Advanced Passenger Train
The Advanced Passenger Train was a tilting high speed train developed by British Rail during the 1970s and early 1980s, for use on the West Coast Main Line. The WCML contains many curves, and the APT pioneered the concept of active tilting to address these, a feature that has since been copied on designs around the world. The experimental APT-E achieved a new British railway speed record on 10 August 1975 when it reached, only to be surpassed by the service prototype APT-P at in December 1979.
Development of the service prototypes progressed slowly, and by the late 1970s the design had been under construction for a decade and the trains were still not ready for service. Facing the possibility of cancellation, BR management decided to put the prototypes into service, with the first runs along the London–Glasgow route taking place in December 1981.
The problems were eventually solved and the trains quietly reintroduced in 1984 with much greater success. By this time the competing High Speed Train, powered by a conventional diesel engine and lacking the APT's tilt and performance, had gone through development and testing at a rapid rate and was now forming the backbone of BR's passenger service. All support for the APT project collapsed as anyone in authority distanced themselves from what was being derided as a failure. Plans for a production version, APT-S, were abandoned, and the three APT-Ps ran for just over a year before being withdrawn again over the winter of 1985/6. Two of the three sets were broken up, and parts of the third sent to the National Railway Museum where it joined the APT-E.
Despite the challenges faced by the APT, its design was highly influential and directly inspired other high-speed trains, such as the Pendolino. The extensive work on electrification carried out alongside the APT was used effectively in later non-tilting designs, including the British Rail Class 91. The APT’s tilting system was reintroduced on the West Coast Main Line with the British Rail Class 390, which was based on the Fiat Ferroviaria tilting train design and built by Alstom. However, certain features introduced by the APT, such as the hydrokinetic braking system, have not been widely adopted.
Background
British Rail Research Division
Following nationalisation of the UK's railways in 1948, British Railways, as it was then known, faced significant reductions in passenger numbers as the motor car rapidly became more popular through the 1950s and 60s. By 1970, passenger numbers were roughly half what they had been immediately prior to World War II. In an attempt to maintain a level of profitability, the government commissioned a report that resulted in the abandonment of many lines as part of the 1963 "Beeching Axe". In spite of this significant restructuring, the organisation was still built on lines that were pre-war, with routings dating into the 1800s. Maintaining the network created problems with derailments increasingly common.In 1962, Dr. Sydney Jones was hired away from the weapons department at R.A.E. Farnborough with the eventual aim of having him take over as BR's research lead from Colin Ingles, who retired in 1964. Looking into the derailment problem, they found that much of the problem could be traced to a problem known as hunting oscillation. This was well known in the railway world, but tended to happen only at high speeds. On the BR network, especially on freight cars with worn wheels, it was being seen at speeds as low as. Jones was convinced that hunting oscillation was an effect similar to the problem of aeroelastic flutter encountered in aerodynamics, and decided to hire someone from the aeronautics field to investigate it.
In October 1962, Alan Wickens was given the position. Wickens was a dynamics expert who had previously worked at Armstrong Whitworth on the Sea Slug missile and then for a period at Canadair in Montreal before returning to the UK and joining the Blue Steel missile project. When the follow-on Blue Steel II was cancelled in favour of the US designed Skybolt, Wickens left A. V. Roe because he "saw the writing on the wall". He answered an ad for BR, and during the interview, he replied that he had no knowledge of, and little interest in, railway bogie design. It was later revealed this was the reason he was hired.
Over the next several years, Wickens' team carried out what is considered to be the most detailed study of the dynamics of steel wheels on rails ever conducted. Starting with incomplete work by F.W. Carter from 1930, the team studied conventional two-axle bogies and quickly discovered that, as Jones had suspected, the problem was dynamic instability. Out of this work came the concept of a critical speed at which point hunting would become a problem. This work was then extended to the unique two-axle bogieless car designs used on the BR freight network, where the problem was further modified by the dynamics of the entire vehicle.
Wickens concluded that a properly damped suspension system could eliminate the problem. The key realization was that the suspension had to be both vertical, as it had been in the past when based on leaf springs, but also horizontally to avoid small displacements triggering oscillation. Computers were used to simulate the motion and develop rules for how much damping would be needed to avoid the problem for any given speed. By 1964 this work had produced the first High Speed Freight Vehicle, HSFV-1, a bogieless freight car capable of travelling safely at speeds up to. The same work suggested there was no practical upper limit to the achievable speeds in terms of dynamics, and that any limitations on maximum performance would be due to other factors like traction or wear on the lines. Eventually a series of six HSFV designs would be tested until 1976, and the last, HSFV-6, entered service that year.
