Toward flight . On July 27, 1899, the brothers put
wing warping to the test by building and flying a biplane kite with a wingspan, and a curved wing with a
chord. When the wings were warped, or twisted, the trailing edge that was warped down produced more lift than the opposite wing, causing a rolling motion. The warping was controlled by four lines between kite and crossed sticks held by the kite flyer. In return, the kite was under lateral control. In 1900 the brothers went to
Kitty Hawk, North Carolina, to begin their manned gliding experiments. In his reply to Wilbur's first letter, Octave Chanute had suggested the mid-Atlantic coast for its regular breezes and soft sandy landing surface. Wilbur also requested and examined U.S.
Weather Bureau data, and decided on Kitty Hawk after receiving information from the government meteorologist stationed there. Kitty Hawk, although remote, was closer to Dayton than other places Chanute had suggested, including California and Florida. The spot also gave them privacy from reporters, who had turned the 1896 Chanute experiments at Lake Michigan into something of a circus. Chanute visited them in camp each season from 1901 to 1903 and saw gliding experiments, but not the powered flights.
Gliders . The the design of their kite and full-size gliders on work done in the 1890s by other aviation pioneers. They adopted the basic design of the Chanute-Herring biplane hang glider ("double-decker" as the Wrights called it), which flew well in the 1896 experiments near Chicago, and used aeronautical data on
lift that
Otto Lilienthal had published. The Wrights designed the wings with
camber, a curvature of the top surface. The brothers did not discover this principle, but took advantage of it. The better lift of a cambered surface compared to a flat one was first discussed scientifically by
Sir George Cayley. Lilienthal, whose work the Wrights carefully studied, used cambered wings in his gliders, proving in flight the advantage over flat surfaces. The wooden uprights between the wings of the Wright glider were braced by wires in their own version of Chanute's modified
Pratt truss, a bridge-building design he used for his biplane glider (initially built as a triplane). The Wrights mounted the horizontal
elevator in front of the wings rather than behind, apparently believing this feature would help to avoid, or protect them from, a nosedive and crash like the one that killed Lilienthal. Wilbur incorrectly believed a tail was not necessary, and their first two gliders did not have one. According to some Wright biographers, Wilbur probably did all the gliding until 1902, perhaps to exercise his authority as older brother and to protect Orville from harm as he did not want to have to explain to their father, Bishop Wright, if Orville got injured.
1900 The brothers flew the glider for only a few days in early autumn 1900 at Kitty Hawk. In the first tests, probably on October 3, Wilbur was aboard while the glider flew as a kite not far above the ground with men below holding tether ropes. Most of the kite tests were unpiloted, with sandbags or chains and even a local boy as ballast. They tested wing-warping using control ropes from the ground. The glider was also tested unmanned while suspended from a small homemade tower. Wilbur, but not Orville, made about a dozen free glides on only a single day, October 20. For those tests the brothers trekked four miles (6km) south to the
Kill Devil Hills, a group of sand dunes up to high (where they made camp in each of the next three years). Although the glider's lift was less than expected, the brothers were encouraged because the craft's front elevator worked well and they had no accidents. However, the small number of free glides meant they were not able to give wing-warping a true test. The pilot lay flat on the lower wing, as planned, to reduce aerodynamic drag. As a glide ended, the pilot was supposed to lower himself to a vertical position through an opening in the wing and land on his feet with his arms wrapped over the framework. Within a few glides, however, they discovered the pilot could remain prone on the wing, headfirst, without undue danger when landing. They made all their flights in that position for the next five years.
