Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors

Self Cite

Birds fly effectively and maneuver nimbly by dynamically changing the shape of their wings during each wingbeat. These shape changes have yet to be quantified automatically at high temporal and spatial resolution. Therefore, we developed a custom 3D surface reconstruction method, which uses a high-speed camera to identify spatially encoded binary striped patterns that are projected on a flying bird. This non-invasive structured-light method allows automated 3D reconstruction of each stand-alone frame and can be extended to multiple views. We demonstrate this new technique by automatically reconstructing the dorsal surface of a parrotlet wing at 3200 frames s −1 during flapping flight. From this shape we analyze key parameters such as wing twist and angle of attack distribution. While our binary 'single-shot' algorithm is demonstrated by quantifying dynamic shape changes of a flying bird, it is generally applicable to moving animals, plants and deforming objects.

Section: Resultsmentioning

confidence: 99%

High-speed surface reconstruction of a flying bird using structured-light

Deetjen

Biewener

Lentink

2017

Self Cite

“…1). Based on recently published aerodynamic measurements on prepared hummingbird wings (Kruyt et al, 2014), we know the leading edge of a hummingbird hand wing (Calypte anna) is thinner than the 3D printed hummingbird wing of Elimelech and Ellington (2013). The leading edge shape of the avian hand wing matters for aerodynamic performance, as reported earlier for swift wing models, which need a sharp leading edge to generate a leading edge vortex (Videler et al, 2004;Videler, 2006), and for gliding barn owls, for which the serration of their leading-edge primary feather helps reduce flow separation (Winzen et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

Feather roughness reduces flow separation during low Reynolds number glides of swifts

Bokhorst

Kat

Elsinga

et al. 2015

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Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small ( proto) birds with an evolutionary window to high glide performance.

“…Furthermore, the quasi-steady model, which uses different equations for modeling lift and drag (Dickinson et al, 1999), is unable to match the time course of either measured force component. Lift predicted by the model typically accounts for only ∼70% of body weight support (Kruyt et al, 2014), so induced drag (drag due to lift) is also underestimated. However, drag tends to be even more greatly underestimated than lift, because total drag force also includes profile drag (drag due to skin friction and the shape of the body), which is difficult to model precisely (Sane and Dickinson, 2001).…”

Section: Wing Stroke and Morphology Functions Unique To Vertebratesmentioning

confidence: 99%

“…Translational lift (C L ) and drag (C D ) coefficients are measured as functions of the angle of attack (α) with a spinning wing. Harmonic functions have been fitted to this data for fruit flies (Dickinson et al, 1999) and hummingbirds (Kruyt et al, 2014). The rotational force coefficient (C r ) and added mass coefficients have been calculated using inviscid flow theory (Dickson et al, 2008).…”

Section: Quasi-steady Modelmentioning

confidence: 99%

Flapping wing aerodynamics: from insects to vertebrates

Chin

Lentink

2016

Self Cite

263

155

More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanismsadded mass, clap and fling, rotational circulation and wing-wake interactions -have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters -the Reynolds number, Rossby number and advance ratio -govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight.