Competition: Californium 2250

[Toxn]

This is the reworked version as it stands at the moment:

 

The length has gone down to around 550mm, while the mass has gone up to around 16kg + 1kg for the pad assembly. The performance has accordingly dropped to about 330m/s from a standing start. The core assembly is now held front and rear, and forms part of the rocket nozzle.

 

The starting velocity is now 1370m/s, going up to perhaps 1600m/s. The penetration is something like 220-310m/s. A bit disappointing, but we'll work on it.

 

Edit: so something I just realised is that once you anchor the shell casing to the rod at two ends, it effectively stiffens the whole thing.

 

Edit 2: I also realised that you get more bang for your buck by saving weight than you do by chasing higher thrust. This is the further revised version:

Penetration is up to around 330mm at the muzzle, while weight is down to around 9.8kg plus a 1kg rear cradle. Initial velocity is up to 1700m/s, which is very respectable.

 

The motor provides enough thrust to reach ~250m/s from a standing start, which is getting to the point where I suspect that it's only going to sustain velocities rather than boost them significantly. Nevertheless, you might see up to 360mm of penetration at maximum here. The motor is used for simulation purposes burns for around 1.5 seconds, so the rod will be around 3km out before velocity starts dropping off.

 

The front assembly is supposed to be aluminium, and tapers from a wall thickness of 2mm to 5mm at the joint. The rear body is 5mm carbon steel, and the assembly is constructed so that the rod pieces effectively brace the whole structure. The entire assembly is actually slightly undersized, with the cradle acting to centre it in the bore (I may consider adding a set of stub fins to the forward body as well).

 

The rod pieces themselves are segmented, with the forward rod having a tungsten bit in it. The final penetration is calculated by lowering the initial rod performance by 15% and then adding the tip performance on.

[Lord_James]

I totally forgot about RAPs; thank you @Toxn. 

 

Hold onto your bagels, everybody, because I just found some inspiration for some new shells and things are about to get weird! 

[Toxn]

5 minutes ago, Lord_James said:

I totally forgot about RAPs; thank you @Toxn. 

 

Hold onto your bagels, everybody, because I just found some inspiration for some new shells and things are about to get weird! 

Yes, yes!

Let the weirdness begin!

[Toxn]

Speaking of which, wouldn't it be great if this competition ended being decided by a RAP battle?

 

I'll see myself out now...

[Lord_James]

@N-L-M, what is the cetane / octane rating for fuels in the DPRC? 

[N-L-M]

JP-8 is the one true fuel for all DC-8 and ground vehicle needs.

[Whatismoo]

 

Report from Lt. Col. [REDACTED] People's Auditory Forces Directorate of Political-Moral Reliability, Auditory and Political Officer for SNVZ and Military-Industry Liaison Officer for RFP "New Battle Tank"

 

Today, exaltedly equal comrades of multitudinous genders, or none at all, I have wonderful news! We will be discussing the ammunition and developmental armor schemes for the SNVZ AFV-50 project. First the ammunition types. 

 

 

• High Explosive-Fin Stabilized
  • The primary general purpose support round for the vehicle, equipped with a standard and super quick fuse setting
  • M/V in excess of 500m/s
  • 6.32kg of TNTe filler
  • Spoiler

    

• High Explosive-Fin Stabilized-Urban
  • A “supercharged” HE-FS round designed for short range demolition work
  • 19.88kg TNTe filler
  • Spoiler

    

• Armor Piercing Capped Ballistic Capped-Fin Stabilized
  • The Primary Anti-Armor kinetic energy round
  • Using highly energetic bursting materials, we have achieved devastating beyond armor effects
  • Meets or exceed armor penetration requirements
• Armor Piercing High Explosive-Fin Stabilized Base Bleed
  • A long range anti-armor round
  • Base bleed reduces drag (and thetan level) throughout the projectile’s flight to ensure optimal retention of auditory capacity.
• [AUDITED]
  • [AUDITED]
  • Spoiler

    

• [AUDITED]
  • [AUDITED]
  • Spoiler

    

• Chemical Effects-Anti Tank
  • An anti-tank projectile which generates its armor penetrating effects from chemical energy (explosives) within the round
  • Spoiler

    

• Multi Chemical Effects Shell
  • A heavy chemical effects shell with improved explosive qualities at the expense of range and velocity to improve the numbers of use cases.
  • Spoiler

    

 

 

These shell types will allow the AFV-50 to engage and defeat all known and planned enemy combat vehicles should they foolishly decide to attack the peace loving peoples’ republic. They are effective at all combat ranges, allowing the gun tank to decisively deconstruct aggressions, micro and macro, and fulfill its combat tasks.

