For the first time, researchers have observed that birds that fly actively and flap their wings save energy.
Researchers showed that jackdaws minimize their energy consumption when they lift off and fly because the feathers on their wing tips create several small vortices – a circular pattern of rotating air left behind a wing – instead of a single large one, which requires more energy.
The researchers say the discovery could lead to more efficient drones based on the design of the jackdaw.
The researchers, based at Lund University in Sweden, published their findings in the Journal of the Royal Society Interface.
Previously, multiple wingtip vortices have only been associated with large gliders such as eagles, vultures and storks.
But now, researchers have discovered the same phenomenon in jackdaws (Corvus monedula), which flap their wings when they lift off and fly.
The researchers conducted the experiments in a wind tunnel at the Department of Biology in Lund, Sweden.
Advanced cameras captured the jackdaw’s lift off and flight through a thin mist that reflects laser light.
Using multiple images from several cameras, the researchers were able to build up three-dimensional images of the air flow around the jackdaw’s wing tips.
Commenting on the findings, Dr Marco Klein Heerenbrink, a co-author of the research and now a post-doctoral researcher at the University of Oxford , ‘By spreading the outer primary feathers, the wing tip effectively acts as several wings stacked on top of each other.
‘Each feather contributes to lift and produces its own little vortex.
‘Together these small vortices form a tip vortex that has a larger radius than for the conventional flat wing.
‘This means it took less energy for the same lift.’
‘The feathers on the wing tips can be compared to the spread fingers of a hand,’ says Dr Anders Hedenström, professor of theoretical ecology and a co-author of the research.
‘The wing tip generates several small air vortices instead of one large vortex, as on an aeroplane with rectangular or elliptical wing tips.
‘It requires more energy and costs more to lift off when only one large wing tip vortex is generated.’
According to the researchers, their finding that not only large gliders generate several small vortices around each wing tip could mean that wing tips with slotted feathers originally evolved to make flapping active flight more efficient.
‘What we found was that the small vortices occur both in gliding flight and in flapping flight,’ said Dr Klein Heerenbrink.
‘For gliding flight it is quite well established that the vertical separation of the outer primaries reduces the cost of lift production and this has been the prevailing explanation for why large soaring birds have these pronounced wing slots.
‘What we found is that this mechanism also works in flapping flight.
‘It is often overlooked that also many small birds, that never soar, also have slotted wing tips, so we think this wing shape might initially have evolved as an adaptation to reduce cost in powered flight.’
The aeronautical industry has already realized that there is money to be made in reducing the strength of a single wing tip vortex.
Some planes are already constructed with wings tips bent upwards, which reduces the strength of the vortex, thereby reducing fuel consumption.
Dr Hedenström says that his and his colleagues’ discovery could also be significant for the design of drones.
‘We could potentially build more efficient drones to fly with active wingbeats.
‘Within a ten-year period, we could see drones which have the morphology of a jackdaw’, he says.