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Active Multiple Winglets for Improved Unmanned-Aerial-Vehicle Performance
Abstract
The addition of a winglet to a flight vehicle is known to enhance cruise performance. The addition of multiple, active winglets to an existing unmanned aerial vehicle (UAV) is studied to determine the potential of these devices to augment both cruise and maneuvering performance. Passive and active multiple winglets are shown to increase range and endurance, providing the potential for increased payload. Active multiple winglets are shown to be a viable replacement for ailerons and to provide gust alleviation for improved handling qualities and sensor performance. Two methods of predicting winglet performance enhancements are applied and compared to the U.S. Marine Corps Dragon Eye UAV configuration.
... As the wing approaches the ground gradually, both trapezoidal sails and elliptical sails show the contribution to lift increase and drag reduction. 28 Some tested Wing configurations: total wing; short wing with five winglets; short wing with three winglets (from left to right) [37] Moreover, there are many UAVs' (Unmanned Aerial Vehicle) design work were inspired by wingtip slot [53][54][55][56]. Inspired by the bionic slotted wingtip concept, Shelton et al. [56] demonstrated that active multiple winglets can be a substitute for ailerons. ...
... 28 Some tested Wing configurations: total wing; short wing with five winglets; short wing with three winglets (from left to right) [37] Moreover, there are many UAVs' (Unmanned Aerial Vehicle) design work were inspired by wingtip slot [53][54][55][56]. Inspired by the bionic slotted wingtip concept, Shelton et al. [56] demonstrated that active multiple winglets can be a substitute for ailerons. With this kind of slotted wing fitted to the UAV "Dragon Eye", its range and endurance can be enhanced by 40%. ...
... The tip fence must be so large that the augment in skin friction drag due to an excessive wetted area far outweighs the drop in induced drag. Likewise, additional area caused by the (C) canted winglets enhances parasite drag and may cut aerodynamic performance at high angles of attacks in addition to the increased [56] weight to the device itself [66][67][68]. The (D) vortex diffuser and the (H) tip turbine aim to diffuse wingtip vortices. ...
Wingtip slots, where the outer primary feathers of birds split and spread vertically, are regarded as an evolved favorable feature that could effectively improve their aerodynamic performance. They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design. This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots. Following a review of previous wingtip slot research, four imperfections are put forward: vacancies in research content, inconsistencies in research conclusions, limitations of early research methods, and shortage of the aerodynamic mechanism analysis. On this basis, further explorations and expansion of the influence factors for steady state are needed; more attention should be poured into the application of flow field integration method to decompose drag, and evaluation of variation in induced drag seems a more rational choice. Geometric and kinematic parameters of wingtip slot structure in the unsteady state, as well as the flexibility of wingtips, should be taken into account. As for the aerodynamic mechanism of wingtip slots, the emphasis can be placed on the study of the formation, development, and evolution of wingtip vortices on slotted wings. Besides, some research strategies and feasibility analyses are proposed for each part of the research.
... Existing work on adaptive wingtips represents a very small fraction of the work done on morphing wings at large [35] and has mostly focussed on the change of a single winglet parameter (the cant angle) [36,37]. Shelton et al. [36] studied both the performance implications and the control possibilities of variable cant winglets; Bourdin et al. [38] have developed considerable work on the potential of variable cant winglets to augment and/or replace traditional control surfaces, finding that split articulated winglets can generate multi-axis control moments which are, in some circumstances, more effective than conventional control systems. ...
... Existing work on adaptive wingtips represents a very small fraction of the work done on morphing wings at large [35] and has mostly focussed on the change of a single winglet parameter (the cant angle) [36,37]. Shelton et al. [36] studied both the performance implications and the control possibilities of variable cant winglets; Bourdin et al. [38] have developed considerable work on the potential of variable cant winglets to augment and/or replace traditional control surfaces, finding that split articulated winglets can generate multi-axis control moments which are, in some circumstances, more effective than conventional control systems. ...
... And whereas Whitcomb's and most subsequent designs took inspiration from nature but evolved into more practical geometries than the split wingtip feathers found in birds, many designs of "multiple winglets" (closely resembling birds' split feathers) have been studied. [36,61,62] The major problem with this concept is that, while a greater number of individual winglets leads to larger reductions in induced drag, this improvement comes at the cost of increased interference 1. Introduction Figure 1.14: Slotted wingtip feathers on a seagull and larger friction drag. [63] A solution to this problem lies in spiroid wingtips proposed independently by different researchers [63,64] and constituting a hybrid of sorts of Whitcomb's single winglet and nature's multiple split feathers: the spiroid wingtip is simply a split-wing loop extending from the tip of the wing (figure 1.15) and combining the optimal vorticity distribution of multiple winglets with the simplicity and absence of interference of single winglets. ...
Economic and environmental factors have spurred major advances in the development of more economical and greener aircraft. Nevertheless, an important limitation stems from the need for an aircraft to perform highly dissimilar tasks throughout the flight. If an aircraft were able to morph so as to adapt to each moment’s requirements, it could assume the most efficient configuration for each task, increasing its capabilities and reducing its consumption and environmental impact. This thesis explores that concept, presenting an adaptive wingtip device mechanism that takes advantage of the wingtip device’s combination of high aerodynamic influence and small size to develop a system with low cost, energy requirements and complexity but possessing significant gains in different flight stages. The detailed design of the mechanism is presented, as are computational models and optimisation algorithms that allowed the analysis of this mechanism and its comparison with conventional wingtip devices. The results show gains in different flight stages, reaching a maximum of approximately 15% reduction in take-off distance. The energy balance and emissions reduction are also quantified. The results obtained lead to the conclusion that the proposed mechanism shows great promise and finally key aspects for further development are outlined.
... Another idea for UAV's winglet is to use a series of small winglets instead of one giant winglet, this idea was presented in 2066 by Shelton and associates (figure 16) [14]. This type will improve efficiency and maneuverability at low speeds. ...
... Reticular winglet[14]. ...
Natural creatures can morph their soft skins to match themselves with the surrounding environments. Morphing structures which that are capable of an extreme autonomous shape transformation, have received importance in aerospace because they removed the need to switch between configurations for optimal performance during the range of operation. To reduce turbulence and drag force on the tip of air vehicle's wing, and to increase the efficiency of UAVs winglets presented. Classic winglets were efficient but not efficient enough for every condition, so to overcome this issue engineers were thinking a way to invent new device to adjust regarding conditions of flight, reduce weight and costs simultaneously. Morphing winglet was the solution, these winglets increased aerodynamic properties, weight loss and reducing the takeoff distance in air vehicles. Current article will consider morphing winglets and reasons for its effectiveness on AVs.
... 图 7 (网络版彩图)应用仿鸟翼梢开缝的"龙眼"无人机 [77] Figure 7 (Color online) Application of the wingtip slots structure on the DragonEye unmanned aerial vehicle [77]. [88] . ...
... 图 7 (网络版彩图)应用仿鸟翼梢开缝的"龙眼"无人机 [77] Figure 7 (Color online) Application of the wingtip slots structure on the DragonEye unmanned aerial vehicle [77]. [88] . ...
