By Murray Hunter
No other concept had been dreamed about more than the ability of man to undertake powered flight. Ever since the Greek Mythology of Icarus and Daedalus, man has been on a great quest to discover the secret of flight and when man finally managed to fly, this discovery was to change the way he lived upon this Earth. Like the advent of the automobile, powered manned flight was not a single invention but a gathering together of necessary knowledge to allow flight to be possible. This knowledge began being collected by the Chinese who flew kites for the first time somewhere around 500 BC.
The kite was an important step in achieving powered manned flight because it showed that something heavier than air could stay aloft. The kite may have been the invention of the Chinese philosophers Mozi and Lu Ban during the 5th Century BC. Although not fully understood at the time, the kite showed the basic laws of aerodynamics at work. Air flowing over a kite’s wing will have a high pressure below the wing and a low pressure above the wing, giving the kite lift. This lift also produces drag at the bottom of the kite opposite to the oncoming wind. When the kite is tethered to a guide-wire the forces of the wind against the tension from the guide-wire forces the kite into the air along a vector opposed to the tension of the guide-wire and wind. Some kites have tails to stabilize the direction of the kite adding the force of drag to the equation pulling on the tail, thus keeping the kite stable and upright.
A box kite design provides relatively high amounts of lift and most of the early aircraft of the Twentieth Century were inspired by this design. The box kite was invented by the Australian inventor Lawrence Hargrave in 1893 in his attempts to develop his own manned flying machine. Series of tandem box kites were able to lift Hargrave 16 feet off the ground.
In 1738 a Dutch-Swiss mathematician published an important aerodynamic principal in his book Hydrodynamica, which stated that any air (or fluid) flow as speed increases will result in a simultaneous decrease in pressure over a solid surface, which became known as Bernoulli’s principal. Air running over the top of an airfoil will run faster than the air running under the bottom of the airfoil thus creating a decrease of temperature and pressure which provides lift. The significance of this to flight is that Bernoulli’s principal explains the concept of lift and allows lift to be calculated on airfoils.
In 1799 Sir George Cayley was credited with formally identifying the four aerodynamic forces acting upon flight – lift, gravity, thrust and drag. Cayley believed that that any drag created by a flying machine must be countered by thrust in order for level flight to occur, which led to a better understanding that any design of a flying machine must minimize drag. These discoveries led to the development of cambered wings, which enabled them to create the force of lift for an aircraft. According to a recent discovery of Cayley’s school notebooks, he pondered over the problems like the angle of attack much earlier than previously thought in his early years. Cayley designed an efficient cambered wing with the correct dihedral angle that provided lateral stability in flight, where he deliberately set the centre of gravity below the wings for that purpose. Cayley’s model gliders incorporated all these features, monoplane wings with back horizontal stabilizers, looking similar to modern aircraft of today. There was possibly a glider built by Cayley in 1853 that was piloted by his grandson George John Cayley.
The propeller has a long history of development for nautical use which had to be applied to flight. One of the major challenges to the Wright Brothers in developing an airplane for their first flight at Kitty Hawk was that there was no aircraft propeller readily developed, so had to develop one on their own. They found that a propeller is essentially a wing and therefore they utilized early wind tunnel data on their wing experiments. They found that the relative angle of attack of the propeller had to be different along the propeller blade and therefore had to be twisted slightly.
The Wright brothers believed that the ability to fly depended upon balance and control, rather than the power of an engine to propel the airplane forward. This perhaps came from their background as bicycle makers where balance was essential. Control in the air was an important issue as there had been many deaths of aeronauts in gliding and balloon accidents over a number of years.
The Wright brothers further believed they had enough knowledge about wings and engines and decided it was important to practice control in gliding before powered flight so the needs of control could be understood. They believed that previous practice used by Lilienthal of balancing and controlling a glider through redistributing body weight was fatally flawed. Many before them including Langley and Chanute considered changing direction in midflight would be like moving a ship’s rudder for steering while the aircraft remained in straight and level flight. Wilbur Wright observed that birds change direction in flight by changing their angle at the end of the wings to make their body’s roll to the left or right and he thought that this would also be a good way for an aircraft to change direction by banking left or right by changing the wing tilt through the use of a moveable airfoil on the sides of the wing. Again this was something similar to a bicycle going at high speed where a rider would distribute his or her weight to the side of a turn.
In 1900 the Wright brothers after researching the best place to do glide tests and taking advice from Octave Chanute went to Kitty hawk, North Carolina. The area had a good breeze coming onshore from the Atlantic, a soft sandy ground to land on, and was relatively remote for privacy. The first glider was based more on the work of previous pioneers and resembled the Chanute-Herring glider which flew well near Chicago back in 1896 and some aeronautical data that Lilienthal had published. The wings were cambered according to the theories of Sir George Cayley. The Wrights placed a horizontal elevator in front of the wings as they believed this would help them stop any nose dives that killed Lilienthal and did not build a tail for the glider as at this stage as they thought it unnecessary. Most of the glider tests were unmanned with the glider held by ropes so glide characteristics could be studied.
The second glider in 1901 had its wings greatly enlarged in an attempt to increase lift. Approximately 100 flights were made at varying distances from 50 to 400 feet. The glider stalled a number of times but “pancaked” out and landed flat due to the forward elevator. This changed the brothers thinking towards the canard design, which they used until 1910. In general the second glider was very disappointing as it failed to yaw adequately to the wing ailerons, where the nose of the glider pointed away from the turn as the wings produced differential drag and didn’t have the lift that they had expected. This left the Wright brothers feeling very down about the prospects of manned flight.
