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Aerospace, Volume 6, Issue 2 (February 2019)

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Cover Story (view full-size image) The development of new aviation technologies typically involves a high risk, which slows down [...] Read more.
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Open AccessArticle Identification of Aeroelastic Models for the X-56A Longitudinal Dynamics Using Multisine Inputs and Output Error in the Frequency Domain
Received: 28 November 2018 / Revised: 1 February 2019 / Accepted: 5 February 2019 / Published: 22 February 2019
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Abstract
System identification from measured flight test data was conducted using the X-56A aeroelastic demonstrator to identify a longitudinal flight dynamics model that included the short period, first symmetric wing bending, and first symmetric wing torsion modes. Orthogonal phase-optimized multisines were used to simultaneously [...] Read more.
System identification from measured flight test data was conducted using the X-56A aeroelastic demonstrator to identify a longitudinal flight dynamics model that included the short period, first symmetric wing bending, and first symmetric wing torsion modes. Orthogonal phase-optimized multisines were used to simultaneously excite multiple control effectors while a flight control system was active. Non-dimensional stability and control derivatives parameterizing an aeroelastic model were estimated using the output-error approach to match Fourier transforms of measured output response data. The predictive capability of the identified model was demonstrated using other flight test data with different inputs and at a different flight conditions. Modal characteristics of the identified model were explored and compared with other predictions. Practical aspects of the experiment design and system identification analysis, specific to flexible aircraft, are also discussed. Overall, the approach used was successful for identifying aeroelastic flight dynamics models from flight test data. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle Process Development for Integrated and Distributed Rotorcraft Design
Received: 30 November 2018 / Revised: 15 February 2019 / Accepted: 17 February 2019 / Published: 21 February 2019
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Abstract
The German Aerospace Center is currently developing a new design environment for rotorcraft, which combines sizing, simulation and evaluation tasks into one toolbox. The complete environment applies distributed computation on the servers of the various institutes involved. A uniform data model with a [...] Read more.
The German Aerospace Center is currently developing a new design environment for rotorcraft, which combines sizing, simulation and evaluation tasks into one toolbox. The complete environment applies distributed computation on the servers of the various institutes involved. A uniform data model with a collaboration and interface software, developed by DLR and open source, are used for exchange and networking. The tools used apply blade element methods in connection with full six degrees of freedom trim, panel methods for aerodynamic loads, different empirical models for sizing, engine properties and component mass estimation and finite element methods for structural design. A special feature is the integration of a higher fidelity overall simulation tool directly into the sizing loop. The paper describes the use of the several tools for the phases of conceptual and preliminary design. A design study is presented demonstrating the sensitivity of the process for a variation of the input parameters exhibiting a broad range for trade-off studies. The possibility to continue for analyzing and sizing of the structural properties is also demonstrated by applying a finite element approach for specific load cases. These features highlight the core of the new design environment and enable the development of goal-oriented design processes for research especially of new and unconventional rotorcraft configurations. The work presented in this paper was conducted throughout the DLR internal project, namely the Technologies for Rotorcraft in Integrated and Advanced Design (TRIAD). TRIAD is a joint project of the institutes of Flight Systems, the institute of Aerodynamics and Flow Technology, the institute of Structures and Design, the System Architectures in Aeronautics and Institute of Aerospace Medicine and receives basic founding. Full article
(This article belongs to the Special Issue Rotorcraft)
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Open AccessArticle Static and Dynamic Performance of a Morphing Trailing Edge Concept with High-Damping Elastomeric Skin
Received: 18 November 2018 / Revised: 7 February 2019 / Accepted: 14 February 2019 / Published: 19 February 2019
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Abstract
Nature has many striking examples of adaptive structures: the emulation of birds’ flight is the true challenge of a morphing wing. The integration of increasingly innovative technologies, such as reliable kinematic mechanisms, embedded servo-actuation and smart materials systems, enables us to realize new [...] Read more.
