Wright Brothers – The Kitty Hawk Years

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

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

George Spratt, a young physician from Coatesville, Pennsylvania, was a good friend of Wilbur and Orville Wright. He was interested in the possibility that man be able to fly from an early age and found a common field of interest with the Wrights. He was with the Wrights at Kitty Hawk during 1901, ’02 and ‘03.

They had a falling out in later years when Spratt claimed that the Wrights didn’t give him sufficient credit for technical suggestions he gave them. Twenty-one years after they met all communications ceased when Spratt, in a letter, called the Wrights “secretive, obstructive and lacking in vision and generosity.”

Spratt once wrote that he was fascinated by flying creatures since boyhood. “Flying has been the dream of my life. I never scared a bird up or saw a valley, but I longed to go with it and envied it.”

The Wrights found Spratt to be a kindred spirit that shared their interest in the study of aeronautics. He was congenial and liked to tell funny stories.

Unfortunately, Spratt had a tragic downside. He was prone to depression that seemed to grow worse with age. The Wrights called the affliction “the blues” and Wilbur on several occasions tried to pull him out of it.

Spratt had a scientific background, having graduated from medical school in 1894. Strangely, the 28-year-old soon after graduating gave up his medical practice, claiming it was too strenuous on his heart and took up farming, which would seem to be a more strenuous physical occupation.

Spratt began his involvement with the Wrights when, like Wilbur, Spratt wrote Octave Chanute seeking information on aeronautics and asked him for a critique on a paper he authored on the possibility of man-flight.

In his letter of 1898 to Chanute he said, “Being very much interested in flying machines and fully believing in their economical practicability, I have had my views on the subject type written and send you a copy. I wrote them down primarily that I might have clearer grounds for experimenting, but am getting discouraged accomplishing so little for various reasons, principally lack of sufficient funds. With the discouragement, boldness makes itself felt and I take this liberty of addressing you. The flying machine must come and it will soon come.

He continued, “Studying the subject principally from observation of birds, etc., in complete isolation from other interest, I am ignorant of the advance made. — Will you do me the favor of reading and criticizing the promises and conclusion? I will surely count it as a favor. Am I on the line of thought generally accepted as correct? How can I keep in touch with the advances made? I want to know more,  I want to do more.”

Spratt shared with Chanute that he was studying the movement of the center of pressure on a curved surface and had designed an apparatus for measuring the lift on airfoils.

Chanute was impressed with his interest and activity and encouraged Spratt to continue his study. He further suggested that Spratt devise methods of testing the lift and movement of the center of pressure on a cambered wing.

Chanute backed-up his encouragement with an offer to pay his expenses for his experiments, including the construction of a full-scale glider.

Even though Spratt had said that he had accomplished little because of insufficient funds, he refused the offer of money because he thought he would “bungle” the job. Apparently Spratt had little confidence in his own ability to actually construct something.

On June 26 and 27, 1901 Chanute visited the Wrights in Dayton where they had a good conversation on what the Wrights were doing and the state of aeronautics in general.

As a result of the visit, Chanute decided that he would provide as much support for the Wrights as he could.

Chanute believed that the complex problem of flight could best be solved through a team approach. Several days after their meeting in Dayton he wrote to the Wrights, offering to send two assistants at his expense to Kitty Hawk for their 1901 test flights. The Wrights didn’t want nor need any help, but didn’t wish to offend Chanute so they accepted his offer but not on the basis of the assistants working for them.

Edward Huffaker, who had worked for Samuel Langley and Spratt, were the two assistants.

The Wrights brought with them to Kitty Hawk the largest glider ever made. They hoped to have solved the previous year’s (1900) problem of inadequate lift. Spratt arrived for his first meeting with the Wrights on July 25, 1901.

While watching the Wrights assemble their glider, both Huffaker and Spratt warned the Wrights that they might encounter a pitching problem during flight because of a phenomenon wherein the center of pressure on a wing quickly reverses itself at low angles of attack. This could cause the pilot to lose control as the glider suddenly pitches downward. (Picture is of Spratt at Kitty Hawk)

The Wrights did experience problems with control and had to reduce the camber of the wings of their glider in order to minimize the phenomenon. The Wrights give credit to both men for pointing this problem out to them.

The Wrights returned home disappointed with their glider’s performance. They began to suspect that there were errors in the lift and drag data in the Lilienthal tables they were using to design their gliders. They decided to develop their own data.

During the lull in the activities at Kitty Hawk, Spratt shared with the Wrights some of his ideas about measuring lift and drift (drag is the modern term). Determining the value for drag was the most difficult to do. He suggested measuring drag as a ratio of “drift to lift” rather than trying to measure it directly.

Subsequently the Wrights designed two different clever mechanical balances for use in their wind tunnel they built. One balance was designed to measure lift and the other to measure drag. They were unlike anything that Spratt had suggested.

Calculation of Lift: Their lift balance measured the angle of deflection resulting from passing air over a sample airfoil and a reference flat surface. An indicator on the bottom of the device registered the angle of displacement in degrees caused by the amount of imbalance produced by the wind over the airfoil.

