September 11, 2010 | David F. Coppedge

Flying Fish Tested in Wind Tunnel: Match Bird Flight

Sometimes engineers investigate things biologists take for granted.  Flying fish have been observed by countless sailors and cruise passengers, and have been described by life scientists.  It took an engineer, however, to investigate these “unexpected fliers” in a wind tunnel.  Surprisingly, though many have speculated about these creatures, “detailed measurement of wing performance associated with its morphometry for identifying the characteristics of flight in flying fish has not been performed” till some engineers caught the inspiration.
    Haecheon Choi, a Korean mechanical engineer, took an interest in flying fish while reading about them to his children.  According to Science Daily, a scientific paper in the Journal of Experimental Biology resulted (see the JEB press release; the paper is available for free).1
    Choi and a colleague Hyungmin Park designed experiments using a wind tunnel to measure the gliding efficiency of flying fish.  It was difficult obtaining specimens, the article told; they couldn’t find them in Japanese fish markets, so they got a permit to fish for them in the open sea.  Out of 40 fish caught, five were dried and stuffed (they would have died anyway in the wind tunnel, you know) and outfitted with sensors to measure their aerodynamics.  Some had their pectoral and pelvic fins outstretched in gliding position, or just the front pectoral fins outstretched, while one, as a control, was measured with all its fins in swimming position.  “For the first time, we have performed a direct wind-tunnel experiment to investigate the aerodynamic properties of flying-fish flight and provided qualitative and quantitative data for the flying fish flight,” they were able to boast.
    The pair was impressed by their gliders.  “Choi and Park found that the flying fish performed remarkably well: the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck,” they said in the JEB paper.  The fish performed best in their natural horizontal position close to the water, avoiding the wing-tip vortices that otherwise would cause the most frictional drag.  When gliding above water, their lift-to-drag ratio actually increased, measurements of flow patterns in the wind tunnel showed.  “Park explains that the tandem arrangement of the large pectoral fin at the front and smaller pelvic fin at the back of the fish’s body accelerates the air flow towards the tail like a jet, increasing the fish’s lift-to-drag ratio further and improving its flying performance even more.”  The fish have other morphologic adaptations to improve lift, such as a torpedo-shaped body, a flattened bottom, and the ability to rapidly wag the tail fin on take-off to get airborne, a behavior called taxiing.
    Not only are their wing-fins well-adapted for gliding in the air, they are also ideal for swimming in the swept-back position.  “So flying fish are superbly adapted for life in both environments,” the article said.  The intro also contained these fast facts: “Flying fish can remain airborne for over 40s, covering distances of up to 400m at speeds of 70km/h” (that’s about a quarter mile in 30 seconds aloft, gliding at over 40 miles per hour).  The authors said, “The aerodynamic performance of flying fish is comparable to those of various bird wings, and the flying fish has some morphological characteristics in common with the aerodynamically designed modern aircrafts.
    It can reasonably be assumed that live fish perform even better in their natural habitat, with wet skin, the ability to adjust wing camber and attack angle using their muscles, and with additional taxiing movements to stay aloft.  With results in hand showing high performance in the flying fish due to good design, the researchers’ thoughts turned to biomimetics: “Having shown that flying fish are exceptional fliers, Choi and Park are keen to build an aeroplane that exploits ground effect aerodynamics inspired by flying fish technology,” the article ended, stating nothing about evolution or how this flight technology might have evolved.

1.  Hyungmin Park and Haecheon Choi, “Aerodynamic characteristics of flying fish in gliding flight,” Journal of Experimental Biology, 213, 3269-3279 (2010); published by The Company of Biologists 2010; doi: 10.1242/jeb.046052.

It is a pleasure to report good scientific work that is not dependent on Darwinian storytelling (cf. 09/10/2010).   Most of the elements of classic science are here: noticing an interesting phenomenon, observing it carefully, asking questions, searching existing literature, proposing an experiment to gather more detailed data, obtaining specimens, designing an experimental apparatus, running controlled experiments and taking measurements, evaluating the findings, publishing, and suggesting applications for the benefit of humanity.  What’s missing is Darwin worship, thank God.
    The original paper had no use for evolutionary theory.  The authors stayed out of political trouble by donating the required pinch of incense to Emperor Charlie: “the flying fish has evolved to have good aerodynamic designs (such as the hypertrophied fins and cylindrical body with a ventrally flattened surface) for proficient gliding flight,” they said, but the emphasis of even that statement was clearly on the design, not the evolution.  From then on, they left the Charlie Temple turnstile behind, and focused on the good engineering (intelligent design) of their fish.
    They did not even try to speculate on the origin of the adaptation, other than to say, “Although reasons for the flight of flying fish have been suggested (i.e. escape from underwater predators or saving of transport cost) (Rayner, 1986Go; Davenport, 1994Go), the exact reason is still not clear.  Nevertheless, their behavioral adaptation for flight is quite unique.”  Those statements would be just as comfortable in a creation paper.  They dodged the temptation to tell an evolutionary just-so story (see next entry), and focused instead on the design.  And thankfully, we were also spared a miracle story about “convergent evolution,” or the genes for flight being pushed back to some imaginary ancestor of fish and birds.  It takes discipline to avoid falling into these Darwin traps.  Engineers are comfortable with the concept of intelligent design.  The authors work for the School of Mechanical and Aerospace Engineering and the Institute of Advanced Machinery and Design at Seoul National University.
    Does design-focused research of the living world produce good science?  Here was one more great example.   Maybe some day we’ll be able to buy cars that can sprout wings and glide across a lake – thanks to flying fish and design-conscious science.

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