Fruit flies can quickly compensate for catastrophic wing injuries, researchers found, and maintain the same stability after losing up to 40% of a wing. This finding could inform the design of versatile robots that face the similar challenge of having to quickly adapt to mishaps in the field.
The Penn State-led team released its findings today (Nov. 18) in scientific advances.
To conduct the experiment, the researchers altered the wing length of stunned fruit flies to mimic an injury that flying insects can sustain. They then hung the flies in a virtual reality ring. Mimicking what flies would see in flight, the researchers played virtual images on tiny screens around 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 harder and decreasing the speed of the healthy wing,” said corresponding author Jean-Michel Mongeau, an assistant professor of mechanical engineering at Pennsylvania State University. “They do this by modulating signals in their nervous system, which allows them to fine-tune their flight even after injury.”
By flapping their damaged wing harder, fruit flies trade some power – which lowers only slightly – to maintain stability by actively increasing damping.
“When you’re driving on a paved road, the friction between the tires and the surface is maintained and the car is stable,” Mongeau said, comparing damping to friction. “But on an icy road, there is reduced friction between the road and the tires, leading to instability. In this case, a fruit fly as a driver actively increases damping with its nervous system to increase stability.”
Co-author Bo Cheng, Penn State Kenneth K., and Olivia J. Kuo Early Career Associate Professor of Mechanical Engineering noted that stability is more important to flight performance than power.
“With wing damage, both performance and stability would normally suffer; However, flies use an ‘internal knob’ that increases damping to maintain the desired stability, even if it results in further performance degradation,” Cheng said. “In fact, it has been shown that it is actually stability and not the required power that limits the maneuverability of flies.”
The researchers’ work suggests that fruit flies, with just 200,000 neurons compared to humans’ 100 billion, use a sophisticated, flexible motor control system that allows them to adapt and survive after injury.
“The complexity that we have discovered here in flies is unmatched by any existing technical system; the sophistication of the fly is more complex than existing flying robots,” said Mongeau. “On the technical side, we’re still a long way from replicating what we see in nature, and this is just another example of how far we have to go.”
With environments becoming increasingly complex, engineers are challenged to design robots that can quickly adapt to mistakes or glitches.
“Flying insects can inspire the design of impact robots and drones that can intelligently respond to physical damage and maintain operations,” said co-author Wael Salem, a graduate student in mechanical engineering at Penn State University. “Like designing a drone that can compensate for a broken motor in flight, or a legged robot that can rely on its other legs if one gives up.”
To study the mechanism by which flies compensate for wing damage in flight, collaborators at the University of Colorado Boulder have developed a robotic prototype of a mechanical wing that is close in size and function to that of a fruit fly. The researchers cut the mechanical wing, replicated Penn State’s experiments, and tested the interactions between the wings and the air.
“With only a mathematical model, we need to make simplifying assumptions about the structure of the wing, the motion of the wing, and the wing-air interactions to make our calculations manageable,” said co-author Kaushik Jayaram, an assistant professor of mechanical engineering at the university of Colorado Boulder. “But with a physical model, our prototype robot interacts with the natural world much like a fly, which is subject to the laws of physics. Therefore, this setup captures the intricacies of the complex wing-air interactions that we do not yet fully understand. “
In addition to Mongeau, Cheng, Salem, and Jayaram, co-authors include Benjamin Cellini, Penn State Department of Mechanical Engineering; and Heiko Kabutz and Hari Krishna Hari Prasad, University of Colorado Boulder.
The Air Force Office of Scientific Research and the Alfred P. Sloan Research Fellowship supported this work.
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