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This study examines aerodynamic stability in pitch in ski jumping. Static stability implies automatic return to trimmed flight after a sudden disturbance and dynamic stability involves gradual damping of oscillatory motion. Both have implications for flight control and safety. A 3-D inertia model of a ski jumper and the Planica K185 jumping hill profile were constructed using computer-aided design. Inertia, jump performance, and aerodynamic efficiency and stability parameters were computed for variations in V-style posture using mathematical modeling. Pitching moment at a 01 angle of attack was positive, and the condition dM/dao0 at equilibrium was satisfied, indicating that the athlete is inherently stable. Enhanced flight posture consists of a ski-opening angle of 301 and a forwardleaning angle of 101. This is a high-lift configuration with a large static margin that triggers a steep dM/da slope and high oscillatory frequency upon deviations from trimmed attitude. Mechanisms of stability in pitch are proposed, founded upon theoretical aerodynamics. r 2009

This study evaluated the adaptation of natural laminar flow airfoils for Grand Touring (GT) sports car racing and the influence of wing geometry and flow control devices on rear-wing aerodynamics. The mean camber lines for the National Advisory Committee for Aeronautics (NACA) 651-412 and National Aeronautics and Space Administration (NASA) LS(1)-0413 airfoils were calculated. Numerical analysis was conducted using thin-airfoil theory and finite-wing theory. Airfoil variables included zero-lift angle of attack and centre-of-pressure location. Wing variables encompassed induced and effective angles of attack, lift and drag coefficients, and lift-to-drag ratio. Modelling consisted of variations in wing aspect ratio and the integration of end plates and a Gurney flap. A tapered rectangular planform is quasi-elliptical and attains near-unity Oswald efficiency. The NASA LS(1)-0413 airfoil is stall resistant and produces high downforce at the expense of extra drag because of factors related to camber, profile thickness, leading edge radius, and concave pressure recovery. The wing should be set at an incidence above that for best lift-to-drag ratio. The NACA 651-412 airfoil is aerodynamically more efficient but produces less downforce and may be used as a stabilizer. Augmented aspect ratio, end plates, and a Gurney flap enhance wing aerodynamics via flow control and modified downwash configuration. The analysis suggests that a tapered LS(1)-0413 wing of 5.56 aspect ratio fitted with end plates and a Gurney flap, set at high incidence, is an appealing single-element arrangement for applications in Grand Touring sports car engineering.

7 children 15 to 30 mo. old participated in a study of 3-dimensional kinematics of overarm throwing. Children of ddferent ages were considered to be at di£ferent developmental stages of motor development. Video recordings were digitised and 3-dimensional coordinates established using the DLT algorithm. Qualitative analysis indicated that the children executed either a 'static' or 'dynamic' throwing action. Either could further be classified as 'arm dominated' or 'sequentially linked.' Maximum elbow extension was no more than 163' for anv child: release velociw was higher for older subjects; and the angle of ball release was large in 'arm-dominated throws' (M=49') and comparatively smaller in 'sequentially linked' throws (M= 15').

This study assessed the development of coordination during the first 8 months of independent walking and identified potential hypotheses that may be tested by further research. The walking gait of a normal child was recorded on video at the onset of independent walking, and thereafter at monthly intervals over a period of 8 months. Video images were digitized and 3-dimensional coordinates obtained. The coefficient of variation was used to measure variability in the movement. Other variables studied included range of movement, relationships between angles, angular velocties, timing relationships, proportional distance and temporal phasing. By adopting a dynamical systems perspective, this study identified variables that challenged the stability of the locomotor system. Coordinative structures were observed to shift from one state to another from age 18 months; such mutations included decreased range of motion, hip knee angle relationship that resemble mature walking, relative time of peak angular velocity, and stability of angle angular velocity phasing.

Different types of rating scales have been developed to guide the qualitative analysis of sports technique and improve rating accuracy However, it remains unclear what type of scale is more accurate and how rating accuracy is influenced by scale effects. This study aimed to: I) investigate the accuracy of rating scale type (analogue, numerical analogue, Likert and numerical Likert) for the rating of kinematic variables; and ii) explore how rating accuracy is influenced by scale effects. One experienced rater constructed the 100 mm-long scales and a group of 327 novice analysts rated the video-recorded soccer kick performance of 32 school children. Estimation error was calculated as the difference between estimated values and objective digitized values. Over-and under-estimation tendencies were assessed. The scale range was divided into equal-length intervals (e.g., low, middle, high angular range) to assess scale effects Statistical analysis consisted of an exploratory principal components analysis with varimax rotation, where items were forced into a three-factor solution. Numerical Likert scale designs may be suggested as optimum for the instruction of novice raters. Central-tendency error adversely affected visual estimations; however, other scale effects enhanced accuracy. The findings have implications for optimum scale design and improved instruction in qualitative analysis.

The walking movement of children of school age and adults can be regarded as very consistent. However, few studies have reported reliability of gait parameters in very young children that may be used as normative data for the clinical assessment of gait. In the present study, nine normal children of ages 10 to 21 mo. were assessed cross-sectionally using three-dimensional video analysis and digitization to assess within-day reliability of gait kinematics. Between-subject differences in gait kinematics were also examined. In addition, one child was assessed at the onset of independent walking and at monthly intervals thereafter to assess changes in gait kinematics during the first 8 mo. of autonomous walking. The case study allowed the acquisition of pilot data for longitudinal studies of this age group. 10 kinematics variables regarded as indicators of efficient walking were measured, and reliability was assessed using one-way analysis of variance and coefficient of variation. The study showed that all children produced reliable within-day results; however, the gait of each child was unique. In the case study, the between-month differences in gait kinematics were significant. The findings may be of clinical interest for pediatricians and child neurologists given the lack of normative data for this age group.

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