Opinions from Others.
Page 21
If you've noticed an error in this article please click here to report it so we can fix it.
r Ise Editor invites correspondence on all sabjects connected with the use of consmer:ial motors. Letters should be on one side of the peePer only, and type-written by preference. The right of abbreviation is reserved, and no responsibilety For views expressed is accepted. In the case of eaberiences, names of towns or localitie,s may be withheld.
Are Tractors Too Powerlul ?
The Editor THE COMMERCIAL MOTOR.
[1282] Sir,—The letter of " Ilepluestus " [No. 1279] in your issue of the 4th December is ot very great interest, but, on reading it, I am unable to trace any answer to the query causing this correspondence. " Hephsestus " is evidently interested in the manufacture of steam tractors, and. it is a little unreasonable of him to try to gloss over the faults of this method of haulage by the suggestion of the use of sackcloth and ashes to prevent the driving wheels of tractors slipping.
" Hephsestus " does not see what appreciable benefit will be gained by inclining the drawbar as suggested. I have many times made use of the sacis trick, but the difficulty of the use of same is increased from the fact that the sack is only brought into use after the slip has taken place. At any rate, the suggested use of a sack by " Hepluestus " shows how very small is the extra increase of adhesion required to prevent the wheels of a tractor from slipping in greasy circumstances. The suggested slight increase of adhesion by an inclined drawbar is a prevention. " Hepluestus " with his sackcloth only suggests a cure. Owners know which is the better of the two.
I would point out that, the 4.3 per cent. increase of adhesion, being automatic sand progressive in relation to the increased incline and resistance, makes say suggestion far more practicable and of a much higher value than his suggestion of "a piece of sacking repeatedly thrown under the driving wheels." Will " Hephsestus " please say how many yards a piece of sacking 3 ft.. by 2 ft. will take a five-ton tractor up an incline of, say, 1 in 4 with his abnormal total load of 12 tons ? Of course, any suggestion may become inappreciable, if only normal figures are taken, but from the first, I have maintained that, to overcome the slip of tractor driving-wheels, almost an inappreciable increase of weight is required. I would venture to point out that an 5 ft. drawbar length is unnecessarily long, and that a resistance equal to an incline of 1 in 6, and a tractive force figure of 112 lb:, cannot be taken as constants. Given these constants, my point is that the slightest increase of adhesion will give the required grip, and that the greater the draught the greater—with my suggestion— tile adhesion, i.e., the 4.3 per cent. adhesive increase may be more than enough to prevent the driving wheels from slipping. Further, if the draught is increased, the adhesion automatically increases. It might be possible, by redesigning the trailer forecarriage, to obtain a drawbar angle of, say, 45 degrees, in which circumstances the increased weight on the driving wheels on the level, where the driving wheels are not so likely to slip, is increased by as much as S per cent. On a gradient of 1 in 6, an increase of as much as 24.6 per cent. would be obtained with an eight-ton load and a five-ton tractor.
Mr. Wedgwood's suggestion of increasing the inclination of the drawbar by attaching same higher up the tender would have the effect, as has already been pointed out, of increasing the lift on the front axle of the tractor—an undesirable result.
Finally, "Heplisestns " will acknowledge that quite a, small increase of adhesion will prevent the slip of tractor driving-wheels, and that –with my suggestion with an abnormal load of 12 tons as suggested by him, with a quite-possible drawbar inclination of 1 in
drawing this load up an incline of 1 in 6, the per centage of increase of weight on the driving wheels would be as much as 8.7 per cent.—a very -useful per
centage of increase of adhesion when we know that even a piece of newspaper placed under smooth-tired wheels 5 ins, on the face. and 3 ft. 6 ins, in diameter, with a three-ton axle-load, has prevented the wheels in question from slipping on a wet asphalt surface. - Yours faithfully, T. C. AVELINO. 91, New Canal Street, Birmingham.
The Editor THE COMMERCIAL MOTOR.
[1283] Sir,—Re letter No. 1275, Mr. Aveling's. Since his suggested drawbar is attached to the outer extremity of the main axle, which must increase some inches the overall width, a condition not to be desired, and since it would have to be negotiated in getting on and off the tractor, I repeat that it would be a nuisance.
I fail to see where I try to improve on his suggestion • in fact, I consider my ideas are quite opposed to Ar. Aveling's. He. says the problem is to get the weight of the trailer transferred to the driving wheels of the tractor without altering the design. If you would be good enough, Sir, to reproduce my drawing and to show this second time a very important point which was eliminated in your last reproduction, it will be seen that I accomplish this. We have pleasure in doing so.—En.] I refer to the arrow pointers which show the pull down at back and lift at front of tractor ; the main axle, becoming the fulcrum, receives as extra tractive force twice the weight taken from front of trailer. Example: If the downward pull at back of tractor is, say, 10 ewt., the extra weight to the point of contact at driving-wheel is approximately one ton, and, as the load increases, this tractive effort improves, whereas Mr. Aveling's suggested drawbar pull from main axle direct always remains the same.
As to alteration of design, this need be very little indeed; the third gear, surely, is common enough, but I maintain that it ought to be an extra-slow speed, instead of an extra-high one—which, by the way, has often been the cause of trouble when brakes have given out. It is significant that " Agricola's " letter, appearing in the same issue as my last, coincides with mine absolutely.
My suggestion is the verified result of having had often to deal with very heavy indivisible loads with a limited weight of tractor. It would, indeed, be interesting to hear what some of our manufacturers have to say on this important matter. It is regrettable they do not appear to appreciate the fact that those who have to _earn their living with the instruments they (the manufacturers produce know just a trifle about what is wanted.--Yours faithfully,
Cobridge, Staffs. ARTHUR WEDGWOOD.