Nonplanar Wings Research Articles

Investigating Planar and Nonplanar Wing Planform Optimisation for Ground Effect Aircraft

Wing-in-Ground (WIG) effect aircraft are gaining attention for their potential in reducing environmental impact. However, optimising wing planforms based solely on aerodynamics might improve performance while compromising static height stability of WIG aircraft. This study investigates the effects of planar and nonplanar wing planform optimisation for regional transport ground effect aircraft. Three distinct multiobjective wing planform optimisations are explored: planar wing optimisation, nonplanar wing optimisation, and nonplanar wingtip optimisation. These optimisations assess the impact on both aerodynamic efficiency and static height stability characteristics of a wing planform in ground effect, at three different flying altitudes. In extreme ground effect, the Pareto set includes wings with negative spanwise camber, enhancing both cushion sensation and aerodynamic efficiency by effectively utilizing ground effect, thus proving advantageous over planar wing configurations.

Aero-structural design of joined-wing aircraft based on high-fidelity model

The joined-wing configuration reduces induced drag and structural weight by connecting the rear wing to the front wing. In addition, the rear wing can replace the role of the horizontal tail of a conventional aircraft, thus eliminating the aerodynamic drag and weight associated with the horizontal tail. This particular shape creates a highly coupled relationship between aerodynamics and structure, which must be fully considered during the overall design process to enhance aircraft performance. In this research, an aero-structural design model of the joined-wing aircraft is constructed based on high-fidelity computational fluid dynamics and structural finite element methods. The model is able to obtain accurate aerodynamic loads for the non-planar wing and to simulate the statically indeterminate structure of the closed wing configuration. The influence of the joined-wing shape parameters on the aerodynamic and structural disciplines, as well as the influence of geometric nonlinear characteristics, deformation constraints and buckling constraints on the structural weight are all taken into consideration. The model is applied to complete the aero-structural design optimization of a high-altitude long-endurance joined-wing aircraft, and wind tunnel tests are conducted. The test results verify the credibility of the design model proposed and the validity of the design environment.

Simulating Airplane Aerodynamics with Body Forces: Actuator Line Method for Nonplanar Wings

Two configurations typical of fixed-wing aircraft are simulated with the actuator line method (ALM): a wing with winglets, and a T tail. The ALM is extensively used in rotor simulations to model the blades by body forces, which are calculated from airfoil data and the relative flow velocity. This method has not been used to simulate airplane aerodynamics, despite its advantage of allowing coarser grids. This may be credited to the failure of the uncorrected ALM to accurately predict forces near the tip of the wings, even for simple configurations. The recently proposed vortex-based smearing correction shows improved results, suggesting those limitations are part of the past. For the nonplanar configurations studied in this work, differences between the ALM with the original smearing correction and a nonlinear lifting line (LL) method are observed near the intersection of surfaces because the circulation generated in the numerical simulation differs from the calculated corrected circulation. A vorticity magnitude correction is proposed, which improves the agreement between the ALM and the LL method. This second-order correction resolves the ambiguity in the velocity used to define the lift force. The good results indicate that the improved ALM can be used for airplane aerodynamics, with an accuracy similar to the LL method.

Solution of a Nonplanar Lifting-Line Model Using the Finite Element Method

A reduction in the structural wing weight is generally followed by an increase in the structural flexibility, leading to a significantly deformed wing configuration. A modified Prandtl’s lifting-line model proposed herein aims to approximate the spanwise lift distribution and the induced drag using a finite element method approach. A numerical validation considering planar elliptical wings is carried out for several mesh configurations. The proposed approach has an optimal agreement to the analytical solution, showing a global error inferior to in terms of the spanwise circulation distribution. Next, analyses of nonplanar wings are made compared to the available literature data. For the first case, the relative difference regarding the lift coefficient is less than 0.3%, whereas for the induced drag, it is less than 2.2%. For the second case, a maximum difference for the lift coefficient is less than 0.5%. The numerical strategy proposed in this paper approximates the solution of the aerodynamic problem to the approach via finite element methods used in structural analysis. The presented approach can later lead to a hybrid finite element with aerodynamic and structural degrees of freedom, which can be helpful for the development of a monolithic approach.

