Dissertations / Theses on the topic 'Blended-wing-body aircraft'

The desire to create an environmentally friendly aircraft that is aerodynamically efficient and capable of conveying large number of passengers over long ranges at reduced direct operating cost led aircraft designers to develop the Blended Wing Body(BWB) aircraft concept. The BWB aircraft represents a paradigm shift in the design of aircraft. The design offers immense aerodynamics and environmental benefits and is suitable for the integration of advanced systems and concepts like laminar flow technology, jet flaps and distributed propulsion. However, despite these benefits, the BWB is yet to be developed for commercial air transport. This is due to several challenges resulting from the highly integrated nature of the configuration and the attendant disciplinary couplings. This study describes the development of a physics based, deterministic, multivariate design synthesis optimisation for the conceptual design and exploration of the design space of a BWB aircraft. The tool integrates a physics based Athena Vortex Lattice aerodynamic analysis tool with deterministic geometry sizing and mass breakdown models to permit a realistic conceptual design synthesis and enables the exploration of the design space of this novel class of aircraft. The developed tool was eventually applied to the conceptual design synthesis and sensitivity analysis of BWB aircraft to demonstrate its capability, flexibility and potential applications. The results obtained conforms to the pattern established from a Cranfield University study on the BlendedWing Body Aircraft and could thus be applied in conceptual design with a reasonable level of confidence in its accuracy.

In recent years unconventional aircraft configurations, such as Blended-Wing-Body (BWB) aircraft, are being investigated and researched with the aim to develop more efficient aircraft configurations, in particular for very large transport aircraft that are more efficient and environmentally-friendly. The BWB configuration designates an alternative aircraft configuration where the wing and fuselage are integrated which results essentially in a hybrid flying wing shape. The first example of a BWB design was researched at the Loughead Company in the United States of America in 1917. The Junkers G. 38, the largest land plane in the world at the time, was produced in 1929 for Luft Hansa (present day; Lufthansa). Since 1939 Northrop Aircraft Inc. (USA), currently Northrop Grumman Corporation and the Horten brothers (Germany) investigated and developed BWB aircraft for military purposes. At present, the major aircraft industries and several universities has been researching the BWB concept aircraft for civil and military activities, although the BWB design concept has not been adapted for civil transport yet. The B-2 Spirit, (produced by the Northrop Corporation) has been used in military service since the late 1980s. The BWB design seems to show greater potential for very large passenger transport aircraft. A NASA BWB research team found an 800 passenger BWB concept consumed 27 percent less fuel per passenger per flight operation than an equivalent conventional configuration (Leiebeck 2005). The purpose of this research is to assess the aerodynamic efficiency of a BWB aircraft with respect to a conventional configuration, and to identify design issues that determine the effectiveness of BWB performance as a function of aircraft payload capacity. The approach was undertaken to develop a new conceptual design of a BWB aircraft using Computational Aided Design (CAD) tools and Computational Fluid Dynamics (CFD) software. An existing high-capacity aircraft, the Airbus A380 Contents RMIT University, Australia was modelled, and its aerodynamic characteristics assessed using CFD to enable comparison with the BWB design. The BWB design had to be compatible with airports that took conventional aircraft, meaning a wingspan of not more than 80 meters for what the International Civil Aviation Organisation (ICAO) regulation calls class 7 airports (Amano 2001). From the literature review, five contentions were addressed; i. Is a BWB aircraft design more aerodynamically efficient than a conventional aircraft configuration? ii. How does the BWB compare overall with a conventional design configuration? iii. What is the trade-off between conventional designs and a BWB arrangement? iv. What mission requirements, such as payload and endurance, will a BWB design concept become attractive for? v. What are the practical issues associated with the BWB design that need to be addressed? In an aircraft multidisciplinary design environment, there are two major branches of engineering science; CFD analysis and structural analysis; which is required to commence producing an aircraft. In this research, conceptual BWB designs and CFD simulations were iterated to evaluate the aerodynamic performance of an optimal BWB design, and a theoretical calculation of structural analysis was done based on the CFD results. The following hypothesis was prompted; A BWB configuration has superior in flight performance due to a higher Lift-to-Drag (L/D) ratio, and could improve upon existing conventional aircraft, in the areas of noise emission, fuel consumption and Direct Operation Cost (DOC) on service. However, a BWB configuration needs to employ a new structural system for passenger safety procedures, such as passenger ingress/egress. The research confirmed that the BWB configuration achieves higher aerodynamic performance with an achievement of the current airport compatibility issue. The beneficial results of the BWB design were that the parasite drag was decreased and the spanwise body as a whole can generate lift. In a BWB design environment, several advanced computational techniques were required to compute a CFD simulation with the CAD model using pre-processing and CFD software.

