Wright Brothers – The Kitty Hawk Years

Articles relating to the years the Wright Brothers spent at Kitty Hawk.

By Darrel Collins

Darrel Collins is the knowledgeable and articulate Wright brothers historian at the Wright Brothers National Memorial Park, Kill Devil Hills, NC. This article is an edited version of one his interpretive talks that he recently gave at the park. Bob Holland and David Brinkley of radio station WCRS Akron, Ohio who provide programming for the blind recorded it.

Control, Key to Human Flight

How many children like homework? The key to the success of the Wright Brothers was that they did do their homework

They didn’t just jump head first to try to solve this problem.

They wrote to the Smithsonian Institution in Washington D.C. in 1899 asking for all available information on man’s early attempt to solve the problem. In essence the Wright Brothers learned from other people’s mistakes. They studied those that had attempted flight as far back as the 500-year-old drawings of Leonardo Da Vinci.

From all the information they identified problems that would have to be solved by the scientific method in order to achieve powered flight. They were true engineers.

The problem the Wright Brothers identified in 1899 as the key to human flight was the problem of control. And that is the problem the Wright Brothers solved at Kitty Hawk. It would take them four years to solve that one problem.

One of the very first books that the Wright Brothers studied on the subject was a book by Octave Chanute. He was an expert at that particular time. He published a book in 1894 named, “Progress in Flying Machines.”

This is a letter that Wilbur Wright wrote to Octave Chanute on May 13, 1900. It is probably the very first letter written by the Wright Brothers dealing with the subject of aerodynamics.

I want you to listen to Wilbur Wright’s passion, his desire, and his commitment in trying to solve this problem.

Dear Sir:

“For some years I have been afflicted with the belief that flight is possible to man. My disease has increased in severity and I feel that it will soon cost me an increased amount of money if not my life.”

On the cold windy morning of Dec. 17, 1903 the dream came true. Wilbur and Orville Wright made the world’s first successful powered flights in a heavy than air machine.

Five years after this historic event in Paris, France after Wilbur Wright had taught the Europeans to fly, at a banquet held in his honor on the evening of Nov. 5, 1908 Wilbur Wright spoke to members of the Aero Club of France.

“It is not really necessary to look to far into the future. We have seen enough already to see that it will be magnificent.”

The prediction is much truer for us today than it was in his lifetime. Four years after that speech in Paris at the age of 45 years old, Wilbur would pass to the great beyond. His brother, Orville Wright, would live to see it all.

Wright Memorial, Kitty Hawk

At the Wright Memorial in Kill Devil Hills, NC there is a large granite boulder that marks the spot where the Wrights made their famous flights in 1903. It was first placed at the site on Dec. 17, 1928 to commemorate the 25th anniversary of the first flight. This boulder was the first marker placed on this site.

We are getting ready for the big celebration now on Dec 17, 2003. It will mark an important milestone in the history of the world – 100 years of powered flight. But it also marks the end of a great era. Technology born at this site shortly after the turn of the 20th century has allowed man to travel to the moon in the lifetime of a human being.

Orville Wright was here for the 25th celebration. Along with Orville was a young lady. She was very much interested in aviation, Amelia Earhart. She had become the first woman to fly the Atlantic Ocean in June 1928.

They started work on this park in 1927. That monument on the hill was dedicated to Wilbur and Orville in 1932. Orville was there that day. Remember his brother, Wilbur, had been dead for 20 years. Wilbur died of Typhoid Fever at the age of 45 in 1912. He didn’t live long enough to see the dream of his and his brother fulfilled.

Orville lived to 76 years of age and died in 1948.

On the other hand, do you realize what Orville Wright saw in his lifetime?

He saw Dogfights of WW I, he saw the rocketry in WW II and the beginning of the jet age with German jets. The year before Orville died, Chuck Yeager broke the sound barrier in the Bell X-1. It was an inventor’s lifetime.

At that time the Wright Memorial was the largest monument and probably still is dedicated to a living human being in America. Other monuments were constructed all over the world for the Wright Brothers in Germany, in France and in Dayton.