1901 Before returning to Kitty Hawk in the summer of 1901, Wilbur published two articles, "The Angle of Incidence" in
The Aeronautical Journal, and "The Horizontal Position During Gliding Flight" in
Illustrierte Aeronautische Mitteilungen. The brothers brought all of the material they thought was needed to be self-sufficient at Kitty Hawk. Besides living in tents once again, they built a combination workshop and hangar. Measuring long by wide, the ends opened upward for easy glider access. Hoping to improve lift, they built the 1901 glider with a much larger wing area and made dozens of flights in July and August for distances of . The glider stalled a few times, but the parachute effect of the forward elevator allowed Wilbur to make a safe flat landing, instead of a nose-dive. These incidents wedded the Wrights even more strongly to the
canard design, which they did not give up until 1910. The glider, however, delivered two major disappointments. It produced only about one-third the lift calculated and sometimes pointed opposite the intended direction of a turna problem later known as
adverse yawwhen Wilbur used the wing-warping control. On the trip home a deeply dejected Wilbur remarked to Orville that man would not fly in a thousand years. The poor lift of the gliders led the Wrights to question the accuracy of Lilienthal's data, as well as the "
Smeaton coefficient" of air pressure, a value which had been in use for over 100 years and was part of the accepted equation for lift. The Wrights used the following lift equation to calculate the amount of lift that a wing would produce: L = kSV^2C_\mathrm{L}, where: • is the lift, in pounds; • is the coefficient of air pressure (the Smeaton coefficient); • is the total area of lifting surface, in square feet; • is the air velocity over the wing (headwind plus ground speed), in miles per hour; and • {{tmath|C_\mathrm{L} }} is the coefficient of lift (varies with wing shape). Over the years a wide variety of values had been measured for the Smeaton coefficient ; Chanute identified up to 50 of them. Wilbur knew that Langley, for example, had used a lower number than the traditional one. Intent on confirming the correct Smeaton value, Wilbur performed his own calculations using measurements collected during kite and free flights of the 1901 glider. His results correctly showed that the coefficient was very close to 0.0033 (similar to the number Langley used), not the traditional 0.0054, which would significantly exaggerate predicted lift. at the Virginia Air and Space Center The brothers decided to find out if Lilienthal's data for lift coefficients were correct. They devised an experimental apparatus which consisted of a freely rotating bicycle wheel mounted horizontally in front of the handlebars of a bicycle. The brothers took turns pedaling the bicycle vigorously, creating air flow over the horizontal wheel. Attached vertically to the wheel were an airfoil and a flat plate mounted 90° away. As air passed by the airfoil, the lift it generated, if unopposed, would cause the wheel to rotate. The flat plate was oriented so its drag would push the wheel in the opposite direction of the airfoil. The airfoil and flat plate were made in specific sizes such that, according to Lilienthal's measurements, the lift generated by the airfoil would exactly counterbalance the drag generated by the flat plate and the wheel would not turn. However, when the brothers tested the device, the wheel turn. The experiment confirmed their suspicion that either the standard Smeaton coefficient or Lilienthal's coefficients of lift and dragor all of themwere in error. They then built a wind tunnel in their shop, and between October and December 1901 conducted systematic tests on dozens of miniature wings. A report was published in the
Journal of the society, which was then separately published as an offprint titled
Some Aeronautical Experiments in a 300 copy printing.
1902 due to poor lift and high drag. In contrast, the 1902 glider flies at a much flatter angle and holds up its tether lines almost vertically, clearly demonstrating a much better
lift-to-drag ratio. Lilienthal had made "whirling arm" tests on only a few wing shapes, and the Wrights mistakenly assumed the data would apply to their wings, which had a different shape. The Wrights took a huge step forward and made basic wind tunnel tests on 200
scale-model wings of many shapes and
airfoil curves, followed by detailed tests on 38 of them. An important discovery was the benefit of longer narrower wings: in aeronautical terms, wings with a larger
aspect ratio (wingspan divided by
chordthe wing's front-to-back dimension). Such shapes offered much better
lift-to-drag ratio than the stubbier wings the brothers had tried so far. With this knowledge, and a more accurate Smeaton number, the Wrights designed their 1902 glider. The wind tunnel tests, made from October to December 1901, were described by biographer Fred Howard as "the most crucial and fruitful aeronautical experiments ever conducted in so short a time with so few materials and at so little expense". In their September 1908
Century Magazine article, the Wrights explained, "The calculations on which all flying machines had been based were unreliable, and ... every experiment was simply groping in the dark ... We cast it all aside and decided to rely entirely upon our own investigations." The 1902 glider wing had a flatter airfoil, with the
camber reduced to a ratio of 1-in-24, in contrast to the previous thicker wing. The larger aspect ratio was achieved by increasing the wingspan and shortening the chord. The glider also had a new structural feature: A fixed, rear vertical rudder, which the brothers hoped would eliminate turning problems. However, the 1902 glider encountered trouble in crosswinds and steep banked turns, when it sometimes spiraled into the grounda phenomenon the brothers called "well digging". According to
