Hybrid-Electric Propulsion (HEP) could be part of the solution to decrease emissions associated with regional commercial aviation. This study presents results for the aircraft level fuel reduction potential of a regional turboprop concept with an HEP architecture and Entry-Into-Service (EIS) in 2035+. The configuration specifically tackles the elaborated challenges of introducing an additional electrical energy source to the configuration by employing a twofold electrical assistance to a turboshaft engine in combination with an innovative thermal management concept. Relevant components and disciplines were modeled and incorporated into an integrated aircraft design environment. The behavior and interaction of the HEP architecture with the aircraft was thoroughly investigated. A best-performing configuration was derived and compared with a conventional reference configuration following a State-of-the-Art (SoA) reference aircraft approach. For a typical mission with 200 nmi range, a block fuel reduction of 9.6% was found. However, the assumed battery performance characteristics limited the reduction potential and led to a fuel burn increase for the 600 nmi design mission. Furthermore, sourcing the non-propulsive subsystems directly from the on-board battery was detrimental. The innovative Thermal Management System (TMS) located in the propeller slipstream showed a synergistic effect with the investigated configuration.

The design of hybrid electric propulsion (HEP) systems involves multiple sizing requirements and operating conditions that affect aircraft performance. Assessing their overall potential requires the coupled consideration of hybridization, battery technology, mission utilization and operational constraints. Therefore, an integrated methodology combining HEP sizing with simplified aircraft design and performance methods is presented. A parallel HEP concept with an electrically assisted compressor is investigated for a 50 PAX regional aircraft and a 19 PAX helicopter, considering an Entry-Into-Service (EIS) in Y2035+. To enable operation without electrical assistance, gas turbine oversizing is applied. This comes with mass and efficiency penalties but significantly expands the operational hybridization range. At a battery system specific energy of 500 Wh/kg, the regional aircraft achieves a 1% block fuel reduction on the design mission (400 nmi), compared with a 22% reduction on the shorter typical mission (150 nmi) through increased battery utilization. For the helicopter, block fuel increases by 11% on the design mission, but decreases by 10% on the typical mission. The results demonstrate that aircraft utilization is a key factor for the sizing and assessment of parallel HEP systems.

Novel aircraft propulsion concepts based on electrochemical conversion technologies, such as solid oxide fuel cells (SOFCs), are being investigated to enable climate-neutral air transport. It is crucial to identify SOFC architectures that are relevant and capable of fulfilling the specific requirements for aerospace applications, i.e., optimization for mass and volume. For a mature design and performance synthesis of propulsion system concepts, including highly integrated SOFCs, more sophisticated component models are necessary for a clean and unified integration of SOFC technology. The models should include both electrochemical performance and sizing, as well as system integration, already at the early stages of system design and analysis. This work presents a MATLAB-based 0D approach within the Bauhaus Luftfahrt Aircraft Propulsion System Simulation (APSS) framework to model the steady-state operational characteristics of an SOFC stack and determine its preliminary size. The results serve as a basis to assess integration aspects and challenges for various SOFC architectures, such as planar or microtubular arrangements. For simulated fuel cell stacks, validation studies are performed to ensure realistic dimensioning, as well as selected analyses showing the sensitivity of the model and resulting stack size to relevant operating parameters, such as temperature or required power. The studies presented within this work are an important step towards enabling the design and subsequent evaluation of overall fuel cell-driven propulsion system concepts.