The design of a new airplane is usually evolutionary; a new airplane is frequently an evolutionary extension of one or more previous design. Even the most revolutionary of new airplane designs contain some of the genes of almost all previous aircraft. The technical evolution of the airplane is divided into four eras: (1) pre-Wright attempts, (2) strut-and-wire biplane, (3) mature propeller-driven airplanes, and (4) jet-propelled airplanes.
(1) Pre-Wight Era
Humans have been fascinated with flight throughout history. Some people had fashioned some kind of wings out of wood or feathers, strapped these wings to their arms, climbed to the roof and jumped off, flapping wildly – the aeronautical historians call such people tower jumpers. As that proved unsuccessful and engineering advanced, mechanical mechanisms were applied to flap the wings up and down, resulting in vehicles known as ornithopters. The great Italian artist, architect, scientist and engineer, Leonardo Da Vinci designed numerous such ornithopters in the period from 1486 to 1490. To this day, no human-powered ornithopter has ever successfully flown.
During the late 18th century and 19th century, some innovative balloons and then dirigibles were designed to pioneer lighter-than-air flight. Heavier-than air flight was still in its infancy in this period. In 1799, an Englishman, Sir George Cayley first devised the concept of modern configuration airplanes that featured fixed wings for generating lift, paddles for propulsion, and a tail unit with horizontal and vertical stabilizers.
The aviation pioneer identified most strongly with gliding flight was the German engineer Otto Lilienthal. In 1889, Lilienthal published his highly influential book Bird Flight as the Basis of Aviation. Before he died in a gliding accident in 1896, he successfully made over 2000 flights during the 5-year period.
At the same year that Lilienthal was killed, an American Samuel P. Langley was successful in flying several small-scale, unmanned, powered aircrafts which he called aerodromes. These 4m-wingspan, steam-powered aerodromes were launched from the top of a small houseboat on the Potomac River, and they flew about a minute, covering a range close to 1.5km over the river. Spurred by the exigency of the Spanish-American war, Langley was given a $50,000 grant from the war department to construct and fly a full-scale, person-carrying aerodrome. This full-scale aerodrome was launched by a catapult mounted on top of a new houseboat on the Potomac River. But, the poor structural design of that full-scale aerodrome resulted in failure of the whole system. In spite of his failure, Langley deserves a lot of credit for his aeronautical works. Langley Theater at the National Air and Space Museum in Washington, NASA Langley Research Center which is built right beside Langley Air Force base in Hampton, Virginia are named after Langley’s name.
(2) Era of Strut-and-Wire Biplanes
The 1903 Wright Flyer indicated the era of successful strut-and-wire biplanes to commence that covered the general period from 1903 to 1930. On 17 December 1903, Orville and Wilbur Wright flew their aeroplane named Flyer I for the first time and covered a distance of 37m in 12s near Kitty Hawk in North Carolina.
The Wrights had the propulsion, aerodynamic and structural aspect of airplane design well in hand. The Wright brothers built a second plane, and in the summer of 1904, they managed to fly on a circular course of 4.45km in a sustained flight that lasted more than 5 minutes. Their breakthrough of aeronautical innovation was the idea of warping the wing tips to provide the rolling motion of the airplane, to jointly control roll and yaw for coordinated turns.
In the following years, several other people began to build and fly aircraft. The wing-warping method of roll control used by the wrights was quickly supplanted by ailerons in most other aircraft. Besides that, the open frameworks of the fuselage were enclosed in later designs. Although the aircraft at the outbreak of World War I were fragile, they were used nonetheless in the conflict. In relation to the thrust minus drag expression T – D, designers of World War I fighter airplanes, in their quest for faster speeds and higher climb rates, increased the thrust rather than decreased the drag. The decade following World War I, there were gradual design improvements, mainly involving some streamlining to reduce drag and gradual increases in engine power to increase thrust.
During this era, strut-and-wire biplanes were dominant due to their structural strength. Two wings of relatively short span, trussed together as a stiff box, were structural sounder than if the same total wing area were spread out over a singer wing with larger span. Moreover, the moment of inertia about the roll axis was smaller for the shorter-span biplanes leading to more rapid rolling maneuverability. For these reasons, designers were reluctant to give up the biplane. However, the struts and wires necessary to structurally strengthen biplane wing configurations are a major source of drag.
