Conventional Control Surfaces Research Articles

Morphing concepts in the field of rotorcraft

Drawing inspiration from avian creatures, aeronautical engineers strive to create an ideal wing design that can seamlessly perform in various flight conditions. Avian creatures, as well as bats and other flying organisms, exhibit a striking aptitude to adjust the lift produced by their wings, displaying the capacity to repeatedly tailor their wing configurations to match specific environmental conditions. An example of this is when their wings are tightly tucked during dives for hunting, or fully extended during gliding to conserve energy. Moreover, these organisms can manipulate the curvature and twist of their wings to maintain precise control over their aerial maneuvers. In contrast, engineers in the aircraft industry continue to rely on the standard, robust and structured “one-point design” approach, which remains the most practical and feasible method to apply. Nonetheless, advancements in technology have emerged to address long-standing challenges in wing manufacturing that were previously deemed insurmountable. This convergence of different technologies has given significant momentum and recognition to the field of “morphing discipline”. When considering an aircraft, shape changes primarily relate to the wing of a fixed-wing aircraft or the blade of a rotorcraft. The concept of achieving a "smooth" shape change stems from the crucial need for drag reduction and improved flow quality, resulting in improved overall performance. The state-of-the-art morphing concepts applied to rotorcrafts comprise a wide range of investigations aimed at improving performance. Looking ahead, the primary challenge for morphing technology will be to persuade the industry of its tangible benefits. This encompasses enhanced aerodynamic efficiency, minimized installation footprint when contrasted with conventional control surface mechanisms, reduced overall weight, and an equivalent standard of safety. This research provides an overview of the current development of different control devices and explores the impact of previous and continuous research endeavors in this field. Numerous ideas for managing airflow have been explored with the aim of enhancing the performance abilities of rotary-wing aircraft. These include active morphing in rotorcraft such as leading edge slats, trailing edge flaps, and passive morphing in rotorcraft such as variable rpm rotorcraft. The aim of these blade modifications is to achieve various desired effects such as increasing the maximum lift coefficient, reducing drag, and minimizing vibratory loads. Convincing the industry of these advantages will play a crucial role in shaping the future of morphing technology.

Full envelope nonlinear flight controller design for a novel electric VTOL (eVTOL) air taxi

AbstractOn-demand urban air transportation gains popularity in recent years with the introduction of the electric VTOL (eVTOL) aircraft concept. There is an emerging interest in short/medium range eVTOL air taxi considering the critical advantages of electric propulsion (i.e. low noise and carbon emission). Using several electric propulsion systems (distributed electric propulsion (DEP)) has further advantages such as improved redundancy. However, flight controller design becomes more challenging due to highly over-actuated and coupled dynamics. This study defines and resolves flight control problems of a novel DEP eVTOL air taxi. The aircraft has a fixed-wing surface to have aerodynamically efficient cruise flight, and uses only tilting electric propulsion units to achieve full envelope flight control via pure thrust vector control. The aircraft does not have conventional control surfaces such as aileron, rudder or elevator. Using pure thrust vector control has some design benefits, but the control problem becomes more challenging due to the over-actuated and highly coupled dynamics (especially in transition flight). A preliminary flight dynamics model is obtained considering the dominant effects at hover and high-speed forward flight. Hover and forward flight models are blended to simulate the transition dynamics. Two central challenges regarding the flight control are significant nonlinearities in aircraft dynamics during the transition and proper allocation of the thrust vector control specifically in limited control authority (actuator saturation). The former challenge is resolved via designing a sensor-based incremental nonlinear dynamic inversion (INDI) controller to have a single/unified controller covering the wide flight envelope. For the latter one, an optimisation-based control allocation (CA) approach is integrated into the INDI controller. CA requires special attention due to the pure thrust vector control’s highly coupled dynamics. The controller shows satisfactory performance and disturbance rejection characteristics. Moreover, the CA plays a vital role in guaranteeing stable flight in case of severe actuator saturation.

