OPINIONS FROM OTHERS.
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The Editor invites correspondence elf all subjects conotected with the use of commercial motors. Leiters should be on one side 01 ihe paper only and typewritten by prejerence. The right of abbreviation is reserved, and no responsibility for views
expressed is accepted,
The Commercial Motor of the Near Future.
The Editor, TEE COMMERCIAL Moron.
[2,339j Sir,—I read with great interest articles in recent issues of The Commercial Motor, also the letter of "Transport Manager," which appeared in the issue of February 10th, on the above subject. I am glad to see those who have the management of fleets giving their opinions as to what departures are necessary for future designs of commercial motors, as it is mostly from them that the designer can learn the requirements of actual service.
I guite agree that the matter of better springing requires atterition. The further experiences of those who have to handle the loads mentioned by "Transport Manager," namely, "loosely packed eggs, soft fruits, confectionery, etc.," would be very enlightening.
Undoubtedly, there is a limit to the flexibility of springs, which have to perform the function of radius rods and torque rods and to take the side strains which must come on to any device which connects the rear axle to the frame. With bodies which stand high, as do all those which are designed to carry bulky loads, there will always be the trOuble due to side roll, so the problem is not easily to be solvietk Could not a series of trials be arranged with a load, such as, for instance, a ho5f of loosely packed eggs, which had to be carried over a certain stretch of road at a given pace, first in a lorry fully loaded up to its capacity, and then over the same groland with nothing but the box of eggs aboard? I think the condition of the eggs at the finish would be a; very good indication of the efficiency of the springing? In the matter of passenger-carrying vehicles the upholsteryhas the effect of adding greatly to the, springing effect, but in those bodies that carry other forms of cargo some similar additional spring arrangement might have th,e desired effect
fully agree .with " Transport • Manager" that many parts, might be standardized with advantage in lorries of different types with our present experience. In the earlier days of the commercial motor it was necessary for the designer to have a free hand in the design of even small details, otherwise we might have chosen a modePto standardize which was not the most perfect that could be produced. As time goes on, however, certain details have proved beyond all doubt their superiority over all other devices.
Now, when'this stage is arrived at, what excuse is there for a manufacturer who fits an unproved device or one obviously less efficient than the admitted best ? I think with "Transport Manager" that the Simms magneto coupling has proved itself to have the greatest number of good points, so why use any other? I know of no better. Nothing is or ever will be perfect; all we can do is to select those devices that have most to recommend them.
With regard. to rubber hose, theremight be two classes, one for pump circulation and one for thermo, as the latter would have to be of larger diameter. Whilst on this subject I think thaf all nozzles cast integral with the radiator should be barred, as in order to remove the radiator it, is necessary to break the joint between the hose and its pipe. This often leads to the breakage of the hose, and a replacement is not always convenient. A better plan is to have a removable flange on both pipes, so that a flat gasket is all that is required should it be necessary to remove the radiator.
Whilst entirely agreeing with "Transport c44 Manager" with regard to the items he enumerates, namely, flexible discs, ball joints ball and roller bearings in gearboxes, etc., I think that at least driving chains might be all of the same length and pith]) for any given load. I should like to add to this list a few items. The clips for securing springs to front and rear axles often give a good deal of trouble when a leaf has to be renewed. In many cases there is a passage down which water can run, which effectually rusts up all nuts. Could not the best of known methods be chosen?
Could not some universal method of securing the gearbox in place be determined, so that it could be lowered without taking half the vehicle to pieces? Could not the necessity for torque rods and radius rods be settled. once and for all? Could not a simpler method of adjusting brakes be settled on— one which does not necessitate anyone crawling under the vehicle and attempting to adjust rusted up nuts? I note the editorial footnote which calls attention to the fact that the S.M.M. and T. are giving attention to several of the details raised, but personally I should rather like to hear what the users have to say about these and other points.—
Yours faithfully, WAIRANGI. Wellington, N.Z.
The London Parade: A Driver's View.
The Editor, TETE COMMERCIAL MOTOR.
[2,340] Sir,—I was-recently entered by my firm with a lorry as part of •a team of three for the C.M.U.A. parade for The Commercial Motor Cup. It was a splendid show and I would not miss it in future. As a driver who has to unload his van, like many others there, it showed me how hard every driver must have worked to get his lorry in such condition. But I am also a man who studies the mechanical side of lorry work as well as the cleaning part, and would like to know if the cup is awarded for "spit and polish" or for mechanical proficiency.
My reason for asking this is (as a regular reader of The Commercial Motor almost from the day when it was first published) that this journal has always taught proficiency and efficiency first. The Cup was awarded to a shell Mex team, including motor No. 2106, which undoubtedly had a beautifully clean polished engine, but I, personally, with a mechanic, pointed out seized spring shackle bolts and dry spring leaves which can he verified by our mechanic. Also the engine next to his had a burst exhaust box.
