Flying Wing Unmanned Aerial Vehicle Research Articles

Wind tunnel experiments of bending-torsion and body-freedom flutter on flying wing unmanned aerial vehicles

Wind tunnel experiments are performed on a flying wing model to investigate the effects of key design parameters and their cross-interactions on the flutter speed and frequency for bending-torsion flutter (BTF) and body-freedom flutter (BFF). These design parameters include wing sweep angle, mass of tip weights, and location of weights along the wingspan. A slider and rail setup for BFF is designed to enable rigid-body pitching and plunging degrees-of-freedom, while a custom fixed clamp is used to perform the BTF experiments. BTF and BFF experiences different dominant modes while undergoing flutter, with the former's dominant mode being torsion and the latter being the rigid-body short-period mode. For BTF, flutter speeds increase as weights are moved towards the wingtip or increasing tip weights, which increases the inertia of the system to enhance stability. The effect is opposite for BFF as the movement of weights outboard or increase of tip weights result in a rearwards shift of the centre of gravity that destabilises the system. In general, a higher sweep angle leads to increased sensitivity of flutter speeds to changes in mass of tip weights or changes to spanwise location of the weights. The findings from this study provide insights to the design of flying wing unmanned aerial vehicles for increased stability margins.

An improved linear parameter-varying modeling, model order reduction, and control design process for flexible aircraft

This paper presents an improved process for the modeling, model order reduction (MOR), and control design of a flexible flying wing unmanned aerial vehicle based on the linear parameter-varying (LPV) technology. By applying the Lagrangian formulation and doublet lattice method, the aeroservoelastic (ASE) model of the flexible aircraft is first derived and then rewritten as an airspeed-dependent LPV system, which consists of rigid-body states, structural modes, aerodynamic states, etc. This leads to a high-order LPV model, and the stability of the system varies from stable to unstable when the speed of the aircraft exceeds the critical flutter speed. To facilitate the control design, an oblique projection-based MOR method is then adopted to reduce the order of the plant. Different from previous studies, the MOR method is improved to systematically generate a reduced-order LPV model with consistent states for both the stable and unstable dynamics parts. Finally, an output-feedback LPV controller is designed to simultaneously achieve the body freedom flutter suppression and longitudinal attitude control. Numerical simulation results show the effectiveness of the improved LPV-based ASE modeling, order reduction, and control design process for the flexible aircraft.

Parametric Investigation of Canards on a Flying Wing UAV Using the Taguchi Method

The current work investigates the effect of canard geometric characteristics on the performance of a lightweight flying wing Unmanned Aerial Vehicle (UAV), capable of both conventional and Vertical Take-Off and Landing (VTOL) flight. The canards are sized as horizontal stabilizers to enhance the UAV’s longitudinal stability and minimize trimming requirements during cruise. Using a Design of Experiments (DOE) approach and, specifically, the Taguchi method, six canards’ design parameters are investigated on three different levels. These parameters are the sweep angle (Λ), aspect ratio (AR), taper ratio (λ), vertical position in relation to the main wing (vpos), incidence angle (ic), and dihedral angle (Γ). An L27 orthogonal array (OA) is used to investigate the influence of these key design parameters using two performance criteria, namely the Lift-to-Drag ratio (L/D) and the pitching moment coefficient (Cm), at cruise conditions (designated as L/Dcruise and |Cm|cruise). The investigation is conducted by using high-fidelity Computational Fluid Dynamics (CFD) methods for each of the 27 configurations defined by the L27 OA, over a range of angles of attack. Based on the CFD results, two distinct combinations are derived for maximum L/Dcruise and minimum |Cm|cruise using the Signal-to-Noise ratio (SNR) analysis. The optimal design parameter combinations for the two performance criteria are A2B1C1D1E1F1 and A2B2C1D2E2F3, respectively. Finally, the Pareto Analysis of Variance (ANOVA) technique is conducted to define the contribution of each of the six design parameters on the L/Dcruise and the |Cm|cruise. More specifically, ic seems to have the most significant effect on L/Dcruise, whereas Λ is the most important parameter for |Cm|cruise.