Real-Time Performance Optimization for a Camber Morphing Wing Based on Domain Incremental Model under Concept Drifting

Compared with traditional wings equipped with conventional control surfaces, variable-camber morphing wings have become a hot research topic in the field of aviation due to their ability to maintain a smooth and continuous overall shape while ensuring excellent aerodynamic performance. This study focuses on a high aspect ratio wing with a continuous variable-camber trailing edge. Two precision models were constructed: an aerodynamic model and an aeroelastic model. Based on simulation data obtained from these models, we developed and updated a surrogate model for the wing, with particular emphasis on an incremental modeling approach that takes concept drift into account. Subsequently, using the aforementioned models, we conducted real-time optimization with feedback considerations to reduce drag, lower stress on the main beam, and minimize actuator energy under either steady or slowly varying target lift conditions. Notably, the optimization process resulted in a 4% reduction in drag or a significant decrease of 18.3% in maximum stress. Through computational comparisons, the accuracy of the proposed surrogate model and incremental learning method is demonstrated, along with their efficiency in the context of optimization problems.

A Self–Tuning Intelligent Controller for a Smart Actuation Mechanism of a Morphing Wing Based on Shape Memory Alloys

The paper exposes some of the results obtained in a major research project related to the design, development, and experimental testing of a morphing wing demonstrator, with the main focus on the development of the automatic control of the actuation system, on its integration into the experimental developed morphing wing system, and on the gain related to the extension of the laminar flow over the wing upper surface when it was morphed based on this control system. The project was a multidisciplinary one, being realized in collaboration between several Canadian research teams coming from universities, research institutes, and industrial entities. The project’s general aim was to reduce the operating costs for the new generation of aircraft via fuel economy in flight and also to improve aircraft performance, expand its flight envelope, replace conventional control surfaces, reduce drag to improve range, and reduce vibrations and flutter. In this regard, the research team realized theoretical studies, accompanied by the development and wind tunnel experimental testing of a rectangular wing model equipped with a morphing skin, electrical smart actuators, and pressure sensors. The wing model was designed to be actively controlled so as to change its shape and produce the expansion of laminar flow on its upper surface. The actuation mechanism used to change the wing shape by morphing its flexible upper surface (manufactured from composite materials) is based on Shape Memory Alloys (SMA) actuators. Shown here are the smart mechanism used to actuate the wing’s upper surface, the design of the intelligent actuation control concept, which uses a self–tuning fuzzy logic Proportional–Integral–Derivative plus conventional On–Off controller, and some of the results provided by the wind tunnel experimental testing of the model equipped with the intelligent controlled actuation system. The control mechanism uses two fuzzy logic controllers, one used as the main controller and the other one as the tuning controller, having the role of adjusting (to tune) the coefficients involved in the operation of the main controller. The control system also took into account the physical limitations of the SMA actuators, including a software protection section for the SMA wires, implemented by using a temperature limiter and by saturating the electrical current powering the actuators. The On–Off component of the integrated controller deactivates or activates the heating phase of the SMA wires, a situation when the actuator passes into the cooling phase or is controlled by the Self–Tuning Fuzzy Logic Controller.

Design Optimization of Grids in Grid Fins for Spacecrafts

Grid fins are a type of aero control surfaces used in missiles and rockets in place of more conventional control surfaces such as the planar fins. Conventional planar fins are designed like miniature wings whereas grid fins have smaller lattice aerostructures arranged within a box-like structure. Most grid fins have square grid aerostructures such as those used in the Falcon 9 rocket manufactured by SpaceX. This paper discusses the introduction of 3 innovative designs namely trapezoidal, triangular and hexagonal grids in two configurations - un-tapered and tapered. The taper angles will be 6, 6.5, 7 and 7.5. These new designs will be modelled and analysed using suitable software. The designed grid fins will be simulated in multiple aerodynamic conditions at various angles of attack. The exit velocity of air at the outlet of the grid fin will be measured and analysed in this paper. Once the simulation is complete, the two best designs will be 3D printed with appropriate materials at appropriate scales for wind tunnel testing. The results will be compared and validated with existing data in order to find the overall effectiveness of the designs.

