Petrol Motor Omnibuses.
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Conclusion of Discussion on Mr. Worby Beaumont's Paper at the Institution of Mechanical Engineers, and reply thereon.
Although the attendance at the adjourned discussion on Mr. Worby Beaumont's paper at the Institution of Mechanical Engineers on Friday last showed some falling off from toe phenomenal audience at the former meeting, interest in the subject to be debated was well maintained, Mr. T. Flurry Riches, the President, was in the chair, and at the teeset Mr. Beaumont supplemented the illustrations in his paper by a series of lantern slides dealing with other, and in some cases later, types of vehicles. These formed an exceedingly interesting group, and it is likely that the suggestion made in the course of the debate that they should be included in the transactions of the Institution will be adopted.
The first of the slides shown by the author illustrated the " Orion " chassis of the " Old Vic " omnibus. In this type is fitted a two-cylinder horizontal engine of 2oh.p. The other features are parallel shafts, chain drive from engine to gear box, and side-chain drive from the 'gear box to road wheels. In this type of omnibus the length of the vehicle is reduced to 18 feet 6 inches against 22 feet 6 inches in the case of the Milnes-Daimler. The third slide illustrated the early single-deck Scott-Stirling omnibus, and Mr. Beaumont maintained that the running of this vehicle showed that, as far as the actual cost of working was concerned, an omnibus carrying 14 passengers could be run to show a profit. Succeeding slides showed the 3oh.p. Wolseley-Siddeley engine and gear box, and attention was particularly directed to the Wolseley practice in respect to three and four row ball bearings with the view to lessening the intensity of stress on balls. Next came the ArrolJohnston 3ob.p., pointed to as the only type of omnibus running with protected chains, the Critchley-Norris 30114p. omnibus, with single unit gear box containing all gear, and the Maudslay, the sequence of which drew from Mr. Beaumont a reference to the growing number of Britishmade chassis now on the market. The other slides included views of the Berliet, the Birmingham Motor Omnibus Company's vehicle to illustrate safe angle of tilting (lent by "THE COMMERCIAL MOTOR "), the Mines-Daimler engine and steering gear, and the Dennis back axle. It would be noted, said Mr. Beaumont that, included in the diagrams* was one showing the angles to which an omnibus could be tilted with a certain righting moment. The diagrams told their own story, and it would be sufficient to point out in general terms that with a motor it was much the safer.
It would be noted, too, that the left-hand side of the diagram showed an ordinary horse omnibus ; on the right was a similar view of an ordinary motor omnibus, while the small diagram showed the righting effort at various degrees of tilt. The diagram gave information as to the height of the centre of gravity with the omnibus empty, with the omnibus loaded on one side on the top seats, and with a full load. Briefly, the effect was to show that the effort necessary to commence tilting of the horse omnibus was approximately 4,26o1b. when fully loaded, and that it was carvespending-Iv less when the load is all on one side, whether a top or an inside load only. On the other hand, the effort necessary to commence tilting with the motor omnibus fully loaded was over 6,000lb. By referring to the diagram giving the righting effort of the motor omnibus when fully loaded on top, and, therefore, under worst conditions, when the omnibus was in an ordinary position this was 6,000lb., at position 2 on the diagram it was about 5.,soolb., and with the increase in tilt it gradually diminished, as might be seen from a reference to the angles and positions. The curved line on the diagram represented the path followed by the centre of gravity, which was also shown by the diagram of the motor omnibus. The result was to show that with the motor omnibus fully loaded on the upper deck and no load whatever on the inside seats it was a much more stable vehicle than a horse omnibus when it had a full inside load. The angle to which the motor omnibus might be tilted was so great that there were hardly any circumstances of service which could produce overturning, the centre of gravity being so low that the righting moment is much greater than would he expected. With a view to. answering criticisms on the subject of the wearing of gears,. he had on the table a gear-wheel of the Milnes-Daimlertype which had run over 22,000 miles, the teeth of the wheel being still almost perfect in form. This admirably illustrated the fact that as long as the gear was only doing the actual work of propulsion that wheel made of the splendid material now available did last a great length of time.
