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{{Short description|Mechanical structure of an aircraft}}
{{for|the novel by Michael Crichton|Airframe (novel)}}
{{More citations needed|date=October 2024}}[[File:RV-14 Cutaway TD - small.jpg|thumb|[[Van's RV-14]] cutaway showing its airframe]]

The [[Structural engineering#Mechanical structures|mechanical structure]] of an [[aircraft]] is known as the '''airframe'''.<ref>{{cite book|title=A Dictionary of Aviation |first=David W. |last=Wragg |isbn=0-85045-163-9 |publisher=Frederick Fell, Inc. |publication-place=New York |date=1974 |edition=1st American |page=22}}</ref> This structure is typically considered to include the [[fuselage]], [[Landing gear|undercarriage]], [[empennage]] and [[wing]]s,  and excludes the [[Air propulsion|propulsion system]].<ref>{{cite web |title=FAA Definitions |url=http://www.faa-aircraft-certification.com/faa-definitions.html |access-date=2020-04-30}}</ref>

[[Aircraft design process|Airframe design]] is a field of [[aerospace engineering]] that combines [[aerodynamics]], [[Materials science|materials technology]] and [[manufacturing]] methods with a focus on weight, strength and [[aerodynamic drag]], as well as [[Reliability engineering|reliability]] and cost.<!--ref>Michael C. Y. Niu (1988). ''Airframe Structural Design''. Conmilit Press LTD.</ref-->

==History==

[[File:Airframe (4 types).PNG|thumb|520px|Four types of airframe construction: (1) Truss with canvas, (2) Truss with corrugate plate, (3) [[Monocoque]] construction, (4) [[Semi-monocoque]] construction.]]

Modern airframe history began in the [[United States]] during the [[Wright Flyer|Wright Flyer's]] maiden flight, showing the potential of [[Fixed-wing aircraft|fixed-wing designs]] in aircraft.

In 1912 the [[Deperdussin Monocoque]] pioneered the light, strong and streamlined [[monocoque]] fuselage formed of thin [[plywood]] layers over a circular frame, achieving {{convert|130|mph|km/h|abbr=on|order=flip}}.<ref name=AW161121>{{cite news |url= http://aviationweek.com/commercial-aviation/designs-changed-way-aircraft-are-built |title= Designs That Changed The Way Aircraft Are Built |date= Nov 21, 2016 |author= Graham Warwick |work= Aviation Week & Space Technology |archive-date= July 11, 2017 |access-date= December 24, 2016 |archive-url= https://web.archive.org/web/20170711075849/http://aviationweek.com/commercial-aviation/designs-changed-way-aircraft-are-built |url-status= dead }}</ref><ref name=ASM0807>{{cite news |url= http://www.airspacemag.com/history-of-flight/airplanes-that-transformed-aviation-46502830/?all |title= Airplanes that Transformed Aviation |date= July 2008 |author= Richard P. Hallion |work= Air & space magazine |publisher= Smithsonian}}</ref>

=== 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 {{lang|de|[[Luftstreitkräfte]]}}, and U.S. [[Glenn Curtiss|Curtiss]] [[flying boat]]s 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<ref>{{cite book |title=German Combat Planes: A Comprehensive Survey and History of the Development of German Military Aircraft from 1914 to 1945 |author1=Wagner, Ray  |author2=Nowarra, Heinz  |name-list-style=amp |year=1971 |publisher=Doubleday |location=New York |pages=75 & 76 }}</ref> - 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 [[longeron]]s and [[Bulkhead (partition)|bulkhead]]s; it was replaced by the prevalent [[stressed skin]] structural configuration as [[metal]] replaced wood.<ref name=AW161121/> Similar methods to the Albatros firm's concept were used by both [[Hannoversche Waggonfabrik]] for their light two-seat [[Hannover CL.II|CL.II]] through [[Hannover CL.V|CL.V]] designs, and by [[Siemens-Schuckert]] for their later [[Siemens-Schuckert D.III]] and higher-performance [[Siemens-Schuckert D.IV|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.{{Original research inline|date=May 2018}}