Nature has many striking examples of adaptive structures: the emulation of birds’ flight is the true challenge of a morphing wing. The integration of increasingly innovative technologies, such as reliable kinematic mechanisms, embedded servo-actuation and smart materials systems, enables us to realize new structural systems fully compatible with the more and more stringent airworthiness requirements. In this paper, the authors describe the characterization of an adaptive structure, representative of a wing trailing edge, consisting of a finger-like rib mechanism with a highly deformable skin, which comprises both soft and stiff parts. The morphing skin is able to follow the trailing edge movement under repeated cycles, while being stiff enough to preserve its shape under aerodynamic loads and adequately pliable to minimize the actuation power required for morphing. In order to properly characterize the system, a mock-up was manufactured whose structural properties, in particular the ability to carry out loads, were also guaranteed by the elastic skin. A numerical sensitivity analysis with respect to the mechanical properties of the multi-segment skin was performed to investigate their influence on the modal response of the whole system. Experimental dynamic tests were then carried out and the obtained results were critically analysed to prove the adequacy of the adopted design approaches as well as to quantify the dissipative (high-damping) effects induced by the rubber foam on the dynamic response of the morphing architecture. Full article
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Open AccessArticle The Replication Hypothesis along the Take-Off Run and a System of Equilibrium Equations at the Lift-Off of a Protobird
Received: 3 November 2018 / Revised: 3 January 2019 / Accepted: 2 February 2019 / Published: 15 February 2019
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Abstract
An extant bird resorts to flapping and running along its take-off run to generate lift and thrust in order to reach the minimum required wing velocity speed required for lift-off. This paper introduces the replication hypothesis that posits that the variation of lift [...] Read more.
An extant bird resorts to flapping and running along its take-off run to generate lift and thrust in order to reach the minimum required wing velocity speed required for lift-off. This paper introduces the replication hypothesis that posits that the variation of lift relative to the thrust generated by the flapping wings of an extant bird, along its take-off run, replicates the variation of lift relative to the thrust by the flapping wings of a protobird as it evolves towards sustained flight. The replication hypothesis combines experimental data from extant birds with evidence from the paleontological record of protobirds to come up with a physics-based model of its evolution towards sustained flight while scaling down the time span from millions of years to a few seconds. A second hypothesis states that the vertical and horizontal forces acting on a protobird when it first encounters lift-off are in equilibrium as the protobird exerts its maximum available power for flapping, equaling its lift with its weight, and its thrust with its drag. Full article
(This article belongs to the Special Issue Bio-Inspired Aerospace System)
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Open AccessReview Innovative Scaled Test Platform e-Genius-Mod—Scaling Methods and Systems Design
Received: 30 November 2018 / Revised: 6 February 2019 / Accepted: 8 February 2019 / Published: 14 February 2019
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Abstract
Future aircraft design highly depends on the successful implementation of new technologies. However, the gap between conventional designs and new visions often comes with a high financial risk. This significantly complicates the integration of innovations. Scaled unmanned aircraft systems (UAS) are an innovative [...] Read more.
Future aircraft design highly depends on the successful implementation of new technologies. However, the gap between conventional designs and new visions often comes with a high financial risk. This significantly complicates the integration of innovations. Scaled unmanned aircraft systems (UAS) are an innovative and cost-effective way to get new configurations and technologies in-flight. Therefore the Institute of Aircraft Design developed the e-Genius-Mod taking into account all relevant similitude requirements. It is a scale model of the electric motor glider e-Genius. Since the Reynolds number for the free-flight model cannot be adhered to, an airfoil was developed with lift-to-drag and lift-to-angle-of-attack courses reproducing the full-scale e-Genius flight characteristics. This will enable testing and assessment of new aviation technologies in a scaled version with an opportunity for free-flight demonstration in relevant environment. Full article
(This article belongs to the Special Issue 8th EASN-CEAS Workshop on Manufacturing for Growth and Innovation)
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Open AccessArticle Probabilistic Safety Assessment for UAS Separation Assurance and Collision Avoidance Systems
Received: 6 September 2018 / Revised: 17 January 2019 / Accepted: 17 January 2019 / Published: 14 February 2019
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Abstract
The airworthiness certification of aerospace cyber-physical systems traditionally relies on the probabilistic safety assessment as a standard engineering methodology to quantify the potential risks associated with faults in system components. This paper presents and discusses the probabilistic safety assessment of detect and avoid [...] Read more.
