RPG vs. Bulletproof Glass (including extreme slo-mo)

[Capt. Toleran]

I know all of us knew it would go down just like this (I mean cmon, plasma stream, right?) but here's a test they did on Japanese TV apparently. The guy who fired it who was talking at the end sounds Vietnamese, maybe they did the show there?

http://www.liveleak.com/view?i=00c_1200817012

[kipanderson]

Hi,

Interesting little film.

I wonder exactly what the warhead was… not real HEAT for sure? Some form of HE I guess.

All the best,

Kip.

[flamingknives]

Why not HEAT, Kip? I suppose that the warhead was a fair way into the glass before it went off. The effect looked like you'd expect from shaped charge though.

Btw, Capt., not a plasma stream, just very, very quick.

[Darius359au]

It was a HEAT warhead but the rocket penetrated the glass before going off - If that had been on any sort of armoured vehicle they'd be having to wash the back out with a hose because the warhead would be going off inside.

[Capt. Toleran]

I was under the impression the focused warhead aspect of a HEAT round created a centrally focused plasma stream after initial impact -- I was also under the impression the whole point of a rpg (the shape) was to be a HEAT round. Was it only a HE? Either way, I'm sure we can all agree that had that been a Stryker or Humvee, it would have experienced some panicking and decreased efficiency. That mannequin's arm was blown off at the wrist, and it got an instant haircut.

[Flanker15]

Yeh it was HEAT for sure, the unfocused jet was caused by the rocket's kinetic energy smashing through the glass before detonation. This means the shaped charge exploded into open air which is ineffective, the glass acted much the same way as armor skirts on WW2 tanks.

If that had detonated on Humvee window and they had all their doors closed, the pressure wave would be very bad for the occupants.

[flamingknives]

The shaped charge propells and focuses a metal liner so you get a jet travelling at up to 7km/s. It isn't plasma though, and doesn't rely on temperature effect to penetrate. Just incomprehensibly high velocity.

[KGB50]

When a HEAT warhead hits the target, the rear of the warhead detonates, cause a stream of molton metal that melts through the armour of the target. It uses the same principle as the German Panzerfaust from WW2.

[Other Means]

What happens to the explosively created penetrator? Does it stay attached to the rest of the warhead or what?

It seems that the actual penetration would not be much bigger than a WWII AT rifle - what happens to the target to make them so effective?

[Flanker15]

It works because it is so hot and traveling so fast that it will bore through pretty much anything. The jet of metal is focused forward by the shape of the explosive (eg shaped charge effect), it requires a pretty flush contact with a solid object to work properly. If it is able to escape out into open air the speed and heat is dissipated ineffectively.

But when it bores through armor into a enclosed compartment the sudden increase in heat and pressure cause instant death to the occupants and ammo explosions.

[Other Means]

It's a pretty small area to be radiating heat, so I don't think that would have more than a very local effect, it's also a pretty small area to cause dramatic overpressure.

I can see that the very high velocity of it could cause a dramatic shockwave with it's over-pressure, but no more than that - but maybe that's enough what do I know?

Is it just that modern tanks are just so full of equipment that something's bound to be wrecked?

[c3k]

What was MORE interesting was the point of impact. The gunner had absolutely perfect conditions. He was close, braced, no wind, aimed, etc., etc., and still just barely hit the panel. It looked to be approximately 18"x30", give or take. And he almost didn't hit it.

Now, how do the CMSF Syrians, under fire, nail a hard moving target at 100's of meters with those things?

Regards,

Ken

[flamingknives]

A shaped charge jet is not inherently hot. If you recover the jet without it hitting somthing hard, there are certain indicators that show it doesn't even melt.

However the jet is travelling between 2 and 7 km/s (it varies down the length) and is separate from the rest of the projectile once formed.

It most certainly does not need a 'flush contact' - in fact that will limit its effectiveness since the jet has no time to form.

What it will do is rip lots of metal off the back-face of armour and whizz it around the inside of the tank and possibly hit something sensitive. The heat and overpressure are not so significant, and there are instances where a penetrating HEAT hit didn't hit anything too sensitive and the crew were entirely unharmed, albeit a bit rattled.

The penetrating mechanism is not heat based - there simply isn't time for it to be effective - it's velocity. Think ten times faster than a rifle bullet.

The lethal mechanism isn't pressure or heat based. It's fragments.