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]].<ref name=AW161121/> 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 [[Tupolev ANT-20|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-[[aircraft engine|engine]], all-metal [[passenger aircraft]], the sole [[Zeppelin-Staaken E-4/20]].<ref name=AW161121/><ref name=ASM0807/> [[Commercial aircraft]] development during the 1920s and 1930s focused on monoplane designs using [[Radial engine]]s. 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 Trimotor]]s in 1926.<ref>{{cite book |author= David A. Weiss |title= The Saga of the Tin Goose |publisher= Cumberland Enterprises |year= 1996 }}</ref>

The [[Hall XFH]] naval fighter [[prototype]] flown in 1929 was the first aircraft with a [[rivet]]ed metal fuselage : an aluminium skin over steel tubing, Hall also pioneered [[flush rivet]]s and [[butt joint]]s between skin panels in the [[Hall PH]] [[flying boat]] also flying in 1929.<ref name=AW161121/> 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]].<ref name=AW161121/>

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 Wills Douglas, Sr.|Donald Douglas]]' firms developed the iconic [[Douglas DC-3]] twin-engined airliner in 1936.<ref>{{cite book |author= Peter M. Bowers |title= The DC-3: 50 Years of Legendary Flight |publisher= Tab Books |year= 1986 }}</ref> 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 specifically constructed with [[cabin pressurization]] to undergo extensive high-altitude flight tests, paving the way for the [[Boeing 307 Stratoliner]], which would be the first aircraft with a pressurized cabin to enter commercial service.<ref name=ASM0807/>

[[File:Vickers Wellington Mark X, HE239 'NA-Y', of No. 428 Squadron RCAF (April 1943).png|thumb|[[Vickers Wellington|Wellington Mark X]] showing the [[geodesic airframe]] construction and the level of punishment it could withstand while maintaining airworthiness]]

=== 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 [[Jet aircraft|jets]] were produced during the war but not made in large quantity.

Due to wartime scarcity of aluminium, the [[de Havilland Mosquito]] fighter-bomber was built from wood—plywood facings [[Wood glue|bonded]] to a [[balsawood]] core and formed using [[Molding (process)|mold]]s to produce monocoque structures, leading to the development of metal-to-metal [[Adhesive|bonding]] used later for the [[de Havilland Comet]] and [[Fokker F27]] and [[Fokker F28|F28]].<ref name=AW161121/>

=== Postwar ===

Postwar commercial airframe design focused on [[airliner]]s, on [[turboprop]] engines, and then on [[jet engine]]s. The generally higher speeds and [[tensile stress]]es of turboprops and jets were major challenges.<ref>{{cite book |author= Charles D. Bright |title= The Jet Makers: the Aerospace Industry from 1945 to 1972 |publisher= Regents Press of Kansas |year=1978 |url= http://www.generalatomic.com/jetmakers/index.html }}</ref> Newly developed [[aluminium]] [[alloy]]s with [[copper]], [[magnesium]] and [[zinc]] were critical to these designs.<ref>{{cite book |work= Key to Metals Database |title= Aircraft and Aerospace Applications |publisher= INI International |year= 2005 |url= http://www.key-to-metals.com/PrintArticle.asp?ID=96 |url-status= dead |archive-url= https://web.archive.org/web/20060308194218/http://www.key-to-metals.com/PrintArticle.asp?ID=96 |archive-date= 2006-03-08 }}</ref>

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 [[Lockheed SR-71|SR-71]] were also mainly titanium, as was the cancelled [[Boeing 2707]] Mach 2.7 [[supersonic transport]].<ref name=AW161121/>

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 structure|honeycomb]] panels and titanium but was cancelled by the time it flew in 1964.<ref name=AW161121/>

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]], [[McDonnell Douglas F/A-18 Hornet|F/A-18 Hornet]] and [[Northrop Grumman B-2 Spirit]].<ref name=AW161121/>

=== Modern era ===
[[File:Shuttle Carrier Aircraft interior bulkhead.jpg|thumb|right|Rough interior of a [[Boeing 747]] airframe]]
[[File:Wing with one spar.JPG|thumb|Wing structure with [[Rib (aircraft)|rib]]s and one [[Spar (aviation)|spar]]]]

