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Aerodynamics of the Cupped Wings during Peregrine Falcon’s Diving Flight

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During a dive peregrine falcons can reach velocities of more than 320 km h‐1 and makes them the fastest animals of the world. The aerodynamic mechanisms involved are not fully understood yet. The search for a conclusive answer to this fact motivates the three‐dimensional (3‐D) flow study of peregrine falcon aerodynamics. Especially the cupped wing configuration which is a unique feature of the wing shape in falcon peregrine dive is our focus herein. In particular, the flow in the gap between the main body and the cupped wing is studied to understand how this flow interacts with the body and to what extend it affects the integral forces of lift and drag. Characteristic shapes of the wings while diving are studied with regard to its aerodynamics using computational fluid dynamics (CFD). The results of the numerical simulations via ICEM CFD and OpenFOAM show predominant flow structures around the body surface and in the wake of the falcon model such as a pair of body vortices and tip vortices. The drag for the cupped wing profile is reduced in relation to the configuration of opened wings (without cupped‐like profile) while lift is increased. The purpose of this study is primarily the basic research of the aerodynamic mechanisms during the falcon’s diving flight. The results could be important for maintaining good maneuverability at high speeds in the aviation sector.
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... As opposed to conventional aircraft the bird does not have a fin and a rudder for lateral control, and therefore uses the wing-tips and the tail to achieve these maneuvers. This is confirmed from the live recordings reported in reference [9][10][11][12] where the bird is seen to open-up its wings laterally, sometimes even close to the M-shape during the high speed dive, however it tucks them back in into the Teardrop-shape immediately after to reduce the drag. ...
... As a continuation of the previous work by Ponitz et al. [5], Gowree et al. [9], Ponitz et al. [10], the present paper analyses the aerodynamics and mechanics of the flight of a falcon in pull-out maneuver with strong wing-morphing, applying classical flight stability criteria in order to draw parallels with current state-of-the-art highly maneuverable flight demonstrators and to explore the possibility of incorporation of the morphing mechanics and control mechanisms in modern Micro-Air-Vehicles (MAVs) and ...
... This asymmetrical morphing is also observed during other phases of the stoop when the bird is re-adjusting it's trajectory. Pure yaw control in the Cupped-shape can be achieved due to the substantial amount of side force generated on the wings as shown in Fig. 7 (compare [10]), also by the strong vortices which are now aligned to the side of the bird. This side force does not degrade significantly while morphing into the M-shape and hence allowing the bird to engage easily into a yaw maneuver, if it needs to turn around for another attempt. ...
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During the pull-out maneuver, Peregrine falcons were observed to adopt specific flight configurations which are thought to offer an aerodynamic advantage over aerial prey. Analysis of the flight trajectory of a falcon in a controlled environment shows it experiencing load factors up to 3 and further predictions suggest this could be increased up to almost 10g during high-speed pull-out. This can be attributed to the high maneuverability promoted by lift-generating vortical structures over the wing. Wind-tunnel experiments on life-sized models together with high fidelity simulations on idealized models, which are based on taxidermy falcons in different configurations, show that deploying the hand-wing in a pull-out creates extra vortex-lift, similar to that of combat aircraft with delta wings. The aerodynamic forces and the position of aerodynamic center were calculated from Large Eddy Simulations of the flow around the model. This allowed for an analysis of the longitudinal static stability in a pull-out, confirming that the falcon is flying unstably in pitch with a positive slope in the pitching moment and a trim angle of attack of about 5°, possibly to maximize responsiveness. The hand-wings/primaries were seen to contribute to the augmented stability acting as 'elevons' would on a tailless blended-wing-body aircraft.
... This is confirmed from the live recordings reported in Refs. [7,8], where the bird is seen to open up its wings laterally, sometimes even close to the M shape during the high-speed dive; however, it tucks them back in into the teardrop shape immediately after to reduce the drag. ...
... As a continuation of the previous work by Ponitz et al. [5], Gowree et al. [7], and Ponitz et al. [8], the present paper analyzes the aerodynamics and mechanics of the flight of a falcon in the pullout maneuver and the wing morphing. The study focuses on the early pullout phase where the transition is from teardrop in three stages toward M shape, whereas we use aerodynamic lifting theory to also extend predictions for the open M in the late phase of pullout. ...
... This asymmetrical morphing is also observed during other phases of the stoop when the bird is readjusting its trajectory. Pure yaw control in the cupped shape can be achieved due to the substantial amount of side force generated on the wings, as shown in Fig. 4 (see also Ref. [8]), as well as by the strong vortices that are now aligned to the side of the bird. This side force does not degrade significantly while morphing into the M shape, hence allowing the bird to engage easily into a yaw maneuver if it needs to turn around for another attempt. ...
