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(a) The experimental setup, consisting of a low-turbulence low-speed wind tunnel, a high-speed stereoscopic PIV system for airflow visualization, and a high-speed stereoscopic video system for flight kinematics analysis. (b) Top view of a flycatcher with the seven natural markers, being (1) the wing tip; (2) the wrist; (3) the shoulder; (4) the side of the rump; (5) the tip of the tail; (6) the indentation between the innermost primary and the outermost secondary feather; and (7) the tip of the third primary. Also, the wing chord behind the wrist and at the wing-body intersection are shown, together with the quarter chord points ( point (8) and (9), respectively). (c) A hypothetical heaving wing with an elliptical spanwise force distribution F, two tip vortices with circulation G tip and spanwise angle (g), and spanwise uniform downwash w.
Source publication
Many small passerines regularly fly slowly when catching prey, flying in cluttered environments or landing on a perch or nest. While flying slowly, passerines generate most of the flight forces during the downstroke, and have a 'feathered upstroke' during which they make their wing inactive by retracting it close to the body and by spreading the pr...
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... experiments were performed in the Lund University low-speed low-turbulence wind tunnel [26], using a high- speed (200 Hz) stereoscopic PIV system (LaVision) for wake analysis and a stereoscopic high-speed (250 Hz) video camera setup for kinematics analysis ( figure 1a), similar to the setup described by Hedenström et al. [27]. ...
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... A body is the vertical wingbeat amplitude of the quarter chord point at the wing -body intersection ( point 9 in figure 1b), determined using the vertical movement of markers 3 and 4. A tip is the vertical The experimental setup, consisting of a low-tur- bulence low-speed wind tunnel, a high-speed stereoscopic PIV system for airflow visualization, and a high-speed stereoscopic video system for flight kinematics analysis. (b) Top view of a flycatcher with the seven natural markers, being (1) the wing tip; (2) the wrist; (3) the shoulder; (4) the side of the rump; (5) the tip of the tail; (6) the indentation between the innermost primary and the outermost secondary feather; and (7) the tip of the third primary. ...
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... amplitude (marker 1 in figure 1b). A Ã body is used in the vortex wake analysis, as described below. ...
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... the vortex wake analysis, the different PIV frames were visualized separately, and the main wake vortices were identified (e.g. the tip vortex, figure 1c). For each of these main vortex structures, the location and time stamp fx,y,z,tg, streamwise peak vorticity fv x,max g and streamwise circulation fG x g were measured and stored. ...
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... should be careful in distinguishing e f from e i . For example, Pennycuick's flight model (Flight 1.22) [1,25], which can be used to estimate power curves for flap- ping flight in birds, uses the flap efficiency rather than the span efficiency to estimate the induced power. Equivalent to Pennycuick's flight model, one can esti- mate the effective induced drag coefficient for flapping flight by [1,25,30] ...
Citations
... This may cause a reduction in flight noise during flapping flight or during turning and breaking maneuvers. During these maneuvers, the vortex pattern around the wing changes, as found in other bird species (Norberg 1990;Hedenström et al. 2006;Tobalske et al. 2009;Lentink et al. 2010;Muijres et al. 2012;Crandell et al. 2015). Serrations might reduce the intensity of vortices, for example, the bound vortex shed during the stopping maneuvers before striking prey. ...
The silent flight of barn owls is associated with wing and feather specialisations. Three special
features are known: a serrated leading edge that is formed by free-standing barb tips which
appears as a comb-like structure, a soft dorsal surface, and a fringed trailing edge. We used
a model of the leading edge comb with 3D-curved serrations that was designed based on 3D
micro-scans of rows of barbs from selected barn-owl feathers. The interaction of the flow with
the serrations was measured with Particle-Image-Velocimetry in a flow channel at uniform steady
inflow and was compared to the situation of inflow with freestream turbulence, generated from
the turbulent wake of a cylinder placed upstream. In steady uniform flow, the serrations caused
regular velocity streaks and a flow turning effect. When vortices of different size impacted the
serrations, the serrations reduced the flow fluctuations downstream in each case, exemplified
by a decreased root-mean-square value of the fluctuations in the wake of the serrations. This
attenuation effect was stronger for the spanwise velocity component, leading to an overall flow
homogenization. Our findings suggest that the serrations of the barn owl provide a passive flow
control leading to reduced leading-edge noise when flying in turbulent environments.
