really cool aerodynamics findings

Written by J Wolfgang Goerlich
Cornell Research into Dragonfly Micro-Air Vehicle (MAV)
Wednesday, 22 February 2006


From houseflies to honeybees, insects inspire us with flight skills
just beyond the grasp of our technology. Z. Jane Wang, a professor at
Cornell University, is working to close this gap between inspiration
and implementation. Wang’s recent work is on dragonflies, and here
she has found some peculiarities.
For example, "an airfoil uses aerodynamic lift to carry its weight.
But the dragonfly uses a lot of aerodynamic drag to carry its weight.
That is weird, because with airplanes you always think about
minimizing drag. You never think about using drag."
Implementing a dragonfly MAV is still an elusive goal, hopefully made
somewhat nearer by Wang’s research. The research and prior art is
summarized in her recent paper, Dissecting Insect Flight. This and
more can be found on her group's website, which appropriately enough
is dragonfly.tam.cornell.edu.
http://tinyurl.com/jauhk

On the wings of dragonflies: Flapping insect uses drag to carry its
weight, offering insight into intricacies of flight
By Lauren Gold
ST. LOUIS -- If mastering flight is your goal, you can't do better
than to emulate a dragonfly. With four wings instead of the standard
two and an unusual pitching stroke that allows the bug to hover and
even shift into reverse, the slender, elegant insect is a marvel of
engineering. Z. Jane Wang, professor of theoretical and applied
mechanics at Cornell University, presented her research on flying
systems and fluid dynamics today (Feb. 19) at the annual meeting of
the American Association for the Advancement of Science. In a seminar
"Falling Paper, Dragonfly Flight and Making a Virtual Insect," she
said the best way to learn about flight is by first looking at what
happens naturally. Look at how such thin structures as falling paper
move through a fluid environment like air, she said, and then examine
how insects use their wings to manipulate that environment and stay
aloft. "The major question I focus on is the question of efficiency,"
Wang said in an interview. "It's the long-standing question: Of birds
and planes, which is better? And if we think planes are better --
why?" Conventional wisdom holds that airplanes (airfoils) are more
efficient because they travel from point to point with no wasted up-
and-down motion. "But there are infinitely many ways you can go up
and down," said Wang. "Of all these paths, are any better than a
straight line? Some are -- that's what I found." The insight came
from dragonflies. "Dragonflies have a very odd stroke. It's an up-and-
down stroke instead of a back-and-forth stroke," she said.
"Dragonflies are one of the most maneuverable insects, so if they're
doing that they're probably doing it for a reason. But what's strange
about this is the fact that they're actually pushing down first in
the lift. "An airfoil uses aerodynamic lift to carry its weight. But
the dragonfly uses a lot of aerodynamic drag to carry its weight.
That is weird, because with airplanes you always think about
minimizing drag. You never think about using drag." The next
question, she said, is whether engineers can use these ideas to build
a flapping machine as efficient as a fixed-wing aircraft. Questions
of size and feasibility remain. "To hover well or to fly for a long
time is hard, especially at slow speeds," she said. "Power is
limited. So finding these efficient motions is very important."
Still, Wang's work moves researchers a step closer to building such a
machine. "I want to build insects on a computer as a way of learning
why almost all things that move in fluid use a flapping motion," said
Wang. "Whether it's a fish which flips its fins or a bird, they're
actually using the same principle. "The way paper or leaves fall, and
how insects fly, may give us some ideas about why animals use these
methods at all," she said.

http://tinyurl.com/hxaw5