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OPINIONS FROM OTHERS.

27th November 1928
Page 33
Page 33, 27th November 1928 — OPINIONS FROM OTHERS.
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Which of the following most accurately describes the problem?

The Editor invites correspondence on all subjects connected with the paper only and, preferably, typewritten. The right of abbreviation 'use of commercial motors. letters should be on, one side of The is reserved, and no responsibility for views expressed is accepted.

The Torque Reaction of Six-wheelers.

The Editor, THE COMMERCIAL MOTOR.

[27081 Sir,—The letter of Mr. C. R. Churn which appears in The Comme'rcial Motor for November 13th raises an interesting point ou wnich it might be to the advantage of the industry if users of six-wheelers would give their experiences, as, although the views of designers and mathematicians may be of use, there are many things which act satisfactorily in automobile construction which, had they been put before the man whose opinions are formed from figures alone, would have been proved to his satisfaction to be impossible, Mr. Churn finds fault with the paragraph which IPPeared in The Commercial Motor for October 16th (page 269), which, dealing with the Whitby sixwheeler, contains a remark that "the torque reactions are taken through the springs to the frame."

He proposes to show that this is not the case, and puts forth. certain arguments which go to prove that the torque reaction sets up a moment around the pivot of the centre point of suspension, which results in either the rearmost or the central axle being pressed downwards, according to the direction in which the vehicle is travelling. He points out that this increases the load on that axle:

In this he is obviously correct when the matter is considered from the purely theoretical point of view. The question is, however—Does this pressure make itself apparent in tyre wear or stress on the bearings? The writer would be inclined to be guided more, by the experiences of those who actually use such vehicles than by arguments based on theory. It is well known that theory and practice must not disagree, but in matters such as these there is always the difficulty of applying the correct theory or of getting a theory complete.

There are many things in autoniobile practice which would appear to disagree with theory, especially in such matters as torque reaction. For instance, the torque transmitted from the gearbox to the final drive should, according to theory, cause a distinct heeling over of the sprung position of the chassis in relation to the unsprung rear axle. That such torque reaction does exist theory proves beyond all doubt, yet under ordinary conditions of driving its effect is practically negligible.

As an instance of theory apparently disagreeing with practice, the aeroplane can be cited. When the Wright brothers made their first aeroplane they

naturally thought that two propellers, running in opposite directions, would be necessary. Practice, however, proved that although the torque reaction must exist there is no need for more than one propeller in the smaller machines, and even in such a powerful machine as the Napier-Supermarine seaplane, using the float on one side as a fuel reservoir serves to balance the torque of the propeller, and the plane does. not revolve around the engine.

Whilst not in any way wishing to disagree with the figures given by Mr. Churn, the writer would point out that the words he disagrees with—" the torque reactions are taken through the springs to the frame" —can -hardly be said to be incorrect, as the torque reaction must be taken through the springs, even if it be finally transmitted to one or other of the road wheels in the manner he describes. The pressure he mentions as being the final effect of the torque reaction must exert a pressure upwards on the central pivot and thence 'to the frame.

If the overload which Mr. Churn refers to has any appreciable etTect on tyres or akle bearings, the users of such vehicles will be able to favour us with their experiences, and the matter could then easily be put right by the designers—probably by shifting the point of the pivot from the centre of the bogie to a place where the load on central and rearmost axles would be equal. There is one point which. Mr. Churn may have/overlooked, and may to some extent counteract the defect lie points out. That is, that when brakes are applied more load must necessarily he thrown ore the central axle.

The matter raised by Mr. Churn appears to bring us back to the old and still unsettled question of torque tube (or its equivalent) versus torque on springs. This matter has been discussed on many occasions in this journal, but it would appear that both plans have their good and bad points, and that is why, in the case of four-wheeled vehicles, thematter is still debatable. The six-wheeler introduces so many new points into the matter that it would appear to be worth while to review the whole question again from the point of view of the six-wheeler.—Youre faithfully,

ENGINEER-DESIGNER.

Servicing Coaches Under Guarantee.

The Editor, THE COMMERCIAL -MOTOR.

[27091 Sir,—With reference to the article on this subject in The Commercial Motor for November 13th, I am of opinion that, if makers stipulated the quality of oil and grease to be used during the period of the guarantee, better satisfaction Would be derived by both maker and user.

It would be advisable to make it a condition of the guarantee that the stipulated grades of lubricant and the recommended frequencies of lubrication of working parts be adhered to.

My experience of over 20 years goes to show that machines are generally run indefinitely without proper attention being given to greasing, resulting in seized joints and, in some cases, broken parts, which the makers are expected to renew free.

With regard to the customary time limit for a guarantee, this I consider ridiculous, considering the amount of mileage which nowadays is covered during a year. Most users have an idea that a few pence saved in buying lubricants is economy. My experience is that, in the long run, the best is the cheapest, as it is more lasting and efficient, whilst a good greaser is as important as a good mechanic.—Yours

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