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Revision of Steam-wagon Design.

8th June 1916, Page 8
8th June 1916
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Page 8, 8th June 1916 — Revision of Steam-wagon Design.
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Which of the following most accurately describes the problem?

By " Hephwatus."

The position of the heavy steam motor wagon in this country at the present day is, without a doubt, more favourable than at any time during its long and varied career: Although large numbers of internalcombustion vehicles • are made to deal with loads of five tons, it cannot be said that they are replacing steam wagons. The increasing use of rubber tires has considerably increased the scope of action of the latter, and placed them on a more equal footing with internal-combustion vehicles.

Steam's Position Unassailable.

The growing popularity of steam has been gained in spite of great opposition by many road authorities, who strongly objected to the heavy axle-weights of these vehicles. No doubt the majority of vehicles turned out by the leading British firms engaged upon this class of work have a very liberal margin of safety over the strength required to withstand the stress and strain of everyday working conditions—some so much so that vehicles designed to carry a net load of five tons have been, to the knowledge of the writer, loaded with seven-and-a-half tons without any visible overstrain. The error of deliberate overloading is grossly unfair to the vehicle, the owner and the maker.

The mechanical reliabilityof these machines has been brought to such a satisfactory state that makers have paused in their efforts at further improvements, under the impression that the goal has been reached. From their point of view no doubt it has, but from that of the user the excessive tare weight is an absolute dead loss. Certain other features of these vehicles are also being strongly criticised at the present time, and the object of this article is to deal with the faults of the steam wagon and to suggest practicable remedies.

Faults which Call for Remedy.

The faults can be summarized as follow : (1) excessive tare weight ; (2) inconvenience of manipulation ; and (3) small radius of action. The greatest of these is excessive weight, and that needs no further explanation. By inconvenience of manipulation is meant• the degree of attention required by the boiler for stoking and water supply, the time " wasted " in lighting up, the heavy steering, the uncomfortable position of the driver and also his obstructed view of the road, the emission of smoke, and the impossibility for the driver to keep clean and tidy. Radius of action is governed by size of water tank, which is also a question of weight. It is quite probable that the "solid " construction of steam wagons has been an important factor in achieving the present popularity, by its effect on the maintenance charges. Now, however, competition demands that the vehicle shall carry the highest possible percentage of the total moving weight as paying load.

Col. Crompton, in a paper before the Institution of Mechanical Engineers in December, 1913, referred to his experience with steam road-trains 35 years earlier, in which trains the naeful load was 55 per cent. of the total moving load. At the present day, with finer-quality materials at our command, higher-class workmanship and tools, and high steam pressures, the useful load of the prevailing overtype steam wagon without trailer is only 40 per cent., and with trailer 45 per cent. of the total moving weight. This refers to wagons loaded to the legal total weight limit ; if the legal individual axle-weight limits are regarded the peacentage would be smaller still.

The Origin of the Overtype Wagon.

Many manufacturers will no doubt claim, and quite justly, that their steam wagons will carry a greater B30 net load than is computed above, and that the legal axle-weights 6.re at lault. This simply proves that the relation of tare weight to total moving weight has never been properly considered.. In fact, the overtype steam wagon was never "designed" for its par• ticular work ; it is really a combined traction engine and trailer wagon; it contains no essential new feature in design. It possesses its progenitors' quality of heaviness—an essential quality in the traction engine. to get the necessary adhesion, but one entirely unnecessary in the steam wagon with which the load performs this duty. To put it concisely, the present type of steam wagon uses a lot of power in moving redundant weight. If this redundant weight were eliminated, the power could be reduced ; this would mean a further saving of weight. The wagon would cost less for material, the tire bill would 'be reduced, and the reduction in power would mean a reduction in fuel and water consumption. In other words, the lighter the vehicle the more efficient it becomes in every respect—vide the L-ra.o.c. motorbus—the salvation of which was the weight limit of three tons. Also, as is. known, steam wagons damage the foundations of the roads, due to excessive weight, whilst petrol wagons damage the surface, due to uneven turning and starting efforts. A steam wagon of equal weight to a petrol wagon would undoubtedly do far less damage to the roads.

