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The in-flight control of the wing shape is widely considered as one of the most promising solutions to enhance the aerodynamic efficiency of the aircraft thus minimizing the fuel burnt per mission ([1]-[26]). In force of the fallout that the implementation of such a technology might have on the greening of the next generation air transport, ever increasing efforts are spent worldwide to investigate on robust solutions actually compliant with industrial standards and applicable airworthiness requirements. In the framework of the CleanSky2, a research program in aeronautics among the largest ever founded by the European Union, the authors focused on the design and validation of two devices enabling the camber-morphing of winglets and flaps specifically tailored for EASA CS-25 category aircraft ([29]). The shape transition was obtained through smart architectures based on segmented (finger-like) ribs with embedded electromechanical actuators. The combined actions of the two smart systems was conceived to modulate the load distribution along the wing while keeping it optimal at all flight conditions with unequalled benefits in terms of lift-over-drag ratio increase and root bending moment alleviation. Although characterized by a quasi-static actuation, and not used as primary control surfaces, the devices were deeply analysed with reference to their impact on aircraft aeroelastic stability. Rational approaches were adopted to duly capture their dynamics through a relevant number of elastic modes; aeroelastic coupling mechanisms were identified in nominal operative conditions as well as in case of systems’ malfunctioning or failure. Trade off flutter and divergence analyses were finally carried out to assess the robustness of the adopted solutions in terms of movable parts layout, massbalancing and actuators damping.

Airfoil camber adaptation may be the key for the performance improvement of wings for many specific applications, including shorter take-off distance, compensation of weight variation and so on. Following the successful experiences gained in SARISTU, where an adaptive trailing edge device was developed for medium to large size commercial aircraft, the authors propose to exploit the developed architecture to a small aircraft wing. The basic reasons behind that mainly rely on the associated possibility to access easier implementation onto a real aircraft instead of referring to wing segments for wind tunnel or ground tests. In this way, many operative problems are faced, that would be otherwise neglected in usual lab experimentation. First of all, the integration of the proposed device onto a flying machine, that in turn pose the problem of facing the interface with the existing systems. Secondly, the necessity of including the device into the flap while fully preserving its current functionality. Furthermore, the necessity of developing a robust design process that allows having the release of the permit-to-fly. Each of the above steps, non-exhaustive in illustrating the difficulty of the addressed challenge, is structured in many other sub-segments, ranging from a suitable FHA analysis to a full re-design of the existing high lift systems or the adaptation of the architecture of the reference morphing trailing edge itself. This last item poses the classical challenge of the scaling issues, requiring the structural and the actuation subsystems to entirely fit into the new geometry. The objective of the present research is then to verify the feasibility of applying a certain architectural morphing philosophy onto a real aircraft, taking into account all the operational difficulties related to such an operation. This paper reports the activities related to the exploitation of the reference adaptive structural architecture, to the geometry of a flap of a small aircraft. In detail, the system layout is presented, followed by a FE analysis of the structural system under the operational loads and an estimation of the weight penalty associated to this transformation. Interfaces of the flap system with the main aircraft body are considered as constraints to the design development, so that the only flap is affected.

The common challenge of all aerospace advancements is greening the air transport. This led the recent research programs towards the study of “metamorphic” wing structures, capable of adapting their geometry to the different conditions of flight. The development of morphing structures allows the reduction of drag and the increase of range, together with the growth of load control effectiveness. In this context, the European research project SARISTU addressed the physical integration of smart and morphing structural concepts, by implementing them on a true scale outer wing belonging to a CS-25 category aircraft finally tested in a large Wind Tunnel. In the framework of SARISTU project, the design of an Adaptive Trailing Edge Device was developed. The morphing skin concept consisted of a segmented skin, with aluminum and silicone foam strips covered by a protective silicone top-layer. A two-bay demonstrator was tested inside the Wind Tunnel at the Department of Industrial Engineering of the University of Naples “Federico II”; experimental analyses were performed in order to verify whether the silicone parts could show out of plane bumps induced by the aerodynamic loads occurring during the Wind Tunnel test campaign. A photogrammetric optic approach was adopted, in order to reach the aforementioned targets in a non-invasive way; such methodology was selected due the high resolution assured at a very low implementation costs. Obtained results allowed to confirm the demonstrator well done design and opened the doors to the next experimental test campaign performed in TsAGI Russian Wind Tunnel, on the outer wing equipped with a five-bay demonstrator of the Adaptive Trailing Edge Device.