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 [[Airbus A320|A320]] in 1987 and [[Airbus A330|A330]]/[[Airbus A340|A340]] in 1994, and the center wing-box and aft fuselage of the [[Airbus A380|A380]] in 2005.<ref name="AW161121" />

The [[Cirrus SR20]], [[type certificate]]d in 1998, was the first widely produced [[general aviation]] aircraft manufactured with all-composite construction, followed by several other [[light aircraft]] in the 2000s.<ref>{{cite news |url= http://www.flyingmag.com/photo-gallery/photos/top-100-airplanes-platinum-edition?pnid=44581 |title= Top 100 Airplanes:Platinum Edition |work= Flying |date= November 11, 2013 |page= 11 |archive-date= January 9, 2016 |access-date= February 20, 2015 |archive-url= https://web.archive.org/web/20160109024332/http://www.flyingmag.com/photo-gallery/photos/top-100-airplanes-platinum-edition?pnid=44581 |url-status= dead }}</ref>

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.<ref name=AW161121/> It has a one-piece carbon fiber fuselage, said to replace "1,200 sheets of aluminium and 40,000 rivets."<ref>{{cite web |author= Leslie Wayne |title= Boeing Bets the House on Its 787 Dreamliner |work= New York Times |date= May 7, 2006 |url= https://www.nytimes.com/2006/05/07/business/yourmoney/07boeing.html }}</ref>

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]].<ref name=AW161121/> In 2016, the [[Cirrus Vision SF50]] became the first certified [[Business jet|light jet]] made entirely from carbon-fiber composites.

In February 2017, Airbus installed a [[3D printing]] machine for titanium  aircraft structural parts using [[electron beam additive manufacturing]] from [[Sciaky, Inc.]]<ref>{{cite news |url= http://aviationweek.com/technology/airbus-3-d-print-airframe-structures |title= Airbus To 3-D Print Airframe Structures |date= Jan 11, 2017 |author= Graham Warwick |work= Aviation Week & Space Technology}}</ref>

{| class="wikitable"
|+ Airliner composition by mass<ref>{{cite journal |last1=Woidasky |first1=Jörg |last2=Klinke |first2=Christian |last3=Jeanvré |first3=Sebastian |title=Materials Stock of the Civilian Aircraft Fleet |journal=Recycling |date=5 November 2017 |volume=2 |issue=4 |pages=21 |doi=10.3390/recycling2040021 |doi-access=free}}</ref>
! Material
! B747 !! B767 !! B757 !! B777 !! B787 !! A300B4
|-
! Aluminium
| 81% || 80% || 78% || 70% || 20% || 77% 
|-
! Steel
| 13% || 14% || 12% || 11% || 10% || 12% 
|-
! Titanium
| 4% || 2% || 6% || 7% || 15% || 4% 
|-
! Composites
| 1% || 3% || 3% || 11% || 50% || 4% 
|-
! Other
| 1% || 1% || 1% || 1% || 5% || 3% 
|}

== 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.<ref>{{cite news |author= Florence Graves and Sara K. Goo |title= Boeing Parts and Rules Bent, Whistle-Blowers Say |newspaper= Washington Post |date= Apr 17, 2006 |url= https://www.washingtonpost.com/wp-dyn/content/article/2006/04/16/AR2006041600803.html |access-date= April 23, 2010}}</ref>

[[File:DH106 Comet 3 G-ANLO FAR 1954.jpg|right|thumb|DH106 Comet 3 G-ANLO demonstrating at the 1954 [[Farnborough Airshow]]]]

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 material]]s that are used in many recent airframes.<ref>{{cite web |author= Todd Curtis |title= Investigation of the Crash of American Airlines Flight 587 |work= AirSafe.com |date= 2002 |url= http://www.airsafe.com/events/aa587.htm }}</ref><ref>{{cite web |author= James H. Williams Jr. |title= Flight 587 |publisher= Massachusetts Institute of Technology |date= 2002 |url= http://web.mit.edu/jhwill/www/Flight587.html |author-link= James H. Williams, Jr }}</ref><ref>{{cite news |author= Sara Kehaulani Goo |title= NTSB Cites Pilot Error in 2001 N.Y. Crash |newspaper= Washington Post |date= Oct 27, 2004 |url= https://www.washingtonpost.com/wp-dyn/articles/A63850-2004Oct26.html |access-date=April 23, 2010}}</ref> The A300 had experienced other structural problems but none of this magnitude.