The most impressive monument, however, is in Kitty Hawk where it all began.

Wright Brothers in Kitty Hawk

They were looking for a place to fly gliders and kites. He wrote to the National Weather Bureau in Washington, D.C. inquiring of a place on the East Coast where the wind was constant.

Kitty Hawk, NC was on the list. They tried to write a letter to all of these places and tried to get people to reply.

Wilbur wrote to the Kitty Hawk weather station, established in 1875. It was located four miles up the beach on the ocean side. That’s where the Federal telegraph office was located.

Somehow this letter ended up in the hands of the postman of Kitty Hawk. His name was William Tate. He was the most educated man living on the Outer Banks at the time. So he was put in charge of writing back to Wilbur Wright.

Tate wrote Wilbur, there are no trees or grass, and this was open beach and deep sand.

To the west was the sound. You might see a few sailboats. To the east you would see waves breaking on the ocean shore.

In a bad hurricane the ocean would wash completely across the narrow beach all the way to the sound. It will still do that today in a bad hurricane.

At the time there was Kill Devil Hill, West Hill and two little hills. West Hill was 90-feet high, as high as Kill Devil Hill is now and there were two little hills that were each 40-feet high. The little hills blew away in a hurricane of 1912, the same year that Wilbur died.

On top of the hills, the Wright Brothers would carry on their glider experiments.

In 1902, the year before they built the first powered airplane; they flew their glider off the tops of these hills 1,000 times over a period of six weeks. Almost 500 times each.

Three-axis Control

In 1899, the Wright Brothers identified control as the key to human flight. It took them four years to solve that one problem.

The three axis of control consist of roll, pitch and yaw.

Roll: Roll is the motion controlled by ailerons. On the Wright machines it was known as wing warping. This is the motion that everyone in the world at that particular time thought was suicidal. No one would ever do this to an airplane or glider except the Wright Brothers. This is the trademark of the Wright Brothers invention. It allowed an airplane to turn under control. No one else in the world could make an airplane turn.

Pitch: Then we have pitch, the up and down motion controlled by the elevator.

Yaw: Then we have that old southern word, yaw, controlled by the rudder in the back.

The control that the Wright Brothers developed at Kitty Hawk in 1902 has withstood the test of time. It has proven to be the fundamental principles around which everything that flies has evolved in the last 100 years.

Airplanes and gliders are not the only man-made flying machines that utilize roll, pitch and yaw. Everything that flies – rockets, missiles, satellites, helicopters and the space shuttle on takeoff and final approach.

This is the immortal legacy of the Wright Brother’s achievements at Kitty Hawk. They did much more than just build and fly an airplane. They changed the world forever.

Flying at Kitty Hawk

Their gliders were hand launched. Two local fellows would take the glider to the top of the giant sand dune. The pilot would lie prone on the long wing of the glider. The two local fellows would run with the glider down the hill into the wind and let her go.

At this point in 1902 the Wright Brothers were having a ball. I don’t know about the local fellows.

Because on days when the wind was blowing right, they would log in that 1902 glider over 100 glides in one day.

Kill Devil Hill is a big pile of sand. In 1902 it was 120 feet high covering 31 acres of sand blowing in the wind. In the 25 years between 1903 and 1928 it had moved 450 feet toward the southwest.

I want you to imagine running up and down in ankle deep sand with an almost 250 pound glider 1,000 times. I don’t know where you are from, but that’s what we on the Outer Banks call southern hospitality.

They had wide-open spaces and deep soft sand to land on.

It was very hard to get here by sailboat. When you got here there weren’t too many people around to make fun of you. The Wrights walked around in suits and ties all day long.

Privacy, secrecy and isolation they found here that they couldn’t find anywhere else.

Tate said, “You boys come on down here and I will help you anyway I can. So they came and they would always come back until they died.

The Wright Brothers truly loved the Outer Banks of NC. They claimed that Kitty Hawk “cured all ills.”