A new wing-tip concept with morphing upper surface and interchangeable conventional and morphing ailerons was designed, manufactured, bench and wind tunnel tested. The development of this wing tip was done in the frame of an international CRIAQ project, and the purpose was to demonstrate the upper surface morphing and aileron morphing capabilities in improving the wing tip aerodynamic performances. During numerical optimization with ‘in-house’ genetic algorithm software, and during wind tunnel experimental tests, it was demonstrated that the air flow laminar state was extended and drag coefficient reduction were obtained., 55th AIAA Aerospace Sciences Meeting, 9-13 January 2017, Grapevine, Texas, USA

Morphing structures have the greatest potential to dramatically improve aircraft aerodynamic performance. They are designed to accomplish with a single device what conventional mechanisms can do with major aerodynamic penalties. In doing so, such systems have to be flexible enough to deliver the desired motion while ensuring a certain structural response under operative loads. In this chapter, focus is given to the structural design of morphing structures. The objective is to develop a generalized scheme, spanning from stress analysis to material selection, to design morphing devices that can morph one shape to another with minimum error. After a brief introduction, general design guidelines and practical tips are provided to ensure satisfactory mechanical structural performance and durability, with an overview of subcomponents and systems validation, design loads and simulation constraints. The application of this approach is demonstrated through an adaptive trailing edge device design example, including FE modeling, simulations and results assessment.

When dealing with the design of morphing wings, conventional structural arrangements are commonly replaced by innovative solutions enabling shape changes through actively controlled elasticity or mechanical systems. In both cases, no simplified rules coming from consolidated experiences may be invoked to guarantee that a specific design will be characterized by stable and sustainable aeroelastic response to external loads expected in service.A rational approach for the aeroelastic analysis of the structural arrangements is therefore recommended since the earliest design stage so that the maturation of unflyable solutions is naturally avoided.The extra-modes method is herein detailed as a dramatically efficient tool to accomplish this paramount task. The morphing device is treated as a substructure and the aircraft (A/C) as the basic system on which the device is installed. Substructure's contribute to the aeroelastic response of the global system is expressed in terms of generalized parameters pertinent to additional and strategically defined modes capturing the substructure dynamics. After recalling the general formulation of the method, two case studies are presented in order to show its great potential to rapidly appreciate the aeroelastic behavior of a given design, irrespective of the maturity level of the design itself.

Morphing of metallic wing structures has fascinated generations of researchers; numerous and sometimes bizarre architectures have been proposed, tailored to specific end-applications and aircraft type. Although different for layout, all of them can be categorized in two basic groups: mechanized architectures and compliant mechanisms.Mechanized architectures implement morphing through the rigid-body motion of stiff subcomponents interconnected by suitably designed kinematic chains and actuation leverages.Each subcomponent of the kinematic chain is sized to provide its own contribution to the adsorption of the external solicitations arising in operative conditions; actuators and actuation transmission line are sized to enable the motion of the system and to preserve given shape configurations while counteracting aerodynamic loads with the minimum need of power.Compliant mechanisms involve the deformation of structural elements to enable the required shape-change; mechanical properties of the structure have to be properly distributed in order to assure adequate morphing compliance and adequate stiffness to withstand external loads.In this chapter, the design philosophy behind each type of morphing structure has been presented, together with practical applications to wing trailing edge camber adaptation.By referring to similar end-application, the adopted design strategies and obtained outcomes are compared, thus better highlighting the advantages and weak points of each morphing solution

The development of adaptive morphing wings has been individuated as one of the crucial topics in the greening of the next generation air transport. Research programs have been lunched and are still running worldwide to exploit the potentials of morphing concepts in the optimization of aircraft efficiency and in the consequent reduction of fuel burn. In the framework of CRIAQ MDO 505, a joint Canadian and Italian research project, an innovative camber morphing architecture was proposed for the aileron of a reference civil transportation aircraft; aileron shape adaptation was conceived to increase roll control effectiveness as well as to maximize overall wing efficiency along a typical flight mission. Implemented structural solutions and embedded systems were duly validated by means of ground tests carried out on a true scale prototype. Relying upon the experimental modes of the device in free-free conditions, a rational analysis was carried out in order to investigate the impacts of the morphing aileron on the aeroelastic stability of the reference aircraft. Flutter analyses were performed in compliance with EASA CS-25 airworthiness requirements and referring -at first- to nominal aileron functioning. In this way, safety values for aileron control harmonic and degree of mass-balance were defined to avoid instabilities within the flight envelope. Trade-off analyses were finally addressed to justify the robustness of the adopted massbalancing as well as the persistence of the flutter clearance in case of relevant failures/malfunctions of the morphing system components.

