This paper presents the mathematical modeling, controller design, and flight-testing of an over-actuated Vertical Take-off and Landing (VTOL) tiltwing Unmanned Aerial Vehicle (UAV). Based on simplified aerodynamics and first-principles, a dynamical model of the UAV is developed which captures key aerodynamic effects including propeller slipstream on the wing and post-stall characteristics of the airfoils. The model-based steady-state flight envelope and the corresponding trim-actuation is analyzed and the overactuation of the UAV solved by optimizing for, e.g., power-optimal trims. The developed control system is composed of two controllers: First, a low-level attitude controller based on dynamic inversion and a daisy-chaining approach to handle allocation of redundant actuators. Secondly, a higher-level cruise controller to track a desired vertical velocity. It is based on a linearization of the system and look-up tables to determine the strong and nonlinear variation of the trims throughout the flight-envelope. We demonstrate the performance of the control-system for all flight phases (hover, transition, cruise) in extensive flight-tests.
Existing work on design, modeling and control of tiltwing UAV's considers tandem-wing @cite_5 @cite_7 @cite_8 and single-wing vehicles @cite_6 @cite_19 @cite_3 . Employed control systems are either unified @cite_19 @cite_3 or switch between different controllers for hover, transition, and cruise @cite_17 . For both attitude- and velocity control, decoupled PID and full state feedback LQR-architectures are reported @cite_7 @cite_13 @cite_3 . They are typically combined with local linearizations and gain-scheduling to address the strong non-linearities. Examples of @math -based attitude- and cruise control are found as well @cite_10 @cite_5 . A popular non-linear control technique involves DI @cite_4 and is used both for tailsitters @cite_18 @cite_24 and tandem TWV @cite_5 . It enables reference-model following but requires an accurate model to estimate state-dependent moments and forces. High-fidelity models are required to address the complex transition phase and typically consider the prominent propeller slipstream interaction with the wing @cite_13 . Instead of modeling, @cite_3 describes a control system that is based exclusively on state- and control derivatives obtained from wind-tunnel testing, @cite_24 and @cite_18 introduce lumped-parameter models to fit experimental data for a flying-wing tailsitter.
@cite_18 @cite_4 @cite_7 @cite_8 @cite_10 @cite_6 @cite_3 @cite_24 @cite_19 @cite_5 @cite_13 @cite_17
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We present a global controller for tracking nominal trajectories with a flying wing tailsitter vehicle. The control strategy is based on a first-principles model of the vehicle dynamics that captures all relevant aerodynamic effects, and we apply an onboard parameter learning scheme in order to estimate unknown aerodynamic parameters. A cascaded control architecture is used: Based on position and velocity errors an outer control loop computes a desired attitude keeping the vehicle in coordinated flight, while an inner control loop tracks the desired attitude using a lookup table with precomputed optimal attitude trajectories. The proposed algorithms can be implemented on a typical microcontroller and the performance is demonstrated in various experiments. This paper describes the development of robust, multi-variable H∞ control systems for the conversion of the High-Speed Autonomous Rotorcraft Vehicle (HARVee), an experimental tilt-wing aircraft. Tilt-wing rotorcraft combine the high-speed cruise capabilities of a conventional airplane with the hovering capabilities of a helicopter by rotating their wings at the fuselage. Changing between cruise and hover flight modes in mid-air is referred to as the conversion process, or simply conversion. A nonlinear aerodynamic model was previously developed that captures the unique dynamics of the tilt-wing aircraft. An H∞design methodology was used to develop cruise and hover control systems because it directly addresses multi-variable and robust design issues. The development of these control systems was governed not only by performance specifications at each particular operating point, but also by the unique requirements of a gain-scheduled conversion control system. The cruise and hover control designs form the basis for the conversion control system. The performance of the resulting conversion closed-loop systems is analyzed in the frequency and time domains. A tilt-wing rotorcraft Modeling, Simulation, Animation, and Real-Time Control (MoSART) software environment provides 3D visualization of the vehicle’s dynamics. The environment is useful for conceptualizing the natural rotorcraft dynamics and for gaining an intuitive understanding of the closed-loop system performance. In this article a Tilt-Wing Unmanned Aerial Vehicle (TW-UAV) and the preliminary evaluation of its hovering characteristics in extended simulation studies are presented. In the beginning, an overview of the TW-UAV's design properties are established, highlighting the novelties of the proposed structure and the overall merits. The TW-UAV's design and structural properties are mathematically modeled and utilized for the synthesis of a cascaded P-PI and PID based control structure for the regulation of its hovering performance. In addition, extensive simulation trials are performed in order to evaluate the structure's efficiency in controlling the TW-UAV's attitude and position under various noise and disturbance scenarios. This paper presents an approach for velocity control of tilt-wing aircraft over their entire flight envelope, ranging from hovering flight to wing-borne flight. With their capability of vertical takeoff and landing operation in combination with efficient cruise flight, tilt-wing aircraft offer multiple benefits in unmanned aerial vehicle applications. Control of tilt-wing aircraft, in particular for fully automated flight, is challenging because along with their versatility comes significant variations in flight mechanics characteristics. Known approaches to this problem subdivide tilt-wing flight into discrete aircraft configurations. The presented control concept omits discrete configurations and instead allows for continuous flight state transitions over a unified flight configuration space. Actuation that is unique to tilt-wing aircraft, for example, tilt angle control, is not only used as an aircraft configuration parameter but also as a full-fledged motion control device. The concept includes a map-... This paper addresses the challenges of the design, development and control of a new convertible VTOL tailsitter unmanned aerial vehicle that combines the advantages of both fixed wing and rotary wing systems. Wind tunnel measurements are used to get an understanding of the control allocation and to model the static forces and moments acting on the system. Based on the derived model, a novel controller that operates in SO(3) and handles the dynamics of the vehicle at any attitude configuration, including the rotorcraft and fixed-wing regimes as well as their transitions, is presented. This unified controller allows the autonomous transition of the system without discontinuities of switching, as well as its overall high performance flight control. The capabilities and flying qualities of the platform and the controller are demonstrated and evaluated by means of extensive experimental studies. This paper describes the development and analysis of gain-scheduled, multi-variable Hinfin control law for the conversion of a linear parameter varying (LPV) model of a high-speed autonomous rotorcraft vehicle (HARVee), an experimental tilt-wing aircraft. Tilt-wing aircraft combine the high-speed cruise capabilities of a conventional airplane with the vertical takeoff and station keeping abilities of a helicopter by rotating their wings at the fuselage. Changing between cruise and hover flight modes in mid-air is referred to as the conversion process, or simply conversion. A nonlinear aerodynamic model was previously developed that captures the unique dynamics of the tilt-wing aircraft. An Hinfin design methodology was used to develop linear controllers along various operating points of a conversion trajectory. The development of these control systems was governed not only by performance specifications at each particular operating point, but also by the unique requirements of a gain-scheduled conversion control system. The performance of the resulting conversion closed-loop systems is analyzed in the frequency and time domains. Performance robustness with respect to variation in the location of the center of gravity (eg) has been studied.