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Comparative Assessment of Strut-Braced and Truss-Braced Wing Configurations Using Multidisciplinary Design Optimization
Abstract
This paper presents a study of aircraft featuring truss-braced wing configurations that have been optimized for minimum fuel consumption using multidisciplinary design optimization. The investigation proceeds following an earlier Boeing SUGAR N+3 study, which selected the truss-braced wing concept as the most promising of several N+3 concept vehicles. This comes from the fact that a significantly higher aspect ratio wing could achieve substantial reductions in induced drag, but requires major structural changes to support such a large span. This problem was explored through the use of a multi-disciplinary design and analysis environment implemented in ModelCenter. Optimization was performed using ModelCenter’s Design Explorer and Darwin genetic algorithm optimizers. Using the multidisciplinary environment, a large multi-dimensional design space featuring design variables spread across the major aircraft design disciplines was explored. Configurations featuring a strut-braced wing, and truss-braced wings with one and two juries were evaluated for different span limits. Subsequently, different laminar wing design options were investigated in conjunction with lift augmentation system options. The multidisciplinary optimization used for this investigation was able to produce candidate designs with the desired attributes and performance improvements, while satisfying all relevant geometric and performance constraints.
... Previous studies on passenger aircraft and transport aircraft mainly use the SBW and 1-jury TBW to reduce energy consumption and takeoff weight. The results show that the performance of SBW is better than the 1-jury TBW [17,18]. After liberating the constraints on the wingspan, the researchers found that 1-jury TBW was significantly better than SBW in terms of fuel consumption and structural performance. ...
... After liberating the constraints on the wingspan, the researchers found that 1-jury TBW was significantly better than SBW in terms of fuel consumption and structural performance. There was no significant difference between the 1-jury TBW and 2-jury TBW [18]. Compared with the SBW and 1-jury TBW, the multijury TBW can achieve a larger aspect ratio [19]. ...
This paper explores the feasibility of using the strut-braced wing (SBW) configuration to improve the flight endurance of the new energy unmanned aerial vehicle (UAV). A conceptual scheme of a new energy UAV with SBW configuration was designed, and the influence of the SBW on the aerodynamic and structural performance was analyzed. The results show that the SBW can improve the structural performance of the wing and increase the solar laying area of the wing, but the aerodynamic performance did not improve significantly. From the perspective of UAV energy consumption in level flight, the subtraction between electric output power and solar input power is selected as the evaluation index of the increasing effect of the flight endurance. A multidisciplinary design optimization (MDO) model was established considering the coupling of aerodynamics, structure, energy, and weight. Surrogate model technology and multiobjective genetic algorithm are used to optimize the SBW configuration. Compared with the conventional configuration, the optimal design result of the SBW configuration can reduce the level-flight output power and increase the solar input power, thus effectively increasing the flight endurance of the UAV.
... Gur et al. [10] extended this framework to encompass both strut-and truss-braced wings. Meadows et al. [11] and Chakraborty et al. [12] then applied it to the study of single-aisle strut-and truss-braced-wing transport aircraft. Owing to the promising fuel savings indicated by these studies, NASA and Boeing investigated a Mach 0.70 truss-braced-wing single-aisle aircraft similar to the Boeing 737-800 [13]. ...
... The optimizer, however, is still permitted to reduce the thickness-to-chord ratio towards the root for a more efficient distribution of structural depth. This results in wing designs that are similar to those that can be found in the literature [11][12][13]. ...
The aerodynamic design and fuel burn performance of a Mach-0.78 strut-braced-wing regional jet is investigated through aerodynamic shape optimization based on the Reynolds-averaged Navier–Stokes equations. Conceptual-level multidisciplinary design optimization is first performed to size the strut-braced-wing aircraft for a design mission similar to the Embraer E190-E2, with a design range of 3100 nmi at a maximum capacity of 104 passengers, and a maximum payload of 30,200 lb. For direct performance comparisons, a conventional tube-and-wing regional jet is also sized and optimized based on the same reference aircraft. Gradient-based aerodynamic shape optimization is then performed on wing–body–tail models of each aircraft, with the objective of drag minimization at cruise over a 500 nmi nominal mission. Design variables include twist and section shape degrees of freedom, which are realized through a free-form and axial deformation geometry control system, whereas nonlinear constraints include constant lift, zero pitching moment, minimum wing volume, and minimum maximum thickness-to-chord ratios. Results indicate that the optimizer is capable of mitigating shock formation, boundary-layer separation, and other flow interference effects from each wing design, including those within the wing–strut junction of the strut-braced wing. With year 2020 technology levels, the strut-braced-wing regional jet offers a 12.9% improvement in cruise lift-to-drag ratio over an Embraer E190-E2-like conventional tube-and-wing aircraft, which translates to a 7.6% reduction in block fuel for the nominal mission.