The Tenacity of the Traction-engine School for Weight and Cheap Materials.

The manufacture of steam wagons is chiefly carried out by traction-engine makers, who, as already stated, have never properly considered this question of tare weight. Compare their methods with those of petrol-wagon makers ; the latter worship weight reduction to the extent of using bolts with heads and nuts of "the next size smaller " on many of the fittings. Take, also, the cylinder casting of an overtype steam wagon which develops 35 b.h.p., at 200 lb. pressure per sq. in. ; it weighs on an average about 4 -cwt., whereas in a four-cylinder petrol engine, which develops 45 b.h.p. and has to 'withstand a maximum working pressure of about 350 lb. per sq. in., the whole engene weighs very little more than the steam engine cylinder casting. ' Surely, there is some blind metal in the latter. A lighter section of steel channel couldbe used for the frame, if greater care were taken in attaching brackets, etc. The usual way is to fix them by bolts passing through• the top or bottom flanges of the girder, and a in. hole through one of the flanges of a 6 in. by 3 in. section weakens it to the extent of over 10 per cent. This could be avoided by putting the bolts through the web of the section, which does not appreciably reduce the strength of the channel to resist bending. Again, properly-designed stiffening plates, riveted to the frame where the greatest load is carried, will allow a further reduction in section. and therefore of weight.

• The "Offence" of the Wheels.

The wheels, considered from the point of view of weight, are very unsatisfactory. Rubber-tired wood wheels are notable offenders, often weighing as much as 28 cwt. the set for a five-ton machine, or 12 per cent. of the total weight of the _vehicle fully loaded. Rubber-tired cast-steel wheels weigh about 22 cwt. the set, or nine per cent. of the total weight. Compare these figures with the L.G.O.C. motorbus cast-steel wheels, which weigh about 71cwt. the set, or six per cent. of the total weight of the vehicle fully loaded ; and these have to bear greater strains, due to higher speeds and more uneven turning effort. Much could be done towards lightening the caststeel wheels of the steam wagon if the problem of internal stresses in the castings were closely studied, and if cognate allowances were made in design. As regards steel-tired wheels, the lightest type is the plated steel disc wheel; but most of these could be made much lighter if a. wood feline were interposed, as it would absorb most of the vibration.

Clumsiness of Some Transmissions and Controls.

Much could be done in the way of lightening all the steel castings, especially the gearwheels, which often weigh as much as 7 cwt. the set in a five-ton vehicle, if the problem were tackled in the proper manner. By using nickel steel As more than one steam-wagon maker has done for years.—ED.], all the shafts and axles could be made smaller, with a consequent reduction in the size of all wheelboxes, etc. Again, many steerage chain barrels are made of a solid mildsteel shaft, with a massive cast-iron worm part for the chain to wind on, as is used on steam rollers. This can be inade a plain hollow cast-iron barrel, with a shalt tube cast in each end for the bearings, and its weight would be less than half that of the former.

Reforming the Boiler.

Most boilers err on the heavy side, particularly the Belpaire type with flat cylinder mountings. "Very often, thicker plates are used than is really necessary, particularly the tube plates ; also, the fire-bars could be made much lighteis if carefully designed. By flanging out the plates, and doing away with the foundation rings and fire-hole rings, and by reducing water spaces to a practicable minimum, a further saving in weight could be obtained. The fitting of a superheater would enable a much smaller boiler to be used, dne to the gain in economy, with a considerable net gain in weight.

Axle Disposition. "

The foregoing are only a few chosen" examples ; , practically every part could be made lighter if proper materials and proper methods. of construction were used, and the total weight of the vehicle could be easily reduced to give an ample margin for a useful load of 50 per cent. without the trailer. The hind axle-weight could be brought within the legal limit by placing the axle behind the centre of the body, and putting the front axle as far back as possible, thus transferring part of the load to the front axle. Care should be taken to avoid making the wheelbase too long, or the front-axle weight so great that the steering became too heavy.

