@inproceedings{KapoorBollerGiljohannetal.2010,
  author    = {Kapoor, Hrshi and Boller, Christian and Giljohann, Sebastian and Braun, Carsten},
  title     = {Strategies for structural health monitoring implementation potential assessment in aircraft operational life extension considerations},
  series = {2nd International Symposium on NDT in Aerospace : November 22-24, 2010 Hamburg, Germany},
  booktitle = {2nd International Symposium on NDT in Aerospace : November 22-24, 2010 Hamburg, Germany},
  publisher = {Dt. Gesellschaft f{\"u}r Zerst{\"o}rungsfreie Pr{\"u}fung},
  address   = {Berlin},
  organization    = {Deutsche Gesellschaft f{\"u}r Zerst{\"o}rungsfreie Pr{\"u}fung},
  isbn      = {978-3-940283-28-3},
  pages     = {9},
  year      = {2010},
  language  = {en}
}
@inproceedings{KapoorBraunBoller2010,
  author    = {Kapoor, Hrshi and Braun, Carsten and Boller, Christian},
  title     = {Modelling and optimisation of maintenance intervals to realize structural health monitoring applications on aircraft},
  series = {Structural health monitoring 2010 : proceedings of the Fifth European Workshop on Structural Health Monitoring held at Sorrento, Naples, Italy, June 28 - July 4, 2010 ; [EWSHM]},
  booktitle = {Structural health monitoring 2010 : proceedings of the Fifth European Workshop on Structural Health Monitoring held at Sorrento, Naples, Italy, June 28 - July 4, 2010 ; [EWSHM]},
  editor    = {Casciati, Fabio},
  publisher = {DEStech Publ.},
  address   = {Lancaster, Pa.},
  isbn      = {978-1-60595-024-2},
  pages     = {55 -- 63},
  year      = {2010},
  language  = {en}
}
@incollection{ReimerBraunWellmeretal.2010,
  author    = {Reimer, Lars and Braun, Carsten and Wellmer, Georg and Behr, Marek and Ballmann, Josef},
  title     = {Development of a modular method for computational aero-structural analysis of aircraft},
  series = {Summary of flow modulation and fluid-structure interaction findings. Results of the Collaborative Research Center SFB 401 at the RWTH Aachen University, Aachen, Germany, 1997-2008 / ed.: Wolfgang Schr{\"o}der. Notes on numerical fluid mechanics and multidisciplinary design. Vol. 109},
  booktitle = {Summary of flow modulation and fluid-structure interaction findings. Results of the Collaborative Research Center SFB 401 at the RWTH Aachen University, Aachen, Germany, 1997-2008 / ed.: Wolfgang Schr{\"o}der. Notes on numerical fluid mechanics and multidisciplinary design. Vol. 109},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {978-3-642-04087-0},
  pages     = {205 -- 238},
  year      = {2010},
  language  = {en}
}
@incollection{ReimerWellmerBraunetal.2009,
  author    = {Reimer, Lars and Wellmer, Georg and Braun, Carsten and Ballmann, Josef},
  title     = {Computational methods for aero-structural analysis and optimisation of aircrafts based on reduced-order structural models},
  series = {MEGADESIGN and MegaOpt - German initiatives for aerodynamic simulation and optimization in aircraft design. Results of the closing symposium of the MEGADESIGN and MegaOpt projects, Braunschweig, Germany, 23 - 24 May, 2007 / Norbert Kroll ... (Eds.) Notes on numerical fluid mechanics and multidisciplinary design. Vol. 107},
  booktitle = {MEGADESIGN and MegaOpt - German initiatives for aerodynamic simulation and optimization in aircraft design. Results of the closing symposium of the MEGADESIGN and MegaOpt projects, Braunschweig, Germany, 23 - 24 May, 2007 / Norbert Kroll ... (Eds.) Notes on numerical fluid mechanics and multidisciplinary design. Vol. 107},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {978-3-642-04092-4},
  pages     = {135 -- 150},
  year      = {2009},
  abstract  = {In this part of the MEGADESIGN project, aeroelastic effects are introduced into the aerodynamic analysis of aircrafts by coupling DLR's flow solvers TAU and FLOWer to a Timoshenko-beam solver. The emerging aeroelastic solvers and a method for the automatic identification of Timoshenko-beam models for wing-box structures were integrated into a simulation environment enabling the combined optimisation of aerodynamic wing shape and structure.},
  language  = {en}
}
@inproceedings{ReimerBraunChenetal.2007,
  author    = {Reimer, Lars and Braun, Carsten and Chen, B.-H. and Ballmann, Josef},
  title     = {Computational aeroelastic analysis and design of the HIRENASD wind tunnel wing model and tests},
  series = {Proceedings / IFASD 2007, CEAS/AIAA/KTH International Forum on Aeroelasticity and Structural Dynamics : June 18 - 21, 2007, Stockholm, Sweden},
  booktitle = {Proceedings / IFASD 2007, CEAS/AIAA/KTH International Forum on Aeroelasticity and Structural Dynamics : June 18 - 21, 2007, Stockholm, Sweden},
  publisher = {KTH},
  address   = {Stockholm},
  pages     = {1 CD-ROM},
  year      = {2007},
  language  = {en}
}
@inproceedings{WellmerChenBraunetal.2007,
  author    = {Wellmer, Georg and Chen, B.-H. and Braun, Carsten and Ballmann, Josef},
  title     = {Numerical prediction of aeroelastic effects on twin-sting-rig mounted models for rear fuselage and empennage flow investigation in transonic windtunnel},
  series = {Proceedings / IFASD 2007, CEAS/AIAA/KTH International Forum on Aeroelasticity and Structural Dynamics, June 18 - 21, 2007, Stockholm, Sweden},
  booktitle = {Proceedings / IFASD 2007, CEAS/AIAA/KTH International Forum on Aeroelasticity and Structural Dynamics, June 18 - 21, 2007, Stockholm, Sweden},
  publisher = {KTH},
  address   = {Stockholm},
  organization    = {Confederation of European Aerospace Societies ; American Institute of Aeronautics and Astronautics, Reston, Va. ; Kungliga Tekniska H{\"o}gskolan, Stockholm},
  pages     = {1 CD-ROM},
  year      = {2007},
  language  = {en}
}
@incollection{ReimerBraunBallmann2007,
  author    = {Reimer, Lars and Braun, Carsten and Ballmann, Josef},
  title     = {Computational study of the aeroelastic equilibrium configuration of a swept wind tunnel wing model in subsonic flow},
  series = {High performance computing in science and engineering '06. Transactions of the High Performance Computing Center Stuttgart (HLRS) 2006 / Wolfgang E. Nagel ... Eds.},
