Ice friction in the sport of bobsleigh

Abstract

The primary objective of this work is to examine the effect of the bobsleigh runner profile on ice / runner friction. The work is centered on a computational model (F.A.S.T. 3.2b) which calculates the coefficient of friction between a steel blade and ice. The first step was to analyze runners used in the sport of bobsleigh. This analysis was performed using a handheld rocker gauge, a device used in speed skating. The size of the device was optimized for hockey, short and long track speed skating, and bobsleigh. A number of runners were measured using the gauge and it was found that the portion of the runner contacting the ice generally has a rocker value of (20 - 50) m. Next, the hardness of athletic ice surfaces was analyzed. The ice hardness was determined by dropping steel balls varying in mass from (8 - 540) g onto the ice surface, from a height of (0.3 - 1.2) m, and measuring the diameter of the indentation craters. The ice hardness was found to be P(T) = ((-0.6 ± 0.4)T + 14.7 ± 2.1) MPa and the elastic recovery of the ice surface was found to be negligible. The F.A.S .T. model was adapted from a speed skate model to calculate the coefficient of friction between a bobsleigh runner and a flat ice surface. The model predicts that maximum velocities are obtained for temperatures between -10 and -20°C, in agreement with observations on the Calgary bobsleigh track. The model for flat ice suggests that the flattest runners produce the lowest coefficient of friction and that the rocker affects friction more than the cross-sectional radius. The coefficient of friction between runners and ice and the drag performance of 2- men bobsleighs were determined from radar speed measurements taken at the Calgary Olympic Oval and at Canada Olympic P ark: at the Ice House and on the bobsleigh track during a World Cup competition. The mean coefficient of friction was found to be ? = (5.3 ± 2.0) x 10- 3 and the mean drag performance was CdA = (0.18 ± 0.02) m2 .