Flying Wing Configuration Research Articles

Researches on the aerodynamic and stealth characteristics for flying wing fighter

Flying wing configuration fighter is very promising for the advanced fighter in the future. This paper studies the aerodynamic and stealth characteristics of flying wing fighter. Firstly, the effect of sharp leading edge on the subsonic, transonic lift and drag characteristics and stealth characteristics of the fighter are studied. The results show that the sharpen of leading edge of the inboard wing could greatly improve the lateral stealth characteristics while maintaining the subsonic and transonic lift characteristics. In order to furtherly improve its aerodynamic and forward stealth characteristics, the aerodynamic/stealth collaborative design optimization method based on discrete adjoint is carried out. And the results presented that there are obvious contradictions in the subsonic, transonic and supersonic lift characteristics of the flying wing fighter, and the improvement of the forward stealth characteristics will also damage the subsonic lift characteristics. Therefore, it is necessary to make a compromise between the subsonic, transonic and supersonic lift characteristics, drag characteristics and stealth characteristics in the shape design of flying wing fighter.

Unsteady aerodynamic characteristics of a morphing tail configuration

Morphing aircraft is an important trend in the future development of next-generation aircraft. This paper focuses on aircraft with a small aspect ratio flying wing configuration that includes morphing tails. The unsteady aerodynamic characteristics of the morphing tail configuration are numerically simulated using the unstructured overset grid technique and the dual-time method, focusing on the effects of the tail deflection angle over time, Mach number, and side slip angle on the unsteady aerodynamic characteristics of the entire aircraft and tails. The second derivative of the tail deflection angle with time should be continuous, and the maximum angular velocity and maximum angular acceleration should be minimized. The hysteresis loop area is closely related to the Mach number. The sideslip angle aggravates the nonlinearity of the unsteady aerodynamic characteristics of the entire aircraft. The unsteady aerodynamic characteristics during tail morphing are affected by static (wing downwash effect and projected area effect) and dynamic (flow field hysteresis effect, additional motion effect, and wall implication effect) characteristics. The enclosed research provides a reference for the aerodynamic and control system designs of morphing tail configurations.

Research on low-speed aerodynamic characterictics of flying wing standard model with low-aspect ratio

In order to study the aerodynamic characteristics of low-aspect ratio flying wing configuration, low speed wind tunnel tests and numerical simulation were carried out base on CHN-F1 standard model. The research results show that the repeatability accuracy of the test data is good for being benchmark to CFD verification and validation. In the range of medium angle of attack (less than 14 °), the aerodynamic coefficient changes linearly, and the root mean square of the test data is small. With the increase of the angle of attack, the aerodynamic coefficient changes nonlinearly. It is found that the simulation results were in good agreement with test data in the lift linear section.

Designing aerodynamic devices for UAV – lessons learned

PurposeDesigning new aircraft that are state-of-the-art and beyond always requires the development of new technologies. This paper aims to present lessons learned while designing, building and testing new UAVs in the configuration of the flying wing. The UAV contains a number of aerodynamic devices that are not obvious solutions and use the latest manufacturing technology achievements, such as 3D printing.Design/methodology/approachThe design solutions were applied on an airworthy aircraft and checked during test flights. The process was first conducted on the smaller UAV, and based on the test outcomes, improvements were made and then applied on the larger version of the UAV, where they were verified.FindingsA number of practical findings were identified. For example, the use of 3D printing technology for manufacturing integrated pressure ports, investigation of the adverse yaw effect on the flying wing configuration and the effectiveness of winglet rudders in producing yawing moment.Practical implicationsAll designed devices were tested in practice on the flying aircraft. It allowed for improved aircraft performance and handling characteristics. Several of the technologies used improved the speed and quality of aerodynamic device design and manufacturing, which also influences the reliability of the aircraft.Originality/valueThe paper presents how 3D printing technology can be utilized for manufacturing of aerodynamic devices. Specially developed techniques for control surface design, which can affect adverse yaw problem and aircraft handling characteristics, were described.

