The Magnus effect - External Ballistics trivia

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GunnyGene

Hawkeye
Joined
Nov 23, 2013
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6,207
Noticed this when shooting my Daisy with BB's. It has a right hand twist rifling, which imparts a clockwise spin from the shooters view point. After about 25 yds of flight the bb takes a hard right turn, which is easily seen.

Known as the Magnus Effect, (aka Spin Drift ). Kinda fun to watch, since it's not usually visible with firearms. :D

220px-Sketch_of_Magnus_effect_with_streamlines_and_turbulent_wake.svg.png


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 yawing motion. This yawing motion along the bullet's flight path means that the nose of the bullet is pointing in a slightly different direction from the direction in which the bullet is travelling. In other words, the bullet is "skidding" sideways at any given moment, and thus it experiences a small sideways wind component in addition to any crosswind component.[22]

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 an observable deflection in the bullet's flight path up or down, thus changing 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 gravity. 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 center 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 center of gravity, the effect is destabilizing; if the center of pressure is behind the center of gravity, the effect is stabilising.

https://en.wikipedia.org/wiki/Magnus_effect
 

Naphtali

Single-Sixer
Joined
Sep 29, 2007
Messages
226
For baseball and football enthusiasts: The Magnus Effect is why "breaking balls" and "knuckle balls'" movement is not an optical illusion. And soccer-style kickers and punters, and passers must account for predictable sideward movement during each one's process.
 

Pierow

Blackhawk
Joined
Jan 25, 2012
Messages
668
Happy to hear you are giving that newly wrapped 880 a workout Gunny. If you have not seen it before there is a video showing the Magnus effect using a basketball dropped off a dam. Once with no spin and once with spin. Pretty neat:

https://www.youtube.com/watch?v=QtP_bh2lMXc
 

Ralph H

Bearcat
Joined
Apr 20, 2006
Messages
16
The magnus effect was incoporated in the rear sight on the Artillery Luger. As the elevation slide moves to the right as it goes up, compensating for right hand rifling twist.
 

GunnyGene

Hawkeye
Joined
Nov 23, 2013
Messages
6,207
Pierow said:
Happy to hear you are giving that newly wrapped 880 a workout Gunny. If you have not seen it before there is a video showing the Magnus effect using a basketball dropped off a dam. Once with no spin and once with spin. Pretty neat:

https://www.youtube.com/watch?v=QtP_bh2lMXc

I've seen other similar demonstrations. Rex goes into some considerable detail in a couple of his videos, as it pertains to long range shooting. https://www.youtube.com/watch?v=OCA1njSxgv4&index=71&list=PLJUaiRIEduNXoal2_PkBZi0vDCIcEPxUn
 

SAJohn

Hunter
Joined
Jan 6, 2007
Messages
2,300
Golf balls dramatically illustrate spin lift. It also has to factored into cables, power lines, tall round chimneys, and bridges. Various types of dampers, helical wraps, or spaced weights are used to prevent structural failure due to these wind induced oscillations.

The most famous structural failure due to Von Karman vortex shedding was the Tacoma Narrows Bridge back in 1940. Here is some of the video of that event:
www.youtube.com/watch?v=j-zczJXSxnw
 

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