Selecting the most promising aircraft configuration for the future short to medium range market segment is a challenging task in aircraft design. Many different unconventional aircraft configurations claim to reduce fuel consumption over a conventional evolutionary design approach, but comparison between the different concepts is often difficult. Hence, within the project NACOR (New innovative Aircraft COnfigurations and Related issues), a downselection process was applied that starts from a wide range of different unconventional aircraft configurations and gradually eliminating configurations that show lower fuel saving potential, while at the same time the applied methods increase in fidelity. The first downselection was based on expert judgement to evaluate the initial variation of twelve different unconventional aircraft configurations. For the second downselection, a literature study was conducted and an assessment process on very-low level of fidelity was applied. The third downselection employed an already established overall aircraft design (OAD) process, which was complemented for the remaining configurations. The final downselection further enhanced the OAD process, and sensitivity studies were conducted to investigate the potential of the configurations. The final result indicated that the blended wing body has a high potential to reduce fuel consumption compared to an appropriate conventional tube and wing aircraft design. This is a suitable starting point for subsequent research that will address the detailed design and identify potential challenges.

To enable a fair comparison when quantifying the impact of revolutionary new aircraft technologies, it is required to establish an evolutionary baseline configuration, having a realistic technology scenario fitting the projected state of the art for the targeted entry into service.To do so, first a reference aircraft that meeting the top-level aircraft requirements has to be selected, which provides a set of known values to calibrate the applied design methods. Then, the aircraft performance has to be forecasted by taking evolutionary technological improvements into account, assuming a technology scenario projected to be the state of the art at the targeted entry into service. Using the resulting configuration as basis, the revolutionary new technologies can be integrated and evaluated on the overall aircraft design level. In this way, it is possible to provide a fair comparison of technological benefits and to identify potential design drivers or challenges that may arise. The primary objective of this study is to assess the uncertainties associated with evolutionary technology assumptions in the context of aircraft design. Specifically, the focus is on evaluating how these uncertainties affect critical metrics such as block fuel, direct operating costs and climate impact. Through a probabilistic assessment, the aim is to present not just a nominal point of comparison for new technologies, instead a spectrum of potential solutions across different scenarios is provided. By incorporating insights from both a literature review on evolutionary technologies and an expert-based technology projection workshop, the uncertainties of the inputs were quantified and embedded in the DLR vehicle design process. The results highlight the impact range each evolutionary technology can have on key aircraft metrics, contributing to a more comprehensive understanding of overall aircraft performance and providing a solid basis for judging future aircraft designs incorporating revolutionary technologies.

For the evaluation of future aircraft architectures or novel technologies, a well-understood and sound reference to compare to is essential to prove the impact of intended changes. A reference aircraft serves as a basis for calibration of the aircraft and is used as a starting point for subsequent investigations, sensitivity studies or optimizations. The prime need for such a reference arose from the European Clean-Sky-2 project HLFC-Win (Hybrid Laminar Flow Control—Wing), where no industrial reference data for a conventional aircraft were available. The project investigates a HLFC system integrated into the wing aiming to reduce the wing drag and consequently reducing the fuel consumption. Therefore, this paper presents the D300-XRF1 designed by DLR, which is based on the AIRBUS research aircraft XRF1 (eXternal Research Forum). It is intended to be used as a reference aircraft database representing aircraft for medium- and long-range missions. A variable fidelity multidisciplinary design analysis and optimization (MDAO) aircraft design environment is set up to provide a consistent estimate of the geometry, mass breakdown, propulsion system, aerodynamics and aircraft performance. A conceptual aircraft design tool is utilized in the aircraft design environment to initialize the process, and higher-fidelity modules are used to enhance the results. The presented results describe the overall aircraft characteristics of the D300-XRF1 based on 2010 entry into service technology level and is offered to be used as a reference within the aviation research community, hopefully reducing similar design efforts in other research projects.The aircraft operates at a design cruise Mach number of 0.83, has a design range of 5500 NM and transports a payload of 31.5 t (300 PAX at 105 kg/PAX). The D300-XRF1 serves as a consistent reference aircraft database and provides a holistic overview of the aircraft’s performance that has been presented to and approved by AIRBUS. Therefore, this reference aircraft design can be used for future studies and to assess new technologies on a sophisticated level.

