Aspect Ratio Wing Research Articles

On the lift-optimal aspect ratio of a revolving wing at low Reynolds number.

Lentink & Dickinson (2009 J. Exp. Biol.212, 2705-2719. (doi:10.1242/jeb.022269)) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

Effect of fuselage diameter on aerodynamic characteristics for straight wing at low and high aspect ratio

A computational code has been developed to investigate the effect of fuselage diameter with a combination of a straight wing on the aerodynamic characteristics. The case studies were performed on both wing-body combination at high wing aspect ratio (AR>4) and low wing aspect ratio (AR<4). The Prandtl’s Lifting Line Theory (LLT) and Helmbold’s Panel Method (HPM) were used to determine the wing lift and drag characteristics while Roskam’s Drag Prediction Method (RDPM) was used to compute the fuselage drag. The computed lift and drag coefficients obtained were then compared to verify the reliability of the computational results. It is found that a larger fuselage diameter contributes to the increment of the total drag of the wing-body combination without significant effect on the lift. The lift is mainly contributed by the wing for both low and high aspect ratio straight wing for low subsonic case.

Species With Greater Aerial Maneuverability Have Higher Frequency of Collisions With Aircraft: A Comparative Study

Antipredator responses may appear unsuccessful when animals are exposed to approaching vehicles, often resulting in mortality. Recent studies have addressed whether certain biological traits are associated with variation in collision risk with cars, but not with higher speed-vehicles like aircraft. Our goal was to establish the association between different species traits (i.e., body mass, eye size, brain size, wing loading, wing aspect ratio) and the frequency of bird collisions with aircraft (hereafter, bird strikes) using a comparative approach controlling for the effects of shared ancestry. We proposed directional predictions as to how each of the species traits would affect the frequency of bird strikes. Considering 39 bird species with all traits represented, the model containing wing loading had the best fit to account for the variance in bird strikes across species. In another model with 54 species exploring the fit to different polynomial models but considering only wing loading, we found that wing loading was negatively and linearly associated with the frequency of bird strikes. Counterintuitively, species with lower wing loading (hence, higher maneuverability) had a higher frequency of bird strikes. We discuss potential non-mutually exclusive explanations (e.g., high wing loading species fly faster, thus gaining some extra time to avoid the aircraft flight path; high wing loading species are hazed more intensively at airports, which could lower collisions, etc.). Ultimately, our findings uncovered that species with low wing loading get struck at a higher rate at airports, which reduces the safety risk for humans because these species tend not to cause damaging strikes, but the consequences of their potentially higher local mortality are unknown.

Numerical study on flow structure and heat transfer in a circular tube integrated with novel anchor shaped inserts

This paper reports a numerical study of the thermal performance enhancement of a circular tube embedded with novel anchor-shaped vortex generators. The three-dimensional turbulent periodic flow in the tube subject to a constant heat-flux wall boundary condition is investigated. The fluid flow and heat transfer characteristics are presented for Reynolds number (Re) ranging from 3000 to 18,000. The influences of pitch ratios (PR = P/D = 1, 1.5, 2, and 2.5) and the anchor vortex wing aspect ratios (σ = b/a = 0.4, 0.6, 0.8, 1, and 1.2) on Nusselt Number (Nu), friction factor (f), and the thermal enhancement factor (TEF) are reported. The vortex flow induced by the anchor vortex generator (AVG) inserts leads to a better fluid mixing, thereby accompanied a high heat transfer rate. The results indicate that the presence of AVG inserts elicits a considerable enhancement of Nusselt number and friction factor, which are about 2.24–4.56 and 4.01–23.23 times of those in the corresponding smooth tube, respectively. The maximum TEF of 1.72 is obtained for b/a = 0.4 and P/D = 1 at Re = 3000. These results provide evidence that the AVG insert is a promising device for turbulent convection heat transfer enhancement in a heat exchanger tube.

New design algorithm and reliability testing of solar powered near-space flight vehicle for defense and security

Broadband telecommunications have become the key factor for economic growths around the world, but rural and hard to reach areas are missing out on the opportunity. To overcome this problem, we propose a pseudo-satellite system where telecommunication devices are carried on a perpetually flying solar aircraft cruising at stratospheric altitude. Our aircraft will combine lighter-than-air technology to augment the lift from the wing. Every major components contributing to the aircraft total weight has been considered, resulting in a range of design solutions. We chose wing span and aspect ratio of 50m and 13 respectively, from which other specifications of the aircraft were fixed to. Our design solution has been validated by power and weight balance analysis. System reliability has been demonstrated by Monte Carlo simulation.

