The Prehistory of the Wind Tunnel to 1958

The growing interest in and institutionalization of aeronautics in the late 19th century led to the creation of the wind tunnel.[531] English scien­tists and engineers formed the Royal Aeronautical Society in 1866. The group organized lectures, technical meetings, and public exhibitions, published the influential Annual Report of the Aeronautical Society, and funded research to spread the idea of powered flight. One of the more influential members was Francis Herbert Wenham. Wenham, a profes­sional engineer with a variety of interests, found his experiments with a whirling arm to be unsatisfactory. Funded by a grant from the Royal Aeronautical Society, he created the world’s first operating wind tunnel in 1870-1872. Wenham and his colleagues conducted rudimentary lift and drag studies and investigated wing designs with their new research tool.[532]

Wenham’s wing models were not full-scale wings. In England, University of Manchester researcher Osborne Reynolds recognized in 1883 that the airflow pattern over a scale model would be the same for its full-scale version if a certain flow parameter were the same in both cases. This basic parameter, attributed to its discoverer as the Reynolds number, is a measure of the relative effects of the inertia and viscosity of air flowing over an aircraft. The Reynolds number is used to describe all types of fluid flow, including the shape of flow, heat transfer, and the start of turbulence.[533]

While Wenham invented the wind tunnel and Reynolds created the basic parameter for understanding its application to full-scale aircraft, Wilbur and Orville Wright were the first to use a wind tunnel in the sys­tematic way that later aeronautical engineers would use it. The broth­ers, not aware of Wenham’s work, saw their "invention” of the wind tunnel become part of their revolutionary program to create a practical heavier-than-air flying machine from 1896 to 1903. Frustrated by the

poor performance of their 1900 and 1901 gliders on the sandy dunes of the Outer Banks—they did not generate enough lift and were uncontrol­lable—the Wright brothers began to reevaluate their aerodynamic cal­culations. They discovered that Smeaton’s coefficient, one of the early contributions to aeronautics, and Otto Lilienthal’s groundbreaking air­foil data were wrong. They found the discrepancy through the use of their wind tunnel, a 6-foot-long box with a fan at one end to generate air that would flow over small metal models of airfoils mounted on balances, which they had created in their bicycle workshop. The lift and drag data they compiled in their notebooks would be the key to the design of wings and propellers during the rest of their experimental program, which cul­minated in the first controlled, heavier-than-air flight December 17, 1903.[534]

Over the early flight and World War I eras, aeronautical enthusi­asts, universities, aircraft manufacturers, military services, and national governments in Europe and the United States built 20 wind tunnels. The United States built the most at 9, with 4 rapidly appearing during American involvement during the Great War. Of the European countries, Great Britain built 4, but the tunnels in France (2) and Germany (3) proved to be the most innovative. Gustav Eiffel’s 1912 tunnel at Auteiul, France, became a practical tool for the French aviation industry to develop high-performance aircraft for the Great War. At the University of Gottingen in Germany, aerodynamics pioneer Ludwig Prandtl designed what would become the model for all "modern” wind tunnels in 1916. The tunnel featured a closed circuit; a contraction cone, or nozzle, just before the test section that created uniform air velocity and reduced turbulence in the test section; and a chamber upstream of the test section that stilled any remaining turbulent air further.[535]