The following is reproduced from Flight International 19 October 1972 © DVV Media International Limited.
The initials APT identify British Rail's Advanced Passenger Train. They could equally well stand for the Anti-Plane Train, because in passenger traffic over sectors up to about 500 miles it may be expected to offer severe competition. And they could also mean Aerospace Philosophy and Technology, because this has provided much of the basis of knowledge that has made the APT possible. The title on the front cover of this issue refers to "The Train the Planemakers Made." In fact only about one-third of the engineers who created the APT at the BR Technical Centre at Derby are refugees from TSR.2, Rolls-Royce and Britain's other aviation troubles, but not even the most dyed-in-the-wool railwayman would deny that APT is very much a case of "if you can't beat them, join them." It is about the nearest thing one could imagine to a modern transport aircraft on rails. |
![]() By Bill Gunston |
It is not so long since railway technology conjured up visions of great masses of shiny mild steel and steaming oily rags, and the scattered assortment of railway laboratories spent most of their time analysing coal. But in 1964 a vast new complex began to function at Derby, which has since grown to surpass any similar research centre in the world. The railways found they needed new technology.
Probably the biggest single task the centre has accomplished has been to solve the complex dynamics of rail vehicles. Previously the mathematics were just too difficult, and so even Pullman cars jerked along the track in a series of lateral oscillations that stopped passengers from writing and sometimes even from reading. Derby set out to discover just how a railway wheel-set, comprising two flanged wheels with new or worn tyres rigidly joined to a live axle, actually runs along the rails. For those who cannot see the problem, it took years of work with large computers to yield useful results. It also required a horde of dynamicists, and the obvious source of these was the aircraft industry. Gradually they discovered how wheels with various cone angles and tyre profiles could be made to roll with perfect stability, without banging from side to side with violent flange contact. They also learned how to make the wheel-sets carry the rolling stock.
The importance of this work cannot be overestimated. It provided the foundation on which the future rail industry will rest. Without it the car, bus and airline might have eliminated steel wheels running on two steel rails before the end of the century. As it is, trains will probably reach double their present maximum speed of some 125 m.p.h., 200km/hr, while guaranteeing a smooth ride over existing track. This is an advance far greater than the New Tokaido and Sanyo lines in Japan. These were totally new routes, laid down for 130 m.p.h. operation over specially straight track and using trains of immense power which are frequently shut down to have the track repaired and the train wheels re-turned on a tyre profiler. Most railways must use the track they already have, with points, crossings and sharp bends; and they cannot afford the soaring costs of maintenance of both track and vehicles. BR's policy on track is gradually to introduce a completely new form of road-bed, needing little or no maintenance for years, but to avoid any new routes other than on a very local scale to remove speed restrictions or bottlenecks. It is "between four and ten times cheaper" to invest in new trains.
The APT is designed to provide superlative passenger comfort at the highest speeds that can ever be reached with the existing BR route network and signal spacing. APT-E, the experimental train now completed, is designed to cruise at 155 m.p.h., 250km/hr and make possible block speeds of at least 100 m.p.h., 160km/hr between city centres (say, London to Bristol in an hour and to Edinburgh or Glasgow in less than four). With much greater power the same train could run over a purpose-built high-speed route, using identical track but with more gentle curves and grades, at 250 m.p.h., 400km/hr. This speed would require greater signal spacing, better train control and communications and such new features as intermediate stations where passengers cannot saunter along the edge of the platform. The 250 m.p.h. train is obviously still some way off in practice, but the 155 m.p.h. APT will cause less noise, less aerodynamic disturbance and less damage to the track than today's trains cause at 100 m.p.h.
APT can be driven either electrically or by gas turbines. It is a multiple-unit train. APT-E comprises a power car at each end with two passenger cars in between, but a commercial set would separate the end power cars by seven to ten trailers. If necessary two sets could be coupled together, but normally it would run as a double-ended unit with a cab at both ends and a mass of airliner-type accessory systems running along the whole length. The interior cross-section is roughly that of a Concorde; in terms of weight and seating capacity the train approximates to a 747.
Originally it was planned to fit each power car with a Rolls-Royce Dart, but at present an APT-E power car contains four Leyland automotive gas turbines identical to those used in many heavy road vehicles. These are free-turbine engines, fitted with heat exchangers for fuel economy, and in theory each ought to give considerably more than 300 s.h.p., 224kW. Obvious possible alternative engines include the Ford 707 and such aircraft gas turbines as the AiResearch 331, Astazou, PT6 and Allison 250. With a free-turbine engine it would be possible to use a mechanical drive direct from the reduction gearbox to the wheels, but for various reasons APT-E at present uses an electric transmission. Each engine drives a 3,000 r.p.m. Houchin 400Hz alternator which feeds through a rectifier to conventional axle-hung d.c. traction motors. Given wheel/rail adhesion of 15 per cent, these could safely operate at a forward speed up to 195 m.p.h., 315km/hr. Later a different transmission may be used, either a body-mounted motor with flexible drive or a mechanical or hydromechanical system. A fifth Leyland gas turbine of the same type is mounted in the rear of the power car to drive a three-phase 50Hz alternator supplying auxiliary power, most of which goes into air-conditioning.
