FLIGHT OPTIMIZATION FOR FLAPPING WINGS
Researchers at Montana State University created a system-level model of a Hawkmoth flight system to optimize flight for future micro-air vehicles.
Written by Kayt Sukel
IT’S A BIRD! IT’S A PLANE! It’s a... flapping wing micro-air vehicle (FWMAV)!
They say that big things come in small packages. But as roboticists have worked to miniaturize robots for specific applications in constricted spaces, they are learning it’s not as simple as shrinking the components of larger flight systems. Mark Jankauski, professor of mechanical and industrial engineering at Montana State University, however, said that engineers can learn a thing or two from Mother Nature—by understanding, in detail, the flying systems of insects.
“To realize these kinds of air vehicles at a smaller length scale, we need to look at the wings. We need to look at the actuation systems. The motors don’t scale well,” he explained. “We can’t just take something big and shrink it down. Which is why we are looking for inspiration from a small thing that already flies well—an insect—and trying to understand how they do that a bit better so we can start realizing aircraft at small length scales.”
To gather that understanding, Jankauski and colleagues created a system-level model of the insect flight system of a hawkmoth, a common night pollinator that weighs approximately two grams. The model includes the insect’s thorax, wings, and wing hinge to replicate how the moth can hover in flight. Deriving such a model, however, required the team to leverage generic algorithm optimization to help fill in some of the blanks regarding the system’s overall parameters.
“When you are working with a biological system, it can be challenging to measure things like the perceived stiffness of the thoracic exoskeleton or wing hinge. Oftentimes, you have to estimate them,” he said. “But while we’re not able to get some of those exact measurements, we can create a sort of template of the system with some uncertainty, and then go through it, parameter by parameter, to understand how this process happens in nature, and use the algorithm to help reconcile some of those uncertainties.”
Taking this approach, the researchers were able to create a “skeleton model” to help them minimize the amount of energy required for the moth to hover in the air. They discovered that favorable flapping kinematics can be achieved by measuring the flapping frequency of the moth between the non-linear resonant frequencies. They could then take those measurements to predict an optimal flapping frequency that could be translated to a FWMAV.
“When we can look at the structural dynamics and aerodynamics, and then link that upstream to the muscles themselves, we can learn some interesting things both mechanically and ecologically.”
—Mark Jankauski, professor of mechanical and industrial engineering at Montana State University
A simplified mechanical schematic of a flapping wing insect shows a flexible thorax exoskeleton connected to a wing via a lever mechanism. Diagram: Mark Jankauski
“When we can look at the structural dynamics and aerodynamics, and then link that upstream to the muscles themselves, we can learn some interesting things both mechanically and ecologically,” he said. “It allows us to answer some questions about the ecological niches that a moth might fulfill relative to something like a bumblebee—and how those particular mechanics enable them to fulfill a specific niche.”
Jankauski said there is still a lot to learn about flying behaviors from different insects that could one day inform the future design of flying systems for FWMAVs so they can be successfully deployed in search and rescue operations or artificial pollination applications. He said when engineers can create models that reflect the biology to improve performance, they can act as a vital driver to help improve flight design.
Yet, that said, Jankauski also believes it’s important that, as engineers consider design optimization for these tiny aircraft, they also think about whether the components they come up with are manufacturable.
“We can say we want a joint to be of this stiffness, for example, but if the manufacturing techniques aren’t there to make it, it’s not something we can readily adopt,” he said. “We need a lot more people to work on these kinds of problems in concert so manufacturing techniques can continue to improve along with our understanding of the biological system and the translation of that biology into these engineered flight systems.”
Kayt Sukel is a technology writer and author in Kansas City.
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