Path Tracking Control for Flying-wing Unmanned Aerial Vehicles: A Lyapunov Based Approach

Path Tracking Control for Flying-wing Unmanned Aerial Vehicles: A Lyapunov Based Approach

Multidisciplinary Analysis and Optimization Method for Conceptually Designing of Electric Flying-Wing Unmanned Aerial Vehicles

Current unmanned aerial vehicles have been designed by applying the traditional approach to aircraft conceptual design which has drawbacks in terms of the individual analysis of each discipline involved in the conception of new aircraft, the reliance on the designer’s experience and intuition, and the inability of evaluating all possible design solutions. Multidisciplinary analysis and optimization focus on solving these problems, by synthesizing all the disciplines involved and accounting for their mutual interaction. This study presents a multidisciplinary analysis and optimization method for conceptually designing electrical flying-wing micro-unmanned aerial vehicles. The conceptual design task was formulated as a non-linear mathematical programming problem. The method considers the trimming of the UAV during each mission profile phase, consisting of the climb, cruise, and descent. We used two algorithms, one for design space exploration and another for optimization. Typical examples of solving conceptual design problems were considered in the work: the modernization of an existing UAV; the effect of the change of the payload and endurance change on the takeoff weight; and the influence of different static margins on aerodynamic characteristics. The advantages of using this design method are the remotion of additional internal cycles to solve the sizing equation at each optimization step, and the possibility of not only obtaining a unique optimal solution but also a vector of optimal solutions.

Global Incremental Flight Control for Agile Maneuvering of a Tailsitter Flying Wing

This paper proposes a novel control law for accurate tracking of agile trajectories using a tailsitter flying wing unmanned aerial vehicle that transitions between vertical takeoff and landing and forward flight. The global control formulation enables maneuvering throughout the flight envelope, including uncoordinated flight with sideslip. Differential flatness of the nonlinear tailsitter dynamics with a simplified aerodynamics model is shown. Using the flatness transform, the proposed controller incorporates tracking of the position reference along with its derivatives velocity, acceleration, and jerk, as well as the yaw reference and yaw rate. The inclusion of jerk and yaw rate references through an angular velocity feedforward term improves tracking of trajectories with fast-changing accelerations. The controller does not depend on extensive aerodynamic modeling but instead uses incremental nonlinear dynamic inversion to compute control updates based on only a local input–output relation, resulting in robustness against discrepancies in the simplified aerodynamics equations. Exact inversion of the nonlinear input–output relation is achieved through the derived flatness transform. The resulting control algorithm is extensively evaluated in flight tests, where it demonstrates accurate trajectory tracking and challenging agile maneuvers, such as sideways flight and aggressive transitions while turning.

Simultaneous Stabilization for Longitudinal and Lateral Dynamics Considering Input Saturation for a Small Flying-Wing Unmanned Aerial Vehicle Only with an Elevon

Simultaneous Stabilization for Longitudinal and Lateral Dynamics Considering Input Saturation for a Small Flying-Wing Unmanned Aerial Vehicle Only with an Elevon

Rope-Hook Recovery Controller Designed for a Flying-Wing UAV

Due to the complexity of landing environments, precision guidance and high-precision control technology have become key to the rope-hook recovery of shipborne unmanned aerial vehicles (UAVs). The recovery process was divided into three stages and a reasonable guidance strategy had been designed for them, respectively. This study separated the guidance and control issues into an outer guidance loop and an inner control loop. The inner loop (attitude control loop) controled the UAV to follow the acceleration commands generated by the outer loop (trajectory tracking loop). The inner loop of the longitudinal controller and the lateral controller were designed based on active disturbance rejection control (ADRC), which has strong anti-interference ability. In the last phase, the outer loop of the longitudinal controller switched from a total energy control system (TECS), which greatly decoupled the altitude channel and speed channel, to the proportional navigation (PN) guidance law, while the outer loop of lateral controller switches from the proportional control law based on the L1 guidance law, which can reduce the tracking error and deviation, to the PN guidance law, which considerably enhances the tracking precision. Finally, the simulation data and flight test data show that the controller has strong robustness and good tracking precision, which ensures safe rope-hook recovery.

