INTRODUCTION: A ski jumping flight phase can be divided into a transitional phase (approximately 17m behind the take off table), a literal flight phase, and a ground approaching phase. We investigated the first two. The transitional phase is characterized by a high angular momentum (nose down), while the flight phase is characterized by a low angular momentum. Virmavirta et al. previously discussed an "early flight phase," but without angular momentum. METHOD: We analyzed the motion characteristics of a) six combined Nordic national athletes (90m hill, Oberwiesenthal), and b) 14 international athletes (125m hill, Oberstdorf). To obtain data regarding body and ski angles, velocity of centre of mass (CM), angular momentum about CM, force momentum, resistance, and lift coefficients, we used two pan, tilt, and zoom Video cameras in case (a); and owing to circumstances six fixed cameras in case (b). The letter coefficients were computed reversing the flight equations in terms of CM. The CM was obtained by a Zaziorski body model including the Parameters of ski, helmet, and footwear. RESULTS: The angular momentum, achieved during take off, declined as long as the air stream struck the skis from above, then it increased until the athletes adopted the flight posture. For the ski jumpers the minimum of angular momentum ranged from -21,5 to -13,3kgm2/s, horizontal velocity ranged from 25,8 to 26,5m/s and absolute vertical velocity was app. -3,1m/s. However the same parameters of the six combined Nordic athletes ranged from -19,7 to -8,8kgm2/s, 24,5 to 25,2m/s, app. -2,6m/s, respectively. DISCUSSION: The results regarding the transitional phase have shown to be repeatedly inconsistent for the derivation of the force momentum after lift. These inconsistencies cause the flight to be unstable. For the literal flight phase we obtained a steady state rotation around CM following exactly the declining angle of air flow. CONCLUSION: Our study aims to investigate the flight behavior of ski jumpers before and after take off. The athletes' problem is to achieve a compromise between high vertical take off velocity and necessary angular momentum: High velocity correlates with a long jumping distance, and a large angular momentum assures an early flight posture and position. Considering the obtained empirical data there are several strategies to solve this problem.
© Copyright 2008 Science and Skiing IV. Published by Meyer & Meyer. All rights reserved.