Design and Analysis of MataMorph-3: A Fully Morphing UAV with Camber-Morphing Wings and Tail Stabilizers

Conventional aircraft use discrete flight control surfaces to maneuver during flight. The gaps and discontinuities of these control surfaces generate drag, which degrades aerodynamic and power efficiencies. Morphing technology aims to replace conventional wings with advanced wings that can change their shape to control the aircraft with the minimum possible induced drag. This paper presents MataMorph-3, a fully morphing unmanned aerial vehicle (UAV) with camber-morphing wings and tail stabilizers. Although previous research has presented successful designs for camber-morphing wing core mechanisms, skin designs suffered from wrinkling, warping, or sagging problems that result in reduced reliability and aerodynamic efficiency. The wing and tail stabilizers of MataMorph-3 feature hybrid ribs with solid leading-edge sections that house servomotors, and compliant trailing-edge sections with integrated flexible ribbons that are connected to the servomotors to camber-morph the ribs. Thin laminated carbon fiber composite skin slides smoothly over the compliant rib sections upon morphing, guided by innovative trailing-edge sliders and skin-supporting linkage mechanisms strategically located between the ribs. Sample prototypes were built and tested to show the effectiveness of the proposed design solutions in enabling smooth camber-morphing. The proposed design provides a better alternative to stretchable skins in morphing airplane designs through the concept of skin sliding.

Study on the Actuation Aspects for a Morphing Aileron Using an Energy–Based Design Approach

Evaluating the impact of morphing devices in terms of actuation energy is a promising approach to quantify, from the earliest stages of wing design, the convenience of active camber morphing compared to the use of conventional control surfaces. A morphing wing device consists of an adaptive structure coupled with an actuation system. The starting point for the design of the adaptive structure is a three-dimensional parametric-geometry-representation technique working on the definition of the external morphing shape. The morphing shape is defined to be feasible from the structural point of view and able to meet the aerodynamic design requirements. The new method presented here enables the computation of the actuation energy as a combination of strain energy and external aerodynamic work. The former is the energy required to deform the skin and can be computed in an analytical way, based on the same quantities used by the parameterization technique. The latter is used to compute the energy needed to counteract the external aerodynamic loads during the deformation. This method is applied to the design optimization of a morphing aileron which is installed on a 24 m span wing, starts at 65% of both the chord and the semi-span and extends for one third of the span. A parametric study shows the superiority of the morphing aileron, compared with an equivalent hinged aileron, in terms of energy saving, weight penalty reduction and ease of on-board installation. The morphing aileron is more compact and requires a lower actuation energy combined with a lower deflection, while providing the same roll moment.

Modeling and control of a class of urban air mobility tiltrotor aircraft

This paper aims at developing a control-centric analytical formulation for aeromechanics and flight dynamics of urban air mobility (UAM) vehicles. Such vehicles feature a hybrid configuration with tiltrotors and fixed wings, enabling vertical takeoff/landing capability while attaining level flight range and endurance. A comprehensive nonlinear rigid-body dynamic model is developed by incorporating multiple tiltrotor dynamics and their gyroscopic and inertial coupling effects. A quasi-steady aerodynamic formulation is used to derive the aerodynamic loads on all lifting surfaces. In addition to the conventional control surfaces of the fixed-wing aircraft, the tiltrotor angular positions and rotational speeds are also considered additional control inputs in the derivation of nonlinear flight dynamic equations. These nonlinear equations are then linearized with respect to a set of trimmed conditions to generate the corresponding linear time-invariant state-space models, which are best suited for flight control design. In particular, to capture the critical dynamical behaviors during the transition from vertical to forward flight, the linear models are attained at various angular positions of the tiltrotors. These linear models are then utilized to develop a linear parameter-varying (LPV) model in which the tiltrotor angular position is considered the scheduling parameter. Subsequently, the adaptive model predictive control (MPC) methodology is used to design the flight controllers to achieve a stable and smooth transition flight. The numerical simulations demonstrate the efficacy of the proposed modeling and control approach.

