. The trackman's helper, a handbook for track foremen, supervisors and engineers . that trains running sixty miles per hour willpress laterally against the outer rail, and if this pres-sure be great it may throw the track out of line orspread the rails. On the other hand, with trains run-ning only twenty miles per hour the weight would begreatest on the lower rail, and while it would tend todepress the rail still more, and perhaps develop swingswhen the ballast is weak, it would not spread thetrack. Effect of speed on elevation. The elevation neces-sary on curves depends on the speed and on th
. The trackman's helper, a handbook for track foremen, supervisors and engineers . that trains running sixty miles per hour willpress laterally against the outer rail, and if this pres-sure be great it may throw the track out of line orspread the rails. On the other hand, with trains run-ning only twenty miles per hour the weight would begreatest on the lower rail, and while it would tend todepress the rail still more, and perhaps develop swingswhen the ballast is weak, it would not spread thetrack. Effect of speed on elevation. The elevation neces-sary on curves depends on the speed and on the de-gree of curve. For instance, if a four-degree curve re-quires 7 inch elevation for speed of fifty miles perhour, for a speed of twenty-five miles per hour it wouldrequire not 31/2 inches but only 1% inches to balancethe weight of trains. This may be illustrated by A weight B is suspended from a rigid support S bya cord A. By giving the weight a circular motion itwill describe a circle C around a center E, and theangle of the cord A B will show what elevation would. ^^L^lCyjci^ Fig. 44. Effect of Speed on Elevation of Curves228 ELEVATION OF CURVES 229 be required if the circle C were a track in order to dis-tribute the weight of B if it were a car bearing equallyon both rails at a given speed; that is, the level of therails should be at right angles to the line S B to givethe curve the proper elevation for the rate of speedat which the weight B moves around the circle. Sup-pose that circle C represents a four-degree curve andthe inner circle D. with but half the radius of C, repre-sents an eight-degree curve. Now, if the weight Bmoves around the outer, or four-degree, curve, in sayfour seconds, it will revolve in continually decreasingcircles, but always in the same period of time, and willmove around the inner circle, or the eight-degree curve,in four seconds also. But the inner circle being butone-half the circumference of the outer, it follows thatthe speed of th
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