The application of morphing wing devices can bring several benefits in terms of aircraft performance, as the current literature shows. Within the scope of Clean Sky 2 AirGreen 2 European project, the authors provided a safety-driven design of an adaptive winglet, through the examination of potential hazards resulting from operational faults, such as actuation chain jamming or links structural fails. The main goal of this study was to verify whether the morphing winglet systems could comply with the standard civil flight safety regulations and airworthiness requirements (EASA CS25). Systems functions were firstly performed from a quality point of view at both aircraft and subsystem levels to detect potential design, crew and maintenance faults, as well as risks due to the external environment. The severity of the hazard effects was thus identified and then sorted in specific classes, representative of the maximum acceptable probability of occurrence for a single event, in association with safety design objectives. Fault trees were finally developed to assess the compliance of the system structures to the quantitative safety requirements deriving from the Fault and Hazard Analyses (FHAs). The same failure scenarios studied through FHAs have been simulated in flutter analyses performed to verify the aeroelastic effects due to the loss of the actuators or structural links at aircraft level. Obtained results were used to suggest a design solution to be implemented in the next loop of design of the morphing winglet.

Future aircraft wing technology is rapidly moving toward flexible and morphing wing concepts capable to enhance aircraft wing performance in off-design conditions and to reduce operative maneuver and gust loads. However, due to the reduced stiffness, increased mass, and increased degree of freedom (DOF), such mechanical systems require advanced aeroelastic assessments since the early design phases; this appears crucial to properly drive the design of the underlying mechanisms since the conceptual phase by mitigating their impact on the whole aircraft aeroelastic stability. Preliminary investigations have shown that the combined use of adaptive flap tabs and morphing winglets significantly improves aircraft aerodynamic performance in climb and cruise conditions by the order of 6%. Additionally, by adapting span-wise lift distributions to reduce gust solicitations and alleviate wing root bending moment at critical flight conditions, significant weight savings can also be achieved. Within the scope of Clean Sky 2 Airgreen 2 project, flutter and divergence characteristics of a morphing wing design integrating adaptive winglets and flap tabs are discussed. Multi-parametric flutter analyses are carried out in compliance with CS-25 airworthiness requirements (paragraph 25.629, parts (a), (b), (c) and (d)) to investigate static and dynamic aeroelastic stability behavior of the aircraft. The proposed kinematic systems are characterized by movable surfaces, each with its own domain authority, sustained by a structural skeleton and completely integrated with EMA-based actuation systems. For that purpose, a sensitivity analysis was performed taking into account variations of the stiffness and inertial properties of the referred architectures. Such layouts were reduced to a stick-equivalent model which properties were evaluated through MSC-NASTRAN-based computations. The proprietary code SANDY 4.0 was used to generate the aero-structural model and to solve the aeroelastic stability equations by means of theoretical modes association in frequency domain. Analyses showed the presence of critical modal coupling mechanisms in nominal operative conditions as well as in case of system malfunctioning or failure. Design solutions to assure clearance from instabilities were then investigated. Trade-off flutter and divergence analyses were finally carried out to assess the robustness of the morphing architectures in terms of movable parts layout, mass balancing and actuators damping.

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Aircraft wings are usually optimized for a specific mission design point. However, since they operate in a wide variety of flight conditions, 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. A shape-shifting surface, or usually referred as 'morphing', potentially enables transport aircraft to reach maximum performance in any flight conditions. Within the framework of the Joint Technology Initiative Clean Sky (JTI-CS) project, and during the first phase of the Green Regional Aircraft Integrated Technological Demonstration (GRA-ITD), the authors focused on the design and technological demonstration of an innovative bi-modal morphing outer wing flap to be installed on the next generation open rotor green regional aircraft. A novel active rib layout was designed to enable the articulation of the entire flap structure by means of multi-box arrangement. In order to prove structural load-carrying capabilities with the reference to a relevant environment, the full-scale morphing flap was properly analyzed by means of detailed finite element model analysis. To the authors' knowledge, there is no morphing concept in literature based on a similar architecture based on distributed servo-mechanical actuators. Hence, a rational review of the potential problems associated with actuators off-design conditions has been conducted to investigate the maturity of the concept and safety issues concerning the flap ground static test. In addition, useful insights have been provided to effectively detect potential failure conditions in service

