4-4-6-4
Encyclopedia
A 4-4-6-4, in the Whyte notation
for the classification of steam locomotive
s by wheel arrangement
, is one that has four leading wheel
s followed by four coupled driving wheel
s, a second set of six coupled driving wheels and four trailing wheel
s.
The Pennsylvania Railroad
's Q2
class were the only locomotives ever to use this arrangement. These were duplex locomotive
s, in which both sets of driving wheels were mounted in a common, rigid locomotive frame
. This locomotive design was a further development of the highly successful 2-10-4
. The divided drive
, or duplex
arrangement, allowed for higher speeds with less damage to the track.
Other equivalent classifications are:
UIC classification
: 2BC2 (also known as German classification and Italian classification)
French classification: 2232
Turkish classification
: 2435
Swiss classification: 2/4+3/5 up to the early 1920s, later 5/9
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...
, is one that has four 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 four coupled driving wheel
Driving wheel
On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons...
s, a second set of six coupled driving wheels and four 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.
The Pennsylvania Railroad
Pennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....
's Q2
PRR Q2
The Pennsylvania Railroad's class Q2 comprised one prototype and twenty-five production duplex steam locomotives of 4-4-6-4 wheel arrangement....
class were the only locomotives ever to use this arrangement. These were duplex locomotive
Duplex locomotive
A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive...
s, in which both sets of driving wheels were mounted in a common, rigid locomotive frame
Locomotive frame
A locomotive frame is the structure that forms the backbone of the railway locomotive, giving it strength and supporting the superstructure elements such as a cab, boiler or bodywork. The vast majority of locomotives have had a frame structure of some kind...
. This locomotive design was a further development of the highly successful 2-10-4
2-10-4
Under the Whyte notation for the classification of steam locomotives, a 2-10-4 locomotive has two leading wheels, ten driving wheels , and four trailing wheels...
. The divided drive
Divided drive (locomotive)
A divided drive locomotive is a steam locomotive that divides the driving force on its wheels by using different cylinders to power different pairs of driving wheels in order to give better weight distribution and reduce "hammer blow" which can be damaging to the track, or else to enable the wider...
, or duplex
Duplex locomotive
A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive...
arrangement, allowed for higher speeds with less damage to the track.
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...
: 2BC2 (also known as German classification and Italian classification)
French classification: 2232
Turkish classification
Turkish classification
In the Turkish classification system for railway locomotives, the number of powered axles are followed by the total number of axles. It is identical to the Swiss system except that the latter places a slash between the two numbers.Thus0-6-0 becomes 33...
: 2435
Swiss classification: 2/4+3/5 up to the early 1920s, later 5/9