THE FUTURE OF THE STEAM VEHICLE.
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An Interesting Comment by an Expert in Steam Vehicle Design Upon a Recent Article by " Hephmstus " in "The Commercial Motor." •
T HAVE read with much interest the article on "The 1 Future of the Steam Vehicle" which appeared in The Commercial Motor of -March 23rd and 30th last and should like to criticize one or two points. The writer of that article says that remarkable results have been obtained "without using ball or roller bearings," from which one might imagine that even better results could be expected from their use. I believe; however, that such would not be the case. A wagon so fitted would be easier to start, but this is not required with a steam wagon, as there is always a sufficient head of steam acting on the pistons to give the torque necessary. When the wagon is actually moving little, if any, saving is likely to be experienced.
Some time ago experiments were tried by one of the leading railway companies. Two exactly similar trains were built, one having plain bearings and the other roller bearings. Although the train with roller bearings was easier to start, as would be expected, the one with the plain bearings used less coal and less power.
The 25-year old conflict between overtype and undertype wagons is likely to end, in my opinion, earlier than some people seem to expect. I imagine that it will eventually become a conflict between single geared and change-gear-fitted undertype wagons. The overtype wagon has certainly a very honourable record, but it would never have come into existence at all had not the early undertype wagons bristled with knotty problems which only assiduous application has solved. By using a little tractor with a wagon platform hitched behind it, the overtype came into existence and got round the problems, instead of solving them, and for many years has given good service. For certain work it will probably be used considerably, but the general design is not in accord with modern road transport requirements.
Where the Undertype is Better.
Originally designed for chain steering, in many cases the front axle has been redesigned and adapted to take a form of Ackerman steering gear, which at the best appears to be rather a makeshift. Then, again, the overtype wagon is about 4 ft. 6 ins, longer overall than an undertype wagon with a body of similar dimensions. This is not conducive to manceuvring in awkward places. Again, its unladen weight is excessive, probably not far short of one ton more than the average undertype, and all of this excess is concentrated on the hind axle, which makes it impossible to carry a really effective load without exceeding the legal axle weight by a considerable amount.
The poor view and discomfort of the driver are also disadvantages of the overtype. The writer took the trouble, some time ago, to obtain certain measurements and he found that the driver could just see the feet of a person standing on the edge of a pavement over the edge of the cylinders at 17 ft. distance, but at 8 ft. distance a small child was invisible, and it would be impossible for the driver to avoid a sudden movement on the part of the latter. In the undertype, the driver's view is better than on any form of vehicle, except the electric lorry, which it practically equals in this respect.
The question of accessibility has always been one which makers of undertype wagons have had to study, and it must be admitted that some of the earlier designs leave something to be desired in this \respect, although a review of the various types now obtainable will show that in many cases accessibility to essential parts is contrived very satisfactorily. It must be remembered that with careful use, and when an engine is enclosed in an oil-bath, there is little to need attention, so that
c40 accessibility is not quite such a vital point, although it is very important.
The second portion of the article dealing with the boiler problem is attractive and most useful and suggestive. I notice that the writer of the article is much intrigued by the possibilities of the Brunler steam generator and, although I think the future of the steam wagon generator may lie along these lines, I do not think he is justified in saying that the efficiency would be practically equal to that of the Diesel engine. He states earlier in the article that a test with a Brunler generator gave an engine consumption of 11 lb. of steam per b.h.p. This is far short of the thermal efficiency of a Diesel engine.
The writer of the article with which I am dealing advocates for weight reduction the use of a high-speed engine which would need a gearbox iti conjunction with it. This raises the question whether the total weight of this arrangement would be much less, if at all, than an engine of larger dimensions, driving direct on to the hind wheels without gears, as so many highly successful steam wagons do to-day.
Another point appears to have been overlooked in connection with the suggestion to use a Brunler type of generator, namely, the air compressor. The writer of the article mentions that with a boiler capable of delivering 1,000 b.h.p. of steam, only 700 b.h.p. was available, the other 300 b.h.p. being represented by the power consumed by the compressor. Assuming that the main engine on a steam wagon is designed to give 60 b.h.p., then, in addition to this, an air compressor requiring at least 18 b.h.p. must be provided. This, on account of the high boiler pressure required, say, 250 lb. per sq. in., would probably have to be a threestage compressor. This would need cooling and would necessitate the carriage of water for the cylinder , jackets, as it seems doubtful if one could depend on air cooling. It appears to me to be a great question whether, when all this plant is assembled on the chassis, including the necessity for greater, not less, water capacity, the weight would be any less than that of a
present-day steam wagon. VAPOUR.