Regarding our own engines, ll that occurred was two judges saw my engine stationary, two tried my lamps, one asked me to remove my footboards and he looked inside. Now that is all that took place to the three Leylands entered by my firm. The engines were not even started to see if we had a valve in them ; nobody glanced under the chassis, and we are wondering how they awarded the Engineers' Prize. We are not the only drivers who make this complaint.
—Yours faithfully, • DRIVER.. London, S.E.5.
[-We give publicity to this letter because the writer of it has, seemingly, not made himself fully aware of the conditions under which The Commercial Motor Cup is offered for competition. We believe we are right in assuming that this was the first Parade in which our correspondent or the company employing him had competed, so that the misunderstanding suggested by his letter is largely excusable. The Cup is given for outward appearance, including good and sound condition of every
visible part, and for " spit and polish," as it is termed, aid competitors may with confidence work upon those lines.
We thought, however, it was desirable that the Chief Motor Engineer of the Shell-Mex fleet should have an opportunity to see our correspondent's letter before it would appear in print, so that the small points raised and reflecting upon mechanical condition of one of the winning teams could be answered at once, particularly in view of the fact that our own observations (looking as we do, when we scrutinize ,any commercial motor vehicle, far beyond the surface) have gone to show that mechanical well-being is a matter which receives more than the usual amount of consideration in the maintenance of the Shell-Mex fleet.—En., CAI.] The Editor, THE COMMERCIAL MOTOR.
[2341] Sir,—We thank you for the opportunity of replying to the letter of " Driver " with reference to the C.IYI.U.A. Parade. It is at least pleasing to know that "Driver " appreciates the hard work each individual man must have put in in order to present his lorry in such excellent condition. With regard to the criticism levelled against our osin vehicles, whilst naturally we are quite• satisfied to leave ourselves entirely in the hands of the judges, we would point out that the first consideration with all our vehicles is mechanical efficiency, the first responsibility of the driver being to make sure that all parts are thoroughly greased and oiled periodically. Cleanliness and polish are encouraged in every way, but never at the expense of mechanical efficiency.
Vehicle Ne. 2,106 can be seen at any time upon the London streets, and, we venture to say, will at all times be equally as clean as on the day of the Parade, and, what is more, thoroughly oiled and greased.
We think " Driver's " examination must have been a very cursory one, as none of our vehicles on parade had a burst exhaust box, and, if he had looked more closely, he would have seen that what appeared to be a burst box was a false outer lagged cover with which the silencer on this vehicle is provided.
Finally, we would like to say that there is the greatest competition amongst our drivers themselves for the honour of being able to compete in each year's Parade, there, obviously, having to be a certain amount of weeding out, owing to our being unable to spare more of these vehicles from service
for half a day. Naturally., it is understood it would be impossible for the judges to make a thorough mechanical examination of all vehicles in the short time available ; however, we should be quite happy as to the result even if this were possible.—Yours
faithfully, SHELL-14E1r, LTD., London, W.C. M. V. AMBLER.
Servo-operated Brakes.
The Editor, THE COMMERCIAL MOTOR.
[234] Sir,—I have not read the original article to which "F.L.R." refers in his letter published in your issue of March 10th, but if servo-operated brakes simply mean that the normal personal effort exerted through the brake lever system is either augmented or entirely superseded by a force derived from some form of friction brake (for instance, the disc brake now fitted by Messrs. Rolls-Royce to their 40 h.p. chassis), then I am in entire agreement with "F.L.II." in that the force produced by such mechanism is not affected by, and is entirely independent of, the velocity of rubbing of the friction surfaces constituting the element of the servo gear produced by the speed of the car. I refer particularly to fabric friction linings and not to metal-to-metal surfaces, for which the coefficient of friction is very inconstant and shows large variation in value at different slipping speeds, pressures and temperatures. With the hest class of fabric lining, the coefficient of friction is practically constant at any reasonable speed, and any pressure up to 400 degrees Fahr. ; above this temperature the coefficient falls slightly. Therefore, if the servo brake was applied, say, during the descent of a long hill, the. power would fall off if the temperature rose beyond the figure I have given ; that is, unless the pressure between the elements of the brake was increased. In short,. the power of any such form of servo brake as described is directly proportional to the pressure and the coefficient of friction.
Differences in slipping speeds may he disregarded; if there is any effect, it would be to reduce the power of the brake by the effect high temperature has on the coefficient of friction.
There is, however, one form of servo gear which gives increased force from increase in rotational speed, i.e, the Hallot servo gear, in which the elements of the clutch are expanded by centrifugal force, This is an entirely different arrangement from the more usual form of servo gears.—Yours faithfully,
Buxton. F. J. Franc.