... Bird flight behaviours have been studied for many years, including detailed examinations of flight kinematics (e.g., Møller, 1997, Krishnan et al., 2022), aerodynamics (e.g., Muijres et al., 2012a, Alerstam et al., 2007 and general aspects such as migration flight strategies (e.g., Mitchell et al., 2015, Jiguet et al., 2019. Despite this, still very little is known about the fundamental aspects of what is required from a bird in terms of flight performance in their day-to-day lives during routine transport flights and foraging flights. ...
... This foraging behaviour may involve high performance flights with high demands for agility and endurance, making these birds ideal for studying activity patterns and flight performance. A lot is known about pied flycatcher kinematics and aerodynamics from previous wind tunnel studies (Muijres et al., 2012a, Muijres et al., 2012b, Johansson et al., 2018 which is relevant when attempting to understand and explain their performance and behaviours in the wild. ...
Flight behaviours have been extensively studied from different angles such as their kinematics, aerodynamics and more general their migration pattern. Nevertheless, much is still unknown about the daily flight activity of birds, in terms of their performance, behaviour and the potential differences between males and females. The recent development of miniaturized accelerometers allows us a glimpse into the daily life of a songbird. Here, we tagged 26 pied flycatchers (Ficedula hypoleuca) with accelerometers and analysed using machine learning approaches their flight performance, activity and behaviour during their chick rearing period. We found that during two hours of foraging chick-rearing pied flycatchers were flying 13.7% of the time. Almost all flights (>99%) were short flights lasting less than 10s. Flight activity changed throughout the day and was highest in the morning and lowest in the early afternoon. Male pied flycatcher had lower wing loading than females, and peak flight accelerations were inversely correlated with wing loading. Despite this, we found no significant differences in flight activity and performance between sexes. This suggests that males possess a higher potential flight performance, which they not fully utilized during foraging flights. Our results thus suggest that male and female pied flycatcher invest equally in parental care, but that this comes at a reduced cost by the male, due to their higher flight performance potential.
... This adaptability enables birds to employ the most efficient modes of motion and flight strategies to accommodate various flight conditions and purposes [3,4]. Previous studies have predominantly relied on methods such as biological observation [5,6], numerical simulations [7,8], and scale-model wind tunnel experiments [9][10][11]. While birds may not match the agility of smaller insects, their larger size grants them access to higher flight altitudes, greater speeds, increased payload capacity, and extended ranges. ...
This study focused on designing a single-degree-of-freedom (1-DoF) mechanism emulating the wings of rock pigeons. Three wing models were created: one with REAL feathers from a pigeon, and the other two models with 3D-printed artificial remiges made using different strengths of material, PLA and PETG. Aerodynamic performance was assessed in a wind tunnel under both stationary (0 m/s) and cruising speed (16 m/s) with flapping frequencies from 3.0 to 6.0 Hz. The stiffness of remiges was examined through three-point bending tests. The artificial feathers made of PLA have greater rigidity than REAL feathers, while PETG, on the other hand, exhibits the weakest strength. At cruising speed, although the artificial feathers exhibit more noticeable feather splitting and more pronounced fluctuations in lift during the flapping process compared to REAL feathers due to the differences in weight and stiffness distribution, the PETG feathered wing showed the highest lift enhancement (28% of pigeon body weight), while the PLA feathered wing had high thrust but doubled drag, making them inefficient in cruising. The PETG feathered wing provided better propulsion efficiency than the REAL feathered wing. Despite their weight, artificial feathered wings outperformed REAL feathers in 1-DoF flapping motion. This study shows the potential for artificial feathers in improving the flight performance of Flapping Wing Micro Air Vehicles (FWMAVs).
