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Aircraft electrification for propulsion is a promising way to alleviate the negative environmental impact of conventional carbon-powered aviation. Inclusion of the electrical powertrain aims to enhance design freedom, allowing for more efficient power systems and operational schemes. In this work, a design space exploration is performed, aiming to derive power management guidelines based on aircraft environmental performance. A 19-passenger commuter aircraft employing the series/parallel partial hybrid-electric architecture is examined. Two underwing-mounted turboprop engines are combined with a boundary layer ingestion fan mounted in the aft of the aircraft and powered by an electrical drive. The primary electrical energy source is a battery system. A multidisciplinary framework is utilized, comprising modeling approaches for multipoint thermal engine design, physics-based electrical component sizing and performance, aircraft sizing, mission design, and environmental assessment. The investigation revealed that the reference designed hybrid-electric configuration with entry-into-service (EIS) 2035 assumed technologies yields roughly 18% improvement in block consumption and emissions, but an 8% increase in maximum takeoff weight (MTOW), compared to its 2014 conventional counterpart. The design space exploration for an optimal power management scheme indicated a minimum average ratio of 1:1.35 between cruise and design point hybridization power. However, even the optimally operated hybrid aircraft showcases worse environmental performance compared to the conventional design of same entry-into-service date. The investigation has revealed that the complex powertrain and hybrid architecture selected may be more suitable for larger class aircraft, where aircraft requirements can be relaxed and higher degrees of electrification are not penalized or confined by set constraints.

Decarbonisation of the energy sector is now an urgent worldwide challenge. Among the different transportation industries, aviation is one of the most difficult in which to achieve this. Towards that goal, this thesis establishes a map for the design and environmental potential of novel hybrid-electric and hydrogen-powered regional aircraft. It does so, by revealing and connecting the multi-disciplinary interactions between propulsion and aircraft systems. It advances the evaluation of novel electrified powertrains from simplistic representations to comprehensive models, capable of credible and consistent conclusions.

The deployed platform for investigations consists of detailed models for turbomachinery components, electrical power system, aircraft/mission and environmental performance. It is capable of the integrated propulsion-aircraft design, considering cross-system top-level requirements and connections. This is complemented by the framework's ability to separate conceptual design stages and quantify their individual impacts.

The system-level impact of critical component interactions is investigated to enhance the conceptual design process' fidelity. By highlighting trade-offs in the sizing and performance of the electrified powertrain, a design and operation balance for favorable environmental performance is established. This reveals and fortifies the understanding of connections between system design choices and optimal power management guidelines. Electrification enables several operational and propulsive synergies, which are conceptualized within the thesis. Their contribution and effects are assessed and quantified. Major gravimetric, volumetric and operational limitations in the design of alternative-energy aircraft are also identified and their impact is quantified. 

The holistic knowledge of opportunities and challenges in hybrid-electric aircraft design crafts a pathway for conscious and effective conceptual design. It reveals the viability of small electrified and H₂-fired regional aircraft and sets a roadmap of necessary component-level advancements that could facilitate their integration in civil aviation.

Hybrid electric aviation is a possible step toward sustainable flight. Several hybrid architectures and synergetic concepts have been investigated. However, environmental performance results seem to be inconsistent due to deviations in technology assumptions and a mismatch between the fidelity of methodologies used for simulation of different aircraft systems. A multidisciplinary framework is developed, consisting of detailed modeling approaches for thermal and turbomachinery components, electrical power system design, aircraft/mission, and environmental analysis. The framework is employed for the investigation of an entry-into-service 2035 30 passenger commuter aircraft with a design mission of 1000 nautical miles. The investigation of parallel hybrid electric, turbo-electric, and series/parallel partial architectures is performed through a systematic conceptual design approach. The analysis reveals a bare minimum battery technology of 0.75 kWh/kg and 0.8 kW/kg, needed to compete with the conventional aircraft's performance. High degrees of hybridization (>20%) trigger the snowball effect of aircraft mass and thrust requirement, counteracting specific fuel and performance benefits generated by electrification. The turbo-electric and series/parallel partial concepts are paired with an electrically driven boundary layer ingestion fan. For those concepts to result in any block fuel and emissions benefits compared to conventional counterparts, a drag reduction from wake ingestion of 7.5–10% is required, with power split ratios between the electrically driven fan and propellers being limited to 15% due to extensive mass increase.