Article
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During the pullout maneuver, peregrine falcons were observed to adopt a succession of specific flight configurations that are thought to offer an aerodynamic advantage over aerial prey. Analysis of the flight trajectory of a falcon in a controlled environment shows it experiencing load factors up to 3g, and further predictions suggest this could be increased up to almost 10g during high-speed pullout. This can be attributed to the high maneuverability promoted by lift-generating vortical structures over the wing. Wind-tunnel experiments on life-sized models in the different configurations together with high-fidelity computational fluid dynamics simulations (large-eddy simulations) show that deploying the hand wing in a pullout creates extra vortex lift, which is similar to that of combat aircraft with delta wings. The aerodynamic forces and the position of the aerodynamic center were calculated from the simulations of the flow around the different configurations. This allowed for an analysis of the longitudinal static stability in the early pullout phase, confirming that the falcon is flying unstably in pitch with a positive slope in the pitching moment and a trim angle of attack of about 5 deg, which is possibly to maximize responsiveness. The hand wings/primaries were seen to contribute to the augmented stability, acting as “elevons” would on a tailless blended-wing/body aircraft.
... did not discuss maximum flight speeds but reported average speeds upwards of 88 to 97 kmh -1 for various raptor species. Peregrine falcons can reach horizontal speeds upwards of 150 kmh -1(Ponitz et al. 2014), and the maximum gliding airspeed recorded for a white-backed vulture (Gyps africanus) was 141 kmh -1 (Tucker 1988).Meinertzhagen (1955) listed maximum recorded speeds across taxa, which included several notes of speeds > 100 kmh -1 . We therefore believe moments of extremely fast speeds may be possible for Swainson's hawks in exceptional environmental conditions.Locations of high speeds clustered towards the beginning and end of migration in both seasons. ...
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Swainson’s hawks (Buteo swainsoni) are a Neotropical migratory raptor species and a common breeding raptor in the High Plains of Texas. Colleagues and I monitored reproduction across a study area in northern Texas over seven years (2012 – 2018) to determine occupancy of large stick nests by Swainson’s hawks and reproductive output. I found that territories were consistently occupied by Swainson’s hawk pairs, and few other raptors or large stick-nesting species occupied the study area at any given time. Reproductive output (55% nesting success and 1.8 fledglings produced per successful nest) was lower than reports from other regions (70% success and 1.9 fledglings per nest) and was likely impacted by frequent droughts. Colleagues and I equipped adult hawks trapped in nesting territories with satellite transmitters in 2012 and 2013 and tracked hawks for up to five years. I examined data to compare migration characteristics, such as timing, routes, distance travelled, and length of migratory periods, to previous research that tracked Swainson’s hawks from other breeding regions. I found that most of the new data suggested agreement with previous conclusions, and differences were mostly attributable to breeding origin/destination. I described new migratory information, such as speed of travel, new staging and stopover locations, and habitat use and selection across the migratory pathway. One interesting finding was that Swainson’s hawks might be capable of surprisingly fast flight speeds (> 100 kmh-1 and > 800 km per day), though average speeds (25 kmh-1 and 189 km per day) agreed with previous research. Habitat use and selection reflected similar patterns as on breeding and nonbreeding ranges, and the most important conclusion was that avoidance of water and other migratory barriers, such as mountain ranges, heavily influences the migration pathway chosen by this species. In 2016 – 2018 I extended the transmitter study by equipping fledgling hawks with lower-resolution satellite transmitters and tracking them for up to four years. I used these data to describe previously unknown information about survival and behaviors during the juvenile and sub-adult life stages, which lasts 3-5 years in this species. I found a longer post-fledging period than previously described and that siblings gain independence from each other at the same time as they gain independence from adults. Juvenile hawks migrated southward with similar timing as adults, though during the first journey several hawks went off track, which proved fatal for most. Some juvenile hawks stopped short at the end of migration to overwinter in northern Argentina, while others completed the journey to the primary wintering grounds across the Pampas. Spring migration took longer than for adult hawks, with some juveniles arriving to the breeding region significantly later, possibly because they had no intention of attempting to breed. During the breeding season, juvenile hawks were nomadic, with only half making visits to natal territories. Survival was lowest immediately post-fledging and increased with time, though I did not track hawks long enough to observe any recruitment into the breeding population. Last, I used transmitter data from both adult and juvenile hawks to assess risk from the wind energy industry (a known hazard for raptorial and migratory species) throughout their global range. I found that Swainson’s hawks are at highest collision risk on their breeding range, though this species may be at lower overall risk than other raptor species, due to differences in behaviors and their long-distance migratory patterns.
... Most falcon top speeds ranged between 100 and 110 km h −1 in this study. The Peregrine is hailed as the fastest animal in the world, with reported dive speeds in excess of 320 km h −1 (Clark 1995;Ponitz et al. 2014). This is much greater than the maximum speed of 196 km h −1 and 140 km h −1 that we and Alerstam (1986) recorded, respectively. ...
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... Within the initial phase of the stoop it adopts a 'teardrop' shape (T-shape) where the wings are folded and feathers tucked in a streamlined shape, which is intuitively the lowest drag configuration. The success of the attack largely depends on the manoeuvrability during the second phase of the stoop, when the bird 1 starts to pull out from the dive, while undergoing two important morphological transformations, namely the cupped-wing shape (C-shape, detail presented in ref. 4 ) and the M-shape (the focus of this manuscript). In C-shape the arms are slighly untucked, creating a cavity between the body and the primary feathers, which are oriented vertically. ...
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