Liquid hydrogen (LH₂) has long been seen as a technically feasible fuel for a fully sustainable greener aviation future. The low density of the cryogenic fuel would dictate the redesign of commercial aircraft to accommodate the large tanks, which are unlikely to be integrated within the whole internal volume of the wing. In the ENABLEH2 project, the morphological aspects of a LH₂ aircraft design are discussed and a methodology for rapid concept comparative assessment is proposed. An exercise is then carried on to down-select short-to-medium range (SMR) and long-range (LR) concepts, able to carry 200 passengers for 3000 nmi and 414 passengers for 7500 nmi, respectively. The down-selection process was split into two phases with the first considering 31 potential airframe architectures and 21 propulsion-system arrangements. The second phase made the final down-selections from a short-list of nine integrated design concepts that were ranked according to 34 criteria, relating to operating cost, revenue, noise, and safety. Upon completion of the process, a tube and wing design with the tanks integrated into extended wing roots, and a blended-wing-body design were selected as the best candidates for the SMR and LR applications, respectively. Both concepts feature distributed propulsion to maximize synergies from integrating the airframe and propulsion systems.

This investigation surveyed the potential and established outcomes for future 19-passenger fixed-wing commuter transport aircraft concepts employing battery-based Voltaic-Joule/Brayton motive power systems with no additional electrical energy drawn from generators mechanically coupled to thermal engines. The morphological approach was that of a tri-prop (two on-wing podded turbo-props and one aft-fuselage mounted electric motor configured as a pusher-on-pylon installation). A Battery System-level Gravimetric Specific Energy (referred to as “battery energy density”) of at least 500 Wh/kg yielded 39%, 25% and 10% block fuel reductions for 150-nm (Design Service Goal), 430-nm (85th percentile) and 700-nm (maximum range) stage lengths, respectively. All quoted comparisons are against a suitably projected turbo-prop only year-2030 aircraft. In contrast to the reference Beech 1900D, block fuel reductions of up to 44-49% were predicted, which could facilitate a significantly lower deficit in relation to the Advisory Council for Aviation Research and Innovation in Europe (ACARE) Strategic Research and Innovation Agenda (STRIA) 55% target for year 2030. This investigation also indicated that, in the future, suitably flexible hybrid-electric architectures could be fashioned allowing possibility for the aircraft to complete any required city-pair operations (within the legitimate payload-range working capacity) irrespective of exchangeable batteries being available at a given station. Finally, it was also established, assuming such a tri-prop morphology, Normal conducting machines delivering maximum shaft power output of 1.1 MW would be required.

Designing commercial aircraft to use Liquid Hydrogen (LH~2~) is one of very few ways to substantially diminish life-cycle CO~2~ emissions from aviation. The merits of hydrogen as an aviation fuel have long been recognized. However, apart from very short-range applications, its integration into commercial aircraft is only viable when it is liquefied, due to the heavy weight and