A new study suggests that the aerodynamics of swifts’ wings enable them to adapt effortlessly to sudden changes in wind speed and direction.
The wings’ crescent shape lessens the effects of blustery conditions, helping to stabilise them as they glide during turbulent weather, researchers say.
This means swifts – which eat, mate and even sleep on the wing – are not forced to use up vital energy to stay on course.
Scientists at the University of Edinburgh constructed a triangular model wing with the characteristic trailing edge shape of swifts’ wings. They studied its aerodynamic properties by fitting it into a water flume that simulated airflow during flight.
Using a laser sheet and a digital camera, researchers tracked the movement of tiny glass balls in the water to reveal how air flows over the wing.
Results showed for the first time that as air passes over the wing, it can form into two or three circulating regions of airflow – known as leading-edge vortices, or LEVs.
In aircraft with triangle-shaped wings – including Concorde – LEVs can generate extra lift, researchers say. In swifts, however, the formation of LEVs appears to serve a different function. Researchers suggest that it may act as a dampening mechanism that helps stabilise the birds’ wings as they glide in blustery weather.
Researchers say the findings could help inform the design of new aerial technology similar to drones – known as micro air vehicles.
The study is published in Royal Society Open Science. It was supported by the Engineering and Physical Sciences Research Council and the Consejo Nacional de Ciencia y Tecnologia.
Dr Ignazio Maria Viola, of the University of Edinburgh’s School of Engineering, who led the study, said:
"One of the most fascinating secrets in nature is how birds and insects can fly so effortlessly in turbulence. These results provide a small breakthrough towards unravelling this precious secret."
The leading-edge vortex is a high lift mechanism used by aircraft with a delta shaped wing, such as the Concord, and by some natural fliers. A highly comparable leading-edge vortex is recorded on a model delta wing, and a model swift-wing shaped delta wing with the same leading-edge geometry. The notable difference between the two is the location of vortex break down along the wing span that may lead to a lower lift for the swift-wing shaped delta wing.
The researchers found that the leading-edge vortex also occurs at low angles of attack, such as those at which a swift glides, but where the leading-edge vortex does not provide any significant lift enhancement. These results suggest that a swift in gliding flight is able to support a leading-edge vortex, however if they did, it would not be to enhance the lift; instead the researchers suggested that it is used to manage wing loading and aerodynamic force fluctuations by acting as a dampening mechanism.
- Muir RE, Arredondo-Galeana A., Viola IM. 2017. The leading-edge vortex of swift wing-shaped delta wings. R. Soc. open sci. 4: 170077.
- Royal Society Open Science
- Engineering and Physical Sciences Research Council (EPSRC)
- Consejo Nacional de Ciencia y Tecnologia
- BBC Scotland News - Swifts' wings 'help them fly through storms'
- Dropbox audio download: BBC Radio Scotland, Dr Ignazio Maria Viola interview
- University of Edinburgh news article
- Dr Ignazio Maria Viola, School of Engineering profile
- Ignazio Maria Viola’s Fluid Dynamics Research Laboratory