“EVOLUTION OF GUIDED LAND TRANSPORT”
A talk by Prof. F.T. Barwell (Member) at Durrington Community Centre, 3rd December, 1985.
The Vice-President chaired the meeting and gave the latest news of the President, Fred Garlick, who had sadly suffered a further heart attack and was currently in hospital. Mr. Fosbrooke then introduced the speaker who had a long career associated with railways and other engineering activities, e.g, GWR at Swindon, National Physical Laboratory (20 years), Director of Electrical Research British Rail, then Professor of Mechanical Engineering, University College, Swansea.
Starting with reference to the development of steam locomotives in the early eighteen hundreds the speaker highlighted problems of poor adhesion and severe track damage. The cast iron plates used as rails could not stand the duty and eventually were discarded for steel rails. Attempts to increase adhesion included Blenkinsops rack and pinion system (l8l2) and the coupling of locomotive wheels. A more revolutionary attempt to improve-adhesion and to reduce noise, vibration, fire risk etc. was that of Clegg and Samuda using the so-called atmospheric propulsion. Lines in Ireland and at Newton Abbott (by Brunei) had a large diameter pipe laid between the rails and a piston in the pipe was connected to the rail borne train through a slot in the top of the pipe. By evacuating the pipe on one side of the piston the train was caused to move by virtue of atmospheric pressure on its other side. Problems of sealing the slot and of high fuel consumption contributed to the demise of this system but the line in Ireland operated from 1843-55. A novel variant of this principle, demonstrated in l864 on a line at Crystal Palace, used a 3m diameter tube in which the whole vehicle fitted and was pulled or pushed by air pressure. By the mid 1850’s these air systems had been discarded, the rack and pinion and rope haulage systems continued to be used only where adhesion was an over riding problem and adhesion railways predominated.
The steel rail and flanged wheel system of support and guidance, using adhesion forces for propulsion and braking, had its own difficulties but over the last hundred years developments had successfully reduced them in spite of ever growing performance demands. Prof. Barwell referred to developments in steam locomotives, the advent and growth of electrification, research into the mechanics and dynamics of bogies, and into vibration, noise, comfort level of passengers, environmental pollution etc.
After the tea interval he concentrated on the present and future solutions to the problems of propulsion and guidance. The Advanced Passenger Train (APT) of British Rail is an approach aimed at increasing speeds around curves on existing lines by tilting the coaches to avoid passenger discomfort. The French “Train Grand Vitesse” (TGV) and the Japanese “Shinkansen” trains run on new alignments with a minimum radius of curveture of 4OOOm and have raised speeds in regular service to 270 and 240 km/h respectively. Electric power is used for traction; the l6 2/3 Hz and the 1.5 kv and 3 kv d.c. system have given way on new railway electrification on main lines to 50 or 60 Hz 25 kv power distribution using overhead current collectors.
Power conditioning has been principally by train-borne transformer, tap-changer and rectifier feeding series wound d.c. traction motors, but thyrister control is now common and some separately excited motors have been used. The three phase squirrel cage motor, obviously desirable in principle, is now becoming viable particularly as gate-turn-off (TGO) thyristers of increasing performance become available. These thyristers simplify the process of cyclical switch-off of power which is inherent in the operation of frequency convertors or invertors. Synchronous traction motors are also being used, particularly in France.
However the adhesion limitations of steel wheels on steel rails still persist, albeit at higher levels due to careful selection of motor characteristics and refined wheel slip detection and control. Higher values are claimed for pneumatic tyres, but in wet and icy conditions serious difficulties occur so trackway heaters are often required. Some urban railways, passenger trains only, used pneumatic tyres, notably in France and Japan and recipients of exports from those countries. Advantages are claimed for them concerning reduction in noise levels and vibration problems and reduced track wear but the overall advantage of pneumatic tyres is contested by many. The Westinghouse “Transit Expressway” was the first fully automated pneumatic tyred guided transport system and is now fully proved in service and installed within several airport complexes, including Gatwick. Many different configurations of support and guidance for pneumatic tyred vehicles have been proposed e.g. monorails and some have been tried; the major difficulty has been the development of a practical system for switching of the vehicles at junctions.
The speaker made reference to the well known system in Paris, Sapporo (Japan), Morgantown (U.S.A.) and Dallas-Fort Worth Airport (U.S.A.), Lille (VAL) and Vancouver. The last mentioned uses steel wheels with special bogies designed to set the axles radial when negotiating curves but uses linear motors for propulsion. Linear motors are also used on non-wheeled vehicles – such as those using air-cushion support or magnetic levitation. The short link at Birmingham Airport recently commissioned has magnetically supported vehicles and high speed vehicle developments in Germany and Japan were described. The air supported “tracked hovercraft” system pioneered in Britain was abandoned some years ago but an urban type vehicle is still under development in the U.S.A. These systems using linear motors which have the great merit of not being dependent on adhesion, for propulsion or braking, and in this respect could be considered as taking over where the atmospheric railway of Brunei failed in the l850’s.
Colin MacDonald in proposing the vote of thanks referred to the very wide scope of the talk and to the way it showed the many problems faced by the early railway engineers. The same challenge applies to the next generation of engineers and one hopes they will find practical and economic solutions which will be of benefit to the community. The meeting warmly endorsed the vote of thanks.