The LEAF project designs a family of low-emission regional aircraft powered by hydrogen combustion turboprop engines. Two variants were developed: LEAF-A for 84 passengers over 1,500 km and LEAF-B for 58 passengers over 1,300 km, with 75.6% component commonality to reduce costs and simplify maintenance.

The aircraft uses a strut-braced wing, lightweight recyclable materials, and a liquid hydrogen tank in the tail for improved efficiency and lower emissions. Compared to conventional aircraft, the design significantly reduces carbon emissions and lowers NOx emissions by 60–90%, depending on flight phase.

Economically, the design is competitive, with direct operating costs below or close to benchmark regional aircraft and a projected 5% return on investment. The main challenges remain hydrogen infrastructure, market adoption, and managing technical risks such as hydrogen safety. ... Read more

This paper develops a system-level techno-economic optimisation framework to assess European aviation transition pathways from 2025 to 2050. The model jointly determines fleet evolution, technology adoption, energy-carrier supply, and infrastructure in a mixed-integer linear programming formulation. A three-objective optimisation over discounted system costs, cumulative well-to-wake CO2 emissions, and upstream clean energy demand is solved using the AUGMECON2 ϵ-constraint method to construct Pareto frontiers, after which a representative compromise is selected via a normalised closest-to-utopia metric. Results show pronounced and asymmetric trade-offs. Cost minimisation yields the lowest expenditures but produces CO2 emissions around six times higher than the emissions-optimal benchmark. Emissions minimisation delivers deep abatement, yet increases both costs and clean energy demand by roughly a factor four due to deployment of capital-intensive and upstream-energy-intensive technologies. Clean-energy minimisation reduces upstream demand but still results in emissions about seven times higher than the emissions-optimal solution. Across scenarios, the relationship between costs and sustainability objectives remains strongly conflicting, while emissions and clean energy demand exhibit a non-monotonic relationship. Closest-to-utopia solutions consistently originate from cost-optimal primary runs, indicating that cost-efficient baselines provide the most flexible starting point for improving emissions and clean energy performance via ϵ-constraints. Sensitivity analysis further shows that emissions outcomes are dominated by well-to-wake assumptions, whereas costs and clean energy demand are mainly driven by market growth and SAF ambition, highlighting clean energy availability as a potential binding constraint. ... Read more

Aviation is difficult to decarbonise due to its reliance on high energy-density fuels, making liquid hydrogen a promising option for reducing in-flight CO2 emissions. This study develops a profitdriven fleet development and network optimisation model for intra-European aviation (2035–2050). The problem is formulated as a rolling-horizon mixed-integer linear programme (MILP); scenario and sensitivity analyses and SHAP-based feature importance are used to interpret results. The model links fleet replacement and route allocation to technology readiness and a staged roll-out of hydrogenready airports with spatially differentiated LH2 prices. In the most favourable scenario, LH2 demand reaches 1.7 Mt/yr by 2050, corresponding to a 24% CO2 reduction relative to the no-hydrogen reference case; less favourable pathways yield lower demand due to delayed entry, operational penalties, and higher LH2 costs. Uptake forms north–south corridors and, as conditions worsen, shifts toward low-LH2-cost airports. Sensitivity results indicate that LH2 cost and operational performance dominate uptake: demand collapses once LH2 costs rise by 20–30% above the assumed price levels, and in a global sensitivity analysis, LH2 cost explains 40–50% of the variance in LH2 demand. Overall, meaningful hydrogen deployment by mid-century is conditional on coordinated progress in hydrogen cost competitiveness, operational efficiency, technology entry, and strategically sequenced airport infrastructure roll-out. ... Read more