Micro-morphological adaptations of the wing nodus to flight behaviour in four dragonfly species from the family Libellulidae (Odonata: Anisoptera)

Adult dragonflies can be divided into two major groups, perchers and fliers, exhibiting notably different flight behaviour. Previous studies have yielded conflicting results regarding the link between the wing macro-morphology and flight style in these two groups. In this study, we present the first systematic investigation of the micro-morphological differences of wings of percher and flier dragonflies in four closely related species from the family Libellulidae. Our results suggest that the shape and material composition of wing microstructural components and, in particular, the nodus are adapted to facilitate the specific wing functioning in fliers and perchers. The findings further indicate a decreasing trend in the area proportion of the soft resilin-dominated cuticle in the nodus in the series of species from typical perchers to typical fliers. Such a reduction in the resilin proportion in the nodus of fliers is associated with an increase in the wing aspect ratio. The knot-shaped protrusion at the nodus of perchers, which becomes notably smaller in that of strong fliers, is likely to act as a mechanical stopper, avoiding large wing displacements. This study aims to develop a novel framework for future research on the relationship between wing morphology and flight behaviour in dragonflies.

Wing morphology, flight type and migration distance predict accumulated fuel load in birds.

Birds often accumulate large fat and protein reserves to fuel long-distance flights. While it is well known that species that fly the longest accumulate the largest amounts of fuel, considerable cross-species variation in fuel load is seen after controlling for overall migration distance. It remains unclear whether this variation can be explained by aerodynamic attributes of different species, despite obvious ecological and conservation implications. Here, we collected data on wing morphology, flight type, migration distance and fuel load from 213 European bird species and explored three questions: (1) does maximum fuel load relate to migration distance across species?; (2) does wing morphology, as described by wing aspect ratio and wing loading, influence maximum fuel load?; and (3) does flight type influence maximum fuel load? Our results indicate that maximum fuel load increases with migration across species, but residual variance is high. The latter variance is explained by aspect ratio and flight type, while wing loading and body mass explain little variance. Birds with slender wings accumulate less fuel than species with low wing aspect ratio when covering a similar migration distance. Continuously flapping species accumulate the largest amounts of fuel, followed by flapping and soaring species and flapping and gliding species, while the smallest fuel loads were observed in birds with passerine-type flight. These results highlight complex eco-evolutionary adaptations to migratory behaviour, pointing toward the importance of energy minimisation.

Spatial Heterogeneity of Fruit Bats in a Primary Tropical Lowland Evergreen Rainforest in Northeastern Luzon, Philippines

In the Philippines, little is known beyond the most basic information on the ecology and biogeography of fruit bats. This is aggravated by the increasing risks on their populations, particularly in primary lowland forests, the most threatened habitat in the country, which these species inhabit and also where chiropteran diversity is highest. In this study, the spatial heterogeneity of fruit bats within a primary lowland forest in Palanan, Isabela, northeastern Luzon was investigated. In addition, habitat partitioning patterns were compared with wing morphology variations. Mist nets were used to sample two vertical strata and three forest landscapes. Wing loading and aspect ratio were measured for all species captured. A total of 1,243 fruit bats representing eight species were caught from a sampling effort of 398,736 m2·h. All species were captured in the canopy, while only six species were captured in the understory. All species were also captured along ridges and forest edges, while only seven were captured along streams. Based on permutational MANOVA, a significant difference was found between the species assemblages in the understory and canopy, but not among ridges, streams, and forest edges. At the population level, Kruskal-Wallis tests were performed on capture rates per species. All eight species exhibited strong preference for the canopy, while only two species were observed to have significantly different capture rates across forest landscapes. Wing morphology patterns based on wing loading and aspect ratio did not show consistent association with vertical strata preference. The varying capture rates of bats along ridges, streams and forest edges may have been influenced by their feeding behavior. This study demonstrates the spatial heterogeneity of fruit bats across vertical strata and across forest landscapes, the most significant of which is the preference for the canopy. Possible factors that could explain these patterns include fruit availability, a cluttered habitat, and tree species distribution, which should be assessed in future studies.

