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{{Short description|Type of locomotive}}
{{No footnotes|date=April 2015}}
[[File:Articul locos.png|thumb|300px|Three methods of articulating a steam locomotive]]
[[File:Union Pacific Big Boy 4014 in Counsman, CA.jpg|thumb|300px|Side profile shot of Big Boy no. 4014, an articulated simple expansion steam locomotive]]
 
An '''Articulated[[articulated vehicle|articulated]] locomotive''' usually meansis a [[steam locomotive]] (rarely, an [[electric locomotive]]) with one or more engine units whichthat can move independentindependently of the main frame. Articulation Thisallows isthe doneoperation toof allowlocomotives athat longerwould locomotiveotherwise tobe negotiatetoo tighterlarge curves.to Articulatednegotiate locomotivesa arerailroad's generallycurves, usedwhether eithermainlines onor special lines with extreme curvature—curvature such as [[LoggingForest railroadrailway|logging]], [[Industrial railway|industrial]], or [[mountain railway]]s, for example—or to allow very large locomotives to run on railways with regular track curvature.
 
Articulated locomotives saw service in many nations, but were very popular on [[narrow -gauge railways]] in Europe. andThe sawlargest theirexamples greatest sizewere developed in the United States, where the [[Union Pacific Big Boy]] [[4-8-8-4]]s and the Allegheny H-8 [[2-6-6-6]]s were some of the largest steam locomotives ever built, with [[Big Boy 4014]] remaining as the largest, and last of its kind to still operate.▼
==Usage==
▲Articulated locomotives saw service in many nations, but were very popular on [[narrow gauge railways]] in Europe and saw their greatest size developed in the United States, where the [[Union Pacific Big Boy]] [[4-8-8-4]]s and the Allegheny H-8 [[2-6-6-6]]s were some of the largest steam locomotives ever built.
 
Many different schemes for articulation were developed over the years. Of these, the [[Mallet locomotive]] and its simple-expansion derivative were the most popular, followed by the [[Garratt locomotive|Garratt]] type (mostly built in the [[United Kingdom]], popular throughout [[Europe]], [[Africa]] and European colonies), and the various [[geared steam locomotive]] types, the latter largely used in logging, mining and industry. Most other types saw only limited success.
 
As distinct from articulated locomotives, a non-articulated locomotive is referred to as a ''straight'' or ''rigid'' locomotive.
==Steam locomotive types==▼
 
▲==SteamArticulated steam locomotive types==
===Major types===
The major types of articulated locomotive are as follows:
* The [[Fairlie locomotive|Fairlie]], with two powered trucks under a double [[locomotive boiler|boiler]], or its [[Fairlie locomotive#Single Fairlie locomotive|Single Fairlie]] single-boiler derivative with one powered and one unpowered truck (known as a [[Mason Bogie]] in the [[United States]]).
* The [[Garratt locomotive]], with an engine unit at each end carrying coal and water supplies, and a boiler unit articulated between them.
* The [[Mallet locomotive]], with one fixed engine under the rear of the locomotive and a radially swinging engine unit in front.
* The [[Meyer locomotive]], with two powered engine trucks under the locomotive (generally with the cylinders inward). Also, the Kitson-Meyer variant with the trucks spread apart to allow a deeper [[Firebox (steam engine)|firebox]] between them.
 
===Simple expansion===
[[Simple expansion steam engine|Simple expansion]], or simple, articulated steam engines had two sets of equally sized cylinders. High-pressure steam was supplied to all cylinders and exhausted out of the stack once it had been used. The American simple-expansion articulated, thanks largely to the smaller mass of the forward cylinders when compared to the compound-expansion Mallets allowing for higher piston speed, were generally better suited for high speed than their compound cousins. Examples of the "simple mallet" design include the [[Union Pacific Big Boy]]s and [[Union Pacific Challenger|Challengers]], the [[Chesapeake and Ohio class H-8]], the [[2-8-8-4]] "Yellowstones", the majority of [[Southern Pacific Transportation Company|Southern Pacific]]'s [[Cab-forward]]s, and the [[Norfolk & Western]] [[Norfolk and Western Railway class A|A-class]].
Simple articulated steam engines had two sets of equally sized cylinders. When the steam was used in the firebox, the high pressure and low pressure came out the smokestack at once, resulting in higher tractive effort. They usually consisted of two smokestacks.
 
