Effects of lifting the outriggers on aerodynamic drag and skiing time in the para-alpine sit-ski

Abstract

　The present study of para-alpine sit-skiing was conducted to investigate the degree to which aerodynamic drag could be reduced and skiing time shortened by lifting one or both of the outriggers forward. For this purpose, the aerodynamic forces on 4 sit-skiers were measured in a wind tunnel while adopting 3 positions: Normal position with both outriggers placed down the body side; One side lifted with the outrigger forward; Both sides lifted with the outriggers forward. Furthermore, skiing simulations were run on the basis of the results obtained.
　In the wind tunnel test, drag areas were 0.360 ± 0.024 – 0.364 ± 0.030 m² in the normal position, 0.307 ± 0.029 – 0.318 ± 0.037 m² in the one-side lifted position, and 0.229 ± 0.026 – 0.239 ± 0.029 m² in the both-sides lifted position. Thus, compared with the normal position, aerodynamic drag was reduced by approximately 15% by lifting one of the outriggers forward and by approximately 35% by lifting both outriggers forward. Both projected area and drag coefficient were especially reduced by lifting both sides. It was considered that this decrease in aerodynamic drag resulted from the smaller projected area of the arms and outriggers, and the change in the overall attitude of the skier to a shape less sensitive to aerodynamic drag.
　The results of the skiing simulation revealed that, in comparison to the normal position, skiing distances of more than 34 m in the one-side lifted position and more than 21 m in the both-sides lifted position were needed to shorten the time by more than 0.01 s. As time is measured in units of 0.01 s for para-alpine skiing, it was considered that if skiers cannot lift one or both of the outriggers forward for longer than those distances, skiing time would not be shortened. On the other hand, if one considers the compressed skiing times classified according to the degree of skier impairment in para-alpine skiing, the effects of lifting the outriggers forward on skiing time would also be compressed according to sport class. Therefore, it is necessary to decide whether lifting the outriggers forward or not according to skiing distance and skier class would be justified.