Numerical Study on Fluid Dynamic Characteristics of a Cross-Flow Fan

This paper focuses on the application of a cross-flow fan (CFF) to generate propulsion for a submersible aircraft with a flying wing configuration. A numerical method is established to simulate the CFF operating both in the air and underwater. This paper then investigates the fluid dynamic characteristics of the CFF, including the velocity field, the pressure field, the cavitation distribution, the lift, and the thrust. It is concluded that proper lifts and thrusts can be obtained when the rotating speed and the angle of attack are reasonably designed. This work provides a valuable numerical methodology for studying the fluid dynamic characteristics of the CFF operating in different media and offers a technical basis for the selection of a motor system for submersible aircraft.

An Optimisation of a Chordwise Slot to Enhance Lateral Flow Control on a UCAV

This research aims to optimise a chordwise slot so that lateral flow control of a flying wing configuration can be enhanced. This was achieved by maximising the airflow rate over the trailing edge control surfaces of the wing. A higher rate of airflow over the trailing edge control surfaces will increase the operationality of control surfaces, resulting in enhanced lateral control of the air vehicle at medium to high angles of attack. Four variables describing the chordwise slot are identified for numerical optimisation. They are: location, width, length, and angle of trajectory of chordwise slot relative to freestream. The results of the airflow rate for the wing with an optimised chordwise slot are compared with a baseline clean configuration. The flying wing configuration with a chordwise slot has shown a higher mass flow rate over the control surfaces of the wing in comparison to the baseline clean configuration, demonstrating that an optimised chordwise slot can be implemented on a flying wing configuration as it successfully controls the lateral flow by maximising the flow rate over the trailing edge control surfaces.

An investigation on the aerodynamic performance of a hand-launched solar-powered UAV in flying wing configuration

Aiming to realize the long-endurance ecological environmental monitoring and the rapid takeoff and landing mission in Tibet, a hand-launched solar-powered unmanned aerial vehicle (UAV) in flying wing configuration is introduced and analyzed in this paper. The low-Reynolds-number (LRN) flow is quasi-steadily simulated by solving the full three-dimensional Reynolds Averaged Navier-Stokes (RANS) governing equations coupled with the kT-kL-ω transition model while the propeller performance is evaluated using the multiple-rotating reference frame (MRF) method. Both the cruise and the low-speed takeoff aerodynamic analyses which include the aerodynamic force analysis and the propeller/wing integrated flow mechanism analysis are performed in details. The results indicate that the present UAV can meet the high-efficiency cruise requirements quite well, at the same time, has the ability to take off at the low-speed hand-launched state and a rather low Reynolds number by making good use of the energy injected from the propeller rotation into the flow field.

Numerical Analysis of Porpoising Stability Limit of a Blended-Wing–Body Aircraft During Ditching

The ditching processes of a blended-wing–body (BWB) aircraft under different initial speeds and pitch angles are simulated by numerically solving the unsteady Reynolds-averaged Navier–Stokes equations and the realizable turbulence model using the finite volume method. The volume-of-fluid model is adopted to capture the water–air interface. The six-degree-of-freedom model is employed to couple fluid dynamics and aircraft rigid-body kinematics. The global moving mesh is used to deal with the relative motion between the aircraft and the water. It is found that the plane composed of initial speed and pitch angle can be divided into two regions by a stability limit line, that is, the porpoising motion region (the aircraft takes coupled oscillatory motion between heaving and pitching) with large initial speeds and pitch angles and the stable motion region with low initial speeds and pitch angles. When the initial speed is large, the aircraft’s pitch-up moment peak and heaving amplitude are enhanced. Hence the aircraft carries out the porpoising motion. For the large initial pitch angle, the water entry depth of the aircraft increases and the waterline moves forward, which produces a more significant pitch-up moment peak and overload peak. As a result, the aircraft conducts the porpoising motion. The porpoising stability of the BWB configuration is obviously worse than the conventional and flying wing configurations. When the BWB aircraft ditches on water, the pilots should reduce the initial speed and pitch angle as much as possible to avoid the dangerous porpoising motion.

