The aircraft’s environmental performance on fleet level is so far completely decoupled from the design process. The climate impact from aviation arising from non-CO2 effects are largely independent from CO2 emissions, but rather depend on the atmospheric state. Previously complex climate-chemistry models were used to evaluate the non-CO2 emissions impact on climate. This is far too computationally demanding for a multidisciplinary design optimisation (MDO) process, requiring a multitude of climate impact evaluations. The question then is, how to efficiently design the next generation climate optimal aircraft? In this paper, a new concept for designing aircraft with minimum climate impact using Climate Functions for Aircraft Design (CFAD) is presented. The content of this paper provides an overview of the development of these innovative CFAD and demonstrates the ability to be integrated in an existing MDO framework. The mitigation potential by optimising aircraft design using CFAD is analysed with respect to different cruise conditions and by minimizing the overall climate impact. To validate the CFAD, a higher fidelity assessment is carried out. Finally, the key performance indicators, i.e. fuel consumption, flight time and operating cost, of the optimised aircraft design are compared to that of the reference aircraft.@en

Aviation contributes to about 3.5% of the total anthropogenic climate change when including non-CO2 effects, e.g., contrail formation and the impact of NOx emissions on ozone and methane. Among various non-CO2 effects, the contrail-cirrus radiative forcing is the largest (~2/3) with large uncertainties. The most critical affecting factor is the huge weather-induced variability of the radiative impact of individual contrails, which imposes challenges on formulating adequate mitigation measures and develop policy-driven implementation schemes, stressing relevance of reliable forecasts. The newly funded EU project BeCoM intends to address the uncertainties related to the forecasting of persistent contrails and their weather-dependent individual radiative effects. The project will focus on: 1) obtaining a larger and higher resolution database of relative humidity and ice supersaturation at cruise levels for assimilation into numerical weather prediction (NWP) models; 2) providing more adequate representation of ice clouds in their supersaturated environment in the NWP models; and 3) validation of the predictions to determine and reduce the remaining uncertainties of contrail forecasts. To facilitate the assimilation and validation process, a novel hybrid artificial intelligence algorithm will be developed. Based on the contrail prediction, the project will develop a policy framework for effective contrail avoidance through a trajectory optimization approach. The results will enable a better understanding of contrail’s climate impact and formulate recommendations on how to implement strategies to enable air traffic management to reduce aviation's climate impact.@en

Aviation ensures mobility for both passengers and goods. It is important as a transport sector for connections on and between continents. Nevertheless, aviation also contributes to anthropogenic climate change. The effects are usually divided in CO2 and non-CO2 effects and therefore not only CO2 emissions but also other emissions (e.g., NOx , water vapour or soot) and contrails are covered. To reduce the effects of aviation’s climate impact, several mitigation options are applied. One approach are climate change functions, which will be addressed here. The concept of climate change functions was used in previous projects, e.g. REACT4C, WeCare, ATM4E. The goal of these functions was to optimize the aircraft routes regarding the calculated climate impact. Climate change functions measure the climate impact per unit emission for a specific day, which considers the current meteorological conditions. Climate change functions were previously used to optimize the aircraft routings. The concept should now be applied for the optimization of the aircraft design as well since the promising concept is currently missing for the application of aircraft design optimization. The climate functions for aircraft design will connect the aircraft design with the climate impact of various emission in order to be able to optimize the aircraft design. For the calculation of the functions, it is necessary to define a specific application. This application results from a combination of aircraft design parameters. Aircraft design parameters can be for example flight altitude, climb rate, speed or range. Based on a resulting emission inventory, the temperature response can be calculated with the model “AirClim”. This model calculates with the input, first, the radiative forcing and based on that the temperature change. The final development step is the verification of the climate functions.@en

Approximately 50–75% of aviation's climate impact is caused by non-CO₂ effects, like the production of ozone and the formation of contrail cirrus clouds, which can be effectively prevented by re-routing flights around highly climate-sensitive areas. Here, we discuss options how to incentivize re-routing approaches and apply multicriteria trajectory optimizations to demonstrate the feasibility of the concept of climate-charged airspaces (CCAs). We show that although climate-optimized re-routing results in slightly longer flight times, increased fuel consumption and higher operating costs, it is more climate-friendly compared to a cost-optimized routing. In accordance to other studies, we find that the averaged temperature response over 100 years (ATR (Formula presented.)) of a single flight can be reduced by up to 40%. However, if mitigation efforts are associated with a direct increase in costs, there is a need for climate policies. To address the lack of incentivizing airlines to internalize their climate costs, this study focuses on the CCA concept, which imposes a climate charge on airlines when operating in highly climate-sensitive areas. If CCAs are (partly) bypassed, both climate impact and operating costs of a flight can be reduced: a more climate-friendly routing becomes economically attractive. For an exemplary North-Atlantic network, CCAs create a financial incentive for climate mitigation, achieving on average more than 90% of the climate impact reduction potential of climate-optimized trajectories (theoretical maximum, benchmark). Key policy insights Existing climate policies for aviation do not address non- (Formula presented.) effects, which are very sensitive to the location and the timing of the emission. By imposing a temporary climate charge for airlines that operate in highly climate-sensitive regions, the trade-off between economic viability and environmental compatibility could be resolved: Climate impact mitigation of non- (Formula presented.) effects coincides with cutting costs. To ensure easy planning and verification, climate charges are calculated analogously to en-route and terminal charges. For climate mitigation it is therefore neither necessary to monitor emissions ((Formula presented.) (Formula presented.), etc.) nor to integrate complex non- (Formula presented.) effects into flight planning procedures of airlines. Its implementation is feasible and effective.

