Maurizio Arena

Modal stability assessment for a morphing aileron subjected to actuation system failures: Numerical analysis supported by test evidence

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.

Preliminary aeroelastic assessment of a large aeroplane equipped with a camber-morphing aileron

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.

Piezoresistive strain sensing of carbon nanotubes-based composite skin for aeronautical morphing structures

Nowadays, smart composites based on different nano-scale carbon fillers, such as carbon nanotubes (CNTs), are increasingly being thought of as a more possible alternative solution to conventional smart materials, mainly for their improved electrical properties. Great attention is being given by the research community in designing highly sensitive strain sensors for more and more ambitious challenges: in such context, interest fields related to carbon nanotubes have seen extraordinary development in recent years. The authors aim to provide the most contemporary overview possible of carbon nanotube-based strain sensors for aeronautical application. A smart structure as a morphing wing needs an embedded sensing system in order to measure the actual deformation state as well as to “monitor” the structural conditions. Looking at more innovative health monitoring tools for the next generation of composite structures, a resin strain sensor has been realized. The epoxy resin was first analysed by means of a micro-tension test, estimating the electrical resistance variations as function of the load, in order to demonstrate the feasibility of the sensor. The epoxy dogbone specimen has been equipped with a standard strain gauge to quantify its strain sensitivity. The voltamperometric tests highlight a good linearity of the electrical resistance value as the load increases at least in the region of elastic deformation of the material. Such intrinsic piezoresistive performance is essentially attributable to the re-arrangement of conductive percolating network formed by MWCNT, induced by the deformation of the material due to the applied loads. The specimen has been prepared within this investigation, to demonstrate its performance for a future composite laminate typical of aerospace structures. The future carbon-fiber sensor can replace conventional metal foil strain gauges in aerospace applications. Furthermore, dynamic tests will be carried out to detect any non-reversible changes to the sensing response.

Experimental validation of a true-scale morphing flap for large civil aircraft applications

Within the framework of the JTI-Clean Sky (CS) project, and during the first phase of the Low Noise Configuration Domain of the Green Regional Aircraft – Integrated Technological Demonstration (GRA-ITD, the preliminary design and technological demonstration of a novel wing flap architecture were addressed. Research activities were carried out to substantiate the feasibility of morphing concepts enabling flap camber variation in compliance with the demanding safety requirements applicable to the next generation green regional aircraft, 130- seats with open rotor configuration. The driving motivation for the investigation on such a technology was found in the opportunity to replace a conventional double slotted flap with a single slotted camber-morphing flap assuring similar high lift performances -in terms of maximum attainable lift coefficient and stall angle- while lowering emitted noise and system complexity. Studies and tests were limited to a portion of the flap element obtained by slicing the actual flap geometry with two cutting planes distant 0.8 meters along the wing span. Further activities were then addressed in order to increase the TRL of the validated architecture within the second phase of the CS-GRA. Relying upon the already assessed concept, an innovative and more advanced flap device was designed in order to enable two different morphing modes on the basis of the A/C flight condition / flap setting: Mode1, Overall camber morphing to enhance high-lift performances during take-off and landing (flap deployed); Mode2, Tab-like morphing mode. Upwards and downwards deflection of the flap tip during cruise (flap stowed) for load control at high speed. A true-scale segment of the outer wing flap (4 meters span with a mean chord of 0.9 meters) was selected as investigation domain for the new architecture in order to duly face the challenges posed by real wing installation. Advanced and innovative solutions for the adaptive structure, actuation and control systems were duly analyzed and experimentally validated thus proving the overall device compliance with industrial standards and applicable airworthiness requirements.

Actuation and control of a novel wing flap architecture with bi-modal camber morphing capabilities

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.

