Editing Magnus effect (section)

== In external ballistics ==
The Magnus effect can also be found in advanced [[external ballistics]]. First, a spinning bullet in flight is often subject to a [[crosswind]], which can be simplified as blowing from either the left or the right. In addition to this, even in completely calm air a bullet experiences a small sideways wind component due to its [[Flight dynamics (aircraft)|yawing]] motion. This yawing motion along the bullet's flight path means that the nose of the bullet points in a slightly different direction from the direction the bullet travels. In other words, the bullet "skids" sideways at any given moment, and thus experiences a small sideways wind component in addition to any crosswind component.<ref>{{cite web |author=Ruprecht Nennstiel |url=http://www.nennstiel-ruprecht.de/bullfly/longr.htm#header_longranges |title=Yaw of repose |publisher=Nennstiel-ruprecht.de |access-date=2013-02-22}}</ref>

The combined sideways wind component of these two effects causes a Magnus force to act on the bullet, which is perpendicular both to the direction the bullet is pointing and the combined sideways wind. In a very simple case where we ignore various complicating factors, the Magnus force from the crosswind would cause an upward or downward force to act on the spinning bullet (depending on the left or right wind and rotation), causing deflection of the bullet's flight path up or down, thus influencing the point of impact.

Overall, the effect of the Magnus force on a bullet's flight path itself is usually insignificant compared to other forces such as [[aerodynamic drag]]. However, it greatly affects the bullet's stability, which in turn affects the amount of drag, how the bullet behaves upon impact, and many other factors. The stability of the bullet is affected, because the Magnus effect acts on the bullet's centre of pressure instead of its [[Center of mass|centre of gravity]].<ref>{{Cite web |url=http://ojs.unsw.adfa.edu.au/index.php/juer/article/viewFile/890/571 |title=The mathematical modelling of projectile trajectories under the influence of environmental effects, Ryan F. Hooke,∗University of New South Wales Canberra at the Australian Defence Force Academy, 2612, Australia |access-date=2 February 2018 |archive-date=4 February 2018 |archive-url=https://web.archive.org/web/20180204153144/http://ojs.unsw.adfa.edu.au/index.php/juer/article/viewFile/890/571 |url-status=dead }}</ref> This means that it affects the [[yaw angle]] of the bullet; it tends to twist the bullet along its flight path, either towards the axis of flight (decreasing the yaw thus stabilising the bullet) or away from the axis of flight (increasing the yaw thus destabilising the bullet). The critical factor is the location of the centre of pressure, which depends on the flowfield structure, which in turn depends mainly on the bullet's speed (supersonic or subsonic), but also the shape, air density and surface features. If the centre of pressure is ahead of the centre of gravity, the effect is destabilizing; if the centre of pressure is behind the centre of gravity, the effect is stabilising.<ref>{{cite web|title=Conditions for Rocket Stability|author=Tom Benson|url=http://exploration.grc.nasa.gov/education/rocket/rktstabc.html|access-date=29 August 2014|archive-url=https://web.archive.org/web/20130513120129/http://exploration.grc.nasa.gov/education/rocket/rktstabc.html|archive-date=13 May 2013|url-status=dead}}</ref>