... Gur et al. [10] extended this framework to encompass both strut-and truss-braced wings. Meadows et al. [11] and Chakraborty et al. [12] then applied it to the study of single-aisle strut-and truss-braced-wing transport aircraft. Owing to the promising fuel savings indicated by these studies, NASA and Boeing investigated a Mach 0.70 truss-braced-wing single-aisle aircraft similar to the Boeing 737-800 [13]. ...
... The optimizer, however, is still permitted to reduce the thickness-to-chord ratio towards the root for a more efficient distribution of structural depth. This results in wing designs that are similar to those that can be found in the literature [11][12][13]. In addition, to prevent the sectional lift coefficients from becoming too large towards the wing tip, which would likely cause shock formation during the high-fidelity simulations, a minimum tip chord constraint is imposed to maintain a reasonable outboard wing segment taper ratio based on the Boeing SUGAR High, but scaled down for the regional jet class. ...
The aerodynamic design and fuel burn performance of a Mach 0.78 strut-braced-wing regional jet is investigated through aerodynamic shape optimization based on the Reynolds-averaged Navier-Stokes equations. Conceptual-level multidisciplinary design optimization is first performed to size the strut-braced-wing aircraft for a design mission similar to the Embraer E190-E2, with a design range of 3,100 nmi at a maximum capacity of 104 passengers, and a maximum payload of 30,200 lb. For direct performance comparisons, a conventional tube-and-wing regional jet is also sized and optimized based on the same reference aircraft. Gradient-based aerodynamic shape optimization is then performed on wing-body-tail models of each aircraft, with the objective of drag minimization at cruise over a 500 nmi nominal mission. Design variables include twist and section shape degrees of freedom, which are realized through a free-form and axial deformation geometry control system, while nonlinear constraints include constant lift, zero pitching moment, minimum wing volume, and minimum maximum thickness-to-chord ratios. Results indicate that the optimizer is capable of mitigating shock formation, boundary-layer separation, and other flow interference effects from each wing design, including those within the wing-strut junction of the strut-braced wing. With current technology levels, the strut-braced-wing regional jet offers a 15.6% improvement in cruise lift-to-drag ratio over the equivalent conventional tube-and-wing aircraft, which translates to a 6.5% reduction in block fuel for the nominal mission.
... Industry and academia are well on track for the short-term fuel efficiency target, since new alternative configurations continue to be studied in order to reduce fuel consumption, noise, and emissions. Some examples include, Blended Wing Body concepts [2,3], Boeing N + 3 SUGAR concepts [4,5], "Double Bubble" D8 aircraft [6], strut-and truss-braced wings [7], PrandtlPlane [8], NOVA (Nextgen Onera Versatile Aircraft) [9], NASA's STARC-ABL aircraft [10], Flying V aircraft [11], among others [12]. The AGILE research project for collaborative Multidisciplinary Design Optimization (MDO) must also be Technical Editor: André Cavalier. ...
Unconventional configurations and innovative propulsion technologies have been continuously developed for reducing both fuel-burn and global net carbon emissions. This article describes an advanced civil transport aircraft designed from the combination of a Box-Wing configuration with a Boundary Layer Ingestion (BLI) propulsion system. A conceptual-level Multidisciplinary Design Optimization strategy provided the main aerodynamic and performance characteristics of the aircraft, based on appropriate design requirements, variables and constraints. For direct performance comparison against a conventional aircraft, a single-point objective function based on minimum block fuel was evaluated by means of low-fidelity aircraft models. Subsequently, a back-to-back Computational Fluid Dynamics assessment of non-BLI and BLI versions of the aircraft was performed. Two major analyses comprised the aerodynamic evaluation: (i) quantification of the BLI benefit using the power balance method, (ii) performance evaluation of the propulsor inlet in terms of the total pressure recovery and the distortion index. The conceptual design results showed the box-wing configuration provided major fuel-burn savings compared to its conventional counterpart. On the other hand, the BLI version reduced engine power requirements at cruise in comparison with the non-BLI version, but decreased the total pressure recovery, resulting in more distortion at the aerodynamic interface plane. The main contribution of this study lies on the potential benefits of such an original unconven-tional configuration, whose technologies increased aerodynamic performance, which reduced fuel consumption and hence carbon emissions.