The First Flight

On that morning of Thursday Dec 17 1903 the wind blew out of the northeast at 27 mph with gusts of nearly 30 mph. The open beach was cold. It had rained the night before and some of the fresh water puddles that had accumulated around the campsite had frozen over.

They waited until about 8 o’clock to see if the wind would die down some, but after a while they figured it wouldn’t get any better.

So Orville tacked a red sheet on the far side of their living quarters That bed sheet was a prearranged signal for the men at the Kill Devil Hills Life Saving Station, a quarter of a mile south on the beach, to come over and help them. They were about to fly the machine and it weighed over 600 pounds. The Wright Brothers couldn’t manhandle it by themselves.

Three men came from the station that morning – Etheridge, Dough and Daniels. A couple of locals also came. Brinkley, from Manteo, and Johnny Moore, a 16-year-old boy who just happened to be passing by.

We don’t know where Johnny Moore was headed. It was 8:30-8:45 Thursday morning. He might have been running a little late. Johnny Moore didn’t make it to school that day. You see, Johnny Moore stopped to see an airplane fly.

They took the plane from the hanger and set it up at the end of the launching monorail. There were no wheels on the plane. They knew about wheels because Orville raced bicycles and they were in the bicycle business. But they couldn’t use wheels on the machine because of the deep sand.

They had to devise a way to launch the airplane. So they had to build a runway. Their runway consisted of just wooden 2 x 4s sitting straight up with a wood crosspiece on the bottom and a little metal strip on top. The four 15-foot long pieces were placed end to end to provide a runway that was 60 feet long. Talk about a short takeoff – 60 feet.

Along this rail a dolly would move down the rail on two bicycle hubs mounted one behind the other. They would balance the main weight of the airplane on the dolly.

This whole starting system cost the Wright Brothers a grand total of $4.00. They only spent $1,200 for the whole five years.

During takeoff the machine and dolly moved down the 60-foot rail driven by the thrusts of two 8-½ foot propellers in the back. They were the world’s first true propellers. They were designed from the Wright Bother’s wind tunnel tests. The Wrights were the first to understand that a propeller is a revolving wing.

Each propeller was hand carved out of laminated spruce from a mathematical equation. The propellers developed 75 pounds of thrust each. So you have 150 pounds of thrust pushing the 750-pound machine through the air.

Once the machine lifted off the rail it would leave the dolly on the rail. The machine had an undercarriage shaped liked a sled to land on the sand.

Then they would have to drag the machine all the way back, set it up on rail and start over again. Later they would put wheels on their airplanes.

One of the Wright’s hobbies was photography. They set the camera up in the background focused on the end of the rail where they thought that the machine would takeoff.

Orville instructed John T. Daniels, one of the witnesses, to squeeze the bulb when the machine took off. Daniels had lived on the Outer Banks his entire life. You had to put a cover over your head and when you looked through the camera everything looked upside down.

When John Daniels saw that 750-pound machine takeoff, he lost it all. He was so excited that he couldn’t remember if he had squeezed the bulb or not.

This was not Instamatic film. These were 5 x 7-inch glass negatives. They had to be kept in solution until you developed them.

Can you imagine the excitement when the Wrights returned to their home in Dayton in their darkroom when the images of that first flight appeared on that glass negative?

It is the most famous picture in aviation – man’s first successful powered flight. And Daniels almost blew it.

When they set the camera up, focused it and told John Daniels to squeeze the bulb, they were looking after every one of us. So when your children or grandchildren have children, they can bring their children here and they can witness for themselves the miracle that occurred at Kitty Hawk.

For many people at that time flight was considered a true miracle

This photograph is just another example of how far Wright Brothers were looking into the future. They say a picture is worth 1,000 words.

When Orville released his restraining bar that was physically holding the machine back, that machine was moving down the rail into an almost 30-mph wind. Moving at about 7-8 mph groundspeed, it was moving so slow that brother Wilbur, dressed in his suit and tie, could run along.

You can see his footprints in the sand as Wilbur ran along keeping the right wing balanced before the machine even took off.

