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Epicyclic motion of a bullet (video)

#8
01-02-2009, 10:14 PM
 Platinum Member Join Date: Jan 2007 Location: MS Posts: 1,652
Re: Epicyclic motion of a bullet (video)

That is exactly as I envisioned it, that is cool. I have banged my head against the wall trying to explain this to a guy. Maybe this will help, thanks for sharing.
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#9
01-02-2009, 10:16 PM
 Platinum Member Join Date: Feb 2004 Location: Pennsyltucky Posts: 2,634
Re: Epicyclic motion of a bullet (video)

thanks for posting. i always thought the path was more circular, with a constantly decreasing radius until it went to sleep.

is it true that, generally speaking,short per caliber bullets have a greater radius of yaw but go to sleep quicker than long VLD type of bullet that might not have as great a radius of yaw but need more time of flight or distance to go to sleep?
#10
01-02-2009, 10:24 PM
 Official LRH Sponsor Join Date: Mar 2007 Posts: 634
Re: Epicyclic motion of a bullet (video)

I think the magnitude of yaw and how much time it takes to go to sleep after a given initial tip-off rate depends mostly on the gyroscopic stability of the bullet. You could get a long bullet to damp oscillations faster than a shorter bullet by spinning it way faster.

In general, shorter bullets have greater gyroscopic stability from a given twist barrel which would lead to quicker dampening.

-Bryan
#11
01-03-2009, 12:55 PM
 Official LRH Sponsor Join Date: Mar 2007 Posts: 634
Re: Epicyclic motion of a bullet (video)

The original video has stirred up quite a bit of discussion on this and other sites about the dynamics of a bullets flight. Unfortunately, there's been a common misunderstanding that the plot is showing the bullet path.

In fact the original video was showing the pitch and yaw angles. The scale showing the size of 1 degree is in the bottom left of the plot.

Anyway, in an attempt to clear up the confusion, I've created another video. This one shows the original yaw-pitch plot, and right beside it shows the actual bullet path from the shooters point of view, so you can see the minor effect of the pitch-yaw angles on the trajectory. The 25 rad/s initial yaw rate causes about a 1 MOA deflection in the opposite direction of the initial yaw, but the actual 'corkscrew' of the trajectory is very small.

Considering the actual bullet path, it's hard to say that such levels of pitching and yawing could be responsible for smaller MOA groups at longer range.

Here's a link to the new video.

-Bryan

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