 

 

 

Secondly for today, the SNVZ collective would like to discuss the early development of our armor schemes. While it is a capital offense to shame for weight, it is important to note that later design iterations have exceeded initial goals. Truly SNVZ and the AFV-50 program have been blessed with the bounty of L Ron Hubbard Thought and it is important to recognize that our vehicle is healthy at any size.

 

Recognizing the threat posed by CE warheads, the design team initially investigated the use of large volumes of Glass Textolite, alongside steel. (Fig.1) Unfortunately the thicknesses required were rather extreme, and resulted in deep inefficiencies. 

 

Spoiler

 

Fig.1

 

To compensate for these deficiencies the ratio of steel to textolite was increased, however this also increased the weight. The integration of layers of ceramic and High-Hardness Steel was investigated, however the density/areal density of these packages was deeply unsatisfactory. (Fig.2)

 

Spoiler

 

Fig.2

 

 

At this time the collective investigated various arrangements of so called “Special” or “Composite” armor arrays. They were found unappealing due to the large volumes needed to contain them, and the angles required for best performance. (Figs. 3, 4, and 5)

Spoiler

 

Fig.3

Spoiler

 

Fig.4

Spoiler

Fig.5

 

 

At this time it is unclear what growth potential the Cascadian tandem-HEAT warhead may have, and/or the Mormohideen 2”/4”. These high lethality threat systems may not be able to be defeated without elaborate and economically infeasible exotic armor schemes, in the view of the SNVZ design collective. At this time the SNVZ collective is pursuing further armor concept development, but it appears that the weight and size of tanks must increase drastically before adequate levels of protection are possible. Therefore it appears that the medium tank as it is known, cannot be survivable on the modern battlefield.

 

The Cascadian introduction and adoption of the <<Norman>> series appears in hindsight to be a drastic misstep. The current service variation (NORMAN-A) appears to utilize conventional steel armor materials in a relatively novel layout. However, this is hopelessly outclassed by modern tandem charge CE technology. The Cascadians appear mindless stooges of chauvinist revanchism and warmongering, however despite their perfidy, they are not stupid. They are likely to be investigating the potential for equipping a derivative of NORMAN-A with exotic “special” or “composite” armor systems. They are fools for doing so! To defeat modern tandem-shaped charges would require far too much volume and weight of armor to fit in a traditional “medium” size tank. But the Cascadian dogs have made their bed, and so they shall sleep in it. They may as well have introduced the kite shields and chainmail of its namesake, for the good it will do them. In the modern threat environment, where tandem charge ATGMs outrange the ability of armor to detect and engage them prior to, or even after, launch, the Medium Tank is dead!

 

For this reason, the SNVZ AFV-50 designs have blossomed through the iterative process, between 20 and 25% over the initial predictions. Fortunately there is historical precedent for such a matter. Ancient pre-war historical texts speak of a mightily effective Main-Battle Tank, the first of its kind. During the Second Great War it was created, and grew through its design process it grew to just over 1.25x the initial design goal. The Tank Struggle Vehicle Mark 5, or “Panther”, was widely regarded by the ancient sages of the “AxisHistory” forum as the best tank of this second of the great wars, with armor, mobility, and firepower an order of magnitude above the delicate, vulnerable, underarmed and expensive Medium tank M4 "Ronson". Clearly in light of this the weight gain of the AFV-50 is not of much relevance. Collective efforts of SNVZ to improve armor protection continue, and appear to be reaching some success. The DPRC, guardians of the people and L. Ron Hubbard Thought, as well as our most eminent and wise leadership, the most Gracious and Serene Majesty Queen Diane Feinstein the VIII, require cheap winners, like the TSV Mk.5 "Panther" of old, rather than "expensive losers" like the "NORMAN" or "Ronson"! On this matter, I assure you that the shock-engineers of SNVZ will deliver!

[Lord_James]

Ammo update: 

 

I haven't completely finished the rough draft for the weird ammo yet (sorry @Toxn), but I did finish the primary ammo types: 

 

155mm S11-I (APCBC-HE-T) 

Spoiler

 

Projectile sans discarding bands is 58.3kg (59.6kg with); 835.8mps at muzzle. 

