Integration Strategies for a Fuel-Driven Range Extender on a 19-Seater Battery-Electric Aircraft

In the government funded LuFo-project TELEM, a battery-electric concept with a fuel-driven range extender has been selected as the most promising aircraft configuration to improve the energy efficiency while aiming to minimize the additional cost brought about by the hybrid-electric power train. Different installation options for the range-extender, such as the nose and the aft section of the fuselage as well as on top behind the wing and in a nacelle, are discussed. The installation in the front and aft section of the fuselage stand out to be two good options and are therefore compared on a quantitative level. Conceptual aircraft design models are created for the hybrid-electric concepts as well as a conventional reference aircraft model based on the Do228 commuter aircraft employing an adapted version of the tool openAD. Furthermore, a fleet-level energy consumption assessment against the reference aircraft is carried out and results in a quasi-parity between the front- and aft-integrated range extenders. A technology scenario with an entry-into-service in 2035 was selected for the electric components. In this scenario large double-digit reductions in energy and fuel consumption compared to the reference aircraft are achieved. This excludes structural or aerodynamic improvements of the airframe and is only driven by the integration of the hybrid-electric concept

Architectural Trade-offs for a Hybrid-Electric Regional Aircraft

Research entities and the aviation industry are collaborating to reduce the greenhouse gas emissions of the global aircraft fleet. To move away from fossil fuels as energy carrier while reducing the aircrafts primary energy demand are the ideal but challenging means to achieve this target. The research activities within the German government funded project TELEM have shown on a conceptual level that both measures could be realized for regional aircraft with an optimized hybrid-electric propulsion (HEP) ar- chitecture. Short, but very frequently flown distances of 200 nm and more could be served fully electri- cally by advanced propeller-driven aircraft with an assumed entry-into-service (EIS) in 2035. This paper gives an overview of integration concepts pursued in the project and reflects on various design aspects of a plug-in hybrid-electric aircraft, featuring a fully electric flight capability and a kerosene-fueled tur- boshaft range-extender. The aircrafts HEP architecture is optimized with regard to the number of pro- pellers, as well as range extenders and their integration concept as to yield the best efficiency and to enable commonality with smaller aircraft leading to potential cost reductions among aircraft classes. Furthermore, a thermal management system, which is essential for the hybrid-electric propulsion archi- tecture and its requirements are discussed and a favorable option selected. The final configuration fea- tures ten propellers and one range extender. The results also confirmed the exceptional efficiency of a plug-in HEP architecture for regional aircraft, showing a 34.6 % reduction in fleet energy and 64.4 % reduction in fuel consumption compared to a conventional turboprop architecture with an EIS in 2035

Conceptual Loads Assessment of Aircraft with Fuselage Integrated Liquid Hydrogen Tank

The advancing climate change and the necessity for climate-neutral mobility to reduce the impact of air traffic on global warming are leading to new demands on the aviation industry. Hydrogen fuel offers a promising opportunity to achieve the high energy requirements of commercial aircraft with zero-emission [1,2]. Hence, aircraft with liquid hydrogen propulsion architecture are one key to meet the challenging requirements for climate-neutral aviation without fundamental configuration changes. Three hybrid-hydrogen aircraft concepts have been already proposed by Airbus as part of their zero-emission (ZEROe) program to develop a zeroemission commercial aircraft by 2035 [3]. The EXACT (Exploration of Electric Aircraft Concepts and Technologies) project of the German Aerospace Center (DLR) the main concern is the investigation and optimisation of hybrid-electric propulsion system concepts and overall aircraft design (OAD) for possible configurations. Furthermore, the impact of those aircraft configurations on climate, energy supply, aircraft costs and their ecological balance during a lifecycle are investigated [4]. This paper presents the current activities of the DLR on liquid hydrogen aircraft configurations in conceptual aircraft design with respect to conceptual loads estimation and analysis. The work in this paper is related to the overall aircraft design of such aircraft configurations with special emphasis on the structural dimensioning and mass estimation of fuselage, wing and liquid hydrogen tank taking conceptual loads into account. For the OAD a multidisciplinary design process was implemented using DLR in-house tools. For this purpose, the Remote Component Environment (RCE) software [5] is utilized, where the available tools are used to build up such an OAD workflow. For the data exchange within RCE the Common Parametric Aircraft Configuration Schema (CPACS) [6] is used, where the parametrized aircraft data are stored. The work briefly presents the analytical handbook methods used in the in-house tools LOADzero [7] and LGLOADzero for the estimation of flight, ground and landing loads. The tools have been designed for quick loads estimation for a rigid aircraft and have been further developed to meet new challenges in liquid hydrogen overall aircraft design. The focus is on the loads assessment of aircraft with fuselage integrated liquid hydrogen tank in conceptual design. The impact of additional masses of the hydrogen tanks and therefore altered mass models on conceptual loads is analysed. Critical load cases crucial for structural dimensioning are identified to investigate the influence of the varying masses in more detail. Therefore, a loads comparison is carried out between the baseline aircraft configuration and aircraft with fuselage integrated liquid hydrogen tanks

Impact of the Number of Wing Stations on the Twist Distribution of a BWB Conceptual Aircraft Design in a MDAO Environment to Match Target Lift Distribution

