By Rochelle Forrester
Ó All Rights Reserved
Publication Date 2006
Human beings have always wanted to fly. The example of birds effortless soaring through the air had many human imitators both in myth and in real life. In myth Daedalus and Icarus are supposed to have made wings of feathers and wax but when Icarus flew to near the sun, his wings melted, and he fell to his death. The same result occurred in real life when people made themselves wings and jumped off buildings and cliffs flapping the wings as they plunged to their deaths. These bird imitation efforts, known as ornithopters, did not work as humans did not have the same muscle and bone structure as birds.
The kite was the first heavier than air machine to actually work. Kites had been flown in China and Japan over two thousand years ago and became known in Europe in the 16th century. Kites flew due to air pressure under the kite providing it with lift.
Gliders became the main focus of aeronautics research in the 19th century. Sir George Cayley built a 5 ft model glider in 1804 and by 1849 he had a glider that flew for a few yards when towed and piloted by a young boy. In 1853 a glider piloted by Cayley’s coachman flew 500 yards. Cayley’s experiments lead to an increasing knowledge of the requirements for flight. Cayley studied bird flight and realized that birds could only stay in the air if they were in constant motion. If they stopped they would fall to the earth. Cayley also realized that the flapping of the birds wings created air currents that were necessary to provide lift. He concluded that a heavier than air machine had to keep moving to stay in the air and needed a means of creating air currents. Cayley investigated various engines such as steam engines and an internal combustion engine driven by exploding gun powder to power an aircraft but he could not find an engine both light enough and powerful enough to make an aircraft fly. Cayley also investigated how to control an aircraft in flight and his gliders had a tail equipped with a rudder and elevator.
Otto Lilienthal began experimenting with gliders in the late 19th century. Like Cayley he studied the flight of birds and from 1891 to 1896 he made controlled flights of up to 750 feet in his gliders. He was killed in a glider accident in 1896 but his book Bird flight as the basis for aviation was very influential and assisted the Wright brothers although not all the information in the book was fully accurate.
The Wright brothers began experimenting with gliders in 1900 and by 1903 they had made more than a thousand flights. They learnt how to control the gliders in flight and in 1903 they built a 12 horsepower internal combustion engine with a propeller they designed themselves. They attached the engine to one of their gliders and in December 1903 they made the first powered flight at Kittyhawk, North Carolina. Some weeks before their flight Dr Samuel Langley attempted a powered flight that failed due to equipment failure. Langley’s plane was later flown in 1914.
The Wright brothers aircraft began to be improved and redesigned with the engine in the nose, a long fuselage and a tail which helped in the control of the aircraft. With such an aircraft Louis Bleriot flew the English Channel in 1909. Better engines and other technical improvements lead to greater speeds, greater carrying capacity, longer ranges and increased reliability. These improvements occurred particularly rapidly in World War 1 and in 1919 John Alcock and Arthur Whitten-Brown made the first non-stop flight across the Atlantic. This feat was repeated in 1927 when Charles Lindbergh made the first solo flight from New York to Paris. Between the wars many long distance flights were made as aircraft performance improved.
The aeroplane works because the wings are tilted slightly upwards in the front, about 4° above the horizontal, and are curved on top so that air traveling over the wing has further to go than air traveling under the wing. This results in air hitting the underside of the tilted wing forcing the wing up as the air pressure on top of the wing falls so there is more air pressure under the wing than on top of the wing and this forces the wing up. This is because air traveling over the wing has to travel further than air under the wing and this forces the air to travel faster and as air speeds up its pressure falls so there is less air pressure on top of the wing than under the wing, which forces the wing to rise. The scientific law that as air travels faster, it losses pressure in known as Bernoulli’s Theorem after Daniel Bernoulli (1700-1782).
In order for the aeroplane to rise of the ground it needs a flow of air over the wings. This is provided by the aircraft moving forward which results from the action of the propeller on the air. The propeller cuts through the air and forces it backwards which drags the plane forwards which creates the flow of air over the wings which causes the plane to rise of the ground.
The next major technological breakthrough was the invention of the jet engine. Work on producing the jet engine began before World War 2 and the first jet planes flew during World War 2. The jet engine was invented separately by Frank Whittle in Britain and by Hans von Ohain in Germany. The jet engine is based on Newton’s third law of motion which states that for every action there is an equal and opposite reaction. The jet engine operates by taking air into the front of the engine where the air hits a rapidly rotating fan which compresses the air and forces it into a combustion chamber where it is mixed with fuel. The mixture is then ignited and expands and shots out of the rear of the engine under great pressure. The gas shooting out of the rear of the engine pushes the plane forward as the opposite reaction to the gas shooting backwards.
The use of the jet engine first in military aircraft and later in civilian aircraft was to result in still greater speeds, range and cargo carrying capacity for aircraft. Passenger transport which began after the First World War expanded greatly after the Second World War with the introduction of the jet engine. In 1937 two million people were carried by the worlds airlines outside the Soviet Union. In 1947 twenty one million people were carried and in 1957 there were ninety million air passengers. Trans-Atlantic air travel multiplied forty times between 1950 and 1975 while the numbers traveling by ocean liners fell by 80%. This caused a massive reduction in the size of the ocean liner industry. Cabin pressurization increased the comfort of air travel and allowed aircraft to fly higher above bad weather. The development of the Concorde meant faster air travel and the introduction of the “jumbo jet” in 1970 lead to more passengers and cheaper air travel. Mail was the first cargo regularly carried by aircraft but as aircraft became larger and were able to carry greater cargo almost any reasonably compact product can be transported by air.
Air travel is only possible due to air passing over an aircrafts curved wing having to travel further and faster than air passing under the wing so that there is less air pressure above the wing than below the wing so the wing and aircraft will lift of the ground. Without this feature of our physical environment and of the behavior of air and gases there would be no air travel. But air travel also requires some sort of engine to drive the aircraft forwards so as to produce a flow of air across the aircraft’s wings. It was not until such an engine, the internal combustion engine, with its relatively high power and low weight became available that powered flight became possible. A further requirement of air travel is some way of controlling the aircraft. If it was not possible to control the aircraft any significant air travel would not be possible. It is only possible to control an aircraft due to the way in which rudders, elevators, and ailerons can alter air flows and because alteration of the air flows will cause the aircraft to turn, lift or dive. If air did not lose pressure when it travels faster, or if internal combustion or jet engines were not possible, for example if gases did not expand when heated, or if aircraft could not be controlled in the air, then air travel would not be possible. This shows how the properties of materials, such as gases, in our natural environment have had a major effect on human social and cultural history. If the properties of those materials were different, then human social and cultural history would be different.
While human beings have always wanted to fly progress could only be made with the scientific study of flight done by people like Sir George Cayley, Otto Lilienthal and the Wright brothers. Prior to such scientific study, the efforts of the ornithopters were going nowhere. However the work of Cayley, Lilienthal and the Wright brothers on gliders could not achieve any useful result until the invention of an engine that was powerful enough to drive the aircraft forwards while at the same time being light enough to be carried by the aircraft. It was not until the internal combustion engine had been invented and improved that such an engine became available. Soon as the engine became available powered flight became a reality.
The next major development in powered flight was the invention of the jet engine. The jet engine only works due to Newton’s third law of motion that to every action there is an equal and opposite reaction. If Newton’s third law did not work there would be no jet engine. The jet engine is also dependent on the behavior of the air-fuel mixture which expands when ignited. If the mixture did not expand when ignited there would be no jet engine. The jet engine only exists due to the third law of motion and the behavior of heated gases.