 

3.5/25crh windshield with hardened steel penetrating cap and base fuse. Same boattail and discarding bands as previous AP shell. 

 

 

155mm S21-I (HE-FRAG-T) 

Spoiler

 

43.7kg without discarding bands (45kg with); 948.2mps at muzzle. 

 

3/9crh windshield with steel hood. Can equip nose and base fuses. Same boattail and discarding bands. 

 

 

C4B (800mm) semi-combustible propellant charge

Spoiler

 

20.6kg of propellant, whole case should be ~21kg when I bother making the brass stub cartidge. 

 

 

Both projectiles are 900mm long with a similar construction to my first shell and are spin stabilized; the propellant charge is the maximum size charge available for C4B guns (all mods). They both also contain the combined tracer / base burner as my first shell. 

 

 

To do: 

 

A. calculate penetration / add masses for each piece of the projectiles. 

B. Ask @N-L-M if 25% is a good velocity conservation modifier for a base burning artillery shell.

C. Ask for the density of A-IX-2 (I want to use that instead of Explosive D for the filler). 

D. fix some errors I may have made (I want the burner to last for 3km [for army versions, navy burners should last out to 15km], but don't know how large to make it). 

 

 

PS. I used the S21 as the largest (by volume) shell to estimate my autoloader's capacity, and it turns out I can only fit 17 such shells I don't have the patience to remodel my ammo for higher autoloader capacity, so I will leave their dimensions as is. 

[Whatismoo]

5 minutes ago, Lord_James said:

A-IX-2

Astrolite A/G has better brisiance, iirc

[N-L-M]

23 minutes ago, Lord_James said:

B. Ask @N-L-M if 25% is a good velocity conservation modifier for a base burning artillery shell.

I don't get what you mean by that.

[Lord_James]

15 minutes ago, Whatismoo said:

Astrolite A/G has better brisiance, iirc

 

per the internet: Astrolite is a liquid, and IIRC liquid explosives are not effective as high velocity bursting chrages, and RDX (the main ingredient of A-IX-2) has a comparable brisance value. 

[Whatismoo]

Just now, Lord_James said:

IIRC liquid explosives are not effective as high velocity bursting chrages

Astrolite has an 8600m/s detonation velocity, though?

[Lord_James]

4 minutes ago, N-L-M said:

I don't get what you mean by that.

 

I mean it reduces the drag by 25% for as long as the burner is active (in this case: 3km), sorry for weird wording. 

 

2 minutes ago, Whatismoo said:

Astrolite has an 8600m/s detonation velocity, though?

 

Liquid explosives are not good in high velocity applications, as in a 155mm naval shell traveling at >800m/s. 

[Whatismoo]

4 minutes ago, Lord_James said:

Liquid explosives are not good in high velocity applications, as in a 155mm naval shell traveling at >800m/s.

I mean if you want to build a tracked light cruiser...

[N-L-M]

10 minutes ago, Lord_James said:

mean it reduces the drag by 25% for as long as the burner is active

Sounds reasonable.

[Lord_James]

Penetration table and velocity charts for S11-I and S21-I (velocity was calculated by multiplying 0.25 to ΔV and adding that product back V_f): 

 

S11-I: 

Spoiler

 

Actual Velocity and Penetration: 

 

000m: 835.8 m/s --------- 392mm 

100m: 820.1 m/s --------- 381mm 

200m: 804.7 m/s --------- 371mm 

300m: 789.5 m/s --------- 361mm 

400m: 774.4 m/s --------- 351mm 

500m: 759.6 m/s --------- 342mm 

1000m: 689.0 m/s ------- 297mm 

1500m: 623.8 m/s ------- 258mm 

2000m: 563.0 m/s ------- 223mm 

2500m: 506.8 m/s ------- 192mm 

3000m: 458.3 m/s ------- 166mm 

 

 

S21-I: 

Spoiler

 

Actual Velocity: 

 

100m: 931.5 m/s 

200m: 915.1 m/s 

300m: 898.8 m/s 

400m: 882.7 m/s 

500m: 866.8 m/s 

1000m: 790.5 m/s 

1500m: 719.7 m/s 

2000m: 654.3 m/s 

2500m: 593.4 m/s 

3000m: 537.0 m/s 

 

[T___A]

On 4/11/2019 at 11:08 AM, Lord_James said:

@N-L-M, what is the cetane / octane rating for fuels in the DPRC? 

 

I'll allow gas turbines with conventional fuels, or better yet, something like alcohol, so we can put our gluten free wheat stockpile to good use.

