The Wright Brothers How They Flew
WHEN OTTO LILIENTHAL, THE GERMAN WOULD-BE inventor of the airplane, died in a glider crash in 1896, the 24-year-old Orville Wright was incubating typhoid fever and about to enter a six-week delirium that would bring him near death. While Orville lay sick, his older brother, Wilbur, thought about the fatal accident. The brothers had followed Lilienthal’s work at a distance through newspaper accounts. When Orville at last began a slow recovery, he and Wilbur discussed the problem of flight.
The Wrights were the stuff of Sinclair Lewis, seasoned with dashes of Thornton Wilder and the Brontë sisters: solidly Midwestern products rooted in mainstream, small-town, agrarian-oriented WASP culture. Their father, Milton Wright, an unbending and contentious bishop in the Church of the United Brethren in Christ, came from old Puritan English and Dutch stock. He had married a shy, studious woman, Susan Koerner, of German-Swiss roots; from this union came seven children, five of whom, four brothers and a sister, survived into adulthood. Wilbur, born in 1867, Orville, born in 1871, and Katharine, born in 1874, formed a natural and mutually supportive team.
A rigid upbringing in a family that would often settle disputations with formal courtlike proceedings and judgments helped give both brothers an inflexible view of every human relationship that bordered on—and sometimes crossed over into—obsession, stubbornness, and suspicion. Unlike some of their siblings, they evinced little interest in leaving home, in part because of the economic depression of the 1890s, but perhaps also because their restless father had made 12 moves in 25 years. Despite this uprootedness, Wilbur apparently had a relatively normal childhood until struck by a flung bat in a game resembling hockey when he was 18. This event turned him into a semi-invalid for several years and prevented his going to Yale, his parents’ dream. It is uncertain how much this stemmed from actual injury as opposed to an unreasoning concern over his health that never really left him. His younger brother Orville, known as “Bubbo” to the family, who was so shy as never to be able, even as an aged and venerated adult, to make the briefest remarks before an audience, left high school before graduation. But they were not uneducated. Both read voraciously across the fields of science, literature, the arts, history, and philosophy. They possessed profound scientific insight, a sure grasp of mathematics, and excellent analytical skills, and clarity, style, and grace mark their writings.
Neither brother had an extensive social life. They certainly did not form any strong emotional attachments. Some who knew them recalled that Wilbur seemed discomfited in the presence of young women, while Orville didn’t notice them. If the brothers simply reflected the generally patriarchal times in which they lived, it was to an exaggerated degree. When a senior British engineering officer visited them in Dayton, Ohio, in 1904, Wilbur felt moved to note that his wife was “an unusually bright woman,” as if discussing a particularly smart racehorse. Yet their own Oberlin-educated sister, Katharine, was herself such a woman, and she shared with them, at least at first, their lack of interest in leaving the family. It was to her that the work-obsessed brothers turned for emotional support, Orville especially, something sadly evidenced by the irrational bitterness he exhibited when, to his surprise, Katharine finally married. Convinced she had willfully and irretrievably broken a family pact, thus leaving him on his own (Wilbur having died in 1912), Bubbo had nothing further to do with her, ignored her pleas for a reconciliation, and only with the greatest difficulty brought himself to be at her bedside as she died.
The brothers inherited a tremendous work ethic and the ability to focus on problems to the exclusion of almost everything else. Orville decided while still in high school to become a printer and, confident in his choice, willingly left before the end of his senior year. The two brothers made a success of a small printing operation and then, in 1892, in response to the bicycling craze sweeping the country, both became involved in a YMCA-sponsored racing league. They proved their skills as mechanics and then, at Wilbur’s suggestion, opened a bicycle shop. By 1896 they were making their own bicycles, having built their production machinery and even a single-cylinder internal-combustion engine to power the works. Orville thought about possibly making automobiles as well, but Wilbur scoffed at the idea. Had this been all they did with their lives, working with bicycles and a printshop, their father could have congratulated himself on having raised two principled, self-reliant, and commercially successful young men. But the brothers would now take their lives in a very different direction.A SEED IS PLANTED
In 1878, succumbing to one of his frequent spasms of wanderlust, Milton Wright had moved his young family to Cedar Rapids, Iowa. Church business frequently took him out of town, and as an attentive and loving parent, he always brought gifts back from his trips. Late that summer, returning from one such journey, he called 11-year-old Wilbur and 7-year-old Orville to his side, and then, as they watched expectantly, he opened his closed hands wide. A toy leaped upward, whirring its way to the ceiling, where it briefly bobbed and bounced as if struggling to drill its way onward to freedom. Years later Orville would recall, “Our first interest [in flight] began when we were children. Father brought home to us a small toy actuated by a rubber spring which would lift itself into the air. We built a number of copies of this toy, which flew successfully.” Attempts to scale up the little helicopter failed, for the boys did not understand what as adults they would, that doubling the size of a model requires an eightfold increase in its power. So they gradually turned to other pursuits. But in the back of their minds a seed continued to germinate, and its first shoots broke through in 1896, when they learned of the death of Otto Lilienthal.
The news galvanized them to action. Clearly Lilienthal had lost control of his glider. They knew he had directed it by shifting his body and they concluded this must be an inferior and potentially fatal means of controlling a flying machine. So, as Orville subsequently recalled, “We at once set to work to devise a more efficient means of maintaining the equilibrium.” Events actually moved more slowly than he remembered. Only in the spring of 1899 did the brothers seek to expand their knowledge, when on May 30 Wilbur Wright wrote to the Smithsonian Institution.
On the morning of Friday, June 2, 1899, Richard Rathbun, assistant secretary of the Smithsonian, sitting at his desk in the Gothic Smithsonian Castle, peered through his spectacles at the letter that had just arrived from Ohio. “I have been interested in the problem of mechanical and human flight ever since as a boy I constructed a number of bats of various sizes after the style of Cayley’s and Penaud’s machines,” the writer began. He went on to explain his faith in human flight and announced his intention to embark on “a systematic study of the subject in preparation for practical work.” Somewhat defensively he concluded: “I am an enthusiast, but not a crank in the sense that I have some pet theories as to the proper construction of a flying machine. I wish to avail myself of all that is already known and then if possible add my mite to help on the future worker who will attain final success.”
