Dandelions hold seed of a revolution in flight
Drones could be designed to mimic the seeds’ use of a bubble of air that allows them to travel 500 miles
FLUFFY dandelion seeds are known to travel 500 miles on the wind, but until now it has been a mystery how they achieve it.
Although light enough to be whisked into the air in updrafts, their downy heads are 90 per cent empty space – a poor design for a parachute – and scientists have puzzled as to how they manage to stay afloat for so long. Now researchers at the University of Edinburgh have discovered that the soft bristles work together to create a ringshaped bubble of air that keeps the seed aloft.
This type of flight has never before been documented in nature and the experts believe it could be used to help windborne micro-drones stay in the air without using power so they can explore remote and inhospitable regions, or even other planets.
Dr Cathal Cummins, of the university’s schools of biological sciences and engineering, who led the study, said: “Taking a closer look at the ingenious structures in nature – like the dandelion’s parachute – can reveal novel insights. We found a natural solution for flight that minimises the material and energy costs, which can be applied to engineering of sustainable technology.
“The dandelion has managed to create a parachute which is virtually entirely empty space. Our research is suggesting that, basically, less is more.”
The unique aerodynamic capabilities of dandelions make them one of the most successful of all wind pollinators, and a single plant can produce 12,000 seeds.
A 2003 study at the University of Regensburg in Germany found that 99.5 per cent of dandelion seeds land within 33ft of their parent, but the University of Cornell calculated that some can travel for 500 miles. To find out how dandelion seeds achieved the feat, researchers at Edinburgh built a tiny vertical wind tunnel which blew air softly upwards, allowing seeds to hover at a fixed height so they could study how air moved around the fluffy seed head, known as a pappus.
They then recorded how air currents moved around the pappus, using longexposure photography and high-speed imaging. The images revealed that a ring-shaped air bubble forms as air moves through the bristles, enhancing the drag that slows each seed’s descent to the ground.
The newly found air bubble – which scientists have named the separated vortex ring – follows the seed like a little halo. This mass of whirling air helps increase the drag on the seed, and is created when neighbouring filaments on the seed interact with each other as it floats along.
The amount of air flowing through, which is critical for keeping the bubble stable and directly above the seed in flight, is precisely controlled by the spacing of the bristles. According to the researchers, it is four times more efficient than what is possible with conventional parachute design.
Researchers suggest that the dandelion’s porous parachute might inspire the development of small-scale drones that require little or no power consumption. Such drones could be useful for remote sensing or air pollution monitoring. The study was published in Nature.