The Evolution of Technology
Advances in technology in the late 19th and early 20th centuries made the first heavier-then-air flying machines possible. Technological progress in the 20th century allowed the development of flight from relatively rudimentary machines to complex vehicles that can fly through the air into space at speeds approaching 20,000 miles per hour (32,187 kilometers per hour). These advances in technology occurred in every system, component, and tool relating to flight—from those that are part of the aircraft itself to those that are on the ground. In addition, government institutions whose focus is flight, as well as enthusiastic supporters of aviation, assisted in advancing this technology.
Historians of 500 years hence may well characterize successful human flight, and all that followed in both air and space, as the most significant single technology of the 20th century. It has fundamentally reshaped our world, at once awesome and awful in its affect on the human condition. It has made movement about the globe common, easy and even luxurious. At the dawn of the 20th century, everyone had to allow days, and sometime weeks, for travel. Jules Verne's character Phineas Fogg of Around the World in Eighty Days was a creature of railroad and steamship timetables that took him all over the globe with some ease, but certainly on a lengthy schedule. At the dawn of the 21st century, when a traveler plans a transcontinental or even transatlantic trip, only a single day may be allowed for travel. We rightfully scoff at 80 days being needed to circle the Earth; after all, anyone can do it in a few hours by airplane and in a few minutes by spacecraft.
How do these advances happen? Sometimes all it takes is intuition or a flash of brilliance. But usually, the engineers and designers who were most successful in furthering the technology of flight used a systematic approach. Simply, they first recognized that something needed to be done—for instance, the need to fly faster. Then, the engineer or designer would propose ways to accomplish this by observing what seemed to work in nature or through documented technical knowledge. For instance, one way to fly faster would be by reducing drag to the aircraft. If one chose to try to reduce drag, then one may ask: what parts of the aircraft produce drag? One part of the aircraft that might produce drag is exposed landing gear hanging below the fuselage. One answer to this problem is designing landing gear that could be retracted into the fuselage, therefore reducing drag.
The designer would also have to determine whether the technology exists to allow retractable landing gear to be constructed. Further, the designer must consider the cost of implementing a system for retracting the landing gear. Would it be too high for most aircraft manufacturers to afford given the amount of drag it would eliminate? Would the system be reliable? Would it create other problems for the aircraft? Are there other solutions to the problem of drag that might be more optimal for the aircraft?
The engineer would weigh the benefits of retractable landing gear against the costs of designing and implementing it. Perhaps another design would produce almost as good results but at less cost. Only after all of these things were considered would the designer actually build a model of a retractable landing gear and test it to see if it performed as intended. This would usually lead to the need to modify the landing gear model according to the test results, probably more than once. The final steps would be to operate the retractable landing gear in real-life conditions and assess how well it worked. So to advance a single aircraft element is not a simple process but requires considerable theoretical study, ground-based analysis, and testing both on the ground and in flight before something new is actually put into commercial use.
In virtually every aspect of an airplane the components and structures have improved tremendously during the last century. We may begin to explore this evolution by looking at the pieces that comprise the modern aircraft and the tools that aircraft designers and engineers have used to develop them.
The wing, or airfoil, is the most important structure on an aircraft, for the wing provides the lift that an aircraft needs to fly. An early question faced by designers was how many wings to place on an aircraftmost early planes were biplanes with two wings mounted atop each other. This design, essentially a type of box kite, allowed for considerable lift of the structure with a modest wind. It was not until significantly more powerful engines were developed that the monoplanes so common today became the norm. A second concern was with the camber, or curvature, of the wing. Aerodynamicists have spent years studying the possible cambers of wings to develop a set of designs that work well with various aircraft types. Using theoretical models, wind tunnels that tested models under conditions approaching actual flight, and during actual flight research, during the first half of the 20th century, aeronautical engineers laboriously developed the knowledge necessary to make possible the airplanes routinely operating today. Designers also looked at the shape, size, and thickness of each wing, its position on the fuselage, and how it was angled outward from the fuselage. They discovered that particular configurations worked best for different types of flight. They also discovered that parts of wings, such as flaps and ailerons, affected the performance of the aircraft, and they added flaps and similar devices to improve aircraft performance and control. Again, all of this work was accomplished through painstaking research using the three elements of aeronautical research: theoretical studies; ground-based research using wind tunnels, computer modeling, and a host of other techniques; and actual flight tests.