For many bureaucrats approaching the end of a workweek, Wright’s words would have earned the letter a quick drop in a wastebasket, its author dismissed as another deluded hayseed. To his very great credit, Rathbun neither pitched the letter nor fobbed it off on an assistant. Instead, with a few quick pen strokes, he directed his staff to assemble some materials for him to send Mr. Wright—probably the most influential action ever undertaken by any Smithsonian administrator. Of course he could not have realized the significance of what he had done. Perhaps as an end-of-week treat he left to lunch at the Cosmos Club with other loyal members. If so, one wonders what he replied when they asked how his day was going: certainly not that he had just played a major role in the transformation of the entire world.
A few weeks later the Wrights received the package of reading materials assembled by Rathbun’s staff, including suggestions referencing virtually every significant text then existing on flight: Octave Chanute’s Progress in Flying Machines ; James Means’s three Aeronautical Annuals for 1895,1896, and 1897; Samuel Langley’s Story of Experiments in Mechanical Flight and Experiments in Aerodynamics ; E. C. Huffaker’s On Soaring Flight ; Louis-Pierre Mouillard’s Empire of the Air ; and Otto Lilienthal’s The Problem of Flying and Practical Experiments in Soaring . The Wrights subsequently credited these works with giving them “good understanding of the nature of the problem of flying” and in particular noted that Mouillard’s and Lilienthal’s writings “infected us with their own unquenchable enthusiasm and transformed idle curiosity into the active zeal of workers.”
It is unclear if the admirable Rathbun ever recollected Wilbur Wright’s letter and his role in instigating the brothers’ work. He probably did not; mention of the Wrights or their correspondence is absent from Rathbun’s obituaries or the recollections of others who knew him. Rathbun died suddenly at the age of 66 on Tuesday, July 16, 1918, having lived long enough to get used to the sight of growing numbers of airplanes flying over the nation’s capital and apparently not realizing his own key role in making it all possible.THE THREE KEYS TO FLIGHT
In 1923 Charles-Edouard Jeanneret-Gris wrote: “The airplane mobilized invention, intelligence and daring: imagination and cold reason . It is the same spirit that built the Parthenon.” Coming as it did at a time when most airplanes remained frail craft of wood and wire, possessing only modest performance, such a statement might well have smacked of exaggeration. But this was no ordinary spokesman, it was the Swiss architect Le Corbusier, the leading exponent of the modern movement that was challenging accepted doctrines and arguing for a new style blending engineering aesthetics and architecture. The French aviator-philosopher Antoine de Saint-Exupéry considered designing an airplane less a matter of engineering than a matter of art, akin to creating a great sculpture. “Have you looked at a modern airplane?” he asked his readers.“Have you ever thought… that all of man’s industrial efforts … invariably culminate in the production of a thing whose sole and guiding principle is the ultimate principle of simplicity?… perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away, when a body has been stripped down to its nakedness.… [The sculptor-designer] is not so much inventing or shaping … as delivering the image from its prison.”
If Le Corbusier’s comments pointed to the significance of what the Wright brothers accomplished, “Saint-Ex” indicated the root of their success, their extraordinary ability to cut to the heart of a design problem, find a solution, pursue it vigorously to completion, and then integrate it with solutions to other challenges, the whole adding up to a successful airplane. Where their predecessors chose complexity, the Wrights chose straightforward design. Where their predecessors slavishly emulated the lines of a bird or a bat, the Wrights selected the purity of the straight line and the Pratt truss. Where their predecessors left only sporadic documentation, the Wrights generated voluminous correspondence, study papers, commentary, critique, and diaries. They were at heart technological minimalists, and through them and their influence it is understandable why Le Corbusier and other prophets of the modernist era (such as Saint-Exupéry, Norman Bel Geddes, and R. Buckminster Fuller) found flight not only congenial but downright seductive.
The key Wright contributions to achieving flight were threefold. First and most significant, the brothers recognized that the most important problem was that of control. All else was secondary. It was not enough to get off the ground with lift and power; one had to be able to guide and steer the airplane and eventually return safely to earth. Second, they recognized the importance of integrating diverse technologies into a single, successful airframe. Third (to put it in somewhat modern terminology), they recognized that developing a successful airplane involved progressive flight research and flight testing, following an incremental path from theoretical understanding through ground-based research methods, then early flight trials with subscale models, and finally flight with full-size piloted machines.
Wilbur Wright expressed this philosophy very well when he compared flying to riding a “fractious horse.” Speaking in Chicago before the Western Society of Engineers in September 1901, he said: “Now, there are two ways of learning how to ride a fractious horse: one is to get on him and learn by actual practice [and] the other is to sit on a fence and watch the beast.… It is very much the same in learning to ride a flying machine; if you are looking for perfect safety, you will do well to sit on a fence and watch the birds; but if you really wish to learn, you must mount a machine and become acquainted with its tricks by actual trial.” In short, the Wrights exemplified the airman’s philosophy, the belief of the practitioner that actual experience must accompany theory.
Four challenges confronted anyone hoping to build a flying machine: designing and fabricating a suitable structure, powering the craft, ensuring it could generate sufficient lift to remain aloft, and giving it some means of control. Thanks to the research of Octave Chanute, structures did not pose a serious problem for the brothers. Likewise, thanks to a variety of pioneers (mostly German), propulsion no longer posed the problems that it had for would-be airmen, though the need for a light, powerful engine still demanded the highest possible engineering standards. But significant challenges remained. Since any successful flying machine must be capable of altering its flight path (climbing, circling, and flying against the wind), control, stability, and lift constituted critical technologies.
In their single-minded emphasis on mastering three-dimensional movement, the Wrights clearly differed from all their predecessors. They recognized immediately that two basic schools of researchers existed: those emphasizing power and lift (such as Samuel Langley and Hiram Maxim) and those emphasizing soaring flight (such as Lilienthal, Mouillard, and Chanute). “Our sympathies,” the brothers wrote in 1908, “were with the latter school.” Lilienthal’s vain struggle to regain mastery over his glider as it pitched upward caused the brothers to focus their work on control. In part they did this under the mistaken assumption that other problems—namely, how to design efficient wings and propellers—had already been resolved; they would soon learn otherwise.