An aircraft is a complex system of systems. The engine, as a subsystem, strongly influences the design of other subsystems in a complex interplay by its performance characteristics, dimensions and mass. The ability to reliably model the overall aircraft and to find optimal designs within a short period of time is critical in the conceptual design phase to provide the basis for sound decision making. However, this is difficult to achieve since simplified engine models may lead to unreasonable results and more sophisticated models usually require the consultation of a propulsion expert. Therefore, a hybrid surrogate-based rubber engine approach is demonstrated that facilitates the exchange of disciplinary knowledge and enables the convenient integration of detailed engine models into multidisciplinary processes for overall aircraft design. A rubberized generic geared turbofan with an entry into service in 2035 is created to equip a long-haul, wide-body aircraft with different suitably sized engines from a multidimensional design space. In order to generate the training data for the surrogate-based rubber engine model, a multidisciplinary process for conceptual engine design is employed, which combines a multi point thermodynamic cycle analysis with flow path sizing, a basic aerodynamic analysis of turbomachinery, mass estimation on the level of single engine parts and a model to predict engine emissions. With the rubber engine model integrated into the aircraft design process, the off-design performance of individual engines is provided on-demand via tabulated maps, which are calculated in-the-loop. For a long-haul aircraft configuration, a bypass ratio of 14 is identified as optimal in terms of mission fuel considering snow ball effects. For growing bypass ratios, the thrust lapse increases leading to higher combustor inlet temperature and pressure at cruise operation. As a result, nitrogen oxide emissions increase with BPR for an assumed rich-burn quick-quench lean-burn (RQL) combustor and counteract savings in carbon dioxide and water emissions leading to minimum climate impact for a bypass ratio of 11. The minimum direct operating costs are realized for a bypass ratio of 12.

Two hybrid-electric 19-seater air vehicle concepts with a focus on noise reduction are designed and evaluated on a conceptual level. The objective is a significant noise reduction compared to a conventional reference aircraft. Short take-off and landing, mixed passenger and cargo transport capability with operations in the low speed domain are identified as suitable aircraft characteristics that could make a viable business case for hybrid-electric commuter aircraft. A parallel and a serial hybrid-electric propulsion architecture are investigated. The resulting aircraft designs are compared against a conventional baseline aircraft that uses state-of-the-art technology. The timeframe of the year of entry into service is set to 2030 in order to match the technology level of next-generation lithium batteries. The results indicate that the serial-hybrid electric architecture has the potential to cut the perceived take-off noise emissions in half and perform better in terms of energy efficiency compared to the parallel-hybrid architecture. Both aircraft designs are shown to reduce the block energy demand on a 200 km sector by more than 70 % compared to the conventional baseline aircraft.

By virtue of using efficient methods to compute the design sensitivities, such as the coupled adjoint methods, gradient-based optimization techniques allow aircraft designers to efficiently obtain an optimum design, that satisfies all considered constraints. The more constraints and disciplines engaged, the higher the reliability of the optimization output. Decision makers in aircraft industry, however, prefer to look at Pareto fronts rather than one optimum design before making their critical decisions, since such diagrams provide better understanding of the main trade-offs and compromises between the different targets that the aircraft is supposed to satisfy. Gradient-free algorithms have better reputation for generating Pareto fronts because these fronts result naturally. These algorithms are, however, relatively inefficient, even for single disciplinary high-fidelity optimizations. They are restricted by the number of design parameters and the size of the design space. Engaging more disciplines, more design parameters and higher fidelity computational models, to increase the reliability of the outputs, can only increase the computational cost of gradient-free algorithms, and quickly announce them to be not usable for the generation of Pareto fronts. This study investigates the generation of Pareto fronts efficiently, using gradient-based algorithms on the industry-relevant aircraft; AIRBUS XRF-1. The approach starts several optimizations with different weighting of objectives, in parallel. The multidisciplinary design chain, which is used in this study, was connected by experts in aerodynamics, structure and loads, propulsion and overall aircraft design. The generation of Pareto front was completed successfully for a multi-point multidisciplinary optimization task, where the use of gradient-free algorithms would have been computationally infeasible. As expected and mentioned in the literature, some regions of the Pareto front were not satisfactorily covered by employing this approach, which shows the necessity to look into different gradient-based approaches that search for optimal designs along the Pareto front.

Within the DLR project VicToria various high fidelity-based MDO processes were set-up as applicalble methods for aircraft design. Apart from aerodynamic optimization using high fidelity-based CFD analysis, the sub-processes overall aircraft design synthesis, loads analysis, and structural optimization were part of the MDO processes. The presented paper expounds such MDO sub-processes in order to exhibit their contributions and capabilities for the respected MDO process.

Cybermatrix is a novel approach to aircraft design through multidisciplinary optimization, developed within the DLR project VicToria. It combines three aspects: representing a design problem by an approximate Karush-Kuhn-Tucker system, distributing the rows of the system among disciplinary groups, and employing large computational resources and many humans experts in a parallel fashion. For demonstration an optimization of a long-range, twin-engine transport aircraft has been performed.

