Competition: Californium 2250

[Whatismoo]

22 minutes ago, Toxn said:

Check here:

From memory it's just steel and rubber layers with no gaps.

Thanks!

[N-L-M]

Segmented rods are indeed Halal! 

You have to make sure the sabot can adequately grip both parts to not leave the rear one behind, and they suffer from a 15% penalty to penetration, and can only be stacked 2 high, but other than that? Go for it!

@Toxn I'm pretty sure the tungsten bit penetrates more like a classic AP driven by the long steel rod and so L-O is not the best at describing it.

 

For the record, I'm willing to accept that a moderately longer 3BM-15 with a shorter WC core would have similar performance at similar velocities.

 

The claimed performance the Soviets got out of the extremely draggy 3BM-15 even at extended ranges suggests a bigger improvement, about which I am open to suggestions regarding how to quantify it. 

PELE is indeed possible if desired.

[Toxn]

2 minutes ago, N-L-M said:

Segmented rods are indeed Halal! 

You have to make sure the sabot can adequately grip both parts to not leave the rear one behind, and they suffer from a 15% penalty to penetration, and can only be stacked 2 high, but other than that? Go for it!

@Toxn I'm pretty sure the tungsten bit penetrates more like a classic AP driven by the long steel rod and so L-O is not the best at describing it.

The claimed performance the Soviets got out of the extremely draggy 3BM-15 even at extended ranges suggests a bigger improvement, about which I am open to suggestions regarding how to quantify it. 

PELE is indeed possible if desired.

No, it seems about right.

 

Modelling just the body you get a penetration of ~280mm at the muzzle. Modelling the body without the penetrator cavity gets you ~265mm

So the simulation results are only about 25-40mm off of where they should be.

 

I'd say model the body (sans insert cavity) and the penetrator separately (for really stubby inserts I use a cheat where you forcibly make the penetrator longer until the L/D is 4 and longrods will work properly, then just divide the penetration to correspond to the real length). Then just add them together to get the penetration at the muzzle. Getting numbers for the 2-4km range will be a bit of a fudge, but then that would be the case regardless.

[N-L-M]

Considering how draggy the Soviet rounds were and the rated performance at 2000m, I'd say Longrods is being pessimistic. 

[Collimatrix]

Yeah, the shorter penetrators mean that the fins have a lot less leverage for stabilizing the dart, which means that the fins are gigantic, which means draggy.  The Soviet insistence on full-caliber fins didn't help either.

[N-L-M]

1 minute ago, Collimatrix said:

Yeah, the shorter penetrators mean that the fins have a lot less leverage for stabilizing the dart, which means that the fins are gigantic

This is factually incorrect. You see, the upending moment is also proportional to the length. For a given upending force on an constant-section solid rod, we therefore find that the upending moment scales with rod length (as the moment arm is half the rod length), but so too does the stabilizing moment from a tail of constant size, as its moment arm is also approximately half the rod length!

And indeed, we find this to be the case:

The tail surface area of all the above darts is very similar.

[Toxn]

So a more banal question: what is the preferred base colour for DPRC vehicles?

[N-L-M]

Sea blue.

[Collimatrix]

1 hour ago, N-L-M said:

This is factually incorrect. You see, the upending moment is also proportional to the length. For a given upending force on an constant-section solid rod, we therefore find that the upending moment scales with rod length (as the moment arm is half the rod length), but so too does the stabilizing moment from a tail of constant size, as its moment arm is also approximately half the rod length!

 And indeed, we find this to be the case:

The tail surface area of all the above darts is very similar.

 

 

So... just don't use full-caliber fins.

 

 

And surely this changes a little if you have a tungsten head on a steel body.

[N-L-M]

3 minutes ago, Collimatrix said:

And surely this changes a little if you have a tungsten head on a steel body.

Yes, it moves the CG forwards, increasing the stability for a given aerodynamic arrangement (or allowing smaller fins to achieve the same stability).

