Trailing wheel

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The trailing wheels (boxed) on a 4-6-2 locomotive. 462trailing.jpg
The trailing wheels (boxed) on a 4-6-2 locomotive.
A cross-sectional view of a rigid trailing truck Locomotive trailing truck.png
A cross-sectional view of a rigid trailing truck

On a steam locomotive, a trailing wheel or trailing axle is generally an unpowered wheel or axle (wheelset) located behind the driving wheels. The axle of the trailing wheels is usually located in a trailing truck. On some large locomotives, a booster engine was mounted on the trailing truck to provide extra tractive effort when starting a heavy train and at low speeds on gradients.

Steam locomotive railway locomotive that produces its pulling power through a steam engine

A steam locomotive is a type of railway locomotive that produces its pulling power through a steam engine. These locomotives are fueled by burning combustible material – usually coal, wood, or oil – to produce steam in a boiler. The steam moves reciprocating pistons which are mechanically connected to the locomotive's main wheels (drivers). Both fuel and water supplies are carried with the locomotive, either on the locomotive itself or in wagons (tenders) pulled behind.

Wheel One of the six simple machines, a circular item that rotates about an axial bearing

In its primitive form, a wheel is a circular block of a hard and durable material at whose center has been bored a circular hole through which is placed an axle bearing about which the wheel rotates when a moment is applied by gravity or torque to the wheel about its axis, thereby making together one of the six simple machines. When placed vertically under a load-bearing platform or case, the wheel turning on the horizontal axle makes it possible to transport heavy loads; when placed horizontally, the wheel turning on its vertical axle makes it possible to control the spinning motion used to shape materials ; when mounted on a column connected to a rudder or a chassis mounted on other wheels, one can control the direction of a vessel or vehicle ; when connected to a crank, the wheel produces or transmits energy.

Axle central shaft for a rotating wheel or gear

An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type axle is referred to as a spindle.

Trailing wheels were used in some early locomotives but fell out of favor for a time during the latter 19th century. As demand for more powerful locomotives increased, trailing wheels began to be used to support the crew cab and rear firebox area.

Trailing wheels first appeared on American locomotives between 1890 and 1895, but their axle worked in rigid pedestals. It enabled boilers to be lowered, since the top of the main frames was dropped down behind the driving wheels and under the firebox. The firebox could also be longer and wider, increasing the heating surface area and steam generation capacity of the boiler, and therefore its power. The concept was soon improved to provide radial lateral movement by placing the pair of trailing wheels and their axle in a fabricated sub-frame or truck, usually with outside bearings as they gave the best lateral riding stability. One-piece cast-steel trailer trucks were developed about 1915, to provide the additional strength for a booster engine to be fitted to the trailing axle. Finally, about 1921 the Delta trailing truck was developed with an inverted-rocker centering device at the rear ends of the truck frame. Delta trucks were soon enlarged to carry four trailing wheels, and later six. [1]

A "Delta" type trailing truck, fabricated using a one-piece casting by Commonwealth Steel Co. Delta trailing truck Commonwealth Steel Co.jpg
A "Delta" type trailing truck, fabricated using a one-piece casting by Commonwealth Steel Co.

In the Whyte notation, trailing wheels are designated by the last numbers in the series. For example, the 2-8-2 Mikado type locomotive had two leading wheels, eight driving wheels, and two trailing wheels. Some locomotives such as the 4-4-0 American type had no trailing wheels and were designated with a zero in the final place.

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 following a December 1900 editorial in American Engineer and Railroad Journal. The notation counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, numbers being separated by dashes. Other classification schemes, like UIC classification and the French, Turkish and Swiss systems for steam locomotives, count axles rather than wheels.

Under the Whyte notation for the classification of steam locomotives, 2-8-2 represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, eight powered and coupled driving wheels on four axles and two trailing wheels on one axle, usually in a trailing truck. This configuration of steam locomotive is most often referred to as a Mikado, frequently shortened to Mike.

4-4-0 locomotive wheel arrangement

4-4-0 is a locomotive type with a classification that uses the Whyte notation for the classification of steam locomotives by wheel arrangement and represents the arrangement: four leading wheels on two axles, four powered and coupled driving wheels on two axles, and a lack of trailing wheels. Due to the large number of the type that were produced and used in the United States, the 4-4-0 is most commonly known as the American type, but the type subsequently also became popular in the United Kingdom, where large numbers were produced.

In the Whyte notation the number designates the number of wheels rather than the number of axles, thus the final 2 in the Mikado's 2-8-2 refers to two wheels (one axle) while the Northern type's 4-8-4 designation refers to four wheels (two axles).

4-8-4 locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, 4-8-4 represents the wheel arrangement of four leading wheels on two axles, eight powered and coupled driving wheels on four axles and four trailing wheels on two axles. The type was first used by the Northern Pacific Railway, and initially named the Northern Pacific, but railfans and railroad employees have shortened the name when referring to the type, and now is most commonly known as a Northern.

The highest number of trailing wheels on a single locomotive is six as seen on 2-6-6-6 Allegheny type and the Pennsylvania Railroad's 6-8-6 steam turbine and 6-4-4-6 duplex locomotives, as well as numerous Mason Bogie locomotives.

The 2-6-6-6 is an articulated locomotive type with 2 leading wheels, two sets of six driving wheels and six trailing wheels. Only two classes of the 2-6-6-6 type were built. One was the "Allegheny" class, built by the Lima Locomotive Works. The name comes from the locomotive's first service with the Chesapeake and Ohio Railway beginning in 1941. The other was the "Blue Ridge" class for the Virginian Railway. These were one of the most powerful reciprocating steam locomotives ever built at 7,500 HP, and one of the heaviest at 386 tons for the locomotive itself plus 215 tons for the loaded tender.

