Wright Brothers – Invention Of The Airplane

Articles relating to the Wright Brothers’ invention of the airplane.

In an extraordinary letter to Octave Chanute on May 13, 1900, Wilbur Wright reveals for the first time in writing his vision, aeronautical principles and plans to develop a machine that man can fly.

He chooses Chanute for his disclosure because of Chanute’s worldwide reputation as an expert on the history of aviation. In 1894, Chanute had published, “Progress in Flying Machines,” a compendium of practically all significant aeronautical works up to that time. Wilbur became aware of the book after his inquiry for information to the Smithsonian Institution the year before.

Wilbur is just beginning to emerge from the depression that has haunted him from the time he was injured in a hockey accident in high school. He knows that he has the ability to do something significant in his life. Solving the riddle of flight may be just that thing. Now he needs someone important involved in flight to give him confidence to proceed with his vision.

The carefully worded letter does the trick and triggers the beginning of a ten-year close relationship between the two, involving some 400 letters of correspondence until Chanute’s death in 1910.

Chanute was 45 years older than Wilbur. Wilbur was looking for feedback and confirmation from the senior engineer.

Here is the letter. I have taken the liberty to comment on its contents at various intervals.

The letter was written on stationery of the Wright Cycle Company, 1127 West Third Street.

“Mr. Octave Chanute, Esq, Chicago, Ill.”

“For some years I have been afflicted with the belief that flight is possible for 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. I have been trying to arrange my affairs in such a way that I can devote my entire time for a few months to experiment in the field.”

Comment: Here we see Wilbur’s passion, desire, and commitment to a task with great odds against success and risk to his life.

“My general ideas of the subject are similar to those held by most practical experimenters, to wit: that what is chiefly needed is skill rather than machinery. The flight of the buzzard and similar sailers is a convincing demonstration of the value of skill and the partial needlessness of motors. It is possible to fly without motors, but not without knowledge and skill. This I conceive to be fortunate, for man by reason of his greater intellect, can more reasonably hope to equal birds in knowledge, than to equal nature in the perfection of her machinery.”

Comment: Wilbur, unlike most if not all other experimenters at the time, points out the importance of a skilled pilot. From his experience with bicycles, he knew that a bicycle rider can control an inherently unstable bicycle once he learns how to do it through practice.

“Assuming then that Lilienthal was correct in his ideas of the principles on which man should proceed, I conceive that his failure was due chiefly to the inadequacy of his method, and of his apparatus. As to his method, the fact that in five years’ time he spent only about five hours, altogether, in actual flight is sufficient to show that his method was inadequate. Even the simplest intellectual or acrobatic feats could never be learned with so short practice, and even Methuselah could never have become an expert stenographer with one hour per year for practice. I also conceive Lilienthal’s apparatus to be inadequate not only from the fact that he failed, but my observations of the flight of birds convince me that birds use more positive and energetic methods of regaining equilibrium than that of shifting the center of gravity.”

Comment: Wilbur had much respect for the German aeronautical pioneer Otto Lilienthal who died in a crash when his glider lost lateral balance in 1896. However, Wilbur points out that Lilienthal was on the wrong track for two reasons. First, Lilienthal failed because his approach was not providing him enough flying time to learn the skills needed to fly. Secondly, his technique was wrong. He tried to maintain equilibrium of his glider by changing the center of gravity through shifting the weight of his body. Sadly, his good intentions, but faulty approach, resulted in his death.

In the next paragraphs Wilbur explains his approach.

“With this general statement of my principles and belief I will proceed to describe the plan and apparatus it is my intention to test. In explaining these, my object is to learn to what extent similar plans have been tested and found to be failures, and also to obtain such suggestions as your great knowledge and experience might enable you to give me. I make no secret of my plans for the reason that I believe no financial profit will accrue to the inventor of the first flying machine, and that only those who are willing to give as well as to receive suggestions can hope to link their names with the honor of its discovery. The problem is too great for one man alone and unaided to solve in secret.”

Comment: Here he lays out his plan to follow the Scientific Method, i.e. gather data, and proceed from hypothesis based on principles and test for practicality. He recognizes that the task is not easy. He will soon change his mind about sharing information with others when he finds that others have little to offer and want to copy his ideas.