Early aircraft were powered by a propeller, a simple twisted wing mounted on a turning shaft. Its performance, and consequently airplane's performance, is affected by its pitch, or the angle at which it cuts through the air. Engineers realized that different angles worked best for different parts of flight. One angle may give the best performance during takeoff or landing, while another was best for level flight. These angles could be determined through wind tunnel tests. But early planes all had fixed-pitch propellers—the pitch of the propeller could not be changed during flight. The invention of the variable-pitch propeller in 1933 allowed the plane to achieve maximum efficiency from its propeller. Many small planes still have only fixed-pitch propellers because improving performance is not as important as in large aircraft and the cost to install variable-pitch propellers and the mechanism for operating them would be too great. This is an instance where the improvement in performance is not enough to warrant the cost required to achieve it.
Huge piston engines drive the propeller through the air, generating the thousands of pounds of thrust necessary to keep an aircraft airborne. Early on, aeronautical engineers learned that the bulk and shape of aircraft engines tended to create drag on the vehicle and sought to find ways to reduce it. A variety of methods emerged, but an important one was the engine cowling developed by engineers at the National Advisory Committee for Aeronautics (NACA). Led by Fred Weick, a research team from the NACA placed the engine cylinders within an enclosure rather than leaving them exposed to the air. This NACA cowling, as it was called, reduced the drag of the engine significantly. This cowling was adopted by every aircraft manufacturer beginning in the late 1920s. The NACA also developed a second element applied to multi-engine planes. Engineers found that placing the cowled engine assemblies directly in a smooth line with the wing and with the propeller well in front of the wing's front edge reduced the amount of drag even more. Both of these advances were relatively inexpensive to implement and each significantly improved the efficiency of the aircraft.
Another structural change also improved aircraft performance. Early aircraft had what was called a "truss" structure where braces at various places supported the weight of the plane. But all of these protruding parts produced considerable drag. In 1912, a European designer came up with the idea of a smooth curved fuselage structure where the supports were all internal. This "monocoque" structure was perfected by the American designer Jack Northrop, who figured out a way to shape the curved surfaces in a mold. This method was successfully used on the Lockheed Vega and became the norm for future aircraft.
The use of metal in aircraft was one design change that did not yield good results at first. Early planes were made of wood and cloth. Designers thought that metal planes would be sturdier and would not burn as readily, so they wanted to build aircraft from these materials. But metal planes weighed too much, and the metal tended to corrode under harsh flying conditions. So metal planes were not too successful until better alloys were produced in the 1920s.
The second most important part of an aircraft is the engine. Engines provide the thrust that move an aircraft forward. Until the internal combustion piston engine became available in the latter part of the 19th century, designing a powered aircraft that could fly was difficult. Earlier engines were much too heavy or did not produce enough power. And even with the piston engine, the challenge was to design an engine that would produce enough power while remaining light in weight and cool enough so it wouldn't overheat.
Piston engines came in several configurations. One early type was the rotary engine, where the entire engine turned. This motion cooled the engine. But it had such enormous drawbacks that by the end of World War I most designers had abandoned the concept. It was replaced by the reciprocating engine, which was stationary with some moving parts. Some were water-cooled while others were air-cooled. Like an automobile engine, water-cooled engines used water that flowed in channels through the engine to carry away the heat. A radiator cooled the heated water. Air-cooled engines were cooled by the air that flowed past them, which generated a lot of drag. The invention of the NACA cowling helped solve this problem. So it is easy to see how advances in technology can be related: a change in one area, in this case a preference for the air-cooled engine, thereby created the need for an advance in a related area—reducing the drag of the engine.
