In hopes of taking humans to the heavens, early flight engineers tried to follow the example of birds. Leonardo da Vinci, for instance, sketched a so-called "ornithopter" in 1485. Yet our winged friends proved less than helpful when it came to revealing the secrets of flight. Numerous inventors fabricated bird-inspired machines, only to watch them flop around helplessly in the dirt.
It became clear that in order for humans to fly, they needed a better understanding of the interplay between wings and winds. So, these fledgling fanciers of flight went in search of hilltops, valleys and caves with powerful, somewhat predictable winds. But natural winds didn't provide the steady flow that could offer helpful design feedback -- artificial winds were necessary.
Enter the whirling arms. In 1746, Benjamin Robins, an English mathematician and scientist, attached a horizontal arm to a vertical pole, which he rotated, sending the arm spinning in a circle. At the end of the arm, he affixed a variety of objects and subjected them to the forces of his homemade centrifuge. His tests immediately confirmed that the shape of things had a tremendous effect on air resistance (also known as drag, an element of aerodynamic force).
Other experimenters, such as Sir George Cayley, soon built whirling arms. Cayley, in particular, tested airfoil shapes, which looked a lot like a cross-section of an airplane wing, to investigate principles of drag and lift. Lift is an element of force that moves perpendicular to the direction of an object's motion.
The rotating arm had a serious side effect, however, in that it chopped up the air as it spun, basically creating hellacious turbulence that greatly impacted all results and observations. But the arm did result in one monumental breakthrough: Engineers began to realize that by quickly propelling an object through the air, they could develop lift. That meant it wasn't necessary to build flapping wings in order to fly. Instead, humans needed enough power and the right kind of wing construction. Scientists needed better investigative tools to work out those important questions. Wind tunnels were the answer.
On the next page, you'll find out how spinning arms evolved into wind tunnels -- and you'll see how those tunnels were instrumental to one of the biggest technological achievements in the history of humankind.