A new turboelectric airliner concept capable of delivering 17 per cent better efficiency over 2050 projections for standard airliners has been unveiled at the AIAA AVIATION Forum.
The aircraft design project, led by the hybrid-electric aviation company Electra and assisted by engineers from the University of Michigan, is part of NASA’s Advanced Aircraft Concepts for Environmental Sustainability programme.
The chief contribution by the University of Michigan Aerospace Engineering team – led by Gökçin Çınar, assistant professor of aerospace engineering – was expanding the design space that the team could explore. Both she and Joaquim Martins, the Pauline M Sherman collegiate professor of aerospace engineering, focus on multidisciplinary design and optimisation, considering multiple aspects of the aircraft at once.
The aerodynamics and structure of the aircraft, as well as its propulsion and heat-management systems, are deeply dependent on one another. For instance, changing the shape of the aircraft, or its weight distribution, affects where the engines should be placed and how much thrust they need to generate. Çınar and Martins coded extensions to NASA’s open-source Aviary aircraft design framework, supporting the simultaneous optimisation of all three of these aspects of airplanes.
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Using this approach, the team evaluated 20 different aircraft architectures and optimised these designs for more than 100,000 scenarios. They found low-fidelity simulations preferred highly distributed propulsion – essentially, many electric propellers along the wings and in the tail. However, their more advanced high-fidelity simulations demonstrated that the weight, drag and challenges dissipating heat tipped the scales to favour a different design.
‘This was one of the findings we scrutinised most carefully, because it challenges some of the assumptions that have shaped parts of the electrified aircraft design literature,’ Çınar said. ‘Low-fidelity models and first-principles analysis remain essential for exploring large design spaces and down-selecting promising concepts early. But once the expected benefits are narrow and the modelling uncertainty is high, you need multi-fidelity analysis with greater subsystem granularity. That is what we were able to achieve together with Electra: we could move from broad concept exploration to a much more detailed understanding of when electrification actually buys its way onto the aircraft.’
In addition to the aircraft’s overall design, Venkat Viswanathan, professor of aerospace engineering at U-M, provided battery modelling to determine the power requirements and performance of battery packs, their size and weight, as well as heat dissipation and degradation over time. Max Li, U-M assistant professor of aerospace engineering, modelled likely future markets for aircraft, answering questions such as, ‘When and for what routes will airline operators be looking to buy next-generation aircraft?’ and ‘What are their requirements likely to be?’
Optimisation pointed the Electra-led team toward a partially electrified design, with a conventional turbofan engine on each wing and electric fans near the rear of the fuselage. The concept uses a wider ‘double-bubble’ fuselage first proposed by a Massachusetts Institute of Technology-led team, so the aircraft body itself contributes lift rather than simply carrying passengers. The electric fans accelerate the slower-moving air over the top of the aircraft, providing thrust while reducing the energy lost in the aircraft’s wake. Known as fuselage boundary-layer ingestion, this advanced design reduces the thrust that the underwing engines must generate.