Modeling and Control of an Articulated Multibody Aircraft

Insects use dynamic articulation and actuation of their abdomen and other appendages to augment aerodynamic flight control. These dynamic phenomena in flight serve many purposes, including maintaining balance, enhancing stability, and extending maneuverability. The behaviors have been observed and measured by biologists but have not been well modeled in a flight dynamics framework. Biological appendages are generally comparatively large, actuated in rotation, and serve multiple biological functions. Technological moving masses for flight control have tended to be compact, translational, internally mounted and dedicated to the task. Many flight characteristics of biological flyers far exceed any technological flyers on the same scale. Mathematical tools that support modern control techniques to explore and manage these actuator functions may unlock new opportunities to achieve agility. The compact tensor model of multibody aircraft flight dynamics developed here allows unified dynamic and aerodynamic simulation and control of bioinspired aircraft with wings and any number of idealized appendage masses. The demonstrated aircraft model was a dragonfly-like fixed-wing aircraft. The control effect of the moving abdomen was comparable to the control surfaces, with lateral abdominal motion substituting for an aerodynamic rudder to achieve coordinated turns. Vertical fuselage motion achieved the same effect as an elevator, and included potentially useful transient torque reactions both up and down. The best performance was achieved when both moving masses and control surfaces were employed in the control solution. An aircraft with fuselage actuation combined with conventional control surfaces could be managed with a modern optimal controller designed using the multibody flight dynamics model presented here.

Hypersonic Flow Control of Kinzhal Missile via Off-Axis, Pulsed Energy Deposition

The interaction of an off-axis, spherical energy discharge with the Kh-47M2 Kinzhal missile at Mach 6 sea-level conditions was simulated. A parametric study of the energy discharge parameter (proportional to the ratio of the energy added to the internal energy within the energy deposition volume) was performed to examine the effect of energy added to the heated region in front of the missile and the changes it causes on the drag force, side (vertical) force, and pitching moment. The peak value for the pitching moment coefficient was shown to be 0.0045 for , which was shown to be 15.5% of the value due to a 10° front finset deflection. Both inviscid and Reynolds-averaged Navier–Stokes simulations were performed. The additional influence of the turbulent boundary layer on the peak value of the produced pitching moment was negligible. The time interval for the variation in the pitching moment coefficient due to energy deposition is 61 times faster than the standard actuation time (0.1 s) for conventional control surfaces, indicating the potential for multiple pulsed energy depositions as a means for hypersonic flight control.

The interaction between active aeroelastic control and structural tailoring in aeroservoelastic wing design

This paper presents an analysis of the interaction and trade-off between active aeroelastic control and passive structural tailoring on a free-flying fully flexible aircraft model. Both technologies are included in the preliminary design of a typical transport aircraft configuration with a conventional control surface layout containing trailing edge control surfaces and spoilers. The passive structural tailoring is facilitated by exploiting the anisotropic properties of composite materials to steer the static and dynamic aeroelastic behaviour. Active aeroelastic control is implemented by scheduled control surface deflections redistributing the aerodynamic loads during manoeuvres to achieve manoeuvre load alleviation and a feed-forward control law for gust load alleviation. The panel-based aerodynamic modelling of spoiler deflections is improved by a correction of the spatial distribution of the boundary condition derived from higher fidelity simulation data. The optimisation of active control laws requires the consideration of constraints of the actuation system, namely rate and deflection saturation, in a nonlinear manner. The interaction of manoeuvre load alleviation, gust load alleviation and passive structural tailoring is investigated on the basis of results of different aeroservoelastic optimisations. Therefore the primary wing structure is simultaneously optimised with the individual technologies being activated or deactivated, resulting in eight different wing structures. The results of the individual and combined optimisations reveal significant design differences. The potentials of the different technologies can only be optimally exploited by simultaneous optimisation. The paper concludes with a study of the sensitivity of the major findings with respect to the knockdown factor for failure applied to the material properties. A substantial shift of effectiveness from active aeroelastic control to passive structural tailoring is observed with increased allowables resulting in more flexible and hence less stiff wing designs.

