Jump to a Breakthrough: Stability and Control Aerodynamics Propulsion
Jump to an Invention: 1899 Kite 1900 Glider 1902 Glider 1903 Flyer 1904 & 1905 Flyers
Between 1899 and 1905, the Wright brothers’ program of research and experimentation led to the first airplane in 1903, and an improved, practical aircraft two years later. Their basic design and elements have been used in all successful airplanes ever since.
The Wrights’ success was rooted in their inventive method. Their specific research techniques, innate skills, and personality traits came together in a unique way and largely explain why they succeeded where so many others failed.
The Wright brothers’ inventive work produced three major accomplishments.
- The Aircraft - The aircraft the Wrights designed and built between 1900 and 1905 were truly revolutionary, incorporating creative solutions to many of the technical problem standing in the way of mechanical flight.
- Aeronautical Engineering - The Wrights developed basic techniques still used by all modern aeronautical engineers, such as their pioneering use of the wind tunnel.
- Flight Testing - Systematic flight testing was critical to the Wrights success. Their method of evaluating data gathered in these tests, then refining their design based on the results, remains an important tool in aerospace research and development.
They designed, built, and flew a series of successful aircraft.
They pioneered the modern practice of aeronautical engineering.
They developed the tool of flight testing and data feedback and applied it to the design of the aircraft.
Looking For a Place to Start
On May 30, 1899, Wilbur Wright wrote to the Smithsonian, declaring his belief that human flight was possible, and asking for any publications the Smithsonian might have that would help with his research. The Smithsonian recommended the publications Progress in Flying Machines by Octave Chanute and The Aeronautical Annuals, which proved to be a solid foundation for their research.
Letter the Wright brothers wrote to the Smithsonian Institution on May 30, 1899, asking for information about flight. (Page 1 of 2)
Letter the Wright brothers wrote to the Smithsonian Institution on May 30, 1899, asking for information about flight. (Page 2 of 2)
After collecting reference material from the Smithsonian and other sources, the Wright brothers began studying their predecessors. They were surprised to learn that, despite humanity’s centuries-old interest in flight, little progress had been made in aeronautics before 1800. During the 1800s, a community of technically trained people interested in flight had evolved. Much of what Wilbur and Orville accomplished was highly original, however these 19th-century experimenters, such as Otto Lilienthal, provided important pieces to the puzzle of human flight.
After researching their predecessors, the Wright brothers decided to follow aeronautical experimenter Sir George Cayley’s lead and reduced the obstacles to flight to three broad categories:
- A set of lifting surfaces, or wings
- A method of balancing and controlling the aircraft
- A means of propulsion
Most earlier experimenters focused only on one of these problems and did not consider the final design from the beginning. The Wrights recognized that each of these areas had to be successfully addressed to build a working airplane. They believed that the wing and propulsion problems would be easier to solve, so they first concentrated on control.
The 1899 Wright Kite
Less than three months after writing to the Smithsonian for information, the Wright brothers had defined the essential requirements of a heavier-than-air flying machine and successfully built and tested a kite that incorporated many of these design features in basic form.
Stability and Control
One obstacle the Wright brothers were hoping to overcome was controlling an aircraft that was unstable. Many earlier experimenters believed that air currents were too strong and unpredictable for human reflexes, so an aircraft had to be inherently stable, or outside the influence of said air currents, for the pilot to be able to maintain control.
Because of the Wrights’ extensive experience with the bicycle—a highly unstable but controllable machine—they reasoned than an airplane could be unstable yet controllable as well.
Wing Warping: The Breakthrough Process
The Wrights knew that a pilot needed to control the lateral movement of the aircraft, balancing the wings, (known as roll), for both balance and turning. They realized that if the wing on one side of the aircraft met the oncoming flow of air at a greater angle than the opposite wing, it would generate more lift—the vertical force which is acting on the wing, on that side. In response, the wing would rise, cause the aircraft to bank. If a pilot could manipulate the wings in this way, they could control the aircraft in roll.
The brothers considered using a system of gears and pivoting shafts to angle the wings in the opposite directions, but such a system would prove too heavy and complex. They then conceived of the elegant concept of twisting, or warping, the wing structure itself, a method they called wing-warping.
The Wrights combined their wing-warping control concept and the structural design of Octave Chanute and Augustus Herring's 1896 glider in their first aircraft, a biplane kite with a 5-foot (1.5 meter) wingspan, built in 1899.
To allow for wing-warping, they left the kite unbraced between the front and rear struts (vertical posts). It was controlled with four lines running from the top and bottom of the front outer struts to a pair of sticks held by the operator. Tilting the sticks in opposite directions caused the wing structure to twist.