The Wrights immediately rejected the idea of following the method used by Lilienthal, Chanute, and others of moving the body to control an airplane, recognizing that the pilot possessed a very limited range of motion and distance over which he could shift his weight; that the forces operating against him increased dramatically with the size of the machine, angle of attack, and speed; and that, finally, the pilot would in any case quickly fatigue himself. Any machine would have to have movable control surfaces, not an operator as a living bobweight. Indeed, the Wrights were the first to appreciate fully that an airplane moves, and thus must be controlled, in climbing and descending flight (nose-up or nose-down longitudinal pitching motion controlled by elevator inputs), yawing flight (nose-left or noseright directional motion controlled by rudder inputs), and banking flight (wing-up or wing-down lateral motion, controlled by wing warping or aileron or, later, spoiler inputs). All other motions are derivations or combinations of these.
Roll control, or “lateral balance,” as the Wrights termed it, constituted the most critical of all these challenges. When the brothers first began working, however, they thought it would be far easier to achieve than longitudinal (pitch) control. Researchers had long recognized the need for a movable rudder for directional (yaw) control and an elevator for longitudinal (pitch) control, but very few had considered the problem of lateral (roll) control. The Wrights focused on this and initially came to believe that if the machine had roll control, it might not require a movable rudder at all but merely a fixed vertical fin. (This was a mistake, rectified in their final glider of 1902-03.) It is likely that the brothers seized upon roll because of their background as bicycle makers. During a turn a bicycle banks into the turn, so that such a motion seemed completely natural to the brothers, in contrast with other aeronautical experimenters who envisioned airplanes making rudder-controlled flat turns similar to an automobile operating on a two-dimensional surface.
The concept of how to achieve control in roll seems to have occurred first to Orville Wright, who realized that if he could vary the lifting characteristics of the wings, the change in lift would cause one wing to rise and the other to descend, thus rolling the plane about its longitudinal axis. He sketched a wing with a fixed center portion but with the outer portions free to be pivoted about long shafts running from wingtip to wingtip. Structural problems kept him from pursuing this design, but then in July 1899 Wilbur Wright conceived of a more structurally sound means of changing the lifting properties of the wing via “wing warping.” The older brother took a cardboard box and demonstrated how one could twist it so that the top and bottom surfaces, representing the top and bottom wings of a flying machine, would flex. Slightly more than two decades later Orville recalled, “From this it was apparent… the wings on the right and left sides could be warped so as to present their surfaces to the air at different angles of incidence and thus secure unequal lifts on the two sides.” The two brothers immediately built a biplane kite spanning five feet. It had a two-bay Pratt-truss layout, with two sets of control cords running to the wingtips and attached at the tops and bottoms of the front support struts. As Dayton schoolchildren nearing the end of their summer vacation watched, the two brothers controlled the kite handily. The next step, they decided, would be a man-carrying machine, built according to the values of Lilienthal’s tables. In November 1899 they wrote to the U.S. Weather Bureau for information on places with suitable winds, thinking of testing their glider near Chicago, as Octave Chanute had done. Then, on May 13, 1900, Wilbur wrote his first letter to Chanute.
The letter begins with some hesitancy, almost a shyness. But very quickly the tone changes to one of surprising confidence, followed by the setting forth of a plan of action. “For some years I have been afflicted with the belief that flight is possible to man,” he states. “My disease has increased in severity and I feel that it will soon cost me an increased amount of money if not my life. I have been trying to arrange my affairs in such a way that I can devote my entire time for a few months to experiment in this field.” For his part Chan ute sent an encouraging reply and offered to meet with Wright any time he might visit Chicago, where the 68-year-old inventor had established a glider camp in the windy dunes of Lake Michigan. Thus began an extraordinary correspondence that would last until Chanute’s death in 1910. He soon became the brothers’ closest professional friend and confidant. Other letters followed, and, emboldened, Wilbur sent one on August 10 that undoubtedly stirred the old engineer. “It is my intention to begin shortly the construction of a full-size glider,” the Daytonian began provocatively, before asking how to procure quality wood and varnish. Chanute responded four days later, sending a recipe for varnish, an address for a suitable Chicago lumber company, and some practical advice: The brothers should select “sapwood, clear, straight-grained, and thoroughly seasoned.”
After receiving Chanute’s reply, in mid-August, the brothers set to work, rapidly building the glider, which followed the general configuration of their 1899 kite but of course was much larger. The glider reflected their thoughts on what a piloted airplane should be. The pilot would lie on, rather than hang from, the lower wing, assuming a prone position to reduce frontal resistance, and operating a “horizontal rudder” (as the brothers termed what is now called an elevator) located ahead of the wing. At first glance this made perfect sense. This “tail-first” or “canard” configuration accomplished two things. First, it gave the rudder much more refined and gentle behavior during a stall, the condition whereby a wing ceases to produce lift, typically at low speed and at a high angle of attack, as had happened in LilienthaPs fatal accident. Most conventional “wing-first” designs dive after a stall, for the wing loses lift, the airplane drops nose down, and the tail stabilizes it. The pilot must wait to recover until the wing is going fast enough to produce lift and the tail surfaces are going fast enough to enable a pullout. Although all this takes only seconds at most, if the airplane is close to the ground, as with Lilienthal, the result can be a catastrophic plunge to the earth. But a tail-first canard configuration has totally different characteristics. The little canard surfaces stall while the main wing is still producing some lift. The airplane typically develops a modest sink rate, but not a headlong dive. Dropping the nose slightly and accelerating beyond stall speed quickly restores control. And the brothers’ choice had a second benefit as well: In the event of a crash, the front structure of the elevator and its supports would act like a supersize shock absorber. Subsequent experience gave the brothers the opportunity to demonstrate both advantages.
