Runner design in bobsleigh engineering is still based on empiric data and experience from geometry and material field testing. There are few approaches to examine the interaction of runner and ice in literature (Hokkirigawa, 1998 and 2002). This is surprising as the runners play a major role in total performance of a bobsleigh team (Morlock 1989). Data about forces, vibration frequencies and induced stress and strain states are needed. In this study the contact force between runner and ice for a 2-men bobsleigh on the track of Koenigssee, Germany was determined. Methods Triangular strain gages were chosen for the instrumentation of the bobsleigh runners. The sensors were mounted close to the running surface onto one side of each of the 4 runners (Fig. 1). The sensor location was optimized in laboratory experiments by applying a point load to the surface of the runner using a compression testing machine. Linear strain gages were mounted on both sides of the runners for temperature compensation. The axis of the bobsleigh were instrumented by strain gages to measure the bending of each axis. The value of bending of each axis corresponds to the normal force applied to the runner. The runners were mounted back to the bobsleigh and data were acquired during a normal run (total time was about 50s). Normal acceleration of the bobsled could be determined by calculating the sum of the 4 bending forces and dividing it by the static weight of bobsled and crew. On-board instrumentation consisted of amplifier, mobile data logger and energy supply. Precautions were taken for the stabilization against accelerations of more than 10g. Temperature resistance down to -30°C was assured. 48 strain gages were measured simultaneously at two frequencies (100 Hertz and 2400 Hertz). 32 runs were recorded with different pilots and bobsleds. The location of force induction into the running surface was determined by geometrical interpretation of stress and strain states. Results Data were in very good agreement with the course of the bobsleigh track. The prominent points of the bobsleigh track could be reproduced very well by the distribution of normal forces (Fig. 2). It could be calculated that, during the run, a maximum of normal acceleration of sixfold gravity is applied to bobsled and team. For a 4-men bobsleigh this means a maximum load applied to each runner of 9000N. There was no significant change of temperature in the runner bulk material detected. It was found that impacts mainly affect the front third of the runner. An instrumentation of bobsleigh runners has been presented for measuring the contact force between runner and ice. Results show that loads of 9000N and impacts are applied to the runners during the run. It is recommended to improve the flexibility of the runner. This will reduce plastic deformation of ice and frictional resistance. In return, a hange in flexibility will affect the vibrating system and new measurements will be needed.
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