFW Aircraft

Synthesizing the efficient cruising ability of conventional FWA(fixed-wing airplane) and the VTOL(vertically take-off and landing) ability of helicopter can enable a vehicle not only to take off or land swiftly in complex circumstances, but also to handle large-range emergencies. Taking off from the islands, mounts or cities, the vehicle can act as a lash-up to provide aerial information support. The vehicle has the both abilities is named VFW(vertically taking-off and landing fixed-wing) aircraft. And it has become a leading edge and hot issue of current research.However, owing to the difference of technical features between the VTOL process and the fixed-wing flight, the existing mixed-mode flight schemes attain both the two operating points by redundancies of thrust components or varistructure, which has caused problems of efficiency and/or reliability and draws back its appliance in small vehicles. It is the main acting point of this paper to jump out of the customary design method, seek a way to simplify and optimize the design of hybrid vehicle, and pursuit the innovation of technical route and integration design.In this paper, the dominated contradiction stands in the way of the development of hybrid vehicle has been figured out: the thrust vector required in cruise quite differs from that in VTOL process, and the integration design method of FWA is incompatible with that of helicopters. On the basis of that, the pursuit of the two operating points would introduce complicated varistructure and unreasonable compromise, along with the problems of additional weight, poor reliability and low efficiency. Thus the two points were handled respectively in a way of unbalanced design of two operating points: one single point was optimized with another considered, which orientated the vehicle as VFW aircraft to handle the emergencies without requirements of long-time hover.To avoid the problems brought out by the complex mechanism and obtain higher cruising performance, a nonsymmetrical Y-configuration with simple and fixed structure was proposed in this paper. The system could gain the required control moment by itself, and the distributed/hybrid propulsion and reused structure were utilized to shorten the thrust difference of the main propulsors between the two flight modes and to reduce the additional weight of the server propulsor, which has improved the reliability and efficiency.Following from that, the fixed-wing cruising mode was taken as the design point. The geometrical and aerodynamic models were built and the three-tunnel static stability features were analyzed, referring to the characteristics of FWA. The geometrical and aerodynamic relationships among the components and the whole vehicle were built; and the co-design method of the tails was investigated. Meanwhile, the vertical flight mode was required to be attainable. Based on quantitative analyses of nonsymmetrical Y-configuration and the four models of ducted fan/windmill in axial/non-axial flow, the relationships of geometry, force and power between the master DFs(ducted fan) and the server DF was built, and the co-design method was attained, and the co-design method of the master/server ducted fans was investigated. The tilting moment of the ducted fans was compared with that of the tails, which has laid a foundation for the followed transition maneuver design.In the end of the paper, the componential weight model was built. By the combination of this weight model and the geometrical and aerodynamic models built above, the componential contribution to the whole weight and the influencing characteristics were researched, which formed a conceptual design loop. Prototypes with 10 kg payload to meet the requirement of reconnaissance appliance and 50 kg payload to meet the requirement of reconnaissance/attack appliance were optimized respectively, and parameters met the design indexes, stability requirements and restriction of rotate speed of engines obtained by the fuel-efficient-objective optimization. Based on the results, the assumptions and estimation utilized before were proved feasible, and the weight and aerodynamic disciplines in condition of lowest fuel consumption were concluded.In this paper, a new concept mixed-mode flight scheme has been built, a nonsymmetrical Y-configuration has been proposed, a fuel-efficient-objective design model has been provided, and the key technologies indexes have been detached, which has laid the foundation of the further design and offered a reference for development of the VTOL FWA.