A multiobjective surrogate-assisted optimisation and exploration of low-boom supersonic transport planforms

Optimal non-planar wing planform geometries for a Mach 2.2 45-seat supersonic transport are generated using Kriging-based Bayesian optimisation techniques on a 22-variable, 3-objective problem for two wing-loading conditions. Sonic boom loudness, drag, and root bending moment are simultaneously minimised at a fixed lift. A Python-based framework is developed for rapid evaluation of designs in a parallel computation environment, automating conceptual geometry generation, optimised mesh griding, Euler CFD evaluation, and thermoviscous atmospheric boom propagation. An empirical turbulent skin friction coefficient is used to correct the Euler drag and an estimate of wave drag is performed. Self-organising maps and polynomial chaos expansion Shapley effects are used to explore the design variables and their associated sensitivities with respect to the design objectives. A geometric centroid-based proxy for trim is used to filter the results; feasible extreme designs and a compromise design are compared and discussed. The results indicate a trade-off between each of the three objectives due to competing design requirements, however an improvement in two of the objective functions is possible by sacrificing the remaining objective. One possible compromise solution reduces the root bending moment coefficient by 25% and the sonic boom loudness by 24% at the cost of a 5% increase in drag.

Aerodynamic Shape Optimization of Highly Nonplanar Raised and Drooped Wings

Aircraft wings are commonly designed with nonplanar geometry, such as winglets, in order to improve aerodynamic efficiency. This work presents a method for generating nonplanar wing designs through gradient-based optimization, which is then used to investigate the performance characteristics of nonplanar wings. The nonplanar parameterization is defined to give a large design space that allows the formation of highly nonplanar features and permits large changes to the geometry. Aerodynamic characteristics are captured using an inviscid three-dimensional panel method with approximations for viscous drag. The methodology is demonstrated by optimizing reference wings from literature and comparing aerodynamic performance. Investigations are also performed on the impact on performance when wings are raised or drooped, and the differences in aerodynamic behavior between the two designs. Results suggest that the converged designs and their performance are highly dependent on how the geometry is restricted. If a large design space is provided, both raised and drooped wings are able to produce designs with similar performance when only inviscid analysis is considered. When accounting for viscous effects, results suggest that drooped wings are not beneficial for drag reduction.

Gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control.

Birds dynamically adapt to disparate flight behaviours and unpredictable environments by actively manipulating their skeletal joints to change their wing shape. This in-flight adaptability has inspired many unmanned aerial vehicle (UAV) wings, which predominately morph within a single geometric plane. By contrast, avian joint-driven wing morphing produces a diverse set of non-planar wing shapes. Here, we investigated if joint-driven wing morphing is desirable for UAVs by quantifying the longitudinal aerodynamic characteristics of gull-inspired wing-body configurations. We used a numerical lifting-line algorithm (MachUpX) to determine the aerodynamic loads across the range of motion of the elbow and wrist, which was validated with wind tunnel tests using three-dimensional printed wing-body models. We found that joint-driven wing morphing effectively controls lift, pitching moment and static margin, but other mechanisms are required to trim. Within the range of wing extension capability, specific paths of joint motion (trajectories) permit distinct longitudinal flight control strategies. We identified two unique trajectories that decoupled stability from lift and pitching moment generation. Further, extension along the trajectory inherent to the musculoskeletal linkage system produced the largest changes to the investigated aerodynamic properties. Collectively, our results show that gull-inspired joint-driven wing morphing allows adaptive longitudinal flight control and could promote multifunctional UAV designs.

Conceptual design of a novel Unmanned Ground Effect Vehicle

In this work, a methodology for the conceptual design of a combined Box-wing and Blended-Wing-Body unmanned aerial platform, which exploits the ground effect, is presented. Ground Effect Vehicles (GEVs) are aircrafts or aerial vehicles capable of flying very close to the surface of water areas, being a promising alternative to ships and seaplanes operating in closed seas. In order to exploit the air cushion that is formed underneath, GEVs have low Aspect Ratio wings. Thus, the Blended-Wing-Body (BWB) layout configuration is an appealing choice due to the large available body surface. On the other hand, a tailless vehicle having the BWB layout is facing challenging stability issues, especially in a turbulent and highly volatile environment as the one close to the sea level. Therefore, the addition of the Box wing configuration, namely a continuous-surface nonplanar wing formation with no wing tips, is deemed beneficiary as a way to overcome the stability challenges and eliminate the wingtip vortices. The combination of these two prominent platforms leads to improved aerodynamic performance and eventually, a reduced fuel consumption. The design methodology starts by the estimation of the most important design parameters, such as aspect ratio, sweep angle, and taper ratio, which are continuously refined in an iterative computational framework during the conceptual design phase. In an initial approach, the flight scenario with no ground effect interference is studied, with the use of both analytical calculations and computational fluid dynamics simulations. The results from the conceptual design phase indicate that the UGEV configuration has a considerable potential as an alternative to ships or seaplanes, based on its ability to carry larger payload than seaplanes and deliver it faster than ships.

