Multiple Control Surfaces Research Articles

Experiments of Lift-Bending Response on a Slender UAV Wing Structure with Control Surface under Extreme Flow Turbulence

The aeroelastic response of lightweight low-speed aircrafts with slender wings under extreme flow turbulence intensity is not well understood. Experiments on a commercial unmanned aerial vehicle (UAV) with a 3 m wingspan and aspect ratio of 13.6 were performed in a large open-return wind tunnel with extreme flow turbulence intensity of ≈10%. The wing bending displacement and the flow beneath the wing were measured by using laser-displacement sensors and tomographic particle image velocimetry (PIV) techniques, respectively. The unsteady lift produced by the wing was also measured by using a high-capacity load cell at an angle of attack of two degrees for three freestream velocities of 13.4 m/s, 17.9 m/s, and 26.8 m/s, representing the UAV’s stall speed, a speed approximately equal to the cruise speed, and a speed considerably higher than the cruise speed, respectively. It was found that a high flow turbulence intensity with large integral length scales relative to the wing chord plays a dominant role in the large unsteady lift and wing displacements measured. The power spectral density (PSD) of the wing structural vibration shows that flow shedding from the wing and the integral length scales have a significant impact on the overall power inherent in the bending vibration of the wing. Computations of the vorticity isosurfaces in the flow measurement volume surrounding the aileron reveal a striking observation: an aileron deflection of 10° becomes less effective in producing additional spanwise vorticity, which is proportional to circulation and lift at 26.8 m/s since the freestream already has elevated levels of vorticity. A paradigm shift in design is suggested for light aircraft structures with slender wings operating in highly turbulent flow, which is to employ multiple control surfaces in order to respond to this flow and mitigate large bending or torsion displacements and the probability of structural failure.

Robust Depth and Heading Control System for a Novel Robotic Dolphin With Multiple Control Surfaces

Robust Depth and Heading Control System for a Novel Robotic Dolphin With Multiple Control Surfaces

Adaptive Feed-Forward Control for Gust Load Alleviation on a Flying-Wing Model Using Multiple Control Surfaces

Based on measured gust information, a multi-input multi-output (MIMO) adaptive feed-forward control scheme for gust load alleviation (GLA) on a semi-span flying-wing aircraft using multiple control surfaces is proposed. In order to remedy weight drift and biased estimation problems that are commonly encountered in adaptive control, the circular leaky LMS (CLLMS) algorithm is employed, which utilizes gust measurement information, filtered reference signals, and error signals to update controller parameters online. The results demonstrate that good load reductions are achieved in both continuous and discrete gust environments. For instance, the designed GLA control system leads to an 80.72% reduction in the root-mean-square (RMS) values of wing-root bending moment in the Dryden gust environment and a 77.59% reduction of its maximum value in the 1-cos discrete gust condition. Based on the limited power of the actuator and the limited authority for control surface deflections when integrating GLA into the flight control system, a weight-updating algorithm with deflection angle and rate constraints on control surfaces is proposed. The simulation results show that the strict constraints on control surface deflections will degrade the GLA performance. Finally, the influence of the partial jamming fault of actuators on GLA performance is studied. It is found that good GLA performance can be preserved despite the degraded performance during the initial stage of the actuator jamming fault. This is due to the robustness brought about by multiple control surfaces and the adaptability of the control algorithm.

Regional Multi-Mission Aircraft in Clean Sky 2: Environmental Impact and Actual Technologies Evaluation from Flight Tests

Airbus Defence and Space, former CASA, has lead the Regional Multi-mission aircraft configuration in the Clean Sky 2 program. The set of technologies selected for this platform have been matured with the support of multiple partners across Europe by means of theoretical studies, tests in laboratories, full scale on ground demonstration in rigs and in flight demonstration in the Regional Flight Test Bed 2 (FTB#2) platform based on an Airbus C295 aircraft. These technologies cover multiple aspects of the aircraft design, manufacturing and operations like innovative materials, systems architectures towards a more electrical aircraft, affordable flight control system devoted to control multiple control surfaces in the wing and new manufacturing and assembly processes. The outputs of the research are taken to evaluate the environmental impact in terms of gaseous emissions (fuel consumption, CO2 and NOx) and noise reduction in take-off and landing of future aircraft with respect of the reference configuration defined at the beginning of Clean Sky 2 program. This paper describes the environmental impact in future Regional Multi-mission configurations and the technology evaluation done with the flight test campaign of the Regional FTB#2 in 2022. The flight test campaign is a cornerstone milestone of the program to demonstrate the most mature technologies.