(3) Era of the Mature, Propeller-Driven Airplane
The period from 1930 to 1950 can be classified as the era of the mature, propeller-driven airplane. During this time, airplane design matured, new technical features were incorporated, and the speed, altitude, efficiency and safety of aircraft increased markedly. Therefore, in particular, the 1930s are considered by many aviation historians as the “golden age of aviation”.
First, the cantilevered-wing monoplane gradually replaced the strut-and-wire biplane. Monoplanes had existed before the 1930s. On 25 May 1909, Frenchman Louis Bleriot became the first person to fly across the English Channel with his Bleriot XI monoplane. Bleriot’s airplane has a design that is regarded as the classic configuration featuring a monoplane wing, a front-mounted propeller and a tail at the rear.
However, the monoplane began its gradual climb to superiority when in 1915 Hugo Junkers, at that time the Professor of Mechanics at the Technische Hochschule in Aachen, Germany, designed and built the first all-steel cantilevered-wing monoplane. This initiated a long series of German advancements in cantilevered-wing monoplane by both Junkers and Anthony Fokker through the 1920s. In 1916, William E. Boeing founded the Pacific Aero Products Company, which he renamed in the following year the Boeing Airplane Company. The monoplane came into its own with the Boeing Monomail of 1930. This airplane embodied two other important technical developments, it had all-metal, stressed skin construction, and its landing gear was retractable.
The U.S. government created National Advisory Committee for Aeronautics and Astronautics (NACA), the predecessor of NASA, in 1915 when it recognized how far it was behind Europe in aircraft production. NACA had developed cowling for radial piston engines. Beginning in 1927, NACA undertook a systematic series of wind tunnel tests with the objective of understanding the aerodynamics of engine cowlings and designing an effective shape for such cowlings. Compared with the uncowled fuselage, a fully cowling reduced the drag by a stunning 60%. Moreover, by proper aerodynamic design of the cowling, the cooling system of the engine was enhanced.
Many other improved design features for modern aircraft appeared in this period such as the variable-pitch propeller (to maintain constant engine speed so that the net power output of the engine-propeller combination can be maintained at an optimum value), high lift devices (flap, slats, slots, etc, which are used to increase the wing loadings – W/S, the ratio of airplane weight to wing area – at cruise), and pressurization for engine & passenger cabin (decrease in atmospheric pressure with increasing altitude).
In 1904, Ludwig Prandtl had introduced the concept of the boundary layer (thin region of an airstream which is immediately adjacent to the surface where the mechanism of air friction is dominant) in Germany, it had been recognized that two types of flow were possible – laminar flow and turbulent flow – in the boundary layer. NACA undertook the development of a series of laminar-flow airfoil which was to have an unexpected impact well beyond this era. It had to do with the boundary layer on a surface in an airstream.
(4) Era of the Jet-Propelled Airplane
The jet engine was developed independently by Sir Frank Whittle in Britain and by Hans Joachim Pabst von Ohain in Germany. On 27 August 1939, the German Heinkel He 178, powered by von Ohain’s jet engine, successfully flew – it was the first gas turbine-powered, jet-propelled airplane in history to fly. (Five days later, Germany invaded Poland, and World War II began.) Two years later, on 15 May 1941, the specially designed Gloster E.28/39 airplane took off from Cranwell, powered by a Whittle jet engine. With these flights in Germany and Britain, the jet age had begun. The German Messerschmitt Me 262 was the first operational jet airplane that was deployed in 1944.
The era of the jet-propelled aircraft is characterized by the advent of the swept wing. For a subsonic airplane, sweeping the wing increases the airplane’s critical Mach number. For a supersonic airplane, the wing sweep is designed such that the wing leading edge is inside the Mach cone from the nose of the fuselage, if this is the case, the component of airflow velocity perpendicular to the leading edge is subsonic and the resulting wave drag is reduced greatly. The concept of the swept wing for high-speed aircraft was first introduced by the German aerodynamist Adolf Busemann. The North American F-86 Sabre was the world’s first successful operational swept-wing aircraft.