  booktitle = {High performance computing in science and engineering '06. Transactions of the High Performance Computing Center Stuttgart (HLRS) 2006 / Wolfgang E. Nagel ... Eds.},
  publisher = {Springer},
  address   = {Berlin [u.a.]},
  isbn      = {978-3-540-36165-7},
  pages     = {421 -- 434},
  year      = {2007},
  abstract  = {In the Collaborative Research Center SFB 401 at RWTH Aachen University, the numerical aeroelastic method SOFIA for direct numerical aeroelastic simulation is being progressively developed. Numerical results obtained by applying SOFIA were compared with measured data of static and dynamic aeroelastic wind tunnel tests for an elastic swept wing in subsonic flow.},
  language  = {en}
}
@inproceedings{ReimerBraunBallmann2006,
  author    = {Reimer, Lars and Braun, Carsten and Ballmann, Josef},
  title     = {Analysis of the static and dynamic aero-structural response of an elastic swept wing model by direct aeroelastic simulation},
  series = {ICAS 2006 proceedings : 25th Congress of the International Council of the Aeronautical Sciences ; Hamburg, Germany, 3 - 8 September, 2006 : 25th International Congress of Aeronautical Sciences},
  booktitle = {ICAS 2006 proceedings : 25th Congress of the International Council of the Aeronautical Sciences ; Hamburg, Germany, 3 - 8 September, 2006 : 25th International Congress of Aeronautical Sciences},
  publisher = {Optimage},
  address   = {Edinburgh},
  organization    = {International Council of the Aeronautical Sciences (ICAS)},
  isbn      = {0-9533991-7-6},
  pages     = {Paper No. 2006-10.3.3},
  year      = {2006},
  language  = {en}
}
@inproceedings{BallmannDafnisBraunetal.2006,
  author    = {Ballmann, Josef and Dafnis, Athanasios and Braun, Carsten and Korsch, Helge and Reimerdes, Hans-G{\"u}nther and Braun, Carsten and Ballmann, Josef},
  title     = {The HIRENASD project: High Reynolds number aerostructural dynamics experiments in the European Transonic Wind Tunnel (ETW)},
  series = {ICAS 2006 proceedings : 25th Congress of the International Council of the Aeronautical Sciences ; Hamburg, Germany, 3 - 8 September, 2006 : 25th International Congress of Aeronautical Sciences},
  booktitle = {ICAS 2006 proceedings : 25th Congress of the International Council of the Aeronautical Sciences ; Hamburg, Germany, 3 - 8 September, 2006 : 25th International Congress of Aeronautical Sciences},
  publisher = {Optimage},
  address   = {Edinburgh},
  organization    = {International Council of the Aeronautical Sciences (ICAS)},
  isbn      = {0-9533991-7-6},
  pages     = {Paper No. 2006-5.11.2},
  year      = {2006},
  language  = {en}
}
@inproceedings{KorschDafnisReimerdesetal.2006,
  author    = {Korsch, Helge and Dafnis, Athanasios and Reimerdes, Hans-G{\"u}nther and Braun, Carsten and Ballmann, Josef},
  title     = {Dynamic qualification of the HIRENASD elastic wing model},
  series = {Motto: Luft- und Raumfahrt: Lehre, Forschung, Industrie - gemeinsam innovativ. Deutscher Luft- und Raumfahrtkongress 2006 : Braunschweig, 06. bis 09. November 2006. Jahrbuch / Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt. 2006},
  booktitle = {Motto: Luft- und Raumfahrt: Lehre, Forschung, Industrie - gemeinsam innovativ. Deutscher Luft- und Raumfahrtkongress 2006 : Braunschweig, 06. bis 09. November 2006. Jahrbuch / Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt. 2006},
  publisher = {Dt. Gesellschaft f{\"u}r Luft- und Raumfahrt - Lilienthal-Oberth (DGLR)},
  address   = {Bonn},
  pages     = {1441 -- 1450},
  year      = {2006},
  language  = {en}
}
@inproceedings{BraunBouckeBallmann2005,
  author    = {Braun, Carsten and Boucke, Alexander and Ballmann, Josef},
  title     = {Numerical prediction of the wing deformation of a high speed transport aircraft type wind tunnel model by direct aeroelastic simulation},
  series = {Conference proceedings : CEAS/AIAA/DGLR International Forum on Aeroelasticity and Structural Dynamics IFASD 2005 : M{\"u}nchen, June 28 - July 1, 2005. DGLR-Bericht. 2005,04},
  booktitle = {Conference proceedings : CEAS/AIAA/DGLR International Forum on Aeroelasticity and Structural Dynamics IFASD 2005 : M{\"u}nchen, June 28 - July 1, 2005. DGLR-Bericht. 2005,04},
  publisher = {DGLR},
  address   = {Bonn},
  isbn      = {3-932182-43-X},
  pages     = {1 CD-ROM},
  year      = {2005},
  language  = {en}
}
@incollection{BraunBouckeBallmann2005,
  author    = {Braun, Carsten and Boucke, Alexander and Ballmann, Josef},
  title     = {Numerical study of the influence of dynamic pressure and deflected ailerons on the deformation of a high speed wing model},
  series = {High performance computing in science and engineering '04. Transactions of the High Performance Computing Center Stuttgart (HLRS) 2004 / Eds.: Egon Krause ...},
  booktitle = {High performance computing in science and engineering '04. Transactions of the High Performance Computing Center Stuttgart (HLRS) 2004 / Eds.: Egon Krause ...},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {3-540-22943-4},
  pages     = {225 -- 236},
  year      = {2005},
  language  = {en}
}
@incollection{BallmannBouckeBraun2003,
  author    = {Ballmann, Josef and Boucke, Alexander and Braun, Carsten},
  title     = {Aeroelastic sensitivity in the transonic regime},
  series = {Symposium Transsonicum IV : proceedings of the IUTAM symposium held in G{\"o}ttingen, Germany, 2 - 6 September 2002 / ed. by Helmut Sobieczky. Fluid mechanics and its applications. Vol. 73},
  booktitle = {Symposium Transsonicum IV : proceedings of the IUTAM symposium held in G{\"o}ttingen, Germany, 2 - 6 September 2002 / ed. by Helmut Sobieczky. Fluid mechanics and its applications. Vol. 73},
  publisher = {Kluwer Academic},
  address   = {Dordrecht},
  isbn      = {978-94-010-3998-7},
  pages     = {225 -- 236},
  year      = {2003},
  language  = {en}
}
@incollection{BrittenBraunHesseetal.2003,
  author    = {Britten, G. and Braun, Carsten and Hesse, M. and Ballmann, Josef},
  title     = {Computational aeroelasticity with reduced structural models},