Acoustic performance assessment of innovative blankets for aeronautical applications

Polyurethane blankets are increasingly used for many aeronautical NVH applications. These foams, generally available in various thickness and density, are great sound absorber, therefore suitable in the aircraft interior. These foams are used as replacement to traditional combination of mineral wools / rock wool along with perforated panels, which require labor and also health hazardous. Polyurethane foams are generally available in various densities and thickness. The acoustic performance of sound absorbing poroelastic materials is characterized by intrinsic physical parameters like flow resistivity, and absorption coefficient. This paper presents a detailed discussion on measurement of flow resistivity as well as acoustic absorption coefficient of PU foam samples. Such numerical database of examined samples has been then validated through other laboratories activities, which shows the good accuracy of the methodology implemented within.Polyurethane blankets are increasingly used for many aeronautical NVH applications. These foams, generally available in various thickness and density, are great sound absorber, therefore suitable in the aircraft interior. These foams are used as replacement to traditional combination of mineral wools / rock wool along with perforated panels, which require labor and also health hazardous. Polyurethane foams are generally available in various densities and thickness. The acoustic performance of sound absorbing poroelastic materials is characterized by intrinsic physical parameters like flow resistivity, and absorption coefficient. This paper presents a detailed discussion on measurement of flow resistivity as well as acoustic absorption coefficient of PU foam samples. Such numerical database of examined samples has been then validated through other laboratories activities, which shows the good accuracy of the methodology implemented within.

Experimental technologies comparison for strain measurement of a composite main landing gear bay specimen

The development of advanced monitoring system for strain measurements on aeronautical components remain an important target both when related to the optimization of the lead-time and cost for part validation, allowing earlier entry into service, and when related to the implementation of advanced health monitoring systems dedicated to the in-service parameters verification and early stage detection of structural problems. The paper deals with the experimental testing of a composite samples set of the main landing gear bay for a CS-25 category aircraft, realized through an innovative design and production process. The test have represented a good opportunity for direct comparison of different strain measurement techniques: Strain Gauges (SG) and Fibers Bragg Grating (FBG) have been used as well as non-contact techniques, specifically the Digital Image Correlation (DIC) and Infrared (IR) thermography applied where possible in order to highlight possible hot-spot during the tests. The crucial points identification on the specimens has been supported by means of advanced finite element simulations, aimed to assessment of the structural strength and deformation as well as to ensure the best performance and the global safety of the whole experimental campaign.

Impact detection method for composite winglets based on neural network implementation

Maintenance tasks and safety aspects represent a strategic role in the managing of the modern aircraft fleets. The demand for reliable techniques for structural health monitoring represent so a key aspect looking forward to new generation aircraft. In particular, the use of more technologically complex materials and manufacturing methods requires anyway more efficient as well as rapid application processes to improve the design strength and service life. Actually, it is necessary to rely on survey instruments, which allow for safeguarding the structural integrity of the aircraft, especially after the wide use of composite structures highly susceptible to non-detected damages as delamination of the ply. In this paper, the authors have investigated the feasibility to implement a neural network-based algorithm to predict the impact event at low frequency, typically due to the bird collision. Relying upon a numerical model, representative of a composite flat panel, the approach has been also experimentally validated. The purpose of the work is therefore the presentation of an innovative application within the Non Destructive Testing field based upon vibration measurements. The aim of the research has been the development of a Non Destructive Test which meets most of the mandatory requirements for effective health monitoring systems while, at the same time, reducing as much as possible the complexity of the data analysis algorithm and the experimental acquisition instrumentation. Future activities will be addressed to test such technique on a more complex aeronautical system.

Chapter 18 – Morphing Aileron

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.

Control strategy of an electrically actuated morphing flap for the next generation green regional aircraft

The design and application of adaptive devices are currently ambitious targets in the field of aviation research addressed at new generation aircraft. The development of intelligent structures involves aspects of multidisciplinary nature: the combination of compact architectures, embedded electrical systems and smart materials, allows for developing a highly innovative device. The paper aims to present the control system design of an innovative morphing flap tailored for the next generation regional aircraft, within Clean Sky 2 – Airgreen 2 European Research Scenario. A distributed system of electromechanical actuators (EMAs) has been sized to enable up to three operating modes of a structure arranged in four blocks along the chord-wise direction: •overall camber-morphing; •upwards/downwards deflection and twisting of the final tip segment. A state-of-art feedback logic based on a decentralized control strategy for shape control is outlined, including the results of dynamic stability analysis based on the blocks rational schematization within Matlab/Simulink® environment. Such study has been performed implementing a state-space model, considering also design parameters as the torsional stiffness and damping of the actuation chain. The design process is flowing towards an increasingly “robotized” system, which can be externally controlled to perform certain operations. Future developments will be the control laws implementation as well as the functionality test on a real flap prototype.