Amateur nineteenth-century aviators typically studied the flight behavior of birds and then built flying machines accordingly. The resulting bird-like craft failed miserably because the builders had no knowledge of aerodynamics and aeronautics, particularly of lift and drag forces acting on surfaces cutting through the air.

The earliest invention for testing flight characteristics was a whirling arm. Benjamin Robbins, an English mathematician, first employed such a device in the eighteenth century. He mounted such shapes as pyramids and oblong plates on the arm tip and spun them in different orientations. He found that no simple theory would account for the complex forces acting on moving objects. George Cayley also used a whirling arm to measure drag and lift in the early nineteenth century. The major drawback to whirling arms was the disturbance of air created; the aircraft models flew into their own wakes, thus precluding any clear...