... For example, the primary goal of Europe's Fight-path 2050 is to reduce CO 2 emissions of aircraft by 75% relative to 2005 levels [2]. In the US, the N+3 goal proposed by NASA is to reduce Nitrogen oxides (NOx) emission by up to 80% in the landing-take-off process and reduce fuel burn by 60% for an airliner entering service in 2030-2035 [3]. To achieve these objectives, a number of technologies, such as shock control [4][5][6][7], laminar flow control [8][9][10][11][12][13][14], turbulent drag reduction [15][16][17][18], as well as novel aircraft concepts, such as BWB or hybrid wing body (HWB) [19], 'double-bubble' [20], truss-braced wing (TBW) [21] and box-wing [22], have been proposed and investigated to explore a better aerodynamic performance. ...
Effective control of aerodynamic loads, such as maneuvering load and gust load, allows for reduced structural weight and therefore greater aerodynamic efficiency. After a basic introduction in the types of gusts and the current gust load control strategies for aircraft, we outline the conventional gust load alleviation techniques using trailing-edge flaps and spoilers. As these devices also function as high-lift devices or inflight speed brakes, they are often too heavy for high-frequency activations such as control surfaces. Non-conventional active control devices via fluidic actuators have attracted some attention recently from researchers to explore more effective gust load alleviation techniques against traditional flaps for future aircraft design. Research progress of flow control using fluidic actuators, including surface jet blowing and circulation control (CC) for gust load alleviation, is reviewed in detail here. Their load control capabilities in terms of lift force modulations are outlined and compared. Also reviewed are the flow control performances of these fluidic actuators under gust conditions. Experiments and numerical efforts indicated that both CC and surface jet blowing demonstrate fast response characteristics, capable for timely adaptive gust load controls.
... Genetic algorithms, an evolutionary approach based on their metaheuristic of reproduction of the fittest, have widespread and effective use in the optimization of aircraft configuration [32] [33]. The procedure of reproduction of the fittest is repeated until some established criterium to close the process is reached. ...
The present work describes an airliner design platform that has been developed over
several years and its application to design airliners based on an efficiency index
developed by the authors of the present work. Among other characteristics, the design
tool can handle airplane geometries with detail and count on a unique and accurate
neural network system to predict aerodynamic coefficients. A new feature for product
classification was incorporated into the framework. It is based on entropy statistics and
was calibrated for jet transport airplanes and the results of classification are analyzed
in the present work. The design of a Middle of Market airplane was then carried out
with the classification provided by entropy statistics set as a constraint. Middle of the
Market is a term that was established to address the commercial aircraft market
segment that encompasses long-haul sectors from 3500 nm to 5000 nm, and airplanes
with single-class passenger capacity between 220 and 250. Until now, this segment was
not extensively explored, and some airlines have been showing interest to purchase
airplanes better suited to it = this category. Multi-objective optimizations were carried
out to determine the best aircraft design that fits into this concept's range and capacity
specifications. The unsupervised learning algorithm based on entropy statistics was
applied for airplane classification into four labels, classic, niche, failure, and
breakthrough designs. A higher fidelity engine model optimization task was also
carried out to search for optimal classic designs. In addition, a robust optimization
considering a fuel price variation on Direct Operating Cost was carried out. All results
raised an important discussion about the benefits and drawbacks of a trijet
configuration for transport airplanes with a capacity of over 200 passengers
... Given the compatibility of its unconventional wing system with conventional fuselage and empennage designs, and that the configuration leaves open the possibility of integration with many other new and emergent technologies, the strut-braced wing represents a reduced risk configuration technology that has a high potential for contributing to a more environmentally friendly aviation industry. Given this potential, the strut-and truss-braced-wing configurations have been the focus of much research over the past few decades, with many of these investigations focusing on the design and performance of the technology through low-order multidisciplinary design optimisation (MDO) (2,3,4,5,6,7) -demonstrating significant fuel burn savings for the single-and twin-aisle classes of aircraft. Recognizing these potential advantages, NASA and Boeing have since initiated investigations into a Mach 0.70 truss-braced-wing single-aisle aircraft similar to the Boeing 737-800 (8) , with some consideration toward hybrid electric variants as well (9) . ...