The Acme of Lightness Coupled with Strength. It seems quite evident that substantial improvement, as regards weight, can be made with the overtype wagon, but its other defects are inherent and cannot be remedied. In the opinion of the writer, the time is very appropriate for the introduction of a lighter type of wagon. Certain light types are at present on the market ; it is not the intention to offer any opinion regarding them, but to put forward suggestions which are the outcome of many years' experience with steam motor vehicles., To be a commercial success, any new type must retam all the present advantages of the overtype machine, which may be summarized as follow :—(1) Low first cost ; (2) simplicity of mechanism ; (3) reliability (i.e., continuing to give full power after it has developed mechanical defects); (4) low running costs ; (5) strength to withstand rough usage ; and (6) reasonable factors of safety. In addition, the present faults, as previously stated, must be eliminated. Nearly all the imperfections of the overtype steam wagon are embodied in the power-producer. The boiler and engine and their accessories are the "sinnets," and ittis in them that radical changes should be made. Take the ease of a five-ton wagon which develops 35 b.h.p. The weight of the boiler and fittings (excluding water tank), in working order, is about 35 cwt., or 112 lb. per b.h.p."; and the engine parts weigh about 10 cwt., or 32 lb. per b.h.p. These give a total far boiler and engine of 144 lb. per b.h.p. A fair average. for petrol engines is about 15 lb. per b.h.p., which " gives one furiously to think."

The weight of the power-producer on the steam wagon is, therefore, about one-third • of the total weight of the vehicle in working order and unloaded. On a petrol vehicle, it is only about one-twentieth of W the total weight. hatever reduction is made in the . boiler and engine will allow a corresponding pro-rata reduction in every other part of the vehicle.

Where Does the Solution Lie?

The solution of the problem can be found in the water-tube boiler and vertical high-speed type of engine. The water-tubeboiler gives the most steam for its Weight of any type of boiler, and it could be made so light as to weigh in working Order under 20 lb. per sq. ft. of heating surface, as .voinpared with 56 lb. for the average: steam-wagon low-type boiler. Roughly speaking, then, it could be made to weigh about 12 cwt. The vertical engine could easily be made to weigh less than a petrol engine, or about

cwt., giving a total Weight of engine and boiler of 15 as compared with 45 cwt. for the overtype engine and boiler, a. saving of qton.

A very suitable type of boiler -would be a singlesided Yarrow, comprising a top cylindrical drum, a nest of straight tubes, and a bottom water drum. Every part is of the simplest and strongest form possible, and capable of being .easily cleaned and repaired. It would be greatly superior to a loco. type in oost, simplicity, reliability, upkeep, etc. Certain features would require careful attention in design, as—the beiler to be worked at.higher pressure ; a. reducing Valve to be fitted to avoid priming; a, water heater to be fitted in the flue and to be easily ac-cesSible for Cleaning out. the impurities which would be deposited there out of the water ; and an automatic feeding arrangement to be provided to keep the waterlevel nearly constant. In addition to -light weight, further advantages • would-be gained. This boiler as a type is adaptable to -1:tse inferior fuel, on account of its large 'combustion Space lined with refractory material ; steam Ca he quickly raised ;. great strength and immunity from accidents are ensured; it gives a quick response. to increased demands, and is easily repaired. All these are valuable qualities in a'steamwagon boiler. The addition of a superheater, a very simple matter with this type of boiler, would further reduce the size and weight of the boiler, due to the increased steaming capacity of the boiler and the reduced steam consumption of the engine. Balanced Engines Needed. The engine would be a separate unit,naounted. on the frame in such a manner that it was under• the observation of the driver 'when running and easily accessible for adjustment and repair. Also, it could be very ea.sily .balanced, a point which is practicaily, ignored at present, but which has a very serious influence on the life of the chassis. Most steam-wagon

• engines are-arranged to work double high pressure as well as compound. Why, not utilise this'arrangement for obtaining the necessary range of power without the introduction of change-speed, gear? Engines are now primarily arranged for working compound, and when the.double high-pressure gear is used excessive strain is put on certain parts; but there is no reason why it should not be primarily designed for working double high pressure, which would leave a margin of strength when working compound. By this means, a direct drive, by chain, worm, or bevel gear. could be used, accomplishing a saving of from five to ten per cent, in the mechanical efficiency of the transmission gear, as well as anconsiderable saving in weight. ' .It would also de away with the necessity for stopping the vehicle on hills to change gear, a condition which ha 's often caused accidents by the vehicle's getting out of Control when in neutral position.

