The Advanced Passenger Train – Experimental.
A condensed history.
By Kit Spackman
In the late 1960s, British Rail found itself in a quandry, both the Class 55 Deltic locos on the East Coast Main line (ECML) and the Class 86 25kV electric locos on the southern part of the West Coast Main Line (WCML) were able to travel at 100 mph and the increased speeds were pulling in large numbers of passengers on those two routes. However the internal airlines still formed strong competition on the routes to Scotland and the North and BR needed to increase the speed of its next generation of passenger trains to maintain its growth. This would not have just meant increasing the locomotive power as the then current wheel/rail technology was approaching its performance limits and any higher speeds would have increased the likelihood of wheel hunting, the lateral instability that occurs under such conditions, leading to high wheel/rail wear, an uncomfortable ride for the passengers, and in the worst case an increased numbers of derailments.
While higher speeds on the ECML would have been a matter of solving the instability problem and increasing the locomotive's power, the WCML north of Crewe exhibited a very different problem. In the hilly counties of the North West and Scotland the line was very heavily curved and steeply graded as a result of it being built very early in the history of railways. The line to Glasgow had been completed by 1849 but in those days it was only possible to follow the contours of the land, not only because of the lack of heavy earthmoving technology but the locomotives of the time were limited in power and were not able to climb very steep inclines. Changes in the routing to ease the curves and grades was not deemed possible in the 60s because of limited funding and the storm of public protest that would surely have arisen as a result of such proposals. That situation has changed little in the years to the present of course.
Oddly enough the potential solution to these problems came from an unexpected quarter of BR. In the late 50s and early 60s very little research was being carried out within BR but the higher ranks of the state run company saw a need for an increased level of research and some recruiting was carried out to improve the knowledge base within BR. One of the engineers recruited at this time was Professor Alan Wickens, who joined BR in 1962 and who came from the aviation industry. He brought with him a high level of experience of stability problems in control systems and within a short while started to investigate the fundamental problems associated with the hunting issue, but at this time the work was mainly directed at the problems exhibited by four wheeled freight wagons. Attempts to run the then current four wheeled stock at higher speeds had resulted in a considerably increased number of derailments and the Chief Mechanical & Electrical Engineer's Dept. (CM&EE) and the Chief Civil Engineer's Dept. (CCE) were blaming each other for the problem but not doing very much about solving it.
Professor Wickens' work involved a detailed study of the actual wheel/rail interaction, something that had never been done at this depth before and certainly not by using the techniques available to him from his previous work. The work involved both theoretical and analytical approaches and eventually resulted in the building of a 4 wheeled test vehicle to evaluate the theories both on a roller rig and on the main line. This test vehicle, HSFV-1, fleet no. RDB511023, eventually ran stably at 100 mph on the main line and at 140 mph on the roller rig, proving the basis of the wheel profiles and suspension settings that had been developed. Incidentally HSFV-1 still exists and is currently located at the Electric Railway Museum at Coventry in the UK.
The work that had been carried out on the wheel/rail relationship was expanded into an idea for a research train which could run at much higher speeds on existing track due to the fact that it could run through curves at high speeds and remain stable. The corollary of this ability was the need to tilt the vehicle bodies in order to maintain passenger comfort. Other requirements for high speed travel were incorporated into the potential project, including light weight construction, high power/weight ratio, good aerodynamics and improved brake systems etc. Hopefully such an experimental programme could be developed into a high speed passenger train that would become BR's next generation of passenger stock. This idea was presented to the BR Board in the late 60s but was unable to be started immediately due to lack of funding within BR itself, but the Ministry of Transport eventually agreed, after much lobbying, to partly fundand the project was given a go ahead in 1969. The Advanced Passenger Train, Experimental (APT-E) project was under way.
Part of the project included a complete new laboratory at the Railway Technical Centre (RTC) in Derby and a 14 mile test track converted from a closed main line running from Melton Mowbray to Nottingham, with a control centre at Old Dalby in north Leicestershire, in addition to offices at the RTC and staff recruitment to start the project. Initially much design work was carried out on the train itself and on test rigs to develop the various systems and components to be used on the train. The initial APT-E design concept was for a four vehicle articulated train powered by gas turbine engines driving alternators that in turn powered a bogie under each Power Car. Two Power Cars, one at each end of the train, sandwiched two Trailer Cars, one of which was to be an Instrumentation and Control Car and the other was to have a properly trimmed passenger compartment to enable evaluation to be carried out of passenger's reactions to high speeds in a 'real railway' environment.