As APT-E is experimental the power cars are constructed as space frames from welded steel box sections. Thus the light-alloy cladding can readily be removed and the interior re-arranged in a way that would be difficult with a monocoque structure. But the trailer cars are built like aircraft - indeed those for APT-E were actually produced by the former English Electric Aircraft Division at Accrington - using a semimonocoque stressed-skin construction of an advanced type, with extruded skin panels and floor beams. Nearly all the body structure is of riveted aluminium alloy, although the ends rest on solebars and a crossbeam of steel. Despite having many new features, these coaches weigh half as much per passenger as conventional BR stock (which itself is lighter than the coaches of many other countries). Further weight reduction would greatly increase cost. The payload area is subdivided into eight modules, each having a double-glazed window on either side, able to accommodate four double seat units facing each other with a table between them. The seat units are secured to six seat rails running the length of the floor, and there are longitudinal baggage racks above. Even the floor itself borrows from aviation, being a sandwich of end-grain balsa between aluminium alloy.
Each trailer body is articulated to the next by being pivoted above a common bogie. These bogies are a visible fruit of the years of research into rail-vehicle dynamics, and although to a layman they look ordinary they are really dramatically new. Possibly a rival team might achieve success merely by trying to do a Chinese copy, but the job would be as difficult as trying to copy a 747 with no help from Boeing or Pratt & Whitney. The theory is involved, but the essential objective is that the two wheelsets of each bogie should be self-stabilising on both straight and curving track. The bogie is constructed as three separate sub-frames which allow the two wheel-sets to yaw relative to each other while steering always along the local direction of the rails, with no flange contact.
The main structural member is a 226in, 5.73m longitudinal bolster called the steering beam which carries the adjacent car bodies on pivots near each end. On a constant-radius curve the beam adopts a true tangential position, and its length reduces the overhang of the car bodies on the inside of the curve. In the vertical plane the unsprung mass is minimised by making the wheel-sets very light, about 1,200kg including special braking systems and axleboxes, and there have been extensive trials with resilient internally sprung wheels. The latter appear unlikely to be needed, and the vertical suspension comprises coil springs and hydraulic dampers which lead to an extremely soft secondary system having a pair of hydraulic struts coupled to nitrogen accumulators, which not only give a comfortable ride but also provide height and level compensation for variations in payload.
Probably the one thing everybody knows about the APT is that the bodies tilt as they go round bends. It could run perfectly well without this feature, and the tilt has no effect on safety but only on passenger comfort. It would be possible to increase the "super-elevation" or cant of the track to a bank angle appropriate to the radius of the curve and a train speed of 155 m.p.h., but this would be uncomfortable for slower traffic and almost hazardous for trains held on the curve by signals. BR does not wish to spend many millions altering its track, and the tilting bodies of APT merely take out the lateral forces that would otherwise be slightly alarming to passengers. Aircraft bank in turns in order to tilt the lift vector inwards. If someone built an aircraft with enough vectored thrust, or enough movable vertical surfaces, it could be made to fly round tight turns with no bank angle at all; but the sensations would be most uncomfortable.
There have been attempts to make high-speed trains with simple pendulously hung bodies which tilt of their own accord, but there are obvious snags caused by time-lags and damping. APT cars contain accelerometers, one in the roof and the other below the floor, which provide signals of lateral acceleration and rate of roll. The processed signals govern electro-hydraulic systems which positively and smoothly tilt the two ends of each car to take out any lateral accelerations. Obviously the outputs of the two accelerometer units in each car can also prevent unwanted tilt being injected by side winds, or passengers getting aboard at a station.
Such a system is simply not possible without adopting aerospace practice in the matter of hardware design, component redundancy, fail-safe (or fail-passive) operation and a mixture of immediate accessibility and maintenance-free design. This is all routine to aerospace, but it is not many years since I rode in a cab of a Gresley Pacific on a very heavy train up the steep tunnel out of King's Cross, with persistent wheel slip, and found that in the absence of any external cues the only way the crew could check that they were moving forwards was by the fireman touching his shovel on the tunnel wall. Today, APT has Doppler speed measurement, and a precise measure of any wheelslip is given by comparing the Doppler output with that from r.p.m. transducers on the powered wheel-sets. Slip should be near zero, especially as wheel adhesion can if necessary be brought to a predetermined level using a gel of fine silica with a witches' brew of other additives which include water, cellulose paste, sodium nitrite (inhibitor), ethylene glycol (anti-freeze) and borax (anti-bacteria). There is no railway term corresponding to avionics - yet - but APT incorporates a mass of electronics in power control, speed control, brake control, public address system, fire warning and suppression, body tilt, air-conditioning, door drives and a remarkable number of alarm, fault-finding and vigilance systems. Small wonder its £750,000 cost is about 50 per cent greater than that of a conventional passenger train, but it will do more than 1½ times as much work in a given time.