No photographs exist of the 1899 kite. However, a reproduction of the 1899 kite can be seen in the image to the left.
Flight Testing the Kite
Wilbur flew the kite at a nearby field in mid-summer. The only witnesses were a group of schoolboys, who were fascinated by the large, unusual-looking kite this adult in business attire was “toying” with. The kite responded quickly and precisely to Wilbur’s commands. Having proven the soundness of their wing-warping control system, the Wrights began designing a full-size, piloted glider.
The 1900 Glider
The Wrights next began to study aerodynamics and structures in preparation for building their first piloted glider. It was one thing to design a set of wings for a small kite, and quite another to build a large, heavy glider, climb aboard, and launch oneself into the air. The brothers considered things such as the precise curve of the wing cross-section, the wing area necessary to lift a pilot, and the type of materials needed to build a glider.
Aerodynamics: Pitch Control, Wing Shape, and Aircraft Size
Having developed wing-warping for lateral control, the Wrights now addressed control in climbing and descending, or pitch. This required understanding the forces acting on a wing and study of wing shape. Beyond control and airfoil shape, another important consideration was wing size. How large a wing area was needed, and how light did the glider need to be to lift the pilot into the air?
Lift is the vertical (up and down) force acting on a wing. The focal point of this lift force is called the center of pressure. In flight, as the wing changes its angle to the oncoming flow of air, the center of pressure moves back and forth along the surface of the wing.
When the center of pressure and the center of gravity coincide, the aircraft continues in level flight. If the center of pressure moves behind the center of gravity, the airplane pitches down. If it moves ahead the center of gravity, the airplane pitches up. To control climb and descent, the pilot must be able to control the movement of the center of pressure.
Otto Lilienthal tried to keep up with the center of pressure’s continual movement by constantly shifting his body weight, which adjusted the center of gravity. The required frequent acrobatic movements that the Wrights felt were impractical or dangerous.
Otto Lilienthal in flight in his Lilienthal (Otto) 1894-96 Glider Normal Segelapparat (Sailing Apparatus); note Lilienthal's legs are swung to left to shift weight for control.
Instead, they controlled the movement of the center of pressure aerodynamically, by mounting a moveable horizontal surface, called an elevator, in front of the wings. As they deflected the elevator up or down, the pressure on it would counteract the upward or downward pitching of the airplane due to the changing position of the center of pressure.
An elevator mounted in front of the wings is known as a canard configuration, such as the elevator seen above. A canard lessens the violent reaction that generally occurs when an aircraft with a rear-mounted elevator stalls, or loses lift. This type of stall cost Otto Lilienthal his life. With a canard, the aircraft settles more gently after a stall, a characteristic that saved the lives of Wilbur and Orville on several occasions.
Designing the shape of the wing cross-section, known as the “airfoil,” was also important. Others had already shown that curved wings generated more lift than flat ones. Most had used a perfect arc, with the high point of the curve in the middle. The Wrights placed the high point of the curve much closer to the wing’s leading edge and made the depth of curvature fairly shallow. They believed this would reduce the movement of the center of pressure making the aircraft more stable and easier to control.
Otto Lilienthal compiled and published a table of coefficients of lift and drag for the airfoil shape he used on his gliders. The table became quite well known and was the starting point for aerodynamic research for many experimenters, including the Wright brothers.
The Famous Lilienthal Table
Otto Lilienthal based his table of the lift and drag characteristics, seen here translated to English in the Aeronautical Annual, of a single airfoil on his own ground-based research. Octave Chanute shared the information with the English-speaking aeronautical community in 1897.
The table served as the starting point for many experimenters, including Wilbur and Orville Wright. When the performance of their early gliders failed to match that predicted by calculations based on a misunderstanding of the table, the brothers used a wind tunnel to gather their own aerodynamic data. This new data opened the way to the development of the first airplane capable of sustained, powered and controlled flight.
Armed with the lift and drag equations, Otto Lilienthal’s aerodynamic data, and their own design concepts for control, wing shape, and structure, the Wright brothers began building their first piloted glider in August 1900. They finished the design and parts in just a few weeks.
The 1900 glider was the Wrights’ first piloted aircraft, flight tested at Kitty Hawk that fall. It incorporated the wire-braced biplane structure and wing-warping control system they developed with their 1899 kite. The glider generated far less lift than the brothers’ calculations had predicted. However, the control systems—wing warping for lateral control and forward elevator for pitch control—worked beautifully. While the Wrights managed only two minutes of free gliding in 1900, those precious seconds in the air proved their innovative control ideas were sound. The Wrights were still a long way from powered flight, but their glider was by far the most advanced aircraft yet created.
