US Army's mobile howitzer "shoot off"

[Mighty_Zuk]

3 hours ago, sunday said:

You may have ETC, the finest digital fire control, and the works. You may even have a fricking laser gun. However, if the barrel plus chamber assembly is travelling inside the mount at the time of firing there will be increased dispersion because there is another source of error, i.e. it is not straightforward to make a system that will ignite always at the same position of travel, and at the same travel velocity.

Ahh yes, that's what I was looking for! Unexpected travel after pulling the trigger. Thank you!

[Mighty_Zuk]

1 hour ago, bojan said:

Timing ignition is a less of the issue. If the barrel moves during firing there have to be tollerances. Even if those are 1mm for a length of the L/52 barrel (8m), calculate how much is that at 32+km. And it is going to be more than 1mm tollerance, else mechanism will seize in extreme heat/cold.

More variables you add, less you are in the control of the situation. Some things (modern recoil mechanisms) are there because things are just inconvenient w/o them, but from the accuracy perspective, the more you move from a totally fixed barrel the more you are in the problem.

It is a great idea for a light howitzers firing at ~10km. For something that people want to fire at 40+km... It just brings problems, w/o really doing anything fundamental. Who really cares that lightter vehicle can be used for it, if it is brigade level, 40+km ranged arty and it still needs shitloads of heavy trucks just to bring it ammo?

 

3 hours ago, sunday said:

You may have ETC, the finest digital fire control, and the works. You may even have a fricking laser gun. However, if the barrel plus chamber assembly is travelling inside the mount at the time of firing there will be increased dispersion because there is another source of error

Quoting both because it's for you two.

This specific example is not related in its subject, to the subject of our debate. It's just an example. The study was not about the feasibility of an ETC gun, and we all know that for the near future, any non-conventional gun is not feasible. The study I was referring to was about possible gains in accuracy by using various non-conventional guns with different firing mechanisms.

Studied cases showed a reduction of the firing delay down to 1/3rd of that of a conventional gun, which vastly reduced the margin of error.

Indeed there are cases where this is not taken into account due to the chaotic nature of high rate of fire. With high RoF medium caliber guns, particularly for air defense, merely achieving contra-harmonic movement of the barrels is a great achievement (no small feat obviously, but it makes firing delay issues much less significant).

Specifically for Bojan now, these firing delays are so tiny that I doubt any sensor would be able to, within that time space, pick up and fixate a movement. Let alone have the FCS do anything about it. Not that I can even imagine what can be done. 

It's just something that the OEM measures during development, documents, and then adds it to the calculation of potential deviation of non-guided shells, where many other factors come in.

[bojan]

You did not get the point. Barrel has to move on it's cradle forward when gun is fired. In order to move there have to be some tolerances built in. Those tolerances result in barrel moving undesirably left or right or down or up compared to what is "theoretical" position of barrel. Sure, it is a small movement, but any such movement will affect accuracy. And realistically... no way it will be just 1mm, that would be 1.24x10^-4 error level. More likely it will be something like 3-5mm, 3.7-6.2x10^-4.

1mm/8060mm error is 4m @ 32km or 0.127mils

3mm is 12m or 0.38 mils

5mm is 20m or 0.63 mils

That is additional dispersion you are gonna have due the barrel moving, even if you time ignition perfectly.

Edited December 20, 2020 by bojan

[Mighty_Zuk]

@bojan how did you get this specific number?

And I agree that recoil management isn't always going to be necessary. But if we are to look at the new L58 XM1299 gun of the ERCA, then there is doubt it will fit on a truck and survive extended firing missions.

It may be necessary to use a turret on a truck to best utilize an L58 gun (i.e fire at a high RoF), but at that point the choice of a truck as a chassis is in doubt, because much of its advantages are thrown out the window, at least that's how I see it.

[bojan]

Knowing general machining precisions for some military hardware moving parts. Generally ways on which barrel moves will be made with ~3-4x10^-4 tolerances, with 1.5-2 x 10^-4 being top of the line stuff generally not used on mundane things like artillery. Then there are additional tolerances to accommodate for thermal expansion/shrinking. So barrel is gonna "wobble" during forward movement, even if only by the few mm at the muzzle end. But those few millimeters quickly translate to meters or 10s of meters at longer range. Problem is that if only this was a factor all would be fine, but then there is an inherent dispersion of the gun tube, projectile and powder charge. So such system will always be less accurate than "regular" one.

As for solving the problem of recoil on truck... Just use jacks to stabilize it FFS, it is not some sort of black art. Also, 58 cal 155mm barrels with 50+km  range are a solution in the search of the problem. 52 cal barrels are already pretty pointless for a brigade level arty, for anyone who can afford more than a 4-5 brigades. If you want those ranges use rockets/missiles.

Edited December 20, 2020 by bojan

[sunday]

Exactly. While a conventional hydro-pneumatic recoil system needs to have tolerances, in conventional systems I guess (I am not mechanical engineer) it is easy to make the barrel to recuperate precisely to the mostly same fixed position for firing, and having the round departing the barrel before the later has moved significantly.

[wendist]

19 hours ago, bojan said:

There are more about it, this shootout is single gun. Then selected one provides additional two for testing (IIRC until the end of 2021) and further 18 for adoption in 24 months starting in 2023 or 2024.

Thanks for answering my question (and to Dawes as well). I guess that this first selection is only preliminary. At what time can a supplier expect to have won the contract? Does the supplier take the full financial risk during this testperiod? I'm asking because as far as I know BAE does not have 18 Archer guns available right now, they would have to start some type of test series production for this which sounds expensive. 

[bojan]

IIRC they provide one for shootout, get paid for 2/18 examples.

