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W. J. Maybury
School of Biological Sciences, University of Bristol

The picture is of a European starling in an airflow of 9 m/s visualized using the smoke-wire technique.

In the smoke-wire technique, a fine stainless steel or nickel-chromium wire stretched across the flowfield, in either the horizontal or vertical plane, coated in an oil, can produce short bursts of smoke controlled electrically by resistive heating. Oil on the wire tends to form into droplets of regular size and spacing, from which smoke appears. The Mineral oil "Shell" Ondina EL is used to coat the wire. The number of droplets per unit length depends on the diameter of the wire and the oil's surface tension, and the smoke duration depends on the current strength and droplet size, but generally lasts under half a second. The smoke-wire technique is ideal to visualize the small wakes this project requires. It can be used in fluid velocities of up to 9 m/s and consists of a large number of very fine, evenly spread discrete smoke filaments and allows for accurate location within the flowfield so that small-scale details may be studied.

Visit the School of Biology, University of Leeds, Animal Flight Mechanics web site at http://www.biology.leeds.ac.uk/staff/jmvr/Flight/flight.htm.

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