Multi-UAV cooperative target tracking via consensus-based guidance vector fields and fuzzy MRAC

Purpose This paper aims to propose a multi-agent approach to adaptive control of fixed-wing unmanned aerial vehicles (UAVs) tracking a moving ground target. The approach implies that the UAVs in a single group must maintain preset phase shift angles while rotating around the target so as to evaluate the target’s movement more accurately. Thus, the controls should ensure that the UAV swarm follows a moving circular path whose center is the target while also attaining and maintaining a circular formation of a specific geometric shape; and the formation control system is capable of self-tuning because the UAV dynamics is uncertain. Design/methodology/approach This paper considers two interaction architectures: an open-chain where each UAV only interacts with its neighbors; and a cooperative leader, where the leading UAV is involved in attaining the formation. The cooperative controllers are self-tuned by fuzzy model reference adaptive control (MRAC). Findings Using open-chain decentralized architecture allows to have an unlimited number of aircraft in a formation, which is in line with the swarm behavior concept. The approach was tested for efficiency and performance in various scenarios using complete nonlinear flying-wing UAV models equipped with configured standard autopilot models. Research limitations/implications Assume the target follows a rectilinear trajectory at a constant speed. The speed is supposed to be known in advance. Another assumption is that the weather is windless. Originality/value In contrast to known studies, this one uses Lyapunov guidance vector fields that are direction- and magnitude-nonuniform. The overall cooperative controller structure is based on a decentralized and centralized consensus.

Adaptive fault-tolerant tracking control of flying-wing unmanned aerial vehicle with system input saturation and state constraints

In this paper, an adaptive fault-tolerant attitude tracking controller based on reinforcement learning is developed for flying-wing unmanned aerial vehicle subjected to actuator faults and saturation. At first, the attitude dynamic model is separated into two dynamic subsystems as slow and fast dynamic subsystems based on the principle of time scale separation. Secondly, backstepping technique is adopted to design the controller. For the purpose of attitude angle constraints, the control technique based on Barrier Lyapunov is used to design controller of slow dynamic subsystem. Considering the optimization of the fast dynamic subsystem, this paper introduces an adaptive reinforcement learning control method in which neural network is used to approximate the long-term performance index and lumped fault dynamic. It is shown that this control algorithm can satisfy the requirements of attitude tracking subjected to the control constraints and the stability of the system is proved from Lyapunov stability theory. The simulation results demonstrate that the developed fault-tolerant scheme is useful and has more smooth control effect compared with fault-tolerant controller based on sliding mode theory.

Robust active suppression for body-freedom flutter of a flying-wing unmanned aerial vehicle

Flying-wing unmanned aerial vehicles have received extensive attention over the past decade because of their excellent aerodynamic and stealth performance. However, the aeroelastic interaction problems among unsteady aerodynamics, flight dynamics, and structural dynamics, such as the body-freedom flutter, are still open. This paper presents the study of a robust control scheme for active body-freedom flutter suppression of a flexible flying-wing unmanned aerial vehicle. The control objective is to expand the boundary of body-freedom flutter and to enhance the control robustness to external unknown disturbance simultaneously. The paper begins with the modeling procedure of a parameter-varying aeroservoelastic plant for the design of control law. Then, it presents how to synthesize a robust controller so as to suppress the flutter instability for a wide flight range of dynamic pressures. Afterwards, the paper shows how to analyze the flutter stability of the closed-loop system and the robustness of the controller, respectively. The numerical results demonstrate that the proposed robust controller can not only expand the flutter boundary of the unmanned aerial vehicle by 30%, but also exhibit the strong robustness to external disturbance.

Kriging Aerodynamic Modeling and Multi-Objective Control Allocation for Flying Wing UAVs With Morphing Trailing-Edge

Flexible skin and continuous deformable control surface are the basic of adaptive wing technology for future aircraft. This paper presents a continuous morphing trailing-edge and its control allocation method for the flying wing Unmanned Aerial Vehicle (UAV). Firstly, we apply the Kriging method to establish the aerodynamic model of the morphing trailing-edge, with the initial sample points generated by the non-uniform optimal Latin Hypercube Sampling (LHS). Then, based on the Kriging model, the multi-objective control allocation problem is converted into a standard optimization form. To solve such problem, we design a Comprehensive Multi-Objective Particle Swarm Optimization (C-MOPSO) algorithm and an improved Hierarchical MOPSO (H-MOPSO) algorithm, in which multiple optimization objectives are prioritized and hierarchically optimized using the PSO algorithm. As for performance analysis, an attitude angle tracking flight control system is established to validate the effectiveness of our proposed control allocation methods. Simulation results show that both the C-MOPSO and H-MOPSO methods have similar performance in attitude angle tracking, while H-MOPSO achieves better multi-objective allocation performance.