The meaningful growth process and the exponential development related to aircraft industry has currently introduced new requirements concerning the fuel burn reduction and the noise emitted. The awareness on meeting the comfort targets implied a significant evolution of the assessments in aircraft design, aimed at reducing the problems that have emerged in empirical investigations. The aircraft renewal process involves targeted technical choices both to careful observance of safety as to the market requirements. In the current 'low-noise' research scenario on a global scale, the morphing technology is playing a dominant role for the many benefits available in the greening of the next generation air transport. The research project CRIAQ-MDO505, born by an intense synergy among industries, research centers and universities has allowed for investigating morphing structures potentials through the design and manufacturing of a variable camber aileron tailored for CS-25 category aircraft applications. In this framework, the authors focused on the setup of an advanced finite element model (FEM) and on its validation through ground resonance tests performed on a true-scale prototype. A very good correlation between numerical and experimental modal parameters was proven thus showing the adequacy of the adopted modelling strategies as well as the reliability of the FEM. Relying upon the validated FEM, sensitivity modal analyses were carried out to evaluate the stability of results with respect to single and combined failures of the actuation line enabling morphing. Modal parameters pertinent to each failure scenario were arranged into a rational database for further studies on the aero-servo-elastic behavior of the morphing system

In the framework of Clean Sky 2 Airgreen 2 (REG-IADP) European research project, a novel multifunctional morphing flap technology was investigated to improve the aerodynamic performances of the next Turboprop regional aircraft (90 passengers) along its flight mission. The proposed true-scale device (5 meters span with a mean chord of 0.6 meters) is conceived to replace and enhance conventional Fowler flap with new functionalities. Three different functions were enabled: overall airfoil camber morphing up to +30° (mode 1), +10°/−10° (upwards/downwards) deflections of the flap tip segment (mode 2), flap tip “segmented” twist of ±5° along the outer flap span (mode 3). Morphing mode 1 is supposed to be activated during take-off and landing only to enhance aircraft high-lift performances and steeper initial climb and descent. Thanks to this function, more airfoil shapes are available at each flap setting and therefore a dramatic simplification of the flap deployment system may be implemented. Morphing modes 2 and 3 are enabled in cruise and off-design flight conditions to improve wing aerodynamic efficiency. The novel structural concept of the three-modal morphing Fowler flap (3MMF) was designed according to the challenges posed by real wing installation issues. The proposed concept consists of a multi-box arrangement activated by segmented ribs with embedded inner mechanisms to realize the transition from the baseline configuration to different target aero-shapes while withstanding the aerodynamic loads. Lightweight and compact actuating leverages driven by electromechanical motors were properly synthesized to comply with stringent requirements for real aircraft implementation: minimum actuating torque, minimum number of motors, reduced weight, and available design space. The methodology for the kinematic design of the inner mechanisms is based on a building block approach where the instant center analysis tool is used to preliminary select the locations of the hinges’ leverages. The final geometry of the inner mechanisms is optimized to maximize the mechanical advantage as well as to provide the kinematic performances required by the three different morphing modes. The load-path was evaluated, and the cross-sectional size of leverages was subsequently optimized. Finally, actuating torques predicted by instant center analysis were compared to the calculated values from finite element analysis. The structural sizing process of the multi-box arrangement was carried out considering elementary methods, and results were compared with finite element simulations.

Modern aerospace research programs are increasingly oriented towards adaptive wing structures for greening the air transport in the near future. New structural concepts implementing and integrating innovative technologies are mandatory for succeeding in this critical task. Among these, the so-called morphing structures are taken into account in aerospace applications, since they ensure the structural shape control in order to optimize the aerodynamic efficiency during the different flight phases. Among the most ambitious research projects launched in Europe, the JTI - Green Regional Aircraft (GRA) is placed in foreground for the design and the demonstration of a true-scale morphing flap applicable to the Natural Laminar Flow (NLF) wing of a 130-seats reference aircraft belonging to EASA CS25 category. In this framework, the authors intensively worked on the definition of a specific actuation and control system layout properly enabling two flap operational modes: overall camber morphing in deployed configuration, during take-off and landing, to enhance high lift performances; upwards and downwards deflection of the flap trailing edge (nearly the 10% of the local chord) in stowed configuration, to improve wing aerodynamic efficiency in cruise. For this purpose, a digital logic control law was opportunely implemented into controller devices by using LTI DriveManager® software. Obtained results have been presented in terms of controlled morphed shapes, showing an excellent correlation with respect to the target geometries imposed by design requirements