Rosario Pecora

A Novel SMA-based Concept for Airfoil Structural Morphing

The adaptive structures concept is of great interest in the aerospace field because of the several benefits which can be accomplished in the fields including noise reduction, load alleviation, weight reduction, etc., at a level in which they can be considered as compulsory in the design of future aircraft. Improvements in terms of the aerodynamic efficiency, aeroelastic behavior, stability, and manoeuvrability performance have already been proved through many international studies in the past. In the family of the Smart Materials, Shape Memory Alloys (SMA) seem to be a suitable solution for many static applications. Their high structural integrability in conjunction with actuation capabilities and a favorable performance per weight ratio, allows the development of original architectures. In this study, a morphing wing trailing edge concept is presented; morphing ability was introduced with the aim of replacing a conventional flap device. A compliant rib structure was designed, based on SMA actuators exhibiting structural potential (bearing external aerodynamic loads). Numerical results, achieved through a FE approach, are presented in terms of trailing edge induced displacement and morphed shape.

Airfoil Structural Morphing Based on S.M.A. Actuator Series: Numerical and Experimental Studies

Multiple flight regimes during typical aircraft missions mean that a single unique optimized configuration, that maximizes aerodynamic efficiency and maneuverability, cannot be defined. Discrete components such as ailerons and flaps provide some adaptability, although they are far from optimal. Wing morphing can significantly improve the performance of future aircraft, by adapting the wing shape to the specific flight regime requirements, but also represents a challenging problem: the structure has to be stiff to maintain its shape under loads, and yet be flexible to deform without collapse. One solution is to adopt structural elements made of smart materials; Shape Memory Alloys (SMAs) have demonstrated their suitability for many static applications due to their high structural integration potential and remarkable actuation capabilities. In this work, the airfoil camber at the wing trailing edge on a full scale wing of a civil regional transportation aircraft is controlled by substituting a traditional split flap with a hingeless, smooth morphed flap. Firstly, the development and testing of an actuator device based on a SMA ribbon, capable of a net rotation of 5 deg, is presented. Then, a flap bay is designed and experimentally tested in presence of static loads, based on a compliant rib built as a series repetition of the proposed actuator. An aero-thermo-mechanical simulation within a FE approach was adopted to estimate the behavior and performance of the compliant rib, integrating both aerodynamic loads, by means of a Vortex Lattice Method (VLM) code, and SMA phenomenology, implementing Liang and Rogers’ constitutive model. The prototype showed good actuation performance even in presence of external loads. Very good numerical-experimental correlation is found for the unloaded case, while some fatigue issues emerged in presence of static loads.

Optimization and integration of shape memory alloy (SMA)-based elastic actuators within a morphing flap architecture

Aircraft morphing architectures are currently worldwide investigated to enhance performance while reducing weights, volumes and costs. A 3-flap wing, for instance, shall pay a penalty up to 100% due to the insertion of mechanical devices in its body. Moreover, the insertion of cover nacelles disturbs the wing aerodynamics itself. In addition, flapped wings are noisy: deformable, instead of slotted and flapped wings, may lead to significant enhancement also in this field. Within Joint European Initiative on Green Regional Aircraft frame, in cooperation with the University of Naples, Department of Aerospace Engineering, the authors with their colleagues came to the definition of dedicated morphing architectures. This paper focuses on the design and optimization of a morphing architecture based on Shape Memory Alloy (SMA) technology, aimed at increasing airfoil trailing edge curvature. The deformable rib system is constituted of four elastic elements. The aerodynamic loads were computed through a classical panel method for the most severe flight condition. The descriptive finite element model underwent an optimization process performed through a proprietary code, based on a genetic selection strategy. Resulting values, from the optimization study were different for the variables referring to each subsystem: plate thickness, depth and length, relative orientation, SMA ribbons thickness, depth and location. Trailing edge vertical displacement was assumed as target. The main features of the 4 elastic elements are presented in the body of the document. As expected, the more rearward is the element position, the less is the weight and size; decreasing values of the aerodynamic load led towards lighter solutions.

Safety and Reliability Aspects of an Adaptive Trailing Edge Device (ATED)

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.

Airfoil Morphing Architecture Based on Shape Memory Alloys

The adaptive structures concept is of great interest in the aeronautical field because of the several benefits which can be accomplished in the design of future aircraft. Improvements in terms of aerodynamic efficiency, aero-elastic behaviour and manoeuvrability were proved by many international studies. The development of new structural architectures implementing and integrating innovative materials is mandatory for succeeding in these critical tasks. The so-called Smart Structure idea is more and more taken into account in aerospace applications Among the family of Smart Materials, Shape Memory Alloys (SMAs) certainly represents a convenient solution for many static applications. In this work, an application for a morphing wing trailing edge is presented as alternative for conventional flap devices. A compliant rib structure has been designed, based on SMA components working both as actuators, controlling wing chamber, and as structural elements, sustaining external aerodynamic loads. Achievable performance has been estimated by a FE approach; SMA behaviour has been modelled through a dedicated routine implementing the Liang & Rogers’ model for evaluating the internal stress and the minimum temperature necessary for activation. The numerical results have been presented in terms of induced displacements and morphed shape.Copyright