The airworthiness certification of aerospace cyber-physical systems traditionally relies on the probabilistic safety assessment as a standard engineering methodology to quantify the potential risks associated with faults in system components. This paper presents and discusses the probabilistic safety assessment of detect and avoid (DAA) systems relying on multiple cooperative and non-cooperative tracking technologies to identify the risk of collision of unmanned aircraft systems (UAS) with other flight vehicles. In particular, fault tree analysis (FTA) is utilized to measure the overall system unavailability for each basic component failure. Considering the inter-dependencies of navigation and surveillance systems, the common cause failure (CCF)-beta model is applied to calculate the system risk associated with common failures. Additionally, an importance analysis is conducted to quantify the safety measures and identify the most significant component failures. Results indicate that the failure in traffic detection by cooperative surveillance systems contribute more to the overall DAA system functionality and that the probability of failure for ownship locatability in cooperative surveillance is greater than its traffic detection function. Although all the sensors individually yield 99.9% operational availability, the implementation of adequate multi-sensor DAA system relying on both cooperative and non-cooperative technologies is shown to be necessary to achieve the desired levels of safety in all possible encounters. These results strongly support the adoption of a unified analytical framework for cooperative/non-cooperative UAS DAA and elicits an evolution of the current certification framework to properly account for artificial intelligence and machine-learning based systems. Full article
(This article belongs to the Special Issue Civil and Military Airworthiness: Recent Developments and Challenges)
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Open AccessArticle Manufacturing Aspects of Creating Low-Curvature Panels for Prospective Civil Aircraft
Received: 11 November 2018 / Revised: 29 January 2019 / Accepted: 30 January 2019 / Published: 14 February 2019
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Abstract
For this study, structural and manufacturing schemes for low-curvature pressurized fuselage panels were proposed, making it possible to provide high weight efficiency for the airframes of prospective civil blended wing-body (BWB) aircraft. The manufacturing scheme for low-curvature panels helped to achieve high strength [...] Read more.
For this study, structural and manufacturing schemes for low-curvature pressurized fuselage panels were proposed, making it possible to provide high weight efficiency for the airframes of prospective civil blended wing-body (BWB) aircraft. The manufacturing scheme for low-curvature panels helped to achieve high strength characteristics of the composite details as well as decreased the labor input necessary for manufacturing and assembling. The beneficial features of the proposed structure are that the panels have a low weight, incur low manufacturing costs, and satisfy the demands of repairability. Full article
(This article belongs to the Special Issue 8th EASN-CEAS Workshop on Manufacturing for Growth and Innovation)
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Open AccessEditorial Special Issue “ECO-COMPASS: Ecological and Multifunctional Composites for Application in Aircraft Interior and Secondary Structures”
Received: 12 February 2019 / Accepted: 13 February 2019 / Published: 13 February 2019
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Abstract
Today, composite aircraft structural parts are mainly made of man-made materials, such as carbon and glass fibres and epoxy resin [...] Full article
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Open AccessArticle Conjugate Heat Transfer Characteristics in a Highly Thermally Loaded Film Cooling Configuration with TBC in Syngas
Received: 12 November 2018 / Revised: 29 January 2019 / Accepted: 30 January 2019 / Published: 13 February 2019
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Abstract
Future power equipment tends to take hydrogen or middle/low heat-value syngas as fuel for low emission. The heat transfer of a film-cooled turbine blade shall be influenced more by radiation. Its characteristic of conjugate heat transfer is studied experimentally and numerically in the [...] Read more.
Future power equipment tends to take hydrogen or middle/low heat-value syngas as fuel for low emission. The heat transfer of a film-cooled turbine blade shall be influenced more by radiation. Its characteristic of conjugate heat transfer is studied experimentally and numerically in the paper by considering radiation heat transfer, multicomposition gas, and thermal barrier coating (TBC). The Weighted Sum of Gray Gases Spectral Model and the Discrete Transfer Model are utilized to solve the radiative heat transfer in the multicomposition field, while validated against the experimental data for the studied cases. It is shown that the plate temperature increases significantly when considering the radiation and the temperature gradient of the film-cooled plate becomes less significant. It is also shown that increasing percentage of steam in gas composition results in increased temperature on the film-cooled plate. The normalized temperature of the film-cooled plate decreases about 0.02, as the total percentage of steam in hot gas increases 7%. As for the TBC effect, it can smooth out the temperature distribution and insulate the heat to a greater extent when the radiative heat transfer becomes significant. Full article
(This article belongs to the Special Issue Cooling/Heat Transfer)
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Open AccessArticle Interdependent Uncertainty Handling in Trajectory Prediction
Received: 8 December 2018 / Revised: 19 January 2019 / Accepted: 4 February 2019 / Published: 12 February 2019
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Abstract
The concept of 4D trajectory management relies on the prediction of aircraft trajectories in time and space. Due to changes in atmospheric conditions and complexity of the air traffic itself, the reliable prediction of system states is an ongoing challenge. The emerging uncertainties [...] Read more.