The Fuel Problem and the Price of Petrol.
Mr. Thomas Clarkson not unnaturally struck a note 4 pessimism. He referred to the interest in the subject of the motor omnibus as evidenced by the number of papers or the subject which had recently been read before technical institutions. It seemed to him n that the chief fault of the present paper was that it was too popular and not sufficiently analytical, technical and critical. Dealing with the fuel question, he would point out that petrol as a fuel for the motor omnibus was by reason of the increase in price becoming almost impossible, and that the paper must, therefore, not be regarded as more than a compilation on thesubject of machines which were within measurable distance of becoming obsolete. It would be interesting to consider
the possibilities in the way of increasing efficiency. The best record of which he had any knowledge showed that with a double-deck omnibus using petrol something likesix miles per gallon could be obtained. The question of increasing the efficiency of the internal-combustion engine had for a long time past been a subject of careful consideration, and it was generally recognised that the practical limits of efficiency were being very closely approached. Whether by the employment of a different cycle, the use of higher temperatures, greater pressures, or a greater ratio. (if expansion, something more could be achieved it was difficult to say, but he did not think that any material advance in the way of efficiency could be looked for. He would say a word or two with reference to the transmission problem. The employment of change gears was indispensable, but attentibn was now being seriously directed to theemployment of electric forms of transmission, and no doubt there was much to be said in their favour. Such a form of transmissian gave some approach to the flexibility of steanl. Something, however, had to be paid for that accomplishment, and it was estimated that, in the conversion of the anechanical energy produced by the petrol motor into eketrical energy, and its re-conversion into mechanical energy :at the road wheels, there was a loss of something between 20 and as per cent. It was a moot question whether the _petrol motor could afford to make a sacrifice of that character, and, indeed, having regard to the probable rise in the price of petrol, he did not see how that was going to get over the difficulty. He disagreed with Mr. Beaumont to some extent in his figures given relating to the weight of vehicles illustrated in the paper. The Straker-Squire complete omnibus weighed 4 tons Scwt., while the Maudslay weighed 4 tons mcwt., and with petrol-electric traos-mission the weight was still greater. He personally was in favour of doing away with the pump, and many years .ago had fitted a car with a system which worked very well. It was found that natural circulation could be easily obtained, and one advantage was that the circulation went on after the engine was stopped, with the result that the engine very quickly cooled. He was glad to note that forced lubrication was being more largely adopted.
How Frames are Weakened.
Mr. E. G. Brewer as a railway engineer was inclined to deride motor-omnibus practice. He dealt with the design of frames, with which he had had a great deal of experience in -railway work. The failures in the case of pressed steel frames could not always be attributed to the steel, but were often due to the treatment the steel received. The frame for a motor omnibus was designed to carry a certain load, and then the user proceeded to drill large holes in the lower web of that frame, in apparent ignorance of the weakening effect thus produced. 1-le had seen examples at the Agricultural Hall Exhibition where a 4-inch wide lower web had a 2-inch hole drilled in it to put the exhaust pipe through. In the channel bar frame, a type used perhaps more than any other, a lower web of 21 inches wide had had a h-inch hole drilled for the purpose of carrying quite an unimportant attachment. The breakage of frames often had its origin in these various holes, drilled where no hole should ever have been allowed to exist. In railway practice the utmost care was taken to avoid drilling holes in the lower members of the frame. Possibly the reason for the weak points to be noticed in omnibus frame design was to he found in the excessive demand from manufacturers, who were chiefly concerned with the question of deliveries rather than with improvement of the omnibus, and in his opinion if orders had not been so -easily obtained there would be a much better vehicle on the road to-day. Another point of importance was the designiing of the omnibus in a series of units. At the present time if an omnibus came into the garage with a particular part broken the omnibus went out of service until the repair could be effected, but if unit designing were adopted the whole of the back axle would be constructed as one unit so that in the event of failure of any part it could be removed and replaced by an axle out of stock. The same thing should apply to the gear box, and another important point was that the removal of the engine as a whole should be made a perfectly simple operation. 