==Alloys for airframe components==
As the twentieth century progressed, aluminum became an essential metal in aircraft. The cylinder block of the engine that powered the Wright brothers’ plane at Kitty Hawk in 1903 was a one-piece casting in an aluminum alloy containing 8% copper; aluminum propeller blades appeared as early as 1907; and aluminum covers, seats, cowlings, cast brackets, and similar parts were common by the beginning of the First World War. In 1916, L. Brequet designed a reconnaissance bomber that marked the initial use of aluminum in the working structure of an airplane. By war’s end, the Allies and Germany employed aluminum alloys for the structural framework of fuselage and wing assemblies.<ref>{{Cite web |title=download |url=https://core.ac.uk/download/pdf/4407543.pdf |website=core.ac.uk}}</ref>

The aircraft airframe has been the most demanding application for aluminum alloys; to chronicle the development of the high-strength alloys is also to record the development of airframes. [[Duralumin]], the first high-strength, heat treatable aluminum alloy, was employed initially for the framework of [[rigid airships]], by Germany and the Allies during World War I. Duralumin was an aluminum-copper-magnesium alloy; it was originated in Germany and developed in the United States as Alloy 17S-T (2017-T4). It was utilized primarily as sheet and plate.

Alloy 7075-T6 (70,000-psi yield strength), an Al-Zn-Mg-Cu alloy, was introduced in 1943. Since then, most aircraft structures have been specified in alloys of this type. The first aircraft designed in 7075-T6 was the Navy’s [[Lockheed P-2 Neptune|P2V patrol bomber]]. A higher-strength alloy in the same series, 7178-T6 (78,000-psi yield strength), was developed in 1951; it has not generally displaced 7075-T6, which has superior fracture toughness.

Alloy 7178-T6 is used primarily in structural members where performance is critical under [[Compression (physics)|compressive loading]].

Alloy 7079-T6 was introduced in the United States in 1954. In forged sections over 3 in. thick, it provides higher strength and greater transverse [[ductility]] than 7075-T6. It now is available in sheet, plate, extrusions, and forgings.

Alloy X7080-T7, with higher resistance to [[stress corrosion]] than 7079-T6, is being developed for thick parts. Because it is relatively insensitive to [[quenching]] rate, good strengths with low quenching stresses can be produced in thick sections.

[[Cladding (construction)|Cladding]] of aluminum alloys was developed initially to increase the corrosion resistance of 2017-T4 sheet and thus to reduce aluminum aircraft maintenance requirements. The coating on 2017 sheet - and later on 2024-T3 - consisted of commercial-purity aluminum metallurgically bonded to one or both surfaces of the sheet.

[[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. When 7075-T6 and other Al-Zn-Mg-Cu alloys appeared, an aluminum-zinc cladding alloy 7072 was developed to provide a relative electrode potential sufficient to protect the new strong alloys.

However, the high-performance aircraft designed since 1945 have made extensive use of skin structures machined from thick plate and extrusions, precluding the use of [[alclad]] exterior skins. 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. They also have been employed extensively in complex [[valve#components|valve bodies]] of hydraulic control systems. The philosophy of some aircraft manufacturers still is to specify castings only in places where failure of the part cannot cause loss of the airplane. [[Redundancy (engineering)|Redundancy]] in cable and hydraulic control systems permits the use of castings.

Casting technology has made great advances in the last decade. Time-honored alloys such as 355 and 356 have been modified to produce higher levels of strength and ductility. New alloys such as 354, A356, A357, 359 and Tens 50 were developed for premium-strength castings. The high strength is accompanied by enhanced structural integrity and performance reliability.

Electric resistance [[spot welding|spot]] and [[seam welding]] are used to join secondary structures, such as fairings, engine cowls, and doublers, to bulkheads and skins. Difficulties in quality control have resulted in low utilization of electric resistance welding for primary structure.

[[Ultrasonic welding]] offers some economic and quality-control advantages for production joining, particularly for thin sheet. However, the method has not yet been developed extensively in the aerospace industry.