Automatic Lubrication.

. The lubrication should be arranged so that it is not necessary for the driver to be often emptying the contents of his oil feeder over the motion work, as with the present overtype ; the greater part of the oil usually drops on to the 'boiler, or is splashed about the vehicle and driver, giving both a very untidy appearance. A large multiple-feed oil box, withsat least one day's supply, placedconveniently near the driver,' with pipes leading to all parts requiring lubrication, or a simple farm of forced lubrication, such as it used on stationary high-speed Vertical engines, would solve the difficulty. This would save a considerable amount of time which is at present wasted going round the engine filling up oil cups two or three times a day.

Radius on One Filling of the Water Tank.

The radius of action of a steam wagon depends on the steam consumption of the engine and the capacity of the water tank. The former would be reduced in direct proportion to the reduction in weight, and also further reduced by using superheated steam. Therefore, with a water tank of the. same capacity as that

• now used, the radius of action would be increased inversely as the consumption of water is reduced. Take the case of a five-ton overtype rubber-tired wagon, which usually carries a tank of 150 gallons capacity, and consumes roughly seven gallons of water per mile ; this gives a radius of action of 20 miles. Assuming a daily mileage of 60, the amount used per day • would be 420 gallons, or nearly three tanks of water. With a reduction in weight of, say, 30 per cent., and

by acing superheated steam an economy of 30 per cent. in water consumption, the water used would be reduced to under 3 gallons per mile, or just over 200 gallons per 60-mile day. This would mean a radius of action of 40 miles with a 150-gallon water tank, and would necessitate only one atop during the days for picking up water. It would be nearly always possible to pick up water when stopping to Set down or pick up loads,, thus eliminating involuntary stops, and countering one of the chief advantages that the petrol wagon has over the steam wagon.

View and Control.

The manipulation of this type could be made quite as convenient as a petrol wagon. The driver's position could be so situated that he has full view of the road, and all operating levers could be placed within easy reach. He would not have to bother about the water-level in the boiler ; also it would not be a very difficult matter to arrange for automatic feeding of fuel. Much better combustion of fuel would be obtained, with a consequent reduction in smoke emitted, and steam could be raised from cold Water in a very short time. Any, type of steering could be fitted, preferably Ackermann type, with three-point suspension, and the wheelbase would be reduced to the minimum.

Users Expect Steam and Steam-wagon Makers to do Something New. , 'The evolution of a more efficient type of steam wagon is principally a commercial rather than a scientific proposition. It has been very difficult in the past to persuade users to buy a new type of motor. wagon, and no doubt this reticence has been beneficial in helping to establish manufacturing businesses.' Now, however, the majority of users has acquired sufficient knowledge to appreciate a new departure, even if it be one of a radical nature, As previously stated, :the manufacture of this class of vehicle is chiefly in the hands of traction-engine men, who have got into such a "rut." that it seems almost hopeless to expect them to tackle the problem scientifically. As long as there is no apparent demand for a more-efficient vehicle, they are content to manufacture in the old "rule Of thumb" style. It is surprising that some of the large haulage companies have not ventured to manufacture their own vehicles, as is done by all our railway companies, and in the motorbus world by the L.G.O.C. Would the London motorbus ever have been evolved by a solelymanufacturing concern? Finality in steam motor-wagon design cannot be said 'to have been reached when the prevailing type expends the greater part of its energy m moving tare load. The requirements of the commercial world demand vehicles that will carry the highest percentage of total moving weight as paying load. Are this . country's steam-wagon men prepared to make a scientific attempt to solve the problem by the use of brains, high-class workmanship, and finest up-to-date raw materials?


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