ABSTRACT
The database for the aerodynamic forces of ski jumping measured using a real sized model in a wind tunnel is now available (Seo, et al, 2004a), and it was used in the jumping flight optimization study (Seo, et al., 2004b). However, the aerodynamic forces for the initial phase of a jumping flight immediately after a take-off could not be measured in our previous wind tunnel tests due to some experimental difficulties. In the initial phase, the ski-body angle is normally very large and rapidly changing from about 90 deg., which brings about a technical problem that the blockage rate in the test section of the wind tunnel becomes too large, as well as the difficulty in the wire support method of a jumper model. Therefore, the aerodynamic force data during initial 1 sec after take-off are the very target of this study. It is also the purpose of this field measurement to investigate whether the unsteady aerodynamic forces are of importance for ski jumping flight, because in the initial phase the skibody angle changes rapidly and in a wide range from about 90 deg. to about 30 deg. In this study as part of a series of researches, we focused on the improvement of the computation procedure for the time series data. In fact, the original time series data include various kinds of noise, and the target aerodynamic data seem as if they are buried in the noise after the straightforward application of numerical differentiations. Therefore, introduction of numerical filtering and curve fitting based on regression analysis is inevitable for meaningful result.
2 Field Measurements