Disturbance rejection enhancement using predictive control for the fixed‐wing UAV with multiple ailerons

SummaryThe performance of small fixed‐wing unmanned aerial vehicles (UAVs) is easily degraded by exogenous disturbances. In an attempt to improve the performance, the structural change is made in conventional small fixed‐wing UAV through segmentation of each aileron control surface into multiples. Detailed system identification experiments are performed on each aileron pair in the wind tunnel to acquire linear dynamic models for the roll attitude of the UAV. These experiments have provided the transfer functions for the aileron control surfaces based on corresponding frequency response. Three distinctive model predictive controllers are designed and deployed in real‐time hardware to achieve the roll attitude control. The roll attitude control experiments are validated in wind tunnel under both normal and turbulent environments. The results show that multiple input and single output control system provides significant improvement in the roll attitude and disturbance rejection performance. The collective actuation of multiple control surfaces improves roll stability by to when compared to the single aileron pair based conventional control in the presence of turbulent flight conditions.

Aeroelastic Shape Control Using Fiber-Optic-Measured Strain Data and Multiple Control Surfaces

The paper presents an experimental study of aeroelastic shape sensing and control based on strain data measured in fiber-optic sensors (FOSs). Past studies demonstrated how FOS strain data could be used to reconstruct the static and dynamic deformed shapes of a flexible wing. The current study further develops these capabilities and demonstrates wing shape control. Specifically, FOS-measured strain data are used in an optimization scheme, with a target of keeping the wing’s elastic deformations small, below a user-defined threshold, while maintaining a constant lift value (as required for trimmed flight) and with minimal usage of the control surfaces. The method is demonstrated computationally and experimentally on a wing model with four control surfaces. The wing was designed for this study, fabricated using additive manufacturing, and wind-tunnel tested. The trim optimization is performed both computationally and experimentally, following the same procedures but using strain and strain-modes data from finite element analysis and experiments. The wind-tunnel study demonstrated how a flexible wing’s shape could be controlled based on experimental strain data only, without resorting to a computational model. In both the computational and experimental parts of the study, considerable control-surface deformations were required. This primarily indicates that large control surfaces are not the optimal means for wing shape control. However, the same strain-based technique can be used with other effectors, such as distributed control surfaces, strain actuators, etcetera. The study opens a path to using FOSs to optimize winged unmanned-aerial-vehicle performance, and thus design lighter and more efficient platforms.

Fault-Tolerant Control for a High Altitude Long Endurance Aircraft

High Altitude Long Endurance (HALE) aircraft consist of extremely light-weight structures in combination with a high wingspan and high aspect ratio. The combination of these properties results in an unique dynamic behavior of the aircraft system featuring a strong interaction of structural and rigid body eigenmodes. These characteristics lead to specific demands on the robustness and fault tolerance of flight control algorithms of such aircraft. The control system must be able to navigate the aircraft safely along defined tracks even in case of fault scenarios. Due to the size of these aircraft they are usually over-actuated featuring multiple redundant control surfaces. This redundancy is used in this paper to design a fault tolerant control system ensuring optimal control performance during fault scenarios. The strategy is based on a fault detection and isolation (FDI) algorithm to detect malfunctioning control surfaces. This fault information is used to switch to alternate control laws in a multi-model control approach. The FDI filters are designed using the nullspace-based design paradigm, while the alternate controllers are synthesized applying structured H∞ control design techniques.

On a Method of Lagrange Multipliers for Cruise Drag Minimization

A blended-wing-body is an example of an aircraft configuration with multiple control surfaces. The most effective use of these control surfaces, e.g. to minimize cruise drag due to pitch trim, or to maximize pitching moment at low speed in an engine-out condition, leads to optimization problems. This kind of control optimization problems can be addressed by the method of Lagrange multipliers; this allows for multiple constraints, e.g. constant lift, pitching or other moments, each associated with one multiplier. The value of the multiplier is a measure of the severity of the constraint, e.g. the drag penalty of imposing pitch trim at constant lift.

