OPINIONS
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QUERIES
HOW MANY CYLINDERS FOR TRACTOR ENGINES?
[50921 I have read with interest the article entitled "One. Two, Three, Four or Six?" in your issue for July 2„ but disagree with some of the conclusions reached.
The author commences to !condemn the singlecylinder tractor by stating the very just claims that these machines have . . "Extreme simplicity; relia bility, low running costs, and are particularly suitable for operation by unskilled farm labour." None of the argurnents which he later brings forward is sufficiently strong or well founded to shake the truth of any of these clairro.
First, the author states that owing to the uneven torque at the back axle, inferior wheel-adhesion is experienced on single-cylinder tractors. It would be interesting to know how the author proposes to bring forward practical proof of this statement.
To begin with, it is doubtful whether the torque is as bad as he would lead us to suppose, as it must be remembered that nearly all tractors of the single-cylinder type employ a two-stroke engine. Manufacturers of singlecylinder tractors also employ a much heavier flywheel, which, in addition to impro-ving the torque, is of great advantage in overcoming overloads and providing flexibility in running. In this respect such tractors put the four-car]inder type, with its light flywheel, in the shade.
I would remind the author that for practically a century the most popular and widely used form of prime mover for industrial and agricultural purposes has been the single-cylinder slow-running steam engine and, later, the single-cylinder four-stroke oil engine. Does he suggest that these engines should be treated to the addi tion of three more cylinders, in order to improve the adhesion of the belt, which is invariably employed to take the drive from flywheel or crankshaft pulley? I would point out that the degree of cyclic irregularity of the average single-cylinder tractor is approximately equal to that of the engines referred to above : this
practice has stood the test of time, and in. view of its success I consider futile any mention of uneven torque at the back axles on single-cylinder tractors,
Further, even supposing the torque at the back axle were of uneven nature, what practical demonstration has the author seen that brings forth proof that such uneven torque is definitely bad for wheel adhesion? Examination of the report of the World Agricultural Trials of 1930 shows, in Table 11, that regarding wheel adhesion, the best of the single-cylinder tractors in bottom and in top gear were fully equal to the best of the four
cylinder. tractors. ,
A further point against the single-cylinder tractor which is brought forward is that its construction naturally leads to a heavier machine. This, to a small extent may be true, but may I point out that the present vogue for pneumatic tyres on the light types of tractor involves their being fitted with special heavy-section cast-iron wheels, which is doubtless done to improve wheel adhesion. Surely this fact contradicts the inference that extra weight, in a reasonable quantity, is undesirable.
The author also makes a number of unsupported and rather loose statements which are difficult to understand, regarding the need for "certain ground conditions." I can definitely say that I have personally seen a number of clear demonstrations where the singlecylinder type of tractor has proved its superior wheel grip under wet and bad conditions over the lighter type of four-cylindered paraffin tractor. This is in direct contradiction to his statement.
He mentions also that the four-cylindered engine is more flexible than the single-cylindered. I take it that by flexibility he means the ability of the machine to deal equally well with light or heavy loads., but it is difficult to um d.erstand Wh y a four-cy Ender ed engin e should be better in this respect than a single-cylindered type Surely, provided the combustion under varying conditions of load be correct and good governing he employed, no advantage would be obtained by a multiplicity of cylinders. It should be noted that in comparing the siugle-cylindered oil engine with the four-cylindered paraffin type, the probability is that in this case the single-cylinder is much more suitable foe dealing with a greater range of loads.
From a maintenance point of view, the suggestion that the much simpler engine holds no advantage will not bear examination.
In conclusion, I would beg to say that in my opinion the single-cylinder oil-engine.d tractor, as at present marketed, not only provides the good features detailed at the commencement of this letter, but is also capable; of better wheel adhesion and superior steady pulling power at all loads than the average type of four-cylinder paraffin machine. E. BURGESS. Gainsborough.
[In fairness to our contributor, we have submitted the above letter to him, so that his reply could be published in the same issue. Below he offers his comments.---ED.]
OUR CONTRIBUTOR DEFENDS THE MULTICYLINDERED ENGINE.
[509'31 .Having carefully read Mr. Burgess's comments on the article "One, Two, Three, Four or Six? " and re-read the article, I am not disposed to modify any of the opinions originally expressed, since they represent conclusions arrived at after practical experience in the field and in the driving seat, which commenced about 15 years before the first modern tractor of the type with which Mr. Burgess is assoeiated appeared.
Figures obtained at tractor trials regarding wheel adhesion are necessarily taken under " standard " ground conditions, fairly firm and dry, and do not reveal the effects of uneven torque at the rear wheels displayed by single-cylinder tractors. On yielding, soft ground the " snatchy " grip tears the soil from under the tractor and brings about slip and. sinkage, accentuated by excessive weight.
I did not refer to the additional tractive' resistance which becomes apparent on wet and uphill land, when the over-weighted tractor of the single-cylinder type is
in question. Mr. Burgess must, however, be conscious of this problem, as he eagerly seizes the advantage of
pneumatic tyres in reducing tractive resistance. Even here the system of adding weight is probably only a passing phase. Adhesion with reasonably weighted tractors can be secured without excessive weight by the use of strake attachments, chains and large-diameter tyres.
