Airframe
[1] This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and excludes the propulsion system.
Modern airframe history began in the United States during the Wright Flyer's maiden flight, showing the potential of fixed-wing designs in aircraft.
By the 1915/16 timeframe, the German Luft-Fahrzeug-Gesellschaft firm had devised a fully monocoque all-wood structure with only a skeletal internal frame, using strips of plywood laboriously "wrapped" in a diagonal fashion in up to four layers, around concrete male molds in "left" and "right" halves, known as Wickelrumpf (wrapped-body) construction[5] - this first appeared on the 1916 LFG Roland C.II, and would later be licensed to Pfalz Flugzeugwerke for its D-series biplane fighters.
[3] It developed further with lighter weight duralumin, invented by Alfred Wilm in Germany before the war; in the airframe of the Junkers D.I of 1918, whose techniques were adopted almost unchanged after the war by both American engineer William Bushnell Stout and Soviet aerospace engineer Andrei Tupolev, proving to be useful for aircraft up to 60 meters in wingspan by the 1930s.
Some were produced as single copies or in small quantity such as the Spirit of St. Louis flown across the Atlantic by Charles Lindbergh in 1927.
Andrei Tupolev's designs in Joseph Stalin's Soviet Union designed a series of all-metal aircraft of steadily increasing size culminating in the largest aircraft of its era, the eight-engined Tupolev ANT-20 in 1934, and Donald Douglas' firms developed the iconic Douglas DC-3 twin-engined airliner in 1936.
Among the best known were the US C-47 Skytrain, B-17 Flying Fortress, B-25 Mitchell and P-38 Lightning, and British Vickers Wellington that used a geodesic construction method, and Avro Lancaster, all revamps of original designs from the 1930s.
[3] Because heat-resistant titanium is hard to weld and difficult to work with, welded nickel steel was used for the Mach 2.8 Mikoyan-Gurevich MiG-25 fighter, first flown in 1964; and the Mach 3.1 North American XB-70 Valkyrie used brazed stainless steel honeycomb panels and titanium but was cancelled by the time it flew in 1964.
[3] A computer-aided design system was developed in 1969 for the McDonnell Douglas F-15 Eagle, which first flew in 1974 alongside the Grumman F-14 Tomcat and both used boron fiber composites in the tails; less expensive carbon fiber reinforced polymer were used for wing skins on the McDonnell Douglas AV-8B Harrier II, F/A-18 Hornet and Northrop Grumman B-2 Spirit.
[10] The Boeing 787, first flown in 2009, was the first commercial aircraft with 50% of its structure weight made of carbon-fiber composites, along with 20% aluminium and 15% titanium: the material allows for a lower-drag, higher wing aspect ratio and higher cabin pressurization; the competing Airbus A350, flown in 2013, is 53% carbon-fiber by structure weight.
"[11] The 2013 Bombardier CSeries have a dry-fiber resin transfer infusion wing with a lightweight aluminium-lithium alloy fuselage for damage resistance and repairability, a combination which could be used for future narrow-body aircraft.
In February 2017, Airbus installed a 3D printing machine for titanium aircraft structural parts using electron beam additive manufacturing from Sciaky, Inc.[12] Airframe production has become an exacting process.
Early models suffered from catastrophic airframe metal fatigue, causing a series of widely publicised accidents.
After 3000 pressurisation cycles in a specially constructed pressure chamber, airframe failure was found to be due to stress concentration, a consequence of the square shaped windows.
The Lockheed L-188 Electra turboprop, first flown in 1957 became a costly lesson in controlling oscillation and planning around metal fatigue.
Its 1959 crash of Braniff Flight 542 showed the difficulties that the airframe industry and its airline customers can experience when adopting new technology.
The incident bears comparison with the Airbus A300 crash on takeoff of the American Airlines Flight 587 in 2001, after its vertical stabilizer broke away from the fuselage, called attention to operation, maintenance and design issues involving composite materials that are used in many recent airframes.
By war’s end, the Allies and Germany employed aluminum alloys for the structural framework of fuselage and wing assemblies.
Electrolytic protection, present under wet or moist conditions, is based on the appreciably higher electrode potential of commercial-purity aluminum compared to alloy 2017 or 2024 in the T3 or T4 temper.
Maintenance requirements increased as a result, and these stimulated research and development programs seeking higher-strength alloys with improved resistance to corrosion without cladding.
Aluminum alloy castings traditionally have been used in nonstructural airplane hardware, such as pulley brackets, quadrants, doublers, clips and ducts.
Electric resistance spot and seam welding are used to join secondary structures, such as fairings, engine cowls, and doublers, to bulkheads and skins.
The internal structure comprises stringers, spars, bulkheads, chord members, and various attaching fittings made of aluminum extrusions, formed sheet, forgings, and castings.
Alloy 6061-T6 and its forging counterpart 6151-T6 often are utilized in miscellaneous fittings for reasons of economy and increased corrosion performance, when the parts are not highly stressed.