  series = {Flow modulation and fluid-structure interaction at airplane wings : research results of the Collaborative Research Center SFB 401 at RWTH Aachen, University of Technology, Aachen, Germany / Josef Ballmann (Ed.) Notes on numerical fluid mechanics and multidisciplinary design. Vol. 84},
  booktitle = {Flow modulation and fluid-structure interaction at airplane wings : research results of the Collaborative Research Center SFB 401 at RWTH Aachen, University of Technology, Aachen, Germany / Josef Ballmann (Ed.) Notes on numerical fluid mechanics and multidisciplinary design. Vol. 84},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {3-540-40209-8},
  pages     = {275 -- 299},
  year      = {2003},
  language  = {en}
}
@article{NeuJanserKhatibietal.2016,
  author    = {Neu, Eugen and Janser, Frank and Khatibi, Akbar A. and Braun, Carsten and Orifici, Adrian C.},
  title     = {Operational Modal Analysis of a wing excited by transonic flow},
  series = {Aerospace Science and Technology},
  volume    = {49},
  journal   = {Aerospace Science and Technology},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1270-9638},
  doi       = {10.1016/j.ast.2015.11.032},
  pages     = {73 -- 79},
  year      = {2016},
  abstract  = {Operational Modal Analysis (OMA) is a promising candidate for flutter testing and Structural Health Monitoring (SHM) of aircraft wings that are passively excited by wind loads. However, no studies have been published where OMA is tested in transonic flows, which is the dominant condition for large civil aircraft and is characterized by complex and unique aerodynamic phenomena. We use data from the HIRENASD large-scale wind tunnel experiment to automatically extract modal parameters from an ambiently excited wing operated in the transonic regime using two OMA methods: Stochastic Subspace Identification (SSI) and Frequency Domain Decomposition (FDD). The system response is evaluated based on accelerometer measurements. The excitation is investigated from surface pressure measurements. The forcing function is shown to be non-white, non-stationary and contaminated by narrow-banded transonic disturbances. All these properties violate fundamental OMA assumptions about the forcing function. Despite this, all physical modes in the investigated frequency range were successfully identified, and in addition transonic pressure waves were identified as physical modes as well. The SSI method showed superior identification capabilities for the investigated case. The investigation shows that complex transonic flows can interfere with OMA. This can make existing approaches for modal tracking unsuitable for their application to aircraft wings operated in the transonic flight regime. Approaches to separate the true physical modes from the transonic disturbances are discussed.},
  language  = {en}
}
@inproceedings{SchildtBraunMarcocca2017,
  author    = {Schildt, P. and Braun, Carsten and Marcocca, P.},
  title     = {Flight testing the extra 330LE flying testbed},
  series = {48th Annual International Symposium of the Society of Flight Test Engineers 2017},
  booktitle = {48th Annual International Symposium of the Society of Flight Test Engineers 2017},
  isbn      = {978-151085387-4},
  pages     = {349 -- 362},
  year      = {2017},
  language  = {en}
}
@inproceedings{LudowicyRingsFingeretal.2018,
  author    = {Ludowicy, Jonas and Rings, Ren{\´e} and Finger, Felix and Braun, Carsten},
  title     = {Sizing Studies of Light Aircraft with Serial Hybrid Propulsion Systems},
  series = {Luft- und Raumfahrt - Digitalisierung und Vernetzung : Deutscher Luft- und Raumfahrtkongress 2018. 4. - 6. September 2018 - Friedrichshafen},
  booktitle = {Luft- und Raumfahrt - Digitalisierung und Vernetzung : Deutscher Luft- und Raumfahrtkongress 2018. 4. - 6. September 2018 - Friedrichshafen},
  pages     = {11 S.},
  year      = {2018},
  language  = {en}
}
@inproceedings{FingerGoettenBraun2018,
  author    = {Finger, Felix and G{\"o}tten, Falk and Braun, Carsten},
  title     = {Initial Sizing for a Family of Hybrid-Electric VTOL General Aviation Aircraft},
  series = {67. Deutscher Luft- und Raumfahrtkongress 2018},
  booktitle = {67. Deutscher Luft- und Raumfahrtkongress 2018},
  pages     = {14 S.},
  year      = {2018},
  language  = {en}
}
@inproceedings{LudowicyRingsFingeretal.2018,
  author    = {Ludowicy, Jonas and Rings, Ren{\´e} and Finger, Felix and Braun, Carsten},
  title     = {Sizing Studies of Light Aircraft with Parallel Hybrid Propulsion Systems},
  series = {Deutscher Luft- und Raumfahrtkongress 2018},
  booktitle = {Deutscher Luft- und Raumfahrtkongress 2018},
  doi       = {10.25967/480227},
  pages     = {15 S.},
  year      = {2018},
  language  = {en}
}
@article{GoettenFingerHavermannetal.2018,
  author    = {G{\"o}tten, Falk and Finger, Felix and Havermann, Marc and Braun, Carsten and Gomez, Francisco and Bill, C.},
  title     = {On the flight performance impact of landing gear drag reduction methods for unmanned air vehicles},
  series = {Deutscher Luft- und Raumfahrtkongress 2018},
  journal   = {Deutscher Luft- und Raumfahrtkongress 2018},
  publisher = {DGLR},
  address   = {Bonn},
  doi       = {10.25967/480058},
  pages     = {11 S.},
  year      = {2018},
  abstract  = {The flight performance impact of three different landing gear configurations on a small, fixed-wing UAV is analyzed with a combination of RANS CFD calculations and an incremental flight performance algorithm. A standard fixed landing gear configuration is taken as a baseline, while the influence of retracting the landing gear or applying streamlined fairings is investigated. A retraction leads to a significant parasite drag reduction, while also fairings promise large savings. The increase in lift-to-drag ratio is reduced at high lift coefficients due to the influence of induced drag. All configurations are tested on three different design missions with an incremental flight performance algorithm. A trade-off study is performed using the retracted or faired landing gear's weight increase as a variable. The analysis reveals only small mission performance gains as the aerodynamic improvements are negated by weight penalties. A new workflow for decision-making is presented that allows to estimate if a change in landing gear configuration is beneficial for a small UAV.},
