With a big enough engine, a barn door will fly. Machine-gun inventor Sir Hiram Maxim declared that, more or less, while building his “Great Kite of War” in 1894. “It is neither necessary nor practical to imitate the bird too closely, because screw propellers have been found to be very efficient,” he wrote in Cosmopolitan magazine. (Who knew Cosmo had been around so long?) “Without a doubt, the motor is the chief thing to be considered.”
Maxim had it all figured out: Unlike a boat that operates in one dimension, he said—that is, left and right—his flying machine operated in two dimensions: left and right, plus up and down. It resembled a sled hauling three broad canvas awnings of varying sizes, and it used two huge, counterrotating propellers and two light steam engines that generated a bruising 180 horsepower each. Aside from canceling out the gyroscopic effect—the right-turning tendency—generated by a single prop, two props had an extra benefit: boosting power to one engine and pulling it back on the other would made the Great Kite turn. Like I said, Maxim had it all figured out.
The Great Kite of War weighed nearly four tons, and it ran on top of iron rails like a train. To prevent the Kite from climbing way high during the first round of tests, Maxim set wooden guardrails above the track. On the first trial run, Maxim and two others, presumably engine operators, climbed aboard, built up a head of steam, and then set off. The Great Kite gathered speed, lurched up, and snapped a guardrail, and after he killed the engines Maxim understood the inherent flaw in his control system: It afforded him no control.
Over on the continent, German Otto Lilienthal followed a different approach: His glider used aerodynamics—curvature of the wing—to stay aloft. Yet he, too, had trouble figuring out how to keep flying straight and level. The year before Maxim’s $45,000 disaster (that’s $1.1 million today), Lilienthal constructed his sixth glider with a swiveling tail, which would allow gusts to move the tail up and down without affecting the glider’s stability. But to keep his gliders under control, Lilienthal, suspended between the wings, shifted his weight. When the left wing rose, he leaned left to keep it level; when the right wing rose, he leaned right.
The ground-bound Maxim called Lilienthal “a flying squirrel.”
In 1896 Lilienthal was flying one of his gliders when a sudden upward gust pushed his machine’s nose straight up, then the left wing dipped, and the glider spun into the ground—perhaps the world’s first stall-spin accident. Lilienthal broke his back, and died the next day at age 48. In the States, a man in Ohio who owned a bicycle shop, Wilbur Wright, read about the crash, and debated it with his brother, Orville. One day, Wilbur checked out buzzards flitting about overhead, and noticed how they handled turbulence: by flexing their wing tips. An upward gust on their left wing prompted an upward flex from the feathers of that wing tip, while simultaneously the feathers on the right wing tip flexed downward. The entire bird rolled left along a line running down the bird’s center, from the head to its tail. No leaning for these buzzards.
Now all Wilbur had to do was figure a way to mimic that action mechanically. A system of shafts and gears, perhaps? Nah, too much weight. As the story goes, one evening in 1899 a customer came into the bike shop and bought an inner tube, and while they were chatting Wilbur unconsciously flexed the empty inner-tube box lengthwise. When he realized what he was doing, he rushed home to Orville and they began constructing a biplane kite with the wings cross-braced laterally, but without fore-and-aft bracing, allowing the wing tips flexibility. They controlled it with four cords attached to two sticks; when they wanted to flex the tips they pulled one stick’s top forward while pulling the other stick’s bottom forward. When they flew the kite in the turbulent sea of the air, it performed remarkably well.
The next year they rode the train—and a boat—to North Carolina’s Outer Banks, and built a bigger kite, one capable of carrying a man. This glider consisted of two wings shaped according to tables of lift published by Lilienthal, which the prone pilot “warped” (their word) by shifting a cradle that he lay upon. It also had a forward elevator, controlled by a stick in the pilot’s right hand. When the brothers tried it out, they discovered that their system of wing warping would indeed keep the glider flying level. They also saw that, with enough warp, the glider turned toward the lowest wing. However, they also discovered adverse yaw when they saw the nose swing in the opposite direction from drag on the upper wing.
The brothers had other issues to work out, namely the wing’s optimum profile (Lilienthal’s lift tables weren’t quite accurate), but when they did in 1902 they also added a controllable rudder, which overcame adverse yaw. Knowing wing warping’s importance (for, indeed, with enough power even a barn door will fly), the brothers filed for a patent on that glider instead of their more famous, powered 1903 Wright Flyer. The U.S. government awarded the patent to them in 1906, and then they began selling their powered flying machine to anyone with $20,000 ($457,000 today) and a dream.
Instead of waiting to buy one, motorcycle-racing legend Glenn Curtiss built one of his own, but he didn’t have the patience to deal with constructing wings that flexed their tips. Instead, he used “movable tips” mounted on the wings’ ends and, by outliving Wilbur, eventually won the long patent-infringement suit filed against him by the Wright brothers.
At that same time the French also adopted similar hinged surfaces, mounted on the wing’s trailing edge, which they called “little wing.” Or, as they say in French, aileron.
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