The concept of 4D trajectory management relies on the prediction of aircraft trajectories in time and space. Due to changes in atmospheric conditions and complexity of the air traffic itself, the reliable prediction of system states is an ongoing challenge. The emerging uncertainties have to be modeled properly and considered in decision support tools for efficient air traffic flow management. Therefore, the subjacent causes for uncertainties, their effects on the aircraft trajectory and their dependencies to each other must be understood in detail. Besides the atmospheric conditions as the main external cause, the aircraft itself induces uncertainties to its trajectory. In this study, a cause-and-effect model is introduced, which deals with multiple interdependent uncertainties with different stochastic behavior and their impact on trajectory prediction. The approach is applied to typical uncertainties in trajectory prediction, such as the actual take-off mass, non-constant true air speeds, and uncertain weather conditions. The continuous climb profiles of those disturbed trajectories are successfully predicted. In general, our approach is applicable to all sources of quantifiable interdependent uncertainties. Therewith, ground-based trajectory prediction can be improved and a successful implementation of trajectory-based operations in the European air traffic system can be advanced. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Mitigation of Impact Damage with Self-Healing and Anti-Sloshing Materials in Aerospace Fuel Tanks
Received: 29 November 2018 / Revised: 24 January 2019 / Accepted: 8 February 2019 / Published: 12 February 2019
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Abstract
In this study, self-healing and anti-sloshing materials are investigated for mitigation of impact-induced damage. The integration of these systems, for the prevention of fire or explosion due to impact or bullet damage, may significantly improve the safety of aerospace fuel tanks. Leakage, after [...] Read more.
In this study, self-healing and anti-sloshing materials are investigated for mitigation of impact-induced damage. The integration of these systems, for the prevention of fire or explosion due to impact or bullet damage, may significantly improve the safety of aerospace fuel tanks. Leakage, after bullet penetration or debris impact, may be prevented or at least limited if the container’s walls are made by materials with self-healing capabilities. The aim of this work is to define the self-healing behavior of the EMAA ionomer (poly-Ethylene-MethAcrylic Acid copolymer), with reference to the energy dissipation mechanisms involved during damage and autonomic healing. An experimental investigation on the healing capacity of the material when perforated by bullets shot at medium velocity (250 m/s−450 m/s) was carried out. In these tests, the influence of friction, temperature, and multiple impacts on the healing process was examined and discussed. Moreover, the material response in operating conditions similar to those encountered in actual aeronautical applications, that is, in presence of pressurized fluid and anti-sloshing material (Explosafe®) was tested. Results show that the presence of the liquid increases the self-healing capabilities, which are, however, slightly affected by pressurization and internal anti-sloshing filler; the contribution in terms of sloshing reduction remains relevant. Full article
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Open AccessArticle High-Bandwidth Morphing Actuator for Aeroelastic Model Control
Received: 31 December 2018 / Revised: 29 January 2019 / Accepted: 30 January 2019 / Published: 1 February 2019
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Abstract
The design and testing of a high-bandwidth continuous actuator for aeronautical applications is presented hereinafter. The actuator has a dual goal of controlling both the aeroelastic behaviour and the flight mechanics of the model in which it is installed. In order to achieve [...] Read more.
The design and testing of a high-bandwidth continuous actuator for aeronautical applications is presented hereinafter. The actuator has a dual goal of controlling both the aeroelastic behaviour and the flight mechanics of the model in which it is installed. In order to achieve these aims, the actuation bandwidth of the active aerofoil, as well as its static camber variation, have to be sufficiently high. The camber morph is achieved by using tailored piezoelectric patches in a sandwich configuration with a linear trailing edge slider to allow the necessary compliance. The morphing actuator is designed for a NACA 0018 aerofoil with a chord of 300 mm and a span of 40 mm. Static and dynamic experimental tests are carried out on a prototype, and a camber variation control technique is implemented. It is proved that the actuator bandwidth is up to 25 Hz and the equivalent maximum deflection is ± 15 degrees. This solution is shown to be a viable light-weight alternative to the conventional brushless/servo-motor approach currently used in aeroelastic models. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle Vortex Dynamics Study of the Canard Deflection Angles’ Influence on the Sukhoi Su-30-Like Model to Improve Stall Delays at High AoA
Received: 19 December 2018 / Revised: 24 January 2019 / Accepted: 30 January 2019 / Published: 1 February 2019
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Abstract
The maneuverability of the Sukhoi Su-30 at very high angles of attack (AoA) was remarkably appealing. Canard angle, in cooperation with aircraft wing, created a flow pattern whereby, in that position, the fighter still had as much lifting force as possible in order [...] Read more.
