Opinions from Others.
Page 25
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Worm-gear Differential.
The Editor, THE ClADRERCIAL MOTOR.
[1169] Sir,-1 notice in your editorial footnote to my letter on this subject in your last issue, you say that " the effect of the absorption of power by the worm-gears in no way transfers nearly all the driving power to one wheel."
Witn this i quite agree, as it would be absurd to contend that the power absorbed was transferred to the other wheel. This, however, is not the idea I intended to convey in my letter, which may not have been very clear.
The fact is, that with the device in question, undoubtedly the greater part of the driving power is
transmitted through one wheel or the other when on bad ground, but no power is absorbed in this case, as, there being no spinning on one wheel, there is no differential movement, the friction producing the effect being purely static.
Consider the case of a car with one back wheel on firm ground and the other on a. slippery surface ; with an ordinary differential of high efficiency, the wheel on firm ground has no more driving power than the other, which spins round. Now lock the differential absolutely ; no spinning can take place, even if the co-efficient of friction between the wheel and the slippery ground is nil.
As the co-efficient of friction is never absolutely nil in practice, the same effect can be obtained by making the differential gear of low efficiency. The wheel on slippery ground will then transmit a little power, but the greater part is transmitted by the wheel on firm ground.
With regard to your comment, that the differential when in action will uselessly absorb much needed power, it is perfectly true that a certain amount of power is absorbed on curves, but it can be shown mathematically that, with a differential of suitably low efficiency, the loss of power on the sharpest curve which the vehicle could take would not exceed 5 per cent., so that the total absorption of power in a day's run would be infinitesimal, probably not as much as .01 per cent.—Yours faithfully,
Gam C. GOODHART.
An Offer from Merryweathers.
The Editor, THE COMMERCIAL MoTon.
[1170] Sir,—We have read with interest the letter printed in your issue of the 23rd January, in which " Surrey Firemaster " declines to visit our works. for the purpose of seeing a test in which we have promised to exceed the figures which he challenged any maker of reciprocating pumps to show. With reference to his remarks upon the subject of h.p., we need only say that we do not use freak engines for any purpose. The machine we mentioned in our former letter is a. 350-gallon 42 h.p. R.A.C. machine, exactly similar to those of our manufacture in use in many English fire brigades. It is four years old, but is nevertherless capable of exceeding the figures mentioned by " Surrey Firemaster."
We offered to run with the old engine, because the test required is not so exacting as to extend our present standard 350-gallon machines to their limit, and the old engine, which is always available at short notice, will do all that is required.
Your correspondent asks for a great deal of .information, some of which is of a 'kind which is not usually published by manufacturers. However, if he will come here, we will answer all the questions contained in his letter, on his undertaking to regard certain information as confidential. The reservation will not apply to the question of h.p. or design of the.petrol motor, and its nature is indicated when we say that " Surrey Firemaster " falls into grave error in assuming that bore, stroke and speed are the only
factors governing the discharge .of a reciprocating p ump. Ot course, if your correspondent still refuses to look at what can be done by a reciprocating pump, we cannot help it ; he cannot, however, expect to be regarded as an expert if he declines to investigate his subject. As we do not think that any comment of ours is likely to intensify the impression a continued refusal to witness the test we otter must make upon the mind of any unbiassed reader, we will merely reiterate that our invitation, is still open for his acceptance.--Yours faithfully,
MERRYWEATHER AND SONS, LTD.
Greenwich Road, S.E.
[We submitted a copy of this further offer to "Surrey. Firemaster." reply is published or. emitter.— Lb.] The Editor, THE COMMERCIAL MOTOR.
[1171] Sir,—Referring to a further letter from your correspondents, I am surprised—if they are convinced that their 350-gallon reciprocating pump will displace 500-600 gallons of water per minute—they will not submit their miracle to a committee of experts for investigation, ana, it substantiated, publication by them to the world, so that they (the makers) could receive the full commercial benefit to which they would be entitled. I notice they still quote 42 h.p. It.A.C., although they advertise their h.p. of chassis as 60, 70 and 90. Which of these is the 42 R.A.O.l
I am unaware that any maker has been accused of using freak engines. What might be termed freak figures are sometimes used in denominating horsepower. In my opinion, R.A.C. figures may often be treak figures. Most manufacturers of motor appliances publish the stroke and bore of their engines, thus giving their clients an opportunity to judge for themselves when going to the market to buy an appliance. There are not many business men to-day who will buy a pig in a poke," and trust to luck. Therefore, I do not think I. have asked for any unusual information or matter that could be classed as confidential.
I do not desire to visit their works unaccompanied.
It is a matter for your correspondents to convince technical experts that they have discovered not a 500-600-gallon pump that will pump 350 gallons of water per minute, but a 350-gallon pump that will displace 500-600 gallons of water per minute. The
rating of pumps is generally that of their maximum output per minute. I am not an expert, but— Yours faithfully, " SURREY FIREMASTER."