Ideally, of course, improved trains work best in an improved environment, just as a 747 would be handicapped flying from Floyd Bennett Field to Croydon. BR, like other railways, has great plans for totally new control and communication systems which have for a long time been in trial use. But the essential feature of APT is that it fits today's infrastructure. This means it needs a man in the cab able to look at four-aspect signals spaced 6,365ft, 1,940m apart and a braking system able to stop from the highest running speed within this distance. Ordinary train brakes have a hard enough life at 100 m.p.h., and 155 m.p.h. would be beyond the economic state of the art. In this case aerospace made little contribution beyond the anti-skid control system. The power-car bogies are braked by using the traction alternators to excite the drive-motor fields against their spinning armatures, the traction motors thus being turned into d.c. generators which feed current dissipated as heat through resistors. The rest of the train has hydrokinetic brakes, each axle containing a device resembling a fluid flywheel which converts the momentum of the train into heat via a water-glycol mixture passed through a cooling radiator circuit. The electric and fluid brakes are used to slow the train to 44 m.p.h., 70km/hr; conventional brakes then come in.
The cab contains just three dial instruments and a large number of coloured indicator push-switches grouped under various control, monitoring and warning functions. I hope aircrews will not be offended if I suggest aviation tends to lag behind the APT in such matters. Far too much information is given to most of today's flight-deck staff, when all they really need to know is "Is it all right?" It is a proof of the APT's automatic nature that there are just two controls of an analogue (as distinct from off/on) nature. On the left is a tiny brake lever, moved forward along arbitrary numbers from zero to 8; on the right is an identical power lever. For shunting there are duplicate controls by the side windows, but these do not influence the argument that a total of two control levers - one GO, the other STOP - is quite remarkable.
At present APT has come an amazingly long way for a total write-off, to date, of around £5 million. A crude space-frame APT has tested bogies and body-tilt up to about 110 m.p.h., 177km/hr. APT-E has been out once, running at 50 m.p.h., 80km/hr, but has for many weeks been caught up in a far-ranging dispute between BR and the train-drivers' union which, hopefully, will soon be resolved. When it is, the E train will be put through exhaustive tests on a special route, no longer used by public traffic, near Melton Mowbray. The results will influence the detail design of two APT-P (prototype) trains, one with gas turbines and the other with a pantograph to collect power at 25kV on the London-Glasgow route. There is no obvious technical objection to an APT picking up current from a third rail. The two P trains will probably be in service in 1974-75, and a year or two after that APT should begin to displace all existing Inter-City trains on British Rail.
APT is in no sense an exotic train for special routes. I believe it will become a conventional way to travel whenever the sector distance is right and there is competition. BR does not expect to charge a premium fare; in its view APT is simply the way passenger trains are going to be, and like today's airliners it ought to do its bit to hold fares down. It could do the same in many other countries, and in the United States everyone from the Secretary of the Department of Transportation downwards is wondering if the APT - not just vague future trains in general but the unique APT in particular - could bring back to Americans the notion that people can travel by train for reasons other than short-distance commuting.
In Britain, former Transport Minister Richard Marsh, now head of, British Rail, has said: "In my view APT kills any future both for VTOL and the hovertrains… It is a waste of money to seek more expensive solutions to a problem we are confident rail can solve." The eagerness of British Rail to dispose of future aircraft and hovertrains is perhaps a tribute to the serious competition such things could offer, but the APT can hardly fail to bring about a massive increase in BR inter-city passenger traffic, much of which will not be at the expense of the airlines but will be new business. The past five years on London-Manchester have seen annual seats sold rise from 1 million to 2 million, and 600,000 of these were new traffic generated by the better train service. APT is planned first to enter full revenue service on this same West Coast main line, at an initial 125 m.p.h., 200km/hr, in 1977. This route will take 80 or 90 trains, about 2½ years' production, after which the next 30 trains will go on the East Coast route, where scheduled time to Newcastle (at present around 3hr 50min) will be reduced to 2hr 40min at the into-service speed, and by a further 20min at the full cruising speed.
It is planned that the APT shall take over all inter-city traffic on British Rail, with the 125 m.p.h. HST - a very fine but essentially conventional diesel train - bridging the gap that would otherwise exist. Not revealed by this figure is the very great accompanying improvement in comfort, because even the ordinary locomotive-hauled coaches will soon almost all be of the outstandingly good Mk IID type introduced last year. All these very big improvements are compatible with the existing rail system, but the APT is expected to generate so much extra traffic that at least the 220 stations on the Inter-City network will probably have computerised seat reservations by 1978. The only obvious compatibility problem is that of slotting in slower freight trains, and it may be that BR will increasingly have to run all its freight at night.
Altogether I believe APT is the biggest single advance in land transport technology that has ever taken place, because its potential is to raise the speed of passenger trains from 100 m.p.h. to something like 250 m.p.h. or whatever future competition and economics shows to be a sensible figure. None of its many rail rivals can claim as much, and it ought to lead to some interesting licensing agreements with the US and some other countries. To many suppliers of aerospace materials and components it means a broadening of the market. To aerospace itself it means keener competition, which is no bad thing. And to the travelling public it ought to be 100 per cent good news.
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This article was accompanied by a cutaway drawing prepared by "Flight" artist Frank Munger.(Prints of the artwork are available from www.flightglobalimages.com). |
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