Tail-sitter Unmanned Aerial Vehicle Research Articles

System Identification and Control for a Tail-Sitter Unmanned Aerial Vehicle in the Cruise Flight

This work presents the implementation of system identification and model predictive control for a tail-sitter unmanned aerial vehicle (UAV) in cruise flight. The mathematical model of longitudinal and lateral directions of the UAV has been derived in the state-space form for grey-box modeling. The least-square regression method is augmented with regulation and solved by applying the trust-region algorithm. Outdoor flight tests were conducted to acquire the data for system identification assisted by a signal generator module. The UAV dynamic was sufficiently excited in both longitudinal and lateral directions during the flight test. The flight data were applied to the grey box system identification, and the parameters were validated by fitting the reconstructed model to a set of flight data with a different excitation waveform. The flight controller with model predictive control was formed using the identified models for flight simulation. The results demonstrate that the system identification results are able to provide reference models for the model-based controller development of the novel-design tail-sitter UAV.

Position control of a tail-sitter UAV using successive linearization based model predictive control

A successive linearization based model predictive control (SLMPC) method is proposed to control a vertical take-off and landing (VTOL) tail-sitter unmanned aerial vehicle (UAV) in hovering flight. The dynamic model of the vehicle is derived, including a low-fidelity aerodynamic model and a propulsion system model. The position controller is developed by a state–space prediction model augmented with estimated disturbance and feedback integration terms. The time-varying weight in the objective function is included and the velocity of vehicle is considered as reference to improve the performance. The system is first tested in a software-in-loop environment followed by the real-time indoor flight tests. The results demonstrate the vehicle can precisely follow a trajectory and stably hold position under unsteady wind disturbance

Model-Aided Wind Estimation Method for a Tail-Sitter Aircraft

This paper presents a wind estimation method for a dual-rotor tail-sitter unmanned aerial vehicle with all flight phases. The large flight envelope and the slipstream generated by the propellers introduce extra challenges to estimating the wind field during flight for dual-rotor tail-sitter aircraft. In this method, a synthetic wind measurement is proposed based on a low-fidelity aircraft model and operated as a virtual sensor. This synthetic wind measurement and the data from the pitot tube are fused with an extended Kalman filter. The simulation and experimental results of the developed estimation method show a good estimation of the wind speed and direction in the hovering phase, transition, and cruising phases. The proposed wind estimation method was also tested in the hovering phase using the aerodynamic coefficients of NACA 0012 airfoil and a flat plate instead of the vehicle's model to provide a compromise solution for vehicles with no precise aerodynamic model.

$L_{1}$ Adaptive Control of a Dual-Rotor Tail-Sitter Unmanned Aerial Vehicle With Input Constraints During Hover Flight

The input constraints of control surfaces may lead to saturations, which could limit the achievable performance or even cause instability of vertical take-off and landing (VTOL) tail-sitter unmanned aerial vehicle (UAV). To improve flight safety and attitude tracking performance, a novel L 1 adaptive control architecture for attitude tracking of a tail sitter subjected to input constraints is proposed in this study. The imprecise mathematical model, low weight, and small size all present different challenges when designing a control system. In this work, a feedforward compensator is first used to narrow down the uncertain bounds with the consideration of finite accuracy from prior knowledge. Second, according to the linearized model, a baseline controller is designed to offer basic performance for a nominal system without uncertainty. Finally, the L 1 adaptive controller is developed to compensate for unmatched uncertainties based on the control system developed before. The stability and performance bounds of the closed-loop system are analyzed to illustrate the impact of input constraints. The numerical simulations and flight tests are carried out to verify the improved attitude tracking performance when input saturation exists.

Simulation and flight experiments of a quadrotor tail-sitter vertical take-off and landing unmanned aerial vehicle with wide flight envelope

This paper presents the modeling, simulation, and control of a small-scale electric powered quadrotor tail-sitter vertical take-off and landing unmanned aerial vehicle. In the modeling part, a full attitude wind tunnel test is performed on the full-scale unmanned aerial vehicle to capture its aerodynamics over the flight envelope. To accurately capture the degradation of motor thrust and torque at the presence of the forward speed, a wind tunnel test on the motor and propeller is also carried out. The extensive wind tunnel tests, when combined with the unmanned aerial vehicle kinematics model, dynamics model and other practical constraints such as motor saturation and delay, lead to a complete flight simulator that can accurately reveal the actual aircraft dynamics as verified by actual flight experiments. Based on the developed model, a unified attitude controller and a stable transition controller are designed and verified. Both simulation and experiments show that the developed attitude controller can stabilize the unmanned aerial vehicle attitude over the entire flight envelope and the transition controller can successfully transit the unmanned aerial vehicle from vertical flight to level flight with negligible altitude dropping, a common and fundamental challenge for tail-sitter vertical take-off and landing aircrafts. Finally, when supplied with the designed controller, the tail-sitter unmanned aerial vehicle can achieve a wide flight speed envelope ranging from stationary hovering to fast level flight. This feature dramatically distinguishes our aircraft from conventional fixed-wing airplanes.

