The "Magnus effect" is a well documented force affecting spinning spheres.
I am acutely aware of the Magnus Effect and how to apply it to a sphere. As I was once a tournament-participating tennis player of several years, playing with spin on tennis balls was a necessity in winning matches (e.g., top spin, back spin, side spin).
For the record, I am a believer of the Magnus Effect. I am not
arguing that spin does not induce lift; from my own experience in tennis and with education of fluid dynamics, spin very much
induces lift; however, the direction of that lift is dependent upon the axis of rotation and direction of rotation. The concept of the Magnus Effect is that the rotating sphere is creating pockets of low and high air pressure, just like an airplane wing. The location of those pockets of different pressure depend, again, on the axis and direction of rotation.
With that out of the way, what I was criticizing wasn't so much your conclusions about the data, but the presentation of the data. It's a chart with squiggly lines, but what those lines represent isn't well defined. For example, why are there two lines for each sample? The chart seems to indicate that it displays both coefficient of drag (CD
) and coefficient of lift (CL
), but which line is which? Also, those numbers are entirely dependent upon the Reynolds number of the sphere... does a paintball have a Reynolds number of 94,000?
By the way, one article that data is from, The Aerodynamics of Golf Balls
, is specific to golf balls. The article also assumes perfect spheres, which our paintballs are most definitely not due to their seam.
Again, I'm not criticizing the conclusions, I'm criticizing the presentation of data. Give context to the numbers. I'm not trying to kill this conversation, just making sure of the quality of presented data.
Edited by MrEeske, 26 December 2011 - 01:09 PM.