More severe regulations are growing worldwide due to increasing air traffic in order to reduce fuel consumption and noise. The achievement of challenging targets in terms of pollutant emissions abatement demands for the development of innovative aircraft technologies. Morphing is one of them and plays an extraordinary role for the improvement of aircraft performance. Many research projects are currently focused on morphing both in US and Europe. Among these, the CRIAQ-MDO505 constitute the first trans-European cooperation project on smart technologies. Its aim is to investigate morphing structures potential through the design and manufacturing of a full-scale variable camber aileron designed according to the requirements of a regional aircraft. This project was carried out by Italian and Canadian academies, research centers, and leading industries. In this framework, the authors worked on the development of this technology addressing both numerical and experimental activities up to a thorough validation of a physical prototype. The effective capabilities of the adaptive prototype were proven by means of wind tunnel and ground test campaigns which successfully demonstrated the feasibility and the reliability of a morphing aileron.

Aircraft wings are usually optimized for a specific design point. However, since they operate in a wide variety of flight regimes, some of these have conflicting impacts on aircraft design, as an aerodynamically efficient configuration in one instance may perform poorly in others. Conventional wing structures preclude any significant adaptation to changing conditions; movable surfaces, such as flaps or slats, lead to limited changes of the overall shape with narrow benefits compared with those that could be obtained from a wing structure that is inherently deformable and adaptable. An adaptive trailing edge concept conceived to enhance wing aerodynamic performance in cruise condition is outlined. The camber of the trailing edge is controlled during flight to compensate the weight reduction following the fuel burning. In this way, the trimmed configuration remains optimal in terms of efficiency (lift to drag ratio) or minimal drag with positive fallouts on aircraft fuel consumption per flight. The main steps concerning the design of the device are reported, with a special focus on each of its relevant architectural elements. In detail, the skin, the structural skeleton, the actuator, sensor, and control systems are dealt with. Some attention is devoted to aspects that are necessary to come to a finalized product of industrial relevance: namely, the aeroelastic and the safety analyses. The former assumes a main relevance because the system has augmented degrees of freedom with respect to a standard layout and then, a more complex dynamic response and a higher risk of instability. The latter is necessary to envisage a future certification process of this kind of device that requires the development of a dedicated path.

Shape control of adaptive wings has the potential to enhance wing aerodynamic performance during cruise and high-speed off-design conditions. A possible way to attain this objective is to develop specific technologies for trailing edge morphing, aimed at variating the airfoil camber. In the framework of SARISTU project (EU-FP7), an innovative structural system incorporating a gapless deformable trailing edge has been developed. A related key technology is the capability to emulate and maintain pre-selected target wing shapes within an established margin, enabling optimal aerodynamic performance under current operational pressure loads. In this paper, the design of a control system aimed at preserving the specific geometry envelope under variable conditions, is numerically and experimentally explored. The actuation concept relies on a quick-return mechanism, driven by load-bearing actuators that act on morphing ribs, directly and individually. The adopted unshafted distributed electromechanical system arrangement uses servo-rotary actuators each rated for the torque of a single adaptive rib of the morphing structure. The adopted layout ensures compactness and weight limitations, essential to produce a clean aerodynamic system. A FBG-based distributed sensor system generates the information for appropriate open- and closed loop control actions and, at the same time, monitors possible failures in the actuation mechanism. The research leading to these results has gratefully received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no 284562.

This paper deals with the design of an adaptive trailing edge aimed at increasing the range capacity of a large commercial aircraft. Moving from the requisites, a brief discus-sion about the expected performance will be introduced together with a suitable layout. Then, the design of the structural system able to guarantee both the deformability and the structural resistance will be presented. The next step is devote to the actuation system design, able to be integrate din the structural body and bear the external aerodynamic load. The external skin contributes to load bearing but also to the actuation effort required. Details refer to other publications while here it is considered though its effect only. An aeroelastic study, ensuring the stability of the proposed device over the whole wing system will be finally dealt with. A discussion on the real applicability in the aeronautics will conclude the work, pointing out at the necessary improvement required. Other work on the same subject, but referring to other design and implementation aspect will be fully referred to.

In morphing structures, actuation is a key system for general aircraft-level functions. Similarly to the demonstration of safety compliance applied to aircraft control surfaces, novel functions resulting from the integration of a morphing device (ATED), imposes a detailed examination of the associated risks. Because of the concept novelty, literature references for a safe design of a morphing trailing edge device are hard to be found. The safety-driven design of ATED requires a thorough examination of the potential hazards resulting from operational faults involving either the actuation chain, such as jamming, or the external interfaces, such as loss of power supplies and control lanes. In this work, a study of ATED functions is qualitatively performed at both subsystem and aircraft levels to identify potential design faults, maintenance and crew faults, as well as external environment risks. The severity of the hazard effects is determined and placed in specific classes, indicative of the maximum tolerable probability of occurrence for a specific event, resulting in safety design objectives. A fault tree is finally produced to evaluate the impact of actuation kinematics on specific aspects of ATED morphing operation and reliability.