Design and implementation of a real-time hardware-in-the-loop testing platform for a dual-rotor tail-sitter unmanned aerial vehicle

Tail-sitter vertical take-off and landing (VTOL) vehicle is a promising airframe among all the unmanned aerial vehicles (UAV), although challenges regarding the control strategies remain for civil applications, such as high susceptibility to wind disturbance while hovering. A real-time hardware-in-the-loop (HIL) simulation method for a tail-sitter UAV, an efficient tool for developing the control system, is presented in this paper. A nonlinear six-degrees-of-freedom dynamic model that covers the full angle-of-attack range is derived using the component breakdown approach. The environmental model is further introduced in the real-time simulation application to provide prevailing and gust wind conditions. A commonly used open-source flight controller was embedded in the proposed HIL framework. This HIL testbed can help researchers minimise the time spent debugging the controller program and moving from the simulation control system to the practical control one. The HIL simulation system was validated with the typical complete flight scenarios of a tail-sitter, including hovering, forward transition, cruise, and back transition. The results demonstrate that the HIL system can be an efficient tool for verifying the performance of hardware and software designs of the control system at the development stage for tail-sitter UAVs.

Development of Model Predictive Controller for a Tail-Sitter VTOL UAV in Hover Flight.

This paper presents a model predictive controller (MPC) for position control of a vertical take-off and landing (VTOL) tail-sitter unmanned aerial vehicle (UAV) in hover flight. A ‘cross’ configuration quad-rotor tail-sitter UAV is designed with the capabilities for both hover and high efficiency level flight. The six-degree-of-freedom (DOF) nonlinear dynamic model of the UAV is built based on aerodynamic data obtained from wind tunnel experiments. The model predictive position controller is then developed with the augmented linearized state-space model. Measured and unmeasured disturbance model are introduced into the modeling and optimization process to improve disturbance rejection ability. The MPC controller is first verified and tuned in the hardware-in-loop (HIL) simulation environment and then implemented in an on-board flight computer for real-time indoor experiments. The simulation and experimental results show that the proposed MPC position controller has good trajectory tracking performance and robust position holding capability under the conditions of prevailing and gusty winds.

Dynamic Inversion and Gain-Scheduling Control for an Autonomous Aerial Vehicle with Multiple Flight Stages

Several configurations of unmanned aerial vehicles (UAVs) were proposed to support different applications. One of them is the tailsitter, a fixed-wing aircraft that takes off and lands on its own tail, with the advantage of high endurance from fixed-wing aircraft and not requiring a runway during takeoff and landing as helicopters. However, the flight envelope of these vehicles contains multiple flight stages, each one with its own particularities and requirements, which makes its control more complex and hampers its use as an autonomous vehicle. Therefore, this paper presents an autopilot structure for a new tailsitter UAV, called Autonomous VerticAL takeOff and laNding (AVALON), with focus in the use of dynamic inversion and gain-scheduling control. Moreover, the AVALON’s equations of motion are described and used to reproduce a simulation environment. The results show the feasibility of these control techniques, with a convergence of the aircraft attitude and velocity during all the different flight stages of AVALON’s operation. We also compared its behaviour with PI controllers that calculates the control surfaces deflections with the attitude, and the use of dynamic inversion with gain-scheduling shows smaller errors in most of the flight stages, with the exception of the horizontal and landing stages.

Electric Aircraft: Exploiting the Synergy between Powertrain, Energy Management and Structure

This study aims at investigating the synergy between powertrain and structure within the design process of a fixed-wing tail-sitter unmanned aerial vehicle (UAV). The UAV is equipped with a pure-electric power system and has vertical take-off and landing capabilities (VTOL). The problem is addressed by running a contemporary optimization of the parameters of both the powertrain and the UAV’s structure, in order to maximize electric endurance and payload weight through the usage of a performant multi-objective evolutionary algorithm named SMS-EMOA. Three different designs are selected, discussed and compared with literature results on the same UAV to quantify the increase of payload and cruise time that can be obtained by exploiting the synergy between structure and powertrain. The potentiality of furtherly improving payload through the usage of multi-functional panels, while keeping the same endurance, is also quantified and compared with the technologies proposed in literature.