But they learned as well about the canard’s surprising disadvantage, a byproduct of a serious weakness in the general study of aviation at the end of the nineteenth century—the lack of understanding of the basic mechanics of flight. To put it bluntly, the two brothers had no appreciation for the subtleties of aircraft motions, but then neither did anybody else. Early pioneers recognized translational motions, those referring to the four forces of flight: lift, produced by the wing; weight, the gravity-imposed burden of flight; thrust, generated by the engine’s power driving the propeller; and drag, the resistance produced by the airplane’s moving through the air. They knew that flight involved a balancing act among these four forces: Lift had to equal weight, thrust had to equal drag, and steady, stable “equilibrium” flight demanded that the center of pressure (the lifting point acting on the wing) should correspond to the airplane’s center of gravity. But they did not appreciate how this changed for an airplane in real-world flight. Gusts of wind and maneuvers, even simple climbs and dives, introduce rotational torques and motions (called moments ) that act upon an airplane, and these demanded a far more sophisticated approach to stability and control—namely, the recognition that an airplane has a neutral point, and as a result (depending on its design) either stable or unstable flying characteristics. Had they known the implications of this, it is likely they would have rejected the canard configuration outright, for it caused a serious stability problem that more than offset its perceived advantages.
The Wrights cannot be faulted for not understanding this concept, which aerodynamicists would first comprehend more than two full decades after the triumph at Kitty Hawk. Every lifting surface has a so-called aerodynamic center where the lift and drag forces act upon a single point. It is normally located at approximately the quarter chord (that is, one-fourth of the distance between the leading and trailing edges). The rotational moment acting about this point is called the pitching moment. Now, if one applies the notion of the aerodynamic center to the entire aircraft, by considering the forces and moments acting on all its lifting surfaces—that is, the wings and tail (or canard) surfaces—one derives an overall single aerodynamic center for the entire aircraft, and that is the neutral point. An aircraft with both its center of gravity and the wing’s aerodynamic center ahead of its neutral point is inherently stable. For example, if it raises its nose, its lift increases, and the pitching moment becomes negative, tending to restore the aircraft to its original position—that is, a state of equilibrium. This is the configuration of the classic “wing forward, tail aft” airplane.
But the canard—“wing aft, tail forward”—airplane has its aerodynamic center behind the neutral point, and typically its center of gravity as well; as such it is inherently unstable. Its stability can be maintained only by the pilot’s deliberately holding (“fixing”) the controls firmly, or by extraordinary ballasting of the nose with compensatory weights (thus bringing the center of gravity forward) to make it inherently stable, or in the modern era by an electronic flight-control system that constantly deflects control surfaces to keep the airplane in trim. By innocently adopting the canard configuration because of what they perceived as desirable stall and safety characteristics, the Wrights unknowingly also adopted an inherently unstable configuration, exacerbated by the mass distribution of the design they eventually produced, which had the pilot, wing cell (the upper and lower wings), and eventually fuel and engine all located very far aft. Thus, that their gliders and powered canard aircraft were all unstable wasn’t the result of the brothers’ deliberate choice but simply an accidental and natural outgrowth of their having selected the canard configuration in the first place. The absence of any inherent stability demanded that the brothers absolutely master flight-control technology, for they would have to work the controls constantly to keep their gliders and powered machines aloft. It is a measure of the brothers, their abilities, and their persistence that they were able to confront these challenges and persevere.KITTY HAWK
The Wright brothers selected Kitty Hawk, North Carolina, for their experiments after studying the data sent them by the U.S. Weather Bureau. The recorded winds were so favorable that they abandoned thoughts of using the far closer (and more crowded) Great Lakes coastline. When Wilbur arrived at Kitty Hawk for the first time, in September 1900, he had with him a 17-foot-wingspan biplane glider. The Wrights made their first flight attempts in early October. They found the glider “a rather docile thing” but to their discomfort also found that its tailfirst configuration lacked the inherent stability they had believed it would possess. In fact, the kite-glider flew with “much improved” stability backward, with the canard elevator behind the wing (that is, like a conventional biplane). At this point the brothers could have abandoned the canard and moved on, adopting configurations more like those seen with the European aircraft after 1907. But so concerned were they about avoiding a Lilienthal-type accident that, as Orville recalled years later, “we retained the elevator in front for many years because it absolutely prevented a nose dive.” So they chose to live with the canard’s nagging instabilities. And they would eventually retain the configuration for too long, until 1911, by which time world aviation design had left it and them far behind.
Despite the lack of stability, tests with an operator on board were highly encouraging; in particular, the ease with which the brothers could control the glider in “fore-and-aft balance [longitudinal control] was a matter of great astonishment to us,” Wilbur Wright wrote to Chanute. “And although in appearance it was a dangerous practice we found it perfectly safe and comfortable … and the machine was not once injured although we sometimes landed at a rate of very nearly 30 miles per hour. The operators did not receive a single bruise.…The distance glided was between three and four hundred feet at an angle of one in six [i.e., one foot in descent for every six feet forward].” Greatly encouraged, the Wrights returned to Dayton and the business of running a bicycle shop in late October, abandoning their first glider on the side of a Kitty Hawk sand dune. A local woman used its French sateen covering to make dresses for her two daughters, and a passing gale destroyed the remains of the historic machine nine months later. The Wrights had demonstrated practical longitudinal and lateral control, basic handling qualities and landings, and had made some rudimentary measurements of lift and drag characteristics. The glider did not have a rudder or even a vertical fin, and much remained to be done, but much had been accomplished.
In July 1901 the brothers returned to Kitty Hawk with a new and much larger biplane glider, spanning 22 feet with a wing area of 290 square feet and also with a forward elevator. Designed in complete accordance with LilienthaPs aerodynamic tables, it had his circular-arc airfoil section for its wings, featuring a thickness-chord ratio (the ratio of wing thickness to the length of the wing from its leading edge to its trailing edge) of 8.33 percent—that is, 1 in 12 (1 inch of thickness for every 12 inches in chord length). The earlier 1900 glider had had much thinner wings, with a thickness-chord ratio of about 4.3 percent, a camber of 1 in 23. Not surprisingly, since lift loves a thick wing, the brothers discovered that the 1900 glider had disappointing lifting characteristics, but they also suspected, for the first time, that perhaps LilienthaPs data might be in error. In any case they were certain the 1901 machine would perform much better.
