Lily the barn owl reveals how birds fly in gusty winds
Newly discovered avian suspension system has implications for bio-
inspired aircraft

Date:
October 21, 2020
Source:
University of Bristol
Summary:
Scientists have discovered how birds are able to fly in gusty
conditions - findings that could inform the development of
bio-inspired small-scale aircraft.



FULL STORY ========================================================================== Scientists from the University of Bristol and the Royal Veterinary College
have discovered how birds are able to fly in gusty conditions -- findings
that could inform the development of bio-inspired small-scale aircraft.


========================================================================== "Birds routinely fly in high winds close to buildings and terrain -- often
in gusts as fast as their flight speed. So the ability to cope with strong
and sudden changes in wind is essential for their survival and to be able
to do things like land safely and capture prey," said Dr Shane Windsor
from the Department of Aerospace Engineering at the University of Bristol.

"We know birds cope amazingly well in conditions which challenge
engineered air vehicles of a similar size but, until now, we didn't
understand the mechanics behind it," said Dr Windsor.

The study, published in Proceedings of the Royal Society B, reveals
how bird wings act as a suspension system to cope with changing wind conditions. The team used an innovative combination of high-speed,
video-based 3D surface reconstruction, computed tomography (CT) scans,
and computational fluid dynamics (CFD) to understand how birds 'reject'
gusts through wing morphing, i.e. by changing the shape and posture of
their wings.

In the experiment, conducted in the Structure and Motion Laboratory at
the Royal Veterinary College, the team filmed Lily, a barn owl, gliding
through a range of fan-generated vertical gusts, the strongest of which
was as fast as her flight speed. Lily is a trained falconry bird who is
a veteran of many nature documentaries, so wasn't fazed in the least by
all the lights and cameras.

"We began with very gentle gusts in case Lily had any difficulties,
but soon found that -- even at the highest gust speeds we could make --
Lily was unperturbed; she flew straight through to get the food reward
being held by her trainer, Lloyd Buck," commented Professor Richard
Bomphrey of the Royal Veterinary College.

"Lily flew through the bumpy gusts and consistently kept her head and
torso amazingly stable over the trajectory, as if she was flying with a suspension system. When we analysed it, what surprised us was that the suspension-system effect wasn't just due to aerodynamics, but benefited
from the mass in her wings. For reference, each of our upper limbs is
about 5% of our body weight; for a bird it's about double, and they
use that mass to effectively absorb the gust," said lead-author Dr Jorn
Cheney from the Royal Veterinary College.

"Perhaps most exciting is the discovery that the very fastest part of
the suspension effect is built into the mechanics of the wings, so birds
don't actively need to do anything for it to work. The mechanics are
very elegant.

When you strike a ball at the sweetspot of a bat or racquet, your hand
is not jarred because the force there cancels out. Anyone who plays
a bat-and-ball sport knows how effortless this feels. A wing has a
sweetspot, just like a bat.

Our analysis suggests that the force of the gust acts near this sweetspot
and this markedly reduces the disturbance to the body during the first
fraction of a second. The process is automatic and buys just enough time
for other clever stabilising processes to kick in," added Dr Jonathan
Stevenson from the University of Bristol.

Dr Windsor said the next step for the research, which was funded by the European Research Council (ERC), Air Force Office of Scientific Research
and the Wellcome Trust, is to develop bio-inspired suspension systems
for small- scale aircraft.


========================================================================== Story Source: Materials provided by University_of_Bristol. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Jorn A. Cheney, Jonathan P. J. Stevenson, Nicholas E. Durston,
Jialei
Song, James R. Usherwood, Richard J. Bomphrey, Shane
P. Windsor. Bird wings act as a suspension system that rejects
gusts. Proceedings of the Royal Society B: Biological Sciences,
2020; 287 (1937): 20201748 DOI: 10.1098/rspb.2020.1748 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201021085117.htm

--- up 8 weeks, 2 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)