Ecomorphology and foraging behaviour of Pacific boobies

Wing size and shape, expressed as wing loading and aspect ratio respectively, together with bill morphology are parameters that can reveal differences related to the foraging ecology of seabirds. Six species of booby (Sulidae) that inhabit the Pacific are the focus of this study: four mainly pelagic species, Masked Booby Sula dactylatra, Nazca Booby Sula granti, Red‐footed Booby Sula sula and Brown Booby Sula leucogaster, and two coastal species, Blue‐footed Booby Sula nebouxii and Peruvian Booby Sula variegata. Pelagic boobies showed segregation among species in body mass and relative bill size, and they differed in wing morphology (wing loading and aspect ratio) from the coastal boobies. The coastal Peruvian and Blue‐footed Boobies are largely allopatric but overlap in northern Peru. In their area of sympatry, they showed evidence of character displacement in body size and in wing and bill morphology, which suggests that competition plays an important role in sympatry. This study improves our understanding of ecological interactions among Pacific boobies and of how selective pressures have shaped their ecomorphology and foraging behaviours.

Effects of spanwise flexibility on the performance of flapping flyers in forward flight.

Flying animals possess flexible wings that deform during flight. The chordwise flexibility alters the wing shape, affecting the effective angle of attack and hence the surrounding aerodynamics. However, the effects of spanwise flexibility on the locomotion are inadequately understood. Here, we present a two-way coupled aeroelastic model of a plunging spanwise flexible wing. The aerodynamics is modelled with a two-dimensional, unsteady, incompressible potential flow model, evaluated at each spanwise location of the wing. The two-way coupling is realized by considering the transverse displacement as the effective plunge under the dynamic balance of wing inertia, elastic restoring force and aerodynamic force. The thrust is a result of the competition between the enhancement due to wing deformation and induced drag. The results for a purely plunging spanwise flexible wing agree well with experimental and high-fidelity numerical results from the literature. Our analysis suggests that the wing aspect ratio of the abstracted passerine and goose models corresponds to the optimal aeroelastic response, generating the highest thrust while minimizing the power required to flap the wings. At these optimal aspect ratios, the flapping frequency is near the first spanwise natural frequency of the wing, suggesting that these birds may benefit from the resonance to generate thrust.

Application of lightweight materials in structure concept design of large-scale solar energy unmanned aerial vehicle

Carbon fiber composites and film materials can be effectively used in light aircraft structures, especially for solar unmanned aerial vehicles. The use of light materials can reduce the weight of the aircraft, but also can effectively improve the aircraft's strength and stiffness. The structure of the large aspect ratio solar energy UAV was analyzed in detail, taking Solar-impulse solar aircraft as an example. The solar energy UAV has a wing aspect ratio greater than 20, and the detailed digital model of the wing structure including beam, ribs and skin was built, also the Finite Element Method was applied to analyze the static and dynamic performance of the structure. The upper skin of the wing is covered with silicon solar cells, while the lower skin is light and transparent film. The single beam truss form of carbon fiber lightweight material is used in the wing structure. The wing beam is a box beam with rectangular cross sections. The box beam connected the front parts and after parts of the ribs together. The fuselage of the aircraft was built by space truss structure. According to the static and dynamic analysis with Finite Element method, it was found that the aircraft has a small wingtip deflection relative to the wingspan in the level flight state. The first natural frequency of the wing structure is pretty low, which is closed to the gust load.

On the dynamics of perching manoeuvres with low-aspect-ratio planforms

The dynamics of a simple perching manoeuvre are investigated using circular and aspect-ratio-two elliptical flat plates, as abstractions of low-aspect-ratio planforms observed in highly-manoeuvrable birds. The perching kinematic investigated in this study involves a pitch-up motion from an angle of attack of to , while simultaneously decelerating. This motion is defined by the shape change number, , which acts as a measure of the relative contributions of added-mass and circulatory effects. This motion has been observed in natural flyers during controlled landings, and has recently been explored through the use of a nominally two-dimensional airfoil. The parameter space of low-aspect-ratio plates therefore serves to elucidate how realistic free-end conditions affect the timescales of vortex evolution, and therefore the relative contributions between added mass and circulation. The results presented herein suggest that for the low-aspect-ratio plates, the shedding of vortices occurs more rapidly than for equivalent two-dimensional cases, and therefore faster pitching motions are required to compensate for the lower levels of lift and drag. Furthermore, the vortex topology and instantaneous forces that arise during the rapid-area changes show no sensitivity to aspect ratio, and strong collapse is observed between both flat plates. Similar aerodynamic advantages may therefore be exploited during perching manoeuvres by birds of various scale regardless of wing aspect ratio.

