Take-off aerodynamics in ski jumping

The effect of aerodynamic forces on the force-time characteristics of the s imulated ski jumping take-off was examined in a wind tunnel. Vertical and h orizontal ground reaction forces were recorded with a force plate installed under the wind tunnel floor. The jumpers performed take-offs in non-wind c onditions and in various wind conditions (21-33 m s(-1)). EMGs of the impor tant lake-off muscles were recorded from one jumper. The dramatic decrease in lake-off time found in all jumpers can be considered as the result of th e influence of aerodynamic lift. The loss in impulse due to the shorter for ce production time with the same take-off force is compensated with the inc rease in lift force, resulting in a higher vertical velocity (V-v) than is expected from the conventional calculation of V-v from the force impulse. T he wind conditions emphasized the explosiveness of the ski jumping take-off . The aerodynamic lift and drag forces which characterize the aerodynamic q uality of the initial take-off position (static in-run position) varied wid ely even between the examined elite ski jumpers. According to the computer simulation these differences can decisively affect jumping distance. The pr oper utilization of the prevailing aerodynamic forces before and during tak e-off is a very important prerequisite for achieving a good flight position . (C) 2001 Elsevier Science Ltd. All rights reserved.