Brake Tests

198 For a fair comparison with point“ B ”No.3 clasp brake this per cent, brak- ing power should have been C X 1.40=147.5 per cent. Point C, corresponding to a braking power of 147.5 per cent, with the No. 2 clasp brake and best stops, indicates that the stop should have been about 975 feet. The difference between this stop and that represented by point “B,” namely 975 feet—873 feet or 102 feet, is believed to be tlie fairest comparison which can be made of the best stops from sixty miles per hour with these two types of brake rigging at a nominal braking power of 150 per cent. Estimated Train Stops, No. 3 CLASP BRAKE. 405. The various types of car brake rigging used during the tests were applied to the twelve (12) cars of the test trains, with the exception of the No. 3 clasp brake rigging. The No. 3 clasp brake was applied to but one car and all tests made in connection with this rigging were single car breakaway stops. It was desired to make the data of these tests comparable with the tests of other types of brake rigging. In order to do this it would be necessary to compute the probable twelve car train stops of the No. 3 clasp brake from the data of the actual single car breakaway stops. With this object in view a series of separate locomotive tests were made in order to accurately determine tlie per- formance of the locomotive for the purpose of such a computation. 406. When the electro-pneumatic equipment is used the following method may be employed for calculating the probable stop of a train of any number of cars and locomotive when tlie length of stop and weight of a single car and the locomotive are separately known. This method of combining the separate locomotive and single car stop data in order to compute the probable train stop is not absolutely accurate because it does not take into account the difference between the time elements of the brake action on the locomotive and on the cars. This difference, however, is very slight, its effect amounting to about three feet in the computation of a 1,000 feet stop and has therefore been neglected with the result that the formula developed is very simple and convenient to apply. Let W. = weight of train, locomotive and cars. W1 = weight of locomotive. Wc = weight of a single car. V = initial speed in m.p.h. St =length of stop of train in feet. S. = length of stop of a single car in feet. Si = length of stop of locomotive in feet. Ft = average retarding force for entire stop of train. Fj = average retarding force for entire stop of locomotive. Fc = average retarding force for entire stop of a single car.