. The Street railway journal . ovement is for an infinitely small period,an infinitesimal turning movement of the entire wheelabout the point A may be substituted for the rolling mo-tion. It then becomes clear at once that all points on thecircumference to the left of A must have an upward move-ment and all points on the right a downward set of points, therefore, is adding load and the otherlosing load in proportion to the distance from A. Fromthis it follows that the pressure resultants of the rail sur-faces no longer will be at A, as in the case when the wheelis at rest, but the
. The Street railway journal . ovement is for an infinitely small period,an infinitesimal turning movement of the entire wheelabout the point A may be substituted for the rolling mo-tion. It then becomes clear at once that all points on thecircumference to the left of A must have an upward move-ment and all points on the right a downward set of points, therefore, is adding load and the otherlosing load in proportion to the distance from A. Fromthis it follows that the pressure resultants of the rail sur-faces no longer will be at A, as in the case when the wheelis at rest, but they will pass through a point on the rightwhich can also be obtained by finding the resultants ofthe wheel pressure and the horizontal force driving thecar forward. It is easy to find the approximate course ofthe curve in this instance through the knowledge gainedthrough a study of the longitudinal section of the contactsurfaces shown in Fig. 2. It must form part of a para-bolic curve of such type that c is the largest and b the. ) FIG. 3.—DIAGRAM OF WHEEL AND RAIL RESULTANTS smallest radius of curvature, which almost correspondswith the radius of the wheel. To secure experimental verification of the foregoing,the model wheel was turned and instantaneously photo-graphed. The result, which is shown in enlarged form inFig. 4, proves what has been said about the shape of thecurve of contact. The same form is shown by the longi-tudinal section of actual corrugations. Besides the pure rolling movement the average car wheelalso slides occasionally, notably during the period ofmaximum braking, when the kinetic energy of the carpushes it forward. In this case there is no longer anydifficulty in conceiving the appearance of the contactcurve. Owing to- the horizontal reaction of the rail ma-terial a pressure is produced on the front half of the wheeltire which is grasping the rail so much as to tend to flattenit. The curve, therefore, corresponds to the one for thestationary wheel, excep
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
