Along with other release parameters, Chiu (2008), also calculated a -10.25° angle of attack as optimal for breaking the current men's world record, and that of -9.25° for breaking the current women's world record. In still air, the optimized attack angle will be at -4 to -10 degrees (Soong, 1976 Frohlich, 1981 Hubbard & Cheng, 2007). At an approximate release angle of 25 degrees, the angle of attack is at zero (Terauds, 1978). Generally, the negative angle of attack should increase as the angle of release increases and decrease as the angle of release decreases. Negative attack angles are the predominant in high level throwing. A negative angle of attack means that the initial direction of the center of gravity points upwards in relation to the long axis of the discus (figure 1), with the opposite being true for a positive attack angle. The optimum angle of attack of the discus depends on the angle of release. The detailed description of any of those theories is beyond the scope of this narrative. They suggested that what is needed is a nontrivial correct theory and he offered a combination of the Bernoulli's principle and Newtonian physics theory as an explanation of how lift is generated. They postulated that the aforementioned theories can be classified according to three conditions: trivial and correct, trivial and incorrect and, nontrivial but incorrect. According to Johnson & Jansson (2015) none of these theories present a correct explanation of flight. Other theories that have been proposed include the Newton's third law theory, the 'longer path' theory, the 'downwash' theory, the Coanda effect theory, the Kutta-Zhukosky lift theory and the Prandtl Drag Theory. That is, it does not explain why the velocity is higher on top, and so the explanation of lift presented is no real explanation, or more precisely it is a trivial truism (Johnson & Jansson, 2015). However, this theory has been challenged as trivial, incorrect or incomplete (NASA). The difference in pressure creates a positive, upward lift.

The typical theory to explain how lift is produced, is with the use of the Bernoulli principle which states, there is a high air speed and low pressure on the top of the air foil (wing-discus-frisbee etc.) and a low speed and high pressure on the lower surface of the foil.

The angles of interest that are formed during the launch of the discus are those of release, attack, inclination, tilt, along with the pitching moment (figure 1).

Those two coefficients along with the pitching moment coefficient depend on the attack angle. The other component, lift, is the product of the same elements but with its own dimensionless coefficient which measures the effectiveness of the implement to produce force perpendicular to the velocity vector. Drag is the product of the dynamic pressure (pressure in the front of the implement is greater than that in the rear), the cross-sectional area and a dimensionless drag coefficient. Those forces act on the center of pressure (CP) which does not necessarily coincide with the center of gravity (CG) of the discus and is located somewhere in front of the CG. During its flight the discus is influenced by gravity and the aerodynamic forces of lift, drag and pitching moment. Those favorable conditions are created as a result of fluctuations in the relative wind speed, primarily, and secondarily, the angle of release, the velocity of release, the attack angle, the inclination angle, the tilt angle, the rotation of the discus around its short and long axes, the effective mass of the discus and, its moment of inertia. So much so that the first author to publish scientific data regarding the effects of wind on the discus Taylor (1932) suggested that it would be unfair to allow records achieved under favorable conditions. Indeed, the aerodynamic forces acting on the discus during its flight can decisively alter the course of its trajectory positively or negatively. In a vacuum, the same author calculated that the silver medalist would have thrown 4.06 meters further than the winner.

However, aerodynamic factors dramatically affected the distance achieved by those two throwers. A notable example is from the men's discus final during the 1976 Olympic Games, where the gold medalist released his discus a significant 1.4 m/sec., less than the silver medalist (25.88 m/sec. This implies that, under certain conditions, the distance thrown can be increased or decreased significantly beyond or below to that expected in a vacuum or in still air. The discus is an extremely aerodynamic implement (Hubbard, 2000). Originally Published in: Techniques Magazine Long Distance - Basic Aerodynamics and Flight

Discus thrower