Imagine you’re driving your car on a clear day. You idly stick your hand out of the window, and tilt your hand, playing airplane as the wind pushes your hand upwards.
That’s lift—the same lift that allows an airplane to stay aloft or a windmill blade to turn. To help these man-made technologies increase maneuverability in the air, scientists took a tip from one of the lift experts of the ocean: the humpback whale.
Unlike many of their whale brethren, the humpback doesn’t survive solely on krill, captured by opening their mouths and swimming straight ahead towards the shrimp-like crustaceans. Instead, humpbacks maneuver to catch fish. And to do so, they’ve got to make some tight turns.
To make those fast course corrections, the humpback has to prevent its flipper from stalling. “If a whale wants to make a tight turn, it’ll need more lift, from a higher angle of attack,” explains Frank Fish, a biologist at West Chester University. “But if that angle of attack is too great when it’s trying to make that circle, it’ll stall”—just like a stomach-dropping moment in an airplane, or skidding on black ice in a car.
Humpbacks can maneuver their flippers to a sharp angle of attack before they start to stall, which lets them develop more lift and make those fish-catching turns. That’s thanks to tubercles, bumps that create scalloped edges on the leading side of their flippers.
Professor Fish and his team engineered flippers with tubercles and without, and tested them in a wind tunnel at the Naval Academy. They found that the tubercles did delay stall, increasing the angle of attack up to 42 percent.
Affixing tubercles to blades has shown similar effects with windmills, fans, surfboard fins, and even a hydroplane. “Because you can go to a higher angle of attack, there’s an increase in the amount of lift that can be generated,” says Fish. That’s especially important for wind turbines: Gusts from two different directions can stall the blade of a windmill, to the point where it’ll actually blow up. “You have to engineer windmills at fairly low angles of attack, so you aren’t getting that much lift and energy in the process,” says Fish. With tubercles, engineers can design windmills with a higher angle, enabling them to get more lift, spin faster, and gather more energy—while (mostly) safely assured that they won’t blow up.
