Purpose -The aim of this study was to first establish foundational algebraic expressions that parametrically describe any advanced dual-energy storagepropulsion-power system (DESPPS) and then proceed to declare the array of fundamental independent variables necessary for the sizing and optimisation of such systems. Upon procurement of a pre-design-level integrated aircraft performance model and the subsequent verification against previously published high-end low-fidelity generated results, opportunity was taken in formulating a set of battery-based DESPPS related design axioms and sizing heuristics. Design/methodology/approach -Derivation of algebraic expressions related to describing DESPPS architectures are based on first principles. Integrated performance modelling by way of full analytical fractional change transformations anchored according to a previously published Energy Specific Air Range (ESAR) figure-of-merit originally derived using the Breguet-Coffin differential equation for vehicular efficiency. Weights prediction of sub-systems that constitute the entire aircraft including DESPPS constituents emphasises an analytical foundation with minimal implementation of linear correlation factors or coefficients of proportionality. An iterative maximum take-off weight build-up algorithm emphasising expedient and stable convergence was fashioned. All prediction methods pertaining to integrated performance were verified according to previously published battery-based DESPPS results utilising high-end low-fidelity methods. Findings -For all types of DESPPS, two new fundamental independent non-dimensional variables were declared: the Supplied Power Ratio (related to converted power afforded by each energy carrier); and, the Activation Ratio (describing the relative nature of utilisation with respect to time afforded by the motive power device associated with each energy source). For a given set of standalone sub-system energy conversion efficiencies, the parametric descriptor of degree-of-hybridisation (DoH) for Power was found to be solely a function of the Supplied Power Ratio, whereas in contrast, the DoH for Energy was found to be a more complex synthetic function described by comingling of Supplied Power Ratio and the Activation Ratio. Upon examination of the integrated aircraft performance model derived in this treatise, for purposes of investigating CO 2 -emissions reduction potential for battery-based DESPPS using kerosene as one of the energy sources, one salient observation was maximising the ESAR figure-of-merit is not an appropriate objective or intermediary function for future optimisation work. It was found maximising block fuel reduction through the use of maximum ESAR would lead to ever diminishing design ranges and curtailment of the payload-range working capacity of the aircraft. Practical implications -Opportunity is now given to design and optimise aircraft utilising any type of DESPPS architecture. It was established that designing for battery-based DESPPS aircraft can be achieved effectively...

Purpose -The aim of this paper is to assess the potential of fuel-battery hybrid narrow-body (180PAX) transport aircraft according to different design ranges for an entry-into-service (EIS) of 2035. Design/methodology/approach -The philosophy used in the design of the twin-engine fuel-battery hybrid concept is to use the power of an electric motor during cruise to drive a single propulsive device, whereas the other one is powered conventionally by an advanced gas turbine. A methodology for the sizing and performance assessment of hybrid energy aircraft was previously proposed by the authors. Based on this methodology, the overall sizing effects at aircraft level are considered to size the hybrid aircraft to different range applications. To evaluate the hybrid concept, performance was contrasted against a conventional aircraft projected to EIS 2035 and sized for identical requirements. Additionally, sensitivity of the prospects against different battery technology states was analysed. Findings -The best suited aircraft market for the application of the fuel-battery hybrid transport aircraft concept considered is the regional segment. Under the assumption of a battery-specific energy of 1.5 kWh/kg, block fuel reduction up to 20 per cent could be achieved concurrently with a gate-to-gate neutral energy consumption compared to an advanced gas-turbine aircraft. However, a large increase in maximum take-off weight (MTOW) occurs resulting from battery weight, the additional electrical system weight, and the cascading sizing effects. It strongly counteracts the benefit of the hybrid-electric propulsion technology used in this concept for lower battery-specific energy and for longer design ranges. Practical implications -The findings will contribute to the evaluation of the feasibility and impact of hybrid energy transport aircraft as potential key enablers of the European and US aeronautical program goals towards 2035. Originality/value -The paper draws its value from the consideration of the overall sizing effects at aircraft level and in particular the impact of the hybrid-electric propulsion system to investigate the prospects of fuel-battery hybrid narrow-body transport aircraft sized at different design ranges.

