Vision-based Navigation For UAV Probe And Drogue Autonomous Aerial Refueling

Aerial refueling can add fuel to the aircraft in flight,and effectively improve the efficiency of flight.With the continuous development of aerial refueling technology,aerial refueling technology has become one of the important trends of development in aviation field.There are two ways of aerial refueling,which are soft way and hard way.The hard aerial refueling has faster oil transportation speed,more convenient docking process,and better stealth performance compared to the soft.At present,China has mastered the core technology of the soft aerial refueling.Therefore,it is very important to develop the hard aerial refueling technology on the platform of the large transport aircraft,which is of great significance to the overall improvement of China’s aerial refueling capability.In this paper,the modeling and control of an unmanned receiver aircraft were analyzed and researched in the process of hard aerial docking and refueling with a complex airflow field.Firstly,according to the way of generation,the complex airflow field in the process of hard air refueling docking and refueling were divided into four categories.A detailed analysis of three kinds of airflow fields was given,which have a greater influence on the receiver aircraft.They were gas tail vortex field,engine jet and atmospheric turbulence respectively.According to the characteristics of each airflow field,the corresponding mathematical model was established,and the distribution of the air flow field was obtained by simulation.Then the influence of the airflow field on the refueled aircraft was analyzed by theory.Secondly,by Newton’s second law,the nonlinear model with disturbance of refueled aircraft was derived in the track coordinate system.Under the setting flight condition of hard aerial refueling,the refueled aircraft model was trimmed,and then the balance point of the nonlinear model was obtained.The equivalent wind velocity and the equivalent wind gradient were added to the model and the response process of the refueled aircraft under various disturbances was obtained though simulation.Thirdly,the linear model with disturbances of the receiver aircraft was obtained after small perturbation linearization at the equilibrium point.Based on the linear model,the optimal linear quadratic controller was designed,and the state feedback controller was obtained.With the action of the optimal linear quadratic control system,simulation and analysis was carried out for the linear and nonlinear model.The result showed that the response process was basically the same.In order to improve the performance of the control system further,a nonlinear dynamic inverse controller was designed based on the nonlinear refueled aircraft model.And based on this,the guidance law,which was introduced interference and sliding model disturbance observer was designed.The disturbance rejection performance of refueled aircraft under different control strategies was simulated and verified.And it is concluded that the robust performance of the dynamic inverse control system is greatly improved when the sliding mode disturbance observer is added to the dynamic inverse control system and the disturbance is introduced into guidance law.Compared the resulted with the response of LQR-PI control system,it was showed that the disturbance rejection performance of dynamic inverse control system based on sliding mode was better than LQR-PI control system,but it’s dynamic performance of target trajectory was poorer than the LQR-PI control system.Finally,according to different docking channels in the docking progression of receiver aircraft and tanker aircraft,the receiver aircraft was simulated in the LQR-PI control system and nonlinear dynamic control system respectively.The result showed that,in the process of hard air docking and refueling while the receiver aircraft was in the wake filed,the disturbance rejection performance of nonlinear dynamic inverse control system was better than the LQR-PI control system.And then two kinds of control systems were simulated with the different intensity of the disturbance of atmospheric turbulence,which showed that two control systems can both restrain disturbance under mild and moderate influence of atmospheric turbulence,but LQR-PI control system was failure with severe atmospheric turbulence disturbance while the sliding model dynamic inverse control system could still work.According to the above,the attention during docking and refueling stage in the process of hard refueling were put forward.