On the Preliminary Structural Design Strategy of the Wing of the Next-Generation Civil Tiltrotor Technology Demonstrator

The T-WING project is a Clean Sky 2 research project aimed at designing, manufacturing, qualifying and flight-testing the new wing of the Next-Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD), as part of the Fast Rotorcraft Innovative Aircraft Demonstrator Platforms (FRC IADP) activities. Requirements, design strategy, methodology and main steps followed to achieve the composite wing preliminary design are presented. The main driving requirements have been expressed in terms of dynamic requirements (e.g., limitations on natural frequencies), aeroelastic requirements, i.e., compliance with European Aviation Safety Agency (EASA) CS-25 and CS-29 Airworthiness Requirements), structural requirements (e.g., target wing structural mass), functional requirements (e.g., fuel tanks, accessibility, assembly and integration, etc.) and wing preliminary loads. Based on the above-mentioned requirements, the first design loop is performed by targeting an optimal wing structure able to withstand preliminary design loads, and simultaneously with stiffness and inertia distributions leading to a configuration free from flutter within the flight envelope. The outcome from the first design loop is then used to refine the model and compute more reliable flight loads and repeat aeroelastic analysis, returning further requirements to be fulfilled in terms of wing stiffness and inertia distributions. The process is iterated till the fulfillment of all the project requirements

Wing structure of the next-generation civil tiltrotor: From concept to preliminary design

The main objective of this paper is to describe a methodology to be applied in the preliminary design of a tiltrotor wing based on previously developed conceptual design methods. The reference vehicle is the Next-Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD) developed by Leonardo Helicopters within the Clean Sky research program framework. In a previous work by the authors, based on the specific requirements (i.e., dynamics, strength, buckling, functional), the first iteration of design was aimed at finding a wing structure with a minimized structural weight but at the same time strong and stiff enough to comply with sizing loads and aeroelastic stability in the flight envelope. Now, the outcome from the first design loop is used to build a global Finite Element Model (FEM), to be used for a multi-objective optimization performed by using a commercial software environment. In other words, the design strategy, aimed at finding a first optimal solution in terms of the thickness of composite components, is based on a two-level optimization. The first-level optimization is performed with engineering models (non-FEA-based), and the second-level optimization, discussed in this paper, within an FEA environment. The latter is shown to provide satisfactory results in terms of overall wing weight, and a zonal optimization of the composite parts, which is the starting point of an engineered model and a detailed FEM (beyond the scope of the present work), which will also take into account manufacturing, assembly, installation, accessibility and maintenance constraints

Acoustic antennas characterization for pass-by-noise tests

Automotive pass-by noise is a complex test that requires the fulfilment of several different standards with regard to the physical track layout, measurement systems, data acquisition, triggering, processing and analysis. This paper describes the system developed by CIRA's vibro-acoustic Lab to provide a novel noise test solution that allows efficient, accurate and repeatable car noise advanced testing for external sound quality characterization and improvement while maintaining the ability of performing vehicle pass-by noise testing. The innovative system, based on two phased array antenna, each one with the main dimension of 1.5 m, 96 MEMs microphones, in a random optimized configuration, and one full HD video-camera, has been developed inside the national project LOWNOISE, funded by MIUR (Italian Ministry of Education, University and Research). Preliminary laboratory tests have been performed in CIRA's hemi-anechoic chamber in order to demonstrate the capabilities of the antennas in the detection and tracking of stationary and moving noise sources by means of broadband beamforming algorithms and TDOA. The performed tests has shown the correct functionality of the system and its accuracy in acoustic noise sources localization. Furthermore, the synchronization between acoustic and video signals has been performed to allow the required data fusion to improve system performance

Pass-by noise tests by means of CIRA acoustic antennas system

In previous works, the system developed by CIRA's vibroacoustic Lab for pass-by-noise tests has been described. This system is made of a couple of synchronized acoustic antennas, with 96 ana-log MEMS microphones and one full HD camera for each antenna. The system developed in the national project LOWNOISE, funded by MIUR (Italian Ministry of Education, University and Research) has been used to perform a test campaign on the environmental noise of a FCA Giulietta equipped with two different kind of tyres: common ones and optimized ones (developed by FCA in LOWNOISE project). Tests have been performed in CIRA plant with different car speed start-ing from 20 kmh up to 50 kmh. These tests have shown the capability of the system to recognize and to separate correctly moving car noise sources, their spectral content and to verify the effec-tiveness in reducing the emitted noise of the optimized tyres respect to the common ones (a re-duction of about 3dB and more has been assessed, with benefit increasing with increasing car speed)

