Science > Physics > Defending Against an Explosively Formed Projectile
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Science > Physics |
| User: |
"Tannhauser Gate" |
| Date: |
27 Apr 2007 11:04:10 AM |
| Object: |
Defending Against an Explosively Formed Projectile |
Our boys are dying in the desert, making it our responsibility, as
scientists, to put our heads together to solve that problem. We need to
find a way to augment the skin of a of an armored vehicle, to protect
those guys from EFP's.
AFAIK, those things pierce armor by melting their way through it,
because they're molten copper whose temperature is above the melting
point of iron. We need to make a list of all the possible mechanisms of
physics that can counteract that particular difficulty, and then make a
decision about what's cheap and easy, versus what's hard and pointless.
As a straw man, I'd like to throw out the idea of rapid cooling. We
increase the engine capacity of the vehicle to allow it to refrigerate
and carry tanks of liquid nitrogen, and when an accellerometer detects
an explosion, an electronic system pinpoints it's direction and
intercepts the copper slugs with a shower of frigid coolant to
neutralize them before impact.
Unfortunately since the slugs come at hypersonic speeds. The shower of
coolant would also have to be hypersonic, and I'm not sure how severe
are the challenges of the "hypersonic shower nozzle," or whether it
would be possible to shoehorn them into a package as small as an APC.
As I said, it's a straw man, and it's intended to inspire brainstorming
(barnstorming?) among us all, to either invent a better way that's
totally different, improve my idea or trigger the thoughts that I need
to fix it myself. Intelligent replies are always greatly appreciated.
?:)
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| User: "Greg Neill" |
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| Title: Re: Defending Against an Explosively Formed Projectile |
27 Apr 2007 11:30:35 AM |
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"Tannhauser Gate" <@Shoulder-of-Orion.com> wrote in message
news:Xns991F7ACF08DC1alphamale@207.115.17.102...
As a straw man, I'd like to throw out the idea of rapid cooling. We
increase the engine capacity of the vehicle to allow it to refrigerate
and carry tanks of liquid nitrogen, and when an accellerometer detects
an explosion, an electronic system pinpoints it's direction and
intercepts the copper slugs with a shower of frigid coolant to
neutralize them before impact.
The energy of the slug is being carried as kinetic energy.
It doesn't get "hot" until impact, when it dumps its
energy into the target, heating itself and the target at
point of impact.
Calculate, using the specific heat and mass of the slug
the amount of energy as heat it's carrying. You'll find
that it's insignificant compared to the kinetic energy,
so cooling it before it reaches the target would not be
effective.
The only things you can do are 1) intercept the round and
have it dump its energy before impact, or 2) modify the
target so that it can safely dissipate the energy.
Both approaches are what might be called "difficult".
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| User: "" |
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| Title: Re: Defending Against an Explosively Formed Projectile |
27 Apr 2007 05:30:15 PM |
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On Apr 27, 9:04 am, Tannhauser Gate <@Shoulder-of-Orion.com> wrote:
Our boys are dying in the desert, making it our responsibility, as
scientists, to put our heads together to solve that problem. We need to
find a way to augment the skin of a of an armored vehicle, to protect
those guys from EFP's.
AFAIK, those things pierce armor by melting their way through it,
No. At the typical impact velocities (>10 km/s) both the projectile
and the armor can be considered incompressible fluids; the projectile
basically relies on raw momentum to push the armor out of its way.
Same goes for so-called reactive armor; the explosives don't have time
to detonate before the projectile plows through them.
We need to make a list of all the possible mechanisms of
physics that can counteract that particular difficulty, and then make a
decision about what's cheap and easy, versus what's hard and pointless.
As a straw man, I'd like to throw out the idea of rapid cooling. We
increase the engine capacity of the vehicle to allow it to refrigerate
and carry tanks of liquid nitrogen, and when an accellerometer detects
an explosion, an electronic system pinpoints it's direction and
intercepts the copper slugs with a shower of frigid coolant to
neutralize them before impact.
Unfortunately since the slugs come at hypersonic speeds. The shower of
coolant would also have to be hypersonic, and I'm not sure how severe
are the challenges of the "hypersonic shower nozzle," or whether it
would be possible to shoehorn them into a package as small as an APC.
Yep, that won't work. Others have proposed mini versions of the
radar-aimed gatlings that protect navy vessels from low-flying
missiles. Same problem of closing velocity. Also active defenses can
break down just when you need them; passive systems are much
preferable.
Typical defenses since WWII are some sort of external "faux" armor
that doesn't actually resist penetration; rather it's intended to set
off the fuzing mechanism early enough that the projectile dissipates
before reaching the actual armor and/or deform the components of the
warhead that shape the molten projectile. The projectile, once formed
(also look up "self-forging), has a fairly short effective lifetime
because at that kind of velocity air is about as compressible as steel
plate, forcing the projectile to expend damn near as much of its
momentum shoving the air out of its way as an equivalent thickness of
armor.
That doesn't help with static devices such as are hidden in
structures near chokepoints armored vehicles must pass close by; the
operator watches from a relatively remote vantage and sets off the
explosive electrically when he thinks it will do the most damage,
typically at a point not covered by the faux armor.
One of the counterintuitive ideas being considered that I know of is
multiple layers of Kevlar-type fabrics spaced just enough to dissipate
the energy of the projectile over a much shorter distance than
equivalent thicknesses of conventional metallic plate ever could; it's
used in spacecraft to stop micrometeoroids traveling at comparable
velocities in fairly short distances. It won't stop anything bigger
than say a bb in a foot or so though. Also it can't withstand multiple
hits in the same spot, though it suffers much less permanent damage
than metal armor does because it doesn't flow away from the point of
impact and stay there afterward; it can stretch away then rebound.
Eventually this means armored vehicles will likely have an external
shell of small-arms proof armor, bulky layers of fabric underneath,
probably with fairly conventional plate under that, just in case.
Mark L. Fergerson
PS I had to trim sci.mil off because Google doesn't support it. Damn.
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| User: "Jan Panteltje" |
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| Title: Re: Defending Against an Explosively Formed Projectile |
27 Apr 2007 12:22:32 PM |
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On a sunny day (Fri, 27 Apr 2007 16:04:10 GMT) it happened Tannhauser Gate
<@Shoulder-of-Orion.com> wrote in <Xns991F7ACF08DC1alphamale@207.115.17.102>:
Our boys are dying in the desert, making it our responsibility, as
scientists, to put our heads together to solve that problem. We need to
find a way to augment the skin of a of an armored vehicle, to protect
those guys from EFP's.
Huh, why not pack up and go home?
that way you will be a bit safer, unless you are at a Tech school.
But Bushman will veto on your safety I'v hear.
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| User: "" |
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| Title: Re: Defending Against an Explosively Formed Projectile |
27 Apr 2007 05:15:02 PM |
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Tannhauser Gate <@shoulder-of-orion.com> wrote:
Our boys are dying in the desert, making it our responsibility, as
scientists, to put our heads together to solve that problem. We need to
find a way to augment the skin of a of an armored vehicle, to protect
those guys from EFP's.
The problem is political, not scientific.
The problem is the Humvee was never designed to be a combat vehicle
and even with the afterthought, bolt on armor (which is in limited
supply) it is still ill-suited for use in active combat.
All the current real armored vehicles are much too big to get
through the streets of urban areas (which is where all the Humvees
are being blown up) and the US Army abandoned armored cars.
The solution (short of coming home); buy armored cars from any
number of countries that build them and only use the Humvee for
what it was designed to do.
--
Jim Pennino
Remove .spam.sux to reply.
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