Footprints in the sand; It always reminds me of footprints that were left somewhere else. Only 66 years after the first flight at Kitty Hawk, man walked on the moon. The footprints are probably still there too.

After a 40-foot run, down the 60-foot rail, the machine lifted into the air and Orville Wright flew 120 feet in 12 seconds. “Twelve seconds to the stars.”

The entire flight could have flown inside a C-5A airplane.

It was a dawning of a new era in the history of mankind. And, life as many of our fathers knew it would never be the same again. Remember that little things do go long ways.

They would take turns after that first flight. They dragged the machine all the way back and set it up on the rail. Wilbur flew the second flight. Orville flew the third Flight.

Do you see what they were doing? Do you remember the first time you ever tried to ride a bicycle? Who was helping you out? Your daddy was helping you out. He propped you up, got you going and let you go. Then what happened? You fell down. He picked you up and got you going again.

There was nothing wrong with your bicycle!

The Wright’s machine was capable of flying eight miles.

Wilbur flew the fourth flight. It went 852 feet and stayed in the air for 59 seconds.

Wilbur and Orville were camera enthusiasts. Even before they got serious about flying, they loved to take pictures of family and home, bicycles, neighbor kids and events. In 1896 they wrote a weekly publication called Snap-Shots. Their father was interested in genealogy and had the children photographed several times as they grew up. So it was only natural that when the brothers began their flying experiments they would take lots of pictures.

Prior to 1902 they used a 4 x 5 camera.

For their later experiments they used one of the best cameras on the market, a “5 x 7” Korona-V made by Ernst Gundlach of the Gundlach Optical Company, Rochester, N.Y. It was a dry glass plate camera mounted on a tripod. Orville paid $85 for the camera, which was a fairly expensive investment for the penny-pinching Wrights.

The Korona-V camera used at Kitty Hawk is on display at the Carillon Historical Park in Dayton.

The Wrights didn’t bother with making detailed engineering drawings, so the best record we have of the invention of flight is revealed in the many pictures they took of their gliders and airplanes from their first glider in 1900 through the first practical airplane in 1905. It is the first major invention whose development was fully documented on film.

For each photo they kept a record of the date, subject, f-stop and type of film. Exposures were rarely shorter than 1/25 of a second.

There are at least 1,500 original prints that exist and some 300 glass-plate negatives that have survived. Some of the negatives, including the picture of the first flight, were damaged from being under water in the Dayton flood of 1913. The brothers printed all their photographs themselves in their darkroom located in a shed behind their house.

Wilbur once remarked: “In the photographic darkroom at home we pass moments as thrilling as any in the field, when the image begins to appear on the plate and it is yet an open question whether we have a picture of a flying machine, or merely a patch of open sky.”

They only took one picture of their glider at Kitty Hawk in 1900. The other pictures were of their surroundings like typical tourists.

In 1901, their friend Octave Chanute advised them to keep a detailed record. “Please take plenty of snapshots. You will want them to illustrate what you write.” But I don’t think they needed any advice because they recognized the important function photography would be in documenting their work.

And of course the most famous picture of all is the one that John T. Daniels, a local man from the life saving station, took of the first flight on the morning of December 17, 1903. Orville had set up the camera and carefully aimed it at the end of the launching rail. A class plate held in an light-tight holder had to be inserted into the back of the camera and the “dark side” removed before each exposure.

He instructed Daniels about how to snap the shutter and told him to do so the instant the Flyer left the rail. The shutter was air driven with a hand-held bulb used to blow air through a tube and push the shutter into action. Daniels had never taken a picture before but miraculously the picture turned out to be perfect.

A life-size sculpture depicting the famous scene has been constructed at the Wright Brothers National Monument. The bronze-and-steel piece will depicts the famous scene of the first flight and will shows Daniels behind the camera.

Most of the surviving photographs taken during 1900 with their 4 x 5 camera were of the landscape at Kitty Hawk and views of their camp. It was like they were tourists on vacation, which in a way they were. The photographs they took were of their glider flown as a kite on a tether.