This paper presents a relative fuel burn evaluation of the transonic strut-braced-wing configuration for the regional aircraft class in comparison to an equivalent conventional tube-and-wing aircraft. This is accomplished through multipoint aerodynamic shape optimisation based on the Reynolds-averaged Navier-Stokes equations. Aircraft concepts are first developed through low-order multidisciplinary design optimisation based on the design missions and top level aircraft requirements of the Embraer E190-E2. High-fidelity aerodynamic shape shape optimisation is then applied to wing-body-tail models of each aircraft, with the objective of minimizing the weighted-average cruise drag over a five-point operating envelope that includes the nominal design point, design points at ±10% nominal CL at Mach 0.78, and two high-speed cruise points at Mach 0.81. Design variables include angle of attack, wing (and strut) twist and section shape degrees of freedom, and horizontal tail incidence, while nonlinear constraints include constant lift, zero pitching moment, minimum wing and strut volume, and minimum maximum thickness-to-chord ratios. Results show that the multipoint optimised strut-braced wing maintains similar features to those of the single-point optimum, and compromises on-design performance by only two drag counts to achieve up to 11.6% reductions in drag at the off-design conditions. Introducing low-order estimates for approximating full aircraft performance, results indicate that the multipoint optimised strut-braced-wing regional jet offers a 13.1% improvement in cruise lift-to-drag ratio and a 7.8% reduction in block fuel over a 500 nmi nominal mission when compared to the similarly optimised Embraer E190-E2-like conventional tube-and-wing aircraft.
... Albuquerque et al. [10] formulated a mission-based MDO methodology tailored for adaptive technologies. Chakraborty et al. [11] created an MDO platform for the comparative assessment of strut-braced and truss-braced wing configurations. Reist et al. [12] presented a multifidelity MDO study incorporating stability and control assessment for blended-wing-body aircraft. ...
Airworthiness certification is a mandatory but expensive process in aircraft development. To reduce certification cost, it is desired to incorporate certification considerations into aircraft early design stages. The tradeoff between performance and certification constraints and the interactions between the behind-the-scene disciplines require a multidisciplinary design optimization (MDO) method implemented to incorporate certification considerations. Several MDO frameworks currently exist with mixing levels of fidelity and multidisciplinary coupling. However, few of them capture the impacts of certification constraints on the overall aircraft performance. Moreover, preceding MDO studies have mostly focused on optimizing a single design point, whereas little attention is paid to design space exploration. To fill these gaps, this paper proposes a certification-driven platform for airframe early preliminary design. With statistical methods applied, this platform allows efficient design space exploration and multi-objective optimization. To demonstrate the capabilities of this platform, a test case of preliminary horizontal tail design of a large twin-aisle aircraft is performed. The feasibility test and multi-objective optimization conducted in the test case prove that certification constraints play a critical role in the design space exploration at the early preliminary stage.
... 3.3.4.1 Classification and Literature SurveyWe now introduce a new approach to classifying MDO architectures. Some of the previous classifications of MDO architectures were based on observations of which constraints were available to the optimizer to control90 , 91 . [Alexandrov and Lewis] 92 used the term "closed" to denote when a set of constraints cannot be satisfied by explicit action of the optimizer, and "open" otherwise. ...
The coupling schemes take us to the essential subject of Multi-Disciplinary Optimization (MDO). The interdisciplinary coupling inherent in MDO tends to present additional challenges beyond those encountered in a single-discipline optimization . It increases computational burden, and it also increases complexity and creates organizational challenges for implementing the necessary coupling in software systems. The increasing complexity of engineering systems has sparked increasing interest in multi-disciplinary optimization (MDO). The two main challenges of MDO are computational expense and organizational complexity. Accordingly the survey is focused on various ways different researchers use to deal with these challenges. The survey is organized by a breakdown of MDO into its conceptual components. Accordingly, the survey includes sections on Mathematical Modeling, Design-oriented Analysis, Approximation Concepts, Optimization Procedures, System Sensitivity, and Human Interface. With the increasing acceptance and utilization of MDO in industry, a number of software frameworks have been created to facilitate integration of application software, manage data, and provide a user interface with various MDO-related problem-solving functionalities.
... In many cases, this architecture has been previously proposed for the narrow-body TBW aircraft. 45 Figure 13. Front view of the TBW configuration with VHBPR. ...
A regional, turbofan-powered, 72-passenger, transport aircraft with very high aspect ratio truss-braced wings is developed with an affordable methodology from an existing 52 passenger, conventional twin-turboprop aircraft. At first, the ration behind the selection of the truss-braced wing configuration is discussed. Next, the methodologies for the sizing, weight, aerodynamics, performance, and cost analysis are presented and validated against existing regional aircraft. The variant configurations and their design features are then discussed. Finally, sensitivity analysis is carried out to investigate the effects of the wing aspect ratio and engine bypass ratio on the aircraft weight, aerodynamics, and cost. It has been found that the penalties associated with the wing weight will prevent the acceptable realization of the high aspect ratio wing benefits, but when it is combined with the very high bypass ratio engines, a 17% reduction in the mission fuel weight is achieved. In contrast, the cost analysis has revealed that the application of higher aspect ratio wings in the truss-braced wing configuration may increase the development and maintenance costs. Consequently, with aspect ratios higher than 24, eventually, these costs may outperform the associated fuel cost reductions.
