In Whyte notation

Whyte notation

The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte and came into use in the early twentieth century encouraged by an editorial in American Engineer and Railroad Journal...

 for the classification of steam locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

s by wheel arrangement

Wheel arrangement

In rail transport, a wheel arrangement is a system of classifying the way in which wheels are distributed beneath a locomotive.. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country...

, a 2-12-4 is a locomotive with one pair of unpowered leading wheel

Leading wheel

The leading wheel or leading axle of a steam locomotive is an unpowered wheel or axle located in front of the driving wheels. The axle or axles of the leading wheels are normally located in a truck...

s, followed by six pairs of powered driving wheel

Driving wheel

On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons...

s, and two pairs of unpowered trailing wheel

Trailing wheel

On a steam locomotive, a trailing wheel or trailing axle is generally an unpowered wheel or axle located behind the driving wheels. The axle of the trailing wheels was usually located on a trailing truck...

s.

Other equivalent classifications are:

• UIC classification
  UIC classification
  The UIC classification of locomotive axle arrangements describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways "Leaflet 650 - Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much...
  
  : 1'F2' (also known as German classification and Italian classification)
• European classification
  European Classification
  The European Classification is a patent classification system maintained by the European Patent Office . The ECLA classification system contains 134 000 subdivisions. It is mainly an extension of the International Patent Classification system, but sometimes modifies its titles and rules...
  
  : 1-6-2
• French classification: 162

Bulgaria

There are only 20 standard gauge

Standard gauge

The standard gauge is a widely-used track gauge . Approximately 60% of the world's existing railway lines are built to this gauge...

  engines with this wheel arrangement that were built for and ran in Europe - class 46 of Bulgarian State Railways

Bulgarian State Railways

The Bulgarian State Railways are Bulgaria's state railway company and the largest railway carrier in the country, established as an entity in 1885. The company's headquarters are located in the capital Sofia. Since the 1990s the BDZ has met serious competition from automotive transport...

(BDZ). They were ordered by BDZ and built according to its specification by two different manufacturers: 12 engines by Cegielski in Poznań (Poland) in 1931, and 8 by Schwarzkopf in Berlin (Germany) in 1943. Although there is a major difference between the two batches — the first 12 engines are type 1'F2'h2Gt - tank-engine for freight service, 2-cylinder system with simple steam expansion (Zwilling) with superheating, while the remaining 8 are 1'F2'h3Gt - 3-cylinder (Drilling) — all were put into the same class 46 and numbered 46.01 - 46.12 and 46.13 - 46.20. They were designed to haul heavy coal trains on mountainous lines with gradients of about 28‰ (1 in 35.7) and more, and they coped with this hard task very well. Bulgarian railwaymen gave them nickname "Mother Bear" because they looked fat, clumsy and compact. These engines appear to be the most powerful steam locomotives in Europe. Two of them (46.03 of Zwillings and 46.13 of Drillings) are preserved.

Technical specifications:

Locomotive No.	46.01 - 46.12	46.13 - 46.20
Gauge, mm	1435	1435
Type (UIC)	1'F2'h2Gt	1'F2'h3Gt
Type (BDZ)	TT1-6-217	TT1-6-218
Builder	Cegielski	Schwarzkopf
Year	1931	1943
Steam pressure, kg/cm2	16	16
Superheater area, m2	83.91	80
Heating area, m2	224.07	223.6
Grate area, m2	4.87	4.87
Cylinders no. x dia. x stroke, mm	2 x 700 x 700	3 x 550 x 650
Driving wheels diameter, mm	1340	1340
Axleload, t	17	18
Adhesive weight, t	101.7	108
Total weight, t	149.1	155.8
Coal, t	10	10
Water, m3	18	18
Total length, mm	18205	18155
Total height, mm	4280	4345
Tractive effort, starting, kN	381	360
Tractive effort @ 20 km/h, kN	307.2	264.1
Max speed, km/h	65	65