On the Comparison of Ten Pitch Trim Strategies for Cruise Drag Minimization

The methods of minimization or maximization of lift, drag and pitching moment are extended to multiple coupled control surfaces with polynomial dependence of any degree on the control surface deflections. This serves as an introduction to the problem of minimization of cruise drag with pitch trim and unchanged lift, i.e. same airspeed and altitude, that is considered for a flying-wing configuration, using ten distinct strategies. Among the first four non-optimal strategies, only strategy II of using the centerbody elevator alone leads to drag reduction, albeit with a large deflection and increased angle-of-attack.

Investigation of Sensors & Actuators based on Hankel Singular Values

The work presented here proposes a method to rank the efficiency of the actuators and sensors for the attenuation of excited structural modes. Aeroelastic wing designed with multiple control surfaces and equipped with sensors at different locations is used as a test case. A unifying theme to this work is the application of Hankel Singular Values (HSV), an analytical approach applied to the experimental data conducted during the Ground Vibrational (GVT) and Wind Tunnel (WT) tests. Modal information gathered from experimental results is used to define actuator/sensor relationships, once the mode of interest is decided then the sensor and actuator location is determined to effectively cater the structural vibrations, it paves the way for the design of specific performance metrics. The research will add redundancy to the available set of instrumentation by paving the way for the dedicated use of control surface for the stable flight mechanics or flight dynamics instability. The results presented here are supported by Power Spectral Densities (PSD’s) and band pass filters.

Research on multi-task command allocation method for flying wing aircraft

Flying wing aircraft adopts redundant multiple control surfaces configuration, especially the new type of drag based yaw control device is used in directional axis. Therefore, its command allocation problem has strong nonlinear and multi-axis coupling characteristics. According to the command allocation characteristics of flying wing aircraft, a multi-objective optimization based nonlinear programming method is used for command allocation, and the differences of the control surface command allocation results under different optimization targets is analyzed. The results are also carried out in the attitude tracking simulation based on flight control system designed with nonlinear dynamic inversion. It demonstrates that the different optimization targets have great and quite different impacts on flight states. It proves that the multi-objective optimization based control allocation method is a highly adaptable and flexible command allocation method for flying wing aircraft.

Fast Hildreth-based Model Predictive Control of Roll Angle for a Fixed-Wing UAV

In this paper we consider model predictive control (MPC) design for roll angle control for a fixed-wing unmanned aerial vehicle (UAV) with multiple segmented control surfaces. The challenge of roll angle control for a fixed-wing UAV consists of switching between inner and outer aileron pairs with hard constraints due to safety, energy saving and switching actuators. The novelty consists of formulating a hybrid control problem as a switched linear constrained MPC-QP problem and switched state observer design for fixed-wing UAV. A fast novel QP-solver based on the active-set QP-solver Hildreth is developed to meet the real-time implementation sampling time of Ts = 10 ms. The designed MPC controllers are simulated using Matlab. Simulations and the CPU-time from the improved QP-solvers show MPC to be a very good solution for real-time roll angle control of fixed-wing UAVs.

Aerodynamic layout optimization design of a barrel-launched UAV wing considering control capability of multiple control surfaces

