Mosquito flight modelling has potential for micro-UAVs

The complex air flow patterns generated by mosquitoes' narrow, fast-flapping wings are crucial to understanding their flight (Credit: Bomphrey/Nakata/Phillips/Walker)

Even the most ardent animal lovers find little to love about mosquitoes. They carry a variety of lethal diseases – by some measures, they have killed more humans than any other animal – their bites are irritating and painful even if they don't transfer nasty parasites; they make a horribly annoying whining buzz and just to add insult to injury, the erratic flight paths make them very difficult to swat. Exactly how they fly has until now been very difficult to determine, because of two factors: their very small size and commensurately tiny wings, which are longer and narrower than other flying insects, and the very high speed with which they flap them, around 800 times per second through an angle less than half that of any other flying insect.

Zoologists from the University of Oxford, working with colleagues from the Royal Veterinary Hospital in Chiba University in Japan, now believe that they have cracked the problem. It took a combination of computer modelling and high-speed photography under exacting conditions to analyse the three-dimensional motions of the insects’ wings. The team set up a dedicated miniature filming studio, equipped with eight infra-red cameras shooting from different angles each recording 10,000 frames per second. In addition to this, they use computational fluid dynamics to model the airflow around the wings and the insects’ bodies. They also had to avoid the problem of the mosquitoes’ trailing wings and antennae obscuring the wing movement.

The team found that mosquitoes use two previously-unknown aerodynamic tricks to fly. “The usual flapping pattern of short, fast sweeps means that mosquitoes cannot rely on conventional aerodynamic mechanisms that most insects and helicopters use,” explained study leader Dr Richard Bomphrey of the Royal Veterinary College. "Instead, we predicted that they must make use of clever tricks as the wings reverse their direction at the end of each half-stroke.”

Like other flying animals, the mosquitoes flapping wings generate rotating vortices – bubbles of low pressure – along their leading edges, which provide lift. But they also use trailing edge vortices and rotational drag, which both help to increase the amount of lift the narrow wings can generate. The trailing edge vortex is a never-before seen form of “wake capture”, where the insects align their wings with fluid flow patterns in the air they made on the previous beat, which recycles energy that would otherwise be lost to the environment.

Dr Toshiyuki Nakata from Chiba, who ran the computer simulations, explained that in most insects, because the wingtip is travelling faster than the wing root, aerodynamic forces increase along the length of the wing. “However, by exploiting aerodynamics that rely on rapid pitching of the wing, the force can be produced along the entire length. Having a long slender wing can therefore increase lift force and simultaneously reduce the cost of flight.”

The team describes its research in a paper in Nature, and hopes that it will help in designing components for very small drones, such as pietzoelectric actuators that would move wings when an electric current was applied to them. “Understanding the genetic make-up and physiology of mosquitos tells us how they are able to fly, but it is also the first step to understanding why," said Dr Simon Walker, of the Oxford Animal Flight Group in Oxford's Department of Zoology, co-author of the Nature study. “There is still much to learn from flying insects, the more we know about them, the better our chance of understanding their flight behaviour, how they carry disease and eventually how to stop them from doing so.”