OPINIONS FROM OTHERS.
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The Editor invites correspondence on all subjects connectedwith the use of commercial motors. Letters 01041 be side of the paper only and typewritten by preference. he right of abbreviation is reserved, and no feepongbi ity tor views expressed is accepted.
Co-operation Among the Associations.
The Editor,THE COMMERCIAL MOTOR.
[1783] Sir,-1 want to draw, the attention of your readers and of the various trade authorities to the position the commercial vehicle trade has been placed in by the separate and disconnected efforts in the formation of associatioas. I have the honour to be chairman of the North Wales Hirers' Section of the M.T.A. and chairman of the local Char-itbanes Owners' Association, and I am positive that the trade's best interests call for sense unity of action between the various associationa, instead of the present position of divided effort and (may / Venture to say `,!) jealousy. Within the last few months there has been a determined attempt in this district bythe A.A. to secure membership to •what they call a Hirers' Section. Whilst 1 agree that the snore the trade is united in its aims and organization the better the results, yet I cannot help but feel that the A.A., which is primarily an association for private owners, is by no means the best to represent the trade, as experience has shown that in matters of legislation interests are conflicting. The M.T.A. and C.M.U.A. are more nearly in agreement ; in fact, I assume they are entirely so, but the former may be reckoned to have the greater power on account of its stop list, and of the fact that the manufacturers and suppliers are all members with a few unimportant exceptions. DO you not think, sir, that the time has come for the a.verage trader like myself, -who provides the, subscriptions which keep the wheels going, to call for a clear statement of policy by those who purport to represent the commercial user and the trader, in the hope that a mutual line of action may be taken with the milted strength of the whale of the commercial trade behind. it) I think everyone will agree that the trend of legislation brings. out one essential point, Which is the need of unity.
I shall be very glad of your own views and the views of your readers.—Yours faithfully, • Llandudno. FRANK A. WILKES.
The Technics of Springing.
Th-e Editor, THE COMMERCIAL MOTOR.
[1784) Sir,—We have not had the pleasure of knowing your contributor who writes under the "nom de plume " of" The Inspector," but we are always .interested in his remarks that appear from time to time in your excellent periodical. We notice that, in a recent issue, he raises the question regarding the technics of springing, and invites u.s to explain to your readers the chief characteristics of the Palladium double-cantilever suspension, and why the same results could not have been obtained by other methods.
In the first place, we would like to State that, so far as comfort is concepned, equal results could have been obtained by fitting single cantilever springs, but we had, however, to consider other features in addition to comfort.
It is well known that, owing to the resiliency of cantilever springs, rolling or side sway is apt to be uncomfortable when cornering, and this would be especially noticeable on chassis fitted with motor coach bodies; or single and double deck buses, owing to the high centre of gravity. The immediate effect of cornering is to throw the load on. to the outside springs and to relieve the inside springs of this load; the consequence is that the bodly heels over to a marked degree, and, if a sharp turn is made the effectis sometimes rather alarming. The effect, however' on the springs themselves is much more Complicated ; as they are more or less rigidly attached to both axle and frame, when a deflection takes place the voring is also twisted and displaced to a small extent bodily sideways.
Now, the main leaf, which is shackled to the trope and attached to the axle, has to take this twisting action practically unassisted ; the other leaves help it to a certain extent, but, as they are not shackled to'the frame, they do not reduce to any marked extent this twisting action. The same remarks also apply to the side displacements that take place. If, now, therefore, we fit two cantilever springs, one Super-imposed over the other on each side, these can be so designed as to give the same resiliency as a single spring, but to resist the twisting and side displacement of the spring, we have now two main leaves .spaced about a foot apart io Minimize this action.
The foregoing facts have been demonstrated to be correct by tests on models, and also—more important —on the road itself. . For this purpose a four ton load was placed 4 ft. above the chassis frame ; seats were placed on the top of -this load, so that the equivalent height of the top deck of an omnibus was reached. When cornering at varying speeds, there was a gentle sway of the body without the slightest resemblance---of a lurch. The effect seemed to be a compromise between " give " and extreme steadiness.
The following other advantages follow the fitting of double-cantilever springs. Owing to the parallel link arrangement of the springs, the rise and fall of the rear axle is practically vertical (a 12 in. vertical movement of the rear axle produced less than in. movement on the sliding splines of the carda,n shaft). The consequent reduction of tyre wear is obvious, as there is no shuffling of the tyres over the ground; also, the tension of the brake rods is unaffected when the axle rises and falls. • A further advantage of this arrangement is that the torque reaction of the axle and the driving and braking thrusts are taken by the swings themselves, thereby dispensing with radius and torque rods or tubes, with a consequent saving of weight and a smoothness in taking up driving anA braking stresses and an entire absence of chatter. Another ad'v'antage of the double-cantilever sus pension is that it is truly a " Safety First" device. Should one spring break, the remaining three will "carry on" supporting the load and taking the drive. Na excessive "list " is noticeable.
We have carried out very searching tests in con.nection with this. As We have been _entirely unable to get a spring to fail • after much drastic testing extending now over several months, we have to approach this from another standpoint. The tests we have carried out consisted in disconnecting, firstly, a top spring entirely from the axle, secondly; disconnecting, a bottom spring entirely from the axle, and, thirdly, disconnecting bo.14 a top spring on one side of the chassis and a bottom, spring on the other side of the chassis from the axle (see sketch).
The results have been surprising under all these tests which have been carried out on the road with a four-ton load up; it has been impossible to get an untoward incident to occur when driving at all speeds, startingand stopping qttickly and generally ill-treating the .chassis.
In conclusion, we..' fully agree with "The Inspector's" remarks concerning the lack of Icriow%ledge and the rule-af-thumb methods that are so apparent in. connection with such a. vital point as suspension. There is not the slightest doubt but that this question must receive more -attention and thought in the future. We had hoped that our challenge to the Giant tyre • manufacturers would have Shown conclusively what a .great improvementcan be effected by means of a rational spring design, but we are afraid we are en-. ereaching on another subject outside the scope of this letter.—Yours faithfully, For Pser.,Auttat AUTOCAitS, LTD., H. F. SMALLWOOD, Chief Engineer.