Purpose -The purpose of this paper is the multi-disciplinary conceptual investigation of a propulsive fuselage (PF) aircraft layout allowing for new performance synergies through closely coupled propulsion/airframe integration. The discussed aircraft layout facilitates the ingestion of the fuselage boundary layer and the utilization of wake filling, thus eliminating a significant share of fuselage drag. Design/methodology/approach -Based on consistent book-keeping standards for conventionally installed and highly integrated propulsion systems, key aspects of conceptualisation regarding airframe and propulsion system are presented. As a result of this, a PF aircraft configuration is proposed featuring a fuselage fan power plant in conjunction with two under-wing podded power plants. Parametric models for integrated aircraft and propulsion system sizing and performance analysis are discussed that are suitable for the consistent mapping of the characteristics intrinsic to a PF layout. In an initial benchmarking exercise, the vehicular efficiency potentials of the previously identified PF configuration are evaluated against an advanced conventional reference aircraft. Findings -During benchmarking, it was found that a best and balanced design for the proposed PF aircraft layout yields an increase in vehicular efficiency of approximately 10 per cent compared to the advanced conventional reference aircraft. Practical implications -The paper gives the reader an idea for the efficiency potentials achievable through a PF aircraft configuration, as well as guidelines for aircraft sizing and integrational aspects. It may serve as a basis for advanced studies in the future. Originality/value -The conceptual investigation of the PF concept idea, contributes to establishing the initial technical feasibility of this novel approach to synergistic propulsion system integration. The methods presented in this paper allow for the multi-disciplinary conceptual design sizing of a PF aircraft.

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Purpose -The aim of the paper is to establish the COst-Specific Air Range (COSAR) as a new figure-of-merit based on the cost of energy to optimise the flight profile of a hybrid energy aircraft. Design/methodology/approach -After reviewing the expression and the application of the specific air range (SAR) and of the energy-specific air range (ESAR), the need of a new figure-of-merit for flight technique optimisation of hybrid energy aircraft is motivated. Based on the specific cost of the energies consumed, the mathematical expression of COSAR is derived. To enable optimum economics operations, a cost index (CI) derivation is introduced for a variety of hybrid-electric concepts to consider the additional time-related cost. The application of COSAR and of the CI is demonstrated for cruise optimisation of a hybrid-electric retrofit aircraft concept. Findings -As a consequence of the consumption of multiple energy sources in a hybrid aircraft, optimisation according to the objective functions SAR and ESAR leads to minimum in-flight CO2 emissions and minimum energy consumption for a given stage length. While the optimisation of a single energy source aircraft according to these figures-of-merit directly results in minimum energy cost for a given unit range, this statement is no longer true for hybrid-energy aircraft. Consequently, introducing a new figure-of-merit established on the specific cost of the energies consumed enables flight technique optimisation for minimum energy cost of hybrid-energy aircraft. Additionally, the related time-cost is taken into account by means of a CI definition for minimum operating cost. Practical implications -COSAR may serve as an alternative to SAR used today as the standard figure-of-merit for fuel optimised flight profile. Using COSAR and the CI allow airlines to adapt the flight profiles of hybrid-energy aircraft fleets according to the energy market price and their related cost of time to determine optimum economical flight profile. Originality/value -Using COSAR as a figure-of-merit, the flight profile of hybrid energy aircraft can be optimised for minimum energy cost. Time-related costs are considered for optimum operating economics by utilisation of the CI definition for hybrid energy aircraft.

The Joule-/Brayton thermodynamic cycle is the base cycle of all major contemporary aero engines. Over the decades, the achievement of further significant improvements has become progressively challenging, and the increase of efficiency approaches physical limitations. In order to meet the ambitious long-term emission reduction targets, the introduction of radical new propulsion system concepts is indispensable. Various cycles promising significant efficiency improvements over the conventional Joule-/Brayton-cycle are being examined by the engine community. However, as no clear favorite has emerged from these potential technical solutions, a transparent methodological approach for the consistent evaluation of the concepts is necessary. Consistent thermodynamic description and performance metrics for three engine cycles are presented in this paper: The turbofan as reference and two radical engine cycles, namely the composite cycle and the cycle-integrated parallel hybrid. Laws for the estimation of component performance for large parametric variations are introduced. A method for the estimation of power plant system mass for the investigated engine cycles is proposed to evaluate fuel burn reduction. The studies substantiated that the turbofan improvement potential is saturating. The composite cycle engine offers a tremendous potential for fuel burn improvement of 24.5% over state of the art turbofan engines, which allows meeting the emission reduction targets in 2035. The cycle-integrated parallel hybrid engine improves the turbofan moderately with year 2035 technology, but is not capable of meeting the corresponding emission reduction targets on a short-to-medium range aircraft platform.

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Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. The first part focuses on the novel steam injecting and recovering aero engine concept. In the second part, the free-piston composite cycle engine concept is presented. Complementary to the two technical publications, this third part describes the cooperative project, which was initiated by an interdisciplinary consortium, aiming at the demonstration and the proof of concept of both aforementioned aero engine concepts. At the beginning of the project, simulations on propulsion, aircraft system, and test bench level will be conducted. On this basis, preliminary tests and fundamental experiments are planned in order to establish a solid basis for the demonstration. Finally, a system demonstration will be carried out at the laboratory level. Thus, the project allows for a final judgement on both the feasibility of the new concepts and the attainability of the requirements for future aircraft propulsion systems.