[Xoon]

16 hours ago, DIADES said:

That is going to need one hell of a traverse drive.  Probably consume more power that required for mobility.  And if the powerpack is in the turret ( the frigging enormous powerpack) then drive to the tracks is hydraulic or electric?  Hydraulic has such poor efficiency that the powerpack would go from frigging enormous to double frigging enormous.  If electric, bear in mind that we don't have fancy electronics so no brushless high efficiency stuff and even brushed stuff will have to use old school magnetic materials - no fancy rare earths..  Then there is CoG height and cross slope stability etc.  But, it would be cool if you can make it work

 

Hydraulic efficiency is not that bad in a closed loop system with a swash plate pump.  Around 80-85%.  Combined with accumulators and very good torque characteristics and they are not that bad. 

When it comes to electric propulsion, simply use two engines, two generators and two motors. Efficiency should be pretty good here, if you can handle the catching on fire and dual engine stuff. 

 

14 hours ago, Collimatrix said:

 

 

@N-L-M and I discussed these crazy all-turret tanks.  He pointed out that this is basically how a lot of backhoes are configured.

I agree that it would basically require electrical or hydraulic drive.

 

I don't understand why you would want to make a tank this way, but Xoon may have some crazy ideas.

I probably wont design a all turret tank, though I like having the option. Maybe if I got some extra time. 

 

I am more aiming at learning and being creative in this competition than actually winning. 

 

 

For now, I am thinking about a Strv 103-BV206 hybrid with hydraulic drive. IF I can't have my microprocessors and transistors, I damn well am going to have my special tank.

[N-L-M]

3 minutes ago, Xoon said:

I damn well am going to have my special tank.

The DPRC strongly encourages diversity and acceptance of the special members of society, as well as their AFV counterparts.

[Collimatrix]

The trickiest thing about S-tank style configurations is ground pressure.  The entire hull is sort of the turret, so the tank needs to be able to turn very, very quickly.  The suspension is also how the gun elevates.  This ends up requiring a fairly short contact length of the track.

 

You can see in this:
 

on page 25 that the S-tank has slightly higher ground pressure than tanks that were a lot heavier.

[LostCosmonaut]

Questions that are actually somewhat relevant I promise:

 

• What are the armor penetrating capabilities of Cascadian LMG and HMG rounds (non-armor piercing)?
• About what technological level is the Calfornian Navy's submarine arm operating at? Is the Project 641 a reasonable comparison?

[N-L-M]

27 minutes ago, LostCosmonaut said:

What are the armor penetrating capabilities of Cascadian LMG and HMG rounds (non-armor piercing)?

Approximately 10mm RHA and 25mm RHA at 50m respectively (7.62 RFN and .50 BMG)

28 minutes ago, LostCosmonaut said:

About what technological level is the Calfornian Navy's submarine arm operating at? Is the Project 641 a reasonable comparison?

The Sea Auditory Forces are mostly a surface force, as the Thetan must not be unduly separated from the clean sea air.

The sub branch is however indeed operating Foxtrot equivalents.

[DIADES]

2 hours ago, Xoon said:

For now, I am thinking about a Strv 103-BV206 hybrid with hydraulic drive. IF I can't have my microprocessors and transistors, I damn well am going to have my special tank

and so you should.  Love hybrid vigor!

[DIADES]

10 hours ago, Toxn said:

the moment is on armament and working out what the minimum armour configurations look like.

Fascinating - we are all playing with the classic trinity.  Firepower, Mobility, Protection.  For me, in that order.

[Lord_James]

well... this is interesting: my 3.39kg steel alloy penetrator travelling at 976m/s at 2000m (1450m/s at muzzle) can penetrate 380mm of armor. 

[Toxn]

19 minutes ago, Lord_James said:

well... this is interesting: my 3.39kg steel alloy penetrator travelling at 976m/s at 2000m (1450m/s at muzzle) can penetrate 380mm of armor. 