... Thus, as expressed in an ONERA publication [89], it is recommended to use FEA as soon as possible to take into account the fuselage shape and cabin / luggage hold layout. Considering now the Truss-Braced Wing concept illustrated in Figure 19, Chakraborty [90] details a design study based on a multidisciplinary process. ...
In the field of civil transport aircraft, environmental constraints set challenging goals in terms of fuel consumption for the next generations of airplanes. With the “tube and wing” configuration offering low expectations on further improvements, disruptive vehicle concepts including new technologies are investigated. However, little information on such architectures is available in the early phases of the design process. Thus, research in Aircraft Design aims at adding knowledge in the Multidisciplinary Design Analysis.This objective is currently achieved with different approaches: implementation of Multidisciplinary Design Optimization, addition of accuracy through high fidelity analyses, introduction of new disciplines or systems and uncertainty management. In a preliminary study, the optimization of an innovative transport aircraft system based on a monolithic architecture and advanced structural models has been completed. The subsequent analysis of the outcomes highlighted specific needs towards the design of a viable concept. This research proposes then to add knowledge through an expansion of the Multidisciplinary Design Analysis and Optimization with a new Certification Constraint Module and full simulation capabilities.Following the development of the Certification Constraint Module (CCM), its capabilities have been used to perform four optimization problems associated to a conventional civil transport aircraft based on the ONERA / ISAE-SUPAERO sizing tool called FAST. Facilitated by the Graphical User Interface of the CCM, the setup time of these optimizations has been reduced and the results clearly confirmed the necessity to consider certification constraints very early in the design process in order to select the most promising concepts.To achieve full simulation capabilities, the multidisciplinary analysis within FAST had to be enhanced. First, the aerodynamics analysis tool has been modified so that necessary coefficients for a 6 Degrees-of-Freedom model could be generated. Second, a new module computing inertia properties has been added. Last, the open source simulator JSBSim has been used including different control laws for stability augmentation and automated navigation. The comparisons between flight trajectories obtained with FAST and real aircraft data recorded with ADS-B antenna confirmed the validity of the approach.
... Non-planar wing configurations have been widely recognised as a means of reducing total drag compared to conventional planar wing systems of the same span and lift (Kroo, 2005). A number of unconventional configurations have so far been proposed including the blended-wing-body (Liebeck et al., 1998;Liebeck, 2004;Lyu and Martins, 2014), C-wings (McMasters et al., 1996), polyplane, ring wings (Terry, 1964), box wings (Miranda, 1972), and joined wings (Wolkovitch, 1986;Lee et al., 2007;Cavallaro and Demasi, 2016), including strut-and truss-braced wings (Bhatia and Kapania, 2012;Chakraborty et al., 2015;Mallik et al., 2015), however, very few exploratory experimental investigations have been conducted on such configurations. In fact, the box wing arrangement among all non-planer configurations was shown by Prandtl (1924) to offer the 'best wing system', achieving the minimum possible induced drag for a given lift and height-to-span ratio (Munk, 1919). ...
... These designs resulted in much larger lift to drag ratio and a much larger wing span than the existing conguration. Similar improved fuel burn and aerodynamic performance by the TBW was also observed for a medium-range mission similar to Boeing 737-800 [8,14]. The eventual outcome was optimized airplane congurations with long, slender and exible wings whose aeroelastic behavior was not studied while performing MDO simulations in the past. ...
This study investigates the effects of a variable-geometry raked wingtip on the aeroelastic behavior and the maneuverability of transport aircraft with very large aspect-ratio truss-braced wings. These truss-braced wing designs are obtained from the multidisciplinary design optimization environment presented here while minimizing the fuel burn of a double-aisle aircraft having a flight mission similar to that of a Boeing 777-200 long-range aircraft. The wingtip can be swept forward and aft relative to the wing by a novel control effector mechanism. Results show that a variable-geometry raked wingtip can be used to achieve required roll control by judiciously sweeping it relative to the wing at various flight conditions. It has an added benefit that it can also be used for flutter avoidance. Such benefits of the variable-geometry raked wingtip allow the operation of truss-braced wing configurations, which have up to 10% lower fuel burn than comparable optimized conventional cantilever wing designs. Without the variable-geometry raked wingtip, such configurations fail to meet the required flutter speed and roll control capability. The variable-geometry raked wingtip is thus an enabling technology for truss-braced wing aircraft and other large aspect-ratio configurations.