[N-L-M]

5 hours ago, Lord_James said:

velocity

Your velocity drops off startlingly fast. I suggest checking the drag and mass properties.

[Lord_James]

4 hours ago, N-L-M said:

Your velocity drops off startlingly fast. I suggest checking the drag and mass properties.

 

I maxed out mass (15000 gn) and minimized diameter (0.10 in) for JBM, while using the G7 coefficient, and I only get an extra 4 m/s at 3km. If I bump up the elevation to 4500ft (Reno, Nevada), I get an extra 50 m/s... but that's at 4500ft, and that extra penetration would be useless against the Deserent wheeled death traps and jihadyotas. If you have an alternate way to calculate drag and ΔV, I'm all ears. 

[N-L-M]

3 hours ago, Lord_James said:

15000 gn

That's roughly 1 kg.

Or around 2% of the usual weight of a 155mm shell.

I have a more robust method I'll be posting a bit later.

[Lord_James]

40 minutes ago, N-L-M said:

That's roughly 1 kg.

Or around 2% of the usual weight of a 155mm shell.

I have a more robust method I'll be posting a bit later.

 

Thank you; my adventures into the internet to find a better solution come up questionable. 

 

Anyway, in reference to NERA: do the brackets and spacers have to be mounted on structural components? 

[N-L-M]

Yes.

[Datengineerwill]

I've been stalking this for a while and decided to start up my own submission.

 

Currently working in Onshape so everyone can go in and poke around the assembly if they want.

I still got a long way to go but it's a start.

Next up is finishing the powerpack, inserting the turret blockout, designing the autoloader, modeling the sponsons, skirt armor, suspension.

I'll Probably be done with most of that by Monday.

 

As a side note a lot of the parts in the assembly don't have the correct mass as of yet...

[Lord_James]

37 minutes ago, N-L-M said:

Yes.

 

Ah fuck... ok, that makes things a little harder. Was working on my arrays and now I need to revise 2 of them 

[N-L-M]

@Lord_James

Alright people, it's time for M A T H. For convenience's sake, all the units in this post are going to be SI, MKS.

Today's episode: external ballistics and differential equations!

So, we know that the force of drag is roughly proportional to the velocity squared (not entirely true, but we'll get back to that later).

Drag equations take the following form:

Where Rho is the air density, a is the reference area of the projectile (for shells and rockets, the convention is that the reference area is the cross sectional area of the projo), and Cd is a dimensionless drag coefficient.

Additionally, we know from Newton's second law that F=m*a, which can be rejiggered to a=F/m.

And we know that acceleration is by definition the derivative of velocity by time.

Combining the above, we get the following differential equation:

Where m is the projectile mass.

Solving this diff eq, (and the one for velocity being the time-derivative of speed), we get:

Where x0 and v0 are the initial position and velocity, and ln is the natural logarithm.

We now have almost everything we need, but where are we going to get drag coefficients for 155mm shells at this time of day?

Why, DTIC of course!

DTIC has helpfully provided the complete measured drag curve for the shell,155mm, HE, M101 (The precursor to the M107, with different driving bands but otherwise identical): https://apps.dtic.mil/dtic/tr/fulltext/u2/209134.pdf

Consulting the graph so helpfully provided, we note something odd about our previous assumption:

The drag coefficient isn't a nice constant value, but instead varies with velocity! this is an outrage!

Except it only varies fairly mildly, so we can assume it to be quasi-constant, and we don't have to solve the diff eq for a velocity-dependent Cd (or Kd in the DTIC paper).

So assuming a M101 equivalent shell, launched at 800m/s, a Cd of 0.1 seems reasonable. Solving the above equations with the following constants:

I suggest shoving the above values and the equations found for velocity and range into Excel, and solving both by t, before observing the velocity as a function of range.

 

We get that for a range of 3000m, we have a ToF of 3.86 sec, at the end of which we have a terminal velocity of 755 m/s - A fairly significant residual velocity, I think you'll agree.

We then go on to note that throughout the flight, the velocity remains over Mach 2.5, and that therefore the choosing of 0.1 for Cd is reasonable, as at no point in the flight would it be any higher.

 

For those planning shells other than 155mm, note that drag coefficients are constant for similar forms, regardless of scaling, but the reference area and mass scale with S^2 and S^3, respectively.

For those considering the drag coefficient plots for more optimized projectile shapes, I suggest consulting @Sturgeon regarding drag coeffs.