Flying fish glide as well as birds

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A new study by South Korean scientists has revealed that flying fish are as good at gliding as many small to medium sized birds such as petrels and wood-ducks.

The scientists examined Cypselurus hiraii, a small species of flying fish from the Northwest Pacific. They selected five similarly sized specimens, dried and stuffed them with the fins in various positions and tested air movement around them in a wind tunnel to measure their flight capabilities.

They also positioned a tank of water under the fish during the test to see how this affected flight characteristics. Measuring the fishes' lift to drag ratio, (a measurement of the horizontal distance travelled relative to the descent in height in a glide) they found it was highest when the fish was parallel with the surface, and that flying above water increased the lift further compared to over a solid surface.

They also discovered that the fish was very stable in flight with its fins extended, but with its fins close to the body it became unstable – ideal for rapid changes in direction underwater.

The species tested has enlarged pectoral and pelvic fins to help it get airborne making it something like a bi-plane in flight, and when smoke was blown over the fish in the wind tunnel it was observed that this arrangement of fins causes jets of air to accelerate towards the tail providing additional lift.

It is hoped that the study may have uses in the aeronautical industry, especially in the area of ground effect aircraft like the famous Russian 'Ekranoplan' more commonly known as 'the Caspian Sea Monster'.

There are over 60 species of 'flying fish' in the family Exocoetidae spread around the world's oceans, largely in tropical and subtropical waters. Some species have been observed 'flying' distances of around 400 m at speeds of 70 kph in the wild, usually just above the surface, sometimes dipping their tail back into the water to regain lost speed and extend the flight.