@inproceedings{FingerBraunBil2020,
  author    = {Finger, Felix and Braun, Carsten and Bil, Cees},
  title     = {Comparative assessment of parallel-hybrid-electric propulsion systems for four different aircraft},
  series = {AIAA Scitech 2020 Forum},
  booktitle = {AIAA Scitech 2020 Forum},
  doi       = {10.2514/6.2020-1502},
  pages     = {15 Seiten},
  year      = {2020},
  abstract  = {As battery technologies advance, electric propulsion concepts are on the edge of disrupting aviation markets. However, 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-, parallel-hybrid-, 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 towards either conventional or hybrid propulsion systems. General aviation aircraft, VTOL air taxis, transport aircraft, and UAVs are chosen as case studies. Typical missions for each class are considered, and the aircraft are analyzed regarding their take-off mass and primary energy consumption. For these case studies, a high-level approach is chosen, using an initial sizing methodology. Results indicate that hybrid-electric propulsion systems should be considered if the propulsion system is sized by short-duration power constraints (e.g. take-off, climb). However, if the propulsion system is sized by a continuous power requirement (e.g. cruise), hybrid-electric systems offer hardly any benefit.},
  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{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}
}
@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{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{FingerKhalsaKreyeretal.2019,
  author    = {Finger, Felix and Khalsa, R. and Kreyer, J{\"o}rg and Mayntz, Joscha and Braun, Carsten and Dahmann, Peter and Esch, Thomas and Kemper, Hans and Schmitz, O. and Bragard, Michael},
  title     = {An approach to propulsion system modelling for the conceptual design of hybrid-electric general aviation aircraft},
  series = {Deutscher Luft- und Raumfahrtkongress 2019, 30.9.-2.10.2019, Darmstadt},
  booktitle = {Deutscher Luft- und Raumfahrtkongress 2019, 30.9.-2.10.2019, Darmstadt},
  pages     = {15 Seiten},
  year      = {2019},
  abstract  = {In this paper, an approach to propulsion system modelling for hybrid-electric general aviation aircraft is presented. Because the focus is on general aviation aircraft, only combinations of electric motors and reciprocating combustion engines are explored. Gas turbine hybrids will not be considered. The level of the component's models is appropriate for the conceptual design stage. They are simple and adaptable, so that a wide range of designs with morphologically different propulsive system architectures can be quickly compared. Modelling strategies for both mass and efficiency of each part of the propulsion system (engine, motor, battery and propeller) will be presented.},
  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}
}
@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}
}
@techreport{ReimerWellmerBraunetal.2007,
  author    = {Reimer, Lars and Wellmer, Georg and Braun, Carsten and Ballmann, Josef},
  title     = {Aerodynamische Simulation und Optimierung in der Flugzeugentwicklung. Teilvorhabenbezeichnung: Aerodynamische Optimierung unter Ber{\"u}cksichtigung von Struktureigenschaften auf der Basis reduzierter Strukturmodelle, Verbundvorhaben MEGADESIGN. Schlussbericht. Berichtszeitraum: 01.06.2003-31.05.2007. BMBF-Forschungsbericht},
  pages     = {41 S.: Ill., graph. Darst.},
  year      = {2007},
  language  = {de}
}
@article{GoettenHavermannBraunetal.2021,
  author    = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees},
  title     = {Aerodynamic Investigations of UAV Sensor Turrets - A Combined Wind-tunnel and CFD Approach},
  series = {SciTech 2021, AIAA SciTech Forum, online, WW, Jan 11-15, 2021},
  journal   = {SciTech 2021, AIAA SciTech Forum, online, WW, Jan 11-15, 2021},
  publisher = {AIAA},
  address   = {Reston, Va.},
  doi       = {10.2514/6.2021-1535},
  pages     = {1 -- 12},
  year      = {2021},
  language  = {en}
}