Watch: Flying Robot Inspiration Drawn from Hummingbirds, BatsTony Pallone | September 26, 2018
Studying the flying capabilities of hummingbirds and bats — the only two vertebrates with the ability to hover in place — could bring new insight to engineering problems such as the design of flying robots and drones.
With that goal in mind, a team led by Stanford University grad student River Ingersoll trekked into the jungle terrain of Las Cruces, Costa Rica, each morning at sunrise. There, the researchers put the finishing touches on near-invisible nets designed to catch, study and release the creatures, which are abundant in the region.
Those nets allowed them to examine over 100 individuals, covering 17 hummingbird and three bat species. A combination of high-speed camera footage and aerodynamic force measurements showed that hummingbirds and bats hover in very different ways, while also revealing similarities shared between the tiny birds and nectar bats — suggesting a different evolutionary path related to diet.
Flying animals support themselves by flapping downward; hovering animals must maintain support while flapping upward as well. This is accomplished by a backward twist of the wings on the upstroke, which continuously pushes air downward to maintain airborne steadiness. The researchers found that all of their subjects exerted a similar amount of energy relative to their weight, but that the hummingbirds were more aerodynamically efficient. The team attributed this to the shape of their wings, which are easier for the creatures to invert. Nectar bats, similarly, can twist their wings more easily than their fruit bat cousins.
Ingersoll, who works in the lab of Stanford assistant professor of mechanical engineering David Lentink, collaborated with a long-standing bird banding project run by Stanford ecologists in Las Cruces for the study. Each animal was placed in a flight chamber outfitted with aerodynamic force sensors that could measure extremely small changes in vertical force at 10,000 times per second. Those measurements were synced with multiple high-speed cameras recording at 2,000 frames per second, which allowed any moment of flight to be isolated and studied.
The results of the research are published in Science Advances.