Turboprops offer a promising pathway for sustainable aviation, as they can achieve high levels of propulsive efficiency and reduced installed drag compared to high bypass ratio turbofans. Turboprop engine cores, though, are rarely designed from scratch; instead, they remain geometrically similar and can be used across several engine variants, which is known as the concept of growth engines or core commonality. This paper investigates the impact of core commonality on the installed performance of the next generation small-core turboprops. First, a turboprop cycle design optimization is carried out based on a multipoint synthesis approach for 2035 entry into service assumptions. The propeller, nozzle, and engine core are individually designed and analyzed. Preliminary design studies of the core compressor are performed using a 2D streamline curvature algorithm, providing insights into the aerodynamic tradeoffs of highly loaded all-axial multistage compressors. The second part of this study examines the performance of growth engine variants by applying the common-core approach to the designed 2035 baseline turboprop engine. In this context, “growth” refers to increasing equivalent shaft power to meet the thrust demands of a derivative aircraft designed for higher passenger capacity and/or extended range. A common-core design methodology is developed and proposed, enabling power growth through zero-staging of the core compressor and power off-take from the free-power turbine to drive electric motors, which in turn power additional e-propellers in electrified turboprop variants. Three optimal growth engine designs are identified, achieving up to 34.8% power growth relative to the baseline turboprop while maintaining design constraints, including high-pressure spool overspeed limits, a fixed propeller design, and considerations for cooled or uncooled free-power turbines. Overall, this study systematically analyzes the common-core concept, reflecting the approach followed by engine manufacturers over the years. Copyright © 2026 by ASME.

The aviation industry faces significant environmental challenges, prompting the implementation of regulations to mitigate the adverse effect of carbon-based energy and associated emissions. While electrified flight is a promising pathway, limitations in specific energy density of batteries narrow down the application space to commuter and regional classes. Towards that direction, this work investigates the design and operation of a series hybrid electric 30-passenger regional aircraft. A multi-disciplinary framework is utilized, comprising modelling approaches for multi-point thermal engine design, physics-based electrical component sizing and performance, aircraft sizing, mission design, and environmental assessment. Distributed propulsion with up to three propellers per wing is evaluated for aerodynamic benefits. With optimal wing redesign, drag reduction benefits only reach 1% for the selected aircraft class and flight velocities. Variable free power turbine speed operation is promising in reducing engine mass and improving performance of both thermal and electrical power systems. A combination of hybridization during take-off, climb and cruise defines the optimal design and operation guidelines for the hybrid concept. However, due to the increased mass of the battery and electrical power system, block fuel benefits only in the order of 5% are reported, compared to a turboelectric aircraft. When compared with a conventional configuration of same entry-into-service year, the series concept is outperformed in the examined range of battery assumed technologies.

The increasing demand for sustainable aviation fuels has prompted the exploration of hydrogen as a viable alternative for reducing carbon emissions in the aviation sector. The high gravimetric energy density of hydrogen makes it a promising candidate for future aviation fuel, offering significant potential to reduce the carbon footprint of air travel. While many articles on hydrogen aircraft design focus on the conceptual layout of fuel systems, they often lack critical details on the mass and size of key components and hydrogen boil-off during ground operation, which are vital for practical implementation. Through modeling and dynamic simulation analyses, this paper investigates the process of hydrogen fuel conditioning for gas turbines in aviation, focusing on the mass, sizing and performance of different components. The aircraft considered for this model consists of a 19-passenger with a 700 NM range that burns hydrogen in the GT directly. The sizing/design approaches of the most critical components, namely, the storage tank, heat exchanger, and pump are presented. The system-level analysis is presented for the flight mission profile. The parametric analysis is performed for a foam-insulated, storage tank with semihemispherical domes for the effects of ullage volume fraction, dormancy duration, and maximum storage pressure on gravimetric efficiency. Maximum efficiency occurs at low ullage fractions (0.05 0.1) and moderate tank pressures (4.0 5.0 bar). However, efficiency decreases with longer dormancy times. Liquid hydrogen is stored at 21 K and 1.5 bar, pressurized to 28 bar using a centrifugal pump consuming 1.47 kW at take-off. The hydrogen is then heated to the required combustor inlet temperature using a compact heat exchanger with an effectiveness of 0.5. The corrected gravimetric efficiency, considering the fuel conditioning system components, is 57% for a 2-hour dormancy and 53% for a 4-hour dormancy. A tank with gravimetric efficiency above 33% means that the combined mass of fuel and its storage will be lower than that of jet fuel. At 33%, the combined masses will be equal. Gravimetric efficiency of 57% is promising for a short and a medium hydrogen aircraft.