... Pennycuick et al. 2003) or aerodynamic investigations (flight power, flight range, lift and drag coefficients, detailed velocity distribution via particle image velocimetry (PIV), e.g. Spedding and Hedenström, 2009;Muijres et al. 2012;Johansson et al. 2018). Especially for migration research a wind tunnel is meanwhile indispensable (Hedenström and Lindström, 2017). ...
A blower-type wind tunnel for physiological bird flight experiments has been developed, constructed and evaluated. Since the birds to be investigated are rather big (Northern Bald Ibis, Geronticus eremita), the cross-sectional area of the test section measures 2.5 m × 1.5 m. The maximum achievable flow speed is approximately 16 ms-1. The wind tunnel exhibits a flexible outlet nozzle to provide up- and downdraft to allow for gliding and climbing flights. The current paper describes in detail the layout, design and construction of the wind tunnel including its control. Numerical simulations of the flow and measurements of the velocity distribution in the test section are presented. Apart from a non-homogeneous flow region in the mixing layer at the boundaries of the free jet, the test section exhibits a very even velocity distribution; the local speed deviates by less than two percent from the mean velocity. The turbulence intensity inside the test section was measured to be between 1 and 2%. As a constraint, a limited budget was available for the project. Four northern bald ibises were hand-raised and trained to fly in the wind tunnel.
Supplementary information:
The online version contains supplementary material available at 10.1007/s10336-021-01945-2.
... Distal (primary) and proximal (secondary) feathers have distinct functions in flight, and so have to withstand forces acting from different directions (Norberg, 1985;Videler, 2005;Usherwood, 2010;Muijres et al., 2012). Primary feathers are responsible for generating not only thrust but also lift (Norberg, 1985;Videler, 2005), whereas proximal wing feathers (secondaries) mostly generate lift (Müller & Patone, 1998). ...
Variation in rachis (central shaft) morphology in individual remiges (flight feathers) within and among species reflects adaptations to requirements imposed by aerodynamic forces, but the fine-scale variation of feather morphology across remiges is not well known. Here we describe how the shape of the rachis, expressed by the height/width ratio, changes along the longitudinal and lateral axis of the wing in four bird species with different flight styles: flapping-soaring (white storks), flapping-gliding (common buzzards), passerine-type (house sparrows) and continuous flapping (pygmy cormorants). Overall, in each wing feather, irrespective of species identity, rachis shape changed from circular to rectangular, from the base towards the feather tip. The ratio between the height and width of the calamus was similar across remiges in all species, whereas the ratio at the base, middle and tip of the rachis changed among flight feathers and species. In distal primaries of white storks and common buzzards, the ratio decreased along the feather shaft, indicating a depressed (wider than high) rachis cross section towards the feather tip, whereas the inner primaries and secondaries became compressed (higher than wide). In house sparrows, the rachis was compressed in each of the measurement points, except at the distal segment of the two outermost primary feathers. Finally, in pygmy cormorants, the width exceeds the height at each measurement point, except at the calamus. Our results may reflect the resistance of the rachis to in-plane and out-of-plane aerodynamic forces that vary across remiges and across study species. A link between rachis shape and resistance to bending from aerodynamic forces is further indicated by the change of the second moment of areas along the wing axes.
... Analysis of birds flying in wind tunnels showed uniformly distributed spanwise downwash. [53] -Hummingbird wings generated a mean downward velocity of 1.1 m/s. [52] -"We show how the air behind the body of a long-eared bat accelerates downwards, …..." [51] However, the research did not directly attribute the downwash created to any lift generated. ...
The same logic applies to skiers, frisbees, and paper airplanes. Newtonian mechanics provides insight to design a better wingsuit.
... The calculation of the angle of attack α is an important item, as the tables of the aerodynamics coefficients depend directly on its value. The angle of attack ( Figure 5) is defined as the angle existing between the wind chord c and the total flow incident on the wing V R , that is the velocity seen by the wing at a distance c / 4 from the leading edge (Muijres et al., 2012), that is estimated as V R = V v a ∞ + , where: V ∞ is the flow velocity far ahead of the body , and v a is the linear velocity of the wing at c / 4 from the leading edge. ...
