A bizarre experiment in which fruit flies carrying tiny magnets are forced to roll in the air has demonstrated the insects’ ability as ‘fly-by-wire’ master aviators.
Scientists wanted to study how the flies manage to fly so well when their small bodies and fast-beating wings make them inherently unstable.
Tiny magnets attached to the flies made it possible to upset the insects by zapping them in mid-flight with brief magnetic pulses, forcing them to roll like out-of-control aircraft.
But the flies did not stay out of control for long. Instead they applied lightning-fast corrective responses, putting them fully back in charge in as little as 23 milliseconds.
Even after meeting their match by being spun multiple times, they were able return to normal flight within three or four wing beats after the scientists turned off their “tractor beam”.
The impressive speed at which the flies react, beating their wings at different rates and stroke angles, is almost unprecedented
The impressive speed at which the flies react, beating their wings at different rates and stroke angles, is almost unprecedented, said the US researchers.
Describing the study in the Journal of the Royal Society Interface, the authors led by Tsevi Beatus, from Cornell University in New York, wrote: “We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air.
“Fast video shows flies correct perturbations up to 100 per cent within 30 (plus or minus seven) milliseconds by applying a stroke-amplitude asymmetry...
“Flies respond to roll perturbations within five milliseconds, making this correction reflex one of the fastest in the animal kingdom.”
Previous studies of fly flight used tethered insects but found that the animals did not respond the same way as they did when flying freely.
In the new experiments, each fly had a magnet glued to its body consisting of a tiny 1.5-2mm long carbon steel pin that did not interfere with its wing motion and added around 20 per cent to its weight.
Around 15 flies were released into a transparent box attached to a pair of ‘Helmholtz coils’, electromagnets that allow precise control of magnetic fields. As the magnetic field was manipulated, the flies were filmed using cameras operating at 8,000 frames per second.
Analysis of one fly recovering from a 60-degree roll showed that it was able to regain control within 35 milliseconds, the equivalent of eight wing beats.
A ‘clear asymmetry’ in wing stroke angles was seen during the fly’s response, which began just five milliseconds after the roll started.
“During the manoeuvre, the left wing stroke amplitude increases, whereas the right wing stroke amplitude decreases,” wrote the scientists.
“After some delay, the fly also spreads its legs from their folded position as in a typical landing response. In addition, smaller deflections of 25 degrees left in yaw and five degrees down in pitch were induced.”
The flies were challenged to the extreme of their ability by using a series of magnetic pulses to spin them round and round in the air, in one case eight times.
Flies forced to perform multiple rolls were “unable to oppose the magnetic torque” and briefly lost control, with one wing seeming to be disconnected from its flight power muscles. The scientists added: “We captured three such events, all showing the same behaviour. Remarkably, once the magnetic pulses stopped, the flies regained control within three to four wing beats.”
The importance of roll control was demonstrated by the fact the roll reflex was 3.5 times faster than responses to yaw and pitch perturbations, said the researchers.
It was also five times faster than the flies’ visual ‘startle response’, their instinctive reaction to threats.
Roll corrections were executed so fast that they were completed before the flies responded to what they were seeing.
In a similar way, the latest ‘fly-by-wire’ military stealth aircraft overcome their inherent instability by making programmed corrections without the pilot’s intervention.