First, this paper tries to review, summarize, and analyze the current status and problems of the aerodynamic mechanism research on the independent and coupling effects among the four factors that would affect the aerodynamic characteristics of bird wings—objectively and comprehensively. Second, based on the analysis and study of the current research results, according to the progress and limitations of calculation and experimental means, the paper puts forward the problems, strategies, and methods that need further study. The four main factors considered in this paper include the static geometric shape of the bird’s wing, four kinematic modes, the dynamic chord- and span-wise flexible deformation of the wing, and three kinds of small-scale flow-control structures that have recently attracted more attention. In this paper, in full consideration of wing static geometry appearance, kinematic modes, and dynamic, flexible deformation, by the analysis of the forces and vortex on a bird’s wing, the strategies and methods to further clarify the individual aerodynamic mechanism and function of the three small-scale flow-control structures are proposed. Furthermore, under the condition of mutual coupling among the four factors, the strategies and methods to obtain the aerodynamic mechanism of a real bird wing are also put forward. The viewpoints, methods, and conclusions of this paper have guiding and reference value for improving a bionic aircraft.
... However, they still need to conduct dynamic tests on the winglet to validate its dynamic response characteristics and are also exploring incorporating additional sensor fibers to create a closed-loop control system. Ursache et al. 11 studied the viability of different composite materials for the design of a flexible skin to support an actuated winglet. They tested the bending and torsional properties of several different composites to develop a skin design that would be stiff enough to support aerodynamic loads, but compliant enough to support the actuation of the winglet. ...
... Below, in Figure 10: Aircraft Axes and Moments, the axes and moments for an aircraft are depicted and named. In Figure 10: Aircraft Axes and Moments, L is the rolling moment and can be described in (11). Often, in order facilitate comparisons, the rolling moment is non-dimensionalized relative to the dimensions of the wing and ambient flight conditions and converted to a rolling moment coefficient which is given by (12), where ρ is the density of the air, V is the velocity of the aircraft, S is the wing's planform area, and b is the wingspan. ...
The design of an active winglet system for use in roll control of aircraft is presented. By varying the cant angle of winglets, the rolling moment generated by a wing can be controlled. Smart materials can respond to external stimuli in the form of shape changes. These morphing capabilities lend themselves well to the design of morphing aircraft structures. One specific type of piezoceramic composite is called a Macro Fiber Composite (MFC). These MFCs can be used to actively morph the winglet, thus providing roll control for the aircraft. The range of deflection achievable for this setup is modelled using the Bernoulli-Euler model. This was then used to determine the required operating voltage range and to study the sensitivity of the deflection to several key parameters. The MFCs were mounted on a 130 mm long aluminum shim that acted as the core of the winglet. This winglet was attached to a wing with a 1.52 m span and a 304.8 mm chord using the NACA 0012 airfoil. A CAD model of this was imported into ANSYS Fluent in order to study the rolling moment generated by the wing and how much it changes due to the deflections from the MFC bimorph bender. In the end, it was found that the MFC bimorph bender can produce deflections of up to about 80° within a range of ± 100 V. This corresponds to a change in rolling moment coefficient of 0.0641. Then, a modal analysis was conducted in order to determine if the vortex shedding frequency of the wing would excite one of its resonant frequencies. It was found that the vortex shedding frequency was not close to any of the natural frequencies of the wing, so it would not excite flutter in the wing.
... The principle is to spread the tip vortex in more vortices of less intensity. A variety of types of multiple winglets have been investigated by many authors in the past, such as Spillman et al. [4,5], Zimmer [6], La Roche and La Roche [7], and more recently by Smith et al. [8,9] and Catalano and Ceron-Munoz [10]. The importance of numerical accuracy and the difficulties in predicting the effect of winglets on drag using numerical methods have been well illustrated by Smith [11]. ...
... To this end, a set of winglets was designed and tested for application onto a hang-glider wing tip. As shown by Smith et al. [8,9] and Catalano and Ceron-Munoz [10], it appears that by using an opportunely designed set of remiges it is possible to improve wing performance by minimizing the hang-glider sink rate of Eq. (1). This is inversely proportional to the endurance parameter C 3=2 L =C D . ...
The main aim of the present paper is to investigate the influence of multiple winglets on hang-glider climbing performance. The study aims to optimize the CL 3/2/CD parameter. The investigation was performed both numerically and experimentally starting from airfoils and winglet shape design. Given the shape of a real hang-glider wing under aerodynamic load the first phase of the work concerned the main geometric characteristics of winglet design : number of winglets, airfoils, planform shape, twist. A 3D wing model was built and using the indications obtained from the design, different sets of winglets were built. The wing model was built to enable winglets to be applied to the wing tip without changing the wing span and aspect ratio. The tests carried out on the hang glider model showed an improvement in wing performance of about 15%. However, the model reproduced a full scale wing flying under aerodynamic load and, according to the model builders, it showed a positive twist angle (leading edge up). This could mean that the winglets were more efficient because the original wing showed a strong tip vortex, A new model wing with an elliptical planform was therefore built to verify this further. The test results on the elliptical wing did not show the same improvement in performance obtained with the hang glider model. Nevertheless, compared to the original elliptical wing an improvement was still found.
... The principle is to spread the tip vortex in more vortices of less intesity. A variety of types of multiple winglets have been investigated by many authors in the past, such as, Spillman [4], [5] , , Zimmer [6], La Roche [7], and more recently by Smith [8], [9] and Catalano [10]. The importance of numerical accuracy and the difficulties in predicting the effect of winglets on drag using numerical methods have been well illustrated by Smith [11]. ...
... To this end, a set of winglets was designed and tested for application onto a hang-glider wing tip. As shown by Smith [8] , [9] and Catalano [10], it appears that by using an opportunely designed set of remiges it is possible to improve wing performance by minimizing the hang-glider sink rateV s (1). This is inversely proportional to the endurance parameter CL 3/2 /CD. ...
The main aim of the present paper is to investigate the influence of multiple winglets on hang-glider climbing performance. The study aims to optimize the CL3/2/CD parameter. The investigation was performed both numerically and experimentally starting from airfoils and winglet shape design. Given the shape of a real hang- glider wing under aerodynamic load the first phase of the work concerned the main geometric characteristics of winglet design : number of winglets, airfoils, planform shape, twist. A 3D wing model was built and using the indications obtained from the design, different sets of winglets were built. The wing model was built to enable winglets to be applied to the wing tip without changing the wing span and aspect ratio. The tests carried out on the hang glider model showed an improvement in wing performance of about 15%. However, the model reproduced a full scale wing flying under aerodynamic load and, according to the model builders, it showed a positive twist angle (leading edge up). This could mean that the winglets were more efficient because the original wing showed a strong tip vortex, A new model wing with an elliptical planform was therefore built to verify this further. The test results on the elliptical wing did not show the same improvement in performance obtained with the hang glider model. Nevertheless, compared to the original elliptical wing an improvement was still found.
... The principle is to spread the tip vortex in more vortices of less intensity. A variety of types of multiple winglets have been investigated by many authors in the past, such as Spillman et al. [4,5], Zimmer [6], La Roche and La Roche [7], and more recently by Smith et al. [8,9] and Catalano and Ceron-Munoz [10]. The importance of numerical accuracy and the difficulties in predicting the effect of winglets on drag using numerical methods have been well illustrated by Smith [11]. ...
... To this end, a set of winglets was designed and tested for application onto a hang-glider wing tip. As shown by Smith et al. [8,9] and Catalano and Ceron-Munoz [10], it appears that by using an opportunely designed set of remiges it is possible to improve wing performance by minimizing the hang-glider sink rate of Eq. (1). This is inversely proportional to the endurance parameter C 3=2 L =C D . ...
