Wright Brothers – Invention Of The Airplane

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

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.

The Power to Fly

by Dr. Richard Stimson

in Inventing The Airplane

Flight is impossible unless there is enough thrust to maintain the flying speed of an airplane. A key factor in determining whether the 1903 Wright Flyer could sustain flight is to know the thrust required to overcome aerodynamic resistance known as drag. Once drag is known, the horsepower required of the engine can be determined.

What follows is an analysis similar to what the Wrights did to answer the question of how much power was required.

Drag is generated by two different surfaces on an airplane as it moves through the air. One is caused by the lifting effect on the wings and the other by the wind resistance caused by the frontal surface area of the airplane. The first is referred to as induced drag and the latter as frictional drag.

Drag

The formula the Wrights used to determine drag is very similar to the formula they used to determine lift. The only difference is that the coefficient of drag (CD) replaces the coefficient of lift (CL) in the formula. The basic formula is as follows:

D = k x S x V² x CD where
D = Drag (pounds)
k = pressure coefficient of air
S = wing area (square feet)
V = relative velocity of air over the wing (mph)
CD = coefficient of drag

For the 1903 Wright Flyer:

k = 0.0033 (Wrights derived from their wind tunnel experiments)
S = 512 (wing area of 1903 Flyer)
V = 30.8 (The wind ranged from 20 mph to gusts of 27 mph at Kitty Hawk on December 17, 1903. I used an average wind of 24 mph on Dec. 17, 1903 plus ground speed of 6.8 mph. Wilbur, running at the right wing tip, had no trouble keeping up with the Flyer as it moved down the starting rail to takeoff.)

The value of the coefficient of drag (CD) in the equation is a little more complicated to determine because the Wrights did not directly measure CD in their wind tunnel tests conducted November 22 through December 7, 1901. Instead, they measured the drag/lift ratio (CD/CL) from which the value of CD can be derived.

The Wrights measured the coefficient of lift (CL) as 0.515 and the drag/lift ratio (CD/CL) as 0.105 in their wind tunnel tests using airfoil #12 and an angle of attack of 5 degrees.

The geometry of airfoil #12 closely resembles the geometry of the wings on the 1903 Flyer. The angle of attack of 5 degrees approximates the angle of attack of the Flyer.

The coefficient of drag is calculated in the following manner:
CD = CL x CD/CL = 0.515 x 0.105 = 0.054

Substituting the appropriate values in the equation for drag:
D = (0.0033) x (512) x (30.8)² x (0.054) = 86.6 pounds

Total Drag

The drag of 86.6 pounds is for the drag attributed to the wings. To determine the total drag of the Flyer, the drag attributed to the wings (D) must be added to the drag generated by the frontal surface area of the airplane (Df).

The Wrights purposely assumed the horizontal position on the wing while piloting their machine to reduce drag. They estimated that the remaining frontal surface area of the Flyer was 20 square feet. Substituting this value in the drag equation:

Df = (0.0033) x (20) x (30.8)² x (0.054) = 3.4 pounds

The total drag (Dt) is therefore:

Dt = D + Df = 86.6 + 3.4 = 90 pounds

On November 23, 1903 from Kitty Hawk, Orville wrote Charles Taylor, their employee who built the engine following the design of the Wrights:

“After a few minutes to get adjustments, and to burn out the surplus oil, the engine speeded the propellers up to 351 rev. per min. with a thrust of 132 pounds. Stock went up like a sky rocket, and is now at the highest figure in its history. We have made some allowance at nearly every point in our calculations, so that with the increase of weight we expect to be a little over 90 pounds, but of course that is coming down to our closest figures.”

Power

Power is force times speed. The power required to overcome drag can now be found by multiplying total drag by velocity:

P = Dt x V = 90 x 30.8 = 2772 pound-miles/hour
Converting this number to horsepower, the power is 7.3

The engine for the 1903 Wright Flyer produced about 12 horsepower. It would reach 16 hp when started, but drop off to 12 hp after a few seconds. While the horsepower of the engine (12) appears to be sufficient to overcome the drag (7.3), there will be additional loss of horsepower attributed to the chain drives that transmit the power from the engine to the propellers. Also, there will be loss of power attributed to the propellers. The propellers had an efficiency of 66%.

The Wrights knew it was going to be a close call. On November 15, Orville wrote home to his father and sister:

“Mr. Chanute says that no one before has ever tried to build a machine on such close margins as we have done to our calculations.” (Octave Chanute was a friend and an aviation historian and experimenter.)

