“While we know birds frequently alter their wing shape, this is the first empirical evidence demonstrating how that wing morphing affects avian stability,” said Douglas Altshuler, senior author of the study published in the Journal of the Royal Society Interface.
“And in this case, the gull’s wing design points to a novel, and fairly simple, avian-inspired joint that may enable aircraft to adjust dynamically to challenging conditions,” said Altshuler.
As wing speeds and maximum gusts increase, gulls sacrifice stability for manoeuvrability. By altering the angle of their elbow joint they shift from extended wing configurations to a flexed configuration, pulling the tips of their wings in and back. The flexed shape gives them more control.
To determine the stability of different wing shapes, researchers prepared gull wings over the anatomical elbow range and measured their performance in a wind tunnel. They also observed gulls in the wild.
“The Wright brothers weren’t the first to design an aircraft that was able to fly, but they were the first to successfully control and stabilise a powered aircraft inflight,” said researcher Christina Harvey from UBC.
“Likewise, it’s not enough for birds to simply produce sufficient lift and thrust. They must also control and stabilise their flight paths to be able to successfully forage and migrate in their natural habitat,” said Harvey, now with the University of Michigan in the US.
To get a fuller picture of how birds maintain their stability while gliding the researchers want to study a wider range of wind perturbations — gulls often encounter unsteady, large-scale turbulence while flying in the wake of buildings or convective air flows over open water.
Atmospheric turbulence in these conditions is likely larger than the wind tunnel turbulence the researchers used in the study.