Non-linear aeroelastic response of high aspect-ratio wings in the frequency domain

ABSTRACTA current trend in the aeronautic industry is to increase the wing aspect ratio to enhance aerodynamic efficiency by reducing the induced drag and thus reduce fuel consumption. Despite the associated benefits of a large aspect ratio, such as higher lift-to-drag ratios and range, commercial aircraft usually have a relatively low aspect ratio. This is partially explained by the fact that the wing becomes more flexible with increasing aspect ratio and thus more prone to large deflections, which can cause aeroelastic instability problems such as flutter. In this work, an aeroelastic study is conducted on a rectangular wing model of 20 m span and variable chord for a low subsonic speed condition to evaluate the differences between linear and non-linear static aeroelastic responses. Comparisons between linear and non-linear displacements, natural frequencies and flutter boundary are performed. An in-house non-linear aeroelastic framework was employed for this purpose. In this work, the influence of the aspect ratio and geometric non-linearity (highly deformed states) is assessed in terms of aeroelastic performance parameters: flutter speed and divergence speed. A nearly linear correlation of flutter speed difference (relative to linear analysis results) with vertical-tip displacement difference is observed. The flutter and divergence speeds vary substantially as the wing aspect ratio increases, and the divergence speeds always remain above the flutter speed. Furthermore, the flutter mechanism was observed to change as the wing chord is decreased.

Morphological constraints on changing avian migration phenology.

Many organisms at northern latitudes have responded to climate warming by advancing their spring phenology. Birds are known to show earlier timing of spring migration and reproduction in response to warmer springs. However, species show heterogeneous phenological responses to climate warming, with those that have not advanced or have delayed migration phenology experiencing population declines. Although some traits (such as migration distance) partly explain heterogeneity in phenological responses, the factors affecting interspecies differences in the responsiveness to climate warming have yet to be fully explored. In this comparative study, we investigate whether variation in wing aspect ratio (reflecting relative wing narrowness), an ecomorphological trait that is strongly associated with flight efficiency and migratory behaviour, affects the ability to advance timing of spring migration during 1960-2006 in a set of 80 European migratory bird species. Species with larger aspect ratio (longer and narrower wings) showed smaller advancement of timing of spring migration compared to species with smaller aspect ratio (shorter and wider wings) while controlling for phylogeny, migration distance and other life-history traits. In turn, migration distance positively predicted aspect ratio across species. Hence, species that are better adapted to migration appear to be more constrained in responding phenologically to rapid climate warming by advancing timing of spring migration. Our findings corroborate the idea that aspect ratio is a major evolutionary correlate of migration, and suggest that selection for energetically efficient flights, as reflected by high aspect ratio, may hinder phenotypically plastic/microevolutionary adjustments of migration phenology to ongoing climatic changes.

Design and flight performance of hybrid underwater glider with controllable wings

Hybrid underwater glider combines motion modes of traditional autonomous underwater glider and those of autonomous underwater vehicles. Different motion modes need different flight performance, including flight efficiency, static stability, and maneuverability. Conventional hybrid underwater glider with fixed wings can’t achieve optimal flight performance in one flight mission demanding various motion modes. In this article, controllable wings for hybrid underwater glider Petrel II are designed. Angle of attack, sweep angle, and aspect ratio of controllable wings can be changed to adapt to different motion modes. Kinematics and dynamics models of Petrel II are established based on multibody theory. Motion simulations of Petrel II with different wing configurations are conducted in three motion modes, including glide motion, spiral motion, and horizontal turning motion. The simulation results show the impact of wing parameters on flight performance. Field trials demonstrate that the controllable wings can improve the flight performance.

Global dynamics of dispersal and diversification among passerine birds

Explaining global variation in geographic and taxonomic diversity gradients represents a central focus of macroecology and macroevolution. Ultimately, these diversity gradients have been generated over deep timescales as a consequence of historical variation in rates of dispersal, diversification, and the capacity of different geographic areas to preserve taxa through time. Here, I assess the relationships among these processes, to elucidate the causes of geographic and taxonomic variation in species richness among the most speciose order of birds: the Passeriformes (c. 6,500 species). To achieve this, I comparatively analyze phylogenetic, distributional and eco-morphological trait data collated at broad taxonomic and spatial scales. The results of my analyses strongly support the prevalence of historical dispersal events across large geographic scales, in addition to spatiotemporal variation in diversification rates. These findings reflect that some lineages and some geographic regions (notably tropical mountain regions and island archipelagoes) generate and maintain a much larger amount of species diversity than others. In addition, the evolution of particular life-history and eco-morphological traits, specifically pair breeding systems, and higher wing aspect-ratios, increased rates of range expansion and diversification. In summary, geographic variation in historical diversification combined with differences in the capacity of lineages to colonize new areas, determines spatial and taxonomic differences in passerine species richness.

