Techniques pour réaliser l'essais de vibrations au sol du Beluga XL d'Airbus

International audienceAfter the completion of the Airbus A350 XWB 900 Ground Vibration Test (GVT) in 2013 and the A320 NEO GVT in July 2014, the ONERA-DLR joined team performed the GVT of the new BelugaXL aircraft in May-June 2018. The test was completed in 8 measurement days for 2 mass configurations, thanks to efficient methods and tools. The originality of this structure comes from its very large fuselage and its rear section with two large additional vertical planes, which made the modal identification particularly challenging. This paper describes the process followed, the methods used, and the interactions with engineers in charge of aeroelastic computations during the test, and how they allowed the success of this campaign.Après les essais de vibrations au sol de l'Airbus A350 XWB 900 en 2013 et de l'Airbus A320 NEO en juillet 2014, l'équipe commune ONERA-DLR a réalisé l'essai du nouvel avion d'Airbus, le Beluga XL, en mai-juin 2018. Le test fut effectué en 8 journées de mesure pour 2 configurations massiques, grâce à des outils et des méthodes efficaces. L'originalité de cette structure réside en la présence d'un fuselage de très grande dimension et d'une partie arrière comportant deux grands plans verticaux additionnels, ce qui rend l'identification modale particulièrement difficile. Cette communication décrit le procédé suivi, les méthodes utilisées et les interactions avec les ingénieurs en charge des calculs aéroélastiques durant le test, et comment ils ont permis le succès de cette campagne d'essais

High-resolution vibroacoustic measurement and analysis of the DLR ISTAR aircraft to assess engine-induced cabin noise

Aircraft engines, especially when mounted directly to the fuselage, inject a considerable amount of tonal vibrations into the airframe causing audible and comfort reducing cabin noise. Reducing this noise requires the development of specialised noise reduction systems. This is a time consuming and expensive endeavour. To speed up and ease this process a sufficiently detailed numerical model of the aircraft structure and the force injected by the engines is required. The DLR ISTAR, a Dassault Falcon 2000LX, was used for an extensive vibration measurement campaign. The goal of this campaign was twofold: Getting spatially dense information about the aircrafts vibro-acoustic behaviour to later update a finite element model for calculations in the mid-frequency range and to analyse the vibration injected by running engines into the fuselage structure. The measurements include the vibration response to both shaker excitation and engine vibration of the DLR ISTAR at about 1300 positions acquired by a rowing grid of sensors. The results are presented in the form of operational deflection shapes and first calculations of energy transfer paths using structural intensity analysi

Pre-Test of a Light-Weight CFRP Wing Segment of a High Altitude Platform for In-flight Load Measurements Based on Strains

For the validation of loads and aeroelastic simulations of a high altitude platform (HAP) in-flight, load measurements are very helpful. One technique to obtain load measurements is to apply strain gages to the primary structure. A calibration procedure enables the reconstruction of the loads from the measured strains. To reduce the risks, gain confidence and establish a feasible measurement set-up, a pre-test based on a CFRP wing segment is performed. This paper presents the theoretical background and the set-up of the measurement equipment. The results of the calibration from three different test cases are presented, showing an excellent agreement between applied and reconstructed loading with a deviation of < +/- 1.0 N and < +/- 2.0 cm for the location. Finally, the strains measured in the experiment are compared with the simulation, showing that a prediction of the strains is possible within a range of < +/- 8%

Entwicklung und Erprobung einer Steuerungseinheit für ein Radiofrequenz-Ionentriebwerk

