Hummingbirds occupy a unique place in nature: they fly like insects, but have the musculoskeletal system of birds. According to Bo Cheng, Kenneth K. and Olivia J. Kuo Early Career Associate Professors of Mechanical Engineering at Penn State, hummingbirds have extreme aerial mobility and flight forms, which is why many drones and other aerial vehicles are designed to mimic hummingbird movement. Using a novel modeling method, Cheng and his research team gained new insights into how hummingbirds generate wing motion, which could lead to design improvements in flying robots.
Their findings were published this week in the Proceedings of Royal Society B.
“We essentially reconstructed the inner workings of the wing-musculoskeletal system — how the muscles and skeleton work in hummingbirds to flap their wings,” said Suyash Agrawal, first author and graduate student in mechanical engineering at Penn State University . “Traditional methods have mainly focused on measuring a bird or insect’s activity when they are in natural flight or in an artificial environment that simulates flight-like conditions. But most insects, and especially among birds, hummingbirds, are very small. The data we can get from these measurements is limited.”
Researchers used literature on muscle anatomy, computational fluid dynamics simulation data, and wing skeleton motion information captured with micro-CT and X-ray methods to inform their model. They also used an evolutionary strategy-based optimization algorithm known as a genetic algorithm to calibrate the model’s parameters. According to the researchers, their approach is the first to integrate these disparate parts for biological aviators.
“We can simulate the entire reconstructed motion of the hummingbird wing, and then simulate all of the flows and forces generated by the flapping wing, including all of the pressure acting on the wing,” Cheng said. “From this we can back calculate the total muscle torque required to flap the wing. And we use this torque to calibrate our model.”
With this model, the researchers uncovered previously unknown principles of hummingbird wing movement.
The first discovery, Cheng says, was that hummingbirds’ primary muscles, their flight engines, don’t just flap their wings in a simple back-and-forth motion, but pull their wings in three directions: up and down, back and forth and Twisting – or pitching – the wing. The researchers also found that hummingbirds flex their shoulder joints in both the up-and-down and tilt directions using several smaller muscles.
“It’s like we’re working out at a gym and a trainer tells you to tone your core to be more flexible,” Cheng said. “We found that hummingbirds use a similar mechanism. They tighten their wings in the pitch and up-down directions, but keep the wing slack in the fore and aft directions, so their wings only appear to flap back and forth while their power muscles or flight engines actually flap the wings in all three directions draw. In this way, the wings have very good agility in the up and down movement as well as in the turning movement.”
While Cheng emphasized that the results of the optimized model are predictions that need to be validated, he said it has implications for aircraft technological development.
“Although the technology is not yet there to fully mimic hummingbird flight, our work provides essential principles for informed hummingbird mimicry, hopefully for the next generation of agile flight systems,” he said.
The other authors were Zafar Anwar, a graduate student in the Penn State Department of Mechanical Engineering; Bret W. Tobalske of the Department of Biological Sciences at the University of Montana; Haoxiang Luo from the Department of Mechanical Engineering at Vanderbilt University; and Tyson L. Hedrick of the University of North Carolina Department of Biology.
The Office of Naval Research funded this work.
Materials provided by Pennsylvania. Originally written by Sarah Small. Note: Content can be edited for style and length.