===Compound expansion===
[[Compound locomotive|Compound expansion]], or compound, articulated steam engines like [[Anatole Mallet]]'s malletoriginal idea, consist of two sets of unequally sized cylinders. The smaller cylinderpair of cylinders near the cab containedwas fed with high pressuredpressure steam directly from the boiler and then itthe steam was passed into a largerpair cylinderof setlow-pressure cylinders at the front, ofwith thelarger enginediameter into lowoffset the lower pressure, before exhausting through the smokestack. ThisWhile the [[thermal efficiency]] was greatly improved through the compound use of steam in Mallet designs, howeverthe large low-pressure cylinders posed unique limitations, resultedboth in lowerterms tractiveof effortloading gauge (the cylinders could only be as large as the track and track-side infrastructure allowed) and in becauseterms of itsperformance lowat efficiencyspeed. TheyThe usuallylarge consistedand consequently heavier pistons caused stability issues at higher speed, which generally limited compound expansion articulated locomotives to below 30 or 40 miles per hour. A notable exception to this was to be found in later iterations of Norfolk & Western Y-class 2-8-8-2s, which could and did often exceed 50 miles per hour in service as well as being one smokestackof the hardest-pulling steam locomotives ever built.
 
The first Garratt locomotives constructed, the [[Tasmanian Government Railways K class]] were also compound locomotives, but were complicated as a result. All subsequent Garratts were simple engines only.
 
===Geared types===
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* [[Heisler locomotive]]
* [[Shay locomotive]]
* [[Willamette locomotive]]
 
===Other types===
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* [[Golwé locomotive]]
* [[Hagans locomotive]], such as the [[Prussian T 13]] (Hagans variant)
* [[KleinKlien-LinderLindner]] locomotive
* [[Krauss-Helmholtz bogie]]
* [[Luttermöller axle]]
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** Swiss [[Crocodile (locomotive)|crocodile locomotives]], [[:de:SBB Ce 6/8 II]] and [[:de:SBB Ce 6/8 III]]
** [[DRG Class E 94]], [[:de:DRB-Baureihe E 94]]
* Two sections which share a central or [[Jacobs bogie|Jacobs]] bogie, e.g.
** [[FS Class E656E.636]] operating in [[Italy]], first built in 1940
** [[HŽ series 1061]], a derivative of E.636 operating in [[Croatia]] - also known as SŽ series 362 in [[Slovenia]] and as JŽ series 362 in [[Yugoslavia]]
** [[FS Class E.646]] in Italy, first built in 1958
** [[FS Class E.656]] operating in Italy since 1975
** [[Rhaetian Railway Ge 6/6 II]] in [[Switzerland]]
** [[New Zealand [[NZR EW class locomotive|New Zealand EW class]], built by [[English Electric]] in 1952.
 
The conventional electric and diesel locomotive dual bogie design uses the same general configuration as the Meyer design but is not considered to be articulated.
 
Electric and diesel bogie locomotives have many construction aspects in common with Meyer type steam locomotives but are not seen as articulated.
 
==See also==
* [[Beyer Peacock]]
* [[Bissel bogie]]
* [[Cleminson's patent]]
* [[Grovers bogie]]
* [[Jacobs bogie]]
 
==References==
{{Reflist}}
{{Refbegin}}
* Wiener, Lionel, ''Articulated Locomotives'', 1930, reprinted 1970 by [[Kalmbach Media|Kalmbach Publishing Company]] as {{ISBN |0-89024-019-1}}
{{Refend}}
 
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{{Commons category|Articulated locomotives}}
* [http://mikes.railhistory.railfan.net/r095.html Articulated locomotives]
* [https://web.archive.org/web/20120402084335/http://www.cabbagepatchrailway.co.uk/mls/g3/articulated.pdf Articulated steam bogie locomotives]
 
{{Whyte types}}
 
[[Category:Articulated locomotives]]
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