Material Composition Based Aerostructural Optimization of High-Aspect Ratio Wings for Reducing Life-Cycle Environmental Impact ^†

Abstract

The rapid growth of global air traffic places the aviation industry under dual pressure: meeting increasing demand for aircraft while substantially reducing life-cycle environmental impacts. As advancements in aerodynamics, propulsion, and the adoption of lightweight composite materials continue to reduce operational fuel burn, the relative significance of manufacturing and End-of-Life phases is expected to increase. This study develops a low-fidelity aerostructural optimization framework for high aspect ratio wings that integrates life-cycle considerations into early-stage material selection. Using aluminum and carbon fiber reinforced polymers (CFRP) as reference materials, the framework quantifies trade-offs in mass savings, fuel burn, and CO₂ equivalent emissions across production, operations, and disposal phases. Results show that while CFRP offers substantial benefits in structural efficiency and operational emissions, aluminum performs more favorably in End-of-Life scenarios due to its high recyclability. The study further evaluates the potential of Sustainable Aviation Fuel (SAF) blending as a complementary decarbonization lever, revealing that moderate SAF adoption can offset part of the operational advantage of CFRP. Overall, this work demonstrates the importance of coupling material choice with life-cycle assessment in aerostructural design and outlines a pathway toward multi-objective optimization frameworks that balance performance with environmental sustainability.

1. Introduction

The global aviation sector is undergoing a profound transformation driven by the simultaneous need to meet increasing air traffic demand and to meet ambitious climate neutrality targets. Commercial aircraft manufacturers are therefore challenged to improve the environmental performance of future fleets throughout their entire life cycle, from raw material extraction to End-of-Life (EOL) processing. Historically, the environmental footprint of aircraft has been dominated by operational fuel burn, representing nearly 90% of total life-cycle emissions for conventional tube and wing configurations [1]. Advances in aerodynamics, high-bypass propulsion systems, and lightweight composite structures have significantly reduced operational emissions in recent decades. However, when these ongoing industry efforts are coupled with disruptive technologies ranging from alternative fuel pathways to novel aircraft configurations, the proportion of environmental impact attributed to manufacturing and EOL stages is projected to increase, making material production, scrap generation, and recycling efficiency increasingly critical [2,3].

The extensive use of carbon fiber reinforced polymers (CFRP) in modern airframes exceeding 50% by mass in aircraft, such as the Airbus A350 [4] and Boeing 787 [5], has enhanced operational efficiency but also introduced new environmental challenges [6]. CFRP manufacturing is highly energy-intensive, produces limited recyclable output, and results in substantial non-recyclable waste [1,7].Conversely, traditional aluminum alloys remain attractive due to their low energy intensity, high recyclability, and well-established supply chains, despite their higher structural weight compared with composites [7]. In this context, determining the optimal material composition for aircraft structures requires a holistic life-cycle perspective rather than a purely performance-driven one.

Previous studies [8,9] have primarily integrated life-cycle assessment with Overall Aircraft Design (OAD) to support decisions such as fuel selection or range optimization, relying largely on empirical aircraft sizing and mass-estimation methods. In contrast, the present work introduces a material-based aerostructural approach that links life-cycle impacts directly to structural design choices.

This work addresses this gap by developing a low-fidelity aerostructural optimization framework for high aspect ratio wings that incorporates life-cycle metrics into material selection. Aluminum and CFRP are evaluated as baseline materials for wing skins and spars, enabling a systematic comparison of mass, structural behavior, fuel burn, Carbon Dioxide Equivalent (CO₂eq) emissions, and waste generation.influence of Sustainable Aviation Fuel (SAF) blending is also examined as a complementary operational decarbonization strategy. In addition, a preliminary multi-objective material optimization is proposed using an “effective material” representing continuous mixtures of metallic and composite properties.

Overall, this methodology supports environmentally informed conceptual aircraft design by quantifying trade-offs between structural performance and life-cycle sustainability.

2. Materials and Methods

The methodology developed in this study integrates physics-based low-fidelity aerostructural optimization with the environmental implications of material choices for the design of a wingbox for comparing aluminum and CFRP material architectures.