Die vorliegende Masterarbeit wurde beim Deutschen Zentrum für Luft- und Raumfahrt (DLR) in Göttingen am Institut für Aerodynamik und Strömungstechnik in der Abteilung Raumfahrzeuge an der Simulationsanlage Treibstrahlen Göttingen für Elektrische Triebwerke (STG-ET) angefertigt. Die STG-ET ist eine Versuchsanlage, deren zentrales Bauteil eine große Vakuumkammer ist, in der weltraumähnliche Bedingungen erzeugt werden können, um elektrische Raumfahrtantriebe (z.B. im Dauerbetrieb) über mehrere Wochen oder Monate zu testen. Sie wurde im November 2011 in den Dienst gestellt und macht Göttingen zu einem weltweit bedeutenden Standort auf dem Gebiet der elektrischen Raumfahrtantriebe. Elektrische Raumfahrtantriebe finden bereits heute schon Anwendung, unter anderem bei der Lageregelung von Satelliten, und haben auch in der Zukunft noch großes Potenzial für weitere Anwendungen in der Raumfahrt. Sie weisen zwar im Vergleich zu den konventionellen chemischen Triebwerken einen deutlich geringeren Schub auf (der meist im mN-Bereich liegt), bieten aber große Vorteile aufgrund der guten Dosierbarkeit des Schubes und der sehr viel höheren Treibstoffeffizienz. Im Rahmen dieser Arbeit soll für das zurzeit an der STG-ET vorhandene elektrische Triebwerk, ein Radiofrequenz-Ionentriebwerk vom Typ RIT10/37, eine Steuerungseinheit entwickelt und erprobt werden, die es ermöglicht, das Triebwerk automatisiert zu starten und während des Betriebes zu überwachen. Hierzu gilt es eine Software zu entwickeln und die einzelnen Hardwarekomponenten, die für den Betrieb des Triebwerks benötigt werden, über geeignete Schnittstellen mit einem Steuerungs-PC zu verbinden. Die Steuerung soll am Ende der Arbeit dazu dienen, den Start des Triebwerks zu vereinfachen und zuverlässiger zu gestalten

Structural Design of an Instrumented Double-Swept Wind Tunnel Model

The design of a highly instrumented, double-swept CFRP wind tunnel model and its experimental setup are presented. A forced sinusoidal pitching motion is applied to the one-sided clamped helicopter rotor blade tip. Challenges of the structural design and the manufacturing process are addressed. A mold with inserts to check the leak-tightness of the pressure transducers and retain the half shells in the mold is presented. Insights in the finite element analysis (FEA) of the blade tip model are given. The strength analysis reveals peak stresses in the adhesive and the spar. The finite element model is validated with an experimental modal analysis. The experimental and numerical mode shapes and eigenfrequencies show an excellent agreement. The design goal of a very stiff lightweight model is met with the first eigenfrequency at 70 Hz. The results of the fluid-structure interaction simulation at Ma=0.4 show no significant differences for the global forces compared to the simulations with the rigid contour. However, the maximum tip deformation is up to 20 mm and a slight excitation of the first bending mode can be observed

Latest design trends in modal accelerometers for aircraft ground vibration testing

Accelerometers are widely encountered in structural analysis applications such as modal analysis with vibrational or impact input excitation and operational modal analysis. This paper aims to outline design trends and requirements for acceleration sensors in order to insure optimal structural analysis measurement results. Key parameters for a performing modal sensor are: sensitivity, mass, noise level, amplitude and phase frequency response, as well as thermal transient response, thermal sensitivity response, transverse sensitivity (cross axis), base strain and survivability which will be taken into detailed consideration in this paper. Nowadays three IEPE (Integrated Electronic Piezo Electric) sensor designs can be considered: piezo-ceramic shear, piezobending beam and piezo-crystal shear mode sensing elements. Unfortunately, none of the sensor technologies available on the market today will allow for the best of all parameters mentioned earlier. Advantages and disadvantages have to be considered in order to make the optimal choice. Even though Variable Capacitive (VC) MEMS sensors can be used in cases of operational modal analysis at ultra-low frequencies, such as Bridge Structural Testing or Monitoring, only IEPE technology will be in this study. Besides the technical properties of an accelerometer, the handling qualities during installation and removal are extremely important for high channel count systems. Installation time, error rate and reliability for more than 10 years during several tests a year are of special interest for the user. Among the considerations made here, easy monitoring and sensitive axis alignment compared to the overall coordinate system will be examined. The German Aerospace Center (DLR) will illustrate the applicability of accelerometers in context of industrial testing such as Ground Vibration Testing (GVT) of aircraft structures or structural and modal testing of wind turbine blades where innovative methods such as allowing one free adjustable degree of freedom around one rotational axis in order to freely orient the sensitive axis