[SlapHappy]

Originally posted by c3k:

Now, how do the CMSF Syrians, under fire, nail a hard moving target at 100's of meters with those things?

Regards,

Ken

Game balance

Oh, you mean in real life? They don't.

[Capt. Toleran]

Well anyways, overpressure or not, that mannequin lost an arm, and there might have been even more molten metal flying around. I'd imagine that had that been an enclosed Humvee, there would at least have been some minor injuries, maybe enough to disable the vehicle for a while.

[MikoyanPT]

The effect of a exploding warhead inside a confined space would be devastating.

That old RPG-7 is still reasonable acurate and efective against soft skinned targets.

A uparmored hummvee wasn't designed to face this kind of weaponry.

[KGB50]

However the jet is travelling between 2 and 7 km/s (it varies down the length) and is separate from the rest of the projectile once formed.

It most certainly does not need a 'flush contact' - in fact that will limit its effectiveness since the jet has no time to form.

What it will do is rip lots of metal off the back-face of armour and whizz it around the inside of the tank and possibly hit something sensitive. The heat and overpressure are not so significant, and there are instances where a penetrating HEAT hit didn't hit anything too sensitive and the crew were entirely unharmed, albeit a bit rattled.

The warhead that rips lots of metal off the backface of the armour is completly different. It is called HESH warhead (High Explosive Squash head). How it works is that when the warhead hits its target, the tip squashs against the armour and detonates, causing a scab of interior metal to break free and ricot around inside a tank.

[Buq-Buq]

KGB50:

The graphic that you've posted is — at best — misleading with regard to HEAT warheads. The graphic gives the impression that HEAT burns through armor, which is definitely not the case. Upon detonation, the liner of the HEAT warhead, deformed by the detonation wave, is translated into a very high velocity piece of ductile material, and in essence becomes a kinetic energy penetrator with an absurdly high velocity and length/diameter ratio.* The difference between HEAT and APFSDS is that HEAT does not have to be delivered to the target at high velocity (which is why it is ideal for ATGMs and shoulder-fired rockets): velocity is imparted to the penetrator of a HEAT warhead by the detonation of its inherent explosive once it has arrived at the target.

The spalling effect that flamingknives is describing ("rip lots of metal off the back-face of armour and whizz it around the inside of the tank") is a function of most armor-piercing projectiles, to include HEAT and APFSDS. Upon penetration, chunks of the perforated armor plate (in addition to the remnants of the penetrator itself) are hurled at high velocity throughout the interior of the vehicle, causing damage to equipment and personnel.

He [flamingknives] knows what he's talking about.

Mark

*I would refer you to an excellent article by Giorgio Ferrari, The "Hows" and "Whys" of Armour Penetration, in Volume XII, Issue 10 (1988) of Military Technology, pages 81-96 for a more detailed analysis of the subject. I am unaware if this article is available online or not.

[YankeeDog]

Indeed. What makes HESH unusual is that it relies *soley* on creating a shockwave in the armor that sends "scabs" off the inside of the armor plate to cause damage; the HESH warhead itself never penetrates the armor at all, and there is usually no perforation from a HESH warhead.

But virtually all armor penetration warheads produce secondary fragments from the armor itself, to one degree or another.

The Ferrari article is a very good one. In brief, HEAT ain't hot, and it don't burn. At least, not on the initial penetration. AFTER the initial penetration, often a fair amount of heat is present around the penetration site, and among the fragments, mostly due to the friction caused by moving all that metal around so quickly. But this isn't the mechanism for penetration.

Welcome to the weird world of hyperbaric physics, and fluid solids.

Cheers,

YD

[KGB50]

OK, thanks guys. Just had a look on wikipedia and realized that I had it all muddled up.

[ January 22, 2008, 08:51 PM: Message edited by: KGB50 ]

[Secondbrooks]

Originally posted by c3k:

What was MORE interesting was the point of impact. The gunner had absolutely perfect conditions. He was close, braced, no wind, aimed, etc., etc., and still just barely hit the panel. It looked to be approximately 18"x30", give or take. And he almost didn't hit it.

Now, how do the CMSF Syrians, under fire, nail a hard moving target at 100's of meters with those things?

Regards,

Ken

Gunner wasn't tranined RPG-gunner

There was notable motion in RPG to right same time he pressed trigger (launch happend shortly after). Either A. gunner didn't know his gear, B. he got nervous and made mistake or C. tigger was stiff. D. All or some earlier combined.