1-fe was extremely pleased to see Mr. Beaumont had such strong opinions on the subject of automatic circulation. He agreed that pumps were unnecessary for the circulation of the water, and would point out that it was absolutely bad designing to put the top of the radiator below the level of the top of the cylinder. One maker of motor omnibuses was a particular sinner in this respect. The proper place for the radiator was on the canopy over the driver's head, and in that position as good results could be obtained without any forced circulation as with the radiator in its usual position. Mr. Clarkson had not given himself sufficient credit in connection with the advent of forced lubrication. Mr. Clarkson's arrangement whereby every pipe that led to individual bearings had periodically forced through it a stream of oil was one particularly adapted to petrol vehicles. The motor-omnibus designer had taken great pains to get excellent material for certain parts, and yet at the same time he often used unsuitable materials for other parts. Cast-iron was used for cranks and for gearcases, which was placing cast-iron in a situation where it had to stand excessive vibration and tensional strain. Castiron was quite unfitted for use in tension, and possibly when a few more hundred gear-cases had broken steel construction would then be employed.
Worm Gearing and Spring Wheels.
Mr. Holroyd Smith believes he is in advance of the times and, posing as a man with a mission, dealt with the advantages of the thermo-syphon for cooling compared with the pump. With the pump in use there was frequently a great difference of temperature between the top and bottom of the radiator, and a 'Mich more equable distribution of temperature was obtained by the discarding of the pump. Several interesting points arose in connection with worm gearing. He had done a good deal of work himself in this direction, and at Bradford in a tramway service on a gradient of r in r i with a car weighing over 5 tons it was found by measuring the electricity for driving the motors and the actual power given off by the axle that there was a combined efficiency of motor and worm gear of 84+ per cent. In some respects the Dennis design was faulty. The best angle of travel for the thread was that it should be equal to the largest diameter of the screw, as by going beyond that the complication of side thrust was introduced. Then again the worm wheel was made too large. On the subject of the lubrication of the worm wheel he approved of the design of the Dennis in placing the worm on top, and disapproved of the Lanchester design which placed it at the bottom. He was bound to controvert the statement that spring wheels were in the experimental stage, and he submitted for their inspection a form of spring wheel which had run for 5,000 miles on a car weighing over 30 cwt. with the renewal of nnlv one spring. Unfortunately, nearly all attempts to use spring wheels had overlooked the fact that the spring must have nothing else to do save to resist the radial movement. The difficulty was to make the spring perform the same Functions as the springs of an ordinary carriage while they were travelling in the wheel, which was accomplished by having the spring under initial compression. In 20 years' time spring wheels would be in common use.
Mr. Edwin Henwood also thought that the spring wheel should be given a fair trial.
Segmental Tires.
Mr. Torkington said that the inventors of the spring wheel nad been working for about two centuries, and it would proably be two centuries more before the right wheel was .volved. He had always been taught that the proper place to absorb vibration was on the periphery of the wheel, and nothing did that so well as rubber tire. Unfortunately the rubber tire was apt to skid, and he regretted that the author lad not given more attention to skidding in his paper. 'Llolone! Crompton had expressed his belief that the remedy would be found in some form of segmental tire, and undoubtedly that form of tire had given satisfactory results when tested, and would probably overcome the skidding difficulty.
Mr. Guy Beaumont referred to the question of worm gearng. If, as Mr. Hoiroyd Smith suggested, the best travel for he worm was that it should not exceed the maximum diameter, he would point out that the adoption of that plan led :0 a difficulty in the matter of gear reduction' which would ..ither be much too great or the diameter of the worm wheel disadvantageously small. It was true that questions of side .hrust were thus introduced, but, as was evident from the ;pecimens exhibited on the table, no harm resulted.
