. Railroad construction. Theory and practice . 7 42 43 44 45 46 47 48 83 29 49 50 89
. Railroad construction. Theory and practice . 7 42 43 44 45 46 47 48 83 29 49 50 same draw-bar pull. At A its ^S^elocity head is that due to 30miles per hour, or feet. At B it has gained 40 feet more,and its velocity is that due to a velocity head of feet, orslightly over 45 miles per hour. At B its velocity is again 30miles per hour and velocity head feet. At C the velocityhead is but feet and the velocity about miles per hour. 464 RAILROAD CONSTRUCTION § As the train runs from Cto D its velocity increases to 30 miles atC and to over 45 miles per hour at D. At E the velocity againbecomes 30 miles per hour. Although there will be some slightmodifications of the above figures in actual practice, yet the aboveis not a fanciful theoretical sketch. Thousands of just suchundulations of grade are daily operated in such a way, withoutdisturbing the throttle or applying brakes, and the draw-barpull, if measured by a dynamometer, would be found to bepractically constant. Of course the above ease assumes that Actual profile Fig. are no stoppages and that the speed through the sags isnot so great that safety requires the application of that the virtual profile is here a straight line—as italwa3^s is when the draw-bar pull is constant. The virtualprofile (in this case as well as in ever}^ other case, illustrationsof which will follow) is found by adding to the actual profilea
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Keywords: ., bookauthorwebbwalt, bookcentury1900, bookdecade1900, bookyear1903