The main aim of this paper is to investigate the influence of multiple winglets on hang-glider climbing performance. The study aims to optimize the C-L(3/2)/C-D parameter. The investigation was performed both numerically and experimentally starting from airfoils and winglet shape design. Given the shape of a real hang-glider wing under aerodynamic load, the first phase of the work concerned the main geometric characteristics of winglet design: the number of winglets, airfoils, planform shape, and twist. A 3-D wing model was built and using the indications obtained from the design, different sets of winglets were built. The wing model was built to enable winglets to be applied to the wing tip without changing the wing span and aspect ratio. The tests carried out on the hang-glider model showed an improvement in wing performance of about 15%. However, the model reproduced a full-scale wing flying under aerodynamic load and, according to the model builders, it showed a positive twist angle (leading edge up). This could mean that. the winglets were more efficient because the original wing showed a strong tip vortex. A new model wing with an elliptical planform was therefore built to verify this further. The test results on the elliptical wing did not show the same improvement in performance obtained with the hang-glider model. Nevertheless, compared to the original elliptical wing an improvement was still found.
... He concluded that the reduction in the induced drag depends solely on the ratio of the winglet length to the wingspan [16]. Figure 3 shows some winglet examples that are designed with the developed algorithm, such as the blended winglet [17], the spiroid winglet [18][19][20][21][22][23] and a first approximation of the wing grid [24][25][26][27]. They were selected due to the previous investigations conducted in the past years. ...
The paper outlines an algorithm for the rapid aerodynamic evaluation of winglet geometries using the TORNADO Vortex Lattice Method. It is a very useful tool to obtain a first approximation of the aerodynamic properties and for performing an optimization of the geometry design. The TORNADO tool is used to systematically calculate the aerodynamic characteristics of various wings with wingtip devices. The fast response of the aerodynamic models allows obtaining a set of results in a remarkably short time. Therefore, the development of an algorithm to generate wing geometries with great ease and complex shapes is of vital importance for the mentioned optimization process. The basic outline of the algorithm, the equations defining the wing geometries, and the results for unconventional wingtip devices, such as blended winglets and spiroid winglets, are presented. Finally, this algorithm allows designing a procedure to study the improvement of aerodynamic properties (lift, induced drag, and moment). Some examples are included to illustrate the capabilities of the algorithm.
... 30,31 Once the flapping wingtip slot structure is applied to MAV on a scale similar to that of birds, it is considered to replace the ailerons and essentially enhance the endurance of MAV. 32 In Ref. 33, we analyzed how dynamic spacing, formed by the unsteady flapping of the slotted wings, affects the aerodynamic interaction between slotted winglets and how that affects the lift generation of the wing in 2D (two-dimensional). Azargoon et al. 34 investigated the changes in flow physics caused by the corrugated trailing edge and wingtip slots. ...
Bird wings have split primary feathers that extend out from the wing surface. This structure is called the wingtip slot, which is recognized as a product of bird evolution to improve flight performance. In this paper, numerical simulations based on RANS (Reynolds-averaged Navier–Stokes) equations are conducted to examine and understand the influence of wingtip slots on six wings at Re = 100 000. The overlapping grid method, driven by an in-house UDF (User Defined Function), is used to model the motion of the bionic slotted wings. The motion law of the winglets is improved based on the law extracted from a level-flying bald eagle. Then the aerodynamic force, pressure distribution, vorticity contours, wake stream, and other flow structures of the slotted wings with different layouts were compared and analyzed. The results show a significant increase in aerodynamic force when the slotted wingtips are employed. The maximum lift-to-drag ratio is also improved in our designed wing model with a non-planar wingtip by a maximum of 34% from the base wing. Each winglet works as a single wing due to the existence of slots, with a chordwise pressure distribution similar to that of the main wing. The vortex structures of slotted wings show expressive changes in the tip vortex as compared with the base wing. Additionally, an innovative bionic slotted wing is proposed with a dynamic wingtip that forms varying gaps between winglets. Due to the collective mechanism of aerodynamic interaction among multiple winglets for the innovative wing, it acquires the optimal time-averaged force during a flapping period. As expected, the slotted wingtip reduces the main wingtip vortex intensity and creates weaker vortices. The non-planarity and relative motion of the wingtip strengthen its weakening effect on the wingtip vortex and wake.
... Studies on actuated wingtips for roll control have so far been limited to UAVs and small-scale aircraft and only account for straight hinge-lines. Shelton et al. [35] investigate a UAV with multiple actuated wingtips. In their study, the actuated wingtips im- prove the low-speed performance of a UAV and increase its range and endurance by 40%. ...
Folding wingtip technologies are in the focus of research for their potential to significantly reduce the induced drag of transport aircraft by increasing the wing's aspect ratio in flight. While state of the art commercial aircraft, such as the Boeing 777X, are equipped with on-ground folding wingtips, manufacturers further develop in-flight folding wingtip technology by adding aeroelastic hinges for load alleviation such as in Airbus' AlbatrossONE project. This paper systematically analyses wingtip functionalities, including wingtip folding, load alleviation, mission adaptability and roll control, collects them in a requirement list and derives design features from this list. The authors develop the identified features into a design for actuated adaptive wingtips based on pressure-actuated cellular structures, allowing in-flight morphing of the wingtips while withstanding significant aerodynamic loading. This study characterises the actuator's maximum deformation and load-bearing capacity within the entire operating envelope, restricted by structural stresses. In contrast to existing folding wingtip technologies, actuated adaptive wingtips can be actively controlled in flight and simultaneously show significant stiffness adaptivity. The actuator's stiffness profile identified in this paper and provided in mathematical equations forms the basis for the actuator's aeroelastic characterisation. The stiffness profile can further be used to investigate the actuator's capability of roll control, load alleviation and mission adaptability.
... Winglets have different shapes and types; however, not all of them are in commercial operation. The well-known commercially adopted shapes are blended winglet, Raked winglet, Active winglet, and Tip fence [4]. An active winglet is controllable, helps handle aerodynamic stalls, and provides more stability and control of the aircraft. ...
The aerodynamic characteristic of a commercial airplane's wing is a crucial parameter in aircraft design. In this context, the addition of the winglet may significantly reduce the lift-induced drag. Three wing designs are investigated numerically using computational fluid dynamics. The simulations are conducted in ANSYS FLUENT solver using the Spalart-Allmaras turbulence model. The Q-Criterion is used to understand the strength and size of the vortical structures shed by the wings. It is found that the raked winglet gives the lowest induced drag.
... A maximum improvement of 20% was seen in the L/D ratio for a bank angle of 30° and a sweep angle of 86°. There have been many investigations and experiments conducted on the shape and usage the winglets (Shelton et al. 2006;Smith et al. 2001;Tamai et al. 2007;Bardera et al. 2019;Liu et al. 2019;Putro et al. 2016) There have also been a few studies attempting to take inspiration from biological phenomena around us to solve the issue at hand. Some birds have been observed to leave behind only minute traces of wingtip vortices when they fly. ...
... This winglet is shown in Figure 23. Ashrafi and Sedaghat [32] examined the effect of using a semi-circular winglet on aerodynamic performance. As a result, as can be seen in Figure 24, they stated that the wingtip vortexes decreased, the drag coefficient decreased while the lift coefficient increased, higher cruise speed was achieved, fuel economy improved and noise decreased. ...
