Biomechanical study on the postural control of ski-jumping : Focused on the second half of the flight phase

The goal of the flight phase in ski jumping is to get the best posture to maximize the flight distance. We focused on the second half of flight for discussing the relationship between the kinematical data from the field study and the aerodynamic data from the wind tunnel experiment. The two jumpers were selected, F.K. and A.S. in FIS Grand Prix (2000/8/26, Hakuba). Using the pan & tilt video system for 3-D motion analysis (PEAK Co.Ltd.), we filmed the posture in the second half of flight (from 64% flight to landing). The variables of attack angle (α), shank-ski angle (θ), trunk-thigh angle (σ) and ski-ski angle (λ) were measured. A full size ski-jumper model was mounted in the 3m low speed wind tunnel with the wind speed of 20 or 25 m/s. The lift, the drag and the pitching moment were measured. In this study, differences of motion in the same V jumping techniques were demonstrated between the two jumpers. The both jumpers changed the flight position 0.6s before landing. The average angles from the flight position to 0.6s before landing were shown as follows: F.K.; α=35.3°, θ=28.1°, σ=14.0°, λ=26.0°. A.S.; α=34.3°, θ=27.6°, σ=16.9°, λ=21.0°. From these results, σ was set as 14.0° and θ was set as 28.1°. When λ was 38.0°, the polar curve reached to the maximum. When increasing λ, the pitching moment decreased. Therefore it was reported that the best ski-ski angle was 38°. The more opened ski-ski angle should be recommended to these two jumpers for getting the better flight, still the nose down pitching moment will effect negatively to jumpers