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A limiting factor in the design of smaller size uncrewed aerial vehicles is their inability to navigate through gust-laden environments. As a result, engineers have turned towards bio-inspired engineering approaches for gust mitigation techniques. In this study, the aerodynamics of a red-tailed hawk’s response to variable-magnitude discrete transverse gusts was investigated. The hawk was flown in an indoor flight arena instrumented by multiple high-speed cameras to quantify the 3D motion of the bird as it navigated through the gust. The hawk maintained its flapping motion across the gust in all runs; however, it encountered the gust at different points in the flapping pattern depending on the run and gust magnitude. The hawk responded with a downwards pitching motion of the wing, decreasing the wing pitch angle to between −20^∘and −5^∘, and remained in this configuration until gust exit. The wing pitch data was then applied to a lower-order aerodynamic model that estimated lift coefficients across the wing. In gusts slower than the forward flight velocity (low gust ratio), the lift coefficient increases at a low-rate, to a maximum of around 2–2.5. In gusts faster than the forward flight velocity (high gust ratio), the lift coefficient initially increased rapidly, before increasing at a low-rate to a value around 4–5. In both regimes, the hawk’s observed height change due to gust interaction was similar (and small), despite larger estimated lift coefficients over the high gust regime. This suggests another mitigation factor apart from the wing response is present. One potential factor is the tail pitching response observed here, which prior work has shown serves to mitigate pitch disturbances from gusts.

 

The physical principles that govern the function of biological structures also mediate their evolution, but the evolutionary drivers of morphological traits within complex structures can be difficult to predict. Here, we use morphological traits measured from 1096 3-dimensional bird wing scans from 178 species to test the interaction of two frameworks for relating morphology to evolution. We examine whether the evolutionary rate (σ²) and mode is dominated by the modular organization of the wing into handwing and armwing regions, and/or the relationship between trait morphology and functional output (i.e. mechanical sensitivity, driven here by flapping flight aerodynamics). Our results support discretization of the armwing and handwing as morphological modules, but morphological disparity andσ²varied continuously with the mechanical sensitivity gradient and were not modular. Thus, mechanical sensitivity should be considered an independent and fundamental driver of evolutionary dynamics in biomechanical traits, distinct from morphological modularity.

 

Flying insects possess sophisticated olfactory systems that they use to find food, locate mates, and avoid predators. It is suspected that insects flap their wings to draw odor plumes toward their antennae. This behavior enhances their olfactory sensitivity and is analogous to sniffing in mammals. However, insects’ wing kinematics change drastically as their flight speed increases, and it is unknown how these changes affect the insect’s odorant perception. To address this question, we simulated odor-tracking hawkmoth fight at 2 m/s and 4 m/s using an in-house immersed-boundary-method-based CFD solver. The solver was used to solve the Navier-Stokes equations that govern the flow, as well as the advection-diffusion equation that governs the odor transport process. Results show that hawkmoths use their wings to significantly increase the odor intensity along their antennae. However, peak odor intensity is 39% higher during 2 m/s flight than 4 m/s flight. We therefore suspect that insects have greater olfactory performance at lower forward flight speed. Findings from this study could provide inspiration for bio-inspired odor-guided navigation technology. 

It is generally accepted among biology and engineering communities that insects are unstable at hover. However, existing approaches that rely on direct averaging do not fully capture the dynamical features and stability characteristics of insect flight. Here, we reveal a passive stabilization mechanism that insects exploit through their natural wing oscillations: vibrational stabilization. This stabilization technique cannot be captured using the averaging approach commonly used in literature. In contrast, it is elucidated using a special type of calculus: the chronological calculus. Our result is supported through experiments on a real hawkmoth subjected to pitch disturbance from hovering. This finding could be particularly useful to biologists because the vibrational stabilization mechanism may also be exploited by many other creatures. Moreover, our results may inspire more optimal designs for bioinspired flying robots by relaxing the feedback control requirements of flight.