An Integrated Altitude Control Design for a Tail-Sitter UAV Equipped With Turbine Engines

An accurate and robust altitude controller is critical for vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs) in achieving quasi-stationary flight. Most UAV altitude control designs neglect the rotor dynamics. Therefore, they cannot be used for a tail-sitter UAV equipped with turbine engines because of the complicated engine dynamics with an apparent time delay. In this paper, we develop an integrated altitude controller that considers the engine dynamics. The new controller consists of a proportional-derivative (PD) control term and an acceleration feedback term. The stability region in the parameter space is analyzed and the controller is designed to achieve specific gain and phase margins. A UAV hover flight experiment is conducted and the results are presented to demonstrate the effectiveness of the proposed altitude controller.

Design and Control of an Unmanned Aerial Vehicle for Autonomous Parcel Delivery with Transition from Vertical Take-off to Forward Flight – VertiKUL, a Quadcopter Tailsitter

This paper presents the design and control of VertiKUL, a Vertical Take-Off and Landing (VTOL) transitioning tailsitter Unmanned Aerial Vehicle (UAV), capable of hover flight and forward flight for the application of parcel delivery. In contrast to existing transitioning UAVs, VertiKUL is not controlled by control surfaces, but exclusively by four propellers using differential thrust during hover flight, transition and forward flight. A numerical design method optimising range and payload is developed for initial sizing. A simulation model is implemented in Simulink to evaluate different control strategies before conducting test flights. A unique mid-level control strategy enabling intuitive control of VertiKUL which requires no pilot skills is developed. Fluent transition from hover to forward flight is achieved through an autonomous control strategy. Attitude control based on quaternions instead of Euler-angles is implemented to avoid singularities. The resulting design, VertiKUL, is built and test flown.

Lift System Design of Tail-Sitter Unmanned Aerial Vehicle

The main advantage of tail-sitter unmanned aerial vehicle (UAV) are introduced. Three design solutions of rotor tail-sitter lift system of UAV have been presented and the respective control strategies and characteristics of three solutions are also analyzed in the paper, through the related experiments the design of twin-rotor lift system is verified, and its feasibility is proved. The characteristics and the applying background of the twin-rotor tail-sitter UAV are described in detail. Some useful conclusions of the lift system for tail-sitter UAV are obtained.

2A1-H10 4ロータテールシッタ無人航空機のホバリング飛行制御(飛行ロボット・メカトロニクス(1))

Quad rotor helicopters has simple mechanism and high stability. However, it is not easy for a quad rotor helicopter to fly long time and long distance, because most of the thrust is consumed to lift the body, and hence horizontal component of the thrust is small. In this paper, we present the experimental results of a quad rotor tail-sitter UAV (Unmanned Aerial Vehicle) which is composed of a quad rotors and fixed wing. Developed UAV can hover like a quad rotor helicopter, and can fly long distance like a fixed wing airplane. We designe attitude and altitude control system of the UAV for hovering. In order to verify the designed control systems, we conducted hovering control flight experiment. Additionally, we identified both the impact of propeller slipstream on yaw control and the solutions.

Design and Attitude Control of a Quad-Rotor Tail-Sitter Vertical Takeoff and Landing Unmanned Aerial Vehicle

In this paper, we present the development of a quad-rotor tail-sitter unmanned aerial vehicle (UAV) that is composed of quad rotors and a fixed wing. The developed UAV can hover like a quad-rotor helicopter and can fly long distance like a fixed-wing airplane. The main wing of the developed UAV is taken from a commercially available radio-controlled airplane and other parts such as the body frame are newly developed. A microcomputer, various sensors and a battery are mounted on the UAV for autonomous flight without any support from a ground system. Attitude and altitude control systems are developed for the UAV. In order to verify the designed controller, a three-dimensional flight simulator of a quad-rotor tail-sitter UAV is developed by use of MATLAB/Simulink. This paper also describes attitude control experiments. The results show that the propeller slipstream has a negative influence on attitude control. Solutions for the negative influence of the propeller slipstream are also discussed in this paper.

Tail-sitter UAV having one tilting rotor: Modeling, Control and Real-Time Experiments

In this paper we address the development of a single-rotor tail-sitter Unmanned Aerial Vehicle (UAV), whose configuration provides structural benefits for flight stabilization. The mathematical model of the vertical take-off landing (VTOL) aircraft is obtained through the Newton-Euler approach. In order to stabilize the vehicle we employ a control algorithm based on separated saturation functions. To perform an on-board control, we have designed and manufactured a customized embedded system. The simulation and experimental results show the good performance of the aircraft in autonomous hover flight, even in the presence of external perturbations.