The energy landscape predicts flight height and wind turbine collision hazard in three species of large soaring raptor

Summary Collisions of large soaring raptors with wind turbines and other infrastructures represent a growing conservation concern. We describe a way to leverage knowledge about raptor soaring behaviour to forecast the probability that raptors fly in the rotor‐swept zone. Soaring raptors are theoretically expected to select energy sources (uplift) optimally, making their flight height dependent on uplift conditions. This approach can be used to forecast collision hazard when planning or operating wind farms. Empirical investigations of the factors influencing flight height have, however, so far been hindered by observation error. We propose a two‐pronged approach. First, we fitted state‐space models to z‐axis GPS tracking data to filter heavy‐tailed observation error and estimate the relationship between vertical movement parameters and weather variables describing the energy landscape (thermal and orographic uplift potential). Second, we fitted a mechanistic model of flight height above ground based on aerodynamics and resource selection theories. The approach was replicated for five GPS‐tracked Andean condors Vultur gryphus, eight griffon vultures Gyps fulvus, and six golden eagles Aquila chrysaetos. In all individuals, movement parameters correlated with thermal uplift potential in the expected direction. In all species, collision hazard was lowest for high thermal uplift potential values. Species specificities in the presence of a peak in collision hazard for medium values of thermal uplift potential could be explained by differences in wing loading and aspect ratio. Synthesis and applications. Our fitted models convert weather data (thermal uplift potential) into a prediction of collision hazard (probability to fly in the rotor‐swept zone), making it possible to prioritize different wind development projects with respect to the relative hazard they would pose to raptors. However, our model should be combined with post‐construction monitoring to document, and eventually account for turbine avoidance behaviours in collision rate predictions.

The influence of aspect ratio and stroke pattern on force generation of a bat-inspired membrane wing.

Aspect ratio (AR) is one parameter used to predict the flight performance of a bat species based on wing shape. Bats with high AR wings are thought to have superior lift-to-drag ratios and are therefore predicted to be able to fly faster or to sustain longer flights. By contrast, bats with lower AR wings are usually thought to exhibit higher manoeuvrability. However, the half-span ARs of most bat wings fall into a narrow range of about 2.5-4.5. Furthermore, these predictions do not take into account the wide variation in flapping motion observed in bats. To examine the influence of different stroke patterns, we measured lift and drag of highly compliant membrane wings with different bat-relevant ARs. A two degrees of freedom shoulder joint allowed for independent control of flapping amplitude and wing sweep. We tested five models with the same variations of stroke patterns, flapping frequencies and wind speed velocities. Our results suggest that within the relatively small AR range of bat wings, AR has no clear effect on force generation. Instead, the generation of lift by our simple model mostly depends on wingbeat frequency, flapping amplitude and freestream velocity; drag is mostly affected by the flapping amplitude.

Ecological implications of the correlation of avian footprints with wing characteristics: a mathematical approach

AbstractThe characteristics of avian wings that evolved for flying appear to show a distinct relationship to the shape of the pes and walking abilities as reflected in footprints. Wing area, wing span and body weight data of modern birds were collected and analysed in order to quantify the possible correlation, which was previously only inferred from empirical data. Discriminant analysis demonstrated that avian wings can be divided into three habitat groups, in a similar way to footprints. Multiple regression analyses revealed that the avian wing loading and aspect ratio were correlated with the parameters of footprint shape and can be expressed by a simple equation. The results may reflect the adaptation of avian locomotion to habitat. The relationships between wing area and wing span, and between wing area and footprint area, which are apparent in modern avians, were derived and used to estimate wing area and wing span from the footprints of extinct Cretaceous avian taxa. The estimated values of body weight, wing span and wing area suggest that the trackmakers of Archaeornithipus meijidei, Hwangsanipes choughi and Yacoraitichnus avis had bodies similar to herons (or cranes), large sandpipers (or small sea birds) and medium‐sized gull‐like birds, respectively.

Behaviour of trailing wing(s) in echelon formation due to wing twist and aspect ratio

In this paper, a novel decambering technique has been implemented using a vortex lattice method to study the effects of wing twist on the induced drag of individual lifting surfaces in configuration flight including post-stall angles of attack. The effect of both geometric and aerodynamic twist is studied. In the present work, 2D data of NACA0012 airfoil from XFoil at Re=1×106 is used to predict 3D post-stall data using geometric twist for a single wing and compared with literature. The effect of aerodynamic twist is implemented by using different airfoils along wing–span and the resulting wing CL–α and Cdi–α are compared with experiment. Study of wings of different aspect ratios with & without aerodynamic twist on both leading and trailing wings helps to understand the effect of twist on the lift and induced drag when they are varied on both wings simultaneously and individually.