Aerodynamic and stability analysis of a VTOL flying wing UAV

The stability analysis of an aerial vehicle is an of great importance integral part of its design procedure. It is of even greater importance in the case of tailless aircraft, which are prone to stability issues. In the present study, the aerodynamic and stability characteristics of a Vertical Take-off and Landing (VTOL) fixed wing Unmanned Aerial Vehicle (UAV), designated as MPU RX-4, are investigated. The MPU RX-4 has a flying wing layout and is capable of performing, both conventional flight, like a regular fixed wing aerial vehicle, as well as vertical hovering, like a multicopter, adapting on different operational demands and achieving rapid field deployment. In this study, the preliminary design phase of the MPU RX-4 is presented and the aerial vehicle’s aerodynamic performance, as well as, its stability and control behavior are assessed using both semi-empirical correlations, specifically modified for lightweight flying wing UAVs, and Computational Fluid Dynamics (CFD) analyses. These correlations are employed to estimate the non-dimensional aerodynamic coefficients for various flight conditions (e.g. cruise, loiter, maximum speed, etc.) of the MPU RX-4 flight envelope. Furthermore, the correlations are validated with dedicated CFD analyses in order to assure their level of accuracy. Finally, the MPU RX-4 stability and control derivatives, and the required control surfaces deflection for steady level flight are computed, in order to assess its overall aerodynamic performance and flight characteristics.

Design of a tilting mechanism for a VTOL flying wing UAV

In this paper, the detailed design of a mechanism for the transition from vertical to horizontal flight of a Vertical Take-off and Landing (VTOL) fixed wing Unmanned Aerial Vehicle (UAV) is presented. The UAV, which is being developed in the framework of the MPU research project, under the designation MPU RX-4, is a lightweight, all electric driven UAV with a flying wing layout. The MPU RX-4 is capable of performing both conventional flight, like a regular fixed wing aerial vehicle, as well as vertical hovering, like a multicopter, adapting on different operational demands. To achieve that, the development of a robust transition procedure from one flight phase to the other is required. This procedure is based on mechanisms capable of altering the flying characteristics of the UAV. More specifically, these mechanisms should be designed in order to change the orientation of the thrust vectors from horizontal to vertical and vice versa. MPU RX-4 uses a configuration of three electric motors (two mounted on the canards, and one in the main body) in order to perform both flight phases. For the transition from the hovering phase to the level flight, the two frontal motors have to be tilted from the vertical position to the horizontal, and the rear motor to be nested in its proprietary position, using four external hatches. Two separate mechanisms are designed, one for the canards’ tilting movement and another one for the extension and retraction of the rear motor hatches. Finite Element Analysis is carried out for the structural sizing of the mechanism (i.e. internal loads, linkages cross-section, joints sizing). The aerodynamic loads, acting on the mechanisms, are derived from Computational Fluid Dynamics analysis performed for the various flight phases (hovering, level flight and transition) of the UAV. Finally, the designed mechanisms are presented as integrated parts of the prototype UAV.

Investigation and Improvement of Pusher-Propeller Installation Effect for Flying Wing UAV

This paper presents a collaborative experimental and numerical research to investigate the influences of the installation of propeller on aircraft aerodynamic performance, and two approaches to mitigate the propeller installation effect are also analyzed. The configuration under investigation is based on a real flying wing unmanned aerial vehicle with a two-bladed pusher-propeller mounted on the aft part of its associated airframe. Reynolds-averaged Navier Stokes simulations coupled with a structured finite-volume cell-vertex based solver are applied to propeller uninstalled and installed configurations, and the numerical results are shown to be in good agreement with the experimental data. The comparative results obtained through prop-uninstalled and prop-installed cases show that the installation of the pusher-propeller leads to the decline of the maximum lift-drag ratio due to aerodynamic interactions between the propeller and airframe. Detailed analysis of the numerical results highlighted that the low pressure areas on the aft part of the airframe generated by the installation of the pusher-propeller will result in an increase of the base drag and hence a decline of the maximum lift-drag ratio. The feasibilities of center shaft extension and the modification of airframe geometry to mitigate the propeller installation effect are verified by numerical simulations, and results showed that proper propeller–airframe spacing and good designs of airframe geometry can effectively improve the flow characteristic and reduce the drag induced by propeller installation effect.