Roll Control of Morphing Aircraft with Synthetic Jet Actuators at a High Angle of Attack

Flow separation and dynamic stall occurring at a high angle of attack will lead to difficulty in control and maneuverability for morphing aircraft. This study proposes a novel active flow control technology using a synthetic jet actuator for the roll motion of morphing aircraft. With the help of the computational fluid dynamics method and vortex lattice method, the roll control model of morphing aircraft undergoing large shape change at a high angle of attack is established. In this model, both the array of the actuator with an optimized cavity shape and morphing span, which are subject to the input saturation constraint, are used to mimic the conventional control surface. Integrated flight control based on the sliding mode control method is designed to ensure the desired closed-loop asymptotic stability, wherein the radial basis function neural network is employed to provide the compensation induced by the input saturation constraint. To demonstrate the effectiveness of the control scheme, various control strategies for different combinations of input are proposed to maintain the roll motion. The numerical results show that the designed control law could track the target signal well, which suggests that the virtual control surface is an effective tool for maintaining the high flight performance of morphing aircraft.

Modeling and simulation of mass-actuated flexible aircraft for roll control

Moving mass control (MMC) is a flight control technique that provides several unique advantages over conventional aerodynamic control surfaces, particularly for near space vehicles. In this study, we propose an MMC strategy for roll control of low-speed flexible HALE aircraft. Two internal moving masses are used to produce rolling moment rather than conventional ailerons. The complete equations of motion of the flexible aircraft carrying moving mass are first derived in terms of quasi-coordinates. A simplified model integrated with unsteady aerodynamic loads is obtained for roll control. The effect of moving mass positions on rigid-body motion and aeroelasticity couplings are analyzed. The feasibility of the mass-actuation concept for roll control of the flexible aircraft is primarily proven. The roll control ability and aeroelastic characteristics can be improved through the reasonable design of the moving mass system. The dynamic behavior of the system, while the mass travels along the wing, is simulated, implying that the elastic motion induces the delay effect in the roll motion of the flexible model compared with the rigid model. A roll rate control system is designed and analyzed to demonstrate the feasibility of using moving masses in real-time flight control.

Optimization of a3D Aircraft Morphing Wing with highly controllable Aerodynamic Performance

the sole purpose of this project is to compare the aerodynamic performance of the modernistic wing with morphing techniques to the conventional one (i.e. wing with ailerons and flaps). The morphing wing is capable of enhancing the mission profiles through its significant geometrical changes in the surface areas (upper and lower area of wing). The primary aspiration is to calculate the CL and CD (coefficient of lift and drag) of real aircraft with conventional control surfaces and to compare its result with morphing wing. The morphing techniques also enables various prevention of aerodynamic losses (drag, vortices, noise, etc) caused due to geometrical discontinuities of conventional wing with aileron and flap in operating conditions (take-off, cruise, loiter, landing).Catia modelling of proposed wing is analysed by CFD method and to compare and contrast the aerodynamic performance with the conventional (hinged) wing.

Control Authority of a Camber Morphing Flying Wing

Flying wings achieve their roll, pitch, and yaw controllability exclusively through spanwise variations of lift and drag due to the lack of an empennage. Instead of using conventional control surfaces, which increase the aerodynamic drag due to gaps and discontinuities, a morphing structure can be employed. This work considers a previously developed camber morphing flying wing, which uses 10 electromechanical actuators to achieve spanwise-varying trailing edge deflections, resulting in variations of the lift and drag distributions and generating moments around the roll, pitch, and yaw axes. To investigate the control authority of the aircraft across all flight maneuvers, a series of multi-objective aerostructural optimizations is carried out. The performance for the individual maneuvers, as well as the interaction of simultaneous roll, pitch, and yaw moments and the resulting control authority, is assessed. Because the same actuators are used for all maneuvers, a high degree of interaction has been found between the achieved rolling and yawing moments. By minimizing the additional drag with the morphing actuation, the undesired effect of adverse yaw is minimized. The results describe a possible control strategy for flying wing aircraft with optimal drag performance.

Numerical study on Longitudinal control of Cessna 172 Skyhawk aircraft by Tail arm length

This paper covers a new method of longitudinally controlling an aircraft by changing the horizontal tail arm length, without the conventional control surface called ‘elevator’. The effects of changing horizontal tail arm length from its steady level trimmed condition are determined numerically for the chosen Cessna aircraft. From the numerical calculations, the possibilities of implementing this type of control in the chosen Cessna aircraft are analyzed. At last, some recommendations are suggested for the effective longitudinal control of the Cessna aircraft by changing horizontal tail arm length. Further, it is also suggested that employing both elevator control and tail arm length control together will make an aircraft to meet any kind of longitudinal controllability and stability requirement at any instant. This optimal aircraft configuration can be achieved by proposing a novel configuration and morphing solutions.