Testing at Kitty Hawk
To test their glider, the Wrights needed a place with wide-open spaces and strong, steady winds. They wrote to the U.S. Weather Bureau in Washington, DC, to find suitable locations. Among the places that seemed promising was Kitty Hawk, North Carolina, a small fishing village on an isolated strip of beach on the mid-Atlantic coast.
The 1901 Glider: Back to the Drawing Board
The poor lift performance of their 1900 glider made the Wright brothers question, but not abandon, the aerodynamic data and equations from others that they had relied on. To increase lift on their next glider, they simply increased the size of the wings and curvature of the airfoil. They returned to Kitty Hawk in 1901 to test the new glider.
The 1901 glider was the Wright brothers’ second, and most problematic, of the three gliders that led to their powered airplane. A 1/16 scale model of the 1901 glider can be seen in this photo.
Problems with Control Arise...
Wilbur and Orville’s proven control system had developed problems. Previously smooth and sure, the elevator control was now overly sensitive and erratic. When they warped the wings, the glider initially turned in the intended direction, but then suddenly reversed itself. They Wrights were utterly baffled.
...While Problems with Lift Persist
The glider produced only one-third the lift that their calculations had predicted. The Wrights suspected the large increase they had made in wing curvature was causing both the lift and pitch control problems.
They rerigged the wings to a shallower curvature by changing the tension on the wires running over the vertical wing posts. The responsive pitch control returned, but lift remained poor.
The 1902 Glider
The Wright brothers had designed the 1900 and 1901 gliders using the accepted lift and drag equations that were developed by their predecessors. However, neither glider produced the lift those calculations predicted. Wilbur and Orville felt it was time to perform their own research.
Tapping their familiarity with bicycles, The Wrights created a device to compare the forces acting on two objects with different shapes.
The Wrights’ gliders produced much less lift than predicted. In the fall of 1901, the Wrights began to test the accuracy of the data they had been using. Adapting a bicycle, they created a device to measure lift and drag forces on the wing.
They mounted a free-spinning wheel horizontally on the front of a bicycle, and attached two objects to the rim: a model wing and a flat plate. When they rode the bicycle, the wind flowing past the two objects balanced, and the wheel reached a new stationary equilibrium position.
To produce the required lift, the Wrights data and calculations showed that the model wing needed to be at an angle to the wind more than three times greater than what Lilienthal’s data had predicted. The bicycle apparatus confirmed that either some or all of their predecessors’ data was wrong. Their next step was to use this force balancing concept in a wind tunnel they would build to get precise data.
The Wright Wind Tunnel
In addition to building the world’s first airplane, the Wright brothers pioneered the modern practice of aeronautical engineering. Central to this was the design and use of their wind tunnel. Their 1903 powered airplane and their wind tunnel should be seen together as the product of the Wrights’ invention of flight technology. Previous experimenters had used wind tunnels, which are devices for studying the effect of moving air on objects. But Wilbur and Orville were the first to use one to generate specific data that were directly used in the design of an aircraft. Their techniques, in basic form, are still used by modern aeronautical engineers.
After building and testing a small wind tunnel, the Wright brothers built a larger, more substantial one in October 1901. They used it extensively to do research that proved essential to designing their 1903 airplane.
What made the Wrights’ wind tunnel unique were the instruments they designed and built to measure lift and drag. Called balances, these instruments measured the forces of lift and drag acting on a wing in terms that could be used in equations.
The original Wright wind tunnel no longer exists. This accurate reproduction was built by the National Cash Register Company in 1952.
The wind tunnel and instruments they designed were accurate and efficient. Not only were they able to check the accuracy of Otto Lilienthal’s table of coefficients for his single wing shape, but they also collected data for dozens of other shapes. This allowed them to select the most effective wing for the aircraft they wanted to build.
Wilbur and Orville conducted preliminary tests on as many as 200 different model wing shapes as they perfected the operation of their wind tunnel. They made formal tests and recorded data on nearly 50 of these.
Wilbur and Orville carefully recorded and graphed the aerodynamic data they collected with their wind tunnel.
A key term in the lift and drag equations was Smeaton’s coefficient, which accounted for the density of air. A value for the coefficient of 0.005 had been widely used since the 1700s. Using measurements obtained from their glider tests at Kitty Hawk and the lift equation, the Wright brothers calculated a new average value of 0.0033 for Smeaton’s coefficient. Modern aerodynamicists have confirmed this figure to be very accurate.