A second type of aircraft engine is the jet engine, pioneered by numerous experimenters but with Frank Whittle in England and Hans von Ohain in Germany receiving the majority of the credit. The jet engine began to be used on a small scale during World War II and frequently in military aircraft by the later 1940s. The first production jet aircraft was the German Messerschmitt Me 262, which entered limited service in July 1942.
Jets gradually were adopted by the commercial sector beginning in the 1950s. In 1952, British Airways introduced the world's first jet airliner. Geoffrey de Havilland was selected to design the aircraft, called the Comet. Based on extensive research provided by other engineers and his own experience with jet engines during World War II, de Havilland knew that jets consumed far more fuel at an altitude of 10,000 feet (3,048 kilometers) than they did at 30,000 feet (9,144 kilometers)three to four times as much. He accordingly set about designing an aircraft that could fly at 35,000 feet (10,668 kilometers) and higher, dramatically reducing fuel consumption. But at these altitudes, there was another problem to be solved: creating a pressurized cabin in which passengers could breathe without oxygen masks. Once the issue of cabin pressurization was resolved, the Comet was ready to be introduced to the public and they loved it. But the original Comet's life span was cut short because of structural problems and just two years after its maiden flight, it went out of production. Although later models were introduced and remained in service for years, the British aircraft industry never recovered from the early problems it encountered with this plane.
Boeing's 707, based on a jet tanker design built for the U.S. Air Force, followed the Comet in 1954, not only addressing the structural problems which doomed the first jetliner but with a newly designed airframe, offering a smoother, faster ride with room for more passengers. The Douglas DC-8, Boeing 747, and Airbus A300 that followed each introduced technological innovations and economies that increased their marketability. The Concorde, the world's only supersonic aircraft, also drew upon technology that gave it the ability to travel at Mach 2.2 (over twice as fast as the speed of sound) at an altitude of 50,000 feet (15,240 meters).
Today, aircraft manufacturers continue to adapt their machines to the market's desire to get there faster, more efficiently, and more comfortably.
A third type of engine, used primarily in military applications and space launch vehicles, is the rocket engine. A rocket engine is really a special type of jet engine that, instead of using air from the atmosphere, carries its oxygen with it. Used effectively in World War II, the German V-2 missile, with its explosive warhead, was the first practical use of a rocket engine. The Messerschmitt Me 163 interceptor fighter developed in 1944 was the most noteworthy example of a plane powered by a rocket engine.
As engines became more and more powerful and able to propel heavier aircraft at greater speeds, planes have been able to fly at higher altitudes. This has made flight much more comfortable (and less nauseating) for passengers because the aircraft encounters less turbulence. But it has made additional technological improvements necessary. As altitude increases, the air becomes thinner. Without pressurized cabins, passengers would suffer from oxygen deprivation. So beginning with the introduction of the Boeing 307 Stratoliner at the end of 1938, aircraft manufacturers began to pressurize their cabins.
Better engines also made it possible for planes to fly farther without refueling. But, especially in the military, sometimes planes needed to be able to fly an even greater distance without landing. Thus, several methods of refueling planes while they were in the air were developed.
When planes began to fly at higher altitudes and also when night flights began, pilots could no longer find their way by seeing landmarks on the ground. First, bonfires were lit that marked the route; then electric beacons replaced the fires. This worked at night or under conditions of poor visibility at fairly low altitudes. But ultimately, the pilot needed to rely on detailed maps and charts or other navigation aids to keep him on route. Electronic aids, both those used by pilots and those by air traffic controllers on the ground, were developed. Both used radio to send and receive location, distance, and weather information and to help navigate. As air traffic increased, keeping planes separated from each other also became necessary and electronic tools were developed to track the location of airplanes. Radar was an important electronic tool beginning in the World War II period that was used for several purposes. Recently, pilots have begun using the Global Positioning System as a navigation aid.
With the development of supersonic flight and the breaking of the sound barrier in 1947, a wide variety of advances in technology were implemented primarily in the military sector. Experimental planes demonstrated technologies relating to the behavior of air flowing over and around a plane flying above the speed of sound. Materials were developed to deal with the high temperatures generated by planes flying at great speeds. Researchers began to think of flying to the edges of and beyond the limits of the atmosphere and returning to Earth as well as having reusable space vehicles that needed to land safely. Methods had to be developed that prevented reentry vehicles from burning up as they reentered the atmosphere. Vehicles with different shapes were developed that shed a good deal of the heat that was produced. These vehicles would soon prove useful in the space program.