The Wright brothers discovered that the equation that Lilienthal had been using to calculate lift was incorrect. Lilienthal and the Wright brothers both used the “Smeaton coefficient” in the lift equation which had a constant of 0.0054, overstating lift. The Wright brothers believed and determined through some bicycle tests that the coefficient was more like 0.0033 and adjusted their designing accordingly. Knowing that building gliders was expensive and trial and error was very time consuming they built their own wind tunnel so they could test models to speed up their experimentation and learning. These experiments proved to be very fruitful and they made an important discovery that longer and narrower wings (i.e., larger aspect ratio) would provide a better lift to drag ratio than broader wings. They also reduced the camber of airfoils which made them more efficient for banking. They totally discarded Lilienthal’s calculations and relied solely on their own data.
The third glider had some other design changes including a rear fixed vertical rudder which would assist in turning. The brothers flew the third glider unmanned like the first two trials. The glider gave the expected lift and allowed tighter turns without the amount of differential wing drag that occurred on the earlier gliders. However the rudder caused a new problem. When in a tight turn and trying to level back out again the glider failed to respond to the airfoil corrections and persisted in a tighter turn where the glider would slide towards the lower wing. The brothers found that by making the rudder movable this problem did not reoccur so with a movable rudder and wing airfoils the pilot had to control both the airfoils and rudder when maneuvering the glider. This enabled the brothers to make very controlled turns.
The three-axis control for the glider was a major breakthrough for controlled flight. It made the aircraft very controllable in flight and was the result of almost 1,000 test glides at Kitty Hawk. Some aeronautical historians believe that this is where the airplane was really invented.
The powered Wright Flyer I constructed of spruce and covered with muslin. The engine was built with an aluminum block by the brothers. The Wrights decided on twin pusher counter rotating propellers to cancel out the torque. They suffered many delays at Kitty Hawk with broken propeller shafts. After a number of attempts the brothers finally got the airplane off the ground on 17th December 1903 with a flight distance of 120 feet. The first flights received little publicity. Over the following year the second aircraft the Wright Flyer II made many flights at Dayton with many hard landings and minor mishaps. Much progress was made in 1904 with some longer flights lasting a few minutes but the airplane was still very difficult to control.
In 1905 the brothers made all the controls independent of each other so pitch, roll, and yaw could be controlled separately of each other. After a nearly fatal crash the brothers rebuilt the flyer with a much larger rudder and forward elevator placed further away from the wings. This made control much easier and led to a number of much longer flights. Ironically the media had ignored this story that Wilbur and Orville Wright made the first flights with a powered flying machine and later would become national heroes at their own doorstep.
The brothers believed that they now had a flying machine with practical utility that they could sell. They were finally granted a patent in 1906 and in 1907 went to Europe to sell their airplane. In early 1908 the Wright brothers finally signed contracts with a French company and the US Army. Wilbur made a number of demonstration flights showing advanced maneuvers during 1908 which captured the attention and admiration of the world.
The Wright brothers’ patent was challenged vigorously in the law courts for a number of years and Wilbur Wright also challenged any other flyer who infringed them. This took up a lot of time and it prevented the brothers from developing new aircraft designs. By 1911 the Wright airplanes were considered inferior to many of the new European designs. Wilbur passed away in 1912 and the brothers won their court case against Curtiss which had been going on for a few years. With the arrival of the First World War, the US Government found that American technology was behind the European builders and encouraged companies to cross license their technologies.
Businesswise the invention of the airplane did not lead to a great number of aircraft sales and the brothers formed an exhibition team which was later disbanded due to a number of team member deaths. Between 1910 and 1916 the Wright Company operated a flying school at Huffman Prairie, Dayton, training more than 100 pilots. In addition with the large number of airplane accidents and deaths the safety of the plane came into question by the US Army. Orville Wright sold the Wright Company in 1915 and took on public service as an elder aviation statesman becoming director of the National Advisory Committee for Aeronautics (NACA), which he served for 28 years. It was only after the First World War when airplanes made a contribution to field warfare as a reconnaissance, fighter and bomber, and larger airplanes could carry passengers and cargo with much better safety that the aviation industry started to boom from the 1920s onwards.
So what are the lessons we learn from the invention of the airplane?
What we see is that an invention cannot occur until all relevant knowledge that makes it possible exists. There must be no knowledge gap, or else any idea is a fantasy. For example, Jules Verne’s imaginative novel From the Earth to the Moon in 1865 could only become reality with the Apollo Moon landing in 1969 when all necessary technology actually existed.
However the inventor must go the final step and either synthesize all previous knowledge or incrementally enhance what knowledge already exists to complete the invention. This often requires having the confidence to disregard previous generally accepted knowledge with your own generated knowledge obtained through your trials and experimentation.
What we also see is that any invention that does not fulfill the present needs of consumers or industry will not initially be commercially viable. In the cases of the early automobiles and aircraft, they were not at an advanced enough state for potential users to accept them because of the primitive state of the invention and social situation surrounding it, i.e., early automobiles not practical due to faults and UK laws had to be amended to make the invention acceptable an means of transport.
Inventions can only be commercially successful is if a use is found for it, i.e., early aircraft could be utilized in a war situation during the First World War. The story of the development of the airplane shows how essential trial and error or learning by doing is essential to the successful development of any invention.
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 However the Wright Brothers themselves can be part of the blame for this as they discouraged media attention in fear of competitors stealing their ideas and they would not be able to get a patent.