Artillery V-terminal?

[GH_Lieste]

I have some reliable muzzle velocity data for HE artillery which is useful for estimating the performance of the weapon over open sights.

For VT and super-quick fuses the terminal velocity is relatively unimportant, but for quick or delay fuses the impact speed would be significant for damage to hardened targets (Bunkers/Light Armour/Penetration of Buildings etc).

What would realistic indirect fire residual velocities be for a Gun-Howitzer (700-800m/s muzzle velocity fired at moderate angle ~ 2/3 max range)?

What would be the angle of descent.

[Ssnake]

We'd need at least one additional data point, e.g. maximum range Y at X° elevation, or projectile velocity V at range Z to shape the air drag, which would be the minimum requirement for getting a good approximation for the whole range, near and far. Also, projectile mass is needed.

[outontheop]

You're in luck, I just happen to have an old 1983 copy of FT 155-AM-2 (firing tables for HE rounds fired from M109A2,3, and towed howitzer M198) that I've kept around for purposes of brushing up on my fire direction procedure.

First, let me note 700-800 m/s is a VERY high muzzle velocity for a howitzer. However, my firing table covers the 155mm/23 caliber cannon, it doesn't cover the much longer 155mm/39 caliber cannon on the M109A5/A6 which significantly increases muzzle velocity (and thereby range).

That said, the only way for the 23 caliber cannon to get even CLOSE to the stated muzzle velocity is by firing charge M119A1 (also known as 'super eight' because it's slightly more powerful than the standard charge 8). This charge is NORMALLY reserved for use with RAP, not standard HE. But, there's nothing stopping it from use with standard HE M107.

That said, muzzle velocity in standard conditions is going to be 684 m/s from the 23 caliber gun. Max range is going to be around 18km, 2/3 of that is 12km.

At 12 km, gun must be elevated 292.7 mils ( about 16.5 degrees), angle of impact is 497 mils (about 27.9 degrees), terminal velocity is 308 meters per second. Max ordinate (the apex of the trajectory) is around 1200 meters, and occurs at around 7200 meters (sorry, the max ord is from a chart rather than a table, so the data is limited by my ability to visually interpolate it). If you're interested in impact energy for some reason, the standard 4-square M107 HE is 95 pounds (squares are marks on the projectiles that note if a particular round is heavier or lighter than the standard, which would affect muzzle velocity).

However, it should be noted that in MOST circumstances, the gun crew would opt to fire charge 7W, NOT charge 8R at that range. 7W will range it, and there's no need to put the extra wear on the barrel... well, there's a few exceptions when you'd want to use the faster round, but not many.

[GH_Lieste]

Ok, what about roughly the same range, but using a much lower charge? How much difference does that make to the V-terminal and angle of descent.

Obviously the round is going to need to depart at a high angle to make best range, and it will always fall steeper than it starts.

[outontheop]

Well, charge 6W will BARELY range 12km (12200m, to be exact), so it doesn't give you any room to make adjustments. So the only logical propellant other than M119A1 would be charge 7W (7 increments of charge M4A2).

With that, at 12km, you're looking at 568 m/s muzzle velocity, 443.5 mils gun elevation (about 25 degrees), 628 mils impact angle (about 35 degrees), and 304 m/s terminal velocity.

OR, if you needed plunging fire, you could fire high-angle charge 7W (with the same muzzle velocity) at gun elevation 1123.9 mils (about 63 degrees), 1247 mils impact angle (about 70 degrees), and 330 m/s terminal velocity.

Most crews tend to avoid high-angle fire unless ABSOLUTELY neccesary. It practically fires that bad boy into low earth orbit, so it makes it real easy for counterfire radar to pick it up, and since it spends so much more time in the air (in this example, 76.2 seconds instead of 37.4), any crosswinds or other atmospheric conditions will have a lot more effect on the accuracy of the round. Not to mention that the maneuver boys probably won't appreciate having to wait the extra 40 seconds for the round to get where they need it!

[Mogwa]

http://www.globalsecurity.org/military/library/policy/army/fm/6-40/Ch7.htm

[outontheop]

Ah, the GFT... I remember learning on the ol' slide rules. They're actually pretty handy. Certainly better than doing the calculations manually.

... manually computing meteorological updates and applying them to registration data, I swear, makes you want to eat your sidearm. It's a slow, painful process. Thank god for AFATDS (and it's successor software).

That site's a reasonably good overview of what the elements of a firing table are. Of course it's barely scratching the surface on how to USE the data, but it's a decent primer for non-artillery guys.

...Of course, that's just sample excerpts, the FT-155-AM-2 I have is the size of a regular bible. There's a LOT of data, and oh by the way, it only covers HE M107, WP M110, smoke M116, and gas projos (they're all ballistically matched to HE rounds; they all have the same firing data), and Illumination rounds (which of course are NOT ballistically matched, and do NOT have the same firing data).

...you need a completely SEPERATE firing table for DPICM M483/ M483A1, improved smoke M825, FASCAM (M692 ADAM-L, M731 ADAM-S, M718 RAAMS-L and M741 RAAMS-S), and the improved HE M795 (longer projo than M107, so it's more ballistically efficient and has greater range. And it's ballistically matched to the M483 DPICM/ FASCAM/ M825 I-Smoke rounds, so you can use registration and adjustment data from those projos for firing it.).

You need yet ANOTHER firing table for M712 Copperhead laser-guided projo (yes, you still have to get it CLOSE to the target, the laser is only for precision terminal guidance within it's tracking limits. You still have to get the projo within a few kilometers).

...And you need still ANOTHER firing table for M549 HE-RAP.

...Oh, and ANOTHER one for M864 ER-DPICM