This study is concerned with a methodology for the aerodynamic analysis and preliminary design of a novel configuration for high subsonic civil transport, based on the flying wing concept, known a Blended Wing Body (BWB). A response surface based optimisation method is developed, enabling the designer to monitor the effect of shape modification on the controllability of the aircraft in both longitudinal and lateral/directional motion and on the Wing structural weight, while maximising the aerodynamic efficiency. The design aspects considered included high- speed aerodynamics, flight static-stability and trim characteristics. The response surface Scheme employs a space filling design of experiment technique to build least square fitting quadratic polynomials, used in place of the original computational modules in a gradient based search. A optimisation test indicated that the present method is more effective in leading the design near to the global optimum as opposed to a conventional gradient method with direct search, despite that the constructed approximation may not represent accurately the actual surface. With this system, multiple constrained optimisation problems are successfully solved in the favourable case of smooth objective/constraint function. Where these functions may exhibit high non-linear trends, an iterative response surface method refining both approximation and bounds of the design space is proposed. The capabilities of such a technique are shown for transonic aerofoil optimisation problems, demonstrating that the proposed method is more efficient and more effective than some other state-of- the-art methods. As a result of these studies, the aerodynamic efficiency of a large capacity BWB configuration has been considerably improved by re-designing the external shape to generate a spanwise loading intermediate between triangular and elliptic. The longitudinal static stability analysis revealed that the aircraft is stable except at low- weights with zero-payload. The lateral/directional analyses showed that the aircraft is stable in roll, but unstable in yaw. Despite that the winglets are found to stabilise the aircraft, it is directionally unstable without additional vertical stabilisers. I

The Blended Wing Body (BWB) aircraft offers a number of aerodynamic perfor- mance advantages when compared with conventional configurations. However, while operating at low airspeeds with nominal static margins, the controls on the BWB aircraft begin to saturate and the dynamic performance gets sluggish. Augmenta- tion of aerodynamic controls with the propulsion system is therefore considered in this research. Two aspects were of interest, namely thrust vectoring (TVC) and flap blowing. An aerodynamic model for the BWB aircraft with blown flap effects was formulated using empirical and vortex lattice methods and then integrated with a three spool Trent 500 turbofan engine model. The objectives were to estimate the effect of vectored thrust and engine bleed on its performance and to ascertain the corresponding gains in aerodynamic control effectiveness. To enhance control effectiveness, both internally and external blown flaps were sim- ulated. For a full span internally blown flap (IBF) arrangement using IPC flow, the amount of bleed mass flow and consequently the achievable blowing coefficients are limited. For IBF, the pitch control effectiveness was shown to increase by 18% at low airspeeds. The associated detoriation in engine performance due to compressor bleed could be avoided either by bleeding the compressor at an earlier station along its ax- ial length or matching the engine for permanent bleed extraction. For an externally blown flap (EBF) arrangement using bypass air, high blowing coefficients are shown to be achieved at 100% Fan RPM. This results in a 44% increase in pitch control authority at landing and take-off speeds. The main benefit occurs at take-off, where both TVC and flap blowing help in achieving early pitch rotation, reducing take-off field lengths and lift-off speeds considerably. With central flap blowing and a lim- ited TVC of 10◦, the lift-off range reduces by 48% and lift-off velocity by almost 26%. For the lateral-directional axis it was shown that both aileron and rudder control powers can be almost doubled at a blowing coefficient of Cu = 0.2. Increased roll authority greatly helps in achieving better roll response at low speeds, whereas the increased rudder power helps in maintaining flight path in presence of asymmetric thrust or engine failure, otherwise not possible using the conventional winglet rudder.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.
This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from department-submitted PDF version of thesis
Includes bibliographical references (p. 99-102).
Multidisciplinary design optimization (MDO) is becoming an essential tool for the design of engineering systems due to the inherent coupling between discipline analyses and the increasing complexity of such systems. An important component of MDO is effective exploration of the design space since this is often a key driver in finding characteristics of systems which perform well. However, many design space exploration techniques scale poorly with the number of design variables and, moreover, a large-dimensional design space can be prohibitive to designer manipulation. This research addresses complexity management in trade-space exploration of multidisciplinary systems, with a focus on the conceptual design of Blended Wing Body (BWB) aircraft. The objectives of this thesis are twofold. The first objective is to create a multidisciplinary tool for the design of BWB aircraft and to demonstrate the performance of the tool on several example trade studies. The second objective is to develop a methodology for reducing the dimension of the design space using designer-chosen partitionings of the design variables describing the system. The first half of this thesis describes the development of the BWB design tool and demonstrates its performance via a comparison to existing methods for the conceptual design of an existing BWB configuration. The BWB design tool is then demonstrated using two example design space trades with respect to planform geometry and cabin bay arrangement. Results show that the BWB design tool provides sufficient fidelity compared to existing BWB analyses, while accurately predicting trends in system performance. The second half of this thesis develops a bi-level methodology for reducing the dimension of the design space for a trade space exploration problem. In this methodology, the designer partitions the design vector into an upper- and lower-level set, wherein the lower-level variables essentially serve as parameters, in which their values are chosen via an optimization with respect to some lower-level objective. This reduces the dimension of the design space, thereby allowing a more manageable space for designer interaction, while subsequently ensuring that the lower-level variables are set to "good" values relative to the lower-level objective. The bi-level method is demonstrated on three test problems, each involving an exploration over BWB planform geometries. Results show that the method constructs surrogate models in which the sampled configurations have a reduction in the system objective by up to 4 % relative to surrogates constructed using a standard exploration. Furthermore, the problems highlight the potential for the framework to reduce the dimension of the design space such that the full space can be visualized.
by Cory Asher Kays.
S.M.