But it didn’t. In fact the 1901 machine performed far worse than the 1900 glider, having a lifting capacity “scarcely one third of the calculated amount.” The brothers concluded that they had several problems: The anemometer used to measure wind speed was off by 15 percent, a number used in determining lift called Smeaton’s coefficient must be off by “at least 20 percent,” LilienthaPs lifting values were wrong by at least 50 percent, and finally, the biplane configuration itself must cause a slight but still significant reduction in lift over a single-wing monoplane having the same total wing area. Further, the front elevator hardly worked at all, requiring extreme inputs to achieve even basic longitudinal control.
This last problem was the most serious and, in view of the pleasing results of the earlier 1900 glider, the most unexpected. From comments by two visitors who had worked with Chanute and were attempting to fly a glider of their own, the Wrights learned that the elevator problem might stem from a reversal of the center of pressure location on the wing’s thicker airfoil at low angles of attack. As the wing’s angle of attack decreased, the center of pressure would move forward. But when the angle decreased to the point where the oncoming wind hit the leading edge of the wing—in other words, the top of the wing’s upper surface—the center of pressure would reverse rapidly, moving toward the trailing edge of the wing. This generated a pronounced nose-down trim problem. If the pilot corrected it by a large control-surface input to the elevator, the angle of attack would increase and the center of pressure would reverse yet again, this time moving forward toward the leading edge, until the angle of attack increased still further, whereby the center of pressure would again move aft. This back-and-forth center-of-pressure travel eventually would get the pilot into what is now termed a “pilot-induced oscillation,” and his efforts to control it might actually make it worse. Besides giving the glider an unseemly up-and-down motion, the problem posed a serious danger of the pilot’s losing control at low altitude and diving into the ground. After thinking about what their visitors said, the Wrights reduced the wing’s camber from 1 in 12 to about 1 in 19, closer to the 1900 glider’s airfoil shape. Thus modified, the glider flew better, more like the 1900 machine. On August 4 Chanute arrived for a week’s stay, and he wrote in his diary: “A number of excellent glides were made, Mr. Wilbur Wright showing good control of the machine in winds as high as 25 miles an hour.… Longest flight about 335 feet.”
Then another problem cropped up. With the longitudinal control problem apparently solved, Wilbur set out to try a turn using wing warping. The Wrights very ingeniously used a hip cradle that the pilot could slide from side to side. The cradle pulled cables that twisted the wings to generate a change in wing camber and hence vary the lifting characteristics between the right and left wings. When Wilbur tried a left turn, the glider obediently started to bank to the left. Then, as the left wing lowered, the turn suddenly reversed, and the plane began rotating to the right. He hastily managed to straighten out and land.
Something was seriously wrong, and it was beyond their ability to resolve at Kitty Hawk. Amid heavy rains mirroring their disappointment and confusion, they broke camp at Kill Devil Hill on August 20 and headed back to Dayton, arriving home two days later. At least they could take comfort in having learned one important lesson from the 1901 glider: Their ideas about longitudinal control and the lifesaving value of the front elevator worked. On their second day of testing, they had faced potential disaster, a mirror image of LilienthaPs fatal accident almost exactly five years before. As Wilbur Wright recalled, “In one glide the machine rose higher and higher till it lost all headway. This was the position from which Lilienthal had always found difficulty in extricating himself, as his machine then, in spite of his greatest exertions, manifested a tendency to dive downward almost vertically and strike the ground head on with frightful velocity. In this case a warning cry from the ground caused the operator to turn the rudder [i.e., elevator] to its full extent and also to move his body slightly forward. The machine then settled slowly to the ground, maintaining its horizontal position almost perfectly, and landed without any injury at all.… Several glides later the same experience was repeated with the same result.”
But this was really the only good news. The Wrights left Kitty Hawk so discouraged that Wilbur confided his worst fear to Orville: Man wouldn’t fly “for fifty years.”WHEN ALL THE DATA WAS WRONG
As the fall of 1901 approached, the Wrights were in serious trouble. After the disappointment with the 1901 glider, lesser men might have walked away from the problem of flight. The Wrights themselves might have wasted time trying to rationalize all the data they had from Lilienthal, Chanute, and the rest of the relevant pioneers. Instead, again exemplifying remarkable self-confidence and perseverance, “we cast it all aside,” as Wilbur put it, “and decided to rely entirely upon our own investigations.” The next phase in the brothers’ work involved comprehensive ground-based research. They built a special test rig with a wheel balance placed on the front of a bicycle and subsequently built a small wind tunnel and measuring balances. The Wrights were setting out to develop their own aeronautical tables.
The result of that work, undertaken over a three-week period, radically reshaped their thoughts and guaranteed the success of their future ventures. They first evaluated approximately 200 wing shapes and then settled on detailed testing of 38 shapes having different cambers and curvatures, a range of aspect ratios (the ratio between length and width) from perfect squares to long rectangles to a variety of curved and elliptical shapes. They made lift and drag measurements, tested airfoil behavior at a variety of angles of attack, and evaluated the influence of multiplane configurations with the test wings mounted one above the other. Out of this work came the most reliable compilation of airfoil data yet assembled. By December 1901 the Wrights had collected a set of data that they could use with total confidence and that was reliable enough to extrapolate from. Only in two areas were their tests deficient: They made no measurements of center-of-pressure travel (which could have given them insight into pitching moments and canard instability), and they spent a great deal of effort determining the optimal lift characteristics of highly cambered airfoils, emphasizing lift at the expense of stability. But, again, in the absence of a broader understanding of flight mechanics, these deficiencies are understandable as well as forgivable.
At this point, to Chanute’s consternation, the brothers had to withdraw briefly from their aeronautical research to look after other affairs, among them planning and manufacturing for the 1902 spring and summer hiking season. But by early summer the brothers could turn their thoughts back to flying. They designed a new biplane glider, spanning 32 feet, weighing about 260 pounds, including the pilot, and having, in addition to its elevator, a fixed, double-surface, nonmoving vertical fin, intended to prevent the kind of turn reversal they had experienced with the 1901 glider. Its wings were long, narrow rectangles, giving it an aspect ratio twice that of their earlier machines. They completed assembly of the glider at midday on Friday, September 19, 1902, incorporating some of the 1901 glider’s wing struts in its structure, and began test-flying it that afternoon. The flights revealed that as it glided down the slope of a dune, it lacked sufficient stability in a crosswind to prevent the gust from raising a wing and upsetting the machine. Earlier, in tests of their original 1900 glider, the brothers had noticed the same problem and related it to the flight of birds, specifically whether a bird flew with its wings dihedral (sweeping upward at the tips), level, or anhedral (sweeping down at the tips). Wilbur Wright had recorded in a notebook, illustrated with little drawings: “The buzzard which uses the dihedral angle finds greater difficulty to maintain equilibrium in strong winds than eagles and hawks which hold their wings level.… a buzzard soaring in the normal position [i.e., with dihedral] will be turned upward by a sudden gust. It immediately lowers its wings, much below its body [i.e., anhedral].”