[[Adhesive bonding]] is a common method of joining in both primary and secondary structures. Its selection is dependent on the design philosophy of the aircraft manufacturer. It has proven satisfactory in attaching stiffeners, such as hat sections to sheet, and face sheets to [[Sandwich-structured composite|honeycomb cores]]. Also, adhesive bonding has withstood adverse exposures such as sea-water immersion and atmospheres.

[[Fusion welding|Fusion welded]] aluminum primary structures in airplanes are virtually nonexistent, because the high-strength alloys utilized have low [[weldability]] and low weld-joint efficiencies. Some of the alloys, such as 2024-T4, also have their corrosion resistance lowered in the heat-affected zone if left in the as-welded condition.

The improved welding processes and higher-strength weldable alloys developed during the past decade offer new possibilities for welded primary structures. For example, the weldability and strength of alloys 2219 and 7039, and the [[brazeability]] and strength of X7005, open new avenues for design and manufacture of aircraft structures.

==Light aircraft==
Light aircraft have airframes primarily of all-aluminum semi-monocoque construction, however, a few light planes have tubular truss load-carrying construction with fabric or aluminum skin, or both.
Aluminum skin is normally of the minimum practical thickness: 0.015 to 0.025 in. Although design strength requirements are relatively low, the skin needs moderately high yield strength and hardness to minimize ground damage from stones, debris, mechanics’ tools, and general handling. Other primary factors involved in selecting an alloy for this application are corrosion resistance, cost, and appearance. Alloys 6061-T6 and alclad 2024-T3 are the primary choices.

Skin sheet on light airplanes of recent design and construction generally is alclad 2024-T3. The internal structure comprises stringers, spars, bulkheads, chord members, and various attaching fittings made of aluminum extrusions, formed sheet, forgings, and castings.

The alloys most used for extruded members are 2024-T4 for sections less than 0.125 in. thick and for general application, and 2014-T6 for thicker, more highly stressed sections. Alloy 6061-T6 has considerable application for extrusions requiring thin sections and excellent corrosion resistance. Alloy 2014-T6 is the primary forging alloy, especially for landing gear and hydraulic cylinders. 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.

Alloys 356-T6 and A356-T6 are the primary casting alloys employed for brackets, bellcranks, pulleys, and various fittings. Wheels are produced in these alloys as permanent mold or sand castings. Die castings in alloy A380 also are satisfactory for wheels for light aircraft.

For low-stressed structure in light aircraft, alloys 3003-H12, H14, and H16; 5052-O, H32, H34, and H36; and 6061-T4 and T6 are sometimes employed. These alloys are also primary selections for fuel, lubricating oil, and hydraulic oil tanks, piping, and instrument tubing and brackets, especially where welding is required. Alloys 3003, 6061, and 6951 are utilized extensively in brazed heat exchangers and hydraulic accessories. Recently developed alloys, such as 5086, 5454, 5456, 6070, and the new weldable aluminum-magnesium-zinc alloys, offer strength advantages over those previously mentioned.

Sheet assembly of light aircraft is accomplished predominantly with rivets of alloys 2017-T4, 2117-T4, or 2024-T4. Self-tapping sheet metal screws are available in aluminum alloys, but cadmium-plated steel screws are employed more commonly to obtain higher shear strength and driveability. Alloy 2024-T4 with an anodic coating is standard for aluminum screws, bolts, and nuts made to military specifications. Alloy 6262-T9, however, is superior for nuts, because of its virtual immunity to stress-corrosion cracking.<ref>[http://www.keytometals.com/Article95.htm Aircraft and Aerospace Applications: Part One]</ref>

==See also==
* [[Longeron]]
* [[Former]]
* [[Chord (aeronautics)]]
* [[Aircraft fairing]]
* [[Vertical stabilizer]]

==References==
{{reflist}}

==Further reading==
* {{cite news |url= https://www.flightglobal.com/news/articles/analysis-are-composite-airframes-feasible-for-narro-449415/ |title= Analysis: Are composite airframes feasible for narrowbodies? |date= 9 July 2018 |author= Michael Gubisch |work= Flightglobal}}

{{Aircraft components}}

[[Category:Aircraft components]]
[[Category:Structural system]]