Inflight-Measurements of Aircraft Undercarriage Vibration during Deployment

Within the EU funded Project AFLoNext (http://www.aflonext.eu/) flow-induced vibrations of aircraft components are under investigation. Aerodynamic or structural devices are designed to mitigate the vibration response levels especially of the deployed landing gear doors. The nose landing gear is emitting vorticity which impacts the downstream located main landing doors. To verify the results of unsteady complex flow simulations of the undercarriage conducted by different project partners, flight tests shall provide a database for calibration of numerical investigations and verify the results. Different types of sensors were installed on the undercarriage of the Advanced Technology Research Aircraft operated by the German Aerospace Center DLR, comprising accelerometers, strain gauges, travel and pressure sensors. To get detailed knowledge of the dynamic interaction of pressure loads and structural response on the nose and main landing gear doors, the simultaneous data acquisition of all signals at high sample rates up to 2 kHz was mandatory during deployment. In addition, monitoring of critical response levels was essential to stay in defined limits during flight. The presentation will give an overview of the selected Flight Test Instrumentation and the preparation of the test aircraft including the documentation and substantiation to get the flight approval

Umsetzung effizienter plattformunabhängiger App-Entwicklung in einer bestehenden Forschungssoftware-Landschaft

Zur Durchführung von Standschwingungsversuchen wird im Institut für Aeroelastik des Deutschen Zentrums für Luft- und Raumfahrt eine Sammlung verschiedener Softwaretools entwickelt. Diese dienen der effizienten Durchführung dieser Versuche und ermöglichen eine hohe Daten- und Ergebnisqualität. Die Nutzung mobiler Endgeräte ermöglicht es die Versuchsprozesse effizienter zu gestalten, da direkt am Versuchsobjekt ein Zugriff auf Daten realisiert werden kann. Daher wird eine neue App in die bestehende Softwarelandschaft integriert. Bei der Entwicklung stehen Plattformunabhängigkeit und eine effiziente Nutzung des bestehenden Codes im Vordergrund. Durch Nutzung von Xamarin konnte dieses Ziel und über 90% gemeinsamer Code erreicht werden

The 250mN Thrust Balance for the DLR Goettingen EP Test Facility

The German Aerospace Center DLR brought into operation a test facility for electric space propulsion in Goettingen, Germany, called STG-ET. This facility has been especially designed for electric propulsion with a vacuum chamber that measures more than 12m in length and 5m in diameter. Besides thruster performance tests the focus is on plume interaction with spacecraft components and on long-term testing. Thrust measurement is a fundamental measurement method for propulsion engine qualification. Ion and Hall effect space thrusters usually produce thrust levels in the milli-Newton range, and thrust balances have to deal with these low values. For the thrust balance of the STG-ET we adopted a thrust balance design based on a counter-balanced, electromagnetic force compensated device. The measurable thrust range is 250mN, but the design can easily accommodate an upgrade to 1N. The maximum allowed thruster assembly mass is 40kg. Several innovative features are implemented in its design

The 250mN Thrust Balance for the DLR Goettingen EP Test Facility

Abstract: The German Aerospace Center DLR brought into operation a test facility for electric space propulsion in Goettingen, Germany, called STG-ET. This facility has been especially designed for electric propulsion with a vacuum chamber that measures more than 12m in length and 5m in diameter. Besides thruster performance tests the focus is on plume interaction with spacecraft components and on long-term testing. Thrust measurement is a fundamental measurement method for propulsion engine qualification. Ion and Hall effect space thrusters usually produce thrust levels in the milli-Newton range, and thrust balances have to deal with these low values. For the thrust balance of the STG-ET we adopted a thrust balance design based on a counter-balanced, electromagnetic force compensated device. The measurable thrust range is 250mN, but the design can easily accommodate an upgrade to 1N. The maximum allowed thruster assembly mass is 40kg. Several innovative features are implemented in its design. Nomenclatur