Airframe

Airframe

[air-freym]
Airframe means the mechanical structure of an aircraft and as generally used does not include the engines. Airframe design is a challenging field of engineering, combining aerodynamics, materials technology and manufacturing methods to achieve favorable balances of performance, reliability and cost. The airframe industry is complex. Its modern history began in the United States when a 1903 wood biplane made by Orville and Wilbur Wright showed the potential of fixed-wing designs.

Many early developments were spurred by military needs during World War I. Well known aircraft from that era include the Dutch Fokker and U.S. Curtiss triplanes and the Italian Taube monoplane. These used hybrid wood and metal structures. Commercial airframe development during the 1920s and 1930s focused on monoplane designs using radial piston engines. Many, such as the Ryan model flown across the Atlantic by Charles Lindbergh in 1927, were produced as single copies or in small quantity. The all-metal Ford 4-AT and 5-AT trimotors and Douglas DC-3 twin prop were among the most successful designs to emerge from the era. During World War II, military needs again dominated airframe designs. Among the best known were the Douglas C-47, Boeing B-17, North American B-25 and Lockheed P-38, all revamps of original designs from the 1930s. The first jets were produced during the war but not made in large quantity.

Postwar commercial airframe design focused on larger capacities, on turboprop engines, and then on jet (turbofan) engines. The generally higher speeds and stresses of turboprops and jets were major challenges. Newly developed aluminum alloys with copper, magnesium and zinc were critical to these designs. The Lockheed L-188 turboprop, first flown in 1957, used some of these materials and became a costly lesson in controlling vibration and planning around metal fatigue. Eventually Boeing in the U.S. and Airbus in France became the dominant assemblers of large airframes. Numerous manufacturers in Europe, North America and South America took over markets for airframes designed to carry 100 or fewer passengers. Many manufacturers produce airframe components.

Four major eras in commercial airframe production stand out: all-aluminum structures beginning in the 1920s, high-strength alloys and high-speed airfoils beginning in the 1940s, long-range designs and improved efficiencies beginning in the 1960s, and composite material construction beginning in the 1980s. In the latest era, Boeing has claimed a lead, designing its new 787 series flagship airframes scheduled for first delivery in 2008 with a one-piece carbon-fiber fuselage, said to replace "1,200 sheets of aluminum and 40,000 rivets. These airframes are designed to transport 220-300 passengers, while chief competitor Airbus has designed its A380 flagship airframes to transport 550-850 passengers. The A380 is also built with a large proportion of composite material.

Airframe production has become an exacting process. Manufacturers operate under strict quality control and government regulations. Departures from established standards become objects of major concern. The crash on takeoff of an Airbus A300 in 2001, after its tail assembly broke away from the fuselage, called attention to operation, maintenance and design issues involving composite materials that are used in many recent airframes. The A300 had experienced other structural problems but none of this magnitude. The incident bears comparison with the 1959 Lockheed L-188 crash in showing difficulties that the airframe industry and its airline customers can experience when adopting new technology.

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