“My plan is this. I shall in a suitable locality erect a light tower about one hundred and fifty feet high. A rope passing over a pulley at the top will serve as a sort of kite string. It will be so counterbalanced that when the rope is drawn out one hundred and fifty feet it will sustain a pull equal to the weight of the operator and apparatus or nearly so. The wind will blow the machine out from the base of the tower and the weight will be sustained partly by the upward pull of the rope and partly by the lift of the wind. The counterbalance will be so arranged that the pull decreases as the line becomes shorter and ceases when its length has been decreased to one hundred feet. The aim will be to eventually practice in a wind capable of sustaining the operator at a height equal to the top of the tower. The pull of the rope will take the place of a motor in counteracting drift (drag). I see, of course, that the pull of the rope will introduce complications which are not met in free flight, but if the plan will only enable me to remain in the air for practice by the hour instead of by the second, I hope to acquire skill sufficient to overcome both the difficulties and those inherent to flight.

Knowledge and skill in handling the machine are absolute essentials to flight and it is impossible to obtain them without extensive practice. The method employed by Mr. Pilcher of towing with horses in many respects is better than that I propose to employ, but offers no guarantee that the experimenter will escape accident long enough to acquire skill sufficient to prevent accident. In my plan I rely on the rope and counterbalance to at least break the force of a fall.”

Comment: The Wrights do not use the tower idea during the first visit to Kitty Hawk. At first they flew the glider like a kite. Then Wilbur found he could safely ride the glider in the prone position down the slope of a sand dune. Chanute in his response to this letter had advised Wilbur not to use the tower, rather glide off the dunes.

Percy Pilcher was an assistant lecturer in naval architecture and marine engineering at the University of Glasgow. He was inspired by the gliding experiments of Lilienthal and even visited Lilienthal in Germany. Pilcher constructed a number of gliders and had plans to apply a motor to one of them. While giving a glider demonstration to a group of Englishman on his estate, he crashed and died in 1899.

“My observation of a flight of buzzards leads me to believe that they regain their lateral balance, when partly overturned by a gust of wind by a torsion of the tips of the wings. If the rear edge of the right wing tip is twisted upward and left downward the bird becomes an animated windmill and instantly begins to turn, a line from its head to its tail being the axis. It thus regains its level even if thrown on its beam ends, so to speak, as I have frequently seen them. I think the bird also in general retains its lateral equilibrium partly by presenting its two wings at different angles to the wind, and partly by drawing in one wing, thus reducing its area. I incline to the belief that the first is the more important and usual method.”

Comment: Wilbur describes his discovery of how birds maintain equilibrium. He applies this concept to the building of a five foot, bi-wing kite in 1899. It works! He’s now ready to apply the concept to a glider that he can fly.

” In the apparatus that I intend to employ I make use of the torsion principle. In appearance it is very similar to the double-deck machine with which the experiments of yourself and Mr. Herring were conducted in 1896-7.”

Comment: He tells Chanute he plans to use Chanute’s idea of a bi-wing, Pratt truss design.

“The point on which it differs in principle is that the cross-stays which prevent the upper plane from moving forward and backward are removed, and each end of the upper plane is independently moved forward or backward with respect to the lower plane by a suitable lever or other arrangement. By this plan the whole upper plane may be moved forward or backward, to attain longitudinal equilibrium, by moving both hands forward or backward together. Lateral equilibrium is gained by moving one end more than the other or by moving them in opposite direction. If you will make a square cardboard tube two inches in diameter and eight or ten long and choose two sides for your planes you will at once see the torsional effect of moving one end of the upper plane forward and the other backward, and how this effect is attained without lateral stiffness.”

Comment: Here Wilbur reveals the concept of “wingwarping.” He believes that effective control is the key to successful flight. Wingwarping provides lateral control of an airplane. Lack of such control is what killed Lilienthal and Pilcher.

Wilbur explains the concept by using as the example the now famous bicycle tube box. Wilbur was talking to a customer one day when he absentmindedly twisted the ends of the narrow box in opposite directions. He immediately conceptualized a pair of biplane wings, vertically rigid yet twisted into opposing angles at the tips.

Chanute never does understand the concept of wingwarping. He was focused on developing a way to build automatic stability into his gliders.

“I plan to attach the tail rigidly to the rear upright stays which connect the planes, the effect of which will be that the upper plane is thrown forward the end of the tail is elevated, so that the tail assists gravity in restoring longitudinal balance. My experiments hitherto with this apparatus have been confined to machines spreading about fifteen square feet of surface, and have been sufficiently encouraging to induce me to lay plans for a trial with a full-sized machine.”

