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Abstract This paper investigates the anti-disturbance constrained trajectory flight control for the ultra-low altitude airdrop under airflow disturbances, by innovatively integrating the finite time convergent high-order sliding mode observer and barrier Lyapunov function-based back-stepping technique. The dynamics of transport aircraft during the airdrop are established based on the fixed-wing aircraft's 6 DOF nonlinear model and are transformed into the affine nonlinear form for the convenient control design. These dynamics include the complex influence of the flow disturbances, the ground effect, the consecutive movement and abrupt extraction of the heavy cargo. Then, the flight controller is divided into several cascade subsystems via back-stepping technique. The items reflect the disturbances during the drop in each subsystem, as well as the items which are independent of the predefined virtual control variables, are taken as components of the "lumped disturbances" which are estimated and compensated by the specially designed finite time convergent high order sliding mode observer. On this basis, a barrier Lyapunov function-based back-stepping flight controller is proposed for the robust and safe flight control of the ultra-low altitude airdrop. And the closed-loop stability is discussed via the Lyapunov stability theorem. Simulation comparisons are conducted to verify the robustness and effectiveness of the proposed airdrop flight control method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel robust back-stepping based trajectory tracking controller for the tanker with strict posture constraints under unknown flow perturbations in Autonomous Aerial Refueling (AAR). Firstly, by using the back-stepping technique, the proposed trajectory tracking control law design is separated into five loops. The 6 DOF model for tanker is tactfully transformed into several strict-feedback nonlinear forms, especially the dynamics of the translational kinematics which are originally non-affine nonlinear forms and are intractable for controller design. The influences of the unknown flow perturbations on tanker in each loop are viewed as the components of the “total disturbances” which are estimated and compensated by extended state observer (ESO). Secondly, the uncontrolled Euler angle constraints, which should also be considered in AAR, are transformed into extra boundary commands for the angular rates. And a novel command limiting tracking differentiator (CLTD), which considers not only the controlled but also uncontrolled state constraints, is specially designed for posture control. Thirdly, an integrated robust constrained posture control scheme is proposed for tanker's posture constraints based on Barrier Lyapunov (BL) function and CLTD. Then, with the position and ground velocity controller based on traditional active disturbance rejection control (ADRC) in the outer loop, a novel robust back-stepping based trajectory tracking controller is proposed for tanker in AAR. Finally, extensive simulations and comparisons on the 6 DOF tanker model are carried out to demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

The carrier aircraft's accurate control plays a fundamental and vital role during the air recovery of swarm unmanned aerial vehicles. To handle the control problem of the air recovery carrier with trajectory and posture constraints under unknown complex airflow disturbances, this paper proposes a robust constrained flight controller by integrating the integral Barrier Lyapunov function (iBLF) based dynamic surface control (DSC) method with the high-order sliding mode disturbance observer. Firstly, the carrier's six DOF affine nonlinear dynamics considering the unknown airflow disturbances are established for controller design convenience. Secondly, several finite-time convergent super-twisting sliding mode observers are designed to accurately observe the "lumped disturbances" in each subsystem composed of the airflow effect and other unmeasured items. Then, by taking these estimated disturbances as a kind of feed-forward compensating signals, an iBLF-based DSC is established for the carrier's constrained flight required by the specific air recovery mission. Moreover, closed-loop stability is analyzed. Finally, the flight simulations are performed to show the constrained control performance and the anti-disturbance ability of the proposed carrier flight controller, even under unknown airflow disturbances. [ABSTRACT FROM AUTHOR]

In this paper, we propose a hybrid approach based on the Lyapunov Guidance Vector Field (LGVF) and the Improved Interfered Fluid Dynamical System (IIFDS), to solve the problems of target tracking and obstacle avoidance in three-dimensional cooperative path planning for multiple unmanned aerial vehicles (UAVs). First, LGVF method is improved for UAV cooperative target tracking in 3D environment by introducing vertical component, with two guidance layers containing steering control and speed control. Second, IIFDS method is presented for UAVs to avoid obstacles or threats in complicated environment, where the local minimum problem is well resolved. Moreover, some cooperative strategies are added into the IIFDS framework to satisfy the constraints of obstacle avoidance and cluster maintenance. Finally, the missions of tracking target and avoiding obstacles can be performed simultaneously, by replacing the original sink fluid of IIFDS with the vector field of LGVF. Besides, the reactive parameters of IIFDS can be adjusted by the rolling optimization strategy to enhance the path quality. The experimental results validate the effectiveness of the hybrid method. [ABSTRACT FROM AUTHOR]