A Question of Adhesion.
Page 14
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The Editor, THE COMMERCIAL MOTOR.
[1565a] Sir,—In your issue of 21st October you show a photograph of the Knox tractor hauling a 33-tun boiler on an 8-ton truck, and in the caption you say "our readers will remark the lack of adhesion on the back wheels." I do not think you intended to convey the impression that this remark gives.
The photograph does not show any lack of adhesion, and we are informed there was none, Perhaps you are misled in this by the sloping tilt of the revolving platform of the tractor, this being purposely tilted.
It may be of interest to your readers to know that the truck carrying the boiler was purposely hooked on the way it was, with the shaft sloping upward, raised high upon the rear of the tractor over a heavy weight and then chained to the frame: the result is that the driving wheels of the tractor are held down to the ground just as much as though there were a considerable load above the driving wheels. The principle is really the same as that demonstrated a few years ago at the Yorkshire Horse Show, where a firm showed a horse-drawn vehicle whereon
B44 the shafts were placed very low down, but just enough to clear the floor, and by having the shafts brought up on a steep slope, the horse was enabled to exercise much greater pulling power than when the shafts were placed horizontally.—Yours faithillily, CHAS. H. FRYER. 11, Southampton Row, W.C.
[Our criticism of the illustration to which Mr. Fryer refers was in no sense intended as disparaging, since we, from practical knowledge, have considerable respect for the Knox tractor ; it was nevertheless based on what appeared to its to be reasonable hypotheses ; moreover, we had allowed for the peculiar feature of inclined towing shaft, which can have but a small effect OD the weight available for adhesion, as the following calculation, which is, from the nature of things, very rough, will show. The slope of the tow-bar appears to be about 1 in 5; the total load behind it is roughly 40 tons, and assuming a road-resistance of 100 lb. per ton, this gives a pull in the bar of 40 x 100 = 4000 lb., the vertical component of this equals 800 lb., an amount of very little real significance, since it could easily be applied more directly.—En.]