The aviation industry needs to reduce its climate impact. There are various research areas currently being investigated to accomplish this, such as the use of alternative fuels, the design of climate-optimized aircraft and/or aircraft designed for those fuels, and the use of operational mitigation strategies. This research focuses on the overlap of these three, examining the effect of alternative fuels and aircraft on a future airline through the use of climate impact taxes in a fleet allocation model. Kerosene and liquid hydrogen climate and cost-optimized aircraft are used in the fleet allocation for regional, small-medium, and long-range aircraft. Sustainable aviation fuel (SAF) allocation is incorporated through the possibility of adding a 50% SAF blend to the kerosene aircraft. This research calculates the climate impact of flights, including CO2 as well as non-CO2 climate effects, with the CLIMaCCF library using ERA5 reanalysis data from ECMWF. These calculations are provided as inputs to the fleet allocation model, which uses dynamic programming and examines the changes in the airline’s profit and overall climate impact for different levels of climate impact tax. The results find a Pareto front between the climate impact reduction and the overall profit, resulting in a climate impact reduction potential of 10-15% at the expense of around 1% profit loss, and around 50-60% at 20-30% profit loss. Increasing climate impact tax levels move the fleet composition through a transition from kerosene, to 50% SAF blend, to liquid hydrogen. The transition differs per aircraft category (regional, small-medium range, and long-range), and shows that the climate-optimized aircraft are scarcely used due to their increased flight time and flight costs, for all levels of climate impact tax. ... Read more

Hybrid aircraft are a necessary step in the energy transition towards sustainable aviation, given current limitations in battery technology. However, hybrid systems face significant economic and technological hurdles of their own. This study investigates whether designing hybrid-electric aircraft as part of a family—with shared components and design commonality—can offset economic drawbacks while maintaining environmental benefits. A novel methodology was developed and validated against existing literature, integrating economic and climate models within a hybrid aircraft family design framework. This approach facilitates aircraft family design by strategically constraining design freedom at the subsystem level, introduces a refined calculation of commonality indices, and incorporates these indices into a bespoke economic evaluation framework specifically tailored for commercial hybrid aircraft. Results from a parametric case study demonstrate that increased commonality yields drastic improvements in economic feasibility —on the order of billions of dollars—, while environmental performance varies by less than5%across design families with differing levels of commonality. These findings underscore the critical role of commonality in determining program viability, an effect not previously quantified for hybrid systems. Additionally, family design trends influence program value and emissions in nuanced ways. This work provides guidance for optimizing hybrid aircraft family designs and highlights opportunities for further research in sustainable and economically viable aviation. ... Read more

The aviation industry continues to grow at a steady annual rate of approximately 4.4%, intensifying global environmental concerns in light of international climate goals. In response, airlines are under increasing pressure to adopt sustainable innovations, with electrified aviation emerging as a promising pathway. One of the main challenges in electrified aviation is planning profitable flight schedules despite long turnaround times for battery recharging. To address this, a Flight Scheduling and Electrified Aircraft Routing (FSEAR) model was developed, advancing beyond models assuming full recharging or battery swaps. It integrates partial recharging through a recursive three-dimensional time-space-energy dynamic programming framework, combining multi-label dominance on profit and energy with a CO2 tax penalty for climate optimization. Based on the KLM Cityhopper network, three case studies with varying demand and distance profiles were developed. Results show that partial recharging increases profit by 22.5% to 27.8% compared to limiting operations to full recharging constraints. Emission reductions of 45.1% and 48.9% were achieved in close-range cases, while the long-range case showed a modest increase of 4.66%, reflecting a trade-off for enabling more profitable
operations with higher flight frequency and greater demand coverage. A consistent reduction in fleet size and a shift to fully all-electric compositions were also observed. This study demonstrates that partial recharging significantly enhances both the operational efficiency and environmental performance of electrified aviation, supporting lower-emission fleet compositions and enabling a more sustainable, cost-effective alternative to regional air transport. ... Read more

