Articulated locomotive: Difference between revisions

TheAn term "'''[[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 be too large to negotiate tightera railroad's curves., Articulatedwhether locomotivesmainlines areor generally used either onspecial 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. Articulation is also applied to some [[electric locomotive]]s, such as the Italian [[FS Class E656]].

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.

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.

[[Simple expansion steam engine|Simple expansion]], or simple, articulated steam engines had two sets of equally sized cylinders. When theHigh-pressure steam was usedsupplied into all cylinders and exhausted out of the fireboxstack once it had been used. The American simple-expansion articulated, thanks largely to the highsmaller pressuremass andof lowthe pressureforward camecylinders outwhen thecompared smokestackto atthe once,compound-expansion resultingMallets inallowing for higher tractivepiston effortspeed, atwere thegenerally costbetter ofsuited morefor fuelhigh burntspeed than their compound cousins. Examples of the "simple mallet" design include the [[Union Pacific Big Boy]]s and [[Union Pacific Challenger|Challengers]], EMthe [[Chesapeake and Ohio class H-18]], Cabthe Forwards[[2-8-8-4]] "Yellowstones", Bigthe Boymajority of [[Southern Pacific Transportation Company|Southern Pacific]]'s [[Cab-forward]]s, Alleghenyand the [[Norfolk & Western]] [[Norfolk and Western Railway class A|A-class]].

[[Compound expansion steam enginelocomotive|Compound expansion]], or compound, articulated steam engines like [[Anatole Mallet]]'s original idea, consist of two sets of unequally sized cylinders. The smaller pair of cylinders near the cab was fed with high pressure steam directly from the boiler and then the steam was passed into a pair of low-pressure cylinders at the front, with larger diameter to offset 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 becausegauge (the cylinders could only be as large as the track and track-side infrastructure allowed) and in terms of itsperformance lowat efficiencyspeed. The large and 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 of the hardest-pulling steam locomotives ever built.

* Two sections which share a central or [[Jacobs bogie|Jacobs]] bogie, e.g.

** [[FS Class E656E.636]] operating in [[Italy]], first built in 1940

** [[New Zealand [[NZR EW class locomotive|New Zealand EW class]], built by [[English Electric]] in 1952.

* Wiener, Lionel, ''Articulated Locomotives'', 1930, reprinted 1970 by [[Kalmbach Media|Kalmbach Publishing Company]] as {{ISBN|0-89024-019-1}}

* [https://web.archive.org/web/20120402084335/http://www.cabbagepatchrailway.co.uk/mls/g3/articulated.pdf Articulated steam bogie locomotives]