  language  = {en}
}
@inproceedings{FingerBraunBil2018,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Case studies in initial sizing for hybrid-electric general aviation aircraft},
  series = {2018 AIAA/IEEE Electric Aircraft Technologies Symposium, Cincinnati, Ohio},
  booktitle = {2018 AIAA/IEEE Electric Aircraft Technologies Symposium, Cincinnati, Ohio},
  doi       = {10.2514/6.2018-5005},
  year      = {2018},
  language  = {en}
}
@article{FingerBraunBil2018,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Impact of electric propulsion technology and mission requirements on the performance of VTOL UAVs},
  series = {CEAS Aeronautical Journal},
  volume    = {10},
  journal   = {CEAS Aeronautical Journal},
  number    = {3},
  publisher = {Springer},
  issn      = {1869-5582 print},
  doi       = {10.1007/s13272-018-0352-x},
  pages     = {843},
  year      = {2018},
  abstract  = {One of the engineering challenges in aviation is the design of transitioning vertical take-off and landing (VTOL) aircraft. Thrust-borne flight implies a higher mass fraction of the propulsion system, as well as much increased energy consumption in the take-off and landing phases. This mass increase is typically higher for aircraft with a separate lift propulsion system than for aircraft that use the cruise propulsion system to support a dedicated lift system. However, for a cost-benefit trade study, it is necessary to quantify the impact the VTOL requirement and propulsion configuration has on aircraft mass and size. For this reason, sizing studies are conducted. This paper explores the impact of considering a supplemental electric propulsion system for achieving hovering flight. Key variables in this study, apart from the lift system configuration, are the rotor disk loading and hover flight time, as well as the electrical systems technology level for both batteries and motors. Payload and endurance are typically used as the measures of merit for unmanned aircraft that carry electro-optical sensors, and therefore the analysis focuses on these particular parameters.},
  language  = {en}
}
@inproceedings{FingerBraunBil2017,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {The Impact of Electric Propulsion on the Performance of VTOL UAVs},
  series = {Deutscher Luft- und Raumfahrtkongress 2017, DLRK , M{\"u}nchen},
  booktitle = {Deutscher Luft- und Raumfahrtkongress 2017, DLRK , M{\"u}nchen},
  year      = {2017},
  language  = {en}
}
@inproceedings{FingerBraunBil2017,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {A Review of Configuration Design for Distributed Propulsion Transitioning VTOL Aircraft},
  series = {Asia-Pacific International Symposium on Aerospace Technology 2017, APISAT 2017, Seoul, Korea},
  booktitle = {Asia-Pacific International Symposium on Aerospace Technology 2017, APISAT 2017, Seoul, Korea},
  pages     = {15 Seiten},
  year      = {2017},
  language  = {en}
}
@inproceedings{FingerBraunBil2018,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {An Initial Sizing Methodology for Hybrid-Electric Light Aircraft},
  series = {AIAA AVIATION Forum 2018 Aviation Technology, Integration, and Operations Conference, Atlanta, Georgia, June 25 - 29, 2018},
  booktitle = {AIAA AVIATION Forum 2018 Aviation Technology, Integration, and Operations Conference, Atlanta, Georgia, June 25 - 29, 2018},
  doi       = {10.2514/6.2018-4229},
  year      = {2018},
  language  = {en}
}
@inproceedings{SchildtMarzoccaBraunetal.2019,
  author    = {Schildt, Philipp and Marzocca, Pier and Braun, Carsten and Dahmann, Peter and Keimer, Jona},
  title     = {Effects of atmospheric excitation on vibration based condition monitoring methods for hybrid-electric aircraft propulsion systems},
  series = {AIAC 2018: 18th Australian International Aerospace Congress: HUMS - 11th Defence Science and Technology (DST) International Conference on Health and Usage Monitoring (HUMS 2019): ISSFD - 27th International Symposium on Space Flight Dynamics (ISSFD)},
  booktitle = {AIAC 2018: 18th Australian International Aerospace Congress: HUMS - 11th Defence Science and Technology (DST) International Conference on Health and Usage Monitoring (HUMS 2019): ISSFD - 27th International Symposium on Space Flight Dynamics (ISSFD)},
  isbn      = {9781925627213},
  pages     = {923 -- 928},
  year      = {2019},
  language  = {en}
}
@inproceedings{GoettenHavermannBraunetal.2018,
  author    = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Gomez, Francisco and Bil, Cees},
  title     = {On the Applicability of Empirical Drag Estimation Methods for Unmanned Air Vehicle Design Read More: https://arc.aiaa.org/doi/10.2514/6.2018-3192},
  series = {2018 Aviation Technology, Integration, and Operations Conference, AIAA AVIATION Forum},
  booktitle = {2018 Aviation Technology, Integration, and Operations Conference, AIAA AVIATION Forum},
  issn      = {1533-385X},
  doi       = {10.2514/6.2018-3192},
  pages     = {Article 3192},
  year      = {2018},
  language  = {en}
}
@article{SchildtBraunMarzocca2019,
  author    = {Schildt, Ph. and Braun, Carsten and Marzocca, P.},
  title     = {Metric evaluating potentials of condition-monitoring approaches for hybrid electric aircraft propulsion systems},
  series = {CEAS Aeronautical Journal},
  journal   = {CEAS Aeronautical Journal},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {1869-5590},
  doi       = {10.1007/s13272-019-00411-3},
  pages     = {1 -- 14},
  year      = {2019},
  language  = {en}
}
@article{FingerBilBraun2019,
  author    = {Finger, Felix and Bil, Cees and Braun, Carsten},
  title     = {Initial Sizing Methodology for Hybrid-Electric General Aviation Aircraft},
  series = {Journal of Aircraft},
  volume    = {57},
  journal   = {Journal of Aircraft},
  number    = {2},
  issn      = {1533-3868},
  doi       = {10.2514/1.C035428},
  pages     = {245 -- 255},
  year      = {2019},
  language  = {en}
}
@inproceedings{LudowicyRingsFingeretal.2019,
