Various forces and moments to which an aircraft is subjected by the airflow cannot be accurately determined by purely theoretical calculations. The aircraft designer must therefore have good knowledge about experimental aerodynamics, which from the earliest days has contributed much to the progress made in aeronautical science.

Wind tunnels have been used for studying the elements of flight since 1871. Initially they were small-scale, open-loop devices such as the Wright Brothers’ tunnel with its 16-inch test section. Wind tunnels grew in size and complexity, particularly after the Ludwig Prandtl first closed-loop tunnel in 1909. Tunnels were built in a variety of sizes and shapes with varying speeds depending on the current technology and their intended areas of study. The Altitude Wind Tunnel (AWT) was the first wind tunnel built to study engine performance in altitude conditions.

Like aircraft, wind tunnels have come a long way in their technological development. Their sophistication has kept pacewith the needs of designers. The first major U.S. Government wind tunnel was built at NASA’s Langley Research Center and became operational in 1921. The Center was the first major research facility of the U.S. National Advisory Committee for Aeronautics (NACA), which was founded in 1915. The NACA later became a part of NASA when it was established on October 1,1958, to carry out space research and exploration and to continue the NACA’s aeronautical work.

The first major U.S. wind tunnel was built at NASA‘s Langley Research Center; Hampton, Virginia in 1920. Late in the last century, however, the first wind tunnels were little more than boxes or pipes. A fan or other device propelled air over a model of an aircraft or of a wing suspended in the pipe or box. Observation instruments were crude. The researchers had to gather many of the test results with their own eyes.

The Wright brothers designed and used such primitive tunnels to develop the wing configurations and control surfaces with which they achieved the first powered human flight early in this century. Today’s aircraft are larger, cruise faster and higher, carry more passengers and cargo, and use less fuel per mile than most of their predecessors. Aircraft now being developed are expected to show significant improvements in all of these performance characteristics.