From the moment they took flight they have enchanted us with their effortless grace and beauty.
But now engineers are turning a high speed camera on butterflies in an attempt to unlock the secrets of their flutter in a new study.
Experts hope by figuring out precisely how butterflies fly among flowers with amazing grace and agility they will be able to apply that knowledge to creating miniature airborne robots.
The research is of particular interest to the military industry which is funding the analysis at Johns Hopkins University in Baltimore, Maryland.
It is believed the techniques and mechanisms used by the creatures could be transferred to machines – commonly called micro aerial vehicles or MAVs – currently being developed for U.S. defence contractors to carry out search-and-rescue and reconnaissance missions.
Whiting School of Engineering undergraduate Tiras Lin, who has been conducting the high-speed video research, said: ‘For military missions in particular, these MAVs must be able to fly successfully through complex urban environments, where there can be tight spaces and turbulent gusts of wind.
‘These flying robots will need to be able to turn quickly. But one area in which MAVs are lacking is manoeuvrability.’
To address that shortcoming, Lin has been studying butterflies.
He said: ‘Flying insects are capable of performing a dazzling variety of flight manoeuvres.
‘In designing MAVs, we can learn a lot from flying insects.’
Lin’s research has been supervised by Rajat Mittal, a professor of mechanical engineering.
‘This research is important because it attempts to not only address issues related to bio-inspired design of MAVs, but it also explores fundamental questions in biology related to the limits and capabilities of flying insects,’ Professor Mittal said.
To conduct the study, Lin has been using high-speed video to look at how changes in mass distribution associated with the wing flapping and body deformation of a flying insect help it engage in rapid aerial twists and turns.
Lin, a junior mechanical engineering major from San Rafael, California, recently presented some of his findings at the annual meeting of the American Physical Society’s Division of Fluid Dynamics.
The student also won second-prize for his presentation of this research at a regional meeting of the American Institute of Aeronautics and Astronautics.
‘Ice skaters who want to spin faster bring their arms in close to their bodies and extend their arms out when they want to slow down,’ Lin said.
‘These positions change the spatial distribution of a skater’s mass and modify their moment of inertia; this in turn affects the rotation of the skater’s body. An insect may be able to do the same thing with its body and wings.’
Butterflies move too quickly for someone to see these wing tactics clearly with the naked eye, so Lin used high-speed, high-resolution videogrammetry to mathematically document the trajectory and body conformation of painted lady butterflies.
They accomplished this with three video cameras capable of recording 3,000 one-megapixel images per second. By comparison, a standard video camera shoots 24, 30 or 60 frames per second.
The Johns Hopkins researchers anchored their cameras in fixed positions and focused them on a small region within a dry transparent aquarium tank. For each analysis, several butterflies were released inside the tank.
When a butterfly veered into the focal area, Lin switched on the cameras for about two seconds, collecting approximately 6,000 three-dimensional views of the insect’s flight maneuvers.
From these frames, the student typically homed in on roughly one-fifth of a second of flight, captured in 600 frames. ‘Butterflies flap their wings about 25 times per second,’ Lin said. ‘That’s why we had to take so many pictures.’
The arrangement of the three cameras allowed the researchers to capture three-dimensional data and analyze the movement of the insects’ wings and bodies in minute detail.
That led to a key discovery. Earlier published research pointed out that an insect’s delicate wings possess very little mass compared to the bug’s body.
As a result, those scholars concluded that changes in spatial distribution of mass associated with wing-flapping did not need to be considered in analyzing an insect’s flight maneuverability and stability. ‘We found out that this commonly accepted assumption was not valid, at least for insects such as butterflies,’ Lin said.
‘We learned that changes in moment of inertia, which is a property associated with mass distribution, plays an important role in insect flight, just as arm and leg motion does for ice skaters and divers.’