Range Report 6-dof

[woostri]

Anyone out there have experience with 6DOF analysis on bullet flight? I have done 3DOF for work, thesis, etc, and recently wrote a 6DOF just for fun (yeah I know...) using Robert McCoy's book, "the launch and flight dynamics of symmetric projectiles." I was able to duplicate the 6DOF results for the 168 Sierra International Bullet that are published in that book. So, I'm just wondering if anyone else has studied this stuff, and also if anyone knows where to access aero coefficients for bullets other than 168 Sierra.

My background: Undergraduate in Aerospace Engineering, Masters in Aerodynamics/Air Weapons/Re-Entry (not 3 masters degrees, just 3 sub-foci), on the job experience with 3DOF analysis, trajectory optimization, etc. All my 6DOF has been off the job, just because I find it interesting to learn more about bullet behavior for my fav hobby: ringing steel with lead at long ranges.

 

[Deleted member 10043]

Brian Litz is my only guess. He is a member of this forum.

 

[woostri]

Thanks

 

[BryanLitz]

woostri,

I also wrote my 6-DOF from McCoy, and validated with his 168 SMK aero. In my previous job (Air Weapons modeling and simulation with the US Air Force) I had access to some aero prediction codes such as MISSILE DATCOM, PRODAS, and AP98. In my current job (Chief ballistician for Berger Bullets) I use PRODAS as a design tool which is probably the best semi-empirical aero prediction method for small arms. I've never really got much into CFD for aero prediction but my perception is that it's getting stronger with the weakest link being the regions of flow dominated by viscous effects.

Unfortunately the aero coefficients most interesting to 6-DOF effects such as Magnus and pitch damping derivatives are also the most difficult to predict (and arise from viscous effects). In other words, you have many options for producing aero models, but nothing but instrumented live fire can be trusted to be accurate.

Hope this helps,
-Bryan

 

[woostri]

Thanks, that does help.

 

[damoncali]

If you spend enough time on google, you can find some military-ish papers that will give you some insight into some of the 6DOF coefficients, but there's not much out there, and it's all military stuff, obviously. I think there is a fairly detailed paper on some .223 bullets floating around, but I can't recall what it's titled. Check the references at the end of each paper and google the titles. You can find a good deal online, just not quite enough.

 

[woostri]

Pretty sure I have that exact paper on the .223. Done by the Army BRL. Lots of partial data, very little complete. I was able to learn quite a bit just by modeling the 168 Sierra but it has odd dynamic stability issues. The more I learn about what can cause dispersal of my groups, the more I appreciate the long range hits.

 

[damoncali]

Bob McCoy has a paper out there that in part discusses the sensitivity of some military 5.56 rounds to aerodynamic jump (he was investigating the apparent innaccuracy of one of the 5.56 designs, and came up with some interesting stuff). That's a pretty interesting topic to me, as it gets right to the heart of the matter of why some bullets are more accurate than others beyond the usual "better quality/balance". But your'e ahead of me - writing a 6DOF solver is still on my "to do" list.

 

[woostri]

Haha, yup. It was on my "to-do" list for many years. Took some serious reading... I'll have to check out the paper you mention, I don't think I've read that one.

 

[damoncali]

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