Editing Advanced Passenger Train (section)

=== British Rail Research Division ===
[[File:GBR rail passengers by year 1830-2023.png|thumb|360px|The period after nationalisation was marked with rapidly falling ridership levels.]]

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 cuts|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 [[Royal Aircraft Establishment|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.{{sfn|Gilchrist|2006|p=19}} 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 {{convert|20|mph}}.{{sfn|Gilchrist|2006|p=20}} 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.{{sfn|Gilchrist|2006|p=19}}

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)|Sea Slug missile]] and then for a period at [[Canadair]] in Montreal before returning to the UK and joining the [[Blue Steel (missile)|Blue Steel missile]] project.{{efn|The National Railway Museum site has the section header entitled "Blue Streak", a contemporary weapon system, but the text clearly states he worked on Blue Steel.}} When the follow-on Blue Steel II was cancelled in favour of the US designed [[GAM-87 Skybolt|Skybolt]], Wickens left [[Avro|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.{{sfn|Wickens|2002}}

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.{{sfn|Wickens|1988}} 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.{{sfn|Gilchrist|2006|p=19}}

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 spring]]s, 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.<ref>{{cite web |url=https://www.therailwayhub.co.uk/11675/pacer-the-bastard-son-of-the-apt/|website=The Railway Hub |first=Bob |last=Gwynne |title= Pacer: the bastard son of the APT |date=22 May 2020}}</ref> 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 {{convert|140|mph|0|abbr=on}}.{{sfn|Wickens|1988}} 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,{{sfn|Gilchrist|2006|p=36}} and the last, HSFV-6, entered service that year.{{sfn|Gilchrist|2006|p=37}}