NERONE: An Open-Source Based Tool for Aerodynamic Transonic Optimization of Nonplanar Wings

Transonic shape optimization of nonplanar wings is a relevant topic in current aeronautical world. Although widely studied, an appropriate level of robustness and automation is still lacking for the inclusion of aerodynamic shape optimization in a Multi-Disciplinary Optimization (MDO) process. In this paper, a new framework, opeNsource-mEsh-geneRation-fOr-aerodyNamic-Evaluations (NERONE), is presented that allows for an automatic transonic shape optimization process within an MDO loop design using open-source libraries, namely OpenCasCade (OCC) for the geometric description, GMSH for grid generation and SU2 multi-physics for aerodynamic analysis and optimization. Wing geometry is defined in the CPACS standard, converted to a mathematical continuous description (NURBS) and passed to the mesher. Grid generation process is driven by user-defined mesh dimensions defined on wing regions and on support domain boundary surfaces. The aerodynamic analysis and optimization are then launched on the obtained grid. SU2 software has been augmented to overcome robustness issues regarding point-inversion algorithm and to control geometric quality during optimization of nonplanar wings. Capability of NERONE is first demonstrated for 2D Euler and RANS simulations (on the RAE2822 airfoil) and on a 3D Euler case (ONERA M6). With very few user-specified parameters, high-quality grids are obtained providing results that correlate well with the literature data. Finally, NERONE is applied to the local shape optimization of a wing–winglet configuration in transonic flight conditions.

A Comparative Aerodynamic study of Nonplanar Wings

A Comparative Aerodynamic study of Nonplanar Wings

Minimum Induced Drag Conditions for Truss-Braced Wings

Traditional monoplane aircraft have been used for many decades. A promising improvement is represented by truss-braced wing configurations because studies have shown potential advantages in terms of fuel savings and overall efficiency. These investigations have been carried out in relatively complex multidisciplinary design and optimization computational frameworks, and thus some theoretical questions regarding the optimal conditions under which the induced drag is minimized need to be specifically addressed. This is achieved in this paper by extending the variationally derived theoretical model that the authors developed for nonplanar wings, closed systems, and multiwings to handle multiple closed paths (typical situation in the case of truss-braced wings) within the wing system. A regularization procedure, based on splines and preserving the continuity of the function and its first and second derivative, is introduced to address the geometrical corners. It is verified that, under optimal conditions, the actual value of the induced drag is a global minimum and that there is an infinite number of possible aerodynamic loads achieving the optimum. In some of them, the central part of the upper wing is more loaded, whereas in other cases, the lower wing and outer portions of the upper wing carry more aerodynamic forces. Finally, it is shown that a jury should be unloaded or at most have constant circulation to avoid penalty on the induced drag.

Conceptual design methodology of a box wing aircraft: A novel commercial airliner

In this work, the development of a conceptual design methodology of an innovative aircraft configuration, known as box wing, is presented. A box wing aircraft is based on a continuous-surface nonplanar wing formation with no wing-tips. The A320 medium range conventional cantilever wing aircraft is used as both the reference aircraft and the main competitor of the box wing aircraft. Based on the A320 characteristics and dimensions, a complete aerodynamic analysis of the box wing configuration is made by means of layout design and computational fluid dynamics studies, highlighting the aerodynamic and operating advantages of the box wing configuration compared to the A320 aircraft. The aspect ratio and the Oswald factor of a box wing aircraft differ significantly from the corresponding ones of A320 and provide increased aerodynamic performance. The increased aerodynamic performance leads by consequence, to lower fuel consumption, thus allowing longer range for the same payload or greater payload for the same range, contributing to the efforts for greener environment. In this work, the design methodology begins by estimating the critical initial design parameters, such as aspect ratio, dihedral angle, sweep angle, and taper ratio, which are continuously refined via an iterative process based on a conceptual design study. Various flying scenarios are studied using computational fluid dynamics and analytical calculations, in order to compare the performance of the box wing and the conventional A320, having always the same mission and payload conditions. The conceptual results show that the novel box wing configuration has considerable aerodynamic performance advantages compared to the conventional A320 aircraft.

