When you wish to learn, study the best. For flight, this means dragonflies. The advance of ultra-high-speed cameras has allowed scientists to observe the way these astonishing creatures have mastered the air like no others. The lessons could be applied to drones and possibly even airplanes for those brave or foolish enough to pilot them.
Fossils indicate the ancestors of dragonflies were already in the air 325 million years ago, becoming the largest insects that ever lived in more oxygen-rich times. Their longevity, and diversification to some 3,000 species, are testaments to the extraordinary agility in the air provided by their four wings, which allow them to snatch prey out of the air while flying upside down.
In A Short History Of Nearly Everything, Bill Bryson notes dragonflies can stop instantly, hover, fly backwards, and lift ridiculous loads before quoting an unnamed commentator; “The US Airforce has put them in wind tunnels to see how they do it, and despaired.” However, that doesn’t mean people have stopped trying.
Dr Huai-Ti Lin of Imperial College London put tiny magnets and motion tracking dots on 20 common darter dragonflies, recording and reconstructing their movements. The magnets allowed Lin and colleagues to attach the insects to magnetized platforms, releasing live, dead and anesthetized dragonflies in a range of positions to observe how they flew (or fell, in the cases of the dead ones).
Other animals – be they flying creatures or those with a talent for falling such as cats – right themselves mid-air by rolling. They rotate themselves around a head-to-tail axis, an approach that minimizes moment-of-inertia and has been adopted by fighter jet designers. However, Lin found dragonflies are more flexible, being also able to do backflips like a gymnast, where the axis of spin is at right angles to the body. They call this Simone Biles-worthy move the dragondrop. When off-balance the dragonflies used the shortest rotation available to right themselves. Even when groggy from anesthetic, they were able to dragondrop.
In Proceedings of the Royal Society B Lin and co-authors reveal we’ve already adopted some of the techniques dragonflies could have taught us. “Planes are often designed so that if their engines fail, they will glide along stably rather than drop out of the sky,” said first author Dr Sam Fabian in a statement. “We saw a similar response in dragonflies, despite the lack of active flapping, meaning that some insects, despite their small size, can leverage passive stability without active control.” For this to work, however, the researchers had to arrange the dead or unconscious dragonflies’ wings into the right position before letting them drop.
A technique that works after death is of no evolutionary advantage, and being drugged is rare in the wild. The researchers think dragonflies evolved passive stability to save energy, being able to right themselves without much strain.
Although the concept of passive stability is familiar to aircraft engineers, Dr Lin thinks dragonflies can still offer lessons on how to do it better. “Drones tend to rely heavily on fast feedback to keep them upright and on course, but our findings could help engineers incorporate passive stability mechanisms into their wing structure.” he said.