Study on circulation control of flying wing based on Coanda effect

In recent years, it has been a hot spot to use flow control technology to generate control capability similar to mechanical rudder. Taking the flying wing configuration as the research object, based on CFD and low speed wind tunnel test, the circulation control of airfoil and wing based on Coanda effect is studied, and the parameter influence law and control effect are given. The results show that: when the rear edge of the wing is opened with the corresponding slot, the control capability of the upper-surface blowing is similar to that of the mechanical rudder; the control capacity of pitch and roll is increased with the decreasing of jet height and the increasing of air pressure ratio, the pitching and rolling capacity increases first and then decreases; the control effect of circular Coanda surface is better than elliptical Coanda surface; the pitching and rolling control effect of the optimized circulation-control scheme in Ma=0.2 is not lower than that of the mechanical rudder, the corresponding flow flux is about 0.05~0.07 kg/s.

Aeroelasticity of Flying-Wing Aircraft Subject to Morphing: A Stability Study

In this work, we present a study on the effects of modifications on wing geometric configurations via morphing. Specifically, we investigate the resulting impacts on aeroelastic stability. In the primary analysis presented, we assess a wall-mounted configuration for an airfoil section of a two-dimensional wing. This morphing-wing system comprises a torsional spring at the trailing-edge flap hinge, which induces the morphing phenomenon. The behavior of this system is studied within the context of divergence and reversal. The analysis following this examines a highly flexible flying-wing configuration, subject to a transient morphing scheme. The geometries corresponding to the unmorphed and morphed configurations are acquired from a physical morphing trailing-edge wing prototype, and the structural modeling and cross-sectional properties are obtained using the Gmsh tool and variational asymptotic beam sectional analysis. Furthermore, we evaluate the effects of the geometric variations on the aeroelastic stability through leveraging the computer program, NATASHA (which stands for nonlinear aeroelastic trim and stability analysis of high-altitude long-endurance aircraft). The results obtained from this analysis insinuate the favorable impact on the aeroelastic stability of the system, namely, in terms of flutter characteristics.

Study on design of low Reynolds number reflexed airfoil for solar-powered UAV in flying wing configuration

Based on the application requirements of a small hand-launched solar-powered unmanned aerial vehicle (UAV) in flying wing configuration, the optimization design of the low Reynolds number (LRN) reflexed airfoil is carried out in this study to meet several requirements such as high lift, mild stall, demanding pitching moment. Firstly, the accuracy and reliability of both quasi-steady and unsteady numerical methods to simulate the LRN transition flow and the stall separated flow at large angles of attack (AOA) are validated by an airfoil case study at specified Reynolds numbers; Secondly, the LRN reflexed air-foil optimization design framework is established by using the CST parameterization method, the multi-island genetic algorithm (MIGA), and the kriging surrogate model; Lastly, the LRN reflexed airfoil optimization study is conducted by using the NACA 8-H-12 reflexed airfoil as the baseline airfoil, it shows that both the lift-to-drag performance and the stall characteristics of the designed airfoil is significantly improved when compared with the baseline airfoil, which are quite beneficial for the small hand-launched solar-powered UAV in flying wing configuration to realize the hand-launched take off and the high-lift long-endurance flight.

Sloshing reduced-order models for aeroelastic analyses of innovative aircraft configurations

The present paper introduces the sloshing effects on aeroelastic stability and response of flying wing configurations. Using reduced order model based on data provided by computational fluid dynamics data, the description of the slosh dynamics is introduced into an integrated modelling that accounts for both rigid and elastic behaviour of flexible aircraft. The fully unsteady aerodynamics, modelled in the frequency domain via doublet lattice method, is recast in time-domain state-space form through the rational function approximation. The reference aircraft is the Body Freedom Flutter equipped with a single tank of cylindrical geometry, partially filled with water, and located underneath the center of mass. The results of the stability and response analyses are compared with the frozen fluid case with the final aim of showing how the fluid movement affects the complete aircraft behaviour.