So in an attempt to enhance the glider’s stability in gusts, they decided to re-rig the wings with a modest anhedral, trussing them spanwise so that they drooped noticeably at the tips when viewed from the front or the rear, four inches lower than in the center of the wing arch above the prone pilot. On Monday, September 22, they tried out the modification, operating the glider as a tethered kite, and noted, “The machine flew beautifully,” weathering crosswinds without upset. But the next day Orville crashed “while sailing along smoothly”; the glider abruptly rolled and yawed, then pitched upward as he tried to return to wings-level flight. It promptly stalled and spun into the dunes, the hapless pilot winding up in “a heap of flying machine, cloth and sticks in a heap, with me in the center without a bruise or a scratch.” Although the brothers didn’t recognize why, the anhedral aggravated the design’s already poor roll characteristics, generating what engineers now call a “spiral-mode instability” and contributing significantly to the tendency of the glider to tighten its turns and begin a spiraling descent into the ground. Repairs took a few days, and then the brothers returned to the air. By early October the Wrights knew they had licked the problem of lift; their glider was flying more than 500 feet, with perfect longitudinal control and gentle flying characteristics. A year before, Wilbur Wright had declared that flight would not be achieved in the brothers’ lifetime. Now he could confide to his father, “We now believe that the flying problem is really nearing its solution.”
But the spiral-mode instability generated serious and continuing problems. The fixed, double-surface, vertical tail, looking like a little biplane itself, did improve the glider’s handling qualities, ending the rapid rotation (virtually a spin) the 1901 machine had encountered after turn reversal. However, now the glider would tighten its turn into a spiral, sliding (what is termed sideslipping) down the inside of the spiral and usually slamming into the ground in a process the Wrights called “well digging.” What caused this was a simple problem: As the glider turned, the lowered wing—the wing inside the turn—would slow, thereby losing lift and naturally lowering even further. Since the Wrights were flying at most a few feet over the dunes, rarely higher than the wingspan of their gliders, the glider would thus occasionally strike the ground.
So the brothers next made their most important change since developing wing warping: They decided to change the fixed vertical tail into a movable rudder, and they linked the rudder to the wing-warping controls so that whenever the pilot warped the wings, the rudder would pivot in the appropriate direction to assist in turning the glider. At the same time, they changed the vertical tail from a two-surface, fixed tail to a single-surface, movable rudder. Having thus modified the 1902 glider, the brothers flew it hundreds of times—375 flights in six days, including about 250 flights in just two days—gliding up to 622 feet at a time. These flights, still unavoidably at low altitudes, could not enable full assessment of turning performance, but the glider did perform much better in its shallow turns and banks, demonstrating that the movable rudder linked to the wing-warping mechanism clearly improved controllability. The movable rudder also compensated for the anhedral-aggravated spiral-mode instability, still unrecognized by the brothers. Though it made the instability controllable, the rudder did not overcome it; that came much later, in 1905.
But things were getting better, to the point where the Wrights could contemplate putting an engine on an airplane and powering their way into the air. They could do so because by now they had no superior in their airmanship or understanding in flight. On October 23 Orville said as much, writing to his sister, Katharine: “The past five days have been the most satisfactory for gliding that we have had.…We have gained considerable proficiency in the handling of the machine now, so that we are able to take it out in any kind of weather.… we now hold all the records!” As this letter reveals, the pace of the Wright brothers’ flight research was nothing short of remarkable. They returned to Dayton on the last day of October 1902, their spirits elevated far beyond where they had been the previous year. Then they had confronted perplexing and seemingly incomprehensible problems. Now, with the 1902 glider, they realized they had at last mastered aircraft design, and in light of this they filed for a patent to protect their rights and secure recognition as the true inventors of the airplane. However premature this may have seemed, however much more remained to be done, they knew they were ready for the final step, building a powered machine.INTERNAL COMBUSTION
The brothers had the good fortune to have their work coincide with the development of the internal-combustion, petroleum-fueled engine. In 1860 two inventors, Pierre Hugon and Etienne Lenoir, independently developed the first modestly successful internal-combustion engines in the world. Hugon’s remained a technological curiosity, but Lenoir’s entered production. Very crude, extremely noisy, and rough-running (to the point of alarming onlookers), this “double-acting” engine burned a mix of air and illuminating gas sucked into a piston and detonated, propelling the piston on its power stroke. Then another mix of air and gas entered behind the piston, detonated, and drove the piston back to its starting position.
In 1876 Nicolaus Otto, a salesman with a penchant for mechanical tinkering, built a model of the Lenoir engine and was determined to smooth and refine its operation. He had an important and surprising insight. An engine would operate more efficiently if it employed four strokes instead of two in each operating cycle: an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. He quickly built a demonstrator engine. First the piston pulled a partial vacuum in the cylinder, drawing in a fuel-air mixture. Next the piston moved toward the top of the cylinder, compressing the fuel-air mix. Then an ignition flame detonated the mix, driving the piston downward. Finally the piston moved back to the top of the cylinder as the waste exhaust gases vented out of the engine. On the face of it, this seemed counterintuitive—if one wished to increase an engine’s operating power and speed, it would seem important to increase the number of power strokes, not reduce them. But it turned out that the compression stroke was every bit as crucial to good engine performance as the power stroke and more than compensated for having only one power stroke in every four.