In this study, the effects of different types of winglets and wingtip devices on aerodynamic performance in aircraft were investigated. Mostly, CFD analyzes were performed with different turbulence models in the examined studies, as well as experimental studies were also conducted. It has been observed that especially k-ε, k-ω and Sparlat Almaras turbulence models are used in calculations. As a result of the investigations, it has been observed that both the use of winglets and the use of a wingtip devices significantly reduce the vortex formation in the wingtips compared to the plain wing. It has been determined that the most effective method in reducing wing tip vortexes is the use of winglet. The reduction of these vortexes resulted in an increase in lift force and a decrease in drag force. Thus, the L/D ratio has increased and as a result; better fuel economy, longer range and higher payload are provided.
... This study also analyses the effect the varying cant angle produces on the flight characteristics of the aircrafts. Earlier research has been conducted for blended winglets [4], multiple winglets [5] and spiroid winglets [6] however this research specifically combines the results for the not only the wingtip devices being used but also presents the effects produced by changing the cant angles of the selected devices. ...
The present study investigates the use of various wingtip devices to analyse the parameters of lift and drag for an aircraft wing. The coefficients of lift and drag are investigated in this research to optimize the wing design for enhancing the aircraft performance. A reduction in the drag produced due to wingtip vortices leads to reduced fuel consumption which contributes to the reduction in fuel emissions. The two-dimensional analysis is carried out for the selection of an apposite aerofoil by comparing the lift/drag characteristics of NACA 0012, 2415 and 23015 respectively at the velocity of 79.16 m/s at the angles of attack of 0°,4°,8°,12°,16° and 20°. The aerofoil section NACA 2415 is used to design the three-dimensional aircraft wing. For the analysis of the various wing tip devices the three-dimensional wing is incorporated with the spiroid winglet, blended winglet, wingtip fence and a mini-winglet. The CFD analysis for the wing designs is carried out for the take-off and landing phases of an aircraft’s flight because the effect of vortices is the highest during these flight phases. The angles of attack range from 0° to 20°. The CFD results reveal that for the wing designs, the plain wing produced the highest drag and the blended winglet proved to be the wingtip device with the most beneficial design. The results obtained for the 30° cant angled blended winglet and 60° cant angled wingtip fence produces additional lift when compared to the results obtained for the counterpart designs. The results obtained from the analysis are in close correlation to the established use of the wingtip devices.
... Recently, many researchers attempt to achieve this experience by exploration of efficient winglets shapes design. Some researchers involved in blended winglet [3,4], multiple winglets [5] and spiroid wingtip [6,7]. Rabbi et al. [8] introduced the slotted winglet effect on wing performance. ...
The Aircraft wingtip seriously affects the flight efficiency. One of the successful methods to improve wing aerodynamics is the winglet. The current work introduces a parametric optimization of the blended winglet. Numerical simulations of Cessna Citation airplane wing with winglet were conducted using CFDRC software. The CFD program uses finite volume technique to solve the RANS equations. The geometric parameters include winglet length, cant angle, taper ratio and twist. The effects of these four parameters are presented versus the aerodynamic performance characteristics of the wing such as lift coefficient, drag coefficient and lift to drag ratio. The results indicate small reduction in lift to drag ratio for different cant angles. Best aerodynamics characteristics at thelength to wing span equal to 15%. The increase in winglet taper ratio reduces the induced drag up to 0.7. The twist improves the lift to drag ratio forboth positive and negative twist values.
... Multiple winglets concept is probably the most non-trivial concept for varying the dihedral angle wingtips where the split wingtips of a flying wing were folded symmetrically or unsymmetrically to achieve longitudinal and/or lateral/directional control. (Shelton, Tomar, Prasad, Smith, & Komerath, 2006)investigated the employment of the active multiple winglets concept on the U.S. Marine Corps Dragon Eye UAV using an aerodynamic panel code and active control simulation to optimize the winglet configuration and to evaluate its maneuvering flight performance. (Bourdin, Gatto, & Friswell, 2007), (Bourdin, Gatto, & Friswell, 2010) also investigated this concept at which they utilized a pair of winglets with adaptive cant angle by mounting them at the tips of a flying wing and actuated independently to investigate the use of variable-cant angle winglets for morphing aircraft control. ...
... In contrast to conventional aircrafts, only few studies on wing extensions and wing tips in the UAV domain can be found in the open literature. Shelton et al. [7] introduced the concept of adding multiple winglet extensions to the basic wing of a UAV. They have shown that a 40% gain in flight endurance could be achieved via using this technique. ...
The favored features of SUAV are countless. To name a few, they need one operator, can access ground targets at closer ranges without being detected, and they are more portable and less expensive in production than larger UAV. Recently, wing extensions have been introduced to the design of SUAV, thus tailoring their performance so as to satisfy predefined missions. Motivated by the shortage in studies on the role of wing extensions design, the present study is conducted. The paper discusses the results of a parametric study on the design of wing tip extensions in a low subsonic freestream. Two design parameters of the wing extensions are discussed here; namely, the span and the taper ratio. The basic wing is a swept trapezoidal flying wing while the wing extensions are of variable spans and taper ratios. Spans of extensions vary from 0.05 to 0.5 of the basic wing span and their taper ratios vary independently from 0.25 to 1. The aerodynamic characteristics of the extended wings are estimated using USAF DATCOM. It was found that the extension span has a dominant role in the aerodynamic characteristics of the extended wings. Wing extensions can contribute to about 100% increase in the SUAV’s endurance.
... Variable winglets to control vortex flow have been investigated [13,14], including active control of multiple winglets [15], where coupled motion resulted in gust alleviation, and hence increased maneuverability. Falcao et al. [16] investigated motor-driven winglets capable of rotating independently in two different axes (toe and cant angles), which produced an adjustable response to external aerodynamic loads. ...
Morphing technology is inspired by biological motion for implementation in missions in a variety of areas without shape-change device. This study investigates the aerodynamic performance of a self-contained morphing winglet for an unmanned aerial vehicle (UAV) that mimics the wing-tip feathers of gliding birds. A smart soft composite (SSC), formed of shape memory alloy (SMA) wires and glass fibers within a soft polymeric matrix, was used to fabricate morphing winglets. Experiments were conducted with various diameters and numbers of embedded SMA wires, and numbers of the glass-fiber fabric lamina, which were compared with an analytical model. Morphing winglets were implemented at both wing tips of a WASP 4/7-scale UAV, and the aerodynamic characteristics were investigated using a wind tunnel testing with various attack angles. As results, when the morphing winglet was actuated, the lift-to-drag ratio increased by 5.8% compared with the flat wing geometry for attack angle greater than 5°.
... The principle is to spread the tip vortex in more vortices of less intensity. A variety of types of multiple winglets have been investigated by many authors in the past, such as, Spillman [5], [6], Zimmer [7], La Roche [8], and more recently by Smith [9], [10] and Catalano [11]. The importance of numerical accuracy and the difficulties in predicting the effect of winglets on drag using numerical methods have been well illustrated by Smith [12]. ...
The main goal of the proposed paper is the numerical and experimental investigation of multiple winglets influence on the reduction of induced drag. This results in the improvement of climbing performances of a motorglider or hang-glider. In a precedent work [1] a set of multiple winglets, very similar to the bird tip feathers called remiges, were designed and optimized for the hang-glider belonging to Angelo D'Arrigo, a world champion hangglider pilot and record holder. The research aims was to optimize the CL1,5/CD parameter since this is directly proportional to the sink rate. In this work the effects of the multiple winglets, set on an elliptical wing and tested in a wind tunnel, are compared to the effects of three different single 'classical' winglets that were designed using a panel method code and were also tested in the same wind tunnel in order to compare their span efficiency to the one of the multiple winglets.