Comparison of box-wing and conventional aircraft mission performance using multidisciplinary analysis and optimization

Box-wing aircraft designs have the potential to achieve significant reductions in fuel consumption. Closed non-planar wing designs have been shown to reduce induced drag and the statically indeterminate wing structure can lead to reduced wing weight. In addition, the streamwise separation of the two main wings can provide the moments necessary for static stability and control, eliminating the weight and aerodynamic drag of a horizontal tail.Proper assessment of the disciplinary interactions in box-wing designs is essential to determine any realistic performance benefits arising from the use of such a configuration. This study analyzes both box-wing and conventional aircraft designed for representative regional-jet missions. A preliminary parametric investigation shows a lift-to-drag ratio advantage for box-wing designs, while a more detailed multidisciplinary study indicates that the requirement to carry the mission fuel in the wings leads to an increase of between 5% and 1% in total fuel burn compared to conventional designs. However, the multidisciplinary study identified operating conditions where the box-wing can have superior performance to conventional aircraft despite the fuel volume constraint.

Study of a C-wing configuration for passive drag and load alleviation

Non-planar wing configurations are often hypothesised as a means for improving the aerodynamic efficiency of large transport aircraft; C-wings may have the ability to exploit and unify drag reduction, aeroelasticity, and dynamics and control but their capacity to do so is ambiguous. The purpose of this work is to provide an experimental demonstration with the aim of verifying the C-wing configurations practical application. Thus, the main objective of this investigation is to quantify the C-wing’s ability for drag and load alleviation relative to a planar wing of equivalent wingspan, lift, and root bending moment at Re=1.5×106. Surface clay flow visualisations have been used to provide insight into the flow over the wing surface. Aerodynamic performance metrics show that despite the C-wing operating with a 19.1% higher wing wetted area, a peak total drag reduction of 9.5% at α=6° is achieved in addition to a 1.1% reduction in the wing root bending moment for equivalent lift. Force platform measurements in combination with laser vibrometry enabled a detailed understanding of the vibrational characteristics between the model and the wind tunnel. It is shown that the C-wing can passively attenuate buffet induced vibrations of the main-wing by up to 68.6% whilst simultaneously reducing total drag without a significant increase in wing weight or root bending moment.

DLR transonic inverse design code, extensions and modifications to increase versatility and robustness

ABSTRACTThe DLR inverse design code computes the wing geometry for a prescribed target pressure distribution. It is based on the numerical solution of the integral inverse transonic small perturbation (TSP) equations. In this work, several extensions and modifications of the inverse design code are described. Results are validated with corresponding redesign test cases. The first modification concerns applications for high transonic Mach numbers or cases with strong shocks. The introduced modifications enable converged design solutions for cases where the original method failed. The second modification is the extension of the code to general non-planar wings. Previously, the design code was restricted to non-planar wing designs with small dihedral or to nacelle design. A third modification concerns aerofoil/wings designed for wind-tunnel design. In order to design a swept wing between two wind-tunnel walls, the solution method was extended to two symmetry planes. The introduced extensions and modifications have increased the robustness and range of applicability of the inverse design code.

Minimum Induced Drag Theorems for Multiwing Systems

Under the assumption of a rigid wake aligned with the freestream velocity, a computationally efficient induced drag minimization procedure, tailored for the preliminary design phases of generic multiwing systems, is presented. The method is based on a variational approach, which leads to the formulation of a system of coupled integral equations in the unknown circulation distributions. It is shown that the augmented Munk’s minimum induced drag theorem has general validity for any given number and types of wings. Under optimal conditions, the aerodynamic efficiency of each wing is shown to coincide with the aerodynamic efficiency of the entire system, regardless of the number of wings and their shapes/wingspans; moreover, the aerodynamic load on each wing cannot be negative. In the past, it was demonstrated that changing the sign of curvature did not affect the optimal circulation and minimum induced drag for single nonplanar wings. This has been proven to be a far more general theorem in which, given an arbitrary number of generic nonplanar wings, the optimal circulations, load repartitions, and induced drag do not change if all lifting lines are replaced with mirrored (with respect to the horizontal plane) counterparts. It has also been verified that any wing system internal to a closed wing should be unloaded under optimal conditions, demonstrating that, if canard/tail are added to Box Wings, these additional lifting surfaces should be placed outside the region identified by the closed wing to avoid penalty on the induced drag. Several other properties of multiwings are presented, with emphasis on the relationship between closed and open systems conceptually filling the space identified by the closed wing. Results present several multiwing systems including nonplanar wings and closed systems. It is verified that the optimal conditions of a closed system part of a more complex multiwing can be studied as a limit case of a C-wing whose tips are brought close to each other or as a limit case of a biwing, confirming the generality of previous findings. The classical straight lifting line has been observed to have the minimum optimal aerodynamic efficiency, in terms of induced drag, for a given wingspan and lift if compared to any optimally loaded generic nonplanar open or closed systems.