Comment: Wilbur’s kite in 1899 was rigged so that he could warp the wings.

The Wrights used a horizontal tail. The vertical tail was first used on the 1902 glider.

“My business requires that my experimental work be confined to the months between September and January and I would be particularly thankful for advice as to a suitable locality where I could depend on winds of about fifteen miles per hour without rain of too inclement weather. I am certain that such localities are rare.”

Comment: Wilbur explains he doesn’t want his experiments to interfere with the bicycle business.

Chanute suggests locations in San Diego, Pine Island, Florida and the Atlantic Coasts of South Carolina and Georgia.

Wilbur also wrote to the U.S. Weather Bureau, which resulted in the selection of Kitty Hawk.

“I have your Progress in Flying Machines and your articles in the Annuals of ’95, ’96 and ’97, as also your recent articles in the Independent. If you can give me information as to where an account of Pilcher’s experiments can be obtained I would greatly appreciate your kindness.”

“Yours truly,

Wilbur Wright”

Comment: Chanute had little to offer on Pilcher.

Wilbur does receive the response he was looking for from his letter when Chanute responded that he was “pleased to correspond with you further and to have a more detailed account of your proposal.”

A reproduction of the 1903 Wright Flyer built by the Wright Experience (WE) made two successful flights at the Wrights Brothers National Memorial Park in December 1903. The flight on Nov. 20 marked the first time in 100 years that an authentic Wright Flyer successfully flew. The flight flew 97 feet into a 12-mph wind out of the north.

A second flight was successfully flown for 115 feet on Dec. 3rd. This flight had to cope with crosswind and upon landing with the left wing low, broke several ribs.

Several replicas of the 1903 Flyer have also flown. Replicas, however, differ in some respect such as materials, engine, and structure from the original Wright Flyer. Even the Flyer that hangs from the ceiling of the Air and Space Museum differs in some subtle respects from its original configuration.

Some of the teams that built replicas claimed that an authentic Flyer could not fly and it was dangerous to try.

The remains of the damaged original Flyer were badly damaged at Kitty Hawk in 1903 and stayed in crates in Dayton for 13 years. They were further abused when the crates were submerged in the great Dayton flood of 1913.

In 1916 Orville reconstructed the Flyer for the first time in thirteen years for display at a dedication of two new buildings at MIT in Cambridge, Mass. Damaged parts and material were replaced at that time. The reconstruction was guided by Orville’s memory because no detailed engineering drawings were ever made. Precise accuracy was not required because the plane was being reconstructed for display and not for flight.

The Flyer underwent another reconstruction in 1925 in preparation for being sent to the Science Museum of London.

The Wright Experience (WE) conducted a detailed investigation into the construction of the original Flyer using photographs and existing artifacts. They found that there were subtle but significant changes between what they discovered and the Smithsonian drawings of the Flyer made in 1985. Those drawings were considered the most accurate at the time and were used in building many of the replicas.

The reproduction Flyer built by the WE reflects changes such as the shape of the canard and the placement of bracing wires.

The WE installed a digital onboard flight data recorder on their Flyer that allowed the acquisition of 15 channels of in-flight data during the evaluation flights. They also conducted 20-hours of simulated flight tests in the wind tunnel at Langley in Hampton, Va.

What follows next is an overall summary of what the WE learned about the behavior of the Flyer.

First of all they confirmed that the Flyer is flyable; however it takes considerable knowledge and experience to do it well. The Wrights said that stability depends on the skill of the pilot because the machine was not designed to have inherent stability. The WE team gained a tremendous respect for the competence of the Wrights as operators of their flying machines, “something that 100 years of flying has not improved upon.

Some of the WE technical findings are provided next.

The lower wing is nominally 2 feet above the ground during the takeoff roll. The resulting ground effect produces a substantial contribution to lift and a reduction in induced drag.

The wings, having an anhedral shape (10-inch droop), also provide a contribution to lift as well as facilitating level flight.

Controlled flight is possible at a few feet of altitude, so the ground effect plays a significant role throughout the flight profile.

The Flyer can only rotate 3.5 degrees on takeoff before the tail will strike the rail. At this point the target rotation speed is 26-mph.

The tail assembly is hinged so that a higher degree rotation does not necessarily result in damage to the plane.