... The other one is to maximize the aerodynamic efficiency by substituting the section that causes aerodynamic losses. A controllable winglet [4,5] to minimize the wing tip vortex is an example. ...
In general, a conventional flap on an aircraft wing can reduce the aerodynamic efficiency due to geometric discontinuity. On the other hand, the aerodynamic performance can be improved by using a shape-morphing wing instead of a separate flap. In this research, a new flap morphing mechanism that can change the wing shape smoothly was devised to prevent aerodynamic losses. Moreover, a prototype wing was fabricated to demonstrate the morphing mechanism. A shape memory alloy (SMA) wire actuator was used for the morphing wing. The specific current range was measured to control the SMA actuator. The deflection angles at the trailing edge were also measured while various currents were applied to the SMA actuator. The trailing edge of the wing changed smoothly when the current was applied. Moreover, the deflection angle also increased as the current increased. The maximum frequency level was around 0.1 Hz. The aerodynamic performance of the deformed airfoil by the SMA wire was analyzed by using the commercial program GAMBIT and FLUENT. The results were compared with the results of an undeformed wing. It was demonstrated that the morphing mechanism changes the wing shape smoothly without the extension of the wing skin.
... Wing morphing concepts involve more radical shape changes than those of airfoil morphing. Some of these concepts are: inflatable wing with new materials for roll control using nastic structures, bump flattening or trailing edge deflection 9,10 ; variable span wing concept 11 with pneumatic telescopic spars 12,13 ; hyper-elliptic wing with variable camber span that uses for actuation a quaternary-binary link configuration mechanism 14 , SMA-based tendons 15 or tendon-actuated N compliant cellular trusses made of octahedral unit cells 16 ; biologically inspired aeroservoelastic control SMA threads or torque rods for high roll control authority in micro air vehicles (MAVs) [17][18][19][20] ; wing with variable cant winglets for roll control 21,22 . Two concepts under the Morphing Aircraft Structures (MAS) Program which have seen enormous developments with full-scale models being built are the folding wing concept of Lockheed Martin with efficient loiter and fast dash configurations [23][24][25][26][27] and the bat wing design of NextGen with high lift and efficient loiter configurations [28][29][30] . ...
This paper presents the work done in designing a morphing wing concept for a small experimental unmanned aerial vehicle to improve the vehicle's performance over its intended speed range. The wing is designed with a multidisciplinary design optimization tool, in which an aerodynamic shape optimization code coupled with a structural morphing model is used to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as the structural model. The aerodynamic shape optimization code, that uses a viscous two-dimensional panel method formulation coupled with a nonlinear lifting-line algorithm and a sequential quadratic programming optimization algorithm, is suitable for preliminary wing design optimization tasks. The morphing concept, based on changes in wing-planform shape and wing-section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between optimized fixed wing performance, optimal morphing wing performance, and the performance of the wing obtained from the coupled aerodynamicstructural solution are presented. Estimates for the performance enhancements achieved by the unmanned aerial vehicles when fitted with this new morphing wing are also presented. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.
... During actuation, the linkage caused the inboard and outboard sections to deflect in opposite directions. Shelton et al. (2006) studied the benefits of active multiple winglets for a UAV. The use of actively controlled winglets can enhance the low-speed performance and maneuverability of the vehicle and can increase the range and endurance of the vehicle by up to 40%. ...
Aircraft wings are a compromise that allows the aircraft to fly at a range of flight conditions, but the performance at each condition is sub-optimal. The ability of a wing surface to change its geometry during flight has interested researchers and designers over the years as this reduces the design compromises required. Morphing is the short form for meta-morphose; however, there is neither an exact definition nor an agreement between the researchers about the type or the extent of the geometrical changes necessary to qualify an aircraft for the title 'shape morphing.' Geometrical parameters that can be affected by morph-ing solutions can be categorized into: planform alteration (span, sweep, and chord), out-of-plane transformation (twist, dihedral/gull, and span-wise bending), and airfoil adjustment (camber and thickness). Changing the wing shape or geometry is not new. Historically, morphing solutions always led to penalties in terms of cost, complexity, or weight, although in certain circumstances, these were overcome by system-level benefits. The current trend for highly efficient and 'green' aircraft makes such compromises less acceptable, calling for inno-vative morphing designs able to provide more benefits and fewer drawbacks. Recent devel-opments in 'smart' materials may overcome the limitations and enhance the benefits from existing design solutions. The challenge is to design a structure that is capable of withstanding the prescribed loads, but is also able to change its shape: ideally, there should be no distinction between the structure and the actuation system. The blending of morphing and smart struc-tures in an integrated approach requires multi-disciplinary thinking from the early develop-ment, which significantly increases the overall complexity, even at the preliminary design stage. Morphing is a promising enabling technology for the future, next-generation aircraft. However, manufacturers and end users are still too skeptical of the benefits to adopt morphing in the near future. Many developed concepts have a technology readiness level that is still very low. The recent explosive growth of satellite services means that UAVs are the technology of choice for many investigations on wing morphing. This article presents a review of the state-of-the-art on morphing aircraft and focuses on structural, shape-changing morphing concepts for both fixed and rotary wings, with particular reference to active systems. Inflatable solu-tions have been not considered, and skin issues and challenges are not discussed in detail. Although many interesting concepts have been synthesized, few have progressed to wing tunnel testing, and even fewer have flown. Furthermore, any successful wing morphing system must overcome the weight penalty due to the additional actuation systems.
Flow control is the attempt to favorably modify a flow field’s characteristics compared to how the flow would have developed naturally along the surface. Natural flyers and swimmers exploit flow control to maintain maneuverability and efficiency under different flight and environmental conditions. Here, we review flow control strategies in birds, insects, and aquatic animals, as well as the engineered systems inspired by them. We focus mainly on passive and local flow control devices which have utility for application in small uncrewed aerial and aquatic vehicles (sUAVs) with benefits such as simplicity and reduced power consumption. We also identify research gaps related to the physics of the biological flow control and opportunities for device development and implementation on engineered vehicles.
