OPINIONS FROM OTHERS.
Page 27
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The Editor invites correspondence on all subjects connected with the use of commercial motors. Letters should be on one sidt3 of the paper only and typewritten by preference, The right of abbreviation is reserved, and no responsibility for views expressed is accepted.
The Trolley-bus for Certain Circumstances.
The Editor, THE COMMERCIAL MOTOR.
[1,911] Sira—With refereace to the article under the heading of "Boom the Bus," which appeared in your issue of the lath instant, " The Inspector " commences by telling us of "The many gallons of hot water into which he has journalistically tumbled
• during the past eight or ten years" in not hesitating to put into black and white his distaste of the trolley-bus.
It will, therefore, come as somewhat of a cold douche to " The Inspector" to hear that the Stra,kerClough trolley-bus is operating at the very low figure of 13 pence per bus-mile, including all maintenance and other charge; such as the overhead equipment, etc.
It is also surprising that our journalistic friend has not (during the past eight or ten years during which he has been suffering from his,distaste of the trolley-bus) seen the many operating statistics whielt have appeared from time to time in the Press, in connection with this type of vehicle.
In districts where cheap electric power can he purchased, and requiring a service of from 21, to 30 minutes, would "The Inspector" advocate operating a petrol-driven vehicle at from 18 to 24 pence in place of a trolley-bus at 13 pence per bus-mile ?
I would suggest that "The Inspector " carefully
• sthdica an article which appeared in The Tramway and Railwa-y World of November last, entitled Trolley Omnibus Developments."
The information given in that article will save " The Inspector" from, perhaps, total immersion in the journalistic hot water referred to above.
Does "The Inspector" doubt the capacity of an electric motor successfullyto drive a trolley-bus? If so. why is such a motor being chosen to operate our
railways in preference to a petrol engine ? •
The trolley-bus requires 1 unite of electric power per bus-mile. Upon systems where this is being purchased at id. per unit, the power cost of the trolley-bus is therefore lid, per bus-mile. Can " The Inspector" give an instance of any petrol omnibus in this country costing less than four times 'this figure in petrol ? Like many others, "The Inspector" is led astray by the cost of the overhead equipment required for the trolley-bus. For a 'Vsminute service, this costa less than id. per bus-mile
• in interest on capital, sinking fund and maintenance charges. This figure is arrived_ at by taking (1) the eost of the overhead equipment at 23,000 per route
; (2) interest and sinking fund charges per annum upon this capital outlay at 5 per cent., and dividing this amount by the -total bus-miles operated per annum per mile of route for the above-mentioned service.
The statement in the concluding paragraph of "The Inspector's " article, that the construction of the trolley-bus is so simple that there is very little profit to be made by the manufacturer, is indirectly the best testimonial that can he given for this new type of vehicle. It is the pure simplicity of construction that has resulted in the extraordinarily low maintenance and operating cost of the vehicle for which "The Inspector" has such a diStaste. The trolley-bus has come to. stay, but it cannot he considered as a competitor to the petrol-driven vehicle an districts where a cheap electric supply is not already available, nor where a less frequent service than 30 minutes is to be catered for—Yours faithfully, For CLOUGH, SMITH AND CO., LTD.,
London, S.W. N. Ceouesr, Director. America and the Crude-oil Engine.
The Editor, THE COMMERCIAL MOTOR.
[1,912] Sir,—A study of the article under the above title by ,your esteemed .contributor, Mr. Henry Sturmey, published in the issue of the lath inst., leaves us with the impression that some points in it require further elucidation.
To begin with Mr. Sturtney states that the fuel may be "either crude oil or paraffin, or a mixture of'the two ; anything, practically, except petrol, which cannot be used at all"; whilst on the previous page he has already definitely informed us of the restriction in these words : "crude oil or any other ,hydro-carbon except petroleum spirit." We are naturally curious to know why petrol, "cannot be used at all, ' but no explanation is given by our sturdy pioneer. The term "hydro-carbon," of course, includes a largenumber of chemical compounds,and one naturally imagines that these would be equally unsuitable. Petrol is a composite spirit, with no fixed chemical composition, so that we presume your contributor uses the term to connote commercially obtainable oils of a certain degree of volatility which are commonly termed "light motor spirit."
We notice on page 892, column 3, that the writer says that the method of burning the fuel in the Dodge engine "avoids the necessity for that excessive strength which is needed with the Diesel system and which accounts for the very great weight of a Diesel type engine." With all due deference to your correspondent, we are unable to see any essential difference between the Dodge engine and the Diesel engine which affects the necessary strength and the weight. In the Diesel engine, combustion of the fuel is effected by high-compression temperature, slow combustion at approximately constant pressure is produced, and there is in no sense an explosion at constant volume similar to that which takes, place in the .gas or petrol engine. The weight of the Diesel engine only becomes excessive with large powers per cylinder, and there is no apparent reason why exactly the same limitation -should not apply to the Dodge engine, if it were attempted to build it in large sizes— of several hundred horse-power per cylinder—as is required in marine practice.
The only essential difference of design between the Dodge engine and the Diesel that is apparent from your correspondent's article would seem to be the method of introducing the fuel. Here, again, though, on further reflection it is realized that there does not appear to be any real difference in the method used in the Dodge engine and that oommon to this country in the Hornsby-Acroyd engine. The tact that the latter is a " semi-Diesel. ' in consequence of the fuel being ignited by a hot bulb (or other specific device), does not affect the point in question. At the conclusion of this article the writer expresses surprise that the Dodge " system" has not been taken up in this country. In the opinion of the Autocraft Board, however, the Dodge engine' is a Diesel type of engine, inasmuch as, in common with the Diesel, it compresses Pure air only, has no ignition apparatus, and burns the fuel at approximately constant pressure. The difference in the method of introducing the fuel can hardly be termed a difference of system. Your contributor states that the fuel is fed to the fuel cup by gravity. We cannot imagine, however, that crude oil will flow down a small pipe, such as that indicated, with the same facility that petrol will flow by gravity into a carburettei !—Yours faithfully, London, W. J. MORSE SCOTT Controller.