The researchers found that fruit flies can quickly compensate for catastrophic wing injuries, while maintaining the same stability after losing up to 40% of a wing. This result could be useful in designing versatile robots, which face a similar challenge of having to quickly adapt to accidents in the field.
The Penn State-led team posted its results today (November 18) at Science advances.
To conduct the experiment, the researchers changed the wing length of anesthetized fruit flies, to mimic an injury that flying insects can sustain. Then they suspended the flies in a virtual reality ring. Mimicking what flies see in flight, the researchers ran virtual images on small screens in the ring, causing the flies to move as if they were flying.
“We found that flies compensate for their injuries by flapping the damaged wing more vigorously and decreasing the speed of the healthy wing,” said corresponding author Jean-Michel Mongo, assistant professor of mechanical engineering at Penn State. “They accomplish this by modulating the signals in their nervous system, which allows them to adjust their flight even after an injury.”
By flapping their damaged wing more vigorously, the fruit flies exchange some performance—which decreases only slightly—to maintain stability by effectively increasing damping.
“If you’re driving on a tarmac, friction remains between the tires and the surface, and the car is stable,” Mungo said, referring to damping as friction. “But on an icy road, there is less friction between the road and the tires, which causes instability. In this case, the fruit fly, as the driver, increases damping with its nervous system in an effort to increase stability.”
Co-authors Bo Cheng, Penn State Kenneth K. and Olivia J. Kuo, assistant professor of mechanical engineering, point out that stability is more important than strength for flight performance.
“Under wing damage, both performance and stability are affected; however, flies use an ‘internal knob’ that increases damping to maintain the desired stability, even if this further decreases performance,” Cheng said. “In fact, it has been shown that it is stability, rather than strength required, that limits the flies’ maneuverability.”
The researchers’ work suggests that fruit flies, which have only 200,000 neurons compared to 100 billion in humans, use a sophisticated and flexible system to control movement, allowing them to adapt and survive injury.
“The complexity we’ve discovered here in flies is unparalleled by any existing engineering systems; the fly’s complexity is more complex than current flying robots,” Mongo said. “We’re still a long way from the engineering side of trying to replicate what we see in nature, and this is just another example of how far we have to go.”
With increasingly complex environments, engineers are challenged to design robots that can quickly adapt to malfunctions or mishaps.
“Flying insects can inspire the design of robots and drones that can intelligently respond to physical damage and maintain operations,” said co-author Wael Salem, a doctoral candidate in mechanical engineering at Penn State. “For example, designing a drone that can make up for a broken engine in flight, or a two-legged robot that can rely on its other legs when one gets out.”
To study the mechanism by which flies compensate for wing damage in flight, collaborators at the University of Colorado Boulder created a robotic prototype of a mechanical wing, close in size and function to a fruit fly. The researchers clipped the mechanical wing, repeated the Penn State experiments, and tested the interactions between the wings and the air.
“Using only the mathematical model, we need to make simplifying assumptions about wing structure, wing motion and wing-air interactions to make our calculations tractable,” said co-author Kaushik Jayaram, assistant professor of mechanical engineering. at the University of Colorado Boulder. “But with the physical model, our robot model interacts with the natural world much like a fly, according to the laws of physics. Thus, this setup captures the intricacies of complex wing-air interactions that we don’t yet fully understand.”
In addition to Mungo, Cheng, Salem, and Jayram, co-authors include Benjamin Cellini, Penn State Department of Mechanical Engineering; and Haiku Kabutz and Hare Krishna Hari Prasad, University of Colorado Boulder.
This work was supported by the Air Force Office of Scientific Research and an Alfred B. Sloan Research.