The electrification of aircraft is an on-going endeavor, currently examined intensively in the general aviation class. However, for the commuter class, the proper selection of the hybrid-electric propulsive architecture is instrumental, to fully exploit the electrification benefit. Within this work, a comparison of two 19-seater aircraft with different hybrid-electric propulsive components is made, using an in-house aircraft conceptual design tool. The first aircraft is based on a twin-turboprop parallel-hybrid configuration that cruises at low Mach number speeds and altitude. On the other hand, the second aircraft variant is based on a tri-fan series/parallel-hybrid configuration with an aft Boundary Layer Ingestion system that operates at both higher altitude and Mach numbers. A design space exploration is performed where different degrees of hybridization and batteries specific energy are considered, to define the technological requirements for each architecture. The evaluation of the propulsive architectures is based on block fuel reduction, overall mission duration, direct operating costs and total environmental impact. The results aim to quantify the benefits of each configuration and determine the one with the closest entry into service. Finally, it is observed that the overall environmental impact reduces by 26 % and 17 % for the turboprop and turbofan variants respectively.
This paper attempts to reduce the gap, when it comes to future aircraft concepts noise and aeroacoustics, and at the same time introduce basic noise aspects for people unfamiliar to it. This is performed by taking into account the following four stages: Identification of conventional aircraft noise sources, overview of the aeroacoustics of future aircraft configurations, derivation of conceptual design considerations for noise issues, and finally, insight on the impact of technology advancements on certification. More specifically, a holistic overview of the aeroacoustics of aircraft was performed. The noise sources were described and made available for those unacquainted with the subject. Aeroacoustic behavior of ContraRotating Open Rotors, Boundary Layer Ingestion and Distributed Propulsion concepts was studied trough the most recent and relevant literature. The phenomena causing noise were highlighted, and the differences between conventional and future designs detected. It was found that generally noise sources are similar, but the intensity of some can be significantly altered. Early design phase guidelines were extracted for each of the concepts. The design considerations are grouped into a matrix showing the relative effect of each on noise emissions. With these guidelines, it is possible to perform design choices in the conceptual level of fidelity for future aircraft concepts. Furthermore, certification aspects and observations considering its future development are presented. Noise emissions are expected to change, and thus certification must be adapted to it. Furthermore, in this quick advancing technology field, virtual certification is advised to be used.
A promising solution for sustainable aviation is hybrid-electric propulsion, which is gaining popularity in recent years. However, hybrid-electric propulsion variants are affected by the technological maturity of electric components, which have a direct impact on the electrification benefit, compared to conventional propulsive configurations. This work aims in investigating three different Entry Into Service dates, i.e., 2027, 2030, and 2040, for two hybrid-electric propulsive configurations, namely the Series and the Parallel. Six hybrid variants are sized, one for each date and configuration, using an in-house tool, and their mission performance metrics, operating costs, and environmental impact are compared to a conventional aircraft with technological assumptions of 2014. Results indicate that the Parallel variants promise a block fuel and energy reduction of up to 33 % and 28 % respectively for 2040, whereas the Series variants show a respective reduction of 66 % and 58 % accordingly. Moreover, the 2027 Parallel aircraft has reduced annual operating costs compared to the Series 2027, whereas a turnaround point exists in which the Series becomes more economical to operate, compared to both Parallel and the Reference aircraft after 2030. Finally, the Life Cycle Assessment suggests that the Series variants have a lower environmental impact compared to the respective Parallel variants and that both configurations have better scores than the Reference aircraft. The Parallel and Series configurations of 2030 promise an environmental impact reduction of up to 22.8 % and 59.8 % respectively, compared to the reference aircraft.
Hybrid-electric propulsion is a promising alternative to sustainable aviation and is mainly considered for the commuter and regional aircraft class. However, the development of hybrid-electric propulsion variants is affected by the technology readiness level of electric components. The components’ technology will determine the electrification benefit, compared to a conventional aircraft, and will suggest which is the most beneficial variant and which has a closer entry into service date. Within this work, three different dates are explored, namely 2027, 2030 and 2040, to size three Parallel and three Series hybrid-electric architecture variants using an in-house aircraft sizing tool. All variants are compared to a conventional configuration sized using technological assumptions of 2014, with the main comparison metrics being the aircraft block fuel, energy consumption, direct operating cost and holistic environmental impact. On one hand, the Parallel configurations have reduced maximum take-off mass and mission energy consumption compared to the Series, however, the latter show a greater potential for block fuel reduction and require less onboard energy for the same mission. The annual operating cost evaluation indicates that the Parallel hybrid variant of 2030 has greater operational costs than the respective Series variant; however, it has reduced capital costs compared to the latter, making it more economical to operate considering both costs. Additionally, in the case of an energy recession, both hybrid variants of 2030 show a further cost reduction, with the Series having a total reduction of 10.4% excluding capital costs, compared to the reference aircraft. Moreover, the life cycle assessment shows that the Series variants have a lower environmental impact, both compared to the reference aircraft and the Parallel variants. The former could be up to 59.7% less detrimental to the environment than the reference aircraft, whereas the latter up to 23.9%, with the integration of renewable sources for electricity production. Finally, by the year 2040, the Series variant shows outstanding performance in all comparison metrics, compared to the Parallel and the reference aircraft.
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