The following years the photographs were mostly of their flying experiments. These were more difficult to do because they had to catch the moving glider within the frame of a camera mounted on a tripod. This required skill as well as a certain degree of luck.

They added to the camera a convertible anastigmatic lens that helped. The lens allowed the Wrights to vary the focal length from a wide angle to a long lens. The combination provided a slightly wide-angle view that was used to increase the probability of the glider being captured on the photographic plate.

The Wrights often discouraged photographs taken of them. In May 1903, Octave Chanute wrote them and requested they send him pictures of themselves to be included in an article on the Wrights that Chanute wrote for publication in the French magazine L’Aerophile.

Wilbur answered, “Your promise of our portraits for L’Aerophile is causing us a great deal of distress. I do not know how to refuse you when you have put the matter so nicely, and on the other hand, we haven’t the courage to face the machine (camera).”

The Wrights didn’t like others taking pictures of their machines either.

In 1905 at Huffman Prairie, reporters began to appear to investigate the increasing reports on the Wright Brothers’ flying activities. Wilbur positioned a person on the entrance road to tell any reporters that cameras were not welcome.

In 1908 in France, Wilbur jumped over a low fence to confront a man who was taking unauthorized pictures of his airplane that was in the process of being prepared for takeoff.

In 1909 at Fort Myer during the Army trial flights, Wilbur discovered a photographer snapping pictures after a minor crash. He picked up a piece of wood and threw it at him, then demanded the exposed plates.

When you look today at the pictures of flight that the Wrights Brothers took, one can almost experience the exhilarating thrill that they must have felt.

Unstable by Design

by Dr. Richard Stimson

in The Kitty Hawk Years

The Wright Flyer has very unstable flying characteristics because of its canard design (elevator in front). Even the Wright Brothers had trouble flying the machine and they had plenty of practice.

At Kitty Hawk Wilbur stalled the machine on his first attempt to fly on December 14, 1903. Three days later Wilbur and Orville were able to fly, but it was an undulating ride as the machine pitched up and down.

On the fourth flight that day Wilbur flew a distance of over 800 feet, but the machine was capable of flying all the way to the village of Kitty Hawk except that it pitched down and hit the sand which ended the flight prematurely.

The Wrights had good reason to select the canard design. They feared the life-threatening stall that killed Lilienthal in 1896. The stall is a condition when the wing ceases to have lift at a high angle of attack and the airplane dives and rolls.

If one is flying close to the ground as the Wrights were, there is no time to recover from a stall before crashing into the ground.

The canard design mitigates this condition. The small wing of the canard design stalls first while the main wing still retains some lift. The machine tends to sink flatly instead of diving steeply.

Another advantage of the canard is that the front elevator acts as a shock-absorber bumper. When Wilbur stalled the machine on December 14th, he broke the front elevator but he himself was unharmed.

The Wrights did not appreciate the aerodynamic forces that produced the instability of the canard design. They were well aware of the four basic forces of flight – lift, weight, thrust and drag – and that flight involved a balancing act among these forces.

What they did not take into account was how this balancing of forces changed when an airplane was flying. Changes in direction caused either by the pilot or the wind introduce rotational torques or moments that act upon the airplane.

Every lifting surface on an airplane can be considered to have a point where the lift and drag forces are focused. Aeronautical engineers call this the “aerodynamic center” and it is usually located approximately one-fourth back from the leading age of a lifting surface.

The total effect of all lifting surfaces on an airplane is centered at a point called the “neutral point.”

Without getting too detailed, here is what all this means.

An inherently stable airplane is one in which the “center of gravity” is located in front of the neutral point.

An inherently unstable airplane is one in which the “center of gravity” is located behind the “neutral point.” This is the case of the Wright Flyer with its canard design.

When the Wright Flyer is in flight, a rise of the nose, increases its lift and the “pitching moment” reinforces the upward movement of the nose.

In a stable configuration, the “pitching moment” resists the upward pitching movement.

