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

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

Conceptual structural design of an automated low altitude air delivery unmanned aerial vehicle

This work presents the conceptual structural design of the unmanned aerial vehicle concepts within the Automated Low Altitude Air Delivery (ALAADy) project of the German Aerospace Center (DLR). Three aerial vehicle concepts of a Gyroplane, a Fixed High-Wing with a Twin Boom V-Tail Aircraft and a Boxed-Wing Aircraft are treated in this work. Each of these aircraft concepts has its individual structure topology design for the same mission requirement. The main focus of this work is on the conceptual loads analysis and the conceptual structural design of each vehicle. The design and analysis of the structure is performed with the parametric finite element model generation and design process, MONA, of the Institute of Aeroelasticity of the DLR. The major result of the work is the estimation of the structural mass of each configuration and the comparison of the mass between these concepts. The mass comparison result is one of the major criteria among others such as the aircraft flight maneuverability that are used for the global evaluation of the aircraft concepts in the ALAADy project

Structural design of heavy-lift unmanned cargo drones in low altitudes

This chapter presents the conceptual loads analysis and the structural design of the unmanned cargo aircraft concepts within the Automated Low Alti-tude Air Delivery (ALAADy) project of the German Aerospace Center, DLR. Three concepts of a gyroplane, a fixed high-wing with a twin boom v-tail aircraft and abox wing aircraft are concerned in the project. The main focus is on the estimation of the structural weight of each unconventional aircraft configuration. However, the application of empirical formulations based on conventional aircraft configurations is not suitable for this task. Instead, the task is performed with a parametric design process which is designed to be used for the structural design of an unconventional aircraft. In this process, the structural models are set up as finite element models ina parametric manner. The loads analysis and the aeroelastic structural dimensioning are then performed using these finite element models. This process is developed by the DLR and it is called the MONA process. The major result of the process is the structural weight of each unmanned aircraft (UA) concept. Finally, the structural weights of all aircraft are compared. The weight comparison contributes to the global evaluation of the aircraft concepts within the ALAADY project. Based on the considered aircraft requirements, the considered load cases and the considered system masses, the gyroplane has the minimum structure weight of 2,720 kg

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

Application of a turbo electric aircraft design environment for boosted turbofan aircraft configuration studies

The current activities at the German Aerospace Center (DLR) and the associated consortium related to conceptual design studies of a Boosted Turbo fan configuration for a typical short range commission are presented. The Boosted Turbofan incorporates parallel hybrid architecture consisting of gas turbine, electric machines and batteries that add electric power to the fans of the engines. Furthermore, even though the fuel is substituted by electrical energy -at the cost of higher battery mass- the airframe of the aircraft is not notably impacted by the HEP system. Hence, it is a reasonable step towards hybrid electric aircraft due to less development risk. These current conceptual aircraft design activities regarding hybrid electric propulsion are organized within the scope of the project “Advanced Engine and Aircraft Configurations” (ADEC) of Clean Sky 2 at the DLR and the “Turbo electric Aircraft Design Environment” (TRADE) consortium consisting of the University of Nottingham, University of Märladalen, Technische Universität Berlin and coordinator Modelon Deutschland GmbH also part of Clean Sky 2. The DLR developed a conceptual aircraft sizing workflow built in the DLR’s “Remote Component Environment” (RCE) incorporating tools that are based on semi-empirical and low level physics based methods to evaluate hybrid electric aircraft. In contrast, the TRADE consortium developed a simulation and optimization design platform with physics-based models of higher fidelity for the analysis and optimization of individual systems and structural components. In contrast to ADEC, no overall aircraft design (OAD) is performed. Their optimization and assessment is based on an A320-like aircraft with a fixed airframe. There is interest to integrate the high-fidelity models into the DLR’s overall aircraft sizing workflow

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

Hybrid wing body as a low-noise aircraft from a multidisciplinary point of view

One important goal when reducing the environmental impact of an aircraft is the reduction of noise. There is a lot of potential for less noise impact when noise is a major objective from the beginning of the design phase. Within this contribution a hybrid wing body concept as a mid-range aircraft will be presented together with detailed studies of different disciplines like aerodynamics, acoustics structure and also handling qualities. How much noise reduction can be achieved? What are the advantages, where are the difficulties and weaknesses of such an aircraft configuration