Flight Control Research Based On Alterable Thrust Direction Uavs

UAV system will be used for reconnaissance missions as well as for strike operations over future battlefield. UAV system's specific characteristics of ability of loitering and performing sudden strikes make it one of the focuses of research and development all over the world. The problem of precise trajectory control is very important for UAV system's development. In view of the future of battlefield environment, this dissertation focus on the problem of trajectory control for alterable thrust direction UAVs.Inspired by the successful application of thrust vectoring techniques in flight control system, techniques we called"alterable thrust direction"are proposed for propeller-driven UAV system. A nonlinear mathematical model is developed for alterable thrust direction UAV systems, and the difference between it and the traditional UAV mathematical model is analyzed. Based on the concept of maneuverability and agility for routine aircrafts, the computation of indexs of energy maneuverability, course manoeuvrability, space maneuverability, transient agility, functional agility and potential agility is deduced, and comparison with those of routine UAVs is made. The result shows that techniques of alterable thrust direction can improve the UAVs'maneuverability and agility under certain conditions.In addition to aerodynamic surfaces control, thrust deflection control is used as well to solve the problem of attitude control for UAVs. And so, a combined attitude control strategy is proposed. In this strategy, the law of alterable thrust direction control and that of aerodynamic surfaces control are consistent in form. The correctness of mathematic model of alterable thrust direction UAVs is verified through simulation of nonlinear object. The simulation also shows that the techniques can improve the maneuverability of UAVs. A control system consisting of inner loop and outer loop is designed to solve the problem of trajectory control. The control variables are still of the three aerodynamic surfaces, but two thrust deflection angles are added into the outer loop. The simulation proves that the alterable thrust direction techniques based on information such as altitude difference and cross track error can improve the precision of UAVs'trajectory control.To further improve this technique's application in UAVs, Brain emotional learning (BEL) model is introduced to design thrust deflection control law, in anticipating the improvement of controller's online adaptive ability. After the stability analysis of the BEL model's inner weights, thrust deflection direct control scheme and indirect control scheme are designed respectively. The simulation results show that effect of control is improved under the two schemes, control system based on BEL model exhibits good autotuning ability and adaptiveness.As for the engineering realization of this control system, besides the discussion of the architecture of alterable thrust direction UAVs, the selection and design of hardware and software are carried out. During the design process, modular techniques are used to solve the problems in hardware architecture and communication software design. In accordance with the mission requirement of flight control, layered software architecture and grading timer are designed. A GUI software kit is developed using VC++ tools for human computer interface. That kit increases the software development efficiency, and the maintainability of software system is also improved.To verify the effectiveness of alterable thrust direction UAV control system, semi-physical simulation is carried out. The constitution of flight simulation platform is discussed, and the hardware selection and software logic design are proposed. The computation efficiencies of various flight simulation algorithms are analyzed to ensure the precision and real-time capability of simulation. In the last part of this dissertation, the specific functions of simulation system and the superiority of alterable thrust direction control techniques are demonstrated through typical semi-physical flight simulations.