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SOME INTERESTING BRAKING EXPERIMENTS.

31st December 1914
Page 15
Page 15, 31st December 1914 — SOME INTERESTING BRAKING EXPERIMENTS.
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Which of the following most accurately describes the problem?

We have to hand an interesting exclusive report of some brake tests carried out on a five-ton lorry in the United States.

The method employed was as follows : A hill having a fairly uniform gradient was selected, arid the wagon allowed to coast down between two marked points, the speed attained by the time the second point was reached being about 15 miles per hour. The brake was then applied, the distance required to pull up in measured, and the brake power deduced therefrom. From calculations based on the results of these experiments the following conclusions were drawn : The greater the area of the brake shoe, the shorter the distance required in which to pull up ; actually the stopping distance varied immensely as the square root of the brake surface. The area should also be sufficiently large to provide for a heat dissipation of not more than 50 B. J'.13. per square inch per minute. For the benefit of our non-technical readers, we might mention that this is equivalent to a stopping power of about 1 h.p. per square inch of brake surface, and that the power required to pull up a five-ton lorry, moving at 15 miles per hour, on a 10 per cent. down grade, and. in a length of 55 ft., is 80 h.p. The brake area necessary for a. lorry of this size is therefore 68 sq. ins. minimum. Another interesting fact which came to light was. that referring to the co-efficient of friction between tire and road, tho figure for this being .25 on a good. limestone Macadam surface.

These data were obtained in America by Mr. H.. Kerr-Thomas, of the Pierce-Arrow Co.

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