The Power and Trailer Cars exhibited radically different methods of construction, the Power Cars being built from a welded steel tube space frame with an aerodynamic aluminium skin applied over the outside, the basic frames being built by Metro-Cammell in Birmingham. The Trailer Cars however were built on aircraft aluminium stressed skin principles by English Electric in Accrington, alongside the production line for the RAF's Lightning F6 fighters.
The four vehicle train was mounted on five bogies - two power bogies and three articulated trailing bogies, one under each joint between vehicles. The two power bogies, designated E1s,were of relatively conventional construction with welded steel box side frames with depressed centres and cross bolsters arranged in an H section. They had conventional coil spring primary suspension and vertical fluid dampers but their ratings and the wheel profiles were developed from Professor Wickens' work. The secondary suspension was by air springs, a new step for BR, but which proved unsuccessful and trouble free in service. The articulated bogies were anything but conventional; almost by definition as such bogies hadn't been used on BR metals for many years. They were designated as Swinging Arm bogies (SA) as one of their visual characteristics were the large triangular swinging arms that located each individually self-steering wheelset. These wheelsets also used the high speed primary spring and damper specifications but the bogie used hydro-static fluid secondary springs which supported a long beam that connected the two vehicles, this being called the Steering Beam. The vehicles themselves were connected to the Steering Beam by means of a large diameter ball joint that transmitted the traction and steering forces along the train.
The initial power unit plans were for a derivative of a Rolls-Royce Dart turbo-prop to the used, one in each Power Car, but Roll Royce and BR couldn't come to an agreement on the technicalities of such an application and the choice eventually came down to the Leyland Truck gas turbine, initially using four of them at approximately 300 bhpeach in each Power Car with a fifth turbine as an APU to produce the relatively large amount of 'house' electrical power that would be needed by the test instrumentation. The Leyland turbine produced approximately 300 bhp at that time, and used two large ceramic disc heat exchangers to improve the fuel consumption. The turbines each drove an alternator providing electrical power which supplied two traction motors on each E1 power bogie via relatively conventional rectifiers and control gear. These traction motors were similar to those fitted to BR Class 37 diesel locos, but higher geared to reach an anticipated 155 mph. The use of a relatively large number of turbines gave a certain amount of redundancy in the case of turbine or alternator faults, and this proved useful later in the programme. One advantage of using the Leyland turbine was that it was already designed to burn standard road diesel fuel and similar fuel was readily available throughout BR for its diesel locomotives.
The trailing bogies used a new concept in railway braking called the Hydro-Kinetic brake (HK brake) which worked like a car's automatic transmission in reverse in that a water/glycol mixture was pumped into the large diameter axles and in between two halves of a rotor/stator pair when braking was required and which was then pumped through coolers to be re-used. As the HK brake's performance diminished at slower speeds the bogies were also fitted with conventional friction tread brakes who's action was blended in with the HK brake as the speed bled off. The Power Cars had rheostatic brakes, driven by the traction motors and conventional tread brakes on the E1 power bogies and as the trailing end of the car was supported by the articulated bogie it also had HK and friction brakes at that end, giving four different braking systems on the same locomotive!
All four vehicles of the train had an active tilt system installed which could tilt the cars through 9 degrees in each direction under power and with 3 degrees more passive tilt available under dynamic conditions. Each vehicle used four vertically aligned tilt jacks, two per bogie, which were powered by an above floor mounted hydraulic power pack which turn was driven by an analogue control system each of which took lateral signals from body mounted accelerometers. The cross section shape of the body shells was determined by the need to tilt the vehicles and yet still remain inside the C1 loading gauge requirements, giving the characteristic oval shape of a tilting body train.
One decidedly different aspect of APT-E was the access arrangements for the train crew and test staff. The Power Cars had conventionally arranged outward opening doors for the driver but with a retractable set of stairs below the door arranged to fit flush into the inward tapered underside of the cab. The stairs could be lowered be means of a large handle mounted inside the cab or by pressing a recessed button in the outer casing of the stairs. This arrangement proved to be a source of some problems as the train could not be allowed to proceed with the stars down and the tilt system active as the lowered stairs would foul the C1 gauge at any tilt angle above around 5 degrees. In addition there were two doors on either side of the auxiliary bay that gave access to the rear portion of the vehicle, but these were generally only used for maintenance purposes.