Combs, "They knew that when the earlier 1901 glider banked, it would begin to slide sideways through the air, and if the side motion was left uncorrected, or took place too quickly, the glider would go into an uncontrolled pivoting motion. Now, with vertical fins added to correct this, the glider again went into a pivoting motion, but in the opposite direction, with the nose swinging downward." over the Kill Devil Hills, October 10, 1902. The single rear rudder is steerable; it replaced the original fixed double rudder. Orville apparently visualized that the fixed rudder resisted the effect of corrective wing-warping when attempting to level off from a turn. He wrote in his diary that on the night of October 2, "I studied out a new vertical rudder". The brothers then decided to make the rear rudder movable to solve the problem. They hinged the rudder and connected it to the pilot's warping "cradle", so a single movement by the pilot simultaneously controlled wing-warping and rudder deflection. The apparatus made the trailing edge of the rudder turn away from whichever end of the wings had more drag (and lift) due to warping. The opposing pressure produced by turning the rudder enabled corrective wing-warping to reliably restore level flight after a turn or a wind disturbance. Furthermore, when the glider banked into a turn, rudder pressure overcame the effect of differential drag and pointed the nose of the aircraft in the direction of the turn, eliminating adverse yaw. In short, the Wrights discovered the true purpose of the movable vertical rudder. Its role was not to change the direction of flight, as a rudder does in sailing, but rather, to aim or align the aircraft correctly during banking turns and when leveling off from turns and wind disturbances. The actual turnthe change in directionwas done with roll control using wing-warping. The principles remained the same when
ailerons superseded wing-warping. With their new method, the Wrights achieved true control in turns for the first time on October 9, a major milestone. From September 20 until the last weeks of October, they flew over a thousand flights. The longest duration was up to 26 seconds, and the longest distance more than . Having demonstrated lift, control, and stability, the brothers now turned their focus to the problem of power. Thus did
three-axis control evolve: wing-warping for roll (lateral motion), forward elevator for pitch (up and down) and rear rudder for yaw (side to side). On March 23, 1903, the Wrights applied for their famous patent for a "Flying Machine", based on their successful 1902 glider. Some aviation historians believe that applying the system of three-axis flight control on the 1902 glider was equal to, or even more significant, than the addition of power to the 1903 Flyer. Peter Jakab of the Smithsonian asserts that perfection of the 1902 glider essentially represents invention of the airplane.
Adding power In addition to developing the lift equation, the brothers also developed the equation for drag. It is of the same form as the lift equation, except the
coefficient of drag replaces the
coefficient of lift, computing drag instead of lift. They used this equation to answer the question, "Is there enough power in the engine to produce a
thrust adequate to overcome the drag of the total frame ...", in the words of Combs. The Wrights then "... measured the pull in pounds on various parts of their aircraft, including the pull on each of the wings of the biplane in level position in known wind velocities ... They also devised a formula for
power-to-weight ratio and propeller efficiency that would answer whether or not they could supply to the propellers the power necessary to deliver the thrust to maintain flight ... they even computed the thrust of their propellers to within 1 percent of the thrust actually delivered ..." In 1903 the brothers built the powered
Wright Flyer, using their preferred material for construction,
spruce, a strong and lightweight wood, and Pride of the West
muslin for surface coverings. They also designed and carved their own wooden propellers, and had a purpose-built gasoline engine fabricated in their bicycle shop. They thought propeller design would be a simple matter and intended to adapt data from shipbuilding. However, their library research disclosed no established formulae for either marine or air propellers, and they found themselves with no sure starting point. They discussed and argued the question, sometimes heatedly, until they concluded that an aeronautical propeller is essentially a wing rotating in the vertical plane. On that basis, they used data from more wind tunnel tests to design their propellers. The finished blades were just over eight feet long, made of three laminations of glued spruce. The Wrights decided on twin "
pusher" propellers (counter-rotating to cancel torque), which would act on a greater quantity of air than a single relatively slow propeller and not disturb airflow over the leading edge of the wings. Wilbur made a March 1903 entry in his notebook indicating the prototype propeller was 66% efficient. Modern wind tunnel tests on reproduction 1903 propellers show they were more than 75% efficient under the conditions of the first flights, "a remarkable feat", and actually had a peak efficiency of 82%. The Wrights wrote to several engine manufacturers, but none could meet their need for a sufficiently lightweight powerplant. They turned to their shop mechanic,
Charlie Taylor, who built an engine in just six weeks in close consultation with the brothers. '', December 17, 1903, Orville piloting, Wilbur running at wingtip To keep the weight down the
engine block was cast from aluminum, a rare practice at the time. The Wright/Taylor engine had a primitive version of a
carburetor, and had no
fuel pump. Gasoline was
gravity-fed from the fuel tank mounted on a wing strut into a chamber next to the cylinders where it was mixed with air: The
fuel-air mixture was then vaporized by heat from the crankcase, forcing it into the cylinders. The propeller
drive chains, resembling those of bicycles, were supplied by a manufacturer of heavy-duty automobile chains. The
Flyer cost less than a thousand dollars, in contrast to more than $50,000 in government funds given to
Samuel Langley for his man-carrying
Great Aerodrome just a few years earlier in 1898. The
Wright Flyer had a wingspan of , weighed , and had a , engine. On June 24, 1903, Wilbur made a second presentation in Chicago to the Western Society of Engineers. He gave details about their 1902 experiments and glider flights, but avoided any mention of their plans for powered flight.
