Aerodynamic investigation of the inrun position in Ski jumping.

This study aims to investigate the inrun position in ski-jumping, in search for factors increasing the inrun speed without compromising the take-off. The inrun position of eight World Cup (WC) and fifteen Continental Cup (COC) ski jumpers were investigated in a wind tunnel at NTNU. A preferred position, replicating a jumper's position in competition, was measured for each athlete. Improvements, based on common sense aerodynamics, with the aim to improve the aerodynamic drag were executed. The aerodynamically best of these was compared with the preferred position. A numerical model simulating the inrun speed in ski-jumping hills was used to evaluate the impact the results will have in different hill sizes, for comparisons of drag measurements and inrun speed in competitions. In the preferred position, COC had 15.5% higher drag area than the WC athletes. In their best tested position, a group difference of 10.8% was found. These differences correspond with speed differences between 0.4 and 1.3 kmh, or 1-3 gates (as found by the numerical model). Group difference in drag was explained by a larger trunk angle for COC. Both groups improved from their preferred to their best position, due to reductions in thigh and leg angle.