The question as to whether they had sufficient power was answered on that fateful day in December. They made four flights on the 17th, the longest flight going 852 feet.

The following year back in Dayton, they were not so fortunate even though they had more horsepower. The 1904 Flyer had trouble getting off the ground. Dayton didn’t have the wind of Kitty Hawk and the air pressure was less because of the higher elevation.

The 1904 Flyer was little changed from the Kitty Hawk Flyer although they did improve the engine so that it produced 15-16 hp. Wilbur wrote to Chanute on August 8, 1904:

“We have found great difficulty in getting sufficient initial velocity to get real starts. While the new machine lifts at a speed of about 23 miles, it is only after the speed reaches 27 or 28 miles that the resistance falls below the thrust.”

They solved the problem by employing a catapult launch system to give the Flyer a boost on takeoff.

The initial Wright engines were crude, but they did the job. They didn’t need a lot of horsepower because the Wrights had designed an efficient aerodynamic flying machine.

In contrast, Dr. Samuel Langley, Director of the Smithsonian Institution, employed a sophisticated engine that generated a whopping 50 hp, but his Aerodrome was poorly designed. It crashed on takeoff nine days before the Wright’s successful first flight.

The immediate impression of the Wright brothers is that they were just two bicycle mechanics from Dayton, Ohio who invented the first successful airplane. Maybe they were just lucky and stumbled on the solution through trial and error because this was a feat that had eluded the best minds for thousands of years.

After all, the brothers didn’t have a scientific degree or any formal education beyond high school. But don’t let that fool you. The reality is that they were brilliant scientists that outperformed the scientific elite of the day in the use of the modern scientific process.

The Airplane Propeller

An example of their prowess is their approach to the solution of an intractable engineering problem associated with their invention of a deceptively simple item, the airplane propeller.

In 1902, after their third trip to Kitty Hawk, they were confident that their glider would fly under pilot control. The next task was to develop a mode of propulsion.

They proceeded to design and build a small gasoline engine weighing 180 pounds that produced 12-horsepower. Now, they needed a propeller to go with it.

That seemed easy enough. Propellers have been used for years on ships. The respected scientist Samuel Langley, the Secretary of the Smithsonian had written in Experiments in Aerodynamics, “there is considerable analogy between the best form of aerial and of marine propellers.”

The Wrights initially thought they could convert the design information on ship propellers to flight technology. “We had thought we could adopt the theory from marine engineers, and then by using our tables of air pressures, instead of the tables of water pressures used in their calculations, that we could estimate in advance the performance of the propellers we could use.”

A trip to the Dayton Public Library quickly disillusioned them of the notion that this was going to be an easy task. Their research found there was no empirical information on how to do this and they didn’t have the time to use the trial-and-error approach used by marine engineers (the Wrights called it “cut and try”). They decided to develop new theory and design the propellers from scratch.

Their usual approach to solving complex problems was to first think about the problem and mentally develop a testable theory. Often, the brothers brainstormed ideas by vigorously debating ideas. Often these debates turned into shouting matches that were annoying to their sister, Katharine. Sometimes they would convince each other of the other’s argument and change sides to argue the opposite point of view.

Propellers as Rotating Wings

Out of this process came the insight that propellers acted like rotating wings traveling in a spiral course through the air. The rotating propeller blades act as airfoils that produce a pressure differential. Less pressure is created on the front of the spinning cambered blade than there is on the back, thus the rotating blade produces thrust that moves the airplane forward.

Now that they had the concept, the problem became how to calculate the thrust of a rotating blade. The blade must produce sufficient thrust to propel the airplane off the ground and sustain it in the air. Flight would not be possible if sufficient thrust couldn’t be generated to overcome drag.

The problem was difficult. Orville describes it best in a December 13 issue of Flying Magazine, “It is hard to find even a point from which to make a start; for nothing about a propeller, or the medium in which it acts, stands still for a moment. The thrust depends upon the speed and the angle at which the blade strikes the air; the angle at which the blade strikes the air depends upon the speed at which the propeller is turning, the speed the machine is traveling forward, and the speed at which the air is slipping backward; the slip of the air backward depends upon the thrust exerted by the propeller, and the amount of air acted upon. When any of these changes, it changes all the rest, as they are all interdependent upon one another.”

The Wrights did have one advantage. They had data from their wind tunnel experiments in which they had tested some 200 airfoils (wing shapes). They selected airfoil number 9 as their baseline because it showed the best efficiency under a variety of conditions.