Conventional airliners use two to four engines in a Cayley-type arrangement to provide thrust, and the thrust from these engines is typically concentrated right behind the engine. Distributed propulsion is the idea of redistributing the thrust across most, or all, of the wingspan of an aircraft. This can be accomplished by using several large engines and using a duct to spread out the exhaust flow to form a jet-wing or by using many small engines spaced along the span of the wing. Jet-wing distributed propulsion was originally suggested by Kuchemann as a way to improve propulsive efficiency. In addition, one can envision a jet-wing with deflected jets replacing flaps and slats and the associated noise.

The purpose of this study was to assess the performance benefits of jet-wing distributed propulsion. The Reynolds-averaged, finite-volume, Navier-Stokes code GASP was used to perform parametric computational fluid dynamics (CFD) analyses on two-dimensional jet-wing models. The jet-wing was modeled by applying velocity and density boundary conditions on the trailing edges of blunt trailing edge airfoils such that the vehicle was self-propelled. As this work was part of a Blended-Wing-Body (BWB) distributed propulsion multidisciplinary optimization (MDO) study, two airfoils of different thickness were modeled at BWB cruise conditions. One airfoil, representative of an outboard BWB wing section, was 11% thick. The other airfoil, representative of an inboard BWB wing section, was 18% thick. Furthermore, in an attempt to increase the propulsive efficiency, the trailing edge thickness of the 11% thick airfoil was doubled in size. The studies show that jet-wing distributed propulsion can be used to obtain propulsive efficiencies on the order of turbofan engine aircraft. If the trailing edge thickness is expanded, then jet-wing distributed propulsion can give improved propulsive efficiency. However, expanding the trailing edge must be done with care, as there is a drag penalty. Jet-wing studies were also performed at lower Reynolds numbers, typical of UAV-sized aircraft, and they showed reduced propulsive efficiency performance. At the lower Reynolds number, it was found that the lift, drag, and pitching moment coefficients varied nearly linearly for small jet-flap deflection angles.