Regarding maintenance, I would point out that it is not only a question of the ease of a simple overhaul.
Single-cylinder machines are undoubtedly sensitive to carbon deposits and other causes of "loss of tune," and overhauls are comparatively frequent. The problem, however, extends to power-driven machines, such as power binders, which may, and do, suffer badly from the effects of a rough single-cylinder drive, which may cost many pounds in a season.
Space does not permit dealing witir all the arguments brought forward, but they suggest one or two queries.
If the big single-cylinder industrial engine is all that is claimed for it, why are so many firms producing multicylinder oilers for this purpose, and why are so many users thankful to change over to electrical equipment?
If such a unit is so excellent for the tractor, why are only two mares of agricultural tractor out of 20, as
shown by The Commercial Motor buyer's guide (May 21, 1937), so equipped, seeing that all the world's best-selling tractors are represented in this?
Finally, why, if such confidence be felt by its designers in the performance of this type of machine, is there no tractor of the make in question entered for the forthcoming R.A.S.E. trials? The user. however, always has the last word, and the one thing he will not have, on most land in this country, is excessive weight. Because he is agriculturally and in an engineering sense correct, no efforts from the drawing
board will convince him otherwise. D.N.Mc1-1. Hatch End.
PROS AND CONS OF FORWARD AND NORMAL CONTROL.
1.50941 I have read recently in your periodical an article dealing with the use of rear engines in horseboxes, which, apparently, are to ensure the comfort of the animal. Nobody seems yet to have considered the discomfort of the driver of the forward-controlled commercial vehicle, for whom engines at the rear or the side would be a tremendous boon.
Those who test new lorries have no knowledge of the position of the driver. There is usually no cab, hence plenty of fresh air and freedom from excessive heat are ensured. There are no leaking exhaust-manifold joints in the new engine to cause drowsiness and fumes which attack the health of the driver and sap his vitality.
But the discomfort to the driver does not form the only disadvantage of the forward control lorry. The whole idea of cramming so much body space on to so short a wheelbase is, in my opinion, to be condemned, as it leads to many difficulties, such as overloading of the front axle—resulting in excessive wear of the tyres. This is still more marked when the wheels are fully locked, especially on soft ground.
If the load be unevenly distributed, with more weight at the front than behind, it is the forward-control ir16 vehicle which feels the resultant stress more. . The adhesion of the driving wheels is then considerably reduced, which disadvantage is again most noted on soft ground.
In my opinion the development of forward-control lorries is taking us back 30 years to the days of the tractor, except that we are pushing the load now instead of pulling it. A wheelbarrow is perhaps no comparison but try to push one over a kerb or something similar, and you find eventually that it, is far wiser to save your energy by pulling it.
I would like to compare the forward-control lorry with, say, the Leyland R.A.F.-type vehicle. The advantages of the latter in efficiency are tremendous; with its forward-pLsitioned engine and the driving axle almost midway along the body, it can handle its load, with a trailer if necessary, in a way impossible to the forward. control type. Some of the lighter class vehicles have a similar advantage. G.S.E. Winchester.
MORE ON VEHICLE-RUNNING RECORDERS.
[:$095] The letters of your correspondents on the subject of vehicle-running recorders are of exceptional interest to me—one of the lesser cogs in the transport industry—as I have had the unpleasant experience of laboriously checking through the discs removed from such devices and comparing them with drivers' timesheets. They certainly serve as an effective check on the movements of vehicles so far as the directorate is concerned, but I.have yet to hear of the driver who has been sanctioned by his employers to produce one of these tell-tale discs in court to substantiate his statement that at no time during the day did he ever exceed the legal limit, when he may have been summoned for doing, say, 23 m.p.h. I am now maintaining and keeping these instruments in order, and if Mr. H. Richards has any conception of what this exactly means with a mixed fleet, he, no• doubt, would be able to understand Mr. J. Walton's objection. I wonder if Mr. Richards could name a single haulage company which extensively uses time recorders, and which could produce a disc after a day's journey that would not " hang " the company as well as the driver?
The arguments in opposition I have heard dozens of times, but why rush into print doubting .others' abilities, for, after all, we are sometimes rather apt to overrate ourselves, even those in the most humble
capacity. FOREMAN -MECHANIC. Southampton.
CARRYING BUILDER'S MATERIALS UNDER CONTRACT.
[50981 As a builder's merchant, I wish to obtain the services of a haulier. I purchase builder's materials for a large contractor, who also requires me to haul bricks for him from a local brickyard. The bricks be buys direct from the manufacturer. Am I entitled to ask the haulier to do this work on a Contract A licence?
Warrington. MERCI3.ANT.
[The haulier cannot carry the materials which pia supply to the contractor, and the bricks which he buys direct, under a Contract A licence. If the contractor purchased the bricks through you, the whole of the materials could be conveyed by your haulier under a contract licence. The contract would have to be with you, personally, for at least a year, and the. vehicle or vehicles employed would have to be wholly engaged on your work.—ED.i