Although inter-compressor cooling has been investigated in the past, it is a completely new way of transferring energy to the hydrogen fuel at this point. High temperature differences from 30 K on the coolant side to more than 300 K after the booster compressor allow for smaller heat exchangers. Comparatively low Mach numbers lead to low pressure losses on the core flow. However, the modeling methods for this type of heat exchanger vary a lot from simple energy balance methods to 3D-CFD. During performance calculations a 3D-CFD is not feasible and more simple methods as the Number of TransferUnits suffer from uncertainties especially during off-design calculation. This paper suggests a conditioning system and a scalable performance map for hydrogen conditioners to be used as "inter compressor cooling"heat exchangers during cycle analysis. A tool for the calculation of heat exchangers in aviation with a higher lever of detail is used to design a tube bundle heat exchanger and create the performance map. A concept for the integration of the heat exchanger in the core engine is presented using 8 stacks distributed around the circumference. For a given geometry, errors in transferred heat below 1 % are achieved across the entire operating range of the engine. A 15 % scaling in effectiveness results in an error of only 3 % at the most loaded operating point. First conducted studies indicate to design an engine for the highest possible fuel temperature while using the least amount of air. This achieves the lowers thrust specific fuel consumption. The direct use of hydrogen as a coolant can lead to problems with icing due to wall temperatures in the heat exchanger matrix being below 0 °C. In addition, there are additional challenges with the safety of such a system. A completely different option for hydrogen conditioning is presented. This is the use of a full electrical conditioning.

Although intercompressor cooling has been investigated in the past, it is a completely new way of transferring energy to the hydrogen fuel at this point. High temperature differences from 30 K on the coolant side to more than 300 K after the booster compressor allow for smaller heat exchangers. Comparatively low Mach numbers lead to low pressure losses on the core flow. However, the modeling methods for this type of heat exchanger vary a lot from simple energy balance methods to 3D-CFD. During performance calculations a 3D-CFD is not feasible and more simple methods as the number of transfer units suffer from uncertainties especially during off-design calculation. This paper suggests a conditioning system and a scalable performance map for hydrogen conditioners to be used as "intercompressor cooling" heat exchangers during cycle analysis. A tool for the calculation of heat exchangers in aviation with a higher level of detail is used to design a tube bundle heat exchanger and create the performance map. A concept for the integration of the heat exchanger in the core engine is presented using 8 stacks distributed around the circumference. For a given geometry, errors in transferred heat below 1% are achieved across the entire operating range of the engine. A 15% scaling in effectiveness results in an error of only 3% at the most loaded operating point. First conducted studies indicate to design an engine for the highest possible fuel temperature while using the least amount of air. This achieves the lowers thrust specific fuel consumption. The direct use of hydrogen as a coolant can lead to problems with icing due to wall temperatures in the heat exchanger matrix being below 0 degrees C. In addition, there are additional challenges with the safety of such a system. A completely different option for hydrogen conditioning is presented. This is the use of a full electrical conditioning.

Hydrogen for propulsion could lead the industry to achieving the set environmental goals. This work performs a comparative cycle and engine design for a hydrogen-fired and conventional Jet-A burning configuration. Aircraft design and mission performance complete the conceptual design loop. A 19-passenger small commuter aircraft is investigated. A multi-disciplinary framework is developed for the study. A multipoint synthesis scheme is employed for conventional, and hydrogen powered engine assessment. Cryogenic hydrogen tanks and a thermal management system are integrated in the aircraft and their volumetric and gravimetric impact are assessed showing an expected 13% increase of aircraft mass. Direct combustion of hydrogen leads to more efficient and smaller turboprop engines due to the increased specific heat capacity of combustion products. Engine cycle design reveals that the optimum aircraft energy consumption lies at an overall pressure ratio at cruise of 15 and a combustor outlet temperature of 1,400 K. However, the hydrogen tanks and fuel conditioning system increase aircraft mass sufficiently to offset the fuel conthe H2 and Jet-A configurations by 3-4%. This work reveals a lower bound of H2 fuel system gravimetric performance due to aircraft weight certification and highlights the design guidelines for the engine, aircraft, and storage system.

Hybrid electric aviation is a possible step towards sustainable flight. Several hybrid architectures and synergetic concepts have been investigated. However, environmental performance results seem to be inconsistent due to deviations in technology assumptions and a mismatch between the fidelity of methodologies used for simulation of different aircraft systems. A multidisciplinary framework is developed, consisting of detailed modelling approaches for thermal and turbomachinery components, electrical power system design, aircraft/mission and environmental analysis. The framework is employed for the investigation of an Entry-Into-Service 2035 30 passenger commuter aircraft with a design mission of 1000 nautical miles. The investigation of parallel hybrid electric, turboelectric and series/parallel partial architectures is performed through a systematic conceptual design approach. The analysis reveals a bare minimum battery technology of 0.75 kWh/kg and 0.8 kW/kg, needed to compete with the conventional aircraft s performance. High degrees of hybridization (>20%) trigger the snowball effect of aircraft mass and thrust requirement, counteracting specific fuel and performance benefits generated by electrification. The turboelectric and series/parallel partial concepts are paired with an electrically driven boundary layer ingestion fan. For those concepts to result in any block fuel and emissions benefits compared to conventional counterparts, a drag reduction from wake ingestion of 7.5-10% is required, with power split ratios between the electrically driven fan and propellers being limited to 15% due to extensive mass increase.