Master of Science

The purpose of this study is to examine the multidisciplinary design optimization (MDO) of a distributed propulsion blended-wing-body (BWB) aircraft. The BWB is a hybrid shape resembling a flying wing, placing the payload in the inboard sections of the wing. The distributed propulsion concept involves replacing a small number of large engines with many smaller engines. The distributed propulsion concept considered here ducts part of the engine exhaust to exit out along the trailing edge of the wing. The distributed propulsion concept affects almost every aspect of the BWB design. Methods to model these effects and integrate them into an MDO framework were developed. The most important effect modeled is the impact on the propulsive efficiency. There has been conjecture that there will be an increase in propulsive efficiency when there is blowing out of the trailing edge of a wing. A mathematical formulation was derived to explain this. The formulation showed that the jet â fills inâ the wake behind the body, improving the overall aerodynamic/propulsion system, resulting in an increased propulsive efficiency. The distributed propulsion concept also replaces the conventional elevons with a vectored thrust system for longitudinal control. An extension of Spenceâ s Jet Flap theory was developed to estimate the effects of this vectored thrust system on the aircraft longitudinal control. It was found to provide a reasonable estimate of the control capability of the aircraft. An MDO framework was developed, integrating all the distributed propulsion effects modeled. Using a gradient based optimization algorithm, the distributed propulsion BWB aircraft was optimized and compared with a similarly optimized conventional BWB design. Both designs are for an 800 passenger, 0.85 cruise Mach number and 7000 nmi mission. The MDO results found that the distributed propulsion BWB aircraft has a 4% takeoff gross weight and a 2% fuel weight. Both designs have similar planform shapes, although the planform area of the distributed propulsion BWB design is 10% smaller. Through parametric studies, it was also found that the aircraft was most sensitive to the amount of savings in propulsive efficiency and the weight of the ducts used to divert the engine exhaust.
Ph. D.

The purpose of this research is to document the design and optimisation of a full suite of guidance, navigation and control (GNC) algorithms for a small unmanned aerial vehicle (UAV), the Skywalker X8. This was performed so as to fill a void in the available literature on the selected airframe, which currently only focuses on aspects such as aerodynamic modelling, advanced controller design, or uses of the airframe to perform higher level tasks. All of these research areas make use of off-the-shelf flight controllers, but these are not always the most appropriate foundations for more advanced work as they are inherently sluggish so as to be broadly applicable to a variety of airframes. Subsequently, the Skywalker X8 airframe was modelled, using existing literature, and then characterised so as to establish what the goals might be for an optimal set of controllers. An autopilot was then designed which was optimised so as to be as close to the identified optimal performance characteristics as possible, with effort being put into ensuring that all non-linearities and disturbances were taken into account. This included advanced modelling of sensors, actuators, the environment, and the system itself. The autopilot design was then extended with a set of guidance and navigation algorithms, also developed as part of this research. This consisted of both path planning and path following algorithms which allowed for the synthesis of general classes of paths useful to the application. With both the autopilot and guidance laws developed, the system could be tested under several atmospheric flight conditions. These took the form of various wind directions and intensity levels being applied to the airframe whilst transitioning between a range of different waypoint configurations. The system was subsequently shown to be able to follow a set of waypoints very accurately, even with winds and turbulence with magnitudes of in excess of 60% of the aircraft's nominal airspeed. With a strong autopilot designed and illustrated in a high fidelity simulation environment, this work can now easily be extended into many fields. All of the tools used for this research are available and well documented, and the processes followed repeatable with all justification available in the text. As such, should a project which aims to extend this work wish to adjust the autopilot design or guidance laws, based on different requirements, this is easily accomplished and recommendations of starting points are provided. The system model and autopilot are also made available and are usable exactly as they are should one wish to undertake additional research which does not aim to modify, but to extend this work.

The blended-wing-body (BWB) configuration appears as a promising contender for the next generation of large transport aircraft. The idea of blending the wing with the fuselage and eliminating the tail is not new, it has long been known that tailless aircraft can suffer from stability and control problems that must be addressed early in the design. This thesis is concerned with identifying and then evaluating the flight dynamics, stability, flight controls and handling qualities of a generic BWB large transport aircraft concept. Longitudinal and lateral-directional static and dynamic stability analysis using aerodynamic data representative of different BWB configurations enabled a better understanding of the BWB aircraft characteristics and identification of the mechanisms that influence its behaviour. The static stability studies revealed that there is limited control power both for the longitudinal and lateral-directional motion. The solution for the longitudinal problem is to limit the static margins to small values around the neutral point, and even to use negative static margins. However, for the directional control problem the solution is to investigate alternative ways of generating directional control power. Additional investigation uncovered dynamic instability due to the low and negative longitudinal and directional static stability. Furthermore, adverse roll and yaw responses were found to aileron inputs. The implementation of a pitch rate command/attitude hold flight control system (FCS) improved the longitudinal basic BWB characteristics to satisfactory levels, or Level 1, flying and handling qualities (FHQ). Although the lateral-directional command and stability FCS also improved the BWB flying and handling qualities it was demonstrated that Level 1 was not achieved for all flight conditions due to limited directional control power. The possibility to use the conventional FHQs criteria and requirements for FCS design and FHQs assessment on BWB configurations was also investigated. Hence, a limited set of simulation trials were undertaken using an augmented BWB configuration. The longitudinal Bandwidth/Phase delay/Gibson dropback criteria, as suggested by the military standards, together with the Generic Control Anticipation Parameter (GCAP) proved possible to use to assess flying and handling qualities of BWB aircraft. For the lateral-directional motion the MIL-F-8785C criteria were used. Although it is possible to assess the FHQ of BWB configuartions using these criteria, more research is recommended specifically on the lateral-directional FHQs criteria and requirements of highly augmented large transport aircraft.