One of these vehicles was the X-15, which throughout the 1960s demonstrated the human capacity to fly even higher, even faster, beyond the Earth's atmosphere. On August 22, 1963, the X-15 set an altitude record of 354,200 feet (67 miles) (1,080 kilometers). Four years later it traveled at Mach 6.7, or 6.7 times faster than the speed of sound. A bridge had just been constructed into the future. When NASA collaborated with the Air Force, the Navy and North American Aviation, Inc., in the X-15 program, they embarked upon a new frontier—exploring the possibilities of a pilot flying rocket-boosted aircraft at hypersonic speeds (equal to or exceeding five times the speed of sound). X-15 research proved that a pilot could undertake and master the skills required for aerospace flight, even weightlessness, which had early on been one of the most feared unknowns. X-15 research also directly contributed to the development of piloted spaceflight programs as well as the Space Shuttle program. Among its many significant accomplishments, the X-15 program can boast of developing the first practical full-pressure suit to protect pilots in space, one, no doubt, that former X-15 test pilot, Neil Armstrong, was grateful for when he became the first human to set foot on the Moon's surface.
One of the most advanced aircraft ever developed is the "stealth" aircraft, a vehicle that is almost invisible to electronic detection in flight. These planes combined technologies relating to shape, materials, and energy and made great use of computer technology in their design. For these aircraft, a number of technologies had to mature, and advances in mathematical theory also needed to occur, before they could be built successfully.
The development of technology relating to rotary-wing aircraft has in many ways been more challenging than for fixed-wing aircraft. In addition to the concerns about lift, drag, and thrust faced by airplane designers, developers of rotary-wing craft had to solve problems of torque, aiming thrust so that the vehicle would move in the desired direction, vibration, and developing adequate lift to lift the vehicle straight up. Many attempted to solve these problems since the late 1800s, but technological advances for rotary craft were very slow in coming.
The development of the lightweight internal combustion engine helped provide adequate lift, and designers realized that counter-rotating blades would solve most problems relating to torque. However, directional control remained a problem. Juan de la Cierva in 1923 and Louis Bréguet in the early 1930s made considerable progress in this area. In 1940, Sikorsky successfully used a small tail rotor rather than counter-rotating blades to control torque in his VS-300, the first production helicopter. After that breakthrough, helicopter development moved forward at a slow but steady pace that allowed it to be used effectively in specialized applications that were unsuited to fixed-wing aircraft.
The development of Vertical/Short Take-off and Landing (V/STOL) aircraft has been another difficult challenge during the last 40 years. V/STOL aircraft use helicopter-like features to take off vertically and then convert to a fixed-wing configuration for forward movement. Successful V/STOL flight requires greater thrust to lift the aircraft straight up and to support its weight, necessitating large engines, high fuel consumption, and complicated flight controls—all of which add to the weight. Another problem lies with pilot control during the transition from vertical to horizontal flight and back again. The development of computerized flight controls and better cockpit displays have helped relieve the pilot of some of this burden.
With almost all of these technological advances, engineers and aerodynamicists are helped by a variety of tools. One of the most widely used is the wind tunnel. Even before the Wright brothers, inventors used wind tunnels to test wings and propellers. These tunnels have become more sophisticated and able to test aircraft and their components at all speeds. Computers have also become common in aircraft design, to help control planes in flight, and to help them navigate to their destinations. The science of computational fluid dynamics has enabled designers to use computer models in place of wind tunnel tests. The computerized "fly-by-wire" control system starting in the 1970s allowed pilots to fly planes that would otherwise be impossible to control. Simulators are another tool used for flight training, to test emergency procedures, and in the design process.
Continuous advances in aero-technology have gotten aviation to its present level of maturity. It remains to be seen what will develop in the future.
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