How Bumps on Whale Flippers Delay Stall

Tubercles, or bumps, on the leading edge of the flippers of humpback whales (Megaptera novaeangliae) increase the angle of attack at which such flippers lose lift dramatically or "stall." This stall-delay is thought to enable greater agility. Brenner has carried out a mathematical analysis of the lifting properties of a wing with slowly varying cross section, and has demonstrated that the bumps alter the pressure distribution on the wing to delay separation of the boundary layer, leading to a gradual onset of stall and higher stall angle. His results agree quantitatively with experiments. The results suggest a new mechanism for increasing the maneuverability of flying vehicles.