  author    = {Ludowicy, Jonas and Rings, Ren{\´e} and Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Impact of Propulsion Technology Levels on the Sizing and Energy Consumption for Serial HybridElectric General Aviation Aircraft},
  series = {Asia Pacific International Symposium on Aerospace Technology. APISAT 2019},
  booktitle = {Asia Pacific International Symposium on Aerospace Technology. APISAT 2019},
  pages     = {14 Seiten},
  year      = {2019},
  language  = {en}
}
@inproceedings{RingsLudowicyFingeretal.2019,
  author    = {Rings, Ren{\´e} and Ludowicy, Jonas and Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Sensitivity Analysis of General Aviation Aircraft with Parallel Hybrid-Electric Propulsion Systems},
  series = {Asia Pacific International Symposium on Aerospace Technology. APISAT 2019},
  booktitle = {Asia Pacific International Symposium on Aerospace Technology. APISAT 2019},
  pages     = {14 Seiten},
  year      = {2019},
  language  = {en}
}
@inproceedings{FingerBraunBil2019,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Impact of Engine Failure Constraints on the Initial Sizing of Hybrid-Electric GA Aircraft},
  series = {AIAA Scitech 2019 Forum},
  booktitle = {AIAA Scitech 2019 Forum},
  doi       = {10.2514/6.2019-1812},
  year      = {2019},
  language  = {en}
}
@inproceedings{GoettenFingerHavermannetal.2019,
  author    = {G{\"o}tten, Falk and Finger, Felix and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees},
  title     = {A highly automated method for simulating airfoil characteristics at low Reynolds number using a RANS - transition approach},
  series = {Deutscher Luft- und Raumfahrtkongress - DLRK 2019. Darmstadt, Germany},
  booktitle = {Deutscher Luft- und Raumfahrtkongress - DLRK 2019. Darmstadt, Germany},
  doi       = {10.25967/490026},
  pages     = {1 -- 14},
  year      = {2019},
  language  = {en}
}
@inproceedings{FingerGoettenBraunetal.2019,
  author    = {Finger, Felix and G{\"o}tten, Falk and Braun, Carsten and Bil, Cees},
  title     = {Mass, Primary Energy, and Cost - The Impact of Optimization Objectives on the Initial Sizing of Hybrid-Electric General Aviation Aircraft},
  series = {Deutscher Luft- und Raumfahrtkongress 2019, DLRK 2019. Darmstadt, Germany},
  booktitle = {Deutscher Luft- und Raumfahrtkongress 2019, DLRK 2019. Darmstadt, Germany},
  doi       = {10.25967/490012},
  pages     = {1 -- 17},
  year      = {2019},
  language  = {en}
}
@article{GoettenHavermannBraunetal.2020,
  author    = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees},
  title     = {Airfoil drag at low-to-medium reynolds numbers: A novel estimation method},
  series = {AIAA Journal},
  volume    = {58},
  journal   = {AIAA Journal},
  number    = {7},
  publisher = {AIAA},
  address   = {Reston, Va.},
  issn      = {1533-385X},
  doi       = {10.2514/1.J058983},
  pages     = {2791 -- 2805},
  year      = {2020},
  abstract  = {This paper presents a novel method for airfoil drag estimation at Reynolds numbers between 4×10⁵ and 4×10⁶. The novel method is based on a systematic study of 40 airfoils applying over 600 numerical simulations and considering natural transition. The influence of the airfoil thickness-to-chord ratio, camber, and freestream Reynolds number on both friction and pressure drag is analyzed in detail. Natural transition significantly affects drag characteristics and leads to distinct drag minima for different Reynolds numbers and thickness-to-chord ratios. The results of the systematic study are used to develop empirical correlations that can accurately predict an airfoil drag at low-lift conditions. The new approach estimates a transition location based on airfoil thickness-to-chord ratio, camber, and Reynolds number. It uses the transition location in a mixed laminar-turbulent skin-friction calculation, and corrects the skin-friction coefficient for separation effects. Pressure drag is estimated separately based on correlations of thickness-to-chord ratio, camber, and Reynolds number. The novel method shows excellent accuracy when compared with wind-tunnel measurements of multiple airfoils. It is easily integrable into existing aircraft design environments and is highly beneficial in the conceptual design stage.},
  language  = {en}
}
@article{BergmannMoehrenBraunetal.2023,
  author    = {Bergmann, Ole and M{\"o}hren, Felix and Braun, Carsten and Janser, Frank},
  title     = {On the influence of elasticity on swept propeller noise},
  series = {AIAA SCITECH 2023 Forum},
  journal   = {AIAA SCITECH 2023 Forum},
  publisher = {AIAA},
  doi       = {10.2514/6.2023-0210},
  year      = {2023},
  abstract  = {High aerodynamic efficiency requires propellers with high aspect ratios, while propeller sweep potentially reduces noise. Propeller sweep and high aspect ratios increase elasticity and coupling of structural mechanics and aerodynamics, affecting the propeller performance and noise. Therefore, this paper analyzes the influence of elasticity on forward-swept, backward-swept, and unswept propellers in hover conditions. A reduced-order blade element momentum approach is coupled with a one-dimensional Timoshenko beam theory and Farassat's formulation 1A. The results of the aeroelastic simulation are used as input for the aeroacoustic calculation. The analysis shows that elasticity influences noise radiation because thickness and loading noise respond differently to deformations. In the case of the backward-swept propeller, the location of the maximum sound pressure level shifts forward by 0.5 °, while in the case of the forward-swept propeller, it shifts backward by 0.5 °. Therefore, aeroacoustic optimization requires the consideration of propeller deformation.},
  language  = {en}
}
@inproceedings{MoehrenBergmannJanseretal.2023,
  author    = {M{\"o}hren, Felix and Bergmann, Ole and Janser, Frank and Braun, Carsten},
  title     = {On the determination of harmonic propeller loads},
  series = {AIAA SCITECH 2023 Forum},
  booktitle = {AIAA SCITECH 2023 Forum},
  publisher = {AIAA},
  doi       = {10.2514/6.2023-2404},
  pages     = {12 Seiten},