Owing to the size limitations of launchers, foldable main wings and foldable vertical tails are usually used in the design of barrel-launched unmanned aerial vehicles (UAVs), and the folding mechanisms are complex and bulky. Further, the coupling effect between aerodynamic performance and control capability is not typically considered in the aerodynamic layout design of traditional drum-launched UAVs; thus, the overall performance is often improved by serial design and multi-turns optimization, which result in low design efficiency. Based on the available research on barrel-launched UAVs, this paper presents an optimal design scheme for non-vertical tail aerodynamic layout considering the control capability of multiple control surfaces. A flying-wing configuration, with two groups of ailerons and one group of all moving tips, is employed in the design, and its control capability and aerodynamic performance are quantitatively described in terms of the volume of attainable moment subset and lift–drag ratio. The focus of the current design is shifted from improvement of single aerodynamic performance to optimization of overall performance. To overcome the computational complexity observed in direct optimization, the number of design variables is reduced by identifying the key test factors. The concept of a surrogate model matrix comprising cell surrogate models is proposed to effectively fit the aerodynamic characteristics and control capability of the wing. A multi-objective optimization based on the surrogate model matrix is carried out using the neighborhood cultivation genetic algorithm, which effectively improves the optimization efficiency. The entire process is implemented on an ISIGHT platform for automatic optimization design of the wing. At two design points selected on the pareto frontier, the results show that the lift–drag ratio is increased by 28.36%, reachable torque space is increased by 64.29% in state 1, lift–drag ratio is increased by 23.11%, and reachable torque space is increased by 164.29% in state 2. These results provide a reference for the aerodynamic layout design of barrel-launched UAVs for practical control requirements.

On the maximisation of control power in low-speed flight

ABSTRACTThe maximisation of control power is considered for an aircraft with multiple control surfaces, with the force and moment coefficients specified by polynomials of the control surface deflections of degree two. The optimal deflections, which maximise and minimise any force or moment coefficient, are determined subject to constraints on the range of deflection of each control surface. The results are applied to a flying wing configuration to determine: (i/ii) the pitch trim, at the lowest drag for the fastest climb, and at the highest drag for the steepest descent; (iii) the maximum and minimum pitching moment; (iv) the maximum and minimum yaw control power and the fraction needed to compensate an outboard engine failure for several propulsion configurations; (v) the maximum and minimum rolling moment. The optimal use of all control surfaces has significant advantages over using just one, e.g. the range of drag modulation with pitch trim is much wider and the maximum and minimum available control moments larger.

Bilevel Programming Weight Minimization of Composite Flying-Wing Aircraft with Curvilinear Spars and Ribs

This paper studies weight minimization of a composite flying-wing aircraft using bioinspired arbitrarily shaped spars and ribs, known as SpaRibs, for the internal structural layout design. A generalized mathematical model is developed to parameterize the shape of SpaRibs using a four-node nonuniform rational basis spline curve. Additionally, for reducing weight, composite structures and lift redistribution using multiple control surfaces are considered. A stacking sequence table is used to parameterize the wing laminate configuration with ply drops for flexible wing design. For the optimization problem including topology as well as discrete and size design variables, a bilevel programming optimization is employed by using a previously developed parallel particle swarm optimization and a gradient-based optimization, respectively, for the upper- and lower-level optimization problems. The upper-level optimization problem is employed to satisfy such design requirements as the flutter constraints for achieving a specific body freedom flutter mode. The lower-level optimization is used to optimize the control surface rotations to minimize the wing root bending moment, which is considered to be a surrogate for wing weight. Different internal structural layouts and flutter constraints are studied for comparison. Optimization studies show that using SpaRibs for aircraft wing box internal structural layout design can reduce the wing weight by 21.8% as compared to the base model and by 7.3% as compared to the wing box with traditional straight spars and ribs. The additional specific flutter result constraints lead to a 4.2% increase in the wing weight for aircraft design with SpaRibs as compared to the one obtained only with the lower bound on the flutter speed.

Design and motion testing of a Multiple SMA fin driven BIUV

Fishes interact with the fluid environment using various surfaces. These multiple control surfaces work in combination to produce the thrust and the balance torques in a steady swimming, to maneuver and to position themselves accurately even in turbulent flows. These motivate us to embark on a research program designed to develop an agile biologically inspired robotic fish based on the performance of multiple fins. To accomplish this goal, a mechanical ray-like fin actuated by the shape memory alloy (SMA) is developed, which can realize the oscillating motion, the undulating motion or even the complex three dimensional motion. The basic unit is the two opposite side SMA-driven plate, namely the fin ray. As a result, a lightweight bio-inspired fin is constructed by placing radially multiple SMA fin rays. A biologically inspired underwater vehicle (BIUV) is later built using the above multiple lightweight bio-inspired fins. Two common arrangement styles of multiple fins on the BIUV are considered here: one is the posterior fin (for the oscillating motion) that is parallel to the anterior fins (for the undulating motion), another one is the posterior fin that perpendicular to the anterior fins. The kinematic modeling, the deformation modeling and the detecting of the SMA fin are made. The thrust generation is also established. Finally, an experiment is conducted to test the performance of the proposed two arrangement styles, including the comparison of the averaged propulsion velocity and the averaged thrust under certain kinematic parameters. Meanwhile, the influence of the frequency and the amplitude of the SMA fin ray on the propulsion performance is also investigated.