2.1. Aerostructural Optimization Framework

The aerostructural analyses are performed using OpenAeroStruct, an open-source framework that couples a vortex lattice aerodynamic model with a finite-element representation of the wingbox, enabling rapid estimation of aerodynamic performance, structural deflections, wingbox mass, and fuel burn [10]. The optimization minimizes fuel burn and wingbox mass by sizing the skin and spar web thicknesses. While high-fidelity effects such as detailed stress concentrations, nonlinear material behavior, and viscous aerodynamics are not explicitly captured, the framework is appropriate for comparative studies at the conceptual design stage. The default OpenAeroStruct formulation assumes a homogeneous wingbox material and was therefore modified to allow independent material assignments for the skins and spars, as shown in Figure 1.

Material-dependent properties such as density $\rho$, Young’s modulus E, shear modulus G, and allowable stress ${\sigma }_{\mathrm{allow}}$ are incorporated directly into the sizing algorithm.

The output of this program gives the fuel burn and the masses of the spars and the skins. Accordingly, 4 possible configurations were analyzed:

• Full Aluminum Wingbox (Al-Al)
• Full CFRP Wingbox (CFRP-CFRP)
• Aluminum skins, CFRP Spars (Al-CFRP)
• CFRP skins, Aluminum Spars (CFRP-Al)

The results from this step were then used to determine the manufacturing and the EOL environmental impacts based on the mass fraction of materials on the structure and their respective environmental properties, as explained in the subsequent subsection. High aspect ratio wings have been demonstrated as an effective means of improving aerodynamic efficiency and are regarded as an important design phase lever towards sustainable aviation. Consequently, the uCRM 13.5 [11] research model was selected as the reference for this study, as it provides a representative high aspect ratio wing geometry of a long-range aircraft suitable for aerostructural analysis and comparative assessment. The mechanical and environmental properties of materials used in this study are given in

Table 1. Pure Material Properties for Al2024-T3 and CFRP UD prepreg Quasi-Isotropic Layup [12].

Property	Al2024-T3	CFRP UD QI
Density (kg/m3)	$2.78\times {10}^3$	$1.57\times {10}^3$
Young’s Modulus (Pa)	$7.30\times {10}^{10}$	$5.50\times {10}^{10}$
Shear Modulus (Pa)	$2.80\times {10}^{10}$	$2.10\times {10}^{10}$
Max Allowable Yield Stress (Pa)	$3.31\times {10}^8$	$6.70\times {10}^8$
Energy (MJ/kg)	110	730
CO2eq Production (kg/kg)	7.9	51
CO2eq End-of-Life (kg/kg)	0.5	2.3
Buy-to-Fly (BtF)	5	1.5
Recyclability (%)	95	0

.

2.2. Environmental Impact

To provide a unified metric for environmental assessment, the impact is expressed in terms of CO₂eq emissions released in each selected phase. The environmental impact is quantified across three principal phases:

• Material production (cradle-to-gate), including embodied energy, CO₂ intensity (kg/kg), buy-to-fly ratios, and manufacturing scrap.
• Operations, where fuel burn predicted by the aerostructural model is converted to CO₂ emissions using a standard conversion factor (1 kg fuel → 3.16 kg CO₂eq) [13].
• End-of-Life (EoL), including recycling efficiency, non-recyclable waste, and CO₂eq emissions associated with disposal.

The workflow for estimating emissions is illustrated in Figure 2 below.

The process begins with the optimized component weight derived from OpenAeroStruct results. The raw material mass required for manufacturing is estimated by multiplying the component weight by the material’s average Buy-to-Fly (BtF) ratio. The CO_2eq emissions for the material stage are then derived by multiplying this raw mass by the material’s carbon intensity.

Simultaneously, the volume of manufacturing scrap is calculated. Depending on the material properties, this scrap either re-enters the loop (recycling, with an associated reprocessing footprint) or becomes non-recoverable waste sent for incineration.

In the operational phase, the component’s contribution to fuel burn, driven by its weight and aerodynamic drag, is converted to emissions (3.16 × Fuel Mass). Finally, at the End-of-Life (EOL), the component is treated similarly to manufacturing scrap: partitioned into recyclable and non-recyclable streams based on recycling efficiency, determining the final carbon footprint.