Uncrewed aerial vehicle (UAV) design has advanced substantially over the past century; however, there are still scenarios where birds outperform UAVs. Birds regularly maneuver through cluttered environments or adapt to sudden changes in flight conditions, tasks that challenge even the most advanced UAVs. Thus, there remains a gap in our general knowledge of flight maneuverability and adaptability that can be filled by improving our understanding of how birds achieve these desirable flight characteristics. Although maneuverability is difficult to quantify, one approach is to leverage an expected trade-off between stability and maneuverability, wherein a stable flyer must generate larger moments to maneuver than an unstable flyer. Bird’s stability, and adaptability, has previously been associated with their ability to morph their wing shape in flight. Birds morph their wings by actuating their musculoskeletal system, including the shoulder, elbow and wrist joints. Thus, to take an important step towards deciphering avian flight stability and adaptability, I investigated how the manipulating avian wing joints affect longitudinal stability and control characteristics. First, I used an open-source low fidelity model to calculate the lift and pitching moment of a gull wing and body across the full range of flexion and extension of the elbow and wrist. To validate the model, I measured the forces and moments on nine 3D printed equivalent wing-body models mounted in a wind tunnel. With the validated numerical results, I identified that extending the wing using different combinations of elbow and wrist angles would provide a method for adaptive control of loads and static stability. However, I also found that gulls were unable to trim for the tested shoulder angle. Next, I developed an open-source, mechanics-based method (AvInertia) to calculate the inertial characteristics of 22 bird species across the full range of flexion and extension of the elbow and wrist. This method allowed a detailed investigation of how manipulating the elbow and wrist angle changed the center of gravity and moment of inertia tensor. Leveraging the previous aerodynamic results, I developed a method to estimate the neutral point of any bird wing configuration and derived a novel metric for pitch agility. With the neutral point and center of gravity, I found that the majority of investigated species had the ability to shift between stable and unstable flight. Further, I implemented an evolutionary analysis that revealed evidence of evolutionary pressures maintaining this capacity to shift, which transforms our understanding of avian flight evolution. Finally, I combined the aerodynamic and inertial results to investigate the dynamic stability of a gull across a range of shoulder, elbow, and wrist angles. This analysis revealed that a positive dihedral and forward-swept wing allowed a trimmed flight condition. For trimmed configurations, I found that high wrist angles were statically unstable and exhibited a non-oscillating, divergent response to disturbances. Lower wrist angles were both statically and dynamically stable and exhibited a short period and phugoid mode like traditional aircraft. I found that most trimmed configurations exhibited short period characteristics that would be flyable by a human pilot, although with a heavily damped phugoid mode. In summary, I found that the avian elbow and wrist joints can act as adaptive controls and permit birds to shift between stable and unstable flight. Identifying these characteristics provides a starting point for future UAV designs that hope to incorporate avian-like maneuverability and adaptability.
The Adaptive Slotted Winglet design using Shape Memory Alloys (SMA) based actuators is optimized for better aerodynamic performance at various stages of flight. Winglets are upward swept extensions of wingtips that reduce the aerodynamic drag associated with vortices that develop at the wingtips as the airplane moves through the air. The conventional static winglet is designed for a particular mission point due to which it compromises between performance at low and high speeds. The base design is optimized to generate improved winglet design compared to the conventional winglet. The slotted winglets are advantageous in itself by producing lift, reduction of acoustic sound, reduction of winglet twisting and better performance. The autonomous adaptive slotted winglet design provides real-time adaptive behavior compared to the present technologies. The Shape Memory Alloy based actuator reduces the system weight by up to 80 percent compared to the traditional systems. The adaptive changing of the Cant angle and twist angle can be achieved between 0 and 70 degrees up and down during flight. The slotted adaptive winglets by design significantly reduce aerodynamic loads at critical flight points having a variable cant angle and trailing edge control. The winglets are designed and optimized using analysis tools for the best performance.
Winglets on a turbine blade can modify flow features and improve a marine current turbine (MCT). In this work, to maximize the power coefficient (CP) and torque (T), cant angle (α), and height (h) of a winglet of an MCT were modified. The problem was solved using a high-fidelity solver code Fluent 2019R2 containing Reynolds-Averaged Navier–Stokes (RANS) equations. The flow domain meshed with tetrahedral elements. Nine different designs were produced to fill the design space for optimization. A set of low fidelity models such as second-order regression, kriging, and neural network models were used to approximate the high-fidelity results. The optimal designs further validated with the high-fidelity simulated results. The optimal design, increased CP by 7% for α = 33.2o and h = 2.04% of the turbine radius, reduced the recirculation zone at the trailing edge, increased the pressure gradient, and reduced the tip vortex.
Five bionic multi-tip winglet configurations, inspired by basic feather shapes and wingtip postures of birds, were designed to suppress the tip-vortex structures around their wingtips. Each of the bionic multi-tip winglet configurations consists of multiple novel feather-shaped winglets and looks like a dihedral (or non-planar) wingtip shape. The influence of the distribution density and chord-directional gap for the feather-shaped winglets on the tip-vortex flow characteristics was investigated experimentally at Re = 83 166. The results reveal that the vorticity levels of the tip-vortex structures in the near-wake region can achieve effective suppression by improving the feather-shaped winglets’ distribution density at the wingtip of the bionic wing configuration. The maximum proportions of the induced drag relative to the total drag for the bionic wing configurations I, II, and III are 25.54%, 21.05%, and 19.47%, respectively. The variation of the feather-shaped winglets’ distribution density significantly affects the lift–drag efficiency of the bionic wing configuration. However, the increase in the feather-shaped winglets’ mounting gap weakens the tip-vortex suppression effect for the bionic wing configuration (equipped with the three feather-shaped winglets) to some degree. The maximum proportions of the induced drag relative to the total drag for the bionic wing configurations IV and V are 27.28% and 28.32%, respectively. Compared with the bionic wing configuration I, the slightly worse aerodynamic performance for the bionic wing configurations IV or V (with the larger feather-shaped winglets’ mounting gap) is closely related to its weaker tip-vortex suppression ability.
Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.
Fixed-wing aircraft are traditionally controlled using deflectable trailing edge rigid flaps, commonly known as control surfaces. When deflected, these flaps modify the camber distribution of the aerofoil, which changes the aerodynamic pressure distribution over the wing. These changes in aerodynamic pressure result in net aerodynamic forces and moments that can be used to control the lift generation and orientation of the aircraft. However, flaps change aerofoil shape in a sharp and discontinuous way, resulting in surface discontinuities and gaps. These discontinuities induce flow separation, which leads to a significant increase in drag. Alternatively, if these control surfaces could vary camber distribution in a smooth and continuous way, similar control authority can be achieved with a significantly reduced drag penalty. This alternative approach is known as camber morphing, and its implementation on fixed-wing aircraft could lead to a reduction in fuel consumption and noise.
One of these promising camber morphing concepts is the Fish Bone Active Camber (FishBAC) device, a compliance-based design capable of achieving large, smooth and continuous changes in camber. A preliminary 3D printed prototype of this concept was wind tunnel tested, and results showed a 25% drag reduction at the 2D aerofoil level when compared to a flap. However, this first-generation of FishBAC devices were designed using low-fidelity structural and aerodynamic models and manufactured using 3D printed plastic. To implement this technology in real aerospace structures, it is necessary to manufacture this morphing device using aerospace-graded materials. Also, it is crucial to develop modelling tools that can fully capture the complex coupled three-dimensional structural and aerodynamic behaviour of a 3D morphing FishBAC wing. These modelling techniques must be physically rich enough to accurately capture the detailed response of the morphing device while also being computationally efficient to allow for rapid design iterations and optimisation that results in better performing devices.
To address the modelling requirements, two discontinuous structural models based on composite plate model theories (i.e. Kirchhoff-Love and Mindlin-Reissner) and an aerodynamic model based Weissinger’s Lifting Line Theory with viscous 2D panel method corrections were developed. Additionally, the large changes in shape that the FishBAC produces are associated with large changes in aerodynamic pressure (and vice-versa), resulting in a strong coupling between aerodynamics and structural loads. Consequently, to accurately capture both structural and aerodynamic behaviour of these morphing wings, a Fluid-Structure Interaction (FSI) analysis that couples the two different physics was developed. These structural, aerodynamic and FSI modelling techniques capture the highly orthotropic structure of the composite FishBAC, the 3D aerodynamics of the morphing wing and the interaction between structural and aerodynamic loads. Moreover, these models have a useful and appropriate level of fidelity for design and optimisation tasks: they converge using one to two orders of magnitude fewer degrees of freedom than fully coupled Computational Fluid Dynamics (CFD)/Finite Element Method (FEM)-based routines and all structural and material properties are parametrically defined and can be easily modified, allowing for wide-ranging explorations of the design space.
