Showing papers by "David Lentink published in 2019"
TL;DR: A method to measure vertical and horizontal aerodynamic forces simultaneously and use it to quantify lift and drag during slow flight is developed and developed, showing how avian precursors may have relied on drag to take off with flapping wings.
Abstract: 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.
24 citations
TL;DR: It is advantageous to be small for stable perching when high friction relative to normal force is required because claws can find more usable surface, but this trend reverses when required friction shrinks, which explains how many animals and robots may grasp complex surfaces reliably.
Abstract: Most of the flying vehicles designed by humans need to land on smooth, standardized surfaces such as runways. A bird, on the other hand, can use structures that vary widely in diameter and texture, from phone lines to branches to statues. Yet, few studies have focused on how these animals transition from the air to a perch, and especially on how they adapt to different surfaces. To fill this gap, Roderick, Chin et al. recorded how Pacific parrotlets landed on nine natural and man-made perches that varied in diameter and texture, ranging from smooth Teflon to rough sandpaper. High-speed cameras tracked each of the landings while sensors measured how hard the birds landed on and squeezed the perches. The experiments revealed that the first landing phase was the same regardless of the nature of the perch. The birds used their wings to slow down, unfurled their feet and claws in preparation for touchdown and then allowed their legs to absorb the landing impact. Once the feet had made contact with the surface, however, the birds used their toes and claws to adapt to different perches. First, they steadied their grasp by tightly squeezing the perches. Then, the parrotlets dragged their claws on the surface of the perches to find minuscule bumps and dips that allowed better stabilization. These movements could be remarkably fast – in the range of one to two milliseconds. The birds also curled their claws more on perches that were harder to grasp. Once secured on the branch, they relaxed their grip. The results by Roderick, Chin et al. will help biologists understand how birds, insects and even large tree-dwelling creatures can grab perches in various environments. This knowledge will also be relevant for engineers who are trying to create robots that can climb or land on diverse surfaces.
21 citations
TL;DR: The way lovebirds glean wind orientation may inform minimal control algorithms that enable aerial robots to maneuver in similar windy and dark environments.
Abstract: Flying birds maneuver effectively through lateral gusts, even when gust speeds are as high as flight speeds. What information birds use to sense gusts and how they compensate is largely unknown. We found that lovebirds can maneuver through 45° lateral gusts similarly well in forest-, lake-, and cave-like visual environments. Despite being diurnal and raised in captivity, the birds fly to their goal perch with only a dim point light source as a beacon, showing that they do not need optic flow or a visual horizon to maneuver. To accomplish this feat, lovebirds primarily yaw their bodies into the gust while fixating their head on the goal using neck angles of up to 30°. Our corroborated model for proportional yaw reorientation and speed control shows how lovebirds can compensate for lateral gusts informed by muscle proprioceptive cues from neck twist. The neck muscles not only stabilize the lovebirds’ visual and inertial head orientations by compensating low-frequency body maneuvers, but also attenuate faster 3D wingbeat-induced perturbations. This head stabilization enables the vestibular system to sense the direction of gravity. Apparently, the visual horizon can be replaced by a gravitational horizon to inform the observed horizontal gust compensation maneuvers in the dark. Our scaling analysis shows how this minimal sensorimotor solution scales favorably for bigger birds, offering local wind angle feedback within a wingbeat. The way lovebirds glean wind orientation may thus inform minimal control algorithms that enable aerial robots to maneuver in similar windy and dark environments.
19 citations
TL;DR: Regulatory, animal care, and training considerations associated with avian flight research are reviewed.
Abstract: A thorough understanding of how animals fly is a central goal of many scientific disciplines. Birds are a commonly used model organism for flight research. The success of this model requires studying healthy and naturally flying birds in a laboratory setting. This use of a nontraditional laboratory animal species presents unique challenges to animal care staff and researchers alike. Here we review regulatory, animal care, and training considerations associated with avian flight research.