As noted before, the Flyer is substantially unstable. The Wrights wanted it that way because they wanted to exercise control over the airplane in flight. The center-of-gravity of the machine is located 2-feet aft of the 6.5-foot leading edge of the wing. The camber of the wing is 5%. The location of the center of gravity is too far to the rear and is responsible for much of the instability that caused undulation during flight.

Because of the machine’s instability, it never flies strictly at trim. It will operate over the full range of canard travel and corresponding variations in the angle of attack.

To maintain control, the Flyer must be operated within a narrow range of warp deflections and sideslip angles. Yaw is affected by the propwash over the vertical tail.

There is large roll power available and that helps reduce the need for full deflection and thereby also reduces adverse yaw.

The flight on Dec. 3rd demonstrated the roll instability of the aircraft and its behavior in side slipping conditions. About one-second after takeoff, a left crosswind caused the airplane to roll right. The pilot, Kevin Kochersberger, compensated for the crosswind by holding a slight right warp during roll.

The right wingtip hit the sand. The airplane recovered and continued to fly, although the ground strike caused a strong left roll. The left wing then struck the sand resulting in terminating the 115-foot flight.

A crosswind complicates the takeoff because warp corrections held on the rail must be lessened immediately at rotation as the angle of attack increases.

Kevin found that a positive canard deflection of least 10 degrees is necessary to initiate flight. Once takeoff speed is reached, the Flyer requires significant positive canard to rotate.

While flying, the unstable machine requires the pilot to continually make adjustments to maintain pitch. Kevin reports that the Flyer has a soft feel to its handling in part caused by the lag between the canard movement and the pitch response.

In addition to the natural instability of the airplane, it is very flexible structurally which makes all control responses a little less crisp than what a pilot would prefer.

With the canard being repeatedly operated almost to its limits, there is a sense by the pilot that the airplane is being over controlled.

The pilots from the WE found that the arched shape of their body they had to assume for forward visibility was not comfortable for long periods of time. They also found that the placement of their elbows was awkward because of the location of the fuel mixture control and the fuel line.

A good grip on the canard actuator was needed to work the hip cradle that required 14 pounds of force (same force as the Wrights found). Otherwise, the pilot’s body moves but the cradle doesn’t.

Stanley Allyn, chief executive officer of the NCR, was with Orville Wright at Wright Field shortly before Orville’s death. They were observing a new airplane in flight test.

Allyn asked Orville how he would like to fly that one. He looked startled for a moment and then answered that he couldn’t begin to.

Orville continued, “Wilbur and I lay on our stomachs, our hips in a cradle which connected to the wing tips by cables. When we shifted our hips to left or right, the wings were warped and the plane banked accordingly. We had no instruments, and had to judge how hard to push by the pressure exerted on our bodies by the plane in flight. You might say the flier just felt his way along.”

And so it was in 2003 also.

Reference: “Flying Qualities of the Wright 1903 Flyer: From Simulation to Flight Test,” by Kevin Kochersberger, Ken Hyde and others, AIAA-2004-0105, 42nd AIAA Aerospace Sciences Meeting, Reno, NV, Jan. 5-8, 2004

A frustrated Wilbur exclaimed to Orville in August 1901, “Not in a thousand years will man ever fly.”

At the time they were on a train returning to Dayton after failing for the second year in a row to achieve the lift for their glider that their calculations predicted. Wilbur recorded in his diary, “Found lift of machine much less than Lilienthal’s tables would indicate, reaching only about 1/3 as much.”

After further thought, Wilbur was cheered by the conclusion that the data they were using might be in error. In a speech on September 18 to the Western Society of Engineers, Wilbur suggested that “the Lilienthal tables might themselves be somewhat in error.” He also questioned the accuracy of the Smeaton coefficient.

Both the Lilienthal data and the Smeaton coefficient are used in the formula for calculating lift.

Otto Lilienthal was a famous German glider experimenter who had published a table containing coefficients of lift in 1895. The coefficient of lift is a multiplying factor that takes into consideration the various angles a wing assumes with regard to the flow of air know as the “angle of attack.” The value of the lift coefficient also varies with the shape of the wing.

The Smeaton Coefficient was used in the calculation of lift at the time of the Wright Brothers. It is a constant number used as a “coefficient of air pressure.” It serves as a multiplying factor used to calculate the numerical value of lift in air, as compared to other mediums, such as water or oil.