By December 1901, the Wright brothers had all the aerodynamic data they needed to build a successful flying machine, but they didn’t try to build a powered airplane right away. They couldn’t be sure that data obtained in their wind tunnel from tiny model wings would translate to a full-size aircraft. And they still had to solve the mysterious control problems that surfaced during the 1901 glider trials. Rather than risk life and limb on a large, heavy, untested, powered flying machine, Wilbur and Orville decided to build one more glider. This latest aircraft had all the basic aerodynamic, control, and structural requirements for human mechanical flight.
The third in a series of gliders leading up to their powered airplane, the 1902 glider was the Wright brothers’ most advanced yet. Reflecting their single, evolving design, it was again a biplane with a canard (forward) surface for pitch control and wing-warping for lateral control. But its longer, narrower wings, elliptical elevator, and vertical tail gave it a much more graceful, elegant appearance.
Like the 1901 glider, this one also had a spruce and ash framework supported within pockets sewn into its muslin fabric covering. The fabric was again applied on the bias (the direction of the weave at a 45-degree angle). The wings were rigged with a slight downward droop to counteract side-slipping due to crosswinds.
Flight Testing the 1902 Glider
Compared to their previous gliders, the Wrights’ 1902 glider had a much thinner airfoil and longer and narrower wings, which their wind tunnel tests had shown to be more efficient. To improve lateral control, they added a fixed vertical rudder to the rear of the glider. They retained the reliable forward elevator for pitch control, but made it elliptical in shape. The improvement in performance from all these changes was dramatic.
Wilbur Wright piloting the 1902 glider in flight at Kitty Hawk, NC. The Wrights added a vertical tail to their glider to deal with the lateral control problems experienced in 1901. The more graceful appearance of the 1902 machine over the previous gliders is evident in this picture.
Changes to the Rudder
After testing the glider by kiting it, Wilbur and Orville began to fly the aircraft as a glider. The new fixed vertical rudder seemed to cure the control reversal problem they experienced in 1901—at least most of the time.
Sometimes, however, the reversal of the turn was even more sudden and violent. The Wrights called these episodes “well digging,” referring to the small crater left in the sand when the glider uncontrollably hit the ground.
To solve the control reversal problem, the Wrights made the rudder movable, rather than static as it was initially designed, so it could be coordinated with the wing-warping. They connected the rudder control cables to the wing-warping hip cradle, so a single motion by the pilot operated both controls. They also changed the original double rudder to a single rudder, as shown here, to simplify the mechanism.
The 1903 Wright Flyer
Thrilled by the success of their 1902 glider, the Wright brothers were no longer content to merely add to the growing body of aeronautical knowledge; they were going to invent the airplane.
Still, much work lay ahead, especially the creation of a propulsion system. During the spring and summer of 1903, they were consumed with clearing that final hurdle into history.
Designing for Propulsion
The last obstacle to powered flight was the propulsion system. The term propulsion system is important, as Wilbur and Orville recognized that developing an effective propeller was just as crucial as building a suitable engine.
Seeking a motor for their airplane, the Wrights contacted many of the dozens of firms that by then were manufacturing gasoline engines. Ten responded, but none could meet the power and weight requirements the Wrights specified at a reasonable price. So, the brothers decided to build their own.
For the design their first powered airplane, the Wrights returned to their wind tunnel data and the lift and drag equations. Their 1902 glider’s wing area was 305 square feet (28 square meters). To carry the weight of an engine, propellers and add structural reinforcement, they had to increase the wing area to more than 500 square feet (46 square meters). Allowing 200 pounds (91 kilograms) for the propulsion system, they estimated that the Flyer with a pilot would weigh 625 pounds (293 kilograms).
Based on this estimate, they concluded they needed an at least a 8-horsepower engine generating 90 pounds (41 kilograms) of thrust to achieve a minimum airspeed of 23 mph (37 km/h) to keep the airplane aloft.
Charlie Taylor, a mechanic the Wrights hired in 1901 to work in their bicycle shop, helped design the engine and did virtually all the machine work on it. He completed the engine after only six weeks and tested it for the first time on February 12, 1903.
The Wright engine was a bit crude, even by the standards of the day. It had four horizontal inline cylinders. The 4-inch (10-centimeters) bore, 4-inch stroke, cast-iron cylinders fit into a cast aluminum crankcase that extended outward to form a water jacket around the cylinder barrels.
