Lilienthal and others had also added horizontal surfaces behind each wing, called elevators, that controlled the glider's pitch up and down, and Lilienthal used a vertical rudder that could turn his glider right or left. But the third axis through which a glider could rotate— rolling to either left or right—remained problematic. Most experimenters of the day thought roll was something to be avoided and worked to offset it, but Wilbur Wright, the older of the brothers, disagreed. Wilbur's experience with bicycles had taught him that a controlled roll could be a good thing. Wilbur knew that when cyclists turned to the right, they also leaned to the right, in effect "rolling" the bicycle and thereby achieving an efficient, controlled turn. Wilbur realized that creating a proper turn in a flying machine would require combining the action of the rudder and some kind of roll control. While observing the flight of turkey vultures gliding on the wind, Wilbur decided that by twisting the wings—having the left wing twist upward and the right wing twist downward, or vice versa—he would be able to control the roll. He rigged a system that linked the twisting, called wing warping, to the rudder control. This coordination of control proved key. By 1902 the Wrights were flying gliders with relative ease, and a year later, having added an engine they built themselves, Orville made that historic first powered flight—on December 17, 1903.
As happens so often in engineering, however, the first solution turned out not to be the best one. A crucial improvement soon emerged from a group of aviation enthusiasts headed by famed inventor Alexander Graham Bell. The Wrights had shared ideas with Bell's group, including a young engine builder named Glenn Curtiss, who was soon designing his own airplanes. One of the concepts was a control system that replaced wing warping with a pair of horizontal flaps called ailerons, positioned on each wing's trailing edge. Curtiss used ailerons, which made rolls and banking turns mechanically simpler; indeed, aileron control eventually became the standard. But the Wrights were furious with Curtiss, claiming patent infringement on his part. The ensuing legal battle dragged on for years, with the Wrights winning judgments but ultimately getting out of the business and leaving it open to Curtiss and others. As happens so often in engineering, however, the first solution turned out not to be the best one. A crucial improvement soon emerged from a group of aviation enthusiasts headed by famed inventor Alexander Graham Bell. The Wrights had shared ideas with Bell's group, including a young engine builder named Glenn Curtiss, who was soon designing his own airplanes. One of the concepts was a control system that replaced wing warping with a pair of horizontal flaps called ailerons, positioned on each wing's trailing edge. Curtiss used ailerons, which made rolls and banking turns mechanically simpler; indeed, aileron control eventually became the standard. But the Wrights were furious with Curtiss, claiming patent infringement on his part. The ensuing legal battle dragged on for years, with the Wrights winning judgments but ultimately getting out of the business and leaving it open to Curtiss and others.
World War I's flying machines, which served at first only for reconnaissance, were soon turned into offensive weapons, shooting at each other and dropping bombs on enemy positions. World War I's flying machines, which served at first only for reconnaissance, were soon turned into offensive weapons, shooting at each other and dropping bombs on enemy positions. Some of the most significant developments involved the airframe itself. The standard construction of fabric stretched over a wood frame and wings externally braced with wire was notoriously vulnerable in the heat of battle. Some designers had experimented with metal sheathing, but the real breakthrough came from the desk of a German professor of mechanics named Hugo Junkers. In 1917 he introduced an all-metal airplane, the Junkers J4, that turned out to be a masterpiece of engineering. Built almost entirely of a relatively lightweight aluminum alloy called duralumin, it also featured steel armor around the fuel tanks, crew, and engine and strong, internally braced cantilevered wings. The J4 was virtually indestructible, but it came along too late in the war to have much effect on the fighting. In the postwar years, Junkers and others made further advances based on the J4's features. For one thing, cantilevering made monoplanes—which produce less drag than biplanes—more practical. Using metal also led to what is known as stressed-skin construction, in which the airframe's skin itself supplies structural support, reducing weighty internal frameworking. New, lighter alloys also added to structural efficiency, and wind tunnel experiments led to more streamlined fuselages.
As early as 1911, airplanes had been used to fly the mail, and it didn't take long for the business world to realize that airplanes could move people as well. The British introduced a cross-channel service in 1919 (as did the French about the same time), but its passengers must have wondered if flying was really worth it. They traveled two to a plane, crammed together facing each other in the converted gunner's cockpit of the De Havilland 4; the engine noise was so loud that they could communicate with each other or with the pilot only by passing notes. Clearly, aircraft designers had to start paying attention to passenger comfort. As early as 1911, airplanes had been used to fly the mail, and it didn't take long for the business world to realize that airplanes could move people as well. The British introduced a cross-channel service in 1919 (as did the French about the same time), but its passengers must have wondered if flying was really worth it. They traveled two to a plane, crammed together facing each other in the converted gunner's cockpit of the De Havilland 4; the engine noise was so loud that they could communicate with each other or with the pilot only by passing notes. Clearly, aircraft designers had to start paying attention to passenger comfort.
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