First powered flight In camp at
Kill Devil Hills, the Wrights endured weeks of delays caused by broken propeller shafts during engine tests. After the shafts were replaced (requiring two trips back to Dayton), Wilbur won a
coin toss and made a three-second flight attempt on December 14, 1903, stalling after takeoff and causing minor damage to the
Flyer. Because December 13, 1903, was a
Sunday, the brothers did not make any attempts that day, even though the weather was good, so their first powered test flight happened on the 121st anniversary of the first hot air balloon test flight that the
Montgolfier brothers had made on December 14, 1782. In a message to their family, Wilbur referred to the trial as having "only partial success", stating "the power is ample, and but for a trifling error due to lack of experience with this machine and this method of starting, the machine would undoubtedly have flown beautifully." Following repairs, the Wrights finally took to the air on December 17, 1903, making two flights each from level ground into a freezing headwind gusting to . The first flight, by Orville at 10:35 am, of in 12 seconds, at a speed of only over the ground, was recorded in a
famous photograph. The next two flights covered approximately , by Wilbur and Orville, respectively. Their altitude was about above the ground. The following is Orville Wright's account of the final flight of the day: Five people witnessed the flights: Adam Etheridge,
John T. Daniels (who snapped the famous "first flight" photo using Orville's pre-positioned camera), and Will Dough, all of the U.S. government coastal lifesaving crew; area businessman W. C. Brinkley; and Johnny Moore, a teenaged boy who lived in the area. After the men hauled the
Flyer back from its fourth flight, a powerful gust of wind flipped it over several times, despite the crew's attempt to hold it down. Severely damaged, the
Wright Flyer never flew again. The brothers shipped the airplane home, and years later Orville restored it, lending it to several U.S. locations for display, then to the
Science Museum in London (see Smithsonian dispute below), before it was finally installed in 1948 in
the Smithsonian Institution, its current residence. The Wrights sent a telegram about the flights to their father, requesting that he "inform press". The Wrights issued their own factual statement to the press in January. Nevertheless, the flights did not create public excitementif people even knew about themand the news soon faded. In Paris, however, Aero Club of France members, already stimulated by Chanute's reports of Wright gliding successes, took the news more seriously and increased their efforts to catch up to the brothers. An analysis in 1985 by Professor Fred E. C. Culick and Henry R. Jex demonstrated that the 1903
Wright Flyer was so unstable as to be almost unmanageable by anyone but the Wrights, who had trained themselves in the 1902 glider. In a recreation attempt on the event's 100th anniversary on December 17, 2003, Kevin Kochersberger, piloting an exact replica, failed in his effort to match the success that the Wright brothers had achieved with their piloting skill.
