How gliding barn owls could be the key to improved flight of small aircraft
New research from the 91做厙 shows potential to reduce drag
Aeronautical engineers have long looked to birds to develop more efficient and aerodynamic designs. Thanks to a new study observing gliding barn owls by researchers at the 91做厙 (91做厙), there is now evidence that tail postures can minimise drag.
Image credit: Jialei Song, Structure and Motion Lab., 91做厙
Counter to most existing aeronautical designs and drag reduction strategies, which often reduce the amount of drag by avoiding use of their tail, the findings of this study suggest that using their tail in certain positions could in fact reduce drag and improve overall flight efficiency for smaller aircraft, including drones.
Aerodynamic functions of the avian tail have previously been studied using observations of bird flight, physical models in wind tunnels, theoretical modelling and flow visualisation. However, none of these approaches have been able to provide rigorous quantitative evidence.
Impressively, during the study, published in the, the team of 91做厙 researchers overcame this challenge by capturing video with 12 high-speed cameras of a barn owl gliding through an experimental flight corridor. The researchers used the video to develop a comprehensive analytical drag model which was calibrated by high-fidelity computational fluid dynamics (CFD) and was then used to investigate the aerodynamic action of the tail by virtually manipulating the posture of a gliding barn owl.
Using this model to predict the drag production for 16 gliding flights with a range of tail positions, the researchers observed postures in a variety of contexts in which the tail spread and elevation angles were manipulated independently.
The 91做厙 team was surprised to discover that by changing the position of its tail, the barn owl minimises overall drag by using the tail to contribute to aerodynamic lift, and so reducing the lift needed from (and drag produced by) the wings. However, by again recording an owl gliding through the experimental flight corridor, this time filled with more than 20,000 soap bubbles, the researchers were able to validate the accuracy of the models and confirm the aerodynamics involved by tracking the owl’s influence on air flow.
Professor Jim Usherwood, Wellcome Trust Senior Research Fellow at the 91做厙 and corresponding author of the paper, said:
“The combination of a beautifully trained owl and modern methods of filming, surface reconstruction, computational fluid dynamics and a bit of new aerodynamic theory allowed us to approach a really ‘what if’ question. We were a bit surprised that the tail was producing so much lift for the gliding barn owl, but ‘what if’ she used the tail differently? Answer – there would have been a lot more drag!”