This research investigates how the obstacles to hydrogen adaptation impact the projected distribution and frequency of hydrogen-powered flights in Europe by 2050. The prioritized obstacles in this research are economic constraints and airport capacity limitations. For the economic constraints two different cost scenarios are analysed, one where hydrogen-aircraft just become competitive with respect to conventional aircraft, and one where hydrogen-aircraft are favoured with respect to conventional aircraft. When considering airport capacity limi- tations, for example due to availability of green hydrogen and infrastructure modifications, a constraint is put on the maximum amount of hydrogen-powered aircraft allowed in the network. In this research, a European Hub & Spoke network for an airline is analysed. In the scenario where hydrogen-powered aircraft are favoured, the variable cost of conventional aircraft is significantly increased in the future. Then, more hydrogen-powered aircraft are de- ployed and these are particularly medium-range hydrogen-powered aircraft. Moreover, under different traffic growth scenarios, the higher the traffic growth, the more routes are flown by hydrogen-powered aircraft. When comparing these two results, the varying of the variable costs of future aircraft is more sensitive to the deployment of hydrogen-powered aircraft than the sensitivity of the traffic growth. When considering the implementation of a fleet constraint for hydrogen-powered aircraft, only in a scenario with high traffic growth from 2025-2050 and a favorable cost for hydrogen-powered aircraft, the capacity constraint is met. Across all scenar- ios, despite varying conditions, the airline’s profit remains reasonably consistent and almost all demand is captured. This study emphasizes that hydrogen-powered aircraft adaptation is highly sensitive to cost dynamics. At policy level regulatory entities should implement mechanisms that create financial incentives for hydrogen adoption and Original Equipment Manufacturers should prioritize cost-efficient design. ... Read more

Aviation is a major contributor to global warming and so pathways for decarbonization need to be explored. As battery technology advances, electric regional aviation emerges as a viable option. A key challenge, however, is that the aircraft batteries degrade over time, progressively restraining the operational capability of electric aircraft. Current approaches do not account for this effect. To address this gap, this research presents the Battery DegradationAware Electric Fleet Assignment framework that enables the integration of battery ageing into tactical scheduling. It does this by combining a rolling-horizon fleet assignment model with a battery degradation module that predicts and updates each aircraft’s state of health based on its flown missions, with battery replacement scheduled according to designated strategies to ensure continuity of operations. This framework is evaluated with five distinct experiments, tested on the KLM Cityhopper network and complemented by an additional case study for validation. The experiments validate the framework’s operational and degradation dynamics and demonstrate that battery degradation has a significant impact, with depreciation costs amounting to 0.91 €/km flown. Degradation reduces fleet range capability, lowering ASKs by 0.96%, revenue by 0.76%, and increasing total operating costs by 9.1% as battery replacements become necessary. The sensitivity analysis indicates that future battery price scenarios can make or break profitability. Consequently, operational models that ignore degradation effects will overstate the profitability of electric aircraft. ... Read more

Electric aircraft (EA) reliance on volatile electricity prices introduces significant financial risk, a challenge often overlooked in strategic planning. We develop a profit maximizing Mixed Integer Linear Program (MILP) with a novel circular-route design to optimize strategic electric airline planning problems, including charge decisions and mixed fleet composition. Our results show that ignoring electricity prices can lead to >35% profit losses during volatile periods. While average prices mitigate this, accurate prices perform best, enabling charging arbitrage such as ferrying and skipping that boosts profits by 1.1% over simple heuristics. A mixed fleet of both electric and kerosene aircraft offers additional benefits, unlocking synergistic profit gains of up to 1.5% while maintaining the financial stability of a pure kerosene fleet. In such a fleet, kerosene aircraft form a network backbone, seen by a 10% kerosene fleet share covering almost 80% of routes. The path to sustainable aviation must therefore anticipate monthly network changes to remain optimal, incorporate accurate electricity prices for strategic charging optimization, and leverage mixed fleets to ease the transition to a more electrified future. ... Read more