How are you working that out?

[Toxn]

So I slapped together a calculator for armour packages:

 

https://drive.google.com/open?id=1Fg4nX85R86fBVpQzkc1WSL0PYejQwAWY

 

The calculator itself is a bit wonkily laid out (you input angles and thicknesses into Column C and can't play around too much with the composition of the various layers too much) because I slapped it together quickly and Solver is fairly stupid about anything that isn't a number. I also generated my own curves for the K1 values and haven't updated with the ones supplied by N-L-M. Finally; I'm still using the old thickness rules for ERA as I couldn't be arsed to change them (my current armour package only uses a single layer of ERA on the skin as an up-armour option).

[Toxn]

12 hours ago, N-L-M said:

The DPRC strongly encourages diversity and acceptance of the special members of society, as well as their AFV counterparts.

What about members who identify as AFVs?

[Lord_James]

13 hours ago, Toxn said:

How are you working that out?

 

I just remembered De Marre doesn’t really work on segmented rods... but I got those numbers by using the method in “estimating tank gun performance” thread, then using De Marre. 

 

My projectile is a segmented, sheathed, tapered rod 950mm long in total, but with a 740mm steel alloy penetrator composed of 2 rods (the forward is 14.5:1 and the rear is 10:1), and tapering down from 30mm to 18mm in a similar fashion to M735. There is also a steel cap (I hope this doesn’t count as a segment). 

[Toxn]

On ‎3‎/‎28‎/‎2019 at 4:13 PM, Toxn said:

Having futzed around a bit with various gun designs, I think I can confidently say that all-steel APFSDS with a 15:1 L/D limit cannot meet the penetration requirements.

@N-L-M Having spliced the monoblock formula into the spreadsheet I've been using, it seems that I was mistaken.

 

You can indeed achieve 350mm of penetration with an all-steel rod so long as you're willing to throw it very, very hard. Like, 2000m/s hard.

 

I now think that 400mm using a 15:1 rod and a tungsten bit is achievable, if difficult.

 

Edit: here's as close as I got using a 125mm gun and a maximum muzzle velocity of 1900m/s:

- Penetrator length: 524mm

- Penetrator diameter: 35mm

- Penetrator mass: 3.9kg

- Sabot: steel ring-type, 2.2kg

- Muzzle velocity: 1900m/s

- Penetration at muzzle (300 BHN RHA, 0'): 348mm

- Notes: no frustrum (lowers penetration). Round would probably use a fibreglass windscreen 

[N-L-M]

Change the reference to 250 BHN, should give a bit of an edge.

[Lord_James]

 

3 hours ago, Toxn said:

 

You can indeed achieve 350mm of penetration with an all-steel rod so long as you're willing to throw it very, very hard. Like, 2000m/s hard.

 

I now think that 400mm using a 15:1 rod and a tungsten bit is achievable, if difficult.

 

Edit: here's as close as I got using a 125mm gun and a maximum muzzle velocity of 1900m/s:

- Penetrator length: 524mm

- Penetrator diameter: 35mm

- Penetrator mass: 3.9kg

- Sabot: steel ring-type, 2.2kg

- Muzzle velocity: 1900m/s

- Penetration at muzzle (300 BHN RHA, 0'): 348mm

- Notes: no frustrum (lowers penetration). Round would probably use a fibreglass windscreen 

 

At what velocity do steel penetrators shatter? I kept my sabot at 1450m/s because I was under the impression that steel couldn’t handle much faster. 

 

 

@N-L-M, just to be extra uber sure, the normalizing cap on a penetrator doesn’t count as one of the 2 segments on a segmented rod, does it? I’m trying to make a ~0.4kg cap for the rod but am a little afraid you might count it as another segment. 

 

Also, for the HEAT rounds: what constitutes high and low pressure? Would it be the difference between a full pressure and recoilless weapon, or is there a difinitive “above X pressure, it is a high pressure gun”?