2.3. Multi-Objective Optimization for Material Composition

Initial OpenAeroStruct analyses of four Aluminum–CFRP wingbox configurations showed that wingbox mass varies non-linearly with material substitution due to coupled structural effects such as stiffness redistribution and resulting aeroelastic deflections. Because simple interpolation could not capture this behavior, a physics-informed surrogate was constructed using a shape-preserving Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) fit through the computed masses, providing a continuous and physically consistent mass function across the design space.

The remaining life-cycle metrics, material-stage CO_2eq emissions and non-recoverable manufacturing/EOL scrap were modeled using mixture rules based on material mass fractions. Together, these components define a three-objective optimization problem with material weight fractions as the design variables:

$$\begin{array}{cc}\hfill \mathbf{Design}\mathbf{variables:}& w_m\hfill \\ \hfill \mathbf{Constraints:}& \sum _m{w}_m=1,w_m\ge 0\hfill \\ \hfill \mathbf{Minimize:}& \left\{\begin{array}{c}{f}_1=\mathrm{wingbox}\mathrm{mass},\hfill \\ f_2=\mathrm{non-recoverable}\mathrm{scrap},\hfill \\ f_3={\mathrm{CO}}_{2}eq\mathrm{material}\mathrm{stage}.\hfill \end{array}\right.\hfill \end{array}$$

Material properties for each composition were computed using the Voigt rule of mixtures,

$${\mathrm{Prop}}_{\mathrm{eff}}=\sum _m{v}_m{\mathrm{Prop}}_m,$$

with volume fractions derived from mass fractions and densities. Validation against two hybrid configurations showed mass-prediction discrepancies below 5%, confirming that the homogenized properties provide sufficient fidelity for optimization.

The optimization was solved using the NSGA-II algorithm, with non-dominated sorting performed in the full three-objective space. A solution is considered non-dominated if no other solution improves at least one objective without degrading at least one of the remaining objectives. The resulting Pareto-optimal set therefore represents the trade-off surface among all three objectives simultaneously. For visualization, two-dimensional projections are shown, with the third objective encoded via a color gradient, restricted to lower percentiles to highlight the minimum cradle-to-gate emissions.

2.4. Hypothesis for Material Composition and SAF Blending for Reducing Environmental Impact

To explore whether the operational advantages of the CFRP can be compensated through alternative decarbonization pathways, this part of the study examines the combined influence of circularity-oriented material choices and Sustainable Aviation Fuel (SAF) blending.

The central question addressed is as follows: If the wing structure were designed using a more circular, aluminum-rich material composition, what level of SAF blending would be required for its operational CO₂eq emissions to match those of a fully CFRP wing operating solely on conventional fuel?

For this analysis, a simplified assumption is adopted whereby a 100% SAF blend yields an 80% reduction in effective CO₂eq emissions [14,15]. Based on this assumption, operational CO₂eq emissions were recalculated using effective emission factors corresponding to SAF blending ratios up to 50%, reflecting the current certified technological limit for drop-in SAF usage [13]. By comparing the resulting operational CO₂eq levels with those of the baseline CFRP configuration, the SAF blending percentage required to achieve equivalent operational performance was identified. Subsequently, a balanced material configuration was selected from the previously generated Pareto front, and its effective material properties were implemented within OpenAeroStruct. This enabled the computation of the corresponding fuel burn and provided a consistent basis for evaluating combined material–fuel decarbonization strategies.

3. Results and Discussions

The first subsection presents the results of the aerostructural optimization for various material combinations and evaluates their associated environmental impacts. The second subsection provides projections for the hybrid approach described in the previous section.

3.1. Aerostructural Optimization and Environmental Impact

The results from the analyses of the four wingbox configurations are summarized in

Table 2. Results from Aerostructural analyses of 4 Wingbox configurations.

