Note: Wilbur Wright child // WrightBrothersHome // 2001 NC Proof
The brothers flew the glider for only a few days in the early autumn of 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 (6 km) south to the Kill Devil Hills, a group of sand dunes up to 100 feet (30 m) 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.
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 50 to 400 ft (15 to 122 m). 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 turn–a problem later known as adverse yaw–when 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.
L = lift in pounds
The Wrights used this equation to calculate the amount of lift that a wing would produce. 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.
To learn whether errors actually existed in Lilienthal's data tables, the brothers used a bicycle for a new type of experiment. They made a model-size airfoil and a counter-acting flat plate, both according to dimensions Lilienthal had specified, and attached them to an extra bicycle wheel, which they mounted horizontally in front of the handlebars. Pedaling strenuously on a local street to create airflow over the apparatus, they observed that the third wheel rotated against the airfoil instead of remaining motionless as Lilienthal's formula predicted. The experiment confirmed their suspicion that either the standard Smeaton coefficient or Lilienthal's coefficients of lift and drag–or all of them–were in error.
They then built a six-foot (1.8m) wind tunnel in their shop and between October and December 1901 conducted systematic tests on dozens of miniature wings . The "balances" they devised and mounted inside the tunnel to hold the wings looked crude, made of bicycle spokes and scrap metal, but were "as critical to the ultimate success of the Wright brothers as were the gliders." The devices allowed the brothers to balance lift against drag and accurately calculate the performance of each wing. They could also see which wings worked well as they looked through the viewing window in the top of the tunnel. The tests yielded a trove of valuable data never before known and showed that the poor lift of the 1900 and 1901 gliders was entirely due to an incorrect Smeaton value, and that Lilienthal's published data were fairly accurate for the tests he had done.
Before the detailed wind tunnel tests Wilbur traveled to Chicago at Chanute's invitation to give a lecture to the Western Society of Engineers on September 18, 1901. He presented a thorough report about the 1900–01 glider experiments and complemented his talk with a lantern slide show of photographs. Wilbur's speech was the first public account of the brothers' experiments. 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 edition.
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 wings of many shapes and airfoil curves, followed by detailed tests on 38 of them. The tests, according to biographer Fred Howard, "were the most crucial and fruitful aeronautical experiments ever conducted in so short a time with so few materials and at so little expense". An important discovery was the benefit of longer narrower wings: in aeronautical terms, wings with a larger aspect ratio (wingspan divided by chord—the wing's front-to-back dimension). Such shapes offered much better lift-to-drag ratio than the broader wings the brothers had tried so far.
With this knowledge, and a more accurate Smeaton number, the Wrights designed their 1902 glider. Using another crucial discovery from the wind tunnel, they made the airfoil flatter, reducing the camber (the depth of the wing's curvature divided by its chord). The 1901 wings had significantly greater curvature, a highly inefficient feature the Wrights copied directly from Lilienthal. Fully confident in their new wind tunnel results, the Wrights discarded Lilienthal's data, now basing their designs on their own calculations.
With characteristic caution, the brothers first flew the 1902 glider as an unmanned kite, as they had done with their two previous versions. Rewarding their wind tunnel work, the glider produced the expected lift. It also had a new structural feature: a fixed, rear vertical rudder, which the brothers hoped would eliminate turning problems.
By 1902 they realized that wing-warping created "differential drag" at the wingtips. Greater lift at one end of the wing also increased drag, which slowed that end of the wing, making the glider swivel—or "yaw"—so the nose pointed away from the turn. That was how the tailless 1901 glider behaved.
The improved wing design enabled consistently longer glides, and the rear rudder prevented adverse yaw—so effectively that it introduced a new problem. Sometimes when the pilot attempted to level off from a turn, the glider failed to respond to corrective wing-warping and persisted into a tighter turn. The glider would slide toward the lower wing, which hit the ground, spinning the aircraft around. The Wrights called this "well digging".
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. Tests while gliding proved that the trailing edge of the rudder should be turned 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 turn—the change in direction—was 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 8, 1902, a major milestone. From September 19 to October 24 they made between 700 and 1,000 glides, the longest lasting 26 seconds and covering 622.5 feet (189.7 m). Hundreds of well-controlled glides after they made the rudder steerable convinced them they were ready to build a powered flying machine.
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.
In 1903 the brothers built the powered Wright Flyer I, 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 met 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. To keep the weight low enough, the engine block was cast from aluminum, a rare practice for 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. The Flyer had a wingspan of 40.3 ft (12.3 m), weighed 605 lb (274 kg) and had a 12 horsepower (8.9 kW) 180 lb (82 kg) engine.
First powered flight
In camp at Kill Devil Hills, they 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 test flight that the Montgolfier brothers had done, 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 27 miles per hour (43 km/h). The first flight, by Orville at 10:35 am, of 120 feet (37 m) in 12 seconds, at a speed of only 6.8 miles per hour (10.9 km/h) over the ground, was recorded in a famous photograph. The next two flights covered approximately 175 and 200 feet (53 and 61 m), by Wilbur and Orville respectively. Their altitude was about 10 feet (3.0 m) above the ground. The following is Orville Wright's account of the final flight of the day:
Wilbur started the fourth and last flight at just about 12 o'clock. The first few hundred feet were up and down, as before, but by the time three hundred ft had been covered, the machine was under much better control. The course for the next four or five hundred feet had but little undulation. However, when out about eight hundred feet the machine began pitching again, and, in one of its darts downward, struck the ground. The distance over the ground was measured to be 852 feet; the time of the flight was 59 seconds. The frame supporting the front rudder was badly broken, but the main part of the machine was not injured at all. We estimated that the machine could be put in condition for flight again in about a day or two.
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 airplane never flew again. The brothers shipped it home, and years later Orville restored it, lending it to several U.S. locations for display, then to a British museum (see Smithsonian dispute below), before it was finally installed in 1948 in the Smithsonian Institution in Washington, D.C., its current residence.
The Wrights sent a telegram about the flights to their father, requesting that he "inform press." However, the Dayton Journal refused to publish the story, saying the flights were too short to be important. Meanwhile, against the brothers' wishes, a telegraph operator leaked their message to a Virginia newspaper, which concocted a highly inaccurate news article that was reprinted the next day in several newspapers elsewhere, including Dayton.
The Wrights issued their own factual statement to the press in January. Nevertheless, the flights did not create public excitement—if people even knew about them—and 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.
Modern analysis by Professor Fred E. C. Culick and Henry R. Jex (in 1985) has 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 exacting replica, failed in his effort to match the success that the Wright brothers had achieved with their piloting skill.