Talk:AAR wheel arrangement

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Article intent

The intent of this page is to eliminate the duplication of text about locomotive wheel arrangements. Instead of adding 90 words to every new locomotive page to describe a particular wheel arrangement, merely insert an internal link to the already existing section in “AAR wheel arrangement”. For example, if a locomotive has a B-B wheel arrangement, put "[[AAR wheel arrangement#B-B|B-B]]" in the Editing box. For more examples, click on “What links here” in the toolbox for “AAR wheel arrangement”. Rmeier 03:18, 25 Oct 2004 (UTC)

Identical?

"three identical trucks" need they be identical? Rich Farmbrough, 11:06, 30 November 2009 (UTC).[reply]

"Trucks, or wheel assemblies"?

Just about every paragraph includes the phrase "...trucks, or wheel assemblies...". Is it necessary to repeat it each time? I think it would be more readable to use "trucks (or wheel assemblies)" in the first occurence, then simply "trucks" afterwards. Thoughts? (As an aside, I think the comma should be removed, or the phrase changed to "...trucks, or wheel assemblies,..." (with TWO commas), but better to drop the repetition altogether). MurfleMan (talk) 03:53, 8 June 2010 (UTC)[reply]

+ in UIC system - how to display it in AAR system?

The UIC system uses the + sign for linked locomotives, e.g. 1'D+D+D1' for the Swedisch SJ Dm3. As the + sign is used otherwise in the AAR notation - can such cases be handled? Or is there no necessity, as the situation never arose in America?! --KnightMove (talk) 18:29, 10 January 2017 (UTC)[reply]

Yes, it's generally easy to represent anything in AAR. The trouble is that AAR is less expressive than UIC. You can represent two different locos with two different UIC arrangements, but they both come out to be the same in AAR. From the AAR you can't tell them apart.

Simple cases are B'B' / Bo'Bo' in UIC which both come out as B-B in AAR: you can't distinguish a diesel-hydraulic from a diesel-electric (with separate axle motors). The British use Bo-Bo, but that's not AAR.

Another one would be the 2-8-8-8-4 triplex Mallet for the Virginian Railway which is (1'D)D+D2' in UIC because the leading truck (and its pilot) is articulated beneath the frame but the trailing truck is a permanently coupled tender. In AAR this is 1-D+D+D-2 and you can't tell if that's articulation, three bogies or a Mallet with only one front articulated bogie and the second set of driving wheels fixed to the frame.

Similarly your 1'D+D+D1' case becomes 1-D+D+D-1 in AAR (if I've got it right!). Which is three coupled locos, two with pony trucks. But it could just as well be three bogies under one frame.

As I understand it, AAR has two meanings for both "+" and "-". "+" broadly means "articulation" and "-" means "from one truck to the next". In the simple case of a two bogie diesel, then "B-B" is used, as there are two sibling bogies beneath. A 1C-C1 (BR Class 40) is a pair of four-axled bogies with one pilot axle, 1+C-C+1 (BR Class 44) is the same, but the pilot axles are pivoted as trucks, rather than fixed in the bogie frame. Simple. The problem is that "+" gets re-used. Some early electrics like the PRR FF1 or the Swiss Crocodiles had single frame-mounted motors and so used articulation in two sections rather than bogies underneath, as a UIC of (1'C)(C1') or AAR of 1-C+C-1 (they also had a pilot truck). The notation has swapped around from the Class 44 form: as they're articulated rather than bogies, the largest joiner is now a "+" rather than a "-", and the poor old pilot axle (which is still attached much the same on both) has to swap from a "+" to a "-" so as to not be confused with it. What a mess! Andy Dingley (talk) 02:34, 11 January 2017 (UTC)[reply]