Aircraft with advanced wing geometry, like the flying wing or blended wing body configuration, seems to be the seed candidate of future aircraft. Compared with conventional aircraft, there are significant aerodynamic performance improvements because of its highly integrated wing and fuselage configuration. On the other hand, due to its tailless configuration, the stability characteristics are not as good as conventional aircraft. The research aims to compare the aerodynamic and stability characteristics of conventional, flying wing and blended wing body aircraft. Based on the same requirement—250 passenger capability and 7,500 nautical miles range, three different configurations—conventional, flying wing and blended wing body options were provided to make direct comparison. The research contains four parts. In the first part, the aerodynamic characteristics were compared using empirical equation ESDU datasheet and Vortex-Lattice Method based AVL software. In the second part, combined with the aerodynamic data and output mass data from other team member, the stability characteristics were analysed. The stability comparison contains longitudinal, lateral-directional static stability and dynamic stability. In the third part, several geometry parameters were varied to investigate the influence on the aerodynamic and stability characteristics of blended wing body configuration. In the last part, a special case has been explored in an attempt to improve the static stability by changing geometry parameters. The process shows that the design of blended wing body is really complex since the closely coupling of several parameters.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009.
This thesis presents the analysis, design, simulation and practical implementation of a novel control system for a variable stability blended-wing-body unmanned aerial vehicle. The aircraft has a moveable centre of mass that allows it to operate in an aerodynamically optimised minimum drag configuration during cruise flight. The primary purpose of the control system is thus to regain nominal static stability for all centre of mass positions, and then to further regulate motion variables for autonomous way point navigation. A thorough analysis of the parameters affected by the varying centre of mass position leads to the identification of the main control problem. It is shown that a recently published acceleration based control methodology can be used with minor modification to elegantly solve the variable stability control problem. After providing the details of the control system design, the customised avionics used for their practical implementation are presented. The results of extensive hardware in the loop simulations verify the functionality of the controllers. Finally, flight test results illustrate the practical success of the autopilot and clearly show how the control system is capable of controlling the variable stability aircraft at centre of mass locations where a human pilot could not.