The DLR project VicToria brings together disciplinary methods and tools of different fidelity for collaborative multidisciplinary design optimization (MDO) of long-range passenger aircraft configurations, necessitating the use of high-performance computing. Three different approaches are being followed to master complex interactions of disciplines and software aspects: an integrated aero-structural wing optimization based on high-fidelity methods, a multi-fidelity gradient-based approach capable of efficiently dealing with many design parameters and many load cases, and a many-discipline highly-parallel approach, which is a novel approach towards computationally demanding and collaboration intensive MDO. The XRF-1, an Airbus provided research aircraft configuration representing a typical long-range wide-body aircraft, is used as a common test case to demonstrate the different MDO strategies. Additional results are presented for the NASA Common Research Model (CRM) to show their flexibility. Parametric disciplinary models are used in terms of overall aircraft design synthesis, loads analysis, flutter, structural analysis and optimization, engine design, and aircraft performance. The different MDO strategies are shown to be effective in dealing with complex, real-world MDO problems in a highly collaborative, cross-institutional design environment, involving many disciplinary groups and experts and a mix of commercial and in-house design and analysis software.

The potential of unconventional configurations to reduce the fuel consumption of future aircraft is investigated in the European Clean Sky 2 (ITD Airframe) ONERA-DLR project NACOR (New Aircraft Concepts Research-Call for Core Partners Wave 1). Two design missions are considered: a short/medium range mission (SMR) based on the requirements of an Airbus A320, and a business jet (BJ) mission. In this paper, an overview of the activities considering the conceptual aircraft design phase including initial high fidelity studies is provided.

Over the past decade, profound attention was given to exploring the benefits of engaging numerical multidisciplinary design optimization in aircraft design. Due to its importance, aerostructural wing design optimization is the most visited multidisciplinary problem in research institutes. To deal with this problem efficiently, gradient-based algorithms are popularly used. The complexity of the gradient-based aerostructural optimization, however, forced researchers to apply several simplifications to the problem formulation, such as neglecting engine effects or oversimplifying the loads process into few predefined load cases. The authors of this paper aim at running a gradients-based multidisciplinary design optimization of a commercial aircraft while including a powered engine and engaging a comprehensive, multi-fidelity loads process, subject to flutter as well as overall aircraft design constraints. The work, done by experts in the mentioned fields, is performed on a commercial aircraft provided by Airbus with many industry-relevant constraints. The results, showed the necessity to include a comprehensive loads process during the optimization. Additionally, it was concluded that engaging powered engines during the optimization is inevitable to come up with realistic designs; significantly different design geometries resulted when engaging a powered engine than when running the optimization with a flow-through nacelle.

In this paper, the preliminary aircraft design tool openAD is presented. Over the past years the DLR has developed a multidisciplinary and multifidelity design environment for aircraft design to evaluate and assess various concepts and technologies at aircraft level. Thereby, a valid and consistent design can be derived by a minimum set of top-level aircraft requirements. This design environment is highly modular where the domain specific tools are provided and hosted across the different DLR institutes. As part of the design process, openAD was developed as the key enabler for overall aircraft design and assessment.

The overall aircraft assessment is based on a wide range of disciplinary methodologies. In addition, a consistent aircraft design must be provided for the beginning of the aircraft design process. For this purpose, the DLR in-house conceptual aircraft design tool openAD has been developed for initialization and subsequent synthesis of results with higher fidelity. Within the aircraft design process, three disciplinary methods are introduced to improve the quality and accuracy of the performed design studies. These methods include engine performance, low speed performance and acoustics characteristics of an aircraft, which allows the predictions of the aircraft performance and noise level during the take-off and landing phase. The engine performance calculation is based on a thermodynamic cycle model and is an extension in openAD. Subsequently, the aircraft and engine performance are fed into the low speed performance tool LSperfo, which estimates the take-off and landing trajectory including the thrust requirements, flight path and aerodynamic forces. The aircraft and engine data are further passed to a noise tool, which predicts the aircraft model noise emission at relevant aircraft certification points. To demonstrate the result validity of the aircraft design environment and its disciplinary tools, a DLR interpretation of a turboprop engine aircraft (ATR 72 similar) is used. Since the tools are based on simple physical models, a proper calibration on appropriate reference aircraft needs be ensured for most overall aircraft design studies. Nevertheless, the results show a good estimation for take-off and landing field length as well as the noise level of the reference cases provided in this paper.