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Approximately two third of aviation’s climate impact is caused by non-CO2 effects, like the production of ozone and the formation of contrail-cirrus clouds, which can be effectively prevented by re-routing flights around highly climate-sensitive areas. Although climate-optimized re-routing results in slightly longer flight times, increased fuel consumption and higher operating costs, it is up to 60% more climate-friendly. However, if mitigation efforts are associated with a direct increase in costs, this immediately raises the question of the willingness of primarily profit-oriented airlines to act in a more climate-friendly manner and the passengers´ willingness to pay for environmental protection. In order to create an incentive for climate-optimized flying, a climate charge is imposed on airlines when operating in these areas. If climate-charged airspaces (CCAs) are (partly) bypassed, both climate impact and operating costs of a flight can be reduced: a more climate-friendly routing becomes economically attractive (explanation video). By implementing the precautionary and polluter-pays principles of environmental economics, the concept introduces key requirements of a sustainable development into the field of aviation. The proposed extension of the accounting system clearly reduces the discrepancy between the marginal costs estimated by the airlines and the consequential costs for society. Accordingly, this resolves the trade-off between economic viability and environmental compatibility and creates a financial incentive for climate mitigation. The feasibility of this concept is demonstrated on a small route network in the North Atlantic flight corridor (NAFC). If flights are completely re-routed around altered CCAs, on average more than 90 % of the mitigation potential of climate-optimized flying is achieved. @en

Aviation is a highly necessary transport sector in our modern society. It guarantees mobility on a short- and long-range spectrum and is still a growing sector. However, aviation also contributes signi_cantly to the anthropogenic climate change via CO2 and non-CO2 e_ects. One possibility to reduce the climate impact of aviation would be to optimize the aircraft at the design level. Another possibility is to optimize the operations, e.g. to avoid climate sensitive regions in the ight route. To derive modelling capabilities, we review the climate impact of aviation with a focus on climate optimization of aircraft operations and design. The overall climate impact of aviation based on CO2 and non-CO2 e_ects is analyzed under consideration of contrails and di_erent emissions like CO2, NOx, and H2O. The connection to the related temperature change is shown via the climate sensitivity for each species. An overview over the most common climate metrics, including radiative forcing, global warming potential, global temperature potential, and the average temperature response is given in order to _nd the most suitable climate metric for aircraft design purposes. During previous studies within various projects, e.g. WeCare, REACT4C, and ATM4E, climate optimization strategies for aircraft operations were investigated. The aircraft routes regarding the ight path or altitude can be adjusted in regard to climate considerations, also in dependence on the current weather situation. In these projects, climate change functions and algorithmic climate change functions were developed which could potentially facilitate the climate optimized routings. The aircraft design for climate optimization di_ers from the approach to optimize the design for reduced cost or reduced fuel burn. For the climate impact, ying slow and low is bene_cial which was shown in the project CATS, but this is not reected in the current aircraft design. Therefore, previous studies propose redesigned aircraft. The relation between climate, aircraft operations and aircraft design is used to point out the requirements for modelling resulting from that. The focus is on the connection between climate and operations on one side, and on the connection between climate and design considerations on the other side. Currently, the model capacity for aircraft design does not support the climate optimized design. Therefore, deriving climate functions for aircraft design is highly important which will be one of the main goals in the Clean Sky 2 project GLOWOPT (Global-Warming-Optimized Aircraft Design). @en

Given the comparably high impact of aircraft emissions, especially their non-CO2 effects, on climate in the order of 5%, aviation stakeholders are required to act to reduce the warming effects of air traffic. Besides new operational procedures, like e.g. climate-optimized routing, this demands the development of completely new global-warming optimized aircraft by aircraft manufacturers. The European Clean Sky 2 project "Global-Warming Optimized Aircraft Design" (GLOWOPT) aims at providing aircraft designers an innovative tool to perform aircraft design studies for minimum climate impact, which we call Climate Functions for Aircraft Design (CFAD). The CFAD will substantially change the way aircraft are designed, while maintaining compatibility to existing Multidisciplinary Design Optimization (MDO) methods. The functions need to integrate a lot of information on the typical aircraft usage, including the routes the aircraft will be operated on. This is because, besides the amount of emissions, the impact of aviation non-CO2 effects, such as NOx, H2O as well as contrails, on climate is highly dependent on location (i.e. latitude, longitude) and altitude. So, the representative operating profile of the aircraft needs to be considered in a characteristic route and fleet model. This work will present the interdisciplinary GLOWOPT approach, which comprises expertise on aircraft design, operations, atmospheric physics and climate. Conceptual thoughts on how the complexity of the operating profile in combination with the geographically variable climate impact of aircraft emissions will be reduced such that it can be used in an aircraft design process are given. @en