Investigation into Aerodynamic Shape Optimization of Planar and Nonplanar Wings

Problems in three-dimensional aerodynamic shape optimization can produce complex design spaces due to the nonlinear physics of the Navier–Stokes equations and the large number of design variables used. In this paper, a Newton–Krylov optimization algorithm is applied to a set of complex aerodynamic optimization problems in order to investigate its behaviour and performance. The methodology solves the Reynolds-averaged Navier–Stokes equations with a parallel Newton–Krylov algorithm. Aerodynamic geometries are meshed using structured multiblock grids, which are then fitted with B-spline control volumes for mesh deformation and geometry control. A gradient-based optimization method is used, with adjoint variables calculated using a Krylov method. The optimization of the Common Research Model (CRM) wing is revisited, with a focus on the effect of varying geometric constraints and on the possibility of multimodality. In addition, several cases are presented that involve a high degree of shape change: two planform optimizations starting from a rectangular wing, and investigation of various wingtip treatments. The results characterize the methodology, demonstrating its robustness and ability to address optimization problems with substantial geometric freedom.

Conceptual design of a nonplanar wing airliner

Purpose This paper aims to compare three closed non-planar wing configurations with a reference conventional wing-plus-horizontal tail aircraft, considering structural aspects, weights and aerodynamic characteristics, as well as operational issues, such as cruise performance. Design/methodology/approach A vortex lattice code is used and coupled with an in-house code for structural beam calculation subroutine to evaluate the configurations as a function of the four main parameters identified in the study. Findings The study concludes that the non-planar wing configurations have better performances than a conventional aircraft. Moreover, the joined-wing configuration seems to be better than the others, including the box-wing configuration, achieving an increase of 17 per cent in the range for maximum payload compared to the reference aircraft and a 3 per cent reduction of maximum take-off weight. Research limitations/implications In the study, characteristic tools for a conceptual design are used, and, thus, absolute results should be considered with caution. Nonetheless, as all the cases are studied in the same way, there is a good precision in comparative or relative results. Practical implications The work shows that the non-planar wing configurations can be used as an alternative to the conventional aircraft to meet the objectives for the future of the aviation industry. Social implications Non-planar wing configurations are able to reduce fuel consumption. Their use could lead to reductions in pollutant emissions and the impact on the environment of commercial aviation. Originality/value This study considers aerodynamic and structural aspects at the same time, as well as several non-planar wing configurations, making possible to obtain a more realistic comparison between them.

English

A novel nonplanar wing concept called C-Wing is studied and implemented on a commercial aircraft to reduce induced drag which has a significant effect on fuel consumption. A preliminary sizing method which employs an optimization algorithm is utilized. The Airbus A320 aircraft is used as a reference aircraft to evaluate design parameters and to investigate the C-Wing design potential beyond current wing tip designs. An increase in aspect ratio due to wing area reduction at 36m span results in a reduction of required fuel mass by 16%. Also take-off mass savings were obtained for the aircraft with C-Wing configuration. The effect of a variations of height to span ratio (h/b) of C-Wings on induced drag factor k, is formulated from a vortex lattice method and literature based equations. Finally the DOC costing methods used by the Association of European Airlines (AEA) was applied to the existing A320 aircraft and to the C-Wing configuration obtaining a reduction of 6% in Direct Operating Costs (DOC) for the novel concept resulted. From overall outcomes, the C-Wing concept suggests interesting aerodynamic efficiency and stability benefits.

Wing weight model for conceptual design of nonplanar configurations

Unconventional aircraft designs, such as nonplanar wings, are being considered for the next generation of transport aircraft. In order to determine the suitability of such designs, conceptual design tools are needed which are both sensitive to these unconventional configurations and capable of obtaining results rapidly. Wings represent a large contribution to an aircraft's empty weight and there are many commonly used conceptual design tools which can accurately estimate this component's weight for conventional designs. However, nonplanar wings can have very different aerodynamic loadings and structural details so existing models cannot be easily extended to treat these complexities. This paper shows the development of a conceptual-level wing weight model which combines a fully-stressed cross-section method with an equivalent beam finite-element structural solver using loads derived from a nonplanar vortex-lattice method. This model is able to obtain accurate aerodynamic loadings for nonplanar wings and can model the statically indeterminate structure of closed wing configurations. It was shown to be as accurate as current approaches when analyzing conventional wings and it is able to show the details of nonplanar wing structures. This model will enable more meaningful multidisciplinary analyses of both conventional and unconventional wing designs by accurately and rapidly predicting both the weight and internal structural details of these designs.