The aim of this paper is to investigate the use of active vibration control in automotive gearboxes mounting brackets to reduce tonal disturbances. A combination of piezoelectric accelerometers and an internally preloaded piezo stack actuator is used to counteract their unbalanced caused vibrations. Initially, a numerical modal analysis was carried out to identify the normal modes in the frequency range of interest. The piezo stack was simulated by a ROD element and its effect numerically characterized. The upper and lower faces of the stack were mechanically coupled with the bracket structure, whereas the active control strategy involved the relative displacement of two opposite points of the bracket. To this aim, dedicated interfaces were designed to integrate the stack into the mounting bracket. In order to control the vibrations in correspondence of the second bending mode (1599.4Hz), the primary disturbance, simulated by a shaker, was modelled in the frequency domain using a white noise signal. A narrow window of 20Hz was initially selected as the control system domain. Then, this frequency range has been made gradually wider around the resonance peak, in order to optimize the control effect, and then extended up to 80 Hz when undesired effects occurred. Primary and secondary control plants were firstly numerically fitted from the measured responses and excitations using system identification techniques, and then used for the active controller design and simulations.

The structural design process of an adaptive wing trailing edge (ATED) was addressed in compliance with the demanding requirements posed by the implementation of the architecture on large aeroplanes. Fast and reliable elementary methods combined with rational design criteria were adopted in order to preliminarily define ATED box geometry, structural properties, and the general configuration of the embedded mechanisms enabling box morphing under the action of aerodynamic loads. Aeroelastic stability issues were duly taken in account in order to safely assess inertial and stiffness distributions of the primary structure as well as to provide requirements for the actuation system harmonics. Results and general guidelines coming from the preliminary design were then converted into detailed drawings of each box component. Implemented solutions were based on designer’s industrial experience and were mainly oriented to increase the structural robustness of the device, to minimize its manufacturing costs, and to simplify assembly and maintenance procedures. The static robustness of the executive layout was verified by means of linear and nonlinear stress analyses based on advanced FE models; dynamic aeroelastic behaviour of the stress-checked structure was finally investigated by means of rational analyses based on theoretical mode association.

“Inspiration from nature” is the key words that lies behind the morphing idea. Just as bird helped to inspire the design of the warping mechanism of the Wright Flyer, nature offers a philosophy inspiration for morphing wing design. Since aviation origin, a connection between bio-inspiration and aeronautical engineering can be found which has led through years at the current idea of a morphing wing as a mechanism capable to adapt its shape as well as the flight conditions change. Design of morphing wings at increasing TRL is common to several research programs worldwide, especially aimed at improving their associated benefits (optimize aerodynamic efficiency, fuel consumption reduction, decrease of COx and NOx emission, etc.) and overcoming classical limits (increasing system complexity, certification, reliability and so on). In this framework, the CRIAQ MD0505 project was launched; a joint research program between Canadian and Italian academies, research centers and leading industries. The target of this research cooperation is the development of combined smart structures systems on a full scale wing tip of a next generation regional aircraft. The complex device combines a modifiable airfoil thickness with a camber morphing aileron. This paper focuses on the preliminary design and the numerical modeling of the aileron architecture. The structural layout consists of a number of deformable ribs, each made of three consecutive blocks connected each other by hinges. Further cross connections between pair of elements, make the system a SDOF finger-like mechanism. The aileron is moved by servo rotary load bearing actuators which drive a kinematic chain and sustain the external aerodynamic pressure distribution. A FE model of the entire architecture was released to verify the structural integrity under prescribed operational conditions.

Aircraft wings are usually optimized for a specific design point. However, since they operate in a wide variety of flight regimes, some of these have conflicting impacts on aircraft design process, as a single configuration may be efficient in one instance but perform poorly in others. In principle, stiff, hardly deformable aircraft structures preclude any adaptation to changing conditions. Alternatively, morphing wings could provide adaptive capabilities to maximize aircraft performance in any flight operation. Inside SARISTU, specific research activities were carried out on the technological development of an Adaptive Trailing Edge Device (ATED) implementing airfoil camber morphing for the maximization of the wing aerodynamic performance during cruise, with the ultimate goal to reduce fuel consumption. Wing shape is changed to compensate weight losses following fuel burning, to keep L/D ratio (or simply drag, D) to its optimal value. ATED camber adaptations are predicted to lead to significant benefits in fuel consumption, estimated from 3 to 5%, depending on a number of initial and boundary conditions. This paper is focused on the design process adopted for the definition and verification of ATED primary structure; fast and reliable elementary methods combined with rational design criteria and advanced FE analyses were adopted to assess the architectural concept and the embedded actuation mechanisms. Structural design was carried out in compliance with the very demanding requirements posed by the implementation of the device on large Aeroplanes (EASA CS25 category).