... References [175][176][177] used MDO to study TBW optimized for minimum fuel consumption. The investigation was conceptually part of the SUGAR N þ 3 study (see the dedicated part on the topic, Section 17), which selected TBW concept as the most promising configuration. ...
Diamond Wings, Strut- and Truss-Braced Wings, Box Wings, and PrandtlPlane, the so-called “JoinedWings”, represent a dramatic departure from traditional configurations. Joined Wings are characterized by a structurally overconstrained layout which significantly increases the design space with multiple load paths and numerous solutions not available in classical wing systems. A tight link between the different disciplines (aerodynamics, flight mechanics, aeroelasticity, etc.) makes a Multidisciplinary Design and Optimization approach a necessity from the early design stages. Researchers showed potential in terms of aerodynamic efficiency, reduction of emissions and superior performances, strongly supporting the technical advantages of Joined Wings. This review will present these studies, with particular focus on the United States joined-wing SensorCraft, Strut- and Truss- Braced Wings, Box Wings and PrandtlPlane.
In recent decades, the environmental impacts of aviation have become a key challenge for the aeronautical community. Advanced and well-established technologies such as active flow control systems, wing-tip devices, high bypass ratio engines, composite materials, among others, have demonstrated fuel-burn benefits by reducing drag and/or weight. Nevertheless, aviation remains under intense pressure to become more sustainable. For this reason, there is a strong drive to explore unconventional aircraft with the aim of reducing both environmental emissions and Direct Operating Cost. This paper presents the current state-of-the-art in the development of future aircraft for civil aviation. The literature review is conducted through an appropriate search protocol to ensure the selection of the most relevant sources. After a brief historical background, progress in the design and development of several unconventional aircraft configurations is presented. Concepts such as Blended/Hybrid Wing Bodies, nonplanar wing designs, next-generation propulsion technologies that are tightly integrated with the airframe, among others, are reviewed. Special attention is given to design methodologies (level-of-fidelity), cruise altitude, aerodynamic performance, and fuel-burn benefits over conventional configurations. The primary contributions of this review are (i) a detailed survey of the design characteristics of unconventional aircraft for non-specialists, and (ii) a comprehensive review of the literature detailing past and current design trends of such configurations for specialists.
This paper describes a study of the effects of several key aerodynamic considerations on the conceptual design of
minimum-fuel/emissions, long-range transport, transonic, truss-braced-wing aircraft configurations. This
unconventional configuration has a large benefit over conventional cantilever wing configurations. The truss
system enables an increased aspect ratio with lower sweep, thickness ratio, and chords, thus exploiting natural
laminar flow. The design problem is solved by a multidisciplinary optimization process, which takes into account
both aerodynamic and structural considerations. This paper contains several studies, each of which investigates the
dependency of the design space on a specific aerodynamic parameter such as the extent of laminar flow on the wing,
cruise Mach number, maximum cruise two-dimensional lift coefficient, supercritical characteristics of the airfoil,
winglet influence, and intersection fairing design. In addition, various fuselage drag-reduction technologies are
investigated: fuselage relaminarization, surface riblets, tailless arrangements, and Goldschmied propulsion
apparatus. All of these studies illustrate the large potential of the truss-braced wing along with additional dragreduction
technologies, which may substantially decrease the fuel weight and vehicle emissions.
This paper presents some studies using a significantly updated structural aeroelastic sizing procedure developed as part of our continuing efforts on multidisciplinary design optimization (MDO) of truss-braced wing airplanes. The primary focus has been to in- clude utter constraints for structural sizing of the wing. The structural sizing uses a gradient-based optimization procedure along with an analytically calculated response func- tion sensitivity with respect to the thickness design variables. It is shown that using the updated routine leads to lower structural mass in comparison with the fully-stressed struc- tural design procedure used in the previous MDO studies. The primary reasons for the lower mass is that inertial weight relief due to secondary structure is now included in the sizing process, and the buckling analysis is now based on a linearized eigenvalue problem, as opposed to a simple beam Euler buckling criteria used for the previous study which was significantly conservative. However, the results show that for a wing with lower mass the utter constraint becomes active for both strut-braced and truss-braced wing configura- tions. Hence, it is important to include those in the MDO studies to maintain feasibility of designs. Two challenges encountered during the process of including structural optimiza- tion with the utter constraint within the system-level MDO architecture are discussed along with the strategies devised to overcome them: convergence of structural optimiza- tion and the resulting numerical noise. A response surface methodology is used to integrate the structural optimization and system-level MDO and some initial results for the design of a truss-braced wing transonic transport airplane for minimum fuel consumption and emissions are presented.
