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Paul F.J. Merkes, Paolo Menaspà and Chris R. Abbiss

therefore extremely important to road cycling performance and even more in sprint performance, as sprinting is likely to be the fastest activity in road cycling (with the exclusion of some descending). Given that the outcomes of road cycling sprints are often decided by very small margins, aerodynamics is

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Vincent Chabroux, Caroline Barelle and Daniel Favier

The present work is focused on the aerodynamic study of different parameters, including both the posture of a cyclist’s upper limbs and the saddle position, in time trial (TT) stages. The aerodynamic influence of a TT helmet large visor is also quantified as a function of the helmet inclination. Experiments conducted in a wind tunnel on nine professional cyclists provided drag force and frontal area measurements to determine the drag force coefficient. Data statistical analysis clearly shows that the hands positioning on shifters and the elbows joined together are significantly reducing the cyclist drag force. Concerning the saddle position, the drag force is shown to be significantly increased (about 3%) when the saddle is raised. The usual helmet inclination appears to be the inclination value minimizing the drag force. Moreover, the addition of a large visor on the helmet is shown to provide a drag coefficient reduction as a function of the helmet inclination. Present results indicate that variations in the TT cyclist posture, the saddle position and the helmet visor can produce a significant gain in time (up to 2.2%) during stages.

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LeRoy W. Alaways, Sean P. Mish and Mont Hubbard

Pitched-baseball trajectories were measured in three dimensions during competitions at the 1996 Summer Olympic games using two high-speed video cameras and standard DLT techniques. A dynamic model of baseball flight including aerodynamic drag and Magnus lift forces was used to simulate trajectories. This simulation together with the measured trajectory position data constituted the components of an estimation scheme to determine 8 of the 9 release conditions (3 components each of velocity, position, and angular velocity) as well as the mean drag coefficient CD and terminal conditions at home plate. The average pitch loses 5% of its initial velocity during flight. The dependence of estimated drag coefficient on Reynolds number hints at the possibility of the drag crisis occurring in pitched baseballs. Such data may be used to quantify a pitcher’s performance (including fastball speed and amount of curve-ball break) and its improvement or degradation over time. It may also be used to understand the effects of release parameters on baseball trajectories.

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Mikko Virmavirta, Juha Kivekäs and Paavo Komi

The effect of skis on the force–time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

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Mike D. Quinn

A mathematical model based on a differential equation of motion is used to simulate the 400-m hurdles race for men and women. The model takes into account the hurdler’s stride pattern, the hurdle clearance, and aerobic and anaerobic components of the propulsive force of the athlete, as well as the effects of wind resistance, altitude of the venue, and curvature of the track. The model is used to predict the effect on race times of different wind conditions and altitudes. The effect on race performance of the lane allocation and the efficiency of the hurdle clearance is also predicted. The most favorable wind conditions are shown to be a wind speed no greater than 2 m/s assisting the athlete in the back straight and around the second bend. The outside lane (lane 8) is shown to be considerably faster than the favored center lanes. In windless conditions, the advantage can be as much as 0.15 s for men and 0.12 s for women. It is shown that these values are greatly affected by the wind conditions.

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Mont Hubbard and Christy D. Bergman

The theory of crossflow aerodynamics is used to estimate the effect of thrower-induced vibrations on javelin mean lift and drag. Vibrations of all modes increase both lift and drag from the vibration-free condition. Percentage in-creases in lift and drag are largest at small mean angles of attack, large vibrational amplitudes, and large relative wind speeds. Thus the consequences of vibration effects on aerodynamics may be most significant for elite throwers.

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Sauli Savolainen

The aerodynamics of the skier’s equipment and the effect of postural changes on the aerodynamic forces acting on the skier during downhill speed racing have been studied theoretically. The aerodynamic characteristics of skier and equipment have been determined by a source panel method based on the velocity potential theory. The calculations indicate that the skier’s torso should be slightly lifted from the tangential direction of downhill during skiing, thus causing a lift force and reducing the friction between the skis and snow. The drag of the torso—tilted by a few degrees—will remain almost the same as the drag of the torso in strict tangential direction. The force acting on the skier’s legs can be directed according to individual needs. The shape of the leg spoilers will give the wanted drag/lift ratio. The optimum shape of the helmet depends on the skiing style. The results introduced here are obtained from theoretical calculations, and their validity should first be tested in a wind tunnel and finally during the normal skiing performance. The calculated drag forces, which are based on the velocity potential theory, do not include the base drag of the skier’s body.

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Mary Ridgway, Carol Pope and Jerry Wilkerson

The purpose of this study was to identify factors affecting efficiency of wheelchair propulsion by male subjects in the 800-m racing event. High-speed films were taken of finalists (n=31) at the 1986 National Wheelchair Track and Field Championships. Kinematic data were calculated on the head, trunk, upper arm, elbow, and thigh in addition to cycle velocity (wheelchair velocity), cycle duration, cycle rate, cycle distance, and percentage of propulsion and recovery. In general, fastest cycle velocities, rates, and greatest distances occurred in the higher classes. During propulsion, head movement was greatest in Classes II/III (13.9°) and trunk movement was greatest in Classes IV/V (7.8°). Additionally, the higher classes exhibited greater movement at the shoulder and elbow than did Classes IA/IB. The thighs were closest to the trunk in Classes IA/IB and were farthest from the trunk in Classes IV/V. Movement of the trunk and head, as well as positioning of the thighs during wheelchair racing, may help in propulsion and with aerodynamics.

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Samuel Sigrist, Thomas Maier and Raphael Faiss

existing reports on cycling energetics and aerodynamics, 8 – 10 it underlines “the importance of drafting and the associated high degree of skill required” 4 in team pursuit with a consequent reduction of air resistance (for the second to the fourth rider) with smaller gaps between riders. 8 Team

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Levi Heimans, Wouter R. Dijkshoorn, Marco J.M. Hoozemans and Jos J. de Koning

efficiency, expressed as a percentage, was predicted for all possible team compositions, given the variation of the aerodynamic characteristics of the current group of cyclists. The team with the lowest average percentage can be considered as optimal regarding team aerodynamics. Moreover, individual