John Smeaton, an engineer, determined the value of this coefficient was 0.005 in 1759, from his study of windmills. Engineers used this value for 150 years, although others questioned its value and thought it was too high, including the famous early aviation pioneer George Cayley in 1809.

Both Lilienthal, in Birdflight, and Octave Chanute, in Progress in Flying Machines, cited the 0.005 value in their books. This heavily influenced the Wrights in using the same value.

The Wrights would soon find that the 0.005 value was too high. The error was a major cause of their calculation of a lift value that was too high.

Note: The Smeaton coefficient is no longer used in modern aerodynamic problems. Problems are formulated differently. My son, who is a graduate aeronautical engineer, had never heard of Smeaton when I first asked him about it.

Smeaton wasn’t the only source of their discrepancy between actual lift and their calculated values. They incorrectly interpreted the Lilienthal tables by not understanding that the table only applied to the one wing shape that Lilienthal used in his study. The wings that the Wrights used in 1900 and 1901 had different aspect ratios as well as differences in the location of the maximum camber of the wing.

The aspect ratio is a measure of the relationship between the length of the wing to the cord (width). The aspect ratio affects the value of the lift coefficient. Lower values of aspect ratio give lower values of the lift coefficient and visa versa within limits.

The aspect ratio for the Wright 1900 glider was 3.5 and the 1901 glider was 3.3. These values were considerably lower than the aspect ratio of 6.8 for the Lilienthal test wing. In other words, the Lilienthal wing was longer and narrower compared to the Wrights’ wing. The lift coefficient from Lilienthal’s tables used by the Wrights should have been reduced by 19% to account for their use of a lower aspect ratio.

Their other problem of interpreting the Lilienthal table had to do with the location of the point of maximum camber (high point on the curved wing).

The Wrights located their maximum camber close to the leading edge of the wing. The Lilienthal test wing was a circular shaped wing with the maximum point located at the middle of the cord. Here again the value coefficient of lift read from the table should have been reduced to account for the difference in location of the maximum camber.

The cumulative impact of the above errors on the calculation of lift amounted to the 1/3 reduction in lift that Wilbur noted for the Kitty Hawk 1900 and 1901 glider flights.

The Wrights decided to take a different approach to the problem of calculating lift. Rather than further examining the existing data provided by others, they decided to compile their own. They built an instrumented wind tunnel and developed their own aerodynamic data by systematically testing some 200 airfoils of widely different shapes and configurations, going well beyond the Lilienthal table.

Shapes included squares, rectangles, and ellipses in configurations such as biplanes and triplanes. They included camber ratios ranging from 1/6 to 1/20 and maximum camber locations ranging from near the leading edge to the 1/2-chord position.

They found that the correct value of the Smeaton coefficient should be 0.003 and developed their own table of lift coefficients (and drag coefficients).

Their airfoil #12 was found to be the most aerodynamically efficient. Its camber was 1/20 and the aspect ratio was 6. This foil was used as a guide in designing their successful 1902 glider and ultimately the successful 1903 Flyer.

The 1902 glider had an AR of 6.7, about twice that of their previous gliders, and used camber ratios much shallower than Lilienthal test wing.

With his new knowledge and understanding, he wrote to Chanute in October 1901, “It would appear that Lilienthal is very much nearer the truth than we have heretofore been disposed to think.”

It turned out to be fortunate that the Wrights had problems with the determination of lift. It led them into doing research that propelled their knowledge far beyond anyone before them and established the Wright Brothers as the leading aeronautical engineers of their day.

Reference: A History of Aerodynamics by John D. Anderson

The age of flight dawned on the morning of December 17, 1903 at Kitty Hawk, NC when the Wright Brothers’ engine-driven heavier-than-air Flyer lifted into the air and traveled 120 feet in 12 seconds. It was an extraordinary moment. The way that the press handled the event was far less than extraordinary.

That afternoon, after eating a leisurely lunch, the brothers set out about 2 o’clock to walk the four miles to the weather station office in Kitty Hawk. They sent a telegram of their success to their 74-year-old father in Dayton, Ohio. Three months earlier, while seeing his sons off in Dayton, Bishop Wright had given them a dollar to cover the cost of sending a telegram as soon as they made a successful flight. Now was the time.

There was no Western Union in Kitty Hawk, but Jim Dosher at the weather station had agreed to communicate with the weather bureau office in Norfolk who in turn would contact Western Union.

