A wide range of aircraft propulsion technologies is being investigated in current research to reduce the environmental impact of commercial aviation. As the implementation of purely hydrogen-powered aircraft may encounter various challenges on the airport and vehicle side, combined hydrogen and kerosene energy sources may act as an enabler for the first operations with liquid hydrogen propulsion technologies. The presented studies describe the conceptual design of such a dual-fuel regional aircraft featuring a retrofit derived from the D328eco under development by Deutsche Aircraft. By electrically assisting the sustainable aviation fuel (SAF) burning conventional turboprop engines with the power of high-temperature polymer-electrolyte fuel cells, the powertrain architecture enables a reduction of SAF consumption. All aircraft were modeled and investigated using the Bauhaus Luftfahrt Aircraft Design Environment. A description of this design platform and the incorporated methods to model the hydrogen-hybrid powertrain is given. Special emphasis was laid on the implications of the hydrogen and SAF dual-fuel system design to be able to assess the potential benefits and drawbacks of various configurations with the required level of detail. Retrofit assumptions were applied, particularly retaining the maximum takeoff mass while reducing payload to account for the propulsion system mass increase. A fuel cell power allocation of 20% led to a substantial 12.9% SAF consumption decrease. Nonetheless, this enhancement necessitated an 18.1% payload reduction, accompanied by a 34.5% increment in propulsion system mass. Various additional studies were performed to assess the influence of the power split. Under the given assumptions, the design of such a retrofit was deemed viable.

When assessing new technologies at the overall aircraft level, it is crucial to establish an appropriate benchmark to evaluate the resulting performance of the final concept aircraft. This publication defines a short-to medium-range baseline aircraft for entry into service in 2035, which serves as a benchmark for the HOPE project. This aircraft is sized using the Bauhaus Luftfahrt Aircraft Design Environment (BLADE), and its engine model is derived using the in-house tool Aircraft Propulsion System Simulation (APSS). The top-level aircraft requirements and technology assumptions for the entire project timeline are also defined and used for the baseline aircraft. Compared to a state-of-the-art aircraft (entry into service in 2015), the baseline aircraft consumes 21.4% less block fuel during the design mission and 20.9% less block fuel during the typical mission, since its operating empty mass is reduced by 13.6%, its aerodynamic performance is improved by 8.5%, and it has 6.4% more efficient engines.

The Composite Cycle Engine (CCE) enhances the conventional Joule/Brayton cycle by replacing the high-pressure compressor with a high-quality piston-based gas generator that enables extremely high compression, combustion, and expansion of the working fluid before entering the classic Joule burner. This piston-based topping cycle unlocks much more efficient fuel utilization. This paper studies a CCE concept featuring a system of free double piston (FDP) units for a potential long-range (LR) application in 2045, benchmarked against an advanced turbofan engine representative of the same time frame. In-house-developed simulation tools for the piston system and the overall power plant, as well as aircraft non-linear trade factor analysis, are used for different levels of conceptual assessment. First, the cooling demand inside the FDP system is determined. An engine cycle parametric study is then performed for the design point top-of-climb (ToC). Off-design performance is further studied, demonstrating a 9.3% improvement in thrust-specific fuel consumption (TSFC) in cruise relative to the baseline engine. After incorporating the engine weight and nacelle geometry effects, the engine reaches a total mission fuel burn reduction of around 14.7% compared to the baseline engine. The concept evaluation shows the fuel burn potential of the CCE in the future LR aviation sector and lays the foundation for further climate impact analysis.

Current research in commercial aviation is exploring numerous propulsion and aircraft technologies to mitigate its environmental impact. While purely hydrogen-powered aircraft face manifold challenges, combining hydrogen and conventional fuel may facilitate the introduction of hydrogen-based flight. This study dives into the conceptual design of a parallel-hybrid dual-fuel regional aircraft retrofit based on the D328eco. The assessed retrofit approach aims to extend airframe service life and reduce emissions by incorporating a novel propulsion system. By integrating high-temperature fuel cells (FCs) to assist conventional turboshaft engines, the powertrain reduces fuel consumption. Utilizing the Bauhaus Luftfahrt Aircraft Design Environment, various aircraft-level sensitivities and hybridization strategies were assessed. The fuel/payload ratio was identified as a key metric, and enabling FC support during diversion climb while minimizing that ratio shifted the corresponding hybridization degree from 20.3% to 37.2%. Retaining the reference turboshaft-engine for reduced retrofit development costs, a hybridization degree of 20.2% was attainable while the minimum allowable payload was carried aboard. Subsequent off-design mission analysis revealed a decrease in transport efficiency for reduced mission ranges, underlining the importance of market-tailored aircraft designs. The main studies were complemented by a higher-level emission and climate impact assessment to set the basis for more generalized retrofit statements.

The present contribution evaluates the responses produced by several semi-empirical wing-mass-estimation methods based on a wide range of parameter variations on the wing of an Airbus A320ceo-class aircraft model. A common wing-parametrization method is established to ensure the appropriate comparison between the results of each method. Six semi-empirical methods are introduced and compared against reported trends and a published surrogate model of a physics-based wing-weight-estimation framework. The investigated methods produce a 7.0% to 34.5% error relative to reference aircraft data for the baseline case. Variations with increasing aspect ratio show that most methods exhibit non-linear trends of decreasing gradients, opposing those found in the literature and numerical models. Removing the inertia relief considerations associated with wing fuel storage yields mass penalties ranging from 3.8% to 11.4% across the interval of wing aspect ratios explored, broadly matching published results. Alterations to the wing reference area and the spanwise location of the centre of pressure yield nearly linear and proportional changes to the wing mass for all the methods analysed, whereas the sensitivity to the engine’s spanwise location is found to be nearly linear or non-linear, depending on the method’s level of detail. To address the identified limitations, one of the simplest of the methods considered is systematically modified by restructuring its geometric terms and introducing a fuel mass relief, and is then calibrated against one of the most detailed, recovering the gradients and dry-wing sensitivity of the latter. This work shows that the simple semi-empirical methods commonly employed during the conceptual and preliminary aircraft design phases cannot fully represent the behaviour of methods of higher fidelity. Thus, future aircraft design studies should adopt more detailed wing-mass-estimation methods or systematically adapt existing ones.