A mathematical calculation was made to find the value of a lift coefficient from the indicated angle (the sine of the indicated angle). Knowing the lift coefficient, the value of lift could be calculated from a lift equation.

Calculation of Drag: The Wrights built a second balance that directly measured the ratio of drag-to-lift as suggested by Spratt. Knowing the lift coefficient from the first balance and the drag-to-lift value from the second balance the coefficient of drag could be calculated.

The calculations were a time consuming job. Chanute spent some of his time helping them. The experiments consumed three weeks of effort. The development of the data was a remarkable achievement.

In 1902 Spratt again joined the Wrights at Kitty Hawk for glider trials. Wilbur told Spratt that the 1902 machine was “an immense improvement over last year’s machine.”

The Wrights continued to enjoy Spratt’s company and their debates on the finer points of aeronautical theory.

After Spratt returned home, he sent $10 to the Wrights to cover some of his expenses for his three-week stay in camp.

Wilbur wrote him back, “Moreover we feel that your help was worth more than your board, so you owe us nothing anyhow. — “We owe you, not you us.”

In truth Spratt had contributed little other than the pleasure of his company and the concept on which the drift balance had been based. The latter was the year before.

The Wrights continued their lively discussion through the mail.

Spratt was working on his own theories but he became discouraged as he viewed that his own progress was not proceeding as well as the Wrights. He also was having trouble coping with the rough and tumble of the Wrights debating style and the realization that he was losing most of the arguments.

Wilbur wrote, “I see that you are back at your old trick of giving up before you are half beaten in an argument.”

In another letter Wilbur chided him, “I felt pretty certain of my own ground but was anticipating the pleasure of a good scrap before the matter was settled. Discussion brings out new ways of looking at things and helps round off the corners.”

Spratt in turn complained that their method of rounding off the corners by switching sides in the middle of an argument struck him as dishonest.

Spratt was invited back again to Kitty Hawk in 1903 to witness the attempt for the first manned-flight of the Flyer. Spratt, a good worker, helped construct the sixty-foot monorail to be used for launching the Flyer.

On November 5, the Wrights started the engine on the Flyer for the first time. The engine ran, but the vibration from several missed explosions caused one of the propeller shafts to twist. The shaft would need repair and both of the shafts strengthened. That would require sending them back to Dayton for repair as soon as possible.

Spratt decided to leave camp for home. He was upset and convinced that the Wrights were heading for disaster. He volunteered to take the shafts with him and arrange to have them shipped back to Dayton from the mainland.

The Wrights didn’t see Spratt again until 1906 although they kept up their correspondence during the interval. In one letter Orville described his joy at their accomplishments by writing, “Isn’t it astonishing that all of these secrets have been preserved for so many years so that we could discover them!”

In another letter Wilbur tried to get Spratt out of one of his periodic bouts of the blues: “I am sorry to find you back at your old habit of introspection, leading to a fit of the blues. Quit it! It does you no good and it does do harm.”

The Wrights were on a business trip in 1906 and stopped by Spratt’s farm in Coatesville for a side visit on their way from New York to Philadelphia. Spratt spoke of an airplane he was designing that didn’t need warping of wings, use of ailerons or a moveable tail to exercise control. He called it the “Equilibrium Machine.”

Spratt believed that the design of the Wrights’ system of control was unsafe. He believed that a way should be found to design a machine that was automatically stable. Spratt later complained that Orville and Wilbur didn’t show any interest in his idea.

By now Spratt was increasingly obsessed with the idea that he hadn’t received credit for being the one that told the Wrights about the measurement of the lift/drag ratio.

In 1908 he sent a harsh letter to the Wrights accusing them of depriving him of the credit for the design of the lift balance used in their wind tunnel experiments in 1901.

Wilbur answered, “We have not wished to deprive you of the credit for the idea, and when we give the world that part of our work, we shall certainly give you further credit.” “— But while we considered the idea good, I must confess that I am surprised and a trifle hurt when you say that the advice and suggestions we gave you in return cannot be considered in any degree a fair compensation.” “— But aside from the ideas and suggestions you received from us, we also furnished you copies of our tables, not only those made on the machine ( drag balance) of which your idea formed a part, but also on the pressure testing machine (lift balance).” — “I can cannot help feel that in so doing we returned the loan with interest, and that the interest many times outweighed in value the loan itself.”

In 1922, Orville was compiling a history of the development of the first airplane and wrote Spratt asking for copies of letters that Wilbur and he had written to him about their wind tunnel and propeller experiments.

Spratt responded by repeating his grievance and refused to send the documents. The friendship soured. Orville never wrote to him again.

One month before Spratt died in November 1934, he flew an airplane that he built. Spratt claimed that the machine incorporated all of his theories about airplane stability that he had devoted most of his life discovering.

It was a bizarre airplane. In an old film clip, Spratt is shown suspended like the weight on a pendulum several feet below the wings of the frail biplane.

Sprat claimed that the machine incorporated all of his theories about airplane stability that he had devoted most of his life discovering.