The delta wing concept was another innovation to come out during the 1930s and 1940s. Dr. Alexander Lippisch was the person who introducing this concept. The first practical delta-wing aircraft was the Convair F-102. However, the prototype F-102 exhibited poor performance and was unable to go supersonic when it was tested at Edwards Air Force Base during October 1953 and then again in January 1954. At the same time, Richard Whitcomb at NACA Langley was conducting wind tunnel tests on his “area rule” concept which called for the cross-sectional area of the fuselage to be reduced in the vicinity of the wing. By so doing, the transonic drag was substantially reduced. The Convair engineers quickly adopted this concept on a new prototype of the F-102, and it went supersonic on its second flight. The area rule was one of the most important technical developments during this era.
England’s de Havilland Aircraft Company led in jet propulsion in the early 1950s. It had designed and flew the first commercial jet transport – the de Havilland Comet. Powered by four de Havilland Ghost Jet engines, the Comet carried 36 passengers for 3200km at a speed of 740km/h, cruising at relatively high altitudes near or above 9km. The Comet was the first pressurized airplane to fly for extended period at such high altitudes. However, in 1954 three Comets disintegrated in flight due to metal fatigue problems and the airplane was withdrawn from service. Had these failures not occurred, de Havilland and England might have become the world’s supplier of commercial jet aircraft rather than Boeing and the United States.
In 1952, the directors of Boeing Company made a bold and risky decision to privately finance and build a commercial jet prototype. This gave to the birth of the Boeing 707. Boeing risky gamble paid off, and it transformed a predominately military company into the world’s leader in the design and manufacture of commercial jet transport.
Boeing made another bold move on 15 April 1966, when the decision was made to “go for the big one”. Boeing had lost a bid to build Air Force’s C-5 for the U.S. Air Force to Lockheed; the C-5 at the time was the largest transport airplane in the world. Taking their losing design a few steps further, Boeing and its engine partner, Pratt and Whitney, decided to make a commercial aircraft capable of carrying up to 500 passengers. The end product was the first so-called wide-body and twin-aisle passenger jet, the four-engine Boeing 747 – affectionately called the jumbo jet. Few aircraft are so widely recognized around the world as the 747 with its upper deck. The 747 had its maiden flight on 9 February 1969 and entered service in January 1970. The aircraft of the U.S. President, Air Force One, is a Boeing 747 (with its military designation VC-25A).
The Boeing 747 exemplified the U.S. dominance in the airline industry. By the 1960s, European countries realized that only a close co-operation between them could create a serious and lasting competition to U.S. manufacturers led by Boeing, McDonnell Douglas and Lockheed. In December 1970, the Airbus Industrie consortium was set up to build a European high-capacity short-haul airliner. French and German companies had a dual role as both shareholders and industrial participants. They were joint by Spanish and British manufacturers in 1971 and 1979, respectively.
Airbus’s premier model, which entered service in May 1974, was the A300B – the world’s first twin-engine wide-body jetliner. The Airbus 310 introduced a two-pilot cockpit and made considerable use of composite materials for the airframe. The short-haul aircraft A320, which entered service in 1988, was the first subsonic commercial aircraft to be designed with electric primary controls, called “fly by wire” and in which mechanical displays and gages were replaced by electronic screens.
The first and so far only, supersonic commercial transport to see long-term, regular service is the Anglo-French Concorde. Designed to cruise at Mach 2.2 carrying 125 passengers, the Concorde first flew on 2 March 1969. It first exceeded Mach 1 on 1 October 1969 and Mach 2 on 4 November 1970. However, the skyrocketing costs of aviation jet fuel wiped out any hope of an economic return from flying the Concorde, and no orders were placed. Only the national airlines of France and Britain, Air France and British Airways, went ahead, each signing up for seven aircraft after considerable pressure from their respective governments.
Fighter technology was further advanced with the introduction of the F-14 Tomcat, F-15 Eagle, F-16 Falcon and F-18 Super Hornet.
Today, we are still in the era of the jet-propelled airplane, and we will be there for the indefinite future. What’re the next commercial jet airplanes in the coming days? The answers are the A380 superjumbo jet (the biggest commercial airplane ever built by human being) and Boeing 787 Drealiner. The Space Ship One, the X-prize – incentive which is aimed at encouraging the development of civilian space travel – winner, which is a rocket plane will be a precursor of commercial space-travel airplane.
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