Biology subjects

Usherwood, J. R.

Publications and source records attributed to Usherwood, J. R..

3 recordsLinked to original sources

bioRxiv2022

Dynamics of hinged wings in strong upward gusts

A birds wings are articulated to its body via highly mobile shoulder joints. The wings possess an impressive range of motion, which allows for movements that can modulate the production of aerodynamic load in flight. This is crucial for stability and control--particularly in gusty or turbulent environments. In this study, we develop a dynamics model to examine how a bird-scale gliding aircraft can use wing-root hinges (analogous to avian shoulder joints) to reject the initial impact of a strong upward gust. Our idea requires that the spanwise centre of pressure and the centre of percussion of the hinging wing start, and stay, in good initial alignment (the centre of percussion here is related to the idea of a sweet spot on a bat, as in cricket or baseball). We propose a method for achieving this rejection passively, for which the essential ingredients are: (i) well-considered lift and mass distributions; (ii) constant-torque hinges; and (iii) a wing whose sections stall softly. When configured correctly, the gusted wings will first pivot on their hinges without disturbing the fuselage of the aircraft, affording time for other corrective actions to engage. We expect this system to enhance the control of aircraft that fly in gusty conditions.

bioengineering↗

bioRxiv2020

From wing shape to fluid dynamics in the barn owl (Tyto alba)

Birds morph their wings and tail in order to glide under a wide range of aerodynamic conditions. Gross wing morphing has been described in a multitude of studies, but the finer details of wing morphing are still unknown. Here, we measured the changes in wing shape and pose in a barn owl, Tyto alba, when gliding across a range of fifteen self-selected speeds. We found that T. alba does not use fine-wing shape control to glide at slow speeds in steady conditions, with the measured wing shapes being highly consistent across all flights. Instead, T. alba relied upon wing postural control (gross pitch) and changes in both tail shape and pose to modulate aerodynamic force. A consistent wing shape provides an exceptional aerodynamic tool for understanding gliding flight in birds through postural change and tail morphing. This geometry was used as the basis for computational fluid dynamics simulations which gave very similar wake measurements and weight support to those measured in flight. This geometry is provided here to assist other researchers interested in exploring the fluid dynamics behind gliding flight in birds.Competing Interest StatementThe authors have declared no competing interest.View Full Text

zoology↗

bioRxiv2017

Minimization of muscle activation costs demanded from mechanical work and power accounts for selection of duty factor in human gaits.

Duty factor DF - the proportion of a stride a foot is in contact with the ground - is of fundamental mechanical importance, and is often viewed as a defining kinematic parameter distinguishing walking (DF>0.5) from running (DF<0.5). However, the mechanical and/or physiological considerations that determine duty factor are not well understood. Here, a model is proposed that focuses on the interaction between mechanical and muscle costs to account for duty factor in human gaits. It minimizes the activation costs associated with mechanical work or power demand during muscle contraction (whichever is the more demanding). Empirical observations match model predictions using initial muscle parameters over a range of speeds within gaits. However, a better match is achieved - and a better account for the walk-run transition - with tuned muscle parameters. The tuned model is validated with responses in duty factor to walking at a range of imposed, unnatural step frequencies.

bioengineering↗