In this chapter, a two-degree-of-freedom controller that exploits the flat properties of a three degree-of-freedom wing type flat-plate for an Ornithopter Autonomous robot is proposed. A set of kinematical patterns inspired by nature is used to simulate the wing's movement around two wingtip trajectories; also, the effects of the aerodynamical forces as a function of the wind velocity and the wing's angle of attack are considered. In order to control the system, the effects of these forces are viewed as disturbs that affect the wing's dynamics. The proposed control scheme drives the device through the desired path by generating a set of desired inputs which are compensated by a feedback loop when the aerodynamical forces actuate upon the system.
... The parrotlets in this study flew at lower speeds and with inclined stroke planes, reaching advance ratios J of only 0.2-0.3. Their mid-downstroke lift-to-drag ratios, which averaged 1.57 ± 0.35 across takeoff and landing wingbeats, (Fig. 4e), are lower than what has been reported for other birds flying at similar advance ratios (J ≈ 0.3, C L /C D = 8-10 12,36,49 ). This discrepancy results from the use of body velocity, rather than wing velocity, to define the directions of lift and drag; in these previous studies, lift is considered a vertical force that counters bodyweight while drag acts horizontally to counter forward thrust 41,49 . ...
... We note that they could be equivalently derived based on the instantaneous single wing lift and drag during peak net force, C L C D ¼ L=:5ρSv 2 2 D=:5ρSv 2 2 ¼ L D . In order to fairly compare our lift-to-drag ratios to those published in the literature, we limited our comparisons to flights made by generalist birds at similar advance ratio (~0.3) 12,36 . We then converted the lift-to-drag ratios published in these studies based on body velocity direction (L′/D′) to lift-to-drag ratios based on the wing velocity direction at r 2 (L/D). ...
The lift that animal wings generate to fly is typically considered a vertical force that supports weight, while drag is considered a horizontal force that opposes thrust. To determine how birds use lift and drag, here we report aerodynamic forces and kinematics of Pacific parrotlets (Forpus coelestis) during short, foraging flights. At takeoff they incline their wing stroke plane, which orients lift forward to accelerate and drag upward to support nearly half of their bodyweight. Upon landing, lift is oriented backward to contribute a quarter of the braking force, which reduces the aerodynamic power required to land. Wingbeat power requirements are dominated by downstrokes, while relatively inactive upstrokes cost almost no aerodynamic power. The parrotlets repurpose lift and drag during these flights with lift-to-drag ratios below two. Such low ratios are within range of proto-wings, showing how avian precursors may have relied on drag to take off with flapping wings. Recent work has suggested that lift and drag may be employed differently in slow, flapping flight compared to classic flight aerodynamics. Here the authors develop a method to measure vertical and horizontal aerodynamic forces simultaneously and use it to quantify lift and drag during slow flight.
... Analysis of birds flying in wind tunnels showed uniformly distributed spanwise downwash. [53] -Hummingbird wings generated a mean downward velocity of 1.1 m/s. [52] -"We show how the air behind the body of a long-eared bat accelerates downwards, …..." [51] However, the research did not directly attribute the downwash created to any lift generated. ...
Albatrosses soar by stealing momentum from the wind, similar to how boats sail into the wind.
... Analysis of birds flying in wind tunnels showed spanwise downwash. [83] -Hummingbird wings generated a mean downward velocity of 1.1 m/s. [82] -"We show how the air behind the body of a long-eared bat accelerates downwards, …..." [81] However, the research did not directly attribute downwash to the lift generated, based on Newtonian mechanics. ...
According to Newtonian mechanics, a bird's wings accelerate (a) a mass of air (m) downwards, to create a downward force (Force =ma). The reaction provides lift that pushes the bird up. The wings impart momentum to the air to create lift. This is similar to how insects fly.
This Newtonian approach challenges the prevailing view that fluid mechanics explain lift by birds' wings.
