THE wandering albatross, long a sign of good luck and source of superstition for sailors, could become a latter-day boon to them as the inspiration for a low-energy scouting aircraft.
The albatross’s ability to fly for thousands of kilometres over oceans with barely a flap of its wings has inspired the concept of a diminutive, ship-launched spotter plane that flies great distances by employing some of the bird’s lift-generating techniques.
The idea is that a drone could help trawler crews spot shoals of fish, or help border patrols spot drug-runners, but with next-to-zero energy cost, says , who leads the project at the Bristol Robotics Laboratory (BRL) in the UK. The idea is the brainchild of Pipe’s colleague, , who flies gliders in his spare time.
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The wandering albatross uses many tricks to gain lift and stay airborne for long periods. “They exploit the updrafts over waves and the shear-layers downwind of wave-crests,” says , a zoologist specialising in animal flight at the University of Oxford.
But another ruse the bird uses is to harness “dynamic soaring”. Unlike thermal soaring over land – flying on rising columns of warm air – dynamic soaring exploits the big differences in wind speed that exist up to about 30 metres above the sea. It is this dynamic soaring capability that the Bristol team want to harness in a 3-metre-wingspan uncrewed aerial vehicle (UAV).
“Dynamic soaring exploits the big differences in wind speed that exist up to about 30 metres above the sea”
The layer of air at the ocean’s surface is slowed by friction against the water, while the layers above move progressively faster. For instance, the air at an altitude of 2 metres may be moving at 7 metres per second, but layers above it move ever faster until, at an altitude of about 30 metres, it will be zipping along at 11 metres per second.
It’s this velocity gradient that lends a speed boost. “When the aircraft leaves the still-air layer and enters the layer with higher wind, it is accelerated, so trajectories can be designed in such a way that the aircraft gains net energy,” says Deittert. “However, its maximum height is limited as the required wind gradients are only found close to the surface of the ocean.”
Now that extensive computer simulations have shown that this type of UAV-flight is possible (Journal of Guidance, Control and Dynamics, ), the BRL team is seeking funding to try it out for real.
It’s a big ask, though, says Thomas. “It’s likely to be a great deal more complicated than computer models suggest. They’ll need lots of UAVs because they will break a fair few of them. But the end result – that of long-range flight without power – is well worth chasing.”