This paper establishes the benefits of a truss-braced-wing transonic transport aircraft configuration compared to the cantilever-wing aircraft and to a strut-braced wing. Multidisciplinary design optimization is used to design aircraft with three wing configurations with, increasing complexity of topology: cantilever, one-member truss (strut), and three-member truss. Three objective functions are studied: minimum takeoff gross weight, minimum fuel consumption and emissions, and maximum lift-to-drag ratio. A mission with a 7730 n mile range at a cruise Mach number of 0.85 is considered. The results show the significant advantage of strut and simple truss configurations over the conventional cantilever configuration. One comparison produces a reduction of 45% in the fuel consumption while decreasing the minimum takeoff gross weight by 15%. For a second comparison, the fuel weight is reduced by 33% with a decreased minimum takeoff gross weight of 19%. Very attractive vehicle performance can be achieved without the necessity of decreasing cruise Mach number. The results also indicate that a truss-braced wing has a greater potential for improved aerodynamic performance than other innovative aircraft configurations. Further studies will consider the inclusion of more complex truss topologies and other innovative technologies that are judged to be synergistic with truss-braced-wing configurations.
Accurate drag estimation is critical in making computational design studies. Drag may be estimated thousands of times during a multidisciplinary design optimization, and computational fluid dynamics is not yet possible in these studies. The current model has been developed as part of an air-vehicle conceptual-design multidisciplinary design optimization framework. Its use for subsonic and transonic aircraft configurations is presented and validated. We present our parametric geometry definition, followed by the drag model description. The drag model includes induced, friction, wave, and interference drag. The model is compared with subsonic and transonic isolated wings, and a wing/body configuration used previously in drag prediction workshops. The agreement between the predictions of the drag model and test data is good, but lessens at high lift coefficients and high transonic Mach numbers. In some cases the accuracy of this drag estimation method exceeds much more elaborate analyses.
This study uses multidisciplinary design optimization to explore strut-braced and truss-braced wing configurations in enhancing the performance of medium-range transonic transport aircraft. The truss- and strut-braced wing concepts synergize structures and aerodynamics to decrease weight and drag. Past studies have found that these configurations can achieve significant performance benefits compared to a cantilever aircraft with a Mach 0.85, long-range Boeing 777-200ER-like mission. The objective of this study was to explore these benefits applied to a medium-range Boeing 737-800NG-like aircraft. Results demonstrate the significant performance benefits of the strut-braced and truss-braced wing configurations. Configurations are also optimized for 1990s or advanced-technology aerodynamics. For the 1990s aerodynamic-technology minimum-takeoff-gross-weight cases, the strut-braced and truss-braced wing configurations achieve reductions in the takeoff gross weight of as much as 6% with 20% less fuel weight than the comparable cantilever configurations. The 1990s aerodynamic-technology minimum-fuel cases offer fuel-weight reductions of about 13% compared to the 1990s aerodynamic-technology minimum-takeoff-gross-weight configurations, and 11% when compared to the 1990s aerodynamic-technology minimum-fuel optimized cantilever configurations. The advanced aerodynamic-technology minimum-takeoff-gross-weight configurations feature an additional 4% weight savings over the comparable 1990s aerodynamic-technology results, while the advanced aerodynamic-technology minimum-fuel cases show fuel savings of 12% over the 1990s aerodynamic-technology minimum-fuel results. This translates to a 15% reduction in takeoff gross weight for the advanced-technology minimum-takeoff-gross-weight cases, and a 47% reduction in fuel consumption for the advanced-technology minimum-fuel cases when compared to the simulated Boeing 737-800NG.
The multidisciplinary design optimization of a strut-braced wing (SBW) aircraft and its benefits relative to a conventional cantilever wing configuration are presented. The multidisciplinary design team is divided into aerodynamics, structures, aeroelasticity, and the synthesis of the various disciplines. The aerodynamic analysis uses simple models for induced drag, wave drag, parasite drag, and interference drag. The interference drag model is. based on detailed computational fluid dynamics analyses of various wing-strut intersections. The wing structural weight is calculated using a newly developed wing bending material weight routine that accounts for the special nature of SBWs. The other components of the aircraft weight are calculated using a combination of NASA's flight optimization system and Lockheed Martin aeronautical systems formulas. The SBW and cantilever wing configurations are optimized using design optimization tools (DOT) software. Offline NASTRAN aeroelastic analysis results indicate that the flutter speed is higher than the design requirement. The minimum take-off gross weight SBW aircraft showed a 9.3% advantage over the corresponding cantilever aircraft design. The minimum fuel weight SBW aircraft showed a 12.2% fuel weight advantage over a similar cantilever aircraft design.