Pennsylvania Railroad former American Class I railroad

The Pennsylvania Railroad was an American Class I railroad that was established in 1846 and was headquartered in Philadelphia, Pennsylvania. It was so named because it was established in the Commonwealth of Pennsylvania.

6-8-6 locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 6-8-6 represents the arrangement of six unpowered leading wheels arranged into a three-axle leading truck, eight powered driving wheels, and six unpowered trailing wheels arranged into a three-axle trailing truck.

In the UIC classification system, the number of axles rather than the number of wheels is counted.

See also

Related Research Articles

2-10-4 locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, a 2-10-4 locomotive has two leading wheels on one axle, usually in a bissel truck, ten coupled driving wheels on five axles, and four trailing wheels on two axles, usually in a bogie. These were referred to as the Texas type in most of the United States, the Colorado type on the Burlington Route and the Selkirk type in Canada.

2-8-8-4 articulated locomotive wheel arrangement

A 2-8-8-4 steam locomotive, under the Whyte notation, has two leading wheels, two sets of eight driving wheels, and a four-wheel trailing truck. The type was generally named the Yellowstone, a name given it by the first owner, the Northern Pacific Railway, whose lines run near Yellowstone National Park. Seventy-two Yellowstone-type locomotives were built for four U.S. railroads.

4-8-8-4 articulated locomotive wheel arrangement

A 4-8-8-4 in the Whyte notation for the classification of steam locomotives by wheel arrangement, is a locomotive with a four-wheel leading truck, two sets of eight driving wheels, and a four-wheel trailing truck. These are commonly known as "Union Pacific Big Boys".

The UIC classification of locomotive axle arrangements, sometimes known as German classification or German system, describes the wheel arrangement of locomotives, multiple units and trams. It is set out in the International Union of Railways (UIC) "Leaflet 650 – Standard designation of axle arrangement on locomotives and multiple-unit sets". It is used in much of the world. The United Kingdom uses the Whyte notation. The United States uses the simplified AAR wheel arrangement for modern locomotives.

Lima Locomotive Works defunct American locomotive manufacturer

Lima Locomotive Works was an American firm that manufactured railroad locomotives from the 1870s through the 1950s. The company took the most distinctive part of its name from its main shop's location in Lima, Ohio. The shops were located between the Baltimore & Ohio's Cincinnati-Toledo main line and the Nickel Plate Road main line and shops.

4-2-0 locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, 4-2-0 represents the wheel arrangement of four leading wheels on two axles, two powered driving wheels on one axle and no trailing wheels. This type of locomotive is often called a Jervis type, the name of the original designer.

6-2-0 locomotive wheel arrangement

In the Whyte notation, a 6-2-0 is a railroad steam locomotive that has an unpowered three-axle leading truck followed by a single powered driving axle. This wheel arrangement is associated with the Crampton locomotive type, and in the USA the single class were sometimes referred to as Cramptons.

2-6-6-4 articulated locomotive wheel arrangement

In the Whyte notation for the classification of steam locomotive wheel arrangement, a 2-6-6-4 is a locomotive with a two-wheel leading truck, two sets of six driving wheels, and a four-wheel trailing truck. All 2-6-6-4s are articulated locomotives, of the Mallet or related simple articulated type.

Under the Whyte notation for the classification of steam locomotives, 0-10-2 represents the wheel arrangement of no leading wheels, ten powered and coupled driving wheels on five axles, and two trailing wheels on one axle.

4-8-8-2 articulated locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, a 4-8-8-2 is a locomotive with four leading wheels, two sets of eight driving wheels, and a two-wheel trailing truck.

4-12-2 locomotive wheel arrangement

Under the Whyte notation for the classification of steam locomotives, 4-12-2 represents the wheel arrangement of four leading wheels, twelve coupled driving wheels, and two trailing wheels. This arrangement was named the Union Pacific type, after the only railroad to use it.

Under the Whyte notation for the classification of steam locomotives, 2-12-2 represents the wheel arrangement of two leading wheels on one axle, twelve powered and coupled driving wheels on six axles, and two trailing wheels on one axle.

A 4-14-4, in the Whyte notation is the classification of steam locomotives by wheel arrangement, is a locomotive with four leading wheels, fourteen coupled driving wheels in a rigid frame, and four trailing wheels.

2-6-8-0 articulated locomotive wheel arrangement

A 2-6-8-0 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has two leading wheels, a set of six driving wheels, a set of eight driving wheels, and no trailing wheels. These locomotives usually employ the Mallet principle of articulation, with a swinging front engine and a rigidly attached rear engine.

Under the Whyte notation for the classification of steam locomotives, a 4-8-6 locomotive would have had four leading wheels, eight coupled driving wheels and six trailing wheels.

An 0-8-6, in the Whyte notation for the classification of steam locomotives by wheel arrangement, is a locomotive with no leading wheels, eight driving wheels fixed in a rigid frame, and six trailing wheels. Examples of this type of locomotive were built by Wilhelm von Engerth.

4-4-6 locomotive wheel arrangement

A 4-4-6, in the Whyte notation for the classification of steam locomotives by wheel arrangement, is a locomotive with:

Leading wheel unpowered wheel at the front of a locomotive

The leading wheel or leading axle or pilot wheel 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 on a leading truck. Leading wheels are used to help the locomotive negotiate curves and to support the front portion of the boiler.

References

  1. Alfred W Bruce.(1952) The Steam Locomotive in America - Its Development in the Twentieth Century New York, U.S.A. : Bonanza Books. p239-40, 256-57
  2. Huddlestone, Eugene L; George M Smerk. Uncle Sam's Locomotives: The USRA and the Nation's Railroads. Indiana University Press. p. 40. ISBN   0-253-34086-1.