Establishing legitimacy in
Wright Flyer II. Flight 85, approximately in seconds, November 16, 1904 In 1904 the Wrights built the
Wright Flyer II. They decided to avoid the expense of travel and bringing supplies to the Outer Banks and set up an airfield at
Huffman Prairie, a cow pasture eight miles northeast of Dayton. The Wrights referred to the airfield as Simms Station in their flying school brochure. They received permission to use the field rent-free from owner and bank president Torrance Huffman. They invited reporters to their first flight attempt of the year on May 23, on the condition that no photographs be taken. Engine troubles and slack winds prevented any flying, and they could manage only a very short hop a few days later with fewer reporters present. Library of Congress historian Fred Howard noted some speculation that the brothers had intentionally failed to fly in order to cause reporters to lose interest in their experiments. Whether that is true is not known, but after their poor showing local newspapers virtually ignored them for the next year and a half. The Wrights were glad to be free from the distraction of reporters. The absence of newsmen also reduced the chance of competitors learning their methods. After the Kitty Hawk powered flights, the Wrights made a decision to begin withdrawing from the bicycle business so they could concentrate on creating and marketing a practical airplane. This was financially risky, since they were neither wealthy nor government-funded (unlike other experimenters such as
Ader,
Maxim,
Langley, and
Santos-Dumont). The Wright brothers did not have the luxury of being able to give away their invention: It had to be their livelihood. Thus, their secrecy intensified, encouraged by advice from their patent attorney,
Henry Toulmin, not to reveal details of their machine. At Huffman Prairie, lighter winds made takeoffs harder, and they had to use a longer starting rail than the rail used at Kitty Hawk. The first flights in 1904 revealed problems with longitudinal stability, solved by adding ballast and lengthening the supports for the elevator. During the spring and summer they suffered many hard landings, often damaging the aircraft and causing minor injuries. On August 13, making an unassisted takeoff, Wilbur finally exceeded their best Kitty Hawk effort with a flight of . They then decided to use a weight-powered catapult to make takeoffs easier and tried it for the first time on September 7. On September 20, 1904, Wilbur flew the first complete circle in history by a manned heavier-than-air powered machine, covering in about a minute and a half. Their two best flights were November 9 by Wilbur and December 1 by Orville, each exceeding five minutes and covering nearly three miles in almost four circles. By the end of the year the brothers had accumulated about 50 minutes in the air in 105 flights over the rather soggy pasture, which, remarkably, is virtually unchanged today from its original condition and is now part of
Dayton Aviation Heritage National Historical Park, adjacent to
Wright-Patterson Air Force Base. The Wrights scrapped the battered and much-repaired aircraft, but saved the engine, and in 1905 built a new airplane, the
Flyer III. However, at first this had the same marginal performance as the first two. Its maiden flight was on June 23 and the first few flights were no longer than 10 seconds. After Orville suffered a bone-jarring and potentially fatal crash on July 14, they rebuilt the
Flyer with the forward elevator and rear rudder both enlarged and placed several feet farther away from the wings. They also installed a separate control for the rear rudder instead of linking it to the wing-warping "cradle" as before. Each of the three axes (pitch, roll, and yaw) now had its own independent control. These modifications greatly improved stability and control, enabling a series of six long flights ranging from 17 to 38 minutes and around the course over Huffman Prairie between September 26 and October 5. Wilbur made the last and longest flight, in 38 minutes and 3 seconds, ending with a safe landing when the fuel ran out. The flight was seen by several invited friends, their father Milton, and neighboring farmers. In October 1904, the brothers were visited by the first of many important Europeans they would befriend in coming years,
Colonel J. E. Capper, later superintendent of the
Royal Balloon Factory. Capper and his wife were visiting the United States to investigate the aeronautical exhibits at the
St. Louis World Fair, but had been given a letter of introduction to both Chanute and the Wrights by
Patrick Alexander. Capper was very favorably impressed by the Wrights, who showed him photographs of their aircraft in flight. The Wright brothers were certainly complicit in the lack of attention they received. Fearful of competitors stealing their ideas, and still without a patent, they flew on only one more day after October 5. From then on, they refused to fly anywhere unless they had a firm contract to sell their aircraft. They wrote to the U.S. government, then to Britain, France and Germany with an offer to sell a flying machine, but were rebuffed because they insisted on a signed contract before giving a demonstration. They were unwilling even to show their photographs of the airborne Flyer. The American military, having recently spent $50,000 on the
Langley Aerodromea product of the nation's foremost scientistonly to see it plunge twice into the Potomac River "like a handful of mortar", was particularly unreceptive to the claims of two unknown bicycle makers from Ohio. Thus, doubted or scorned, the Wright brothers continued their work in semi-obscurity, while other aviation pioneers like Santos-Dumont,
Henri Farman,
Léon Delagrange, and American
Glenn Curtiss entered the limelight. ==European skepticism==