Drag reduction is being pursued for next generation aircraft to reduce fuel consumption and pollutant production. Drag reduction of fuselages is now receiving more consideration, because the fuselage represents 30% of the drag of the entire aircraft. This paper presents numerical simulations of earlier experimental studies using aft suction slots and embedded propulsor systems to reduce fuselage drag. Detailed grid refinement studies were conducted, and different turbulence models were evaluated. A simulation of an airship with a boundary-layer suction slot and an embedded engine with aft injection of the ingested flow for propulsion was conducted. The simulations require significantly more propulsor power to achieve a self-propelled condition than reported in the experiments, which were subject to large experimental uncertainties. The computational fluid dynamics flowfield can be interrogated in detail, leading to improved understanding of the performance and integration of all system components. The particular arrangement studied in the experiments was shown to be limited by significant internal flow losses. This study provides the basis for the much improved integration of an embedded engine and gives the starting point for a wider analysis of more slender bodies operating in a transonic flowfield for application to modern transport aircraft.
This paper discusses current work on STRUCTURAL ASPECTS OF the design optimization of a Truss Braced Wing (TBW) configuration. These wings offer significat potential for performance improvements in terms of fuel effciency, but also offer challenges for a structural designer. The details of the structural analysis and design methodology are presented. Two different design methodologies are discussed: structural sizing based on beam idealization considering only bending stiffness and static analysis, and a finite element based sizing optimization approach including aeroelastic effects. The paper reports all aspects of the two approaches: design parameterization, model geometry and mesh generation, analysis and optimization. The first approach has been used in the past at Virginia Tech for Multidisciplinary Design Optimization (MDO) studies of a Strut-Braced Wing (SBW), and extensions to sizing of a more general TBW configuration are discussed. The second approach is used to perform some parametric studies presented here. Comparative studies are performed for wings designed for rigid and exible trim subject to static stress constraints. The aeroelastic performance of some TBW configurations is investigated. Only structural sizing parameters are treated as design variables. Conclusions are drawn from these results for guidance to the ongoing MDO studies of the TBW, to be reported in future papers.
Recent transonic airliner designs have generally converged upon a common cantilever low-wing configuration. It is unlikely that further large strides in performance are possible without a significant departure from the present design paradigm. One such alternative configuration is the strut-braced wing (SBW), which uses a strut for wing-bending load alleviation, allowing increased aspect ratio and reduced vying thickness to increase the lift to drag ratio. The thinner wing has less transonic wave drag, permitting the wing to unsweep for increased areas of natural laminar how and further structural weight savings. High aerodynamic efficiency translates into smaller, quieter, less expensive engines and less pollution. A multidisciplinary design optimization (MDO) approach is essential to realize the full potential of this synergistic configuration caused by the strong interdependence of structures, aerodynamics, and propulsion, NASA defined a need for a 325-passenger transport capable of flying 7500 n miles at Mach 0.85 for a 2010 service entry date. Lockheed Martin Aeronautical Systems (LMAS), as Virginia Polytechnic Institute and State University's (Virginia Tech) industry partner placed great emphasis on realistic constraints, projected technology levels, manufacturing, and certification issues. Numerous design challenges specific to the strut-braced wing became apparent during the study. Modifications were made to the Virginia Tech formulation to reflect these concerns, thus contributing realism to the MDO results. The SEW configuration is lighter, burns less fuel, requires smaller engines and costs less than an equivalent cantilever wing aircraft.
A structural and aeroelastic model for wing sizing and weight calculation of a strut-braced wing is described. The ming weight is calculated using a newly developed analysis accounting for the special nature of strut-braced wings. A specially developed aeroelastic model enables one to consider wing flexibility and spanwise redistribution of the aerodynamic loads during in-flight maneuvers. The structural model uses a hexagonal wing-box featuring skin panels, stringers, and spar caps, whereas the aerodynamics part employs a linearized transonic vortex lattice method. Thus, the wing weight may be calculated from the rigid or flexible wing spanload. The calculations reveal the significant influence of the strut on the bending material weight of the wing. The strut enables one to design a wing featuring thin airfoils without weight penalty. It also influences the spanwise redistribution of the aerodynamic loads and the resulting deformations. Increased weight savings are possible by iterative resizing of the wing structure using the actual design loads. As an advantage over the cantilever wing, the twist moment caused by the strut farce results in increased load alleviation,leading to further structural weight savings.
Final Report-Truss-Braced Wing Aircraft Configuration Studies NIA VT-03-1, 2749-VT
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Subsonic Ultra Green Aircraft Research: Phase I Final Report
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