  year      = {2023},
  abstract  = {Dynamic loads significantly impact the structural design of propeller blades due to fatigue and static strength. Since propellers are elastic structures, deformations and aerodynamic loads are coupled. In the past, propeller manufacturers established procedures to determine unsteady aerodynamic loads and the structural response with analytical steady-state calculations. According to the approach, aeroelastic coupling primarily consists of torsional deformations. They neglect bending deformations, deformation velocities, and inertia terms. This paper validates the assumptions above for a General Aviation propeller and a lift propeller for urban air mobility or large cargo drones. Fully coupled reduced-order simulations determine the dynamic loads in the time domain. A quasi-steady blade element momentum approach transfers loads to one-dimensional finite beam elements. The simulation results are in relatively good agreement with the analytical method for the General Aviation propeller but show increasing errors for the slender lift propeller. The analytical approach is modified to consider the induced velocities. Still, inertia and velocity proportional terms play a significant role for the lift propeller due to increased elasticity. The assumption that only torsional deformations significantly impact the dynamic loads of propellers is not valid. Adequate determination of dynamic loads of such designs requires coupled aeroelastic simulations or advanced analytical procedures.},
  language  = {en}
}
@inproceedings{GoettenFingerHavermannetal.2020,
  author    = {G{\"o}tten, Falk and Finger, Felix and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees},
  title     = {Full Configuration Drag Estimation of Small-to-Medium Range UAVs and its Impact on Initial Sizing Optimization},
  series = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020},
  booktitle = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020},
  year      = {2020},
  language  = {en}
}
@inproceedings{BergmannGoettenBraunetal.2022,
  author    = {Bergmann, Ole and G{\"o}tten, Falk and Braun, Carsten and Janser, Frank},
  title     = {Comparison and evaluation of blade element methods against RANS simulations and test data},
  series = {CEAS Aeronautical Journal},
  volume    = {13},
  booktitle = {CEAS Aeronautical Journal},
  publisher = {Springer},
  address   = {Wien},
  issn      = {1869-5590 (Online)},
  doi       = {10.1007/s13272-022-00579-1},
  pages     = {535 -- 557},
  year      = {2022},
  abstract  = {This paper compares several blade element theory (BET) method-based propeller simulation tools, including an evaluation against static propeller ground tests and high-fidelity Reynolds-Average Navier Stokes (RANS) simulations. Two proprietary propeller geometries for paraglider applications are analysed in static and flight conditions. The RANS simulations are validated with the static test data and used as a reference for comparing the BET in flight conditions. The comparison includes the analysis of varying 2D aerodynamic airfoil parameters and different induced velocity calculation methods. The evaluation of the BET propeller simulation tools shows the strength of the BET tools compared to RANS simulations. The RANS simulations underpredict static experimental data within 10\% relative error, while appropriate BET tools overpredict the RANS results by 15-20\% relative error. A variation in 2D aerodynamic data depicts the need for highly accurate 2D data for accurate BET results. The nonlinear BET coupled with XFOIL for the 2D aerodynamic data matches best with RANS in static operation and flight conditions. The novel BET tool PropCODE combines both approaches and offers further correction models for highly accurate static and flight condition results.},
  language  = {en}
}
@article{GoettenHavermannBraunetal.2020,
  author    = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees},
  title     = {Wind-tunnel and CFD investigations of UAV landing gears and turrets - Improvements in empirical drag estimation},
  series = {Aerospace Science and Technology},
  volume    = {107},
  journal   = {Aerospace Science and Technology},
  number    = {Art. 106306},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1270-9638},
  doi       = {10.1016/j.ast.2020.106306},
  year      = {2020},
  abstract  = {This paper analyzes the drag characteristics of several landing gear and turret configurations that are representative of unmanned aircraft tricycle landing gears and sensor turrets. A variety of these components were constructed via 3D-printing and analyzed in a wind-tunnel measurement campaign. Both turrets and landing gears were attached to a modular fuselage that supported both isolated components and multiple components at a time. Selected cases were numerically investigated with a Reynolds-averaged Navier-Stokes approach that showed good accuracy when compared to wind-tunnel data. The drag of main gear struts could be significantly reduced via streamlining their cross-sectional shape and keeping load carrying capabilities similar. The attachment of wheels introduced interference effects that increased strut drag moderately but significantly increased wheel drag compared to isolated cases. Very similar behavior was identified for front landing gears. The drag of an electro-optical and infrared sensor turret was found to be much higher than compared to available data of a clean hemisphere-cylinder combination. This turret drag was merely influenced by geometrical features like sensor surfaces and the rotational mechanism. The new data of this study is used to develop simple drag estimation recommendations for main and front landing gear struts and wheels as well as sensor turrets. These recommendations take geometrical considerations and interference effects into account.},
  language  = {en}
}
@article{GoettenHavermannBraunetal.2020,
  author    = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees},
  title     = {Improved Form Factor for Drag Estimation of Fuselages with Various Cross Sections},