The objective of this research is to examine how to design low-noise transport aircraft using Multidisciplinary Design Optimization (MDO). The subject is approached by designing for low-noise both implicitly and explicitly. The explicit design approach involves optimizing an aircraft while explicitly constraining the noise level. An MDO framework capable of optimizing both a cantilever wing and a Strut-Braced-Wing (SBW) aircraft was developed. The framework employs aircraft analysis codes previously developed at the Multidisciplinary Design and Analysis (MAD) Center at Virginia Tech (VT). These codes have been improved here to provide more detailed and realistic analysis. The Aircraft Noise Prediction Program (ANOPP) is used for airframe noise analysis. The objective is to use the MDO framework to design aircraft for low-airframe-noise at the approach conditions and quantify the change in weight and performance with respect to a traditionally designed aircraft. The results show that reducing airframe noise by reducing approach speed alone, will not provide significant noise reduction without a large performance and weight penalty. Therefore, more dramatic changes to the aircraft design are needed to achieve a significant airframe noise reduction. Another study showed that the trailing-edge (TE) flap can be eliminated, as well as all the noise associated with that device, without incurring a significant weight and performance penalty. To achieve approximately 10 EPNdB TE flap noise reduction the flap area was reduced by 82% while the wing reference area was increased by 12.4% and the angle of attack increased from 7.6 degrees to 12.1 degrees to meet the required lift at approach. The wing span increased by approximately 2.2%. Since the flap area is being minimized, the wing weight suffers only about a 2,000 lb penalty. The increase in wing span provides a reduction in induced drag to balance the increased parasite drag due to a lower wing aspect ratio. As a result, the aircraft has been designed to have minimal TE flaps without any significant performance penalty. If noise due to the leading-edge (LE) slats and landing gear are reduced, which is currently being pursued, the elimination of the flap will be very significant as the clean wing noise will be the next 'noise barrier'. Lastly, a comparison showed that SBW aircraft can be designed to be 10% lighter and require 15% less fuel than cantilever wing aircraft. Furthermore, an airframe noise analysis showed that SBW aircraft with short fuselage-mounted landing gear could have similar or potentially a lower airframe noise level than comparable cantilever wing aircraft. The implicit design approach involves selecting a configuration that supports a low-noise operation, and optimizing for performance. A Blended-Wing-Body (BWB) transport aircraft has the potential for significant reduction in environmental emissions and noise compared to a conventional transport aircraft. A BWB with distributed propulsion was selected as the configuration for the implicit low-noise design in this research. An MDO framework previously developed at the MAD Center at Virginia Tech has been refined to give more accurate and realistic aircraft designs. To study the effects of distributed propulsion, two different BWB configurations were optimized. A conventional propulsion BWB with four pylon mounted engines and two versions of a distributed propulsion BWB with eight boundary layer ingestion inlet engines. A 'conservative' distributed propulsion BWB design with a 20% duct weight factor and a 95% duct efficiency, and an 'optimistic' distributed propulsion BWB design with a 10% duct weight factor and a 97% duct efficiency were studied. The results show that 65% of the possible savings due to 'filling in' the wake are required for the 'optimistic' distributed propulsion BWB design to have comparable $TOGW$ as the conventional propulsion BWB, and 100% savings are required for the 'conservative' design. Therefore, considering weight alone, this may not be an attractive concept. Although a significant weight penalty is associated with the distributed propulsion system presented in this study, other characteristics need to be considered when evaluating the overall effects. Potential benefits of distributed propulsion are, for example, reduced propulsion system noise, improved safety due to engine redundancy, a less critical engine-out condition, gust load/flutter alleviation, and increased affordability due to smaller, easily-interchangeable engines.
Ph. D.

Radical aircraft and propulsion system architecture changes may be required to continue historic performance improvement rates as current civil aircraft and engine technologies mature. Significant fuel-burn savings are predicted to be achieved through the Distributed Propulsion concept, where an array of propulsors is distributed along the span of an aircraft to ingest boundary layer air and increase propulsive efficiency. Studies such as those by NASA predict large performance benefits when integrating Distributed Propulsion with the Blended Wing Body aircraft configuration, as this planform geometry is particularly suited to the ingestion of boundary layer air and the fans can be redesigned to reduce the detrimental distortion effects on performance. Additionally, a conventional aircraft with Distributed Propulsion has not been assessed in public domain literature and may also provide substantial benefits. A conceptual aircraft design code has been developed to enable the modelling of conventional and novel aircraft. A distributed fan tool has been developed to model fan performance, and a mathematical derivation was created and integrated with the fan tool to enable the boundary layer ingestion modelling. A tube & wing Distributed Propulsion aircraft with boundary layer ingestion has been compared with a current technology reference aircraft and an advanced turbofan aircraft of 2035 technology. The advanced tube & wing aircraft achieved a 27.5% fuel-burn reduction relative to the baseline aircraft and the Distributed Propulsion variant showed fuel efficiency gains of 4.1% relative to the advanced turbofan variant due to a reduced specific fuel consumption, produced through a reduction in distributed fan power requirement. The Blended Wing Body with Distributed Propulsion was compared with a turbofan variant reference aircraft and a 5.3% fuel-burn reduction was shown to be achievable through reduced core engine size and weight. The Distributed Propulsion system was shown to be particularly sensitive to inlet duct losses. Further investigation into the parametric sensitivity of the system revealed that duct loss could be mitigated by altering the mass flow and the percentage thrust produced by the distributed fans. Fuel-burn could be further reduced bydecreasing component weight and drag, through decreasing the fan and electrical system size to below that necessary for optimum power or specific fuel consumption.

