Cab forward
From Wikipedia, the free encyclopedia
The term cab forward refers to various rail and road vehicle designs which place the driver's compartment substantially farther towards the front than is common practice.
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[edit] Locomotives
In steam locomotive design, a cab forward design will typically have the driver's compartment placed immediately forward of the firebox at the very front of the engine while the fireman's station remains on the footplate behind the firebox (for obvious reasons). This type of design was widely, though not commonly, used throughout Europe in the first half of the 20th century, often in conjunction with an enclosed body design and/or streamlining.
[edit] Italy: Ferrovie dello Stato italiane (FS)
The state owned Italian FS had several cab forward locomotives, 4-6-0 types group 670, 671, 672 and 0-10-0 types 470. The 670 to 672 group engines had a 3 axle tender, the nickname was "mucca" (cow). The engines (construction year 1902, top speed 110 km/h) were used to haul passenger trains on the east coast line.
[edit] Southern Pacific
In contrast however, the best known example of the cab-forward design in the United States, the Southern Pacific Cab-Forward (also known as "Cab-in-fronts") placed the cab at the front by the simple expedient of turning the entire locomotive, minus the tender, by 180 degrees, an arrangement made possible by burning fuel oil instead of coal.
The cab forward design was widely used by the Southern Pacific Railroad, which developed it to deal with the peculiar problems of its routes. The 39 long tunnels and nearly 40 miles (64 km) of snow sheds of the Sierra Nevada Mountains could funnel dangerous exhaust fumes back into the crew compartment of a conventional locomotive. After a number of crews nearly asphyxiated, someone had the idea of running his locomotive in reverse. This meant that the tender was leading the train, which introduced new problems. The tender blocked the view ahead and put crewmen on the wrong sides of the cab for seeing signals. The tenders were not designed to be pushed at the lead of the train, which limited speeds. Southern Pacific commissioned Baldwin Locomotive Works to build a prototype cab-forward locomotive, then ordered more before the prototype had even arrived.
All of the cab-forwards were oil-burning locomotives, which meant there was little trouble involved putting the tender at what would normally be the front of the locomotive. The oil and water tanks were pressurized so that both would flow normally even on uphill grades. Visibility from the cab was superb, such that one crewman could easily survey both sides of the track. There were concerns about what would happen to the crew in the event of a collision, and at least one fatal accident occurred on the Modoc Line when a moving locomotive struck a flat car. Turning the normal locomotive arrangement around also placed the crew well ahead of the exhaust fumes, insulating them from that hazard. One problematic aspect of the design, however, was the routing of the oil lines; because the firebox was located ahead of the driving wheels (instead of behind them, the usual practice), oil leaks could cause the wheels to slip. A nuisance under most conditions, it resulted in at least one fatal accident. This occurred in 1941 when a cab-forward with leaking steam and oil lines entered the tunnel at Santa Susana Pass near Los Angeles. The tunnel was on a grade, and as the slow-moving train ascended the tunnel, oil on the rails caused the wheels to slip and spin. The train slipped backwards and a coupler knuckle broke, separating the air line, causing an emergency brake application and stalling the train in a tunnel that was rapidly filling with exhaust fumes and steam. The oil dripping on the rails and ties then ignited beneath the engine cab, killing the crew.
No other North American railroad ordered cab-forward locomotives. Built to deal with difficult terrain, these remarkable locomotives became an easily recognizable symbol of the Southern Pacific. One example of the type, Southern Pacific 4294, is kept at the California State Railroad Museum in Sacramento, California. It is a 4-8-8-2 locomotive and is the only one to escape being scrapped.
Oliver Bulleid's ill-fated Leader is sometimes referred to as a cab-forward locomotive, but since it had a cab at each end like a typical modern electric locomotive this designation is at best misleading.
[edit] Road vehicles
In road vehicle design, Cab forward, also known as Cab-over, COE (Cab Over Engine), or forward control, is a body style of truck or van that has a vertical front or "flat face", with the cab sitting above the front axle. This truck configuration is currently common among European and Japanese truck manufacturers, because the laws governing overall vehicle lengths are strict and the body style allows longer trailers or a longer cargo area for the same overall length than a standard truck (with an engine compartment ahead of a conventional cabin). Better visibility and manoeuvrability in tight quarters, such as for city delivery, is a benefit of locating the truck's cab up front. Large trucks of this type are most often described as cab over engine (COE) or cab over models.
In passenger vehicle design, the term is also used to refer to a collection of styling tropes commonly used by the Chrysler Corporation since 1993, in which the passenger cabin is "pushed forward" so that the front wheelwell directly abuts the leading edge of the front doors, and the windshield extends forward near the front axle, while the rear wheels are "shifted" towards the back corners of the vehicle. This is mainly done to expand interior room. Several models built from 1993 to 2004 on the Chrysler LH platform were marketed as cab forward cars.
However, the first modern mass production automobile design using the cab forward concept was the Pacer that was introduced in 1975 by American Motors (AMC). Richard Teague, AMC's Vice President for Styling, jettisoned the 1970s stereotypical blunt, boxy cars with long hoods, as well as the cramped interiors of small cars. The Pacer's layout included wheels located at the extreme corners, a wide body, and its windshield over part of the engine compartment. The cab forward and other design breakthroughs allowed the passenger area to be much larger than in other similar sized automobiles.
[edit] External links
- A site with a good selection of photographs of cab-forward locomotives.
- Steam Locomotive.com's Southern Pacific Cab Forward article, including detailed specs.
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