Computing Shell range.

[mbear]

Hello everyone. While looking for a new job, I've taken on a project to keep my brain sharp. In this case it's a theoretical refitting of the U.S.S. Iowa.

It's almost completed (it should be after about a year of effort), but I have run into a small problem: I don't know how to compute shell range for my theoretical 16" rounds. I've found the formula for the range of a projectile at Wikipedia (Range of a projectile), but that doesn't factor air resistance (drag), shell weight, etc.

Later, I found an article called Shell Aerodynamics 101 and discovered that I need the coefficient of drag (Cd). OK. I found a program called MC Drag that can compute that for me.

What I can't seem to figure out is how do I apply the Cd info to the ranges I get. If I compute a drag coefficient of 0.35, do I multiply the max theoretical range given in the Wikipedia formula by 0.65 to get a realistic measure?

And how does shell weight factor into this, if at all? I assume a 700 lb 8 inch shell would go farther than a 1900 lb 16 inch shell, but would it go (1900/700=) 2.7 times as far?

Thanks in advance for any help you can provide. I greatly appreciate it.

[Shamus]

And how does shell weight factor into this, if at all? I assume a 700 lb 8 inch shell would go farther than a 1900 lb 16 inch shell, but would it go (1900/700=) 2.7 times as far?

Here's another factor in the equation for you...Momentum......expressed as P=MV (where P is momentum,M is mass of projectile and V is velocity of projectile).If I recall my WWII Naval history correctly the battleships could stand off and make minced meat out of an 8 inch gunned cruiser with their 16 inch rifles.With relatively similiar muzzle velocity I believe the round with more momentum has the range advantage although I'm probably barking up the wrong tree .One of our battleship mavins could tell you much better than I can,good luck:) .

[mbear]

Here's another factor in the equation for you...Momentum......expressed as P=MV (where P is momentum,M is mass of projectile and V is velocity of projectile).If I recall my WWII Naval history correctly the battleships could stand off and make minced meat out of an 8 inch gunned cruiser with their 16 inch rifles.With relatively similiar muzzle velocity I believe the round with more momentum has the range advantage although I'm probably barking up the wrong tree .One of our battleship mavins could tell you much better than I can,good luck:) .

Great. Here I was hoping to reduce the number of things I need to take into account, and you go and make more work for me! ;)

Seriously, I hadn't heard that before. Thanks for bringing it to my attention.

[Leo F]

Exterior ballistics is not a simply subject. You might want to check out this web site.

How do bullets fly?

[T_igger_cs_30]

And how does shell weight factor into this, if at all? I assume a 700 lb 8 inch shell would go farther than a 1900 lb 16 inch shell, but would it go (1900/700=) 2.7 times as far?

No expert on this by far but would it not depend on the tangent elevation and size of (bag) charge used?

[Dreadnought]

Lots of homework here to be done.;):P

[Shipwreck]

Exterior ballistics is not a simply subject. You might want to check out this web site.

How do bullets fly?

Are you the same Leo F who was working at FMC in the 1970s-1980s by any chance ?

[Leo F]

Yes.

[Shipwreck]

Yes.

Wow, another guy from the good ol' days !

Welcome aboard. :)

[Leo F]

Thanks for the welcome. I'm still working for the company although we have been bought by BAE Systems. Did you work for FMC in that time frame?

[Shipwreck]

Did you work for FMC in that time frame?

No, but we've met a few times back then.

[mbear]

Whew! Status update

Lots of homework here to be done.;):P

No kidding.

Here's where things stand:
I've found a version of MC DRAG [Note 1]written in JavaScript by a German gentleman. MC DRAG computes coefficient of drag.

From NASA, I found a web page, Flight Equations with Drag, which explains the equations as simply as they can be explained, and a Java applet that computes ballistic rocket (stomp rocket) altitude and flight time, including the effects of drag, but because it's for rockets, it has a fixed launch angle of 90 degrees. This tool won't help me too much, but it does account for atmospheric density, and source code is included in the downloadable version.

I've also found a series of DTIC documents that explain how to model the flight path of shells, with several neat equations. Document "ADA462493 Development of An Artillery Accuracy Model" looks particularly relevant.

Notice that the two programming languages mentioned above are Java and JavaScript. These are not my preferred languages, but I can convert them into the Python language without too much trouble. And I've even found an extension for Python called SciPy that "is open-source software for mathematics, science, and engineering. " So I should be able to use this extension to create a decent range estimation application.

Unfortunately my physics knowledge is... ummm... limited. (Sounds better than non-existent, doesn't it?) So I'll have to re-learn these concepts. I've already purchased a copy of The Complete Idiot's Guide to Physics* to help with this.

To sum up, I'm going to put this particular project on hold. I need to devote more time to this than I currently have available, so I'm just going to put the finishing touches on my Iowa reactivation plan as it is now, and add the shell range info once I've put together the program.

Once the program is complete, I'll make it and the source code available to everyone from my web site. I'm currently planning to produce downloadable versions written in Python, online versions for quick evaluations (JavaScript & Flash), and a version that could be used in a spreadsheet (Excel VBA).

In the meantime, I want to thank you all for your tips and suggestions. I really appreciate them.

Matt

[Note 1] "This report presents a FORTRAN program 'MC DRAG' for estimating a projectile's zero-yaw drag coefficient from the given values of certain size and shape parameters. The results are valid over a Mach number range of 0.5 to 5 and a projectile diameter range of 4 to 400 millimetres. A user's guide and a FORTRAN listing of MC DRAG is provided. The program is applied to three illustrative examples: (1) an experimental low-drag small arms bullet, the 5. 56mm BRL-1 design; (2) a 55mm scale model of the Minuteman re-entry stage vehicle; (3) the 155mm long-range artillery shell M549. The MC DRAG program estimates drag coefficient to within 3% error at supersonic speeds, 11% error at transonic speeds, and 6% error at subsonic speeds."

* I don't like to think of myself as a complete idiot, but in this case it's unfortunately accurate. Though I personally think ignorant is a more accurate description, as ignorance can be fixed, but idiocy is a permanent condition.

[Gun Grape]

And you haven't scratched the surface of interior ballistics yet.

Why would you put yourself through such pain? Might want to take a look at chapter 3 of FM 6-40.

Its S-2s bible:)

Went to your web site. I agree about Smash lab. Dumbest show yet. And shouldn't those "engineers" have tech advisers to catch all the stupid things that they do.

[S2]

G.G. Reply

"Its S-2s bible"

FM 6-50 actually, but FM 6-30, 40, and 50 make a wonderful collection to grace any cannoneer's bookshelf and hours of fascinating reading pleasure.

I can't step under the stars without wanting to do a simo-observation and transfer directional control to SOMEBODY.

G.G., do you ever view a ridgeline to your immediate front and find yourself estimating site and range to crest? Or how many guns you could squeeze into a playground?:))

I wish mbear luck. It sounds like he's trying to reconstruct TFTs for 16" without benefit of measuring actual shot. The calculations would be endless.
What a chore.

[Shamus]

And you haven't scratched the surface of interior ballistics yet.

My absolute favorite subject to put an entire roomful of people to sleep with;) .