Edited December 20, 2020 by bojan

[Dawes]

There's also the cost of integrating the selected gun system on to a US chassis (Oskosh HEMTT, etc.). Or in the case of the Archer, for example, would it be desirable (financially or operationally) to just buy the system as-is?

[wendist]

BAE have already shown a MAN based version of the Archer system so I guess they are ready to adopt it to any suitable vehicle the customer prefers. What I would like to know is where they will get the gun from.

[bojan]

Slovakia, one of the few remaining in Europe that can make gun from the beginning to the end. IIRC Germans at some moment considered buying blanks from them for new production of PzH2000.

Edited December 20, 2020 by bojan

[wendist]

22 minutes ago, bojan said:

Slovakia, one of the few remaining in Europe that can make gun from the beginning to the end. IIRC Germans at some moment considered buying blanks from them for new production of PzH2000.

Interesting! Who would that be? Or does BAE have the capability in house?

ETA: Are we talking about ZTS-Special?

Edited December 20, 2020 by wendist

[Olof Larsson]

59 minutes ago, wendist said:

BAE have already shown a MAN based version of the Archer system so I guess they are ready to adopt it to any suitable vehicle the customer prefers. What I would like to know is where they will get the gun from.

Like the existing Archers, I guess they would have to get them from Slovakia.

[wendist]

5 minutes ago, Olof Larsson said:

Like the existing Archers, I guess they would have to get them from Slovakia.

Are you saying that the 48 Archers that have been produced so far has gun barrels from Slovakia?

[bd1]

13 hours ago, bojan said:

 

As for solving the problem of recoil on truck... Just use jacks to stabilize it FFS, it is not some sort of black art. 

i actually think Hawkeye 105 on humvee is great idea since being based on humvee the loader does not need any special help loading the gun, but could the humvee chassis (if hydraulic jacks are lowered to the ground) carry any other 105mm howitzers like hawkeye? i guess the russian Nona 120 could be carried and shot of course, but anything else? 

would be cool if 105 humvee mounted howitzer were possible, that would be one of very few occasions where humvee size would be spot-on

Edited December 20, 2020 by bd1

[JWB]

14 hours ago, bojan said:

So barrel is gonna "wobble" during forward movement.........

Center of mass of vehicle/mount will shift forward potentially causing vehicle and gun to tilt.

[CaptLuke]

Just now, JWB said:

Center of mass of vehicle/mount will shift forward potentially causing vehicle and gun to tilt.

The XM-204 had stability problems (euphemistically referred to as "baseplate hop") during misfire when it was emplaced on slopes greater than 5 degrees.  If the forward momentum of the barrel assembly was not stopped by firing then there was baseplate hop and instability which, if a story I remember running across but can't reference was true, means that the howitzer fell over.

This brings up some associated design requirements for FOOB guns; this is from TMIL-HD6K-78S(AR) Design of Towed Artillery Weapons:

Quote

The soft recoil mechanism, however, creates unique new design requirements - buffers at the forward end of the recoil
travel stroke and overshoot buffers at the rear of the stroke - to prevent damage in the case of cookoff or zone
setting errors.

Presumably the buffer at the forward end of the recoil travel stroke is for misfire, while the overshoot buffer is in case of cookoff/zone-error.

BTW: just to put a date on it, the XM-204 was tested in 1977.

[bojan]

1 hour ago, JWB said:

Center of mass of vehicle/mount will shift forward potentially causing vehicle and gun to tilt.

That also, through it is theoretically possible to compensate for that.

As I have noted, best thing for accuracy is fixed mount gun. But since that is utterly impractical compromises are made, but more factors and tolerances you enter more dispersion will be there. No free lunch.

Edited December 20, 2020 by bojan

[bojan]

2 hours ago, wendist said:

Are you saying that the 48 Archers that have been produced so far has gun barrels from Slovakia?

It is possible those were locally finished, but IIRC only Slovakia makes blanks. Well, Russians also do.

Edited December 20, 2020 by bojan

[bojan]

1 hour ago, bd1 said:

...Hawkeye 105 on humvee...

Problem with 105mm is at what level is it supposed to be?  Bn? 120mm mortars and especially gun mortars give it a real run for money, almost comparable range, but less weight and more payload. For a Bde level it is horribly obsolete.

Edited December 20, 2020 by bojan

[Dawes]

Whoever the winner is, it seems that they'll have to set up a US production line or team with a US manufacturer.

[bd1]

1 hour ago, bojan said:

Problem with 105mm is at what level is it supposed to be?  Bn? 120mm mortars and especially gun mortars give it a real run for money, almost comparable range, but less weight and more payload. For a Bde level it is horribly obsolete.

batallion, with modern dispersed fighting the howitzer range advantage is probably needed, and since it can be shot at lower elevation, it´s more survivable against counterbattery radars. besides, on brigade level it can do some missions, like supression way more economically than 155.

besides - at batallion level the ammo weight differences between 105H and 120M are not that big, so no big differences in logistics

[sunday]

4 hours ago, bojan said:

Slovakia, one of the few remaining in Europe that can make gun from the beginning to the end. IIRC Germans at some moment considered buying blanks from them for new production of PzH2000.

When we visited Rheinmetall's facility at Unterluss, we saw a PzH 155mm barrel blank being prepared, still in the stage of a big cylindrical chunk of cast steel, possibly forged already. The firm's representative told us the blank had come from Thyssen.

[bojan]

So they do have production capabilities. Wonder why they considered Slovakia as a source, possibly alternative source or just cheaper?

[sunday]

48 minutes ago, bojan said:

So they do have production capabilities. Wonder why they considered Slovakia as a source, possibly alternative source or just cheaper?

Well, that was in 2011, they could have shut down the necessary facilities since then, but I think the fleet of PzH2000 still needs spare gun tubes.

Edited December 20, 2020 by sunday