The development of these novel modelling techniques is complemented and validated by the design, manufacture and test of a composite FishBAC wind tunnel wing model. This prototype was manufactured using a combination of manufacturing techniques, including autoclave curing of carbon fibre prepreg, additive manufacturing (3D printing), and traditional metal machining. The composite FishBAC wing was then tested under static actuation loads, and these results were used to validate structural models. Additionally a 2D wind tunnel test was performed, where force balance, wake rake and Particle Image Velocimetry data were collected and analysed to further explore the aerodynamic behaviour of the FishBAC, and to benchmark it against both rigid (non-morphing) and flapped aerofoils.
Results presented in this thesis show that the discontinuous Mindlin-Reissner plate-based model predicts the structural behaviour of the FishBAC using 99% fewer degrees of freedom than FEM, whereas the aerodynamic viscous corrected Lifting-Line model is suitable to analyse the 3D aerodynamics of the FishBAC morphing wing at low Mach numbers and at attached flow regimes. Additionally, the FSI results showed that the 3D FishBAC wing can achieve a lift control authority (i.e. change in lift coefficient) between 0.5 and 0.63 for a wide range of angles of attack. In terms of aerodynamic efficiency, the FishBAC wing showed a 44% increase in lift-to-drag ratios at low lift coefficients, when compared to a flap. Lastly, the 2D wind tunnel test results showed efficiency gains over flaps of between 16% and 50% at the 2D aerofoil level. In summary, these results highlight the potential aerodynamic benefits that a FishBAC morphing wing can bring to a full-size aeroplane and also suggest that the developed modelling tools are suitable for future design iteration and optimisation studies of composite morphing aerostructures.
This review is mainly based on the aerodynamic analysis and optimization of winglets, as well as the summarized induced drag (Di) and vortex detection on different types of aircraft winglets. These winglets are optimal wing tip shape changers. Each optimized winglet model has its improvement toward uncertainty under various operating regimes. The phases of winglet design and development process are discussed. Special attention is provided to the performance of winglets with the change in design aspects. Experimental and theoretical investigations are exhibited under different operating conditions to access the performance. This review highlights previous research on different types of winglets, such as blended, spiroid, multi-tip, sharklets, raked wingtips, and wing fences. This survey determines that several drag reduction techniques use optimized winglets. The effect on the reduction of Di will gradually increase the profile drag, which plays a challenge of balancing the two criteria.
Friedrich A. Kipp addressed in two papers with rather different contents questions that are still topical today in 1936 and 1956, respectively. In 1956, he interpreted the juvenile plumage of woodpeckers as being evolutionary more advanced than the adult one, thus anticipating a future stage of the adult plumage. This view is not compatible with the notions in modern evolutionary biology. However, it does point to the fact that even today there is little research concerning the biological role of juvenile traits. The conspicuous head coloration of juvenile together with specific acoustic signals constrained to this ontological stage probably play an important role in the communication between fledglings and parents. Kipp also developed an index that relates the primary projection to total wing length. This index proved to be a reliable indicator of long-distance flight performance of birds. Both, comparative and physiological studies confirmed its predictive power. Despite substantial progress in ornithological and biomimetic research, we are still missing a complete and quantitative description and explanation of the physical processes at the wing-tip during flapping flight that would explain small-scale interspecific differences at the wing-tip quantitatively. The paper also attempts to show the relationships between Kipp's personal philosophical views - he had strong links to the anthroposophical movement - and his approach to solving scientific questions that interested him.
Winglets can inhibit the formation of wingtip vortices and reduce the induced drag. The height of a winglet is one of the most critical parameters in drag reduction efficiency. Current winglet designs are typically optimized for cruise conditions. But they are inefficient in off-design conditions, such as takeoff, climb and landing. Morphing winglets can optimize the drag reduction efficiency through changing their geometric dimensions during flight. This paper investigates a retractable grid for morphing winglets which are actuated by a stepper motor to change the winglet heights at various flight conditions. According to the dynamic analysis based on automatic dynamic analysis of mechanical systems (ADAMS), the change rate of the winglet height reaches up to 13.9% and the cycle is less than 4.4 s when the motor torque is 970.9 N·mm. The simulation has been verified by model test. Subsequently, the effects of a morphing winglet on wingtip vortices and aerodynamic performance are estimated through computational fluid dynamics (CFD) and wind tunnel test. The test results show that increasing the winglet height is beneficial to inhibiting the wingtip vortices. The maximum decrease of wingtip vortices can be as high as 47.7%. With the increase of winglet height, the lift coefficient is also improved by 3.5% and the drag coefficient is reduced by 4.8% during the takeoff phase (Mach number Ma=0.1, angle of attack α=6°). Therefore, morphing winglet with retractable grid has the potential of improving aircraft takeoff performance.
The scope of the current investigation incorporates the entire process involved in design and
developmentofShapeMemoryAlloy(SMA)actuatedwingintendedtofulfillmorphingmissions.
Atthedesignstep,twoDegree-of-Freedom(DOF)mechanismisdesignedthatisappropriatefor
morphingwingapplications.Themechanismisdevelopedinsuchwaythatitcanundergotwo
differentDOF, i.e.gullandsweep,so that thewingcanhavemaneuvers thataremoreefficient.
Smartmaterialsarecommonlyselectedastheactuatorsduetotheirsuitablethermo-mechanical
characteristics. Shape Memory Alloy (SMA) actuators are capable of providing more efficient
mechanisms in comparison to the conventional actuators due to their large force/stroke
generation,smallersizewithhighcapabilitiesinlimitedspaces,andlowerweight.AsSMAwires
havenonlinearhysteresisbehavior,theirmodelingshouldbeimplementedinmeticulousway.
In thiswork, after proposing twoDOFmorphingwing,anaerodynamicanalysis of thewhole
wingforunmorphedandmorphedwingsispresented.Theresultsshowthattheperformanceof
themorphedwinginspecialflightregimesisimproved.
The scope of the current investigation incorporates the entire process involved in design and development of a Shape Memory Alloy (SMA) actuated wing intended to fulfill morphing missions. At the design step, a two Degree-Of-Freedom (DOF) mechanism is designed that is appropriate for morphing wing applications. The mechanism is developed in such a way that it can undergo different two DOF so that the wing can have maneuvers that are more efficient. Smart materials commonly are selected as the actuators due to their suitable thermo-mechanical characteristics. Shape Memory Alloy (SMA) actuators are capable of providing more efficient mechanisms in comparison to the conventional actuators due to their large force/stroke generation, smaller size with high capabilities in limited spaces, and lower weight. As SMA wires have nonlinear hysteresis behavior, their modeling should be implemented in a meticulous way. In this work, after proposing a two DOF morphing wing, an aerodynamic analysis of the whole wing for unmorphed and morphed wings is presented. The results show that the performance of the morphed wing in special flight regimes is improved.