The design of a blended wing body (BWB) has been the subject of numerous research projects worldwide, as it offers significant advantages over a conventional tube-and-wing configuration. The European Clean Sky 2 project NACOR investigated the potential of innovative unconventional aircraft architectures. A BWB configuration was identified to reducing fuel consumption by 10% compared to a relevant reference aircraft with entry into service 2035 and prevailed against box-wing or strut-braced wing aircraft. For this reason, the need to be capable of designing and evaluating BWB configurations was recognized. Especially for the design of BWBs, an optimized wing twist is important to achieve high aerodynamic performance, but on conceptual design level the number of wing stations is often limited to reduce complexity which impedes this optimization. Computationally expensive calculations such as Reynolds-averaged Navier-Stokes (RANS) or Euler method are required to optimize wing twist, but this reduces the number of possible designs examined in a given time. Therefore, this paper presents the feasibility of flexible number of wing stations to achieve an aerodynamically optimized wing twist for BWB architectures on conceptual aircraft design level with embedded low fidelity multi-lifting line approach. The aim of the flexible wing modelling combined with a multi-disciplinary design analysis and optimization (MDAO) aircraft design environment is to exploit the benefits of low computational costs and high flexibility with respect to the vehicle architecture to be analyzed with an adequate level of fidelity. The resulting fast analysis capability enables a wide range of possible sensitivity studies and optimizations to ensure a more robust aircraft design space exploration. The target lift distribution is determined by high fidelity RANS calculations and used as an objective function for the twist optimization. In addition, typical lift distributions, i.e. elliptical and triangular lift distributions, are used to benchmark the results. The final results show the influence of the number of wing stations on the resulting twist distribution, induced drag as well as the CPU cost, and provide a proposal for an appropriate number of wing stations to be used

Analytical fuselage structure mass estimation using the PANDORA framework

Air traffic emissions have a significant impact on our environment and on the climate change. Since 2020, multiple research activities have been conducted at the German Aerospace Center (DLR) in the project “Exploration of Electric Aircraft Concepts and Technologies” (EXACT) to analyse the potential of eco-efficient aircraft concepts to reduce emissions. To handle the complexity on aircraft pre-design level, the usage of multidisciplinary design optimization (MDO) workflows and a common aircraft description format are an established procedure at DLR. The framework “Remote Component Environment” (RCE, [1]) is used to build MDO-workflows while the aircraft is described using the “Common Parametric Aircraft Configuration Schema” (CPACS, [2]). Different specific disciplines for aircraft design are part of the EXACT project to assess hybrid-electric aircraft concepts including the estimation of flight performance, loads and structural masses of the aircraft. At the Institute for Structures and Design (BT) the primary fuselage structural mass is estimated for different aircraft concepts using fast analytical methods based on the fuselage geometry, the definition of primary structures like frames and stringers and the application of cut-loads on the fuselage for different loadcases. This capability is implemented in the Python-based modelling and sizing framework called “Parametric Numerical Design and Optimization Routines for Aircraft” (PANDORA, [3]), which is under development since 2016. The PANDORA environment integrates developments like generating finite element (FE) models of aircraft based on CPACS parameters, converting FE models between different solver formats, creating and editing CPACS models and numerical as well as analytical sizing of aircraft models. In addition, more detailed FE models with different discretization approaches can be generated for crash and ditching simulations (EASN 2021 [4]). An overview of the PANDORA framework and some results of the EXACT project are given in this presentation

Semi-Physical Method for the Mass Estimation of Fuselages carrying Liquid Hydrogen Fuel Tanks in Conceptual Aircraft Design

Hydrogen-powered aircraft can contribute to the effort of reducing aviation´s climate impact. A better understanding of the hydrogen storage with respect to airframe integration is required to improve the predictive qualities of overall aircraft design studies. This paper presents recently developed disciplinary models and their synthesis into overall aircraft design. The focus is the assessment of non-integral liquid hydrogen tanks and their impact on fuselage structures. The introduction of loads analysis and analytical design of primary fuselage structures is able to capture more design sensitivities and reduces the uncertainties compared to a design process that fully relies on empirical methods. Particularities due to unconventional fuel tank integrations for instance in the back of the fuselage are reviewed and quantified by means of the presented tool landscape

System noise assessment of conceptual tube-and-wing and blended-wing-body aircraft designs

Within the DLR’s internal project SIAM, future low-noise aircraft designs for a medium range civil transport aircraft are created. An existing system noise simulation process is further upgraded in order to process aircraft designs and expert input from other DLR expert groups and enable a specified and documented overall assessment. Vehicle concepts from different groups are processed and subject to a comparative assessment in order to judge the acoustic performance of these vehicles against each other. The selected vehicles are evolutionary concepts in the form of low-noise variants of conventional tube-and-wing aircraft and revolutionary blended-wing-body concepts. Specific project goals are defined for this comparative assessment. One project goal is to reduce the total aircraft noise by at least 2 EPNdB at each certification location relative to a current state-of-the-art reference aircraft designed for an entry into service in 2035. In addition, since airframe noise is typically not relevant at the certification locations, an airframe specific noise goal is defined, which requires the airframe noise level during approach to be lower than for the reference aircraft’s. This goal is assessed in the maximum A-weighted SPL metric, because the EPNL metric cannot be evaluated for individual components. In addition to the two project noise goals mentioned above, the SEL contour areas along approach and departure are evaluated, because they determine the overall impact of new vehicles on long-term noise contours when operated in a fleet or assessed within an airport scenario. However, those aspects are not covered within this study, because its focus lies on single event noise. Ultimately, all vehicles are evaluated against the ambitious "Flightpath 2050 goal" for perceived noise level reduction. While it is demonstrated that significant noise reductions can be achieved in certification levels and SEL contour areas, the "Flightpath 2050" goal cannot be achieved at the sideline location. To reach this goal, additional technical measures are required

Preliminary Design of Composite Wings using Beam-based Structural Models

In this contribution a multidisciplinary process for the conceptual wing design is presented. The process chain covers the calculation of flight, ground and landing loadcases as basis for the wing sizing, where a gradient-based structural optimisation framework is used. Therefore, stresses and displacements for the criteria evaluation are provided by a beam-based structural model with high computational efficiency