The primary research objective was to develop a methodology to support conceptual design of the Hybrid Wing Body (HWB) configuration. The absence of a horizontal tail imposes new stability and control requirements on the planform, and therefore requiring greater emphasis on control authority assessment than is typical for conceptual design. This required investigations into three primary areas of research. The first was to develop a method for designing an appropriate amount of redundancy. This was motivated widely varying numbers of trailing edge elevons in the HWB literature, and inadequate explanations for these early design decisions. The method identifies stakeholders, metrics of interest, and synthesizes these metrics using the Breguet range equation for system level comparison of control surface layouts. The second area of research was the development trim analysis methods that could accommodate redundant control surfaces, for which conventional methods performed poorly. A new measure of control authority was developed for vehicles with redundant controls. This is accomplished using concepts from the control allocation literature such as the attainable moment subset and the direct allocation method. The result is a continuous measure of remaining control authority suitable for use during HWB sizing and optimization. The final research area integrated performance and control authority to create a HWB sizing environment, and investigations into how to use it for design space exploration and vehicle optimization complete the methodology. The Monte Carlo Simulation method is used to map the design space, identify good designs for optimization, and to develop design heuristics. Finally, HWB optimization experiments were performed to discover best practices for conceptual design.

The blended wing body (BWB) is a tailless aircraft with the potential to use 27% less fuel than a conventional aircraft with the same passenger capacity and range. The primary purpose of the current study was to determine the handling qualities of the BWB, using piloted-handling trials in a moving-base simulator. The secondary purpose was to determine the effect of simulator motion on handling-quality ratings. De Castro conducted piloted-handling trials in a fixed-base simulator. De Castro's tasks and flight model were modified in the current study. In the current study, three subjects rated the handling qualities as Level 1 or 2, depending on the task. Simulator motion did not have a significant effect on the results.

Increasing environmental concerns and fuel prices motivate the study of alternative, unconventional aircraft configurations. One such example is the blended-wing-body configuration, which has been shown to have several advantages over the conventional tube-and-wing aircraft configuration. In this thesis, a blended-wing-body aircraft is studied and optimized aerodynamically using a high-fidelity Euler-based flow solver, integrated geometry parameterization and mesh movement, adjoint-based gradient evaluation, and a sequential quadratic programming algorithm. Specifically, the aircraft is optimized at transonic conditions to minimize the sum of induced and wave drag. These optimizations are carried out with both fixed and varying airfoil sections. With varying airfoil sections and increased freedom, up to 52% drag reduction relative to the baseline geometry was achieved: at the target lift coefficient of 0.357, a drag coefficient of 0.01313 and an inviscid lift-to-drag ratio of 27.2 were obtained.

碩士
淡江大學
航空太空工程學系碩士班
98
Aircraft manufacture companies have introduced new aircrafts with high fuel-efficiency to reduce the operation cost of flight vehicle in recent years; the blended-wing-body (BWB) aircraft is another solution besides the strategies of the improvement in structure/material and aircraft enlargement. But we cannot grasp the characteristics of manufacturing; flight efficiency, etc.; because the configuration of BWB is so different from the conventional one. So in recent years the related researches about this modern BWB aircraft become the topic of many research projects. This thesis refers and imitates the aircraft of NASA’s X-48, and then simulates the three-dimensional flow field with the flight condition of Mach 0.85 cruise at the high altitude using the existing computational fluid dynamics (CFD) software named “Fluent”. And then it evaluates the efficiency of flight performance with different wingtip devices. The wingtip devices of this research are the general common winglet and the novel configuration of C-wing. In addition, this research also enlists the BWB geometry from another fellow student, while computing and comparing with these different configurations. Another theme of this research is to do the optimisation study of the imitative X-48. We choose two values of twist angle parameter of the aircraft geometry, using software of CAD, grid generation, flow solver, and homemade programming codes. We expect that will improve the airflow on the surface of aircraft, move the position of shock wave, and weaken the strength of shock wave. Finally it increases the efficiency of aircraft for an apparent range. The result of this research will provide aircraft manufacture companies some inspiration of aircraft design, increased flexibility in the choice of design tools, and the preliminary understanding on flight performance of a new type of aircraft. We even investigate the pros and cons of structured and unstructured grid, and the difference in their simulated aerodynamic coefficients is quite large. One important finding of this study is that at least for our BWB configurations, the C-wing model does not seem to improve the cruise performance at all.