The Trailer Cars had no doors at all in the sides of the vehicle, access was only via doors in the vehicle ends. These doors led into the area between vehicles and immediately above the Steering Beam and that area was filled with a strangely shaped fairing entitled the Joint Module. The Joint Module was shaped to fit closely to the end structures of both types of vehicle on the train and incorporated a pair of outward opening doors on each side. The Joint Module rode on small tracks built into the ends of its connecting vehicles and was moved laterally during curving by a drive rod connecting it to the Steering Beam. In addition the floor of the module was constructed of a number of RHS sections that could take up a median position between the positions of its two connecting vehicles, and as they could vary in yaw and roll angles this floor could take up some very strange shapes. To improve the aerodynamics of the whole train the slots between the Joint Modules and their adjacent vehicles were sealed by a flexible rubber diaphragm that could theoretically accommodate both opposing full tilt and yaw angles at the same time, but this would prove not to work in reality and the diaphragms were removed early on in the programme. This resulted in a 150 mph air stream rushing past the open 6” gaps in each side of the Joint Modules during any high speed testing.
One of the first pieces of rail-borne hardware to appear was a two vehicle articulated test train entitled 'POP Train', standing for 'Power-0-Power'. Each vehicle of POP Train consisted of the space frame of an APT-E Power Car but without any skin and no power units. The POP train was used as a test bed to verify the various components that were intended to be used in the final vehicles. these being replicated by ballast weights, but each car had a small off-centre cabin which contained the auxiliary power packs and controls for the HK brake system, the tilt system, the friction brakes and the hydro-static secondary suspension located in the same positions on the POP vehicles as they would be in the proper Power Cars. The two car test train was supported on three SA bogies, the outer pair of which only had a vestigial Steering Beam as they were in the same position as the E1 bogies would be on the real Power Cars. These two vehicles were numbered PC3 and PC4 but carried no RDB series numbers at this time.
Metro-Cammell supplied just the bare POP Train structures to the Railway Technical Centre in late 1970 and all the systems installation was carried out by the relatively newly recruited Advanced Projects Division staff in the equally newly built Advanced Projects Laboratory building. The three SA bogies were build at BR's Derby Locomotive Works directly opposite the RTC across the main line to Nottingham, Leicester and London, a line that would become only too familiar to the test train staff over the following years. The various auxiliary systems for the POP Train had been developed in the APD Lab earlier in the project although they were far from refined and in some cases were found to be totally inadequate for their intended tasks. Nevertheless the various power packs and control units were installed in the two POP vehicles and commissioned as well as possible without actually running the train.
By late 1971 the POP vehicles were ready for track testing and to this end they were formed into a three vehicle train, with a laboratory coach leading the two POP cars. The laboratory coach, usually Lab Coach 3, RDB 975002, was fully instrumented to measure the various suspension and brake performance parameters and was able to supply a limited amount of house power from its on-board generator. In later months a fourth vehicle, usually a BSK or a BG, was added to the train with a much larger generator and this became the standard consist for the POP Train test runs. Initially POP Train was taken out to the Old Dalby test track at low speed and with only the hydro-static suspension systems powered up. Slow speed runs at the test track went without incident and both the braking and tilt systems powered up for further tests as the speeds were increased.
By this time computer and laboratory tests on the SA bogies indicated that all was not well with the design, due to weight growth and excess friction in the multitude of joints and pivots throughout the bogies amongst other issues. The initial POP Train tests were carried out using a Mercedes Unimog road/rail vehicle as a locomotive and as a result speeds did not exceed 20 mph but later BR's last remaining Class 17 locomotive was used and speeds were able to be increased markedly. However the SA bogie issues mentioned above were predicted to cause serious hunting at around 45 mph on the turned rails that were part of the test track's comprehensive collection of varying track types. The hunting occurred only too readily at the predicted speeds and the excess lateral accelerations on the POP vehicles caused both tilt systems to exceed their hydraulic capacity and fall over onto their bump stops. While no damage was caused the issues with the SA bogies were emphasised and work to cure the problems back at Derby was accelerated.