. The science of railways . in miles head pr hr. In ft. pr hr. in ft. 10 28 27 83 11 29 12 30 13 31 14 32 15 33 16 34 17 10 26 35 43 49 18 36 19 37 20 38 21 39 22 40 23 41 24 42 62 62 25 43 26 44 68 73 27 45 580 APPENDIX H. The engine tractive power is least at high speed and shortcut off, and greatest at low speed and full stroke, asshown in Fig. 1. The mean tractive power of these engines from differentrates of spee
. The science of railways . in miles head pr hr. In ft. pr hr. in ft. 10 28 27 83 11 29 12 30 13 31 14 32 15 33 16 34 17 10 26 35 43 49 18 36 19 37 20 38 21 39 22 40 23 41 24 42 62 62 25 43 26 44 68 73 27 45 580 APPENDIX H. The engine tractive power is least at high speed and shortcut off, and greatest at low speed and full stroke, asshown in Fig. 1. The mean tractive power of these engines from differentrates of speed to ton miles per hour is given by the tablefollowing Fig. 1, or may be deduced from the diagram. The maximum available power for overcoming rolling andgrade resistance is represented by the product of the trainweight and its velocity head, added to the product of the meanengine tractive power, and the time or distance over whichthe power is exerted, illustrated, in short, in the effectproduced by taking a run at the U if MIL a 30 KK it HQUf « 41 W Fig. 3. DIAGRAM OF TRAIN RESISTANCE IN POUNDS PER TON.(From A. M. Wellington s Railway Location.) i APPENDIX E. 581 Rolling tesistance for trains at all speeds is given by Fig. 3,from which mean resistances between different rates of speedmay also be readily computed. The simplest rule for computing grade resistance is as fol-lows: Resistance (in lbs. per ton) = rate of grade (in feet)X 20. A gradient of equivalent resistance to the force exerted bythe engine is the virtual grade, or real resistance taxingthe engine cylinders. The virtual grade line may be plottedwith the assistance of Figs. 1, 2 and 3, or computed in accord-ance with the general principles before given. Momentum or velocity grades may be used with duecaution to avoid increasing rate of ruling grades, or to avoidlarge construction expenditures otherwise necessary. In allsuch cases train stops, grade crossing and limiting or dan-gerous curvature must be avoid
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