It was a breakthrough, even though Otto himself seems not to have fully appreciated just how much the four-stroke cycle revolutionized engine design. Four other Germans, Gottlieb Daimler (who had worked for Otto), Karl Benz, Wilhelm Maybach, and Rudolf Diesel, played key roles in making the four-cycle engine a transportation success, particularly by reducing its weight, by introducing carburation, a liquid fuel (gasoline), and electrical ignition, and (in the case of Diesel) by abandoning conventional carburetion and ignition in favor of high working internal pressures allowing the use of crude, heavy fuels. The first automobile engines from Daimler, Benz, and Maybach furnished about one horsepower for 150 pounds of engine weight. Then, after continued refinement, in 1901 the first Mercedes automobile appeared, with a 35-horsepower engine weighing only 14 pounds per horsepower. This rapid development removed the last propulsion barrier to the practical airship and airplane. Thus, when the Wrights needed a power plant, the technology base existed for them to make one.
So fortunately all the elements that would make a successful airplane—structures, aerodynamic understanding, controls, and propulsion—were readily at hand. After having returned to Dayton and caught up on work, the brothers sent out letters to the leading internal-combustion engine manufacturers around the world, soliciting information on obtaining an engine producing at least 8 horsepower and weighing no more than 180 pounds. Most companies ignored the inquiry or sent dismissive or overly optimistic replies. At worst the brothers found this an annoyance, for they had, after all, already designed and built the engine that powered their bicycle factory. And they had an ace in the hole as well, a very gifted self-taught mechanic, Charles (“Charlie”) Taylor. Born in Illinois in 1868 and raised in Nebraska, Taylor met the Wrights through his wife, Henrietta, who knew their father. He moved to Dayton in 1896, set up a machine shop, and worked as a subcontractor for the brothers, making bicycle repairs and specialized parts. In 1901 he joined the Wrights full-time, in part because the brothers needed someone to run their business while they undertook their flying experiments in North Carolina. Taylor very much became a member of the Wright “team.”
The Wrights seem never to have thought about a twin-engine airplane, though they deliberately chose a twin-propeller approach. As in everything else about their work, practicality dominated. Here was where Taylor’s superior mechanical skills came into play, as he took charge of transforming the brothers’ plans into a workable engine by using a lathe and drill press. Concerned about vibration, the brothers chose a four-cylinder configuration for their engine, to achieve smoothness of operation, and, in a bid to keep weight low, opted for forming the crankcase and water jacket as a single one-piece aluminum casting. (Dayton possessed a number of small specialized machine shops, and finding a qualified local foundry to do the casting proved no difficulty.) It had a machined steel crankshaft connected to a heavy flywheel, with cast-iron cylinder barrels and pistons. Overall, it measured not quite 33 inches long, 27 inches wide, and 16 inches high, and with its flywheel-driven, ignition-sustaining magneto installed, weighed a total of 179 pounds. The Wrights and Taylor began construction of the engine in December 1902 and had it ready for testing in early February. On Friday, February 13, the engine fractured, requiring a new aluminum casting, which did not arrive until mid-April. Thereafter, testing went smoothly, the Wrights bettering their estimated performance requirement of 8 horsepower with an actual attainment of 12 horsepower at 1,090 revolutions per minute. Now they had their engine.
The brothers realized that propulsion involved more than merely developing an engine. The power had to be transmitted to the propellers, and the propellers themselves had to be as efficient as possible. Here too the Wrights’ directness and preference for the simple clearly showed. They chose a twin-propeller layout (for two propellers would act upon a greater quantity of air) and located the propellers behind the wings, making them turn in opposite directions to cancel out each other’s torque. When viewed from behind the airplane, the left propeller would rotate counterclockwise and the right one clockwise. The single engine would drive both, but rather than rely on some sort of complicated and heavy shafting and gearing arrangement, they chose a simple approach that reflected their bicycle business: two bicyclelike sprocket chains running from the engine hub, one to each steel-tube propeller shaft. This chain-drive system was simple, effective, and low risk. Moreover, it enabled the brothers to experiment with a wide range of speed ratios for their propellers, something that direct drive would have prevented.
As for the propellers, the Wrights recognized, as had few other pioneers, that a propeller is really a rotating wing with a twist, following a helical path through the air. It generates a forward lift vector, in contrast with the popular image of an “airscrew” that somehow bores its way through the sky. Thus maximum propeller efficiency demanded the same kind of refined aerodynamics that the brothers had already demonstrated with their gliders. They quickly discovered that the existing literature on maritime propellers had no relevance to the kind of propeller they needed for a flying machine. Therefore, in mid-December 1902, they began an aggressive program of research, eventually arriving at a long, elegant, high-aspect-ratio propeller shape far superior to the fan, screw, angled flat-plates, and “bird feather” approaches taken by other would-be aviators. Shaping wooden propellers requires careful woodworking to ensure balance and match the lifting characteristics of the blades, for an unbalanced propeller can induce vibration and loads, destroying an engine or tearing it from its mount. Again their confidence showed, for the brothers did their own woodwork, bonding three laminations of spruce together and, after it thoroughly dried, hewing the complex shape with a hatchet and drawknife, carefully varying the blades’ angle of attack from eight and a half degrees at the tip to four degrees near the root. Overall the propeller had a diameter of eight and a half feet and a maximum blade width of eight inches.THE FLYER
Compared with the propulsion challenges, the airframe of the new airplane represented simply a larger extrapolation of the 1902 glider, but with reinforced ribs, longer landing skids, a 10-inch wing droop for stability (a mistaken continuation of the anhedral idea), a 1-in-20 airfoil camber, and a double-surface—not single-surface—rudder. It spanned 40 feet 4 inches, with a wing chord of 6 feet 6 inches, and had a total wing area of 510 square feet. The “horizontal rudder” (canard elevator) had an area of 48 square feet, and overall the machine had a length of 21 feet 1 inch and a maximum weight of 750 pounds, including the pilot, giving it the very low wing loading of 1.47 pounds per square foot. It still had the inherently unstable tendencies of its predecessors, and no wonder. Fully 94 percent of the empty weight of the 1903 Flyer was bounded by the distance from the leading to the trailing edge of the wing, giving it an extreme-aft center-of-gravity location (well behind the neutral point). The pilot still lay prone in a hip cradle offset just to the left of the aircraft’s centerline, and the engine counterbalanced him by being offset to the right. Here too the Wrights had given clear thought to safety, for they had no desire to risk the engine’s breaking loose in a crash and crushing or pinning the pilot, as might be the case if it were installed behind him. (To offset the heavy engine, which weighed 34 pounds more than the pilot, the right wing had an additional four inches of span.) A small tank containing a quart of gasoline was affixed to the top of the left inboard wing strut, feeding the engine by gravity, and the radiator ran vertically along the right inboard strut. The plane, which they called the Flyer , would rest on a small takeoff dolly or truck running along a 60-foot monorail launching track pointing into the wind. They finished the new craft over the summer of 1903 and then, in late September, left with it for Kitty Hawk.