Numerical study on the influence of wall temperature gradient on aerodynamic characteristics of low aspect ratio flying wing configuration

With the aim for a low-aspect-ratio flying wing configuration, this study explores the influence of wall temperature gradient on the laminar and turbulent boundary layers of aircraft surface and determines the effect on the transition Reynolds number and wall friction drag. A four-equation turbulence model with transition mode is used to numerically simulate the flow around the model. The variation of wall friction coefficient, transition Reynolds number, and turbulent boundary layer flow with wall temperature are emphatically investigated. Results show that when the wall temperature increases from 288 to 500 K, the boundary layer transition Reynolds number for the wing section increased by approximately 28% and the surface friction drags decreases by approximately 10.7%. The hot wall enhances the viscous effects of the laminar temperature boundary layer, reduces the Reynolds shear stress and turbulent kinetic energy, and increases the flow stability. However, the velocity gradient and shear stress in the bottom of the turbulent boundary layer decreases, which leads to reduced friction shear stress on the wall surface. Therefore, for the low-aspect-ratio flying wing model, the hot wall can delay the boundary layer transition and reduce the friction drag coefficient in the turbulent region.

Multi-objective aerodynamic optimization of flying-wing configuration based on adjoint method

In order to solve the multi-objective multi-constraint design in aerodynamic design of flying wing, the aerodynamic optimization design based on the adjoint method is studied. In terms of the principle of the adjoint equation, the boundary conditions and the gradient equations are derived. The Navier-Stokes equations and adjoint aerodynamic optimization design method are adopted, the optimization design of the transonic drag reduction for the two different aspect ratio of the flying wing configurations is carried out. The results of the optimization design are as follows: Under the condition of satisfying the aerodynamic and geometric constraints, the transonic shock resistance of the flying wing is weakened to a great extent, which proves that the developed method has high optimization efficiency and good optimization effect in the multi-objective multi-constraint aerodynamic design of the flying wing.

Analisis karakteristik aerodinamika telescopic wing dengan konfigurasi sayap flying wing dan glider menggunakan metode pendekatan simulasi CFD

A telescopic wing is a shape-changing method of the aircraft wing known as the morphing wing system. Wingspan extends capability on telescopic wing increasing the aspect ratio to get a high lift force. The telescopic wing on a flying wing configuration as an external wing and glider wing as an internal wing can be used to increase the coefficient lift (CL) when carrying out special missions. The aerodynamic characteristics using the Computational Fluid Dynamic (CFD) simulation approach is presented. For the 40% internal wingspan, the highest CL increment was 12.9% at a 10o angle of attack. For the 50% internal wingspan, the highest CL increment was 14.9% at a 10o angle of attack. on the 40% internal wing, the highest coefficient drag (CD) increment was 4.7%, and the largest CD increment on 50% internal was 9.5% at the angle of attack of 20o. The pressure distribution along the internal wingspan was uneven from an angle of attack of 15o due to the wing tip vortices of the external wing. Streamline pattern shown a bubble separation from the leading edge at an internal wing root by external wing tip vortices.Keywords: Morphing wing, telescopic wing, flying wing, glider

On the Comparison of Ten Pitch Trim Strategies for Cruise Drag Minimization

The methods of minimization or maximization of lift, drag and pitching moment are extended to multiple coupled control surfaces with polynomial dependence of any degree on the control surface deflections. This serves as an introduction to the problem of minimization of cruise drag with pitch trim and unchanged lift, i.e. same airspeed and altitude, that is considered for a flying-wing configuration, using ten distinct strategies. Among the first four non-optimal strategies, only strategy II of using the centerbody elevator alone leads to drag reduction, albeit with a large deflection and increased angle-of-attack.