Dosher, however, was unable to deliver the news because of a break in the telegraph line. He telephoned Alpheus Drinkwater at another location on the Outer Banks who transmitted the coded message of the Wright Brothers’ successful flight to Norfolk. Drinkwater later said he was bit annoyed that he had to relay a few unimportant telegrams to the mainland.

(Note: The accuracy of the last paragraph involving the role of Drinkwater is in some dispute among historians. On the occasion of the dedication of the Wright Memorial in 1932, Orville Wright was asked who sent the first message – Drinkwater or Dozier? Orville stated: “The first message was sent by W. J. Dozier.” – News and Observer, Nov. 20, 1932 )

Orville wrote the message that was sent as follows:

“Success four flights Thursday morning all against twenty one mile wind started from level with engine power alone average speed through air thirty one miles longest 57 seconds inform press home Christmas. Orvevelle Wright”

An error in transmission cut two seconds off the longest flight time of 59 seconds and Orville’s name was misspelled. The wind speed of 21 mph is confusing. What Orville meant to say is that the wind was at least 21 mph during each of the four flights. The first successful flight was against a 27-mph wind.

The Norfolk operator sent a return message asking if he could share the news with a reporter at the “Norfolk Virginian-Pilot.” The Wrights gave an emphatic no! They wanted the first news of the event to be from Dayton.

The Norfolk operator, Jim Gray, ignored the negative answer and provided the information to a friend, H. P. Moore, at the paper. Having little information other than that provided in the telegram, the “Virginian-Pilot” fabricated a fanciful and inaccurate story that was published the next morning with the headline:

“Flying Machine Soars 3 Miles in Teeth of High Wind Over Sand Hills and Waves at Kitty Hawk on Carolina Coast.”

They also offered the story to the Associated Press (AP) and when they declined the story, offered the story to twenty-one newspapers.

Meanwhile Orville’s telegram arrived at 5:25 that evening. The Wrights’ father, Milton Wright, instructed daughter Katharine to walk over to her brother Lorin’s house and ask him to take the telegram to the local newspaper office for publication.

Lorin went downtown to the offices of the “Dayton Journal” and spoke to Frank Tunison, local representative of the Associated Press. Tunison was unimpressed with the telegram saying, “If it had been 57 minutes then it might have been a news item.”

Two other Dayton papers did publish an account the next day in the afternoon editions. The account in “The Dayton Daily News” gave a reasonably accurate account except that it made a big mistake in indicating that the Wrights were imitators of the world famous Alberto Santos-Dumont. The headline read “DAYTON BOYS EMULATE GREAT SANTOS-DUMONT.”

Santos-Dumont was a Brazilian who pursued aviation in France. In 1901, he had dazzled the French public by rigging an engine to a hot-air balloon and flew around the Eiffel Tower. The Dayton news-editor didn’t recognize the vast difference between balloons and airplanes.

The account in “The Dayton Evening Herald” under the heading of “Dayton Boys Fly Airship,” was a 350-word rehash of the fabricated story that had earlier appeared in the “Norfolk Virginian-Pilot.” The AP, the day after the first flight, had sent out an abbreviated version of the Norfolk piece.

The story was full of errors. “The machine flew for three miles — and then gracefully descended to earth at a spot selected by the man in the navigator’s car —.” “Preparatory to flight the machine was placed on a platform on a high sand hill —.” “When the end of the incline was reached the machine gradually arose until it obtained an altitude of sixty feet —.” “There are two six-blade propellers, one arranged just below the frame so as to exert an upward force when in motion and the other extends horizontally to the rear from the center of the car, furnishing the forward impetus.” Orville had run around shouting, “Eureka!”

The Wrights, mystified how a short low-keyed message in a telegram could have gone so wrong, prepared a correct story on January 5th of their successful flights and gave it to the AP with a request that it be printed. It appeared in a majority of the AP newspapers the next day.

Exactly one month after the historic flight, the New York Herald still had it wrong and published an article showing a picture with two “six-bladed” propellers and an engine beneath the airplane to provide lift.

Wilbur and Orville gave no details about their airplane. It was their invention, developed at their own expense, and they did not yet intend to provide any pictures or detailed descriptions of their Flyer.

A Beautiful Body

by Dr. Richard Stimson

in Inventing The Airplane

The Wrights’ flying machine had to be structurally strong, but light enough to fly. The task was made more difficult because in order to implement their wing warping system of flight control, the wings, in addition to being structurally sound, had to be flexible.

