AA Stuff

[Symon]

You got a fiz-max-slant, fiz-max-horizontal, fiz-max-vertical. Then you got a max-eff-slant, max-eff-horizontal, max-eff-vertical, and max-eff-fire-control-altitude. And on top of all this, you have max-fuse-setting-time-out. So there’s 8 different choices for ceiling for a gun and boy-oh-boy do the fanboi sites milk this for all it’s worth.

Wikipoedia just publishes the data from the most popular websites, so it’s 100% wrong 92% of the time. The last 8% will become important as shown further on. But so many people just post up Wikipoedia crap as though it was something worth looking at. It isn't.

The “fiz” refers to fiziks (physics), the Isaac Newton stuff. The math is middle school level (maybe high school). What goes up, will come down. A mass (shell) M leaving the earth at velocity V and at angle A, against the force of gravity ‘g’, and against an air resistance ‘k’ (that decreases with altitude according to a known parameter), will describe a very well behaved curve. So it’s incredibly simple to make fiz-max curves for any gun, given shell weight and muzzle velocity. Woof !!!

But AA guns aren’t shot quite that way. They are most effective at their best ‘slant’ range, usually 70 to 75 degrees. Ok, so plug in 75 for angle A and get more curves. That’s fiz-max-slant. Now, one has to look at the ‘effective’ part of the thing.

Simple Newton is cool, but you also have atmospherics. Cross-wind shear buffeting, at multiple altitudes will affect a 12-14 lb shell way more than a 28 lb shell, according the a power law function applied to the wt/aeral cross section presentation. Because of this spread, accuracy needs to be adjusted on a shell wt basis. So a really shoot-hot, hi-velocity 75mm, might have exceptional technical characteristics, but fall short of a lower velocity, higher caliber, weapon when it gets down to “effectivity” cases.

And then there’s an effective fire control altitude, but that depends on national technical means, which are impossible to determine with any degree of accuracy for the various nations represented.

And then there’s a physical/time altitude defined by the shell fuse type/timing. Again, a national technical means thing, which is impossible to determine with any degree of accuracy for the various nations represented.

Best guess I can come up with is generate the fix-max-slant curves, and adapt them with the atmospheric parameter. Then get the best data I can for FC and Fuse timing, graph that and pull everything else onto that curve and get arbitrary for some specific weapons.

It really is a graphical solution, with Newtonian physics as a baseline, atmospheric effects as an adder, and a modulo plus/minus on the later war FC/Fuse data.

Does this help at all? JWE

[PaxMondo]

Well, first off, I'm not a Ft Sill graduate ... but I do have an engineering degree around here somewhere and i've been modeling stuff since the Intel 4004 ...

yeah, you're doing exactly what I would do for this. utilize some fundamental theory to establish your basic curve fits against empirical data. Establish boundary conditions and limits. Call it done.

[Symon]

Oh, yeah, this is wicked cool. Got a very nice ballistics program with shell radius, shell mass, drag coefficient, and atmospheric density inputs; outputs based on incident angle (assume uniform 75 degree slant) and initial (muzzle) velocity. Simple, but effective. Hootz pazzoties. The theoretical results overlay the empiracal stuff perfectly.

Danm ... Fiziks is fun [;)] Great thing about this techy nonsense is that it actually works for JFBs, because there's some righteous specs for certain guns that are not acommodated in game. But then, of course, there's that lack of fire-control and fusing.

God !!! If there was one thing I wish (well, one of maybe 4 or 5 things), it would be "screw the algorithm, let's get FC righteous". Sorrowfully, that will not happen, so best we can do is get as righteous as possible within the game parameters as they are presented.

Ok, so it ain't perfect, but it is self-consistent and reasonable. It sets up very nicely with Navweaps, or any other serious organizational source. A bit more informative than the typical Wikipoedia stuff.

Anyway, it's all self consistent. A good thing,

Ciao. JWE

[DaveConn]

Is is possible/feasible to represent FC upgrades by defining different "weapons" (maybe with changed accuracy) when the FC upgrades, and then requiring ships to upgrade to get the "new weapons" and benefit from the FC improvements?

--Dave

[Sardaukar]

Weapon/ship upgrades should be easy, you just might need to ask Symon what values to use. I cannot see any reason why it shouldn't be too difficult. (But I have been wrong before...[:D])

[Symon]

ORIGINAL: Sardaukar
Weapon/ship upgrades should be easy, you just might need to ask Symon what values to use. I cannot see any reason why it shouldn't be too difficult. (But I have been wrong before...[:D])

No, you are quite right, Sardakuar. Very straight forward. Just a bit painstaking, but nothing too difficult.