Longitudinal Static Stability Analysis with Wing Swept Angle Variation Of UAV Flying Wing Surveilance Adelaar 2 Use Software XFLR 5

Aircraft stability is very important for calculated in aircraft design, specially for UAV which will be used for air surveillance. The purpose of aircraft stability analysis to find aircraft stability characteristic. Aircraft static stability can be analyzed by XFLR 5 Software which is can calculate characteristic of aircraft static stability, show visual, graph, and simulation of aircraft stability. Adellar 2 is UAV with flying wing configuration and will be analyzed use software XFLR 5 with the input of aircraft mass with the centre of gravity wil be located in 5% of mean aerodynamic chord in front of neutral point and aircraft geometry types of airfoil in chord root, tip, span , winglet geometry and wing swept. With the result that Adelaar 2 is qualify for longitudinal static stability after the author analyze use XFLR5 with the parameter Cma<0 and obtained character of stability for 22.5 o , 25 o , 27.5 o and 30 o wing swept angle.

Investigation of Sloshing Effects on Flexible Aircraft Stability and Response

The present paper provides an investigation of the effects of linear slosh dynamics on aeroelastic stability and response of flying wing configuration. The proposal of this work is to use reduced order model based on the theory of the equivalent mechanical models for the description of the sloshing dynamics. This model is then introduced into an integrated modeling that accounts for both rigid and elastic behavior of flexible aircraft. The formulation also provides for fully unsteady aerodynamics modeled in the frequency domain via doublet lattice method and recast in time-domain state-space form by means of a rational function approximation. The case study consists of the so-called body freedom flutter research model equipped with a single tank, partially filled with water, located underneath the center of mass of the aircraft. The results spotlight that neglecting such sloshing effects considering the liquid as a frozen mass may overshadow possible instabilities, especially for mainly rigid-body dynamics.

Shape optimization of a blended-wing-body underwater glider using surrogate-based global optimization method IESGO-HSR.

As a novel flying-wing configuration underwater glider, the blended-wing-body underwater glider (BWBUG) has the satisfactory hydrodynamic performance in comparison to the conventional cylindrical autonomous underwater gliders (AUGs). The complicated shape optimization of BWBUG is significant for improving its hydrodynamic efficiency while it has to require huge computation time and efforts. A novel surrogate-based shape optimization (SBSO) framework is proposed to deal with the BWBUG shape optimization problem for improving the optimization efficiency and quality. During the optimization search, the parametric geometric model of the BWBUG is constructed depending on seven specific sectional airfoils, with the planar surface being unaltered. Moreover, an improved ensemble of surrogates based global optimization method using a hierarchical design space reduction strategy (IESGO-HSR) is used for optimizing the chosen sectional airfoils. The optimum shape of BWBUG can be obtained using all sectional airfoils which are successfully optimized. The maximum lift to drag ratio (LDR) of the optimal BWBUG is improved by 24.32% with acceptable computational resources. The optimization results show that the proposed SBSO framework is more superior and efficient in handling the BWBUG shape optimization problem.

Design studies and multi-disciplinary assessment of agile and highly swept flying wing configurations

This article belongs to a series of publications on the design and assessment of the MULDICON UCAV configuration. MULDICON is a 53° swept flying wing combat aircraft concept, investigated in a common effort between the DLR research project Mephisto and the NATO STO Research Task Group AVT-251. This article focuses on the development of the overall concept starting from its predecessor, the SACCON configuration, and the requirements which had been defined for the MULDICON design task. A second focus is placed on the investigation of the vortex-dominated flow topology arising around such a configuration and its sensitivity to specific geometric changes. Furthermore, the article briefly introduces the DLR conceptual aircraft design system and the extensions which have been developed for improving its capabilities for UCAV assessment. Finally, an industrial view on the MULDICON design task is provided, as well as a conclusion of the Mephisto results and an outlook upon further work.