An unstable machine requires the pilot to continually make adjustments to maintain pitch. The Wrights desired a machine that was unstable because they wanted to control it. They got more than they wished for.

In 1904 the problem of undulating flight at Huffman Prairie was causing them a lot of problems. They tried changing the center of gravity by moving the pilot position and the engine to the rear. That made things worse. They then moved the center of gravity forward by adding 20 pounds of ballast beneath the front elevator. That helped some

In 1905, they were still having undulation problems. The situation came to a head on July 14 when Orville lost control of the elevator and crashed at a speed of 30 mph. He was lucky not to have been badly injured. When he hit the ground, he was thrown through a broken section of the top wing and ended up in a tangle of the broken elevator dazed and bruised.

They then modified the machine by enlarging the elevator and moving it some four feet further out from the wing. The changes made a significant improvement in the flying ability of the airplane.

On October 5, Wilbur flew thirty circles over Huffman Prairie, landing only when his plane ran out of gas. He had been in the air over 39 minutes. It was the world’s first practical airplane.

The Wrights can’t be faulted for not understanding all the dynamic forces that were present while flying. It would be another two decades before aeronautical engineers began to understand them.

Fly Like an Eagle

by Dr. Richard Stimson

in The Kitty Hawk Years

Wilbur used to sit along the Miami River south of Dayton in a place called the Pinnacles and observe the birds flying. In his notes of 1900 he wrote, “The buzzard that uses the dihedral angle (v-shaped) finds greater difficulty to maintain equilibrium in strong winds than eagles and hawks which hold their wings level.”

The Wrights would remember that observation in designing the 1903 Wright Flyer. The Flyer had wings that drooped like an eagle in what is known as the anhedral configuration.

During their first flights of the 1902 glider on September 19, 1902 they found that while gliding down the slope of a sand dune, crosswinds would upset the glider. Orville first used the anhedral on the 1902 glider on the occasion of his first flight. (Wilbur didn’t let his younger brother fly before this time because he felt responsible to not let him hurt himself). This change, Orville said, would reduce the effects of unexpected winds that struck the glider from the side.

The brothers re-rigged the wings with a slight anhedral by trussing them so the wing tips drooped about 4 inches lower than the center of the wing.

They tried out the new configuration by flying the glider as a kite and found that it seemed to solve the problem. The glider-kite flew in crosswinds without an upset.

What they didn’t know was that they had created another problem. The anhedral configuration magnified the gliders already poor roll characteristic.

The next day Orville crashed when the glider suddenly rolled, turned up sidewise and slid into the sand in spite of all the warp that was applied. This happened on several occasions for no apparent reason. The brothers flew relatively low to the ground, so it didn’t take much of a loss of altitude for the lower wing to hit the sand and dig a small hole. Wilbur gave it the name, “well digging.”

Orville gave the following explanation of what occurred:

When the machine became tilted laterally it began to slide sidewise while advancing, just as a sled slides down hill or a ball rolls down an inclined plane, the speed increasing in an accelerated ratio. If the tilt happened to be a little worse than usual, or the operator were a little slow in getting the balance corrected, the machine slid sidewise so fast that this movement caused the vertical vanes to strike the wind on the side toward the low wing, instead of on the side toward the high wing, as it was expected to do. In this state of affairs the vertical vanes did not counteract the turning of the machine about a vertical axis caused by the difference of resistance of the warped wings on the right and left sides. On the contrary, the vanes assisted in the turning movement, and the result was worse than if there were no fixed vertical tail.

Orville thought of a solution one night when he had trouble falling asleep. He reasoned that making the stationary vertical tail movable would allow the pilot to turn the tail as a rudder to assist in making a controlled turn.

Wilbur liked the idea and improved on it by suggesting that the rudder be connected to the wing warping controls so that when the pilot warped the wings, the rudder would automatically move in the appropriate direction. The change significantly improved controllability, but did not solve it completely. That would have to wait until 1905.

The 1903 Flyer continued to use the anhedral design by incorporating a 10-inch droop in the wings.