Nature and chance still held surprises for the Wrights. A fire destroyed a railroad depot in Elizabeth City, North Carolina, together with a quantity of shipped goods, but fortunately not those of the Wrights, which had passed through a few days earlier. Several days after they had set up their camp and made some refresher flights in the 1902 glider, a 75-mile-an-hour gale blew through, driving five vessels ashore, threatening to tear apart their shed and all within and forcing the brothers to take hammer and nails to the roof in the midst of howling wind and drenching rain. When the weather cleared, the brothers continued their flights in the glider and assembled what they called “the whopper flying machine,” finishing by November 5.
The Wrights were in for one last bad scare when they discovered they had underestimated the plane’s weight by more than 75 pounds. Could the engine haul the extra weight? Fortunately, tests at Kitty Hawk revealed they had also underestimated the performance of their propellers, which produced over 50 percent more thrust than they had anticipated. The two underestimates canceled each other out: The Flyer could fly. The last great challenge the Wrights faced was getting the propulsion system to work smoothly. Engine runs revealed irregular operation, loosening chain sprockets, and fracturing propeller shafts. They adjusted the gasoline feed to smooth out the engine and eventually fixed the sprocket nuts in place with tire cement, curing that problem, but the fracturing steel-tube propeller shafts proved more difficult to resolve. Eventually Orville returned to Dayton and made solid-steel shafts, the single greatest reason why the Flyer could not attempt its first flight until mid-December.
On December 12 the brothers installed the new propeller shafts. Two days later they made their first flight attempt. A coin toss decided in favor of Wilbur, and the brothers placed the launch track on a small incline, facing downhill. They started the engine, and the Flyer roared down the track and into the air. Wilbur overcontrolled the sensitive front elevator, and the unstable Flyer pitched up, stalled, and settled gently to earth 60 feet beyond the end of the launch rail not quite four seconds into its flight, though not gently enough to avoid breaking some of its front elevator supports. Any previous pioneer—and many afterward—would have been happy to claim this as a first flight, but not the brothers, who had every confidence they could soar high over the dunes, perhaps as high as 1,000 feet. Repairs took the next two days. Even so, the brothers were confident and sent a message to their father concluding, “success assured keep quiet.”
The next attempt came on Thursday, December 17. Earlier in the week the weather had been warm, but the seventeenth dawned fiercely cold, with a 27-mile-an-hour wind gusting across the hills from the north. Winter was settling in, and the Wrights were running out of time to make a first flight before having to break camp and return to Dayton. But nothing was going to stop them now, and they pressed on. Volunteers from the Kill Devil Hill lifesaving station helped them take out the Flyer and lay down the sections of launch rail, this time on a level stretch of ground, an important distinction that would aid them in silencing other claimants for the first-flight crown in years ahead. As his colleagues W. S. Dough, A. D. Etheridge, and W. C. Brinkley, along with Johnny Moore, a teenage boy from nearby Nags Head, watched the brothers, John T. Daniels waited by the camera, perhaps little realizing that he would capture one of the most important images ever on film; at a distance Capt. S. J. Payne and Robert Wescott watched through spyglasses from different stations.
Orville carefully got on the machine and lay down in the hip cradle, his left hand holding a vertical lever on his left that controlled the front elevator. With his right he started the engine by moving a small horizontal lever on the wing, rotating it horizontally like the hands of a clock from the one o’clock “off” position to the twelve o’clock position, to open a fuel cock, priming the engine. Behind him Wilbur swung one of the propellers, and the engine fired. It settled down to a steady rasping putter, the chains racing with their characteristic clicking sound as they passed over the gear teeth, and the twin propellers thrummed like giant fans. Satisfied, at 10:35 A.M. Orville moved the starting lever to the eleven o’clock position, breaking a frail cotton tie-down that tethered the Flyer to its launching rail. At once the Flyer began to move down the rail, supported by the little carrying truck and heading into the teeth of the wind. Wilbur ran alongside, steadying the right wing, and Orville carefully controlled the elevator with his left hand, holding on to the wing’s leading edge with his right and bracing the insteps of both his feet against footrests at the trailing edge of the lower wing.
Orville wrote in his diary: “On slipping the rope the machine started off increasing in speed to probably seven or eight miles. The machine lifted from the truck just as it was entering on the fourth rail [section]. Mr. Daniels took a picture just as it left the tracks. I found the control of the front rudder quite difficult on account of its being balanced too near the center and thus had a tendency to turn itself when started so that the rudder was turned too far on one side and then too far on the other. As a result the machine would rise suddenly to about ten feet and then as suddenly, on turning the rudder, dart for the ground. A sudden dart when out about 100 feet from the end of the tracks ended the flight. Time about 12 seconds (not known exactly as watch was not promptly stopped).”
Daniels’s photograph is one of the seminal images of the twentieth century, and indeed one of the most remarkable documents, visual or otherwise, from all human history. It shows a revolutionary moment. The Flyer has lifted off the launch track, Orville is struggling with the elevator (almost fully deflected), and Wilbur, excited, is running alongside. Wilbur made the next flight, then Orville his second, and finally, at noon, Wilbur flew for 852 feet in 59 seconds. Shortly after, an errant wind gust rolled the machine over, breaking it up; it would never fly again. Orville Wright immediately sent another telegram home: “Success four flights Thursday morning all against 21 mile wind started from level with engine power alone average speed through air thirty-one miles longest 57 seconds inform press home Christmas.”
The world had changed forever, as young Johnny Moore realized: He ran down the beach after the last trial exuberantly shouting to another native, “They done it, they done it, damned if they ain’t flew!”