The President, before calling upon Mr. Beaumont to reply, )riefly referred to the live character of the subject under dis:ussion and to the attention it deserved at the hands of the rigineers.
Mr. Beaumont Replies on the Discussion.
Mr. Worby Beaumont defended his figures of working !osts on the ground that they were such as might be ex
nected in the near future. He was unable to accept Mr. a aampbell Swinton's figures, which in some respects were ex
;essive, particularly under the heading of grease and oil and -ent, rates and taxes. His own figures for repairs and maintenance, which had been challenged, were based on ictual experience. He agreed with Colonel Crompton as to he value of the Work done by Willans, and reference might ilso he made to the work of Brotherhood and Hardingham, mt would point out that Willans attained his results not by ugh piston speed but by high revolution and high pressures. Nith regard to the size of engine the 45h.p. engine was not iecessary for economical working. The statistics quoted by gr. French in connection with a particular type of omnibus yore such as should be experienced in motor omnibuses z-enerally within a comparatively short period. He was dis)osed to agree with Mr. French that 15 per cent. deprecia tion was sufficient assuming that at the end of the period the vehicle was taken as of practically no value, but in assuming: a basis of zo per cent. he did so on the understanding that that allowed the vehicle to be sufficiently well maintained to be of some value after its period of public service. He accepted Mr. Douglas Mackenzie's correction as to the proportion of British and foreign-made omnibuses in London,• but it could not be denied that the number of vehicles of foreign origin was very large. It was to be noted that many of the new types of vehicles were being fitted with the multiple disc dutch with fiat rings, so that although there were not many of these in use at present the number would shortly show a considerable increase. He disagreed with. Dr. Archibald Barr. If one wanted piston speed that could be obtained comparatively easily. The difficulty whiehs Daimler had overcome was the high rotation, and in sue-. ceeding in producing an engine to run t,000 revolutions per minute, as compared with what had been previously accomplished with the internal-combustion engine, a great advance. had been accomplished. Mr. Clarkson had complained that the paper was not sufficiently critical and analytical, but he would point out that, in dealing with such a wide subject as that covered by the title of the paper, it was practically impossible to go into details, as many of the subjects referred to were of sufficient importance to merit the writing of a separate paper. On the fuel question Mr. Clarkson had apparently overlooked the possibility that kerosene and other fuels might be employed in the internal-combustion engine,. so that the possible rise in the price of petrol to a point which would prohibit its use was not a vital objection. Referenca had been made to the weigh( question, but it should not beforgotten that a good deal depended on the design and construction of the omnibus body, which, under the present regulations, was often responsible for an increase in weight. lie agreed with Mr. Brewer that well-designed frames had often been badly treated by having holes drilled in inappropriate parts. He was not at all converted by Mr. Holroyd Smith's statement on behalf of the spring wheel, but the only reply he would make was that, if Mr. Holroyd Smith required the complicated arrangement he had described, inside the wheel, he, himself, preferred to add a little to the cost of the springs, and improve the method of carrying a wellmade wheel and axle on the lines which were at present adapted. He admitted that he had said very little on the subject of tires, and in truth that was a subject on which it is difficult to say anything without writing a paper. Mr. Torhington had referred to the segmental tire, and he happened to know that Mr. Torkinglon was associated with a successful tire of that type, which had given excellent results. in tests which had been made. The lubrication question was an important one, and every engineer would realise the nece,ssity of giving close attention to the lubrication of everypart of a high-speed engine. As the President had said, the road motor question was obviously a live subject. it had been a live topic ever since the day when a French engineer showed that he had devised an internal-combustion motor which would drive a carriage from Paris to Bordeaux and back at an average speed of 16 miles per hour. He would point out, however, that the road motor was A live question in England 70 years ago, so that, although in the modern development France had been the pioneer, English engineers has really been the first in the field. He believed that England would now again begin to take first place. This country had already taken first place with regard to the commercial side of motor engineering, and what had been done in this direction would go a good deal towards showing the world that in England we had mechanical engineeringability second to none in connection with the road motor problem.