The Airplane - Jay Spenser [45]
Collaborating with John Browning, who did the constructing, Wenham had the world’s first wind tunnel up and running at the start of the 1870s. It was a magic chamber in which patient thinkers would coax flight’s secrets out of hiding.
A hollow box about 10 feet (3 meters) long, the tunnel was open at the ends and employed a fan to drive air through at a constant rate. A window let experimenters observe how different wing shapes performed in this artificial airflow.
The airfoil section under test was mounted on a balance that deflected under aerodynamic forces. By testing different airfoils at various angles of attack (orientations to the airflow), the lift and drag characteristics of these airfoils could be tabulated and plotted.
This first-ever wind tunnel provided very little usable data because it suffered from flaws. The air flowing through it was neither smooth nor constant, and the mounting balance was insufficiently sensitive. Horatio Phillips, a young member of the Aeronautical Society, built an improved tunnel in the 1880s that addressed these failings, and began pioneering research that continues today.
Cayley said that wings should be cambered, not flat. He based this guidance on methodical airfoil studies. He measured their lift, the movement of their center of pressure as the angle of attack changed, and their air resistance. He even correctly theorized that airfoils create lower pressure above the wing than below.
Having learned so much, it is ironic that he offered future researchers little specific guidance on the wing’s shape. Moreover, his own full-size gliders relied on fabric wings indiscriminately billowed to a camber by the air. While he foresaw the need for rigid airfoils in the future, he also apparently felt such refinements were not necessary for the low speeds and weights of his gliders. Consequently, the craft he built late in life were paragliders.
In contrast, Otto Lilienthal’s gliders had rigid wings. The great German pioneer chose an arc for his airfoil, whereas birds’ wings employ parabolic cambers with the greatest curvature near the front. Efficiently honed by evolution, this latter shape affords the most lift.
It is just possible that Lilienthal was fooled in his anatomical studies. Absent active muscular control, a dead bird’s wing might not always display its normal flight camber. However, it is more likely that Lilienthal fell prey to the ancient Greeks’ fondness for classic geometric forms, a love strongly echoed in the teachings of nineteenth-century Europe. Whatever the reason, Lilienthal selected the arc—a section of a perfect circle—for his airfoil camber. This decision compromised the stability and performance of his gliders; it may even have cost him his life.
Down near the Baja border east of San Diego, twenty-five-year-old Californian John J. Montgomery and his younger brother James jumped down from the plank seat of their buckboard. Setting aside rifles, they hefted a compact glider off the wagon. The horse shied as they carried the two-winged contraption to the edge of a gradual hill nearly a mile long.
Setting the glider down, the young men surveyed the landscape. California’s Otay Mesa spread before them, an undulating panorama of sagebrush, cactus, buckwheat, and sunflower. Home to rattlers, tarantulas, scorpions, foxes, coyotes, vultures, and other wildlife, its scrub-covered folds were also dotted here and there with ranches and somnolent cattle. A red-tailed hawk burst from a tall lemonadeberry and plunged to the ground, rising again with a lizard in its talons. Sunlight flashed russet in the bird’s tail, and the world was again still.
It was August 28, 1883, a sweltering day in the American Old West. Less than two years had passed since the infamous shootout