Trajectory optimisation of six degree of freedom aircraft using differential flatness

ABSTRACTThe flatness of a six-degree-of-freedom (6DoF) aircraft model with conventional control surfaces – aileron, flap, rudder and elevator, along with thrust vectoring ability is established in this work. Trajectory optimisation of an aircraft can be cast as an inverse problem where the solution for control inputs that yield desired trajectories for certain states is sought. The solution to the inverse problems for certain systems is made tractable when they exhibit differential flatness. Flatness-based trajectory optimisation has a significant advantage over an equivalent collocation-based method in terms of computational efficiency and viability for real-time implementation. An application for the flatness of 6DoF aircraft is shown in the trajectory optimisation for dynamic soaring, and its connection with an equivalent 3DoF flatness-based implementation is also brought out. The results are compared with that from a collocation-based approach.

Planform, aero-structural and flight control optimization for tailless morphing aircraft

Tailless swept wing airplanes rely on variations of the spanwise lift distribution to achieve controllability in all axes. As every flight condition requires different control moments, the conventional discrete control surfaces will be practically continuously deflected, leading to drag penalties. Shape adaptation base on chordwise morphing can achieve continuous deformations of the wing profile, leading to local lift variations with minimum drag penalties. As the shape is varied continuously along the wingspan, the lift distribution can be tailored to each flight condition. Tailless aircraft appear therefore as prime candidates for morphing, as the attainable benefits are potentially significant. This work presents a methodology to determine the optimal planform, profile shape, and morphing structure for a tailless aircraft. The employed morphing concept is based on a distributed compliance structure, actuated by piezoelectric elements. The multidisciplinary optimization considers the static and dynamic aeroelastic behavior of the structure and aims to maximize the aerodynamic efficiency of the plane while guaranteeing its controllability by means of morphing. The potential of the resulting wing design is fully exploited by means of a second optimization process, which identifies the actuation configuration resulting in the highest aerodynamic efficiency for a wide variety of control moments.

Fluidic Flow Control Effectors for Flight Control

This paper overviews research undertaken to develop and demonstrate active flow control technologies based on the application and manipulation of Coanda flows, with the objective of developing systems having adequate control authority to trim and maneuver an aircraft without the use of conventional control surfaces. The development of circulation control and fluidic thrust vectoring concepts and the contributions of numerous researchers to the current understanding of supersonic wall jets are reviewed and placed into context with the authors’ own research. The value of supplementing fundamental experimental and numerical research with more practical system integration studies and small-scale flying demonstration activities is shown to be a valuable approach to providing focus and direction for the research. Simple technology demonstrators have also proved to be valuable motivators for the research team and provided important focus in promoting the technologies and ideas to the wider stakeholder community. Outcomes of the research are now being explored in the context of taking them to the next stage of practical maturity.

Computational and experimental investigation of fluidic thrust vectoring actuator

Fluidic thrust vectoring (FTV) control is an innovative technique employed to affect the pitch control of an air vehicle or an unmanned air vehicle in the absence of conventional control surfaces such as elevators. The main motivation in using FTV is to render the aircraft low observable. In this work, a relatively new concept called co-flow type of FTV concept is investigated. Wherein, a high velocity secondary jet is injected into the boundary layer of the primary jet causing deflection of main primary jet thereby enabling generation of pitch moment. Two sets of numerical simulations studies were undertaken, one for different ratios of Coanda surface radius (R) and primary height (hprim) while the other for different ratios of secondary gap height (∆h) and primary height (hprim). The insight gained from simulations guided the design of a working FTV test rig. A static test rig was manufactured where blower and a compressor were used to provide primary and secondary flows, respectively. Comparison of vectored jet behaviour predicted by computational fluid dynamics analyses is found to be in agreement with those obtained through experimentation.