Material (Skin-Spar)	Al-Al	CFRP-CFRP	CFRP-AL	Al-CFRP
Mass Skins (kg)	$2.68\times {10}^4$	$8.13\times {10}^3$	$8.07\times {10}^3$	$2.19\times {10}^4$
Mass Spars (kg)	$1.87\times {10}^3$	$7.56\times {10}^2$	$1.28\times {10}^3$	$1.21\times {10}^3$
Total Mass (kg)	$2.87\times {10}^4$	$8.89\times {10}^3$	$9.35\times {10}^3$	$2.31\times {10}^4$
Fuel Burn (kg)	$8.14\times {10}^4$	$6.56\times {10}^4$	$6.58\times {10}^4$	$8.16\times {10}^4$

. Material selection significantly influences the mass and aerodynamic performance (CL/CD), which together impact fuel consumption over the mission range.

These results were further extended to study their environmental tradeoffs. The summary of these assessments is given in Figure 3. It was observed that CO₂eq emissions during the material production stage (b) closely follow the trend in wingbox mass (a), indicating a mass-dependent impact. However, it is important to note that, although the full Al structure is more than three times heavier than the full CFRP structure, its CO₂eq emissions in the material stage are only about 1.6 times higher than those of CFRP. This discrepancy is primarily due to Al’s high BtF ratio. If the BtF ratios were equalized, the Al structure would produce significantly lower emissions in the material production stage. During the operational phase, CFRP offers an advantage over Al, resulting in approximately 20% lower emissions (c). At the EOL stage, however, the scenario is reversed. Under the current assumptions that CFRP is fully non-recyclable due to its thermoset nature, it becomes the less favorable option. In contrast, Al, being mostly recyclable, requires less energy and generates fewer emissions during reintegration into the production cycle, making it more circularity-friendly (d).

3.2. Hybrid Material and SAF Approach

The Pareto-optimal solutions from the multi-objective optimization are shown in Figure 4. The point just below the CFRP–Al case (marked in blue) corresponds to the blend with the lowest cradle-to-gate CO₂eq emissions. To verify the surrogate material-property model, several Pareto points were re-evaluated in OpenAeroStruct; wingbox masses differed by under 5%, confirming adequate accuracy.

For an operational assessment, a representative hybrid composition (65% Al, 35% CFRP) from the central Pareto region was analyzed to obtain its mission fuel burn and CO₂ emissions. These emissions were then combined with the SAF-blend model to compute mission CO₂ across the full SAF range. Figure 5 compares this hybrid design with the four baseline configurations.

Annotations in the figure indicate the SAF level at which each design matches the operational emissions of the full-CFRP wingbox. The aluminum wingbox requires about 24.5% SAF—an ambitious target given current supply, whereas the 65% Al/35% CFRP composition needs only 5.6% SAF.

This demonstrates that a hybrid material + SAF blend solution can reduce manufacturing and EOL waste relative to full CFRP while also achieving competitive operational emissions under realistic SAF availability.

4. Conclusions

This study presented an integrated aerostructural and life-cycle based framework to evaluate the environmental implications of material choice for preliminary aircraft component design. The methodology provides quantitative insight into the trade-offs between operational performance, manufacturing, and End-of-Life impacts in a low-fidelity setting.

The results indicate that CFRP-rich designs substantially reduce structural mass and operational fuel burn, but generate significantly higher non-recoverable waste compared with aluminum structures.Aluminum, in contrast, offers superior recyclability and End-of-Life performance at the expense of operational efficiency. The effective material formulation demonstrates how multi-objective optimization can identify balanced material compositions that improve sustainability across multiple life-cycle phases. CFRP is conservatively assumed to be non-recyclable at End-of-Life; accounting for emerging recycling pathways would reduce the associated CO_2eq burden and shift the Pareto front towards higher CFRP content.

The integration of SAF further demonstrated a pathway where significant operational CO₂ reductions can partially offset the structural mass disadvantages of heavier metallic materials, which are otherwise favorable for achieving circularity.

Future work will focus on increasing the fidelity of the aerostructural analysis to better capture nonlinear effects, detailed stress distributions, and aeroelastic interactions. The optimized material compositions will also be assessed from a manufacturing feasibility perspective, including compatibility between materials on adjacent components. In addition, the material dataset will be expanded to include a broader range of aerospace-relevant materials, enabling additional objectives such as cost, supply criticality, and recyclability to support more realistic decision-making.