The Wrights flew in a straight line into the wind on Dec. 17th. Their major control problem during their four flights that day was maintaining pitch.

It wasn’t until 1905 that the Wrights solved their major control problems and produced a practical airplane. By then they had made a number of design changes to their machine including eliminating the anhedral wing configuration.

The Wrights were never interested in designing a machine that was inherently stable. They wanted a machine that they could control in flight.

Flying like an eagle with drooping wing tips may have worked for their 1903 machine. They would later learn at Huffman Prairie during 1904/1905 that flying like an eagle was not the best configuration for handling pitch, roll and yaw and they produced the first practical flying machine in the world.

Roller Coaster Flight

by Dr. Richard Stimson

in The Kitty Hawk Years

When Wilbur made the first attempt to fly a powered machine on December 14, 1903, the Flyer rose in the air steeply to about fifteen feet, stalled and crashed into the sand. He blamed the crash on his unfamiliarity with the sensitive elevator control.

Forewarned, the four successful flights on December 17 were handled better but still resulted in roller coaster rides that could have flown farther if not for the sensitive elevator control.

This wasn’t the first time that they experienced problems using the elevator for pitch control. The elevator on their 1901 glider hardly worked at all. This was an unexpected result that they didn’t understand because they hadn’t experienced this problem with their previous year’s glider.

E. C. Huffaker and George Spratt, two of their visitors, suggested that the problem might be the reversal of the center-of-pressure on the wings. They had experienced similar problems in their own work.

The brothers didn’t think this was their problem because they were using a wing camber similar to what Otto Lilienthal had used successfully and they didn’t think he had run into this problem.

At this point in time the Wrights didn’t understand the true nature of the center-of- pressure on a curved wing and what was happening as the angle of attack changed.

Here is a brief explanation. When a flat surface is at right angles to a stream of air, the center of this pressure lies exactly at the center of the surface. As the angle of the surface is reduced (smaller angle of attack) the center-of-pressure moves forward toward the leading edge. It continues moving forward as the angle is reduced until the surface is parallel to the stream of air. The center-of-pressure is now directly against the leading edge.

The behavior of a curved surface operates differently. As the angle of attack decreases, the center-of-pressure moves towards the leading edge as before.

However, when the angle of attack nears zero, the center of pressure reverses and moves rearward on the surface. In the case of a cambered airplane wing, this movement of the center-of-pressure forces the rear of the wing upward and consequently the airplane into a sudden dive.

The Wrights decided to test the wing of their glider to determine what was happening. They removed the top wing of their glider and affixed two lines to the front edge. They flew the wing as a kite under a variety of wind conditions.

They observed that in light winds the wing pulled upward on the lines indicating that the center of pressure was in front of the center of gravity and the leading edge was forced upward.

In stronger winds the wings were forced down at a smaller angle of attack and pulled down on the lines. This demonstrated that the center of pressure had moved behind the center of gravity toward the trailing edge of the wing.

The brothers now knew that the control problem with the 1901 glider was caused by the sudden reversal of the center of pressure at low angles of attack. These sudden reversals required frequent movements of the forward elevator to maintain stability in pitch.

The back-and-forth center of pressure travel produces what is called a “pilot induced oscillation,” in which the pilot’s efforts to control pitch might actually make it worse.

Fortunately the Wrights had made the wings on the 1901 glider so that the camber could be easily adjusted. They reduced the camber from 1 in 12 to 1 in 19. The glider handled much better after the change.

The problem of pitch control returned in 1903. Part of the problem this time was that the elevator was hinged at its center. With this configuration, the airflow forced the elevator to sharply deflect on its own after only a small movement away from the neutral position. Once the oscillation started it was very difficult for the pilot to regain control of pitch, resulting in a roller coaster ride that ended with a premature crash into the sand.

The brothers had lengthened the lever that operated the elevator by four inches after Wilbur’s control problems on December 14th. It did provide 65% more leverage but it is doubtful that it did much good.

Despite their problems on December 17, 1903