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Stealthflanker's avatar

Longinus APFSDS The Introduction

Err supposedly this image is not simply depiction of APFSDS (Armor Piercing Fin Stabilized Discarding Sabot) promotion and introduction but rather a part of my "infographics" Project of "APFSDS-101 What, Why and How" Containing some explanation and bit history of APFSDS. Nonetheless i foresee that i would encounter difficult problem in explaining mechanism of penetration or perforation of the round.

Why such problem ? Because there are still debates regarding how actually APFSDS round work, how it can penetrate and later perforate (if one prefer to differentiate between perforation and penetration ) its target. For steel target (RHA) It might be quite well established that the round may "shorten" Itself due to immense amount of stress during penetration process and later once it reach end of the armor plate the round will break into spall (Both large and small) For rounds made out of DU (Depeleted Uranium) Another process may occur where the fragments of the round can burn (Pyrophoric effect)

Modern armor however are NOT only composed of homogenous steel but rather layered with different materials. For example the British made "Cobham" Which currently become mainstay of NATO armor technology consist of steel outer plate backed with some layers of other material (Classified unfortunately) Those materials have different density and physical properties Thus will behave differently when hit by APFSDS.

Modeling penetration/perforation on such armor material are not simple, one must actually do "trial and error" by live fire testing Or FEM (Finite Element Modelling) Computation to get his/her result which unfortunately beyond my ability.  Current "measure of effectiveness" By "RHAe" or RHA Equivalent value or "Thickness effectiveness" Value (Anyone playing WOT and visit its forum or visit forum must have already know the famous "Armor Basics" pdf by Paul Lakowski) Are "under attack" and in my view at won't stand the scrutiny.

There are however some papers one can find and download at DTIC website containing penetration test result on ceramic armor material but it's only deal with single homogenous material instead of combination of different materials modern armor has.  Debates so far are not helpful for me because the arguments are seriously flawed by the fact that anyone claiming RHA Equivalent method are unable to provide comparable model of penetration.  Basically they knew it wrong but don't know how to fix it.

Thereby my decisions however is to hold any claims, statements and calculations regarding to the APFSDS mechanisms of penetration/perforation until i managed to find a way to model it. Thus i won't claim any penetration/perforation depth figure for the APFSDS and perhaps relies more on "artistic license".. This is deviant art after all not hyper physics forum.


The Longinus is the improved version of our previous "Lohengrin" APFSDS round, it boasts more accuracy due to provision of better sabot with two area of contacts which will reduce in barrel yaw. Sabot material is also improved by introduction of composite material to reduce parasitic weight thus allow higher muzzle velocity compared to conventional steel-aluminum sabot.

The kill vehicle or "dart" is a monoblock tungsten heavy alloy with very high Length to Diameter ratio (L/D) of 30 to help the penetrator to resist yaw induced by either sloping or Explosive Reactive Armor.

The APFSDS round can be fired by our standard 138mm gun and accommodated in already exist autoloader design of our AFV's
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What is the length of this SABOT? 41 inches? 
   StelthFlanker thanks for the work and information. 

   Do you know if the 4Km/s limit applies to copper cone of shaped charge? Density would seem to play a large role but I *am guessing* here. DU is far denser than Cu, yet Cu cuts deep, AFAIK 3BK-31 rounds may penetrate up to 800 mm of RHA 

   Speed v.s. fluids v.s. pure kinetic energy 
Stealthflanker's avatar
I wonder.

In fact tho there is still much to learn about shaped charge phenomenon. The material crystal structure appears to play more roles in shaped charge penetration than raw density.

There is a paper about it which i need to find first.. hope i could find and link to you later :D
Schaghticokekid's avatar
The question is, can it penetrate an AT Field?

Seriously though, a very neat concept piece.
Stealthflanker's avatar
This thing is designed for engaging modern tank armor. not angel AT field :3
Schaghticokekid's avatar
That, my friend, is what I call a lack of ambition! A spear to the face is one thing, but let's see what an APFSDS round can do! 
canuleyo's avatar
So in a Ace Combat like universe, Vihenia would be an eequivalent to which nation of Strangereal?
Stealthflanker's avatar
i wonder... Yuktobania maybe.
canuleyo's avatar
Yeah, closer to Yuktobania.
Stealthflanker's avatar
but we don't have scinfaxi or other fancy stuff :3
canuleyo's avatar
A middle point bewteen Yuktobania and Usean continent (ISAF) then :D
Stealthflanker's avatar
nuuu :3.. Strngereal have no dragons and elves
Stealthflanker's avatar
Thanks a lot, and thanks for the watch :3
malovence's avatar
Wonder what would happen if you further accelerated the round within a linear accelerator?
I've been trying some calculations(very basic mind you, not all the details that go into muzzle velocity calculations), I've tried to do it for a theoretical 20mm sabot round fired with normal propellants shot through a linear accelerator. Got 7-8 km/sec out of it. The linear accelerator slapping on another 5-6 km/sec on top of the theoretical 20mm sabot shot. 
Stealthflanker's avatar
Then the penetration will go hydrodynamic, similar as penetration of shaped charge jet (HEAT) Based on graphics i see in Technology of Tanks however, against steel target, penetration depth become constant (Not increasing further) After velocity of 4 km/s.

Penetration depth can be approximated using Newton Impact theory…
malovence's avatar
So there actually is a limit of penetration capability then? I suppose after that the only purpose for the added acceleration would be range I suppose? Excessive to the extreme perhaps but a purpose still. Along with the actual projectile travel time. 
Stealthflanker's avatar
Well one can try extending the length of the rod to gain some (but not as much) More penetration ability but this in turn will increase the propellant and perhaps material requirement for the gun as increase in projectile mass correspond to increased pressure that demand better material for conventional gun.

and yes the added acceleration can be used for extended range for indirect fire case as US Navy railgun program.
Somnium-23's avatar
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