Ciao. JWE

[Symon]

Ok, got AA altitude results and they are shocking, when compared to the game values for ceiling. Some guns with ceilings of 40000+ got cut to 33/35000. Some went from 41000 to 41300. Many, many values are close to game values. That’s good. Many, many values are significantly different. That’s bad. I think that many ceiling values were harvested from the internet, without regard to thought. Some are at 85 degrees slant, some 75 slant, some are “effective”, some “max” (whatever that means). And some are just physically impossible.

You got a 4.5in/45 QF (MkIII) gun with a “reported” ceiling of 41000 (old game), 39000 (Babes), with an calc of 30300; and you get exactly the same gun system (MkIV), with a “reported” ceiling of 29900 (and a calc of 30300). I mean, what’s up with that?

So, run the math with a program having totally self-consistent values. Inputs are the shell radius, the shell mass, muzzle velocity, a uniform slant angle of 75 degrees, and uniform air density of 1.25 kg/m^3, and a drag coefficient. The drag coefficient is first order dependent on initial muzzle velocity; this is because of a power law decrease in density with altitude, but a power law increase of the drag front with initial velocity. Math folks will kick my butt over this, but as a first order approximation, I think it’s fair.

Just for grins and giggles, I ran my program, for the 5.25in/50 QF MkI, with the identical inputs for the AA case, but set the incident angle for max horizontal range (45 degrees). The results were 68,304 horizontal feet (22,768 yards). Nathan Oakun’s program gives about 24,000 yards as the max range for this weapon.

Verified the result by doing the same thing for the 4.5in/45, the 5in/38, the 12cm/45, and the 12.7cm/50. My model puts the max range of all of these within 12% of Nathan’s FaceHard program, so I’m feeling pretty darn good about the AA altitude results right about now.

I can post my spreadsheet if people want.

Now, it’s off to get the Acc values. That's what's gonna make the fanbois howl !! [8D]

Ciao. JWE

[Sardaukar]

Great job!

AAA has always been my pet issue, but I suck in math and of course don't know the formulas used.

[MateDow]

ORIGINAL: Symon

I can post my spreadsheet if people want.

Me want!
[:D]

Now, it’s off to get the Acc values. That's what's gonna make the fanbois howl !! [8D]

Ciao. JWE

I assume that you are still using the formula that was discussed a few weeks ago?

[bigred]

JWE, thx for your attention.

[oldman45]

John, thanks so much for the work and the offer of the spread sheet. Shipboard AAA never felt right and I am looking forward to the "joy" of modding using your numbers.

Thanks!

[Symon]

Thanks, all of you, for your kind support and encouragement.

ORIGINAL: MateDow
Me want! [:D]
I assume that you are still using the formula that was discussed a few weeks ago?

Yes. Mouth (fingers) got a little ahead of my brain. Suddenly remembered that AA Acc is a function that depends on the Nav Acc function. So MUST complete the Nav stuff. Then the AA stuff is plug-it-in-and-turn-the-crank. [8D] So, off my butt.

Butt (arr, arr, arr) [;)] here's a sneak preview of the Ceiling stuff. Finished Japan and getting done with US and UK. Last page is "Other", which is Russia, Netherlands and France. China and Philippines used US/Euro weapons, so they will backfill to US/UK/Whatever. No more "leftover" lo mein or manok.

As you can see, the program is behaving very nicely. The Game Ceilings are from Babes, where we did our best to use good and consistent data. Nice to see that many of the reported values come right close to calculated values. Ok, these were generated with specific, repeatable, and standardized inputs. The calculated cielings are uniformly at a slant angle of 75 degrees. Every calculation on every Allied gun, will be done in exactly the same way. So expect unpleasant surprises.[;)]

Coming to a carwash/bordello near you soon. Ciao. JWE

[Symon]

Ok, so here's some Allied numbers. Obviously, they don't fit. But they should. They do in many respects. But in a lot of ways, they are fanboi fever dreams, and not physically possible.

You got this wikipoedia nonsense that gives a 3.7" Mk VI AA Gun a ceiling of 50,000 feet, with Col Probert's magic barrel and shell design. Can you say male cow fewmets? Given the shell size, weight, and muzzle velocity, it is PHYSICALLY IMPOSSIBLE to put a shell at 50,000 feet. So, that bad boy sits at 33k. And then there's the AFB crap that puts DP guns at 38/39000 feet, when they really got to 30/31000. Woof !!

[JuanG]

Hey, great looking stuff. Very much approve of your approach to work everything out from the actual raw numbers. Can't comment in too much depth until I get back home on Saturday, but this caught my eye;

ORIGINAL: Symon
You got a 4.5in/45 QF (MkIII) gun with a “reported” ceiling of 41000 (old game), 39000 (Babes), with an calc of 30300; and you get exactly the same gun system (MkIV), with a “reported” ceiling of 29900 (and a calc of 30300). I mean, what’s up with that?

