Park and Choi’s specimens were caught in the Sea of Japan and formally belonged to Cypselurus, a flying fish genus with a cylindrical body, exceptionally broad pectoral fins and unusually developed pelvic fins near its tail. Another genus, Exocoetus, has narrower pectoral and smaller pelvic fins; researchers liken them to biplanes and monoplanes.

Propelled by a tail-motor action on the surface of waves, the fish regularly make gliding flights of more than a hundred feet, at speeds above 30 miles per hour. (In a widely circulated video shot from a Japanese ferry, a fish stayed aloft for 45 seconds.) Flying helps the plankton-eating fish escape from predators.

With the fish dry-mounted and filled with urethane to maintain shape in wind tunnel tests, Park and Choi were able to measure the fishes’ lift-to-drag ratios, how far they moved horizontally per unit of vertical fall, and other aerodynamical measures.

At their precise angle of exit from the water, the fish achieve their greatest lift. The fin arrangement pushes air down the fishes’ bodies towards their tails, like a jet. And when the fish are just above the water’s surface, they benefit from a ground effect, in which air pressure underneath their fins creates lift.

The researchers are now curious about the potential role of texture differences between the top and bottom of flying fish pectoral fins.

The pair are also designing a flying fish-inspired plane. In an email, Choi gave few details, but it would appear to be quite low-flying.

“The ground effect for reducing the drag force is very important in the design,” he said.

Images: 1). Diagram of flying fish in wind tunnel, and depiction of air flow around its body at a flat (top) and 10 degree (bottom) angle./Journal of Experimental Biology. 2) Diagram of flying fish./JEB.

See Also:

• Video: How Leaping Fish Species Left the Water — For Good
• Amazing Starling Flocks Are Flying Avalanches
• High-Speed Video Shows How Flies Change Direction So Quickly
• Secret Law of Flying Could Inspire Better Robots
• Video: Maple Seeds Ride Self-Generated Tornadoes
• Video: Leaping Lizard’s Tail-Free Mid-Air Wipeout

Citation: “Aerodynamic characteristics of flying fish in gliding flight.” By Hyungmin Park and Haecheon Choi. Journal of Experimental Biology, Vol. 213 Issue 18, September 2010.

Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on an ecological tipping point project.

Authors: Brandon Keim

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