Wind tunnel

1871 Wind tunnel

The book of science

Tom Sharp

Francis Herbert Wenham aerodynamics Wind tunnel

Wind tunnel

Francis Herbert Wenham was totally interested in testing his theories by building and testing manned gliders, but these always resulted in failure. Earlier scientists—Benjamin Robins, John Smeaton, George Cayley, and Otto Lilienthal— used whirling arms to test the lift and drag of airfoils. Wenham had enough experience designing boat propellers to recognize that a whirling arm, in moving the air around it, made all measurements imprecise. A wing could not be supported by air that it forces downward, but only by advancing forward to be supported by undisturbed air. Instead of moving an object through the air to test his theories about how birds fly, Wenham designed a box that moved air past a stationary model. The Aeronautical Society of Great Britain raised the funds, and John Browning, a fellow member of the Society, build for Wenham the first wind tunnel.

Study of flight

Francis Herbert Wenham was a keen observer of birds in flight. He noted that the wings of the sea gull required no discernible angle or upward rise, and compared the ratio of birds’ weight to wing-surface against John Smeaton’s table of atmospheric resistances, noting that the ratio in birds ranged from half (for ducks) to double (for swallows) the ratio of the surface of a parachute to support the weight of a man falling at a safe fifteen miles per hour. There were obviously other forces at play here, which Wenham recognized as controlled, “when the plane is urged forward horizontally . . . by the form and arrangement of the surface.” Wenham thought that forward movement through the air, multiplying the weight of air under the wings, was enough to support the flights of birds.

Testable hypotheses

It’s OK to have opinions, but working hypotheses are better if they can be tested. Maybe the wings of birds stretch across the sky to find more air for support. Maybe any animal with a brain has feelings and can reason with abstractions. Maybe a device can be built that distorts time and space like gravity. Maybe dreams of flying are not always a symptom of overreaching.

Francis Herbert Wenham was the first person to suggest that lift could be improved using multiple stacked wings (“superposed aeroplanes”). The Wright brothers benefited from this and other ideas from Wenham.

We know from the work of Wilber and Orville Wright that John Smeaton’s tables were essentially correct, although the coefficient of air pressure that he calculated was 53% higher than the correct value.

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