Strut-braced Wing Aircraft Research Articles

Geometrically Nonlinear Coupled Adjoint Aerostructural Optimization of Natural-Laminar-Flow Strut-Braced Wing

Novel aircraft concepts employing ultrahigh-aspect-ratio wings, such as the strut-braced wing (SBW) configuration, are promising ways to achieve the next-generation sustainable and fuel-efficient aviation goals. However, as the wing aspect ratio increases, the wing increasingly exhibits more flexibility, higher deformation, and geometrically nonlinear behavior that cannot be accurately simulated by conventional sizing methods and typical linear structural analysis models. This paper establishes a framework for SBW aircraft conceptual design, conceptual optimization, and aerostructural optimization. The presented aerostructural optimization method has medium-fidelity and physics-based features. A geometrically nonlinear structural analysis solver and a quasi-three-dimensional aerodynamic solver are coupled for the aerostructural optimization of composite natural-laminar-flow SBW aircraft. A medium-range (MR)-SBW aircraft is initially designed and optimized in the conceptual design stage. A gradient-based aerostructural optimization is performed using the proposed tool for minimizing the fuel mass of the initially sized and optimized MR-SBW aircraft. The optimization results in a more than 10% reduction in fuel mass, a more than 8% reduction in aircraft maximum takeoff mass, and a more than 30% reduction in wing and strut structural weight by optimizing the wing box structure, the wing planform, and the airfoil shape while satisfying the constraints on structural failure, wing loading, and aileron effectiveness.

RANS-Based Aerodynamic Shape Optimization of a Strut-Braced Wing with Overset Meshes

The strut-braced wing aircraft configuration promises to reduce fuel burn by enabling higher spans that reduce lift-induced drag. A successful design for this configuration depends on a careful trade-off between the various sources of drag and structural weight. When using computational fluid dynamic tools for aerodynamic shape optimization, generating high-quality structured meshes for the strut-braced wing configuration becomes challenging, especially near junctions. Furthermore, mesh deformation procedures frequently generate negative volume cells when applied to these structured meshes during optimization. This paper addresses this issue by using overset meshes and a component-based parametrization technique to achieve a flexible design optimization cycle capable of handling changing junctions. This study uses this approach to minimize drag of the PADRI 2017 strut-braced wing benchmark for a fixed lift constraint at transonic flight conditions. The drag of the optimized configuration is 15% lower than the baseline due to the reduction of shocks and separation in the wing-strut junction region. This result represents an example in which high-fidelity modeling is required to quantify the benefits of a new aircraft configuration and address potential issues during the conceptual design.

Mitigating the Climate Impact from Aviation: Achievements and Results of the DLR WeCare Project

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.

Wing weight estimation in conceptual design: a method for strut-braced wings considering static aeroelastic effects

This paper presents a method for the wing weight estimation of strut-braced wing aircraft in conceptual design. The method is simple to implement while still capturing important effects for early design estimates. Static aeroelastic loads, aeroelastic divergence and aileron reversal criteria are calculated directly with small matrices suitable for implementation in spreadsheet software. Maneuver, gust and ground cases are considered. A direct non-iterative method is used for the strut and wing internal loads calculation. The wing and strut load-carrying structures are sized with analytical box-beam equations for strength, buckling and fatigue criteria. Aluminum or composite laminates can be considered. Semi-empirical methods are presented for non-optimal mass components and the secondary structure. The aeroelastic effects and strut reaction estimations are compared for a wide range of design parameters with Nastran validating the proposed method. The weight estimations are verified with conventional aircraft data and strut-braced wing studies available in the literature, showing good accuracy. Design trade studies are presented illustrating typical applications of the method. A potential to reduce the wing mass in about 18 % or to increase the aspect ratio from 10 to 16 compared to a cantilever wing is identified.