The reason is probably that the majority of MkIV used the MkV single mounting, which was only capable of 55 degree elevation. Only the Battle class had the MkIV mount which was capable of 80 degrees.

Have not had a chance to check through that list of yours to see if this might be the case for any other weapons, but it might be an idea to list maximum elevation on that table just to account for these oddities.

ORIGINAL: Symon
You got this wikipoedia nonsense that gives a 3.7" Mk VI AA Gun a ceiling of 50,000 feet, with Col Probert's magic barrel and shell design. Can you say male cow fewmets? Given the shell size, weight, and muzzle velocity, it is PHYSICALLY IMPOSSIBLE to put a shell at 50,000 feet. So, that bad boy sits at 33k. And then there's the AFB crap that puts DP guns at 38/39000 feet, when they really got to 30/31000. Woof !!

You have it in your table as 810m/s MV, which does make it impossible, but I've seen the MkVI listed as 1040m/s MV for a new gun. Might make the difference.

[MateDow]

It does look good

[Symon]

ORIGINAL: JuanG
You have it in your table as 810m/s MV, which does make it impossible, but I've seen the MkVI listed as 1040m/s MV for a new gun. Might make the difference.

Too right !! I was pulling out my hair wondering what-in-the-world !!! There's a typo in the stuff I got from Larkhill. Reversed the I and V so data is titled Mk VI but is actually for the Mk IV. Same basic gun system as the Mk I-III. No wonder. If I just went a few pages further ...

Oh, well, totally different gun. Bigger charge, but about the same shell; different drive bands, slight change to ogival radius. Sorry about that.



BTW, thanks Juan. Always good to have more than one set of eyes on things.

[Symon]

ORIGINAL: JuanG
The reason is probably that the majority of MkIV used the MkV single mounting, which was only capable of 55 degree elevation. Only the Battle class had the MkIV mount which was capable of 80 degrees.

Yes. I think the best solution is dink with type for the Mk III/IV (there's 3 entries for these) to make one of them a Nav gun. If you can't get above 55 degrees, you ain't AA. Good thinking.

You know, I should actually read the stuff I have instead of just looking at the data tables. Have an Ordnance Manual for 3” AA guns from 1928 and the text is pretty interesting. Section on the base 3”/40 M1918 is very informative, as is the section on the base 3”/55 M1917. Then there’s a section on the new gun (what would be the M3). That was an eye popper.

Designed to chamber M1917/18 rounds, but also a “new” round with a slightly different projectile (5.9kg as opposed to 6.82kg); same case dimensions, better propellant. Chamber and breech were designed for a working pressure of 2700 kg/cm^3 that would “allow” a muzzle velocity of 2800 fps (853 m/s), but barrel wear forced a reduction in working pressure resulting in a muzzle velocity of 2700 fps (823 m/s).

All the rounds were fungible. That’s why the Philippine reports are so interesting; they may have had M3 model ordnance, but they were using War-I vintage M1918 ammo.

Shoulda thoughta this. I’m supposed to know this. Ciao. John

[Mac Linehan]

JWE -

Awesome stuff, thanks for sharing the math!

AE Fanboi Mac

[MateDow]

May I make a request when you are crunching the numbers?

Would you mind running the numbers for the Mk. 16 6"/47 DP and the Mk. 22 3"/50?

I am sure that I am not the only one that was looking at modding ships and refits that would have appeared in 1946.

Thank you in advance for your help.

[Symon]

Ok. Here's the Altitude spreadsheet. Couple of notes:

Wherever I could, I used shell weight for dedicated AA rounds, so it may differ slightly from shell weight for AP, HE, etc.. Whever I could, I used muzzle velocity for the weapon firing dedicated AA rounds, so it may differ slightly from muzzle velocity for AP, HE, etc.. (@Kereguelen - for example, the Sov 7.62s are shooting the O-361K [;)])

@Matedow - stuck your requests in at the bottom of the Allied sheet. Couldn't find any different ballistics data for the 3" Mk-22 (assume you are really talking about the 3"/50RF Mks 33/34). Same basic gun, same basic ballistics, just a nifty autoloader that puts out a poop-load of nastiness. So the gun is the gun. The 1946/1980 model will have to be accommodated by the accuracy part. Did the 6"/47 Mk-16. This is another one of those wtf-Batman things. Using Navweaps data the best I can see is 35/36000 feet. It would require a muzzle velocity of 1000 m/s to get to the "reported" 78 degree ceiling of 48000. That's a loong, loong way from 812 m/s. I realize Navweaps does its best and its my go-to place, but JuanG taught me to always take a jaundiced second look. The Ord Manual from 1957 for 6"/47 gives the same 815 m/s specs and says 78/slant is 38000. Go figure. [:)]

Anyway, here it is. Acc and other stuff in process. Ciao, JWE