Japanese are not using PRG-7 but M72, are they? This was either Russian or Chinese RPG, wasn't it? These were Japanese, weren't they?

Btw. There was cameras around, lots of hazzle around he might have spent 30 minutes in that positions -> he knees hurts, colonel was there, his mates told that firing RPG-7 is like gettin hit from shovel into head (this was how we were instructed with Apilas Damn we feared it at start), it's his first time with RPG-7... Can't say that it would be battlefield, but overall this situation can be quite stressing.

[Flanker15]

I'm pretty sure blast wave is one of the factors that cause damage with a HEAT round, at least it's modeled in simulators where the gas is pushed into the enclosed space suddenly causing heat and pressure.

I checked and the liner on the HEAT round is optional, the effect works with just the high velocity gas boring through the armor. Although having a spike of metal plasma helps allot I'd imagine.

[YankeeDog]

"I'm pretty sure. . ."

*sigh*. Famous last words.

Look, don't take my word for it. I'm not a physicist, I've just read the papers written by the phyicists.

Read up on the actual physics yourself. Buq-Buq has already listed one excellent article that will confirm what I'm saying, and there are others out there. I think you'll find, once you've read up on the subject, Those That Know believe that, based on strong experimental data, the HEAT penetrator is *not* a plasma or a gas, and that furthermore it does not use a "blast wave" or "heat" as the primarly mechanism of penetration.

Rather, the HEAT penetrator is a fluid (most likely solid) kinetic penetrator, moving at extremely high velocity, and kinetic energy is the primary penetration mechanism.

Of course, it is the uniquely shaped "blast wave" created by the shaped charge, and accompanying extremely high-pressure condition that creates this high velocity, high pressure penetrator. But in and of itself, the "blast wave" is not what does the penetrating, any more than the explosive going off in the chamber of a traditional gun AT round is what penetrates the armor.

Of course, in both cases the explosive is the ultimate source of the energy that pushes the projectile though the armor.

Now, AFTER the penetration event, you do have a lot of hot metal, gas, etc. flying around, both inside and outside the armor; that's the inevitable after-effect of the explosion and the friction inherent in forcing the penetration plume through the armor. And these certainly do contribute to damage. They're just not primary to how the HEAT charge penetrates the armor.

Again, don't take my word for it. Read and Research.

Cheers,

YD

Edited to add:

On re-reading some of the stuff I have lying around on this, current theory is that the shaped charge tip penetrates through mechanisms called hydrodynamic penetration and plastic deformation. The whole thing goes under the term a "hypervelocity hydrodynamic impact". Chew on that one for a while, if you like.

A pretty decent article on global security:

global security page on shaped charges

Note the very specific experimental data that the penetration jet is, indeed a fluid-solid, and not a gas or plasma.

[ January 24, 2008, 10:53 AM: Message edited by: YankeeDog ]

[Panzer76]

Regarding RPG effect on Humvees:

Here is one that just keeps on rolling after being hit:

http://www.liveleak.com/view?i=2b4_1180908686

While I dont think these will be moving anywhere soon:

http://www.liveleak.com/view?i=8f4_1177581052

http://www.liveleak.com/view?i=8f4_1177581052

I guess its dependant on what kind of warhead you use and where you hit.

While the first Humvee kept on rolling, I think some of the occupants can very easily have been injured or killed.

[Battlefront.com]

Secondbrooks,

Gunner wasn't tranined RPG-gunner

And an Abrams is a bit larger than 18"x30"

Btw. There was cameras around, lots of hazzle around he might have spent 30 minutes in that positions -> he knees hurts, colonel was there, his mates told that firing RPG-7 is like gettin hit from shovel into head (this was how we were instructed with Apilas Damn we feared it at start), it's his first time with RPG-7... Can't say that it would be battlefield, but overall this situation can be quite stressing.

Ain't that the truth! I saw a live fire of Javelin against a T-72 with reactive armor at a couple thousand meters. The gunner, a huge slab of NCO, was there sitting around for most of the day before he actually got to fire. He was in the firing position for what seemed like an eternity because they kept finding some reason to stop the firing. Like one of the cameras within the T-72 falling off everytime they sealed up the driver's hatch, then the guy doing it would go back to the little command hut and find out, then go back to fix it, back to the command hut, etc. We almost missed the test itself because we had to fly back. If it went off as planned we would have had hours of sitting around. As it was, we got to the airport just as they closed the plane's door. Too close

Steve