This study investigates the optimisation of design variables for the unconventional Flying-V-900 aircraft to minimise its climate impact, taking into account operational costs. The study
examines the compromises between operational costs and climate factors. A multidisciplinary
analysis and optimisation framework is developed in order to minimise the Flying-V-900’s
impact on global warming, cash operating costs, and fuel efficiency. This study investigates
the influence of geometry, turbofan engine, and mission design variables on these objectives.
The findings indicated that fuel- and cost-optimised designs demonstrated nearly identical
performance, whereas a climate-optimised design exhibited contradictory performance. These
results indicate that adopting a climate-optimised Flying-V-900 could potentially reduce the
impact of global warming compared to a conventional aircraft, as measured by the average
temperature response over a 100-year period, by approximately 60%. However, it is important
to note that this transition would come with a significant increase in cash operating costs,
specifically by 32%. This analysis considers the impacts of both CO2 and non-CO2 factors,
including contrail formation and NO𝑥 emissions. It demonstrates that the climate-optimised
Flying-V aircraft give priority to flying at a low altitude of 6km and a velocity of Mach 0.60 in
order to minimise contrail formation and NO𝑥 emissions. However, achieving this requires a
20% increase in fleet size to maintain productivity. ... Read more

Aircraft redesign and flight path optimisation offer promising methods of rethinking how we fly. As the effects of aviation on the planet are becoming better understood, focus has shifted from cost minimisation to climate impact mitigation. In this study, simultaneous aircraft design and trajectory optimisation is used to investigate the trade-off between direct operating costs (DOC) and the global average temperature response (ATR) associated with a typical medium range flight. It is shown for a representative mid-latitude atmosphere and narrowbody aircraft that the ATR can be reduced by 49% with approximately 0.5% increase in operating costs through 2-dimensional flight path optimisation. With simultaneous wing planform optimisation, the DOC-ATR trade-off is even more favourable, leading to a 56% ATR reduction with no increase in operating costs. Results indicate that contrail avoidance is a highly cost-effective method of minimising the climate effects of aviation. ... Read more

With the aviation sector growing each year, the need for a reduced climate impact is becoming increasingly important. Electrification of the propulsion system is believed to offer promising avenues in achieving this reduction. Additionally, airlines operating these aircraft have to adapt their operations and network to optimally utilize these aircraft. This research presents a methodology for the coupled design of a hybrid-electric aircraft fleet with strategic airline planning to optimally serve a specific network. The objective is to maximize the airline profit and minimize the network CO2 emissions. Aircraft design trade-offs in payload, range and runway length will guide the creation of new aircraft until the optimal aircraft fleet is determined. The methodology is tested in a case study for the regional airline network of SATA Air Acores. The study investigates the impact of introducing new hybrid-electric aircraft designs in the fleet on the creation of new aircraft, the aircraft allocation and the network performance. By directly integrating hybrid-electric aircraft design (having a parallel hybrid architecture) with strategic airline planning, it is possible to reduce the network CO2emissions by -11% at the cost of an airline profit decrease of -13%. When including a climate optimization, an additional reduction of network CO2 emissions is achieved of -27% with a small additional decrease in profit of -1%. Network profitability and climate impact are mainly dictated by the fleet diversity and the assumed technology level of the batteries employed in the aircraft. This research highlights the importance of including climate optimization in the design of new aircraft and the need for more advanced hybrid-electric propulsion architectures (such as distributed propulsion systems) to further contribute to climate impact reduction. ... Read more

To reduce the climate impact of the turbofan dominated aviation industry, a conceptual propeller aircraft study has been performed to see the a possible reduction in climate impact between the two. The results analysed showed great promise for the reduction of the climate impact at the cost of block time. Additionally, a loss in productivity or fleet size is observed for the climate impact seen. The change in productivity or fleet size is remedied with an decrease in block time, however this results in an increase in climate impact, especially when compared to the turbofan aircraft. Overall it is safe to say that the climate impact can be reduced by utilising propeller aircraft, however either the productivity or fleet size must be changed. Additionally, the costs per flight potentially go up. All for a more sustainable and greener aviation industry. ... Read more