  series = {Journal of Aircraft},
  journal   = {Journal of Aircraft},
  publisher = {AIAA},
  address   = {Reston, Va.},
  issn      = {1533-3868},
  doi       = {10.2514/1.C036032},
  pages     = {1 -- 13},
  year      = {2020},
  abstract  = {The paper presents an aerodynamic investigation of 70 different streamlined bodies with fineness ratios ranging from 2 to 10. The bodies are chosen to idealize both unmanned and small manned aircraft fuselages and feature cross-sectional shapes that vary from circular to quadratic. The study focuses on friction and pressure drag in dependency of the individual body's fineness ratio and cross section. The drag forces are normalized with the respective body's wetted area to comply with an empirical drag estimation procedure. Although the friction drag coefficient then stays rather constant for all bodies, their pressure drag coefficients decrease with an increase in fineness ratio. Referring the pressure drag coefficient to the bodies' cross-sectional areas shows a distinct pressure drag minimum at a fineness ratio of about three. The pressure drag of bodies with a quadratic cross section is generally higher than for bodies of revolution. The results are used to derive an improved form factor that can be employed in a classic empirical drag estimation method. The improved formulation takes both the fineness ratio and cross-sectional shape into account. It shows superior accuracy in estimating streamlined body drag when compared with experimental data and other form factor formulations of the literature.},
  language  = {en}
}
@article{FingerBraunBil2020,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Comparative assessment of parallel-hybrid-electric propulsion systems for four different aircraft},
  series = {Journal of Aircraft},
  volume    = {57},
  journal   = {Journal of Aircraft},
  number    = {5},
  publisher = {AIAA},
  address   = {Reston, Va.},
  issn      = {1533-3868},
  doi       = {10.2514/1.C035897},
  year      = {2020},
  abstract  = {Until electric energy storage systems are ready to allow fully electric aircraft, the combination of combustion engine and electric motor as a hybrid-electric propulsion system seems to be a promising intermediate solution. Consequently, the design space for future aircraft is expanded considerably, as serial hybrid-electric, parallel hybrid-electric, fully electric, and conventional propulsion systems must all be considered. While the best propulsion system depends on a multitude of requirements and considerations, trends can be observed for certain types of aircraft and certain types of missions. This Paper provides insight into some factors that drive a new design toward either conventional or hybrid propulsion systems. General aviation aircraft, regional transport aircraft vertical takeoff and landing air taxis, and unmanned aerial vehicles are chosen as case studies. Typical missions for each class are considered, and the aircraft are analyzed regarding their takeoff mass and primary energy consumption. For these case studies, a high-level approach is chosen, using an initial sizing methodology. Only parallel-hybrid-electric powertrains are taken into account. Aeropropulsive interaction effects are neglected. Results indicate that hybrid-electric propulsion systems should be considered if the propulsion system is sized by short-duration power constraints. However, if the propulsion system is sized by a continuous power requirement, hybrid-electric systems offer hardly any benefit.},
  language  = {en}
}
@inproceedings{HippeFingerGoettenetal.2020,
  author    = {Hippe, Jonas and Finger, Felix and G{\"o}tten, Falk and Braun, Carsten},
  title     = {Propulsion System Qualification of a 25 kg VTOL-UAV: Hover Performance of Single and Coaxial Rotors and Wind-Tunnel Experiments on Cruise Propellers},
  series = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020},
  booktitle = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020},
  year      = {2020},
  language  = {en}
}
@inproceedings{FingerGoettenBraunetal.2019,
  author    = {Finger, Felix and G{\"o}tten, Falk and Braun, Carsten and Bil, C.},
  title     = {On Aircraft Design Under the Consideration of Hybrid-Electric Propulsion Systems},
  series = {APISAT 2018: The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018)},
  booktitle = {APISAT 2018: The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018)},
  publisher = {Springer},
  address   = {Singapore},
  isbn      = {978-981-13-3305-7},
  doi       = {10.1007/978-981-13-3305-7_99},
  pages     = {1261 -- 1272},
  year      = {2019},
  abstract  = {A hybrid-electric propulsion system combines the advantages of fuel-based systems and battery powered systems and offers new design freedom. To take full advantage of this technology, aircraft designers must be aware of its key differences, compared to conventional, carbon-fuel based, propulsion systems. This paper gives an overview of the challenges and potential benefits associated with the design of aircraft that use hybrid-electric propulsion systems. It offers an introduction of the most popular hybrid-electric propulsion architectures and critically assess them against the conventional and fully electric propulsion configurations. The effects on operational aspects and design aspects are covered. Special consideration is given to the application of hybrid-electric propulsion technology to both unmanned and vertical take-off and landing aircraft. The authors conclude that electric propulsion technology has the potential to revolutionize aircraft design. However, new and innovative methods must be researched, to realize the full benefit of the technology.},
  language  = {en}
}
@inproceedings{GoettenFingerBraunetal.2019,
  author    = {G{\"o}tten, Falk and Finger, Felix and Braun, Carsten and Havermann, Marc and Bil, C. and Gomez, F.},
  title     = {Empirical Correlations for Geometry Build-Up of Fixed Wing Unmanned Air Vehicles},
  series = {APISAT 2018: The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018)},
