Johns Hopkins undergraduate Tiras Lin used high-speed video cameras to analyze the flight dynamics of painted lady butterflies. Photo: Will Kirk/Johns Hopkins University |
To improve the next generation of insect-size flying
machines, Johns Hopkins engineers have been aiming high-speed video cameras at
some of the prettiest bugs on the planet. By figuring out how butterflies
flutter among flowers with amazing grace and agility, the researchers hope to
help small airborne robots mimic these maneuvers.
U.S.
defense agencies, which have funded this research, are supporting the
development of bug-size flyers to carry out reconnaissance, search-and-rescue,
and environmental monitoring missions without risking human lives. These
devices are commonly called micro aerial vehicles or MAVs.
“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,” said Tiras Lin, a Whiting School of
Engineering undergraduate who has been conducting the high-speed video
research. “These flying robots will need to be able to turn quickly. But one
area in which MAVs are lacking is maneuverability.”
To address that shortcoming, Lin has been studying
butterflies. “Flying insects are capable of performing a dazzling variety of
flight maneuvers,” he said. “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,” Mittal said.
To conduct this 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, Calif.,
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, working with graduate student
Lingxiao Zheng, 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 3D 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 3D 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.”
He said this discovery should be considered by MAV designers
and may be useful to biologists who study insect flight dynamics.
Lin’s newest project involves even smaller bugs. With
support from a Johns Hopkins Provost’s Undergraduate Research Award, he has
begun aiming his video cameras at fruit flies, hoping to solve the mystery of
how these insects manage to land upside down on perches.