KRISTINA: Kinematic rib-based structural system for innovative adaptive trailing edge

Nature teaches that the flight of the birds succeeds perfectly since they are able to change the shape of their wings in a continuous manner. The careful observation of this phenomenon has re-introduced in the recent research topics the study of “metamorphic” wing structures; these innovative architectures allow for the controlled wing shape adaptation to different flight conditions with the ultimate goal of getting desirable improvements such as the increase of aerodynamic efficiency or load control effectiveness. In this framework, the European research project SARISTU aimed at combining morphing and smart ideas to the leading edge, the trailing edge and the winglet of a large commercial airplane (EASA CS25 category) while assessing integrated technologies validation through high-speed wind tunnel test on a true scale outer wing segment. The design process of the adaptive trailing edge (ATED) addressed by SARISTU is here outlined, from the conceptual definition of the camber-morphing architecture up to the assessment of the device executive layout. Rational design criteria were implemented in order to preliminarily define ATED structural layout and the general configuration of the embedded mechanisms enabling morphing under the action of aerodynamic loads. Advanced FE analyses were then carried out and the robustness of adopted structural arrangements was proven in compliance with applicable airworthiness requirements.

Wing chamber control architectures based on SMA: numerical investigations

Benefits in terms of aerodynamic efficiency, aeroelastic behaviour, stability and manoeuvrability performance coming from the adaptive variation of wing geometric (e.g. thickness and chamber) and mechanical (e.g. rigidity) parameters were widely proved. In this scenario, more and more efficient architectures based on innovative materials like shape memory alloys, piezoelectrics, magneto-rheologic fluids were ideated and related morphing ability was tested. Due to the large transmitted forces and deformations, for static applications, SMA based-on architectures were implemented. The essential idea of all these architectures is to integrate a SMA actuator, lacking of remarkable structural value, within a classical wing structure or within a suitably designed one. The main disadvantage of such architectures derives by the necessity of deforming a classical structure, not designed for reaching large displacements. In order to avoid these problems, in this work, the idea of integrating compliant structures by SMA elements, was considered. Some deformation strategies, focused on the wing aft part morphing, were ideated; related performance in terms of vertical displacement and rotation of the trailing edge was estimated by a FE approach. Each architecture is characterised by SMA rod elements able to guarantee large deformations and shape control under aerodynamic loads.

Toward the bi-modal camber morphing of large aircraft wing flaps: the CleanSky experience

The Green Regional Aircraft (GRA), one of the six CleanSky platforms, represents the largest European effort toward the greening of next generation air transportation through the implementation of advanced aircraft technologies. In this framework researches were carried out to develop an innovative wing flap enabling airfoil morphing according to two different modes depending on aircraft flight condition and flap setting: - Camber morphing mode. Morphing of the flap camber to enhance high-lift performances during take-off and landing (flap deployed); - Tab-like morphing mode. Upwards and downwards deflection of the flap tip during cruise (flap stowed) for load control at high speed and consequent optimization of aerodynamic efficiency. A true-scale flap segment of a reference aircraft (EASA CS25 category) was selected as investigation domain for the new architecture in order to duly face the challenges posed by real wing installation issues especially with reference to the tapered geometrical layout and 3D aerodynamic loads distributions. The investigation domain covered the flap region spanning 3.6 m from the wing kink and resulted characterized by a taper ratio equal to 0.75 with a root chord of 1.2 m. High TRL solutions for the adaptive structure, actuation and control system were duly analyzed and integrated while assuring overall device compliance with industrial standards and applicable airworthiness requirements.

Distributed Actuation and Control of a Morphing Wing Trailing Edge

In a morphing wing trailing edge device, the actuated system stiffness, load capacity, and integral volumetric requirements drive flutter, actuation strength, and aerodynamic performance. Design studies concerning aerodynamic loads, structural properties, and actuator response provide sensitivities to aeroelastic performance, actuation authority, and overall weight. Based on these considerations, actuation mechanism constitutes a very crucial aspect for morphing structure design because the main requirement is to accomplish variable shapes for a given trailing edge structural mechanism within the limits of the maximum actuation torque, consumed power, and allowable size and weight. In this work, a lightweight and compact lever driven by electromechanical actuators is investigated to actuate the morphing trailing edge device. An unshafted distributed servoelectromechanical actuation arrangement driven by a dedicated control system is deployed to realize the transition from the baseline configuration to a set of design target ones and, at the same time, to withstand the external loads. Numerical and experimental investigations are detailed to demonstrate system effectiveness and reliability using a feedback sensing data from integrated FBG sensors.

Structural Design of an Adaptive Wing Trailing Edge for Large Aeroplanes

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.