The maneuverability of the Sukhoi Su-30 at very high angles of attack (AoA) was remarkably appealing. Canard angle, in cooperation with aircraft wing, created a flow pattern whereby, in that position, the fighter still had as much lifting force as possible in order not to stall. The behavior of changing canard angle configuration played an essential role in creating the strong vortex core so that it could delay the stall. The study of vortex dynamics at canard deflection angle gave an essential function in revealing the stall delay phenomenon. In this study, one could analyze the flow patterns and vortex dynamics ability of the Sukhoi Su-30-like model to delay stall due to the influence of canard deflection. The used of water tunnel facilities and computational fluid dynamics (CFD) based on Q-criterion has obtained clear and detailed visualization and aerodynamics data in revealing the phenomenon of vortex dynamics. It was found that between 30° and 40° canard deflection configurations, Sukhoi Su-30-like was able to produce the most robust flow interaction from the canard to the main wing. It was clearly seen that the vortex merging formation above the fighter heads was clearly visible capable of delaying stall until AoA 80°. Full article
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Open AccessArticle Manufacturing Process of High Performance–Low Cost Composite Structures for Light Sport Aircrafts
Received: 13 December 2018 / Revised: 23 January 2019 / Accepted: 24 January 2019 / Published: 1 February 2019
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Abstract
This work describes the technological and scientific efforts on designing, manufacturing and testing validation for high performance-low cost composite structures for Light Sport Aircrafts (LSA). A Mexican initiative to conceive, manufacture and assembly a Light Sport Aircraft has been developed by using Computational [...] Read more.
This work describes the technological and scientific efforts on designing, manufacturing and testing validation for high performance-low cost composite structures for Light Sport Aircrafts (LSA). A Mexican initiative to conceive, manufacture and assembly a Light Sport Aircraft has been developed by using Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and Liquid Composite Manufacturing (LCM). These consolidated techniques are used to characterize novel approaches to manufacturing and assembly carbon-fiber based structural components. As large structures are manufactured via Vacuum Assisted Resin Infusion (VARI), impregnation strategies are studied to minimize inner flaws and also to improve the manufacturing time and surface quality of each component. The first case of study, to validate this methodology, involves non-structural components such as the cowling. Control surfaces (ailerons, rudder, elevator and flaps) have been manufactured, each of them having common issues but also unique challenges. As an example, a second case of study, the aileron main beam is analyzed. Furthermore, test portfolio will be developed with the goal to perform 1-to-1 scale mechanical tests for validation in compliance with ASTM standards. Full article
(This article belongs to the Special Issue 8th EASN-CEAS Workshop on Manufacturing for Growth and Innovation)
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Open AccessArticle Challenges of Fully-Coupled High-Fidelity Ditching Simulations
Received: 5 November 2018 / Revised: 11 January 2019 / Accepted: 14 January 2019 / Published: 22 January 2019
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Abstract
An important element of the process of aircraft certification is the demonstration of the crashworthiness of the structure in the event of an emergency landing on water, also referred to as ditching. Novel numerical simulation methods, that incorporate the interaction between fluid and [...] Read more.
An important element of the process of aircraft certification is the demonstration of the crashworthiness of the structure in the event of an emergency landing on water, also referred to as ditching. Novel numerical simulation methods, that incorporate the interaction between fluid and structure, open up a promising way to model ditching in full scale. This study focuses on two main issues of high-fidelity ditching simulations: the development of a suitable fluid-structure coupling framework and the generation of the structural model of the aircraft. The first issue is addressed by implementing a partitioned coupling approach, which combines a finite volume hydrodynamic fluid solver as well as a finite element structural solver. The developed framework is validated by means of two ditching-like experiments, which consider the drop test of a rigid cylinder and a deformable cylindrical shell. The results of the validation studies indicate that an alternative to the standard Dirichlet-Neumann partitioning approach is needed if a strong added-mass effect is present. For the full-scale simulation of aircraft ditching, structural models become more complex and have to account for damage. Due to its high localization, the damage creates large differences in model scale and usually entails severe non-linearities in the model. To address the issue of increasing computational effort for such models, the process of developing a multi-scale model for the simulation of the failure of fuselage frames is presented. Full article
(This article belongs to the Special Issue 8th EASN-CEAS Workshop on Manufacturing for Growth and Innovation)
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