碩士
淡江大學
航空太空工程學系碩士班
98
The goal of aircraft design is to achieve safe and efficient flight. In the world of civilian air transport, efficient, economically attractive configurations are urgently needed. As for civilian commercial aircrafts, studies have shown remarkable performance improvements for the Blended Wing Body (BWB) over conventional subsonic transport. On the other hand, global warming has led to extreme weather around the world frequently, if aircraft taking-off and landing will unavoidably meet with the strong crosswind or/and heavy rain, then aircraft designer must put these severe werather influence into considerations in the conceptual design phase phase. One way to investigate the BWB airplane performance degradation is through CFD calculation. The detrimental crosswind effects to Blended Wing Bod aircraft longitudinal, lateral and directional stability situation will be presented in this study. The speed of crosswinds considered here are 10m/s, 20m/s and 30m/s. Comparing with Boeing 747-100, no matter BWB is static stable or not, its stability derivative values under crosswind are always smaller than Boeing 747-100, representing the intrinsic nature of BWB static unstable tendency. Also, the heavy rain influence of different rain rates is that the lift coefficient is decreased and drag coefficient is increased at all different angle of attack spectrum. Comparing the different rain rates, liquid water content 39 g/m3 is more influential than 25 g/m3, with maximum reduction of lift coefficient is at angle of attack 0 degree and maximum increase of drag coefficient is at angle of attack 6 degree. In this study, Fluent is used as a simulation tool, the structure grid is chosen and generated by Gambit, and the standard M6 wing is first validated to ensure this simulation process is correct. This study hope to recognize and comprehend the basic aerodynamic performance for Blended Wind Body aircraft under severe weather situation, and the information gained here will be helpful for future transport aircraft designers.

碩士
淡江大學
航空太空工程學系碩士班
101
In pace with the modern airplane development motivated by fuel efficiency and environmental conservation, many different aircraft configurations and design concepts are created in last two decades to accommodate these challenges. Blended Wing Body aircrafts (BWB) are created for the same reason, and remains to be one of the most promising flight vehicle concepts for future generations to come. But this plane are seldom seen, people are still study its aerodynamic analysis at the beginning stage, moreover the aerodynamic performance of BWB with its engines on. In this research, based on previous works at Tamkang, we construct geometry model first and now this BWB is with engine added on. Then, software ANSYS is implemented to generate different types of mesh, such as structured, unstructured, and hybrid grids. The flow solver routine with proper turbulence model selection is first tested on our previous UAV, M-6 wing, and BWB configurations, and then this simulation routine is also extended to the incompressible take-off speed and 0.85 Mach cruise conditions. After that, we select the surrogate model to find the BWB optimum angle of attack (AOA) and vertical height for engine positions. The surrogate model is a relatively new method for optimum engineering design, which is especially suited for CFD optimization computation and contains several different modules, and the model we select is the Kriging model. Without spend too much effort on the time consuming CFD simulation for every different AOA and engine positions, it allows us to find the best possible configuration conditions from a mere of about ten properly chosen design of experiment (DOE) cases. This model is verified by first predicting the best AOA value for BWB without engines, and a normalized optimization parameter or objective function is created, which composed of both the lift and drag coefficients. Thus we can predict the optimum AOA for BWB and its engine vertical positions. After the predicting value is achieved, new engine position geometry will be generated according to the surrogate model prediction. Results show that the close agreement between our Kriging model prediction and CFD computation represent a first triumph in the surrogate model implementation, and this could imply tremendous saving in future aerodynamic simulation in the airplane design phases.

碩士
淡江大學
航空太空工程學系碩士班
97
The detrimental effects of some meteorological phenomenon such as wind shear, thunderstorm, ice/snow etc, to aviation safety are relatively well known. But aerodynamic influences due to heavy rain are still the on-going research subject, and needs further investigation. But for the past decades there are neither experimental nor numerical researches about heavy rain except our research team conducted at 2003 and 2008. This paper first reviews some research findings in creating a geometrical model of Blended-Wing-Body configuration and its aerodynamic performance degradation due to heavy rain effects. Secondly, a commercial CFD package FLUENT and preprocessing tool Gambit is used as our main analytical tools, and the simulation of heavy rain is accomplished by using two-phase flow approach’s Discrete Phase Model (DPM) provided by FLUENT. The results shows that this research successfully simulate the Blended-Wing-Body aerodynamic efficiency at cruise condition and the degradation effect under the heavy rain at low speed. The BWB aerodynamic degradation rate increases with the rain rate as expected. When comparing with experimental data, our numerical results show that the lift coefficients decrease, drag coefficients increase. It is expected that the quantitative information gained in this paper could be useful to the operational airline industry, and greater effort should put in this direction to further aircraft design and improve aviation safety for future Blended-Wing-Body transport aircraft.