Yaw control of a flying-wing unmanned aerial vehicle based on reverse jet control

Due to its layout, there are difficulties in realizing heading attitude control of a flying-wing unmanned aerial vehicle. In this paper, a reverse jet control scheme has been designed: (1) to replace the resistance rudders that are used for the yaw control of a conventional flying-wing unmanned aerial vehicle, (2) to assist and optimize heading attitude control, eliminate the adverse effects of the control surface and enhance stealth performance, and (3) to promote the use of rudderless flight for flying-wing unmanned aerial vehicles. To explore the control mechanism and the flow field of the reverse jet scheme, three-dimensional numerical simulations and low-speed wind tunnel experiments were carried out. First, the numerical simulations evaluated the feasibility and effectiveness of the reverse jet control scheme and explored and optimized the excitation parameters for the scheme. Then the forces were measured in a wind tunnel, and particle image velocimetry experiments were carried out. A reverse jet actuator was independently designed to verify the results of the numerical simulation. The results show that when the reverse jet excitation is applied, the jet obstructs the mainstream, destroys the flow field at the excitation position, and causes early separation of the flow, which increases the pressure drag on the wings and produces a control effect. The control effect mainly depends on the separation degree of the leeward surface. The larger the jet momentum coefficient is, the smaller the jet angle is, and the closer the excitation position is to the leading edge, the greater the separation degree of the leeward surface is, the better the heading attitude control effect is.

Practical control implementation of tri-tiltRotor flying wing unmanned aerial vehicles based upon active disturbance rejection control

Tilt rotor unmanned aerial vehicles exhibit their effectiveness via a novel and convenient structure. However, the flight control system is a critical problem in need of a robust solution. Focusing on its flight features, which display strong nonlinear and varying dynamics, caused by complexity in the aerodynamic layout and tilting structure, a practical control scheme is proposed to meet such technical issues. This paper first develops the nonlinear model, consisting of the interference between rotors and the wing body, relying on wind tunnel technology. A simplified linear model that decomposes the longitudinal and lateral components is used in order to facilitate controller design. Then, a time-scale separation decoupling control scheme based upon active disturbance rejection control is proposed to cope with control challenges. Introducing the concept of virtual control input, an effective control allocation is obtained by choosing the appropriate bandwidth in the frequency domain. The extended state observer is applied to estimate and compensate for unknown total disturbances and model uncertainties. Finally, robustness verification, successful test-bench experiments, and practical flight tests that show the fast tracking and disturbance rejection of the active disturbance rejection control controller are discussed. The proposed practical coupling rejection control design demonstrates its capability to employ a single input single output method to control a tri-tiltRotor flying wing unmanned aerial vehicle relying on active disturbance rejection control.

An Experimental Study on Nonlinear Guaranteed Cost Control Approach to Automatic Flight and Landing of a Small Flying-Wing Unmanned Aerial Vehicle

An Experimental Study on Nonlinear Guaranteed Cost Control Approach to Automatic Flight and Landing of a Small Flying-Wing Unmanned Aerial Vehicle

R-functions in the Analytical Description of the Surface of a Flying Wing Unmanned Aerial Vehicle

R-functions in the Analytical Description of the Surface of a Flying Wing Unmanned Aerial Vehicle

Design, Manufacturing, and Flight Testing of an Experimental Flying Wing UAV

This paper presents the design, manufacturing, and flight testing of an electric-powered experimental flying wing unmanned aerial vehicle (UAV). The design process starts with defining the performance requirements including the stall speed, maximal speed, cruise altitude, absolute ceiling, and turn radius and speed. The wing loading and associated power loading are obtained based on the defined performance requirements. The wing area, UAV mass, and power requirements are determined from the endurance and payload requirements. The power requirement determines the motor size. Aerodynamics and stability designs are obtained based on the selected airfoil and obtained wing area. After completing the design, the UAV is manufactured using composite materials. The UAV is equipped with an AXi 4130/20 kv305 brushless motor and a Pixhawk flight control board. Its total weight is 8.6 kg. Flight tests were conducted to evaluate the UAV’s performance and dynamic characteristics and to demonstrate the success of the design.