Airframe | Wikipedia audio article

The mechanical structure of an aircraft is
known as the airframe. This structure is typically considered to
include the fuselage, undercarriage, empennage and wings, and exclude the propulsion system. Airframe design is a field of aerospace engineering
that combines aerodynamics, materials technology and manufacturing methods with a focus on
performance, as well as reliability and cost.==History==Modern airframe history began in the United
States when a 1903 wood biplane made by Orville and Wilbur Wright showed the potential of
fixed-wing designs. In 1912 the Deperdussin Monocoque pioneered
the light, strong and streamlined monocoque fuselage formed of thin plywood layers over
a circular frame, achieving 210 km/h (130 mph).===First World War===
Many early developments were spurred by military needs during World War I. Well known aircraft from that era include
the Dutch designer Anthony Fokker’s combat aircraft for the German Empire’s Luftstreitkräfte,
and U.S. Curtiss flying boats and the German/Austrian Taube monoplanes. These used hybrid wood and metal structures. 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 – this first appeared on the 1916 LFG Roland C.II, and would later be licensed
to Pfalz Flugzeugwerke for its D-series biplane fighters. In 1916 the German Albatros D.III biplane
fighters featured semi-monocoque fuselages with load-bearing plywood skin panels glued
to longitudinal longerons and bulkheads; it was replaced by the prevalent stressed skin
structural configuration as metal replaced wood. Similar methods to the Albatros firm’s concept
were used by both Hannoversche Waggonfabrik for their light two-seat CL.II through CL.V
designs, and by Siemens-Schuckert for their later Siemens-Schuckert D.III and higher-performance
D.IV biplane fighter designs. The Albatros D.III construction was of much
less complexity than the patented LFG Wickelrumpf concept for their outer skinning.German engineer
Hugo Junkers first flew all-metal airframes in 1915 with the all-metal, cantilever-wing,
stressed-skin monoplane Junkers J 1 made of steel. 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.===Between World wars===
The J 1 of 1915, and the D.I fighter of 1918, were followed in 1919 by the first all-metal
transport aircraft, the Junkers F.13 made of Duralumin as the D.I had been; 300 were
built, along with the first four-engine, all-metal passenger aircraft, the sole Zeppelin-Staaken
E-4/20. Commercial aircraft development during the
1920s and 1930s focused on monoplane designs using Radial engines. 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. William Stout designed the all-metal Ford
Trimotors in 1926.The Hall XFH naval fighter prototype flown in 1929 was the first aircraft
with a riveted metal fuselage : an aluminum skin over steel tubing, Hall also pioneered
flush rivets and butt joints between skin panels in the Hall PH flying boat also flying
in 1929. Based on the Italian Savoia-Marchetti S.56,
the 1931 Budd BB-1 Pioneer experimental flying boat was constructed of corrosion-resistant
stainless steel assembled with newly developed spot welding by U.S. railcar maker Budd Company.The
original Junkers corrugated duralumin-covered airframe philosophy culminated in the 1932-origin
Junkers Ju 52 trimotor airliner, used throughout World War II by the Nazi German Luftwaffe
for transport and paratroop needs. 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’
firm’s developed the iconic Douglas DC-3 twin-engined airliner in 1936. They were among the most successful designs
to emerge from the era through the use of all-metal airframes. In 1937, the Lockheed XC-35 was the first
aircraft specifically constructed with cabin pressurization to underwent extensive high-altitude
flight tests, paving the way for the first pressurised transport aircraft, the Boeing
307 Stratoliner.===Second World War===
During World War II, military needs again dominated airframe designs. 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. The first jets were produced during the war
but not made in large quantity. Due to wartime scarcity of aluminum, the de
Havilland Mosquito fighter-bomber was built from wood—plywood facings bonded to a balsawood
core and formed using molds to produce monocoque structures, leading to the development of
metal-to-metal bonding used later for the de Havilland Comet and Fokker F27 and F28.===Postwar===
Postwar commercial airframe design focused on airliners, on turboprop engines, and then
on Jet engines : turbojets and later turbofans. The generally higher speeds and tensile stresses
of turboprops and jets were major challenges. Newly developed aluminum alloys with copper,
magnesium and zinc were critical to these designs.Flown in 1952 and designed to cruise
at Mach 2 where skin friction required its heat resistance, the Douglas X-3 Stiletto
was the first titanium aircraft but it was underpowered and barely supersonic; the Mach
3.2 Lockheed A-12 and SR-71 were also mainly titanium, as was the cancelled Boeing 2707
Mach 2.7 supersonic transport.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.Computer-aided
design system was developed in 1969 for the McDonnell Douglas F-15 Eagle, which first
flew in 1974 along 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.===Modern era===Airbus and Boeing are the dominant assemblers
of large jet airliners while ATR, Bombardier and Embraer lead the regional airliner market;
many manufacturers produce airframe components.The vertical stabilizer of the Airbus A310-300,
first flown in 1985, was the first carbon-fiber primary structure used in a commercial aircraft;
composites are increasingly used since in Airbus airliners: the horizontal stabilizer
of the A320 in 1987 and A330/A340 in 1994, and the center wing-box and aft fuselage of
the A380 in 2005.The Cirrus SR20, type certificated in 1998, was the first widely produced general
aviation aircraft manufactured with all-composite construction, followed by several other light
aircraft in the 2000s.The Boeing 787, first flown in 2009, was the first commercial aircraft
with 50% of its structure weight made of carbon-fiber composites, along 20% Aluminum 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. It has a one-piece carbon fiber fuselage,
said to replace “1,200 sheets of aluminum and 40,000 rivets.”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..==Safety==
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. A landmark in aeronautical design, the world’s
first jet airliner, the de Havilland Comet, first flew in 1949. Early models suffered from catastrophic airframe
metal fatigue, causing a series of widely publicised accidents. The Royal Aircraft Establishment investigation
at Farnborough Airport founded the science of aircraft crash reconstruction. 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 windows had been engineered to be glued
and riveted, but had been punch riveted only. Unlike drill riveting, the imperfect nature
of the hole created by punch riveting may cause the start of fatigue cracks around the
rivet. 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. The A300 had experienced other structural
problems but none of this magnitude.==See also==
Longeron Former
Chord (aeronautics) Aircraft fairing
Vertical stabilizer

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