August 2, 2014
Hummingbird Wings Generate Lift More Efficiently Than The Best Micro-Helicopter Blades
redOrbit Staff & Wire Reports - Your Universe Online
Hummingbird wings are more efficient than even the highest-quality helicopter blades when it comes to generating lift, according to new research appearing in the current issue of the Journal of the Royal Society: Interface.However, experiments conducted by Stanford University professor David Lentink indicate that the gap between nature and human engineering is closing. While the best hummingbird was found to be over 20 percent more efficient than the world’s most advanced micro-helicopters, BBC News science reporter Victoria Gill indicates that average hummingbirds and helicopters are just about equal.
The experiment involved pinning the wings of 12 different hummingbird species, all of which were obtained from an existing museum collection, to a special device designed to test the aerodynamics of helicopter blades. Lentink and his colleagues used cameras to visualize airflow around the wings, and measures the drag and lift force they exerted at various angles and speeds using sensitive load cells.
Afterwards, the study authors repeated the experiment using the blades from a ProxDynamics Black Hornet, which is said to be the most sophisticated type of autonomous micro-helicopter on the market today. The Black Hornet is roughly the same size as a hummingbird, and is being used by the UK military during its ongoing campaign in Afghanistan. Regardless, the study revealed the cutting-edge technology came up short against the miracle of nature.
“Even spinning like a helicopter, rather than flapping, the hummingbird wings excelled: If hummingbirds were able to spin their wings to hover, it would cost them roughly half as much energy as flapping,” the university explained in a statement. “The microcopter's wings kept pace with the middle-of-the-pack hummingbird wings, but the topflight wings – those of Anna's hummingbird, a species common throughout the West Coast – were still about 27 percent more efficient than engineered blades.”
Lentink said he was not surprised by the results, as previous research had indicated hummingbird wings were incredibly efficient. However, he was impressed with the helicopter’s performance. He added that he believed the experiment indicates that the rotor power of a microcopter could still be improved by up to 27 percent.
“A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it's amazing that we're getting closer,” he said. “It's not easy to match their performance, but if we build better wings with better shapes, we might approximate hummingbirds.”
Hummingbirds are the only birds capable of sustained hovering, Gill said, and the experiment indicates that they use less power to overcome drag than the manmade blades of a similarly-sized helicopter. However, the professor told BBC News it also demonstrates that if the wing designs of drones are improved, that they can be built to hover equally as efficiently – if not more efficiently – than even the top hummingbird species.
“This shows that if we design the wings well, we can build drones that hover as efficiently, if not more efficiently, as hummingbirds,” said Lentink. “Clearly we are not even close to hummingbirds in many other design metrics, such as wind gust tolerance, visual flight control through clutter, to name a few. But if we focus on aerodynamic efficiency, we are closer than we perhaps ever imagined possible.”
The experiment also revealed that the muscles of a hummingbird produce 130 watts of energy per kilogram, far more than the 100 watts per kilogram average managed by other birds and most other vertebrates. However, the study authors are still unclear how a hummingbird manages to maintain their flight when faced with strong wind gusts, how they navigate through things like branches, or how they can change their direction so quickly.
Lentink said he also wants to study the aspect ratios of hummingbird wings, which at 3.9 are much lower than most wings used in aviation – including those of the Black Hornet (4.7). The professor said he wants “to understand if aspect ratio is special, and whether the amount of variation has an effect on performance.”
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