…by using the wind assistance. Recently we published a post on our Facebook fanpage that picked up a significant amout of feedback. Because of the fact that many throwers have no idea why´s all the noise about wind, we decided to publish an article about scientific research and prove those by adding several examples. All you are about to read is proven through many decades.
How wind helps?
Based on “The Physics Of Sports” by Angelo Armenti Jr. ( Ed. ), chapter 8 “Fluids and Sports”. Aerodynamic effects on discus flight ( by Cliff Frohlich ).
In it the author reviews the available literature on the physics of discus and analyzes its flight under the combined influence of gravity, aerodynamic drag and aerodynamic lift. He then calculates differences in the horizontal range of a well- thrown discus caused by changes in wind velocity, altitude, air temperature, gravity and release velocity.
As to relative magnitudes ( which means all the calculations are approximate ), Frohlich notes that:
a discus can travel: 1) 8.2 meters farther against a 10- m/s wind; 2) 0.13 m farther at 0°C than at +40°C; 3) 0.19 m farther with no wind at the elevation (geometric height from the sea level) of Rome than at the elevation of Mexico City; 4) 0.34 m farther at the equator than at the poles.
It´s remarkable for 2 reasons:
- The ironic state of affairs stems from the fact that, while aerodynamic drag¹ and aerodynamic lift² are both increased by the presence of a head wind, the increased aerodynamic lift more than makes up for the increased aerodynamic drag, threreby resulting in additional range, at least for head wind velocities of 20 m/ s or less.
¹ force that acts opposite to the direction of the movement of the discus, put your head out of a driving car and you can feel the drag
² the component of the aerodynamic forces acting on an airfoil that opposes gravity
Also, due to aerodynamic factors, the launch angle for maximum range for a discus is about 35° as compared to the familiar 45° for projectiles in a vacuum.
Frohlich notes that considering the importance of the aerodynamic forces affecting discus flight, it is surprising that record books make no distinctions between marks recorded in still air and wind-aided marks.
Effect of rotation of the discus
The most important effect of the discus rotation is to stabilize its orientation during flight. Upon release the discus rotates at ~ 7 rps. In the absence of applied torques the discus initial orientation is preserved throughout its flight.
At the moment of release, the discus thrower will usually attempt to orient the discus so as to maximize the lift forces and minimize the drag forces while the discus is travelling upward and outward.
Most investigators agree that the optimum strategy in still air is to release the discus so that its inclination angle alfa is about 5° to 10° less than the release angle R. Although this results in negative lift during the very beginning of the flight, it allows for a minimum drag and optimum average lift throughout the upward part of its flight.
In fact, the torques applied by aerodynamic forces during flight are not negligible, although they are quite small. If one carefully observes the orientation of a discus in flight, one notices that for a right- handed thrower the left side of the discus tilts ( rolls ) gradually downward about 10° during the latter portion of its flight. Why?
One effect of air on the discus is to create torques that change the orientation of the axis of rotation of the discus. For the discus tilted with front slightly upwards and moving to the right the largest torques are caused because the lift forces are larger on the forward half of the discus than the rear half. Thus the lift force acts at point A and creates a torque that causes the angular momentum vector to move in space. This causes the right edge of the discus to tilt slowly upwards during the flight.
Similarly, because of the discus rotation, the relative velocity is greater on the left side of the discus than the right, causing a net upwards force to act on the left side of the discus. This force creates a torque which causes the forward edge of the discus to tilt progressively upwards during flight.