  booktitle = {APISAT 2018: The Proceedings of the 2018 Asia-Pacific International Symposium on Aerospace Technology (APISAT 2018)},
  publisher = {Springer},
  address   = {Singapore},
  isbn      = {978-981-13-3305-7},
  doi       = {10.1007/978-981-13-3305-7_109},
  pages     = {1365 -- 1381},
  year      = {2019},
  abstract  = {The results of a statistical investigation of 42 fixed-wing, small to medium sized (20 kg-1000 kg) reconnaissance unmanned air vehicles (UAVs) are presented. Regression analyses are used to identify correlations of the most relevant geometry dimensions with the UAV's maximum take-off mass. The findings allow an empirical based geometry-build up for a complete unmanned aircraft by referring to its take-off mass only. This provides a bridge between very early design stages (initial sizing) and the later determination of shapes and dimensions. The correlations might be integrated into a UAV sizing environment and allow designers to implement more sophisticated drag and weight estimation methods in this process. Additional information on correlation factors for a rough drag estimation methodology indicate how this technique can significantly enhance the accuracy of early design iterations.},
  language  = {en}
}
@article{GoettenFingerHavermannetal.2021,
  author    = {G{\"o}tten, Falk and Finger, Felix and Havermann, Marc and Braun, Carsten and Marino, M. and Bil, C.},
  title     = {Full configuration drag estimation of short-to-medium range fixed-wing UAVs and its impact on initial sizing optimization},
  series = {CEAS Aeronautical Journal},
  volume    = {12},
  journal   = {CEAS Aeronautical Journal},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {1869-5590 (Online)},
  doi       = {10.1007/s13272-021-00522-w},
  pages     = {589 -- 603},
  year      = {2021},
  abstract  = {The paper presents the derivation of a new equivalent skin friction coefficient for estimating the parasitic drag of short-to-medium range fixed-wing unmanned aircraft. The new coefficient is derived from an aerodynamic analysis of ten different unmanned aircraft used for surveillance, reconnaissance, and search and rescue missions. The aircraft is simulated using a validated unsteady Reynolds-averaged Navier Stokes approach. The UAV's parasitic drag is significantly influenced by the presence of miscellaneous components like fixed landing gears or electro-optical sensor turrets. These components are responsible for almost half of an unmanned aircraft's total parasitic drag. The new equivalent skin friction coefficient accounts for these effects and is significantly higher compared to other aircraft categories. It is used to initially size an unmanned aircraft for a typical reconnaissance mission. The improved parasitic drag estimation yields a much heavier unmanned aircraft when compared to the sizing results using available drag data of manned aircraft.},
  language  = {en}
}
@inproceedings{ThomaFisherBraun2020,
  author    = {Thoma, Andreas and Fisher, Alex and Braun, Carsten},
  title     = {Improving the px4 avoid algorithm by bio-inspired flight strategies},
  series = {DLRK2020 - „Luft- und Raumfahrt - Verantwortung in allen Dimensionen"},
  booktitle = {DLRK2020 - „Luft- und Raumfahrt - Verantwortung in allen Dimensionen"},
  pages     = {10 Seiten},
  year      = {2020},
  language  = {en}
}
@article{FingerGoettenBraunetal.2020,
  author    = {Finger, Felix and G{\"o}tten, Falk and Braun, Carsten and Bil, Cees},
  title     = {Mass, primary energy, and cost: the impact of optimization objectives on the initial sizing of hybrid-electric general aviation aircraft},
  series = {CEAS Aeronautical Journal},
  volume    = {2020},
  journal   = {CEAS Aeronautical Journal},
  number    = {11},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1869-5590},
  doi       = {10.1007/s13272-020-00449-8},
  pages     = {713 -- 730},
  year      = {2020},
  abstract  = {For short take-off and landing (STOL) aircraft, a parallel hybrid-electric propulsion system potentially offers superior performance compared to a conventional propulsion system, because the short-take-off power requirement is much higher than the cruise power requirement. This power-matching problem can be solved with a balanced hybrid propulsion system. However, there is a trade-off between wing loading, power loading, the level of hybridization, as well as range and take-off distance. An optimization method can vary design variables in such a way that a minimum of a particular objective is attained. In this paper, a comparison between the optimization results for minimum mass, minimum consumed primary energy, and minimum cost is conducted. A new initial sizing algorithm for general aviation aircraft with hybrid-electric propulsion systems is applied. This initial sizing methodology covers point performance, mission performance analysis, the weight estimation process, and cost estimation. The methodology is applied to the design of a STOL general aviation aircraft, intended for on-demand air mobility operations. The aircraft is sized to carry eight passengers over a distance of 500 km, while able to take off and land from short airstrips. Results indicate that parallel hybrid-electric propulsion systems must be considered for future STOL aircraft.},
  language  = {en}
}
@inproceedings{FingerdeVriesVosetal.2020,
  author    = {Finger, Felix and de Vries, Reynard and Vos, Roelof and Braun, Carsten and Bil, Cees},
  title     = {A comparison of hybrid-electric aircraft sizing methods},
  series = {AIAA Scitech 2020 Forum},
  booktitle = {AIAA Scitech 2020 Forum},
  doi       = {10.2514/6.2020-1006},
  pages     = {31 Seiten},
  year      = {2020},
  language  = {en}
}
@inproceedings{FingerGoettenBraunetal.2019,
  author    = {Finger, Felix and G{\"o}tten, Falk and Braun, Carsten and Bil, Cees},
  title     = {Cost Estimation Methods for Hybrid-Electric General Aviation Aircraft},
  series = {Asia Pacific International Symposium on Aerospace Technology. APISAT 2019},
  booktitle = {Asia Pacific International Symposium on Aerospace Technology. APISAT 2019},
  pages     = {1 -- 13},
  year      = {2019},
  language  = {en}
}