It is a sad commentary on Spratt’s life that a man who had been a confident of the Wrights and an eye witness to the events at Kitty Hawk, was featured with his airplane in a humorous newsreel clip called Aeronautical Oddities.

References: The Bishops Boys by Tom Crouch; Wilbur and Orville by Fred Howard; “The Forgotten Third Wright Brother” by Joe D’Angelo, Coatesville Ledger.

Edward Huffaker was another of the young men that Chanute sponsored. He was building a glider for Chanute and Chanute prevailed on the Wrights to allow Huffaker to test the glider at Kitty Hawk while the Wrights were camping there during their own 1901 glider experiments.

It wasn’t long after Huffaker’s arrival that the Wrights found he was a disagreeable presence, unlike the friendly feeling for George Spratt, another protégé of Chanute who joined them.

On June 26 and 27, 1901, Chanute visited the Wrights on the way to Chuckey, Tennessee where Huffaker was building a glider designed by Chanute. Two days after visiting Huffaker, Chanute wrote Wilbur asking for his permission for Huffaker to bring the glider to their camp and attend the Wrights’ test flights at Kitty Hawk. Huffaker could test Chanute’s glider and be of help to the Wrights. Chanute assured Wilbur that he was reliable.

Wilbur agreed to his attendance as a favor to Chanute.

On paper Huffaker appeared to be a valuable person to have around. He had attended college at Emory and Henry where he graduated in 1876, and completed a master’s degree in physics from the University of Virginia in 1883.

He was interested in aeronautics and began making small glider models in 1892. From 1895 to mid 1896 he worked for Samuel Langley at the Smithsonian Institution, designing wings for Langley’s Aerodromes, and now he was working for Chanute.

When Wilbur wrote the Smithsonian in 1899 asking for information on aeronautics, one of the papers he received was “Soaring Flight” by Huffaker.

Langley praised, “Soaring Flight.” In the introduction to the paper Langley wrote, “I put trust in the good faith with which he reports his observations and in the conscientious care with which he has made them.”

Langley, who was fastidious, didn’t approve of Huffaker’s habits. He read documents with his feet on the table and he chewed tobacco and would squirt a stream of tobacco juice into a spittoon on the other side of the room.

The Wrights arrived at Kitty Hawk on May 10th and established their camp four miles south at Kill Devil Hills where they were soon plagued by mosquitoes. When Huffaker arrived one week later, Orville wrote to Katharine, “He can’t decide which is worse, the mosquitoes or Huffaker.”

Orville and Wilbur found it difficult not to laugh when they first saw the glider Huffaker brought with him.

The wing struts for the 5-wing glider were made of cardboard tubing instead of wood. The wings were designed to fold for easy storage and the fabric was attached to the wings so as to automatically vary their curvature with changes in the wind.

The design was in keeping with Chanute’s idea that a glider could be made that would provide automatic control in flight.

When Chanute saw that Huffaker had substituted cardboard for wood in the struts, he was not happy. He decided to go ahead with test flights at Kitty Hawk anyway.

At Kitty Hawk, the glider was found to be too frail to fly and failed to survive a heavy rain. Huffaker quickly gave up any attempt to fly before Chanute even arrived in camp.

Wilbur took a picture of the rain-soaked remains of the glider and later sent a picture of it to Spratt with the advisory, “If you feel the you have not got much to show for your work and money expended, get out this picture and you will feel encouraged.”

During the remainder of Huffaker’s stay in camp he helped launch the Wright’s glider and took notes. He and Spratt also provided some technical help when they advised the Wrights that the pitching problem Wilbur was experiencing during flight might be caused by the sudden reversal of the center of pressure on the wings.

Overall Huffaker was amazed at what the Wrights were achieving with their glider. The Wrights didn’t share his enthusiasm. They knew that there were serious theoretical problems with lift and control yet to be solved. Wilbur was so depressed on the trip home that he said man might never fly in his lifetime.

Chanute had instructed Huffaker to keep a daily record of the gliding experiments until his arrival. When the Wrights examined the notes after they returned home, they found them to be “inaccurate, as the man was shiftless.”

What really infuriated Wilbur was that Huffaker would lay the stopwatches and anemometers in the sand and use Wilbur’s camera box as a stool.

Also, the Wrights, sons of a Bishop, weren’t appreciative of Huffaker’s habit of delivering lectures on character building.

Wilbur thought he was “priggish and lazy.”

Wilbur thought he looked a bit sheepish when he finally left camp on August 8 with Wilbur’s blanket. He had the habit of borrowing tools and personal items without permission and not taking care of them.

He was still wearing the shirt he had put on soon after his arrival. On top of other everything else, Huffaker’s personal hygiene was poor.

The Wrights arrived home on Thursday, August 22. Katharine wrote her father, “They can only talk how disagreeable Mr. Huffaker was.”

A year later the Wrights were still upset. Chanute had written them about sending another protégé to their camp. Wilbur wrote back, “It was our experience last year that my brother and myself, while alone, or nearly so, could do more work in one week, than in two weeks after his (Huffaker’s) arrival.”