Just nine days before the Wrights’ successful first powered flight, the issue of structural integrity was dramatically highlighted when Langley’s highly touted aerodrome broke-up during launching. Post mortem analysis revealed inadequate structural analysis and design.

The Wrights, on the other hand, conducted careful stress analysis using engineering handbooks available at the time to estimate structural loadings on the wing spars and struts and to size and select materials.

The Wrights were concerned about safety from the very beginning, as was their father. In order to calm his fears, Wilbur wrote to their father in 1900 that “I am constructing my machine to sustain about five times my weight and am testing every piece.”

The Railroad Truss

The Wrights adopted a trussed biplane design as their basic approach. The concept was adopted from their friend Octave Chanute, a retired railroad bridge builder, who had adapted a “Pratt truss” design used on railroad bridges to a biplane glider he built in 1896.

Using the Pratt truss concept, the Wrights’ designed a bi-wing structure in which the upper and lower wings were trussed one above the other with struts and cross wires to form light, sturdy wing modules. Most builders of airplanes adopted this configuration for the next two decades.

Each wing was composed of eight such cross-braced modules. The trailing edge of the outer two modules on each end was not cross-braced to allow flexibility for wing warping. In this manner they had ingeniously solved the problem of how to twist the wings tips and still retain structural integrity.

The ribs of the wings were constructed of thin strips of ash that were bent to the desired camber. Blocks of wood were glued between the two strips and glued into position. The result was a strong, lightweight rib.

Bending the wings and the wingtips to the proper curvature was farmed-out to a local firm that made parts for the carriage industry. The Wrights didn’t have the necessary equipment for steaming the ash wood and then bending it to the proper camber. The wing tips were made from off-the-shelf carriage bows.

The ribs were attached to spars of kiln dried spruce. The spruce for the spars was procured from a local lumberyard. It was ordered cut into pieces of approximate length and shape. The Wrights then shaped the pieces using draw knives and spoke shaves.

All the wood pieces were painted with several coats of varnish to protect them from the high moisture environment of Kitty Hawk.

The fabric, made of Pride of the West Muslin procured from Rike-Kumler Co., a local department store located in downtown Dayton in the same block as one of their bike shops. The muslin was cut into strips and then machine-sewed with bias so that it would fit on the ribs on a 45 degree diagonal. It was then stretched over both the top and bottom sides of the spars and ribs, with each rib fitted into a sewed-in pocket. The design provided for strength as well as maintaining wing camber under stress in flight.

The wooden structure was assembled using waxed linen cord instead of nuts, bolts or screws. This design created a flexible joint that could withstand hard landings without breaking.

Orville commented that “these I believe, were the first double-surfaced airplanes ever designed or built.”

Seventy-inch spruce struts supported the upper and lower wings. The Wrights realized that a vertical column of this length would require a substantial cross-section to withstand the compression load without bending and possibly breaking. This had the potential of adding considerable unneeded weight and drag.

The Wrights solved the problem by adding a horizontal wire passing through the center of the highly loaded struts in order to prevent them from bending. By this means the cross-section of the struts could be reduced and still retain structural integrity. The proof that it worked is that none of the struts failed in wings gusts of over 27 mph during their first flights on December 17, 1903.

Back To The Future

As airplanes got faster and heavier, wing warping was replaced by the use of ailerons because of structural problems. The uses of ailerons, however, do have a down side. They increase drag and weight and therefore reduce fuel efficiency and overall performance.

Because of this performance degradation, NASA, the Air Force and Boeing are working on a $41 million project to modify an F/A-18A Hornet fighter jet with a twistable wing. The purpose of the project, Active Aeroelastic Wing, is to demonstrate that subtly twisting a wing a few degrees (up to five) can control its roll with less need for big control surfaces on the wings and horizontal tail. They hope to demonstrate that the lighter-weight flexible wings will improve the maneuverability of high-performance aircraft.

The project leaders envision that the benefits of this wing warping could apply to both military and commercial airplanes.

A traditional rollout ceremony was held on March 27, 2002 at NASA’s Dryden Flight Research center. The official Centennial of Flight logo in commemoration of the Wright Brothers first powered flight in 1903 was prominently displayed on the aircraft.

The ideas of Orville and Wilbur are still fresh after 100 years.