The study of a small expendable Unmanned Aerial Vehicle (UAV) that is capable of operating in harsh storm-like conditions is presented. Investigation shows that the selection of certain aerodynamic derivatives combined with a suitable control system has a profound effect on the gust response of a simulated UAV. Simulation comparison of this newly formulated Autonomous Gust Insensitive Aircraft (AGIA) to a conventionally developed aircraft suggests a significant reduction in the required capability of the autopilot control system. Simulation results are presented that show, although the AGIA requires closed-loop control for even still-air flight, the operation of this aircraft in a gusty environment does not significantly increase the requirements of the control system beyond what is typically used for a UAV autopilot. These results are contrasted with a conventionally designed aircraft that does not require automated closed loop control for stable still air flight, but requires more closed loop control than the AGIA for operation in gusty conditions. This result suggests that designing an aircraft with the AGIA formulated flight characteristics offers the benefit of operability in gusty environments using a low-cost autopilot system on a small, perhaps expendable UAV. © 2008 by the American Institute of Aeronautics and Astronautics, Inc.
The question of what is necessary for the US to provide its fighting forces with continuously available surveillance of the battlefield is considered. The anticipated technological improvements forecasted to 2025 all support the conclusion that sufficient capabilities will exist should the US government choose to collect them into a single system. The resulting unmanned system will likely be a lighter-than-air vessel capable of operating for months or a stealthy derivative of the RQ-4 Global Hawk. The single largest hurdle for either system is the lack of political and military support for expanding existing unmanned systems. An Air Force sponsored survey conducted with several military, corporate and university experts which supports these conclusioins is also presented.
Research on aircraft morphing has exploded in recent years. The motivation and driving force behind this has been to find new and novel ways to increase the capabilities of aircraft. Materials advancements have helped to increase possibilities with respect to actuation and, hence, a diversity of concepts and unimagined capabilities. The expanded role of unmanned aerial vehicles (UAVs) has provided an ideal platform for exploring these emergent morphing concepts since at this scale a greater amount of risk can be taken, as well as having more manageable fabrication and cost requirements. This review focuses on presenting the role UAVs have in morphing research by giving an overview of the UAV morphing concepts, designs, and technologies described in the literature. A presentation of quantitative information as well as a discussion of technical issues is given where possible to begin gaining some insight into the overall assessment and performance of these technologies.
This effort examined the potential of multi-winglets for the reduction of induced drag without increasing the span of aircraft wings. Wind tunnel models were constructed using a NACA 0012 airfoil section for the untwisted, rectangular wing and flat plates for the winglets. Testing of the configurations occurred over a range of Reynolds numbers from 161,000 to 300,000. Wind tunnel balances provided lift and drag measurements, and laser flow visualization obtained wingtip vortex information. The Cobalt60 unstructured solver generated flow simulations of the experimental configuration via solution of the Euler equations of motion. The results show that certain multi-winglet configurations reduced the wing induced drag and improved lift by 15-30% compared with the baseline 0012 wing. A substantial increase in lift curve slope occurs with dihedral spread of winglets set at zero incidence relative to the wing. Dihedral spread also distributes the tip vortex. These observations supplement previous results on drag reduction due to lift reorientation with twisted winglets set at negative incidence.
A transonic model and a low-speed model were flutter tested in the Langley Transonic Dynamics Tunnel at Mach numbers up to 0.90. Transonic flutter boundaries were measured for 10 different model configurations, which included variations in wing fuel, nacelle pylon stiffness, and wingtip configuration. The winglet effects were evaluated by testing the transonic model, having a specific wing fuel and nacelle pylon stiffness, with each of three wingtips, a nonimal tip, a winglet, and a nominal tip ballasted to simulate the winglet mass. The addition of the winglet substantially reduced the flutter speed of the wing at transonic Mach numbers. The winglet effect was configuration-dependent and was primarily due to winglet aerodynamics rather than mass. Flutter analyses using modified strip-theory aerodynamics (experimentally weighted) correlated reasonably well with test results. The four transonic flutter mechanisms predicted by analysis were obtained experimentally. The analysis satisfactorily predicted the mass-density-ratio effects on subsonic flutter obtained using the low-speed model. Additional analyses were made to determine the flutter sensitivity to several parameters at transonic speeds.
Small cambered and twisted surfaces, called sails, fitted to the wing tips of an aircraft can reduce its lift-dependent drag by up to 30%. Flight tests on a Paris aircraft show a 25% increase in maximum lift-drag ratio. Three or four sails per wing tip, each having a span of about a quarter of the wing tip chord and a root chord of about 16% of that of the wing tip seem to give the greatest vortex drag reductions when fitted, almost horizontally, outboard of the rear half of the wing tip. The sails need to be set in a spiral array round the tip, each sail being further away from the top surface of the wing, by 15 degree or more, than the sail in front of it. The sails need to turn the air smoothly from the spiral flow from lower to upper surface round the tip to a near streamwise direction. This requires the root sections of the sails to have circular arc camber lines bringing the tangent to the camber line at the nose of the sail more nearly into line with the local flow direction at positive wing incidences.
An extensive experimental study is conducted to examine the effects of winglet-shapes and orientations on the static surface pressure, wake, and the flowfield of a swept wing at angles of attack between -10 to 15 degrees. Four types of winglets, spiroid (forward and aft), blended winglets, and winggrid are used in this investigation. Wing static surface pressure measurements are obtained for both chordwise and spanwise, as well as the wake profiles at various angles of attack using the aforementioned winglets. Further, the effect of addition of turbulator strip on the wing upper surface is examined. The results are compared with the wing without winglet. The results show that addition of winglets change the flowfield over and around the wing significantly. Furthermore, it is found that certain winglet configurations improve both the wake and the wing pressure distribution. The total pressure in the wake of the model varies drastically when the wing is equipped with winglets.
The effect of sideslip on winglet loads and selected wing loads was investigated at high and low subsonic Mach numbers. The investigation was conducted in two separate wind tunnel facilities, using two slightly different 0.035-scale full-span models. Results are presented which indicate that, in general, winglet loads as a result of sideslip are analogous to wing loads caused by angle of attack. The center-of-pressure locations on the winglets are somewhat different than might be expected for an analogous wing. The spanwise center of pressure for a winglet tends to be more inboard than for a wing. The most notable chordwide location is a forward center-of-pressure location on the winglet at high sideslip angles. The noted differences between a winglet and an analogous wing are the result of the influence of the wing on the winglet.
A 0.36-scale model of a canard general-aviation airplane with a single pusher propeller and winglets was tested in the Langley 30- by 60-Foot Wind Tunnel to determine the static and dynamic stability and control and free-flight behavior of the configuration. Model variables made testing of the model possible with the canard in high and low positions, with increased winglet area, with outboard wing leading-edge droop, with fuselage-mounted vertical fin and rudder, with enlarged rudders, with dual deflecting rudders, and with ailerons mounted closer to the wing tips. The basic model exhibited generally good longitudinal and lateral stability and control characteristics. The removal of an outboard leading-edge droop degraded roll damping and produced lightly damped roll (wing rock) oscillations. In general, the model exhibited very stable dihedral effect but weak directional stability. Rudder and aileron control power were sufficiently adequate for control of most flight conditions, but appeared to be relatively weak for maneuvering compared with those of more conventionally configured models.
Winglets, which are small, nearly vertical, winglike surfaces, substantially reduce drag coefficients at lifting conditions. The primary winglet surfaces are rearward above the wing tips; secondary surfaces are forward below the wing tips. This report presents a discussion of the considerations involved in the design of the winglets; measured effects of these surfaces on the aerodynamic forces, moments, and loads for a representative first generation, narrow body jet transport wing; and a comparison of these effects with those for a wing tip extension which results in approximately the same increase in bending moment at the wing-fuselage juncture as did the addition of the winglets.
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