Projectile fire questions

Guns, torpedoes, mines, bombs, missiles, ammunition, fire control, radars, and electronic warfare.
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tommy303
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Re: Projectile fire questions

Postby tommy303 » Tue Sep 27, 2011 6:02 pm

PS: Isn't that Seydlitz's motif, the BC of BC's, if I am not mistaken?


It is indeed.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Wed Sep 28, 2011 3:32 pm

@Bill Jurens

Many thanks. Without modifying anything in the present code but the shell mass, velocity and frontal area to these respective values (870.91 kg, 746.95 m/s, 0.113048 m²), ie; your provided values converted to SI, I get;

25,762 meters range (28,166 yards)
29.5º impact angle
453.2 m/s final velocity (1486.5 ft/sec)

Looks like it is a case of the drag coefficient interpolation model being a bit higher for this particular 15" shell than for the USN 16" (which was almost bang on with the model of the "bullet" of the Wiki page). I found this http://www.navweaps.com/index_tech/tech-094.htm straight off the bat by simply searching 15" 4CRH. Also, the frontal area used in the calculations is not 100% correct. As pointed out before in this thread, the shell had a certain angle of attack to its flight path, which would present part of the plan to the airflow. This will undoubtedly have an effect. I will look into that when I get the time again.

@tommy303

Off topic:
Thought so. About two years ago I started scratch building a balsa model of this BC, from a color plate in an old book of mine that's somewhere around here still (The Encyclopedia of Sea Warfare, 1975). I did not get very far, as other obligations got in the way of its progress and it got forgotten. It was going to be for the entertainment of a kid, and was going to be motorized to sail on a pond. I wanted it to be something a bit more specific and detailed than those generic plastic mold motorized "lumps" that you can sometimes find in toy stores, which generally have some distant semblance of Bismarck or Iowa. Might start it again now. Why Seydlitz? It's story at Dogger Bank and Jutland impressed me. Here's a snap...

Image

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Sat Oct 01, 2011 6:04 pm

This is a bit of a hopeful request...

For my comparisons, please does anyone have any data on the divergence angle of the longitudinal axis of a shell relative to its flight path (vertically, not laterally), at different points along the trajectory? Any gun will do, as long as it is identified.

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Sun Oct 02, 2011 3:50 am

Go ahead and test the mock up. Pull it to bits, please, your knowledgeable criticism helps. Console application, as yet...

Win7_Binary if you are on windows
or;
build the source on g++, if you are on Linux.

https://sourceforge.net/projects/shipgunmodel/files/

.

dunmunro
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Re: Projectile fire questions

Postby dunmunro » Sun Oct 02, 2011 6:07 pm

CuttleFish wrote:Go ahead and test the mock up. Pull it to bits, please, your knowledgeable criticism helps. Console application, as yet...

Win7_Binary if you are on windows
or;
build the source on g++, if you are on Linux.

https://sourceforge.net/projects/shipgunmodel/files/

.


Hi, great work!

I would like to suggest a few options:

1) ability to use metric or imperial units

2) AA option; input range, height, course and speed of an aircraft, and the program outputs required gun elevation, and time of flight

thanks

Duncan

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Thu Oct 06, 2011 12:05 am

Thanks Duncan, much appreciated.

Item 1 is already a foregone conclusion in the next update. If you are interested in the progress of my "hobby" level gun sim, take a look at the Sourceforge page every month or so to see if I had the time to do anything new.

Item 2 is also possible. Looks like a 3D sine law problem, at first glance. It will have to wait until I have a 3D version of the model, however.

Thanks again.

lwd
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Re: Projectile fire questions

Postby lwd » Thu Oct 06, 2011 2:09 pm

Thanks for making this available.

Oh by the way dunmunro doesn't give out complements freely and is more than willing to challenge even small errors on most occasions. I'd take a complement from him of that sort as very high praise indeed.

mike1880
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Re: Projectile fire questions

Postby mike1880 » Thu Oct 06, 2011 10:38 pm

Cuttlefish, if you do a bit of googling you can probably find the source code (in Basic) for the late Robert L McCoy's programs "mctraj" (trajectory calculation, as you'd expect) and "mcdrag" (estimate of drag coefficent for a specified mach number, given some projectile shape parameters) and probably some java or c code to model the ICAO standard atmosphere, if you adapt those you'll have pretty much everything you're looking for with minimal effort on your own part. McCoy's book "Modern Exterior Ballistics" will, iirc, tell you how to add the effects of cross wind and range wind (and I think - without actually making the effort to walk across the room to the book shelf to check - probably vertical wind as well).

Mike

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Sat Oct 08, 2011 1:27 am

lwd wrote:Oh by the way dunmunro doesn't give out complements freely and is more than willing to challenge even small errors on most occasions. I'd take a complement from him of that sort as very high praise indeed.