Within this study, the lack of incentivizing airlines to internalize their climate costs is tried to be closed by the introduction of climate-charged airspaces, as non-CO2 emissions have locationand time-dependent effects upon the climate. In order to create an incentive for airlines to minimize flight time and emissions in highly climatesensitive regions, a climate charge is imposed for airlines when operating in these areas. Costminimizing airlines are expected to re-route their flights to reduce their climate charges and hence cash operating costs. Accordingly, this leads to the desired outcome of incentivizing climate mitigation and even of driving technological innovation towards cleaner technologies. The evaluation of the climate impact mitigation potential of climate-charged airspaces is performed based on optimal control techniques. Climate sensitivities are expressed by climate change functions characterizing the climate impact caused by an emission at a certain location and time. The cost-benefit potential (climate impact mitigation vs. rise in operating costs) is investigated for a Transatlantic route and benchmarked against climate-optimized trajectories. @en

Besides CO2, the climate impact of commercial aviation is strongly influenced by non-CO2 effects, which are highly sensitive to meteorological conditions and their spatial variations. To assess the cost-benefit potential (climate impact mitigation vs. cost increase) of climate and weather optimized flight trajectories in the North Atlantic flight corridor, optimal control techniques are applied. However, the execution of multi-criteria route optimizations for an intercontinental route network and various weather patterns is computationally highly intensive. Since computational resources are limited, a reduced surrogate route network is generated and evaluated first with regard to the computational effort, the coverage in terms of available seat kilometers, as well as the accuracy of reproducing the original route network with regard to climate impact. The proposed reduced route network consists of 40 routes (original network: 1,359) and is able to reproduce the climate impact of the original route network with reasonable climate impact deviations of 2.5%. The evaluation of climate and weather optimized trajectories is performed for the top route of the surrogate network. The maximum climate impact reduction potential is differing strongly from 9% up to 60% for varying North Atlantic weather patterns. Averaged over the weather patterns, a maximum climate impact mitigation potential of about 32%, going along with a cost increase of about 8% has been estimated. However, at a cost penalty of 1%, a potential climate impact reduction of 24% has been observed @en

The WeCare project (Utilizing Weather information for Climate efficient and eco efficient future aviation), an internal project of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR), aimed at finding solutions for reducing the climate impact of aviation based on an improved understanding of the atmospheric impact from aviation by making use of measurements and modeling approaches. WeCare made some important contributions to advance the scientific understanding in the area of atmospheric and air transportation research. We characterize contrail properties, show that the aircraft type significantly influences these properties, and how contrail-cirrus interacts with natural cirrus. Aviation NOx emissions lead to ozone formation and we show that the strength of the ozone enhancement varies, depending on where within a weather pattern NOx is emitted. These results, in combination with results on the effects of aerosol emissions on low cloud properties, give a revised view on the total radiative forcing of aviation. The assessment of a fleet of strut-braced wing aircraft with an open rotor is investigated and reveals the potential to significantly reduce the climate impact. Intermediate stop operations have the potential to significantly reduce fuel consumption. However, we find that, if only optimized for fuel use, they will have an increased climate impact, since non-CO2 effects compensate the reduced warming from CO2 savings. Avoiding climate sensitive regions has a large potential in reducing climate impact at relatively low costs. Taking advantage of a full 3D optimization has a much better eco-efficiency than lateral re-routings, only. The implementation of such operational measures requires many more considerations. Non-CO2 aviation effects are not considered in international agreements. We showed that climate-optimal routing could be achieved, if market-based measures were in place, which include these non-CO2 effects. An alternative measure to foster climate-optimal routing is the closing of air spaces, which are very climate-sensitive. Although less effective than an unconstrained optimization with respect to climate, it still has a significant potential to reduce the climate impact of aviation. By combining atmospheric and air transportation research, we assess climate mitigation measures, aiming at providing information to aviation stakeholders and policy-makers to make aviation more climate compatible.@en

A method is developed for the conceptual design of the root airfoil of aft-swept wings, based on wing planform parameters and a baseline airfoil in the outboard wing. The aim of the design is to reduce form drag at the root by creating straight upper-surface isobars. The analysis of the pressure distribution over the root airfoil is based on two analytical methods: one for estimating the root e ect due to thickness and one for estimating the root e ect due to lift. These methods are combined with a vortex lattice method and a two-dimensional panel method to be able to estimate the pressure distribution over the root airfoil. This method is coupled with an optimization algorithm to allow for the design of the root airfoil using a CST parametrization. Results show that the designed airfoils have the expected characteristics of a typical swept-wing root airfoil in terms of camber, position of maximum thickness and incidence angle. However, further refinements to the method are required to predict the increase in thickness-to-chord ratio.@en