|
A hovertrain is a type of high-speed train that replaces conventional steel wheels with hovercraft lift pads, and the conventional railway bed with a paved road-like surface, known as the ''track'' or ''guideway''. The concept aims to eliminate rolling resistance and allow very high performance, while also simplifying the infrastructure needed to lay new lines. Hovertrains were seen as a relatively low-risk and low-cost way to develop high-speed inter-city train service, in an era when conventional rail seemed stuck to speeds around or less. By the late 1960s, major development efforts were underway in France, the UK and the USA. While they were being developed, British Rail was running an extensive study of the problems being seen at high speeds on conventional rails. This led to a series of new high-speed train designs in the 1970s, starting with their own APT. Although the hovertrains still had reduced infrastructure costs compared to the APT and similar designs like the TGV, in practice this was offset by the fact that they needed entirely new lines. Conventional wheeled trains could run at low speed on existing lines, greatly reducing capital expenditures in dense areas. Interest in hovertrains waned, and major development had ended by the mid-1970s. Hovertrains were also developed for smaller systems, including personal rapid transit systems that were a hot topic in the late 1960s and early 1970s. In this role their ability to float over small imperfections and debris on the "rails" was a practical advantage, although it competed with the maglev concept that had the same advantages. The only hovertain to see commercial service was the Otis Hovair system. Originally developed at General Motors as an automated guideway transit system, GM was forced to divest the design as part of an anti-trust ruling. The design eventually ended up at Otis Elevator who later replaced its linear motor with a cable pull and sold the resulting design for people mover installations all over the world. Hovertrain is a generic term, and the vehicles are more commonly referred to by the projects that developed them in different countries – in the UK they are known as tracked hovercraft, in the US they are tracked air-cushion vehicles, and in France they are the aerotrains. News sources often conflate maglev trains with hovertrains, as both are levitated above the running surface, "hovering" over them. ==Basic concept== It was noticed early on that the energy needed to lift a hovercraft was directly related to the smoothness of the surface it traveled on. This was not surprising; the air trapped under the hovercraft's skirt will remain there except where it leaks out around the bottom of the skirt where it contacts the ground – if this interface is smooth, the amount of leaked air will be low. What was surprising was that the amount of energy lost through this process could be lower than steel wheeled vehicles, at least at high speeds. At high speeds, trains suffer from a form of instability known as "hunting oscillation" that forces the flanges on the sides of the wheels to hit the sides of the rails, as if they were rounding a tight bend. At speeds of or over, the frequency of these hits increased to the point where they became a major form of drag, dramatically increasing rolling resistance and potentially causing a derailment. That meant that for travel above some critical speed, a hovercraft could be more efficient than a wheeled vehicle of the same weight. Better yet, such a vehicle would also retain all of the positive qualities of a hovercraft. Small imperfections in the surface would have no effect on the ride quality, so the complexity of the suspension system could be reduced. Additionally, since the load is spread out over the surface of the lifting pads, often the entire underside of the vehicle, the pressure on the running surface is greatly reduced – about the pressure of a train wheel, about of the pressure of a tire on a road.〔Volpe 1969, p. 54〕 These two properties meant that the running surface could be considerably simpler than the surface needed to support the same vehicle on wheels; hovertrains could be supported on surfaces similar to existing light-duty roadways, instead of the much more complex and expensive railbeds needed for conventional trains. This could dramatically reduce infrastructure capital costs of building new lines and offer a path to widespread use of high-speed trains. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hovertrain」の詳細全文を読む スポンサード リンク
|