Aerodynamic Assessment of a Propeller-Driven, Battery-Electric Large Transport Aircraft with Distributed Propulsion

Abstract

With the E9X, Elysian Aircraft aims to develop a battery-electric aircraft for 90 passengers and a useful range of 800 km, equivalent to 430 NM. Comparing these values to the estimations from recently published conceptual aircraft design studies [1], this goal appears challenging. Elysian Aircraft’s conviction that it can nevertheless achieve these targets is based on the view that four misconceptions lead to the rather cautious prevailing assessments to date. One of those relates to the aerodynamic performance in particular during cruise flight. In contrast to assumptions of achievable lift-to-drag ratios for this type of aircraft lying between 14 to 18, Elysian Aircraft aims to achieve a comparably high lift-to-drag ratio of around 23 at mid cruise conditions. While this target seems ambitious in itself, there is the additional challenge of enabling sufficient high-lift performance of CL,max ≈ 2.5 in order to achieve the desired approach category C. The present paper gives an overview on the work that has been performed in order to support Elysian Aircraft’s initial assumption that a lift-to-drag ratio of 23 can indeed be achieved by such a configuration. Starting from a conceptual design, a preliminary aerodynamic design of the wing and the propellers was carried out. RANS simulations have then been performed to evaluate the aerodynamic performance of the configuration, also considering the propeller-wing interaction. Further RANS-based design studies allowed the introduction of local wing shape modifications and an improved aerodynamic nacelle design, eventually showing the potential to indeed achieve the targeted lift-to-drag ratio. The aerodynamic potential of high-lift systems with varying complexity ranging from plain flaps to double-slotted fixed-vane flaps has been investigated in order to meet this requirement. The paper gives insight into the high-lift design approach based on sectional and lifting line optimizations followed by an aerodynamic analysis utilizing RANS simulations. The limitations of plain flaps and the potential of slotted flaps to meet Elysian Aircraft’s aerodynamic requirements are illustrated for the present aircraft design. In summary, the studies show that Elysian Aircraft’s aerodynamic assumptions appear to be reasonable and that there is the potential to actually achieve the required aerodynamic objectives. The integration of the nacelles thereby plays a central role in achieving a suitable compromise between cruise and high-lift.