. Train resistance : a consideration of its elements and a discussion of experiments made with the university dynamometer car . car is approximately 9 feet by 9 feet,and the pressure ofa head wind on this is 81F in which F is an average pressure persquare foot. Now if this same wind was blowing at an angle of 45degrees it would produce a presstire of F on the head end,and inaddition to this a pressure of 25«4/r for every opening between twocars; therefore a wind blowing at an angle of 45 degrees with thetrain produces, for every three openings between cars,a resistanceabout equal to the h
. Train resistance : a consideration of its elements and a discussion of experiments made with the university dynamometer car . car is approximately 9 feet by 9 feet,and the pressure ofa head wind on this is 81F in which F is an average pressure persquare foot. Now if this same wind was blowing at an angle of 45degrees it would produce a presstire of F on the head end,and inaddition to this a pressure of 25«4/r for every opening between twocars; therefore a wind blowing at an angle of 45 degrees with thetrain produces, for every three openings between cars,a resistanceabout equal to the head resistance produced by the same wind deadahead. These statements neglect friction along the sides of thecars and the effect of the numerous counter currents which alwaysexist,but we can see that for an ordinary train a wind blowing atan angle of 45 degrees may produce four or five times as much resist-ance as the same wind dead ahead. Wind also has another effect when blowing against the sideof a train. The flanges on the leeward side are crowded againstthe rail thus increasing flange friction. This increased flange. 24 friction is partly balanced by the effect of more than half theweight being thrown on cne rail,which is to decrease rolling frictioij. The amount of the air resistance is involved in much doubt,as was already indicated. Wellington estimates the air resistanceagainst the end of a box car as less than tv/o tenths of a pound persquare foot for a velocit3 of ten miles per hour and increasing(presumably) as the square of the velocity. In the Purdue experi-ments the air resistance for passenger or freight trains was foundto be represented by the formula, A= (L+347)y2in which Z. is the length of the train in feet, r the velocity inmiles per hour. This formula gives a resistance of about poundsper ton for a twenty-car train of empty box cars having a velocityof forty miles per hour,and pounds per ton for loaded box cars. The general conclusion to be
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