Indeed, I do, before and especially now that you mention this. No one can be faulted for having perfectionism as their standard. Thanks.

mike1880 wrote:Cuttlefish, if you do a bit of googling you can probably find the source code (in Basic) for the late Robert L McCoy's programs "mctraj" (trajectory calculation, as you'd expect) and "mcdrag" (estimate of drag coefficent for a specified mach number, given some projectile shape parameters) and probably some java or c code to model the ICAO standard atmosphere, if you adapt those you'll have pretty much everything you're looking for with minimal effort on your own part. McCoy's book "Modern Exterior Ballistics" will, iirc, tell you how to add the effects of cross wind and range wind (and I think - without actually making the effort to walk across the room to the book shelf to check - probably vertical wind as well).

Mike


Thank you for the information, Mike. I will have a search on your recommendations. Anything at all related is good as a reference, at this stage.

All the best.

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Thu Oct 27, 2011 9:08 pm

Hello,

Nope, sorry for this post. I had placed a link to the latest version of the model here, but I spotted an error myself which had slipped by before. The muzzle velocity is defaulting to a single value. Correcting.

All the best!

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Sun Oct 30, 2011 11:50 pm

Sorted,

Still in prototype phase, but you've got a GUI now, at least. Tested on Windows XP 32 bit through Windows 7 64 bit. Pretty self explanatory.

Windows users, it is the GunSimV11.7z file you would be needing. There is a possibility you may also require the MS VC++ 2008 run-time redistributable package download from MicroSoft, but I doubt it.

http://sourceforge.net/projects/shipgunmodel/files/GunSim_V1_1/

My thanks.

CuttleFish
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Re: Projectile fire questions

Postby CuttleFish » Fri Nov 04, 2011 9:41 pm

Again, another post to keep track of my thoughts, but any comments and corrections are always welcome.

In some off hand calculations addressing PMI's, with the object of determining the lateral angle of the shell with respect to its flight path, I was lead to the conclusion that it was not so complex after all. Silly me for not having seen it straight of the bat. The amount by which the shell's centerline is going to angle off to the side of it's flight path is proportional to the longitudinal angle rate of change. We are talking about cross sectional symmetry, after all. If the shell dips through 1º per second while it follows it's ballistic trajectory, then precession is going to see to it that the angle of lateral angular offset is also going to be 1º over that second, to the side of the rotation. Barring one exception that I read about once (where some obscure, un-rifled naval gun design employed “flattened” shells, and if someone has any more info on this, please post!), just about all shells' bodies are generally cylindrical, barring the conical nose, and will be subject to this property.

The PMI comes back into the question when we address the property of gyroscopic rigidity. Though I did not learn anything new which I did not know before or have otherwise learned while doing this programming “project”, the following link was informative;

http://www.navweaps.com/index_tech/tech-073.htm

Spin a shell to rapidly, and it is going to resist the aerodynamic forces that allow it to dip it's nose gradually to permit its centerline to stay (roughly) aligned with it's actual flight path, and will consequently experience less precession. As far as the program is concerned, the simplest way to implement this is going to be to do the PMI calculations once for some different spin rates, bores, and shell masses, to establish the properties of rigidity of each, tabulate the results, and read them into the program for later interpolation. The less tendency the shell's nose has to “follow it's flight path”, the less precession is going to occur.

Once the lateral angle of the shell can be determined this way, and a coefficient of force for the shell's side angle can be derived, establishing the lateral acceleration that causes the “drift” is simple enough case of (discounting Coriolis, of course);

Acceleration m/s2 = Newtons of (side) Force / Mass Kg

..and the amount of side velocity is cumulative of this acceleration;

Side drift velocity = Side drift velocity + Acceleration

...for every second .

In looking at some of the tables provided me here on this thread, the amount of lateral deviation off the bore-sight axis is not too great, in relation to the distance traveled. As the shell is symmetrical, the force of lift that is provided by the shell's angle of attack to its flight path's relative wind is going to be much the same (unless, of course, rigidity prevents it from nodding over properly). Therefore, the lift produced by the shell is not of any great significance it extending the range. In fact, it is detrimental, as it adds induced drag.

mike1880
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Re: Projectile fire questions

Postby mike1880 » Sat Nov 05, 2011 2:14 am

Read the McCoy book.

Mike

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Re: Projectile fire questions

Postby Neoconshooter » Thu Dec 06, 2012 4:52 am

CuttleFish wrote:Well, well! Thanks for those links, they are very helpful. It seems, by the results, that my physics were about right. The main "problem", if I can call it that, is that the coefficient of drag was a bit low at 0.22. Values between 0.25 to 0.27 hit it on the money.

Thanks again!

I find it very interesting that your program works with a BC of 0.22/.25/.27! Or about what a typical .30 caliber hunting rifle has? I can not remember whether the BC number for large caliber Naval Arty shells as used in other Ballistic Programs is 3.x or 5.x, but it is definitely in that range. The tables were first calculated by Krupp, IIRC, by observing the performance of a 25 MM pointed and streamlined shot that weighed one pound! The empirical formula for such things, large caliber arty, that is, being the same all over the world.

Ideal shot weight = Caliber in inches, cubed / 2 = weight in pounds, OR Caliber in MM cubed divided by 72.25384259 = weight in Grams, or caliber in cM and weight in Kilograms. Then they stipulated that that projectile had a BC of 1.000! Which given what they knew back then amaizes me. A good .50 caliber sniper rifle munition has a BC of well over 1.06!


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