Butterflies cup their wings to produce tiny jets and evade predators
By analyzing the way butterflies rapidly take flight in wind tunnel experiments, scientists have uncovered new detail around how the insects evade predators. The mechanics of their wings were found to help generate small pockets of air that can quickly propel them forward, with the researchers hopeful of applying these lessons to the design of small aircraft.
The discovery is the result of research carried out at Sweden’s Lund University, where scientists probed the mysteries of butterfly flight by studying their wingbeats during take-off in wind tunnel experiments. This close examination revealed how during the upstroke, the wings actually cup together to form tiny pockets of air in between. They then go on to collide, rapidly pushing the air out and generating tiny jets that help propel the insects forward.
“That the wings are cupped when butterflies clap them together, makes the wing stroke much more effective,” says biology researcher Per Henningsson. “It is an elegant mechanism that is far more advanced than we imagined, and it is fascinating. The butterflies benefit from the technique when they have to take off quickly to escape from predators.”
This cupping mechanism during the upward stroke had been theorized by scientists for almost 50 years, but only now have researchers been able to observe it in action. The downward stroke, meanwhile, was found to help the butterflies remain in the air rather than falling to the ground. The researchers built on these findings by creating mechanical wings with the shape and flexibility of butterfly wings.
“Our measurements show that the impulse created by the flexible wings is 22 percent higher and the efficiency 28 percent better compared to if the wings had been rigid,” says study author Christoffer Johansson.
By studying animals in flight in this way, scientists have previously unraveled secrets that could lead to aircraft with improved aerodynamics, feature shape-shifting wings, or an ability to avoid mid-air collisions. Similarly, the authors of this new study believe these findings could be harnessed to improve the flight performance of small drones.
The research was published in the Journal of the Royal Society Interface, while the short video below offers a quick look at the butterflies in flight.
Source: Lund University