The brothers developed a series of quadratic equations from which they designed the propeller. All this work was accomplished before the advent of computers. Based on their calculations, they used hatchets and drawknives to carefully carve a piece of wood into an eight-foot propeller with a helicoidal twist based on airfoil number 9.

After three months of effort, they tested their propeller in their bicycle shop using a two-horsepower motor with excellent results. The thrust achieved was found to be within 1% of what they had calculated — a truly amazing result.

Orville gleefully wrote to George Spratt, “Isn’t it astonishing that all these secrets have been preserved for so many years just so that we could discover them.”

Success

In June, they designed and made two propellers to be used on their machine, the Flyer. They determined that they could achieve greater thrust with two propellers rotating slowly, than they could with one propeller rotating faster.

Orville wrote, “all the propellers built heretofore are all wrong.”

Each propeller was 8.5 feet in diameter and made of three 1 1/8 inch thick laminations of spruce with the wing tip covered with light duck canvas glued on to prevent the wood from splitting. The entire propeller was then coated with aluminum paint.

The propellers were connected to the engine through a chain, gear and sprocket system, similar to a bicycle design. The propellers rotated 8 revolutions for every 23 revolutions of the engine. The two propellers were designed to provide a combined thrust of 90 pounds at airspeed of 24 mph and turning at 330 rpm.

The linkage was designed to rotate the propellers in opposite directions so as to counteract the torque effect of each rotating blade. This was achieved by crossing one set of chains in a figure eight and encasing the chains in medal tubes to keep them from flapping. The chains were procured from the Diamond Chain Company of Indianapolis.

The propellers were mounted at the rear of the wings as “pushers” to eliminate the effect of turbulent airflow upon the wings.

The finished product produced a maximum efficiency of 66% (Some recent tests achieved 70%). That means that 66% of the horsepower of the small motor was converted by the propellers into thrust. This was far superior to any other inventors who were attempting to fly with engines of much greater horsepower and still couldn’t sustain flight.

On December 17, 1903, the little engine with the efficient propellers pulled Orville off the launching rail and into the air producing the first heavier than air flight in the history of mankind.

Their remarkable achievement demonstrates the genius of the Wright Brothers and places them within the ranks of the greatest inventors in history.

Final Notes

An exact reproduction of the 1903 Flyer is scheduled to fly at Kitty Hawk on December 17, 2003 to celebrate the centennial anniversary of the first flight. The Wright Experience of Warrenton, Va., headed by Ken Hyde, is researching and building the Flyer.

Larry Parks, a volunteer working for Wright Experience, is carving the propellers using mainly antique tools. A member of the Wright family has provided an original 1904 propeller to aid in the project.

The Wrights continued to improve their propellers after 1903. One of the more interesting improvements was the so-called “bent end” propeller introduced in 1905. The purpose of the design was to prevent twisting under pressure.

Ken Hyde had one of their remanufactured 1911 bent end propellers that was used on Wright Model B airplane tested at the Langley Full Scale Wind Tunnel. It achieved an efficiency of 77% operating at a flying speed of 40 mph.

Hyde commented, “The performance of our remanufactured Wright propeller was amazing, when you consider that today’s wood propellers are only 85% efficient.”

The Secret of Flight

by Dr. Richard Stimson

in Inventing The Airplane

Since ancient times mankind has looked up to view birds flying and dreamed of flying.

The Wright brothers were no different. They often rode their bicycles to a popular picnic area south of Dayton called the “Pinnacles” to observe the many birds that flew there. Early on they decided that practical flight was possible by man using soaring large birds as their model.

The Pinnacles consisted of a gorge with a river flowing through it and unique large boulders created during the ice age on its slopes. The updraft created by the terrain attracted soaring birds. The Wright brothers regularly observed birds there from 1897 to 1899.

The Wrights developed their wing warping theory in the summer of 1899 after observing the buzzards at Pinnacle Hill twisting the tips of their wings as they soared into the wind.

The Wrights made the right decision by focusing on large birds. It turns out that small birds don’t change the shape of their wings when flying, rather they change the speed of their flapping wings. For example, to start a left turn, the right wing is flapped more vigorously.

To turn right the speed of flapping is changed to the other wing.

To fly straight, both wings are flapped at the same speed.

Incidentally, the technique is the same for creatures from fruit flies and moths to hummingbirds and cockatoos.

These findings were found through research with high-speed video of seven species at the universities of Delaware and North Carolina.