Actuation System Design for a Morphing Wing Trailing Edge

Shape control of adaptive wings has the potential to improve aircraft aerodynamic performance during cruise. In recent years, several patents have been issued for inventions in the field of morphing wings, using hydraulic, electromechanical or smart material-based actuation concepts and architectures. In the framework of SARISTU project (EUFP7), the joint integration of different conformal morphing concepts in a laminar wing is investigated to improve aircraft performance through a 6% drag reduction, with a positive effect on fuel consumption and required take-off fuel load. An innovative seamless morphing wing incorporating a gapless morphing leading edge, a morphing trailing edge and a wingtip active trailing edge is developed to pursue optimal wing geometry for any flight condition. This paper proposes a state of the art technology to design the actuation system of a morphing trailing edge, consisting of a flexible outer skin and an internal driving mechanism. Focus is given to the modeling and analysis of the morphing actuation, and its integration in the seamless flexible trailing edge control surface. The actuation system is driven by servo rotary actuators and it is designed and established to control the wing trailing edge in order to obtain pre-defined airfoil shapes maximizing wing aerodynamic efficiency. The actuation concept relies on a quick-return mechanism driven by load-bearing actuators controlling the morphing ribs individually. The actuation system is both analytically and numerically addressed. To validate the design, experiments are then carried out with the purpose of estimating the control movement functions suitable for single airfoil camber variations. The morphing rib kinematics including the actuation system is designed to withstand operational pressure loads and actuation forces

Numerical Analysis Results of Debonding Damage Effects for an SHM System Application on a Typical Composite Beam

In the aeronautical field, the damage that occurs to a carbon-fibre-reinforced polymer (CFRP) structure analysis is a crucial point for further improving its capability and performance. In the current the state of the art, in fact, many issues are linked to the certification process more than to technological aspects. For the sake of clarity, it should be added that regulations call for technological solutions that are invasive (in terms of weight and manufacturing costs) or exploit technologies that are not fully mature. Thus, the truth is in between the above statements. One of the possible solutions to bypass this issue is the assessment of a structural health monitoring system (SHM) that is sufficiently reliable to provide a full-state representation of the structure, automatically, perhaps in real-time, with a minimum intervention of specialized technicians, and that can raise an alert for safe maintenance whenever necessary. Among the different systems that have been proposed in the scientific and technological literature, SHM systems based on strain acquisitions seem very promising: they deduce the presence of flaws by analysing the variations of the intimate response of the structure. In this context, the SHM using fibre optics, supported by a dedicated algorithm, seems to be able to translate the effects of the damage reading the strain field. This means that is necessary to have a full comprehension of the flaws’ effects in terms of strain variation to better formulate a strategy aimed at highlighting these distortions. It should be remarked that each type of damage is distinct; imperfections of the bonding line are herein targeted since the quality of the latter is of paramount importance for ensuring the correct behaviour of the referred structure. This presents paper focuses on a deep investigation on the strain field peculiarities that arise after the imposition of irregularities in the adhesive region. The aim is to explore the damage dimension versus its effect on the strain map, especially when bonding connects different parts of a complex composite beam. By means of finite element method applied on a typical aeronautical beam, a parametric numerical simulation was performed in order to establish the influence of a debonding dimension on a reference strain map. This work provides evidence that these effects on strain flaw decrease the distancing itself of the damage. The knowledge of these effects can be highly helpful during the design of a preliminary phase of an SHM system in order to choose the most suitable sensor in terms of reading sensitivity error, the number to be used, and their location

Numerical and Experimental Studies of Free-Fall Drop Impact Tests Using Strain Gauge, Piezoceramic, and Fiber Optic Sensors

The present work is framed inside a broader activity aimed at improving the accuracy of numerical models in predicting the crashworthiness behavior of flexible fuel tanks. This paper describes a comprehensive experimental and numerical study aimed at estimating the impact force of a test article, consisting of a soft nylon bag filled with water, subjected to crash impact tests. In order to understand and improve response predictions, the test article drops freely from different heights, and then strikes onto a rigid plate which is instrumented with different types of sensors. Strain gauges, piezoceramic sensors, and fiber optics are used to measure the strain induced by the impact force during the experiments. To tune the test matrix and the measurement chain parameters, numerical computations are carried out to predict the dynamics of drop impact through FE explicit analyses. Through analysis and comparison with experimental results, a relationship between strain and impact energy correlated with the drop height is established, and the overall accuracy of the entire measurement chain is assessed to determine the effectiveness of such a methodology in a full-scale test on a flexible fuel tank structure

Wing Structure of the Next-Generation Civil Tiltrotor: From Concept to Preliminary Design

The main objective of this paper is to describe a methodology to be applied in the preliminary design of a tiltrotor wing based on previously developed conceptual design methods. The reference vehicle is the Next-Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD) developed by Leonardo Helicopters within the Clean Sky research program framework. In a previous work by the authors, based on the specific requirements (i.e., dynamics, strength, buckling, functional), the first iteration of design was aimed at finding a wing structure with a minimized structural weight but at the same time strong and stiff enough to comply with sizing loads and aeroelastic stability in the flight envelope. Now, the outcome from the first design loop is used to build a global Finite Element Model (FEM), to be used for a multi-objective optimization performed by using a commercial software environment. In other words, the design strategy, aimed at finding a first optimal solution in terms of the thickness of composite components, is based on a two-level optimization. The first-level optimization is performed with engineering models (non-FEA-based), and the second-level optimization, discussed in this paper, within an FEA environment. The latter is shown to provide satisfactory results in terms of overall wing weight, and a zonal optimization of the composite parts, which is the starting point of an engineered model and a detailed FEM (beyond the scope of the present work), which will also take into account manufacturing, assembly, installation, accessibility and maintenance constraints