Deformation Control of Highly Flexible Aircraft in Trimmed Flight and Gust Encounter

High-altitude long-endurance unmanned aerial vehicles are inherently highly flexible, and therefore are more susceptible to very large structural deformation in trimmed flight and in atmospheric turbulence. This work aims to avoid these large wing deformations by incorporating and deflecting multiple redundant control surfaces along the leading and trailing edges of the wing. These surfaces are used in both trim optimization to constrain wing deformation to a user-defined value in steady trimmed flight and in minimizing the dynamic response to gust encounter via a feedback controller. Trim optimization is performed using the simplex algorithm. Concurrently, a robust control scheme is designed and applied using loop shaping to demonstrate that, although the control surfaces are used for trimming the aircraft, they have enough authority left to effectively minimize elastic wing deformations during gust penetration. The aforementioned methodology is demonstrated on a highly flexible flying wing. Trim optimization effectively allows trimmed flight at various load factors in the flight envelope while maintaining small structural deformations. The designed controller significantly reduces the maximum wing deflection experienced by a gust disturbance, which is bounded below a user-specified value.

Supervisory adaptive fault‐tolerant control against actuator failures with application to an aircraft

SummaryIn this paper, a supervisory adaptive fault‐tolerant control scheme is proposed for a class of uncertain nonlinear systems with multiple inputs. The multiple inputs are the outputs of an actuator group that may act either on one control surface or on multiple control surfaces and may fail during operation. With some actuator groups as backups, the supervisory adaptive control includes 2 modes: the adaptive compensation mode and the switching mode. The former is used to compensate for the failure of an actuator group as long as at least one actuator of the group works normally, and the latter, to switch the controller from a failed group to a healthy one when the failure is detected by one of the monitoring functions that are constructed to supervise some variables related to system stability. It is shown that with the proposed scheme, all signals of the closed‐loop system are bounded, and prescribed transient and steady state performance of the tracking error can be guaranteed. An aircraft example is used to demonstrate the application of the proposed scheme.

Receptance-Based Active Aeroelastic Control with Embedded Control Surfaces Having Actuator Dynamics

To implement active aeroelastic control, control surfaces on a given wing configuration are moved using actuators having their own dynamic characteristics. The inclusion of actuator dynamics leads to the coupling of aeroelastic and actuator modes, and may result in instability in the closed-loop coupled aeroservoelastic system. During the design phase, various types of actuators may be considered, and hence, the stability and performance of the coupled system needs to be evaluated. In this research, a simultaneous control for aeroelastic and actuator poles is developed, which allows for the desired pole placement in a coupled aeroservoelastic system. This enables flutter boundary extension and suppression of flutter instabilities. The design of the controller is based on the method of receptances and requires the transfer functions associated with the aeroelastic structure and the actuators. This approach also allows the partial control of some selected aeroelastic modes without influencing the actuator modes, which ensures the stability of a coupled aeroservoelastic system irrespective of the selected actuator model. Different wing models having multiple control surfaces have been considered in the simulation. By using the associated numerical receptances, several examples have also been presented to demonstrate the solution strategy and performance of the controller.

Optimization of an Aeroservoelastic Wing with Distributed Multiple Control Surfaces

This paper considers the aeroelastic optimization of a subsonic transport wing box under a variety of static and dynamic aeroelastic constraints. Three types of design variables are used: structural variables (skin thickness, stiffener details), the quasi-steady deflection scheduling of a series of control surfaces distributed along the trailing edge for maneuver load alleviation and trim attainment, and the design details of a linear quadratic regulator controller (for flutter suppression), which commands oscillatory hinge moments into those same control surfaces. Optimization problems are solved where a closed-loop flutter constraint is forced to satisfy the required flight margin, and mass reduction benefits are realized by relaxing the open-loop flutter requirements.