Cant and tilting trains
During this period, BR's Passenger Business division produced a report suggesting rail could compete with road and air, but only if the trains ran faster. Studying the increase in ridership due to the introduction of the British Rail Class 55 "Deltic" engines on the East Coast Main Line, and the effects of electrification on the WCML which improved journey times 20 to 30%, they concluded that every increase in speed would result in a 1% increase in passengers. This basic rule was apparently proven in Japan, when the Tokyo-Osaka Shinkansen line was operating from 1964 to huge success.The Shinkansen provided a smooth ride at speeds as high as by laying new lines dedicated to high speed travel. BR's most used route, the WCML, had in the order of 6 million passengers a year between London and Manchester, a far cry from the Tokyo-Osaka's 120 million. Funding for a new line for high speed use was highly unlikely given these passenger levels. This presented a problem for any sort of high-speed operation on the route because the existing line contained many turns and curves, and rounding these at high speed would cause lateral forces that would make walking difficult, and throw items off tables onto the floor.
The traditional solution to this problem is to tilt the rails into the turns, an effect known as superelevation or cant. This has the effect of making the lateral forces more in line with the floor, reducing sideways forces. Because larger amounts of cant are more difficult to construct and maintain, and also because of the need to accommodate slower-moving traffic or the possibility of a train coming to a stand within the curve, long experience had shown that the maximum amount of cant that could be applied to lines with mixed traffic was 6.5 degrees.
Given the curve radii typically encountered on the WCML, this meant that even with the maximum permissible amount of cant applied, speeds couldn't be increased much above the range without once again experiencing excessive lateral forces. As the initial factor limiting speeds is not safety against derailing or overturning, but rather only passenger comfort, the solution to increasing speeds further is therefore having the train car bodies tilt as well – while this doesn't influence the forces acting at the wheel-rail level, it keeps the lateral forces experienced inside the passenger compartment at a comfortable level even at further increased speeds.
Talgo introduced the first practical design for a tilting carriage in the late 1950s. This consisted of a single bogie placed between the train cars with the car bodies suspended from an A-frame centered on the bogie with a pivot near the top. When the train rounded a bend, the centrifugal forces caused the car body to swing out like a pendulum, reaching the proper tilt angle naturally. However, this system had a distinct delay between entering the curve and the body swinging out, and then swung past this angle and then oscillated briefly until settling at the right angle. When traversing a series of curves, like in a switchyard, it tended to swing about alarmingly. Although a number of semi-experimental designs of the 1970s made use of it, like the UAC TurboTrain, the concept was not widely used.
APT's origins
In 1964, a number of BR's formerly-dispersed research groups were organised into the new Derby Research Division. It was here that the final work on Wickens' HSFV was being developed. At first there was some argument about whether or not a high-speed train would be supported; in the aftermath of the 1963 Beeching Axe it was not clear what size of network the government was willing to support, and whether a new design should be aimed at higher-speed intercity service, where a new locomotive would be needed to replace the ageing Deltics anyway, or a simpler system for better performance in the suburbs.In 1965, Wickens had hired an intern, Dutch engineer A.J. Ispeert, and had him do some early work on active tilt systems. These would replace the passive pendulum-like Talgo system with a system using hydraulic cylinders that would quickly drive the car to the proper angle and hold it there without any swinging. A major advantage for BR use was that the center of rotation could be through the middle of the car, instead of the top, meaning the total movement would fit within the smaller British loading gauge. Ispeert returned a report on the concept in August 1966.
Wickens noted that BR's single-axle suspension system would have less drag at high speed, and that its lighter weight would make it more stable at high speeds than conventional dual-axle bogies. In November 1966 he wrote a report calling for a two-year programme to build and test a High Speed Passenger Vehicle, essentially an experimental car like HSFV-1 but for passenger use instead of freight. The original plans called for a single dummy body and two bogies to test the suspension and tilting system at high speed. They set the maximum tilt angle at 9 degrees, which could be added to any cant in the underlying railbed.
The design programme was organised under Mike Newman, while Alastair Gilchrist headed the research side. Newman noted that a single car was unlikely to answer practical questions like how the train would operate as a complete unit, and that a dummy body would not answer the question of whether the tilt mechanism could really be built under the floor without projecting into the cabin. Accordingly, later that same November, Newman and Wickens drew up plans for a complete experimental train with the design goal to be not only to study the tilt system, but do so on actual lines.
Wickens took the plans to Sydney Jones, who immediately took up the idea. They set the performance goal at the nicely rounded figure of. In keeping with BR management goals to provide quicker travel times rather than just faster speeds, they also required the train to round corners 40% faster. They named the proposal the Advanced Passenger Train. Jones took the proposal to the BR chairman, Stanley Raymond, who liked the idea. However, the board was unable to provide enough funding to develop it, and encouraged Jones to approach the Ministry of Transport for additional funding.
Jones did so, and spent the next two years walking the corridors of Whitehall when one civil servant after another agreed that it was a great idea but that it was really the job of someone else to approve it. In spite of being repeatedly put off, Jones persisted, especially with Government Chief Scientist, Solly Zuckerman, to arrange a stable funding system for the entire topic of railway research. This was finalised as the Joint Programme between the Ministry of Transport and the British Railways Board, sharing the costs 50:50. The Programme would run sixteen years from January 1969 to March 1985. The first two programmes were APT and the Train Control Project.