The Wright engine’s aluminum crankcase marked the first time this breakthrough material was used in aircraft construction. Lightweight aluminum became essential in aircraft design development and remains a primary construction material for all types of aircraft. The engine was cooled by water from a narrow vertical reservoir mounted on a forward strut.
- Gasoline was gravity-fed from a small quart-and-a-half tank mounted on a strut below the upper wing.
- The gasoline entered a shallow chamber next to the cylinders and mixed with the incoming air.
- Heat from the crankcase vaporized the fuel-air mixture, causing it to pass through the intake manifold into the cylinders.
- Ignition was produced by opening and closing two contact breaker points in the combustion chamber of each cylinder via a camshaft.
- The initial spark for starting the engine was generated with a coil and four dry-cell batteries, not carried on the airplane.
- A low-tension magneto driven by a 20-pound flywheel supplied electric current while the engine was running.
Making the Propellers
One of the most innovative aspects of the 1903 Flyer was its propellers. The Wrights decided to treat the propeller as if it were a rotary wing. They reasoned that the same physics that generated an upward force (lift) on a curved surface in a flow of air would also produce a horizontal force (thrust) when such a surface was positioned vertically and rotated to create the airflow.
Each propeller was 8½ feet (2.8 meters) in diameter and made from two laminations of 1¾-inch (4.4 centimeters) spruce. The blades were shaped with a hatchet and a drawknife and the tips covered with fabric and varnished to prevent splitting. The Wrights decided to use two, slow-turning, large propellers, because this arrangement offered great efficiency, and the propellers could be spun in opposite directions to neutralize the gyroscopic effects of the whirling blades.
The 1903 Wright Flyer made four flights at Kitty Hawk, North Carolina, on December 17, 1903, the best covering 852 feet (284 meters) in 59 seconds. It was the first heavier-than-air, powered aircraft to make a sustained, controlled flight with a pilot aboard.
The Wrights used their proven canard biplane configuration, which was rooted in their initial 1899 kite design. Key to the Flyer’s success was its three-axis control system, which featured wing-warping for lateral balance, a moveable rudder, and an elevator for pitch control.
The right wing was four inches (10 centimeters) longer than the left to compensate for the engine being heavier than the pilot and mounted to his right. The wings were rigged with a slight droop to reduce the effects of crosswinds.
Have you ever taken a close look at the picture of the Wright brothers' first flight? There are amazing details that tell a lot about this famous day. Take a deep dive into this famous first flight photo with Curator Emeritus, Tom Crouch.
The 1904 and 1905 Flyers
While the Wrights had achieved powered flight, they had not yet created a practical airplane. The 1903 Flyer had only performed short, straight-line flights. To successfully market their invention, they had to show that it could turn and fly over more commonplace terrain than the sandy open spaces of Kitty Hawk. With this goal in mind, Wilbur and Orville refined their design with two more powered aircraft in 1904 and 1905.
Increasing stability
The 1903 airplane’s main problems were pitch instability and an overly sensitive elevator. To deal with the instability, the Wrights added weight to the front of their 1904 Flyer to shift the center of gravity forward. They also moved the elevator farther ahead of the wings, which dampened the control response and made the aircraft easier to fly.
The 1904 Flyer: The First Circular Flight
To experiment and practice more easily, and to avoid the tedious journey to Kitty Hawk, the Wrights got permission to fly off a local cow pasture known as Huffman Prairie, a few miles outside Dayton.
They built a hangar on the field and began experimenting with their second powered airplane in May 1904. They began using a tower-and-drop-weight catapult launching device to help takeoff in lighter winds.
Improvement came slowly. The Wrights did not match their 59-second flight of 1903 until the 49th flight of their 1904 airplane. On October 20, 1904, the Wrights finally flew their first complete circle. The flight lasted 1 minute, 36 seconds and covered 4,080 feet (1,243 meters).
The 1905 Flyer: The First Practical Airplane
By the fall of 1905, the Wright brothers’ experimental period ended. With their third powered airplane, they now routinely made flights of several minutes. On October 5, Wilbur made a spectacular flight in which he circled the field 30 times in 39 minutes for a total distance of 24½ miles (39 kilometers).
In every sense, the Wrights now had a practical airplane, so they turned their attention to securing their patent and seeking a customer for their invention. They did not fly again for 2½ years.
The 1905 Wright Flyer is on display at Carillon Historical Park, Dayton, Ohio. The 1904 Flyer no longer exists.
Now that you've learned all about how the Wrights developed the first airplane, help Wilbur and Orville assemble the 1903 Flyer and compare it to the parts of a modern airplane. While aviation technology has developed a lot since the Wrights time, not much about the basic components of an aircraft has changed!