The Airplane - Jay Spenser [49]
The next glider, built in the new year, incorporated this longer, narrower wing with its flatter camber. Tested the following summer and fall at Kitty Hawk, the Wright 1902 Glider matched its predicted performance and rewarded the brothers with the longest glides yet.
Controllable with the addition of a movable rudder, the Wright 1902 Glider set the stage for the Wright brothers’ invention of the airplane the following year.
“Our new machine is a very great improvement over anything…anyone has built,” Wilbur wrote in October 1902. “Everything is so much more satisfactory that we now believe that the flying problem is really nearing its solution.”11
Enlarged further to accommodate an engine, this breakthrough wing became the aerodynamic and structural heart of the Wright 1903 Flyer, history’s first airplane. Louis Blériot, Glenn Curtiss, Igor Sikorsky, and countless other early fliers would trust their lives to essentially similar wings for the next fifteen years.
Then something unexpected happened. Human beings bid farewell to the thin, bird-inspired wings that had first carried them aloft. It was all because a German university professor in his fifties asked a radical question.
6 WINGS, PART II
CLOUD-CUTTING CANTILEVERS
You cannot fly like an eagle with the wings of a wren.
—WILLIAM HENRY HUDSON (1841–1922)
Thin wings gave aviation its start. They did most of the fighting over Europe in World War I. And thanks to Hugo Junkers, they died a casualty of that conflict.
Junkers is, of course, the German industrial engineer we met earlier because of his all-metal airplanes. In an era when wings were thin and bird-like, he alone thought to wonder whether thick wings too could be made to fly. It was so heretical an idea that it is a bit startling he came up with it, but there was method to his madness.
The strut and wire bracings between the thin wings of World War I biplanes are fine from a structural standpoint. Aerodynamically, however, they come at a high price because they significantly retard the airplane’s passage through the air. As a result, externally braced biplanes are known for high drag, not just high lift.
The Rumpler Taube shows off its thin, bird-inspired airfoil. Although Taube is German for dove, Austrian designer Igo Etrich reportedly modeled this airplane’s graceful wing after the zanonia seed.
National Air and Space Museum, Smithsonian Institution
Early monoplanes didn’t do much better on this front. The Fokker Eindeckers, Rumpler Taubes, and other World War I monoplanes (like the Blériots and Antoinettes that preceded them) had fewer struts but featured correspondingly more wires. Extending outward from a kingpost atop the fuselage, they braced the thin wings from above while more wires from below tied them into a bottom post or perhaps the landing gear.
Physics decrees that aerodynamic drag increases proportionally to the square of an object’s speed through the air. Thus, an airplane flying twice as fast encounters four times the drag. This physical limitation became all too apparent as people tried to go faster using World War I–era aviation technology. It’s also why old-time pilots often joked that their airplanes came with built-in headwinds.
Although the wing struts of a biplane looked to be most of the problem, it turned out that bracing wires, thin as they were, were just as culpable. The cylindrical cross section of a wire presents a blunt, symmetrical, and unstreamlined profile to the relative wind that makes it a particularly bad shape to drag through the air. The result is turbulence that translates into drag.
One clue that this was happening was that bracing wires sometimes vibrated audibly in flight. When World War I flying aces spoke of hearing their wires singing during high-speed chases, they weren’t merely waxing poetic; airflow ambivalence was vibrating these wires like a bow drawn across the strings of a great cello.
Biplane manufacturers finally addressed this drag penalty in the 1920s—and in the process ended the