TY  - JOUR
A1  - Finger, Felix
A1  - Braun, Carsten
A1  - Bil, Cees
T1  - Comparative assessment of parallel-hybrid-electric propulsion systems for four different aircraft
JF  - Journal of Aircraft
N2  - 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.
Y1  - 2020
U6  - http://dx.doi.org/10.2514/1.C035897
SN  - 1533-3868
VL  - 57
IS  - 5
PB  - AIAA
CY  - Reston, Va.
ER  - 
TY  - JOUR
A1  - Götten, Falk
A1  - Havermann, Marc
A1  - Braun, Carsten
A1  - Marino, Matthew
A1  - Bil, Cees
T1  - Airfoil drag at low-to-medium reynolds numbers: A novel estimation method
JF  - AIAA Journal
N2  - 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.
Y1  - 2020
U6  - http://dx.doi.org/10.2514/1.J058983
SN  - 1533-385X
VL  - 58
IS  - 7
SP  - 2791
EP  - 2805
PB  - AIAA
CY  - Reston, Va.
ER  -