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Sturgeon's House

Bronez' place to dump interesting things he stumbles upon


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When browsing various papers and publications I usually stumble on quite interesting information every so often, but it's usually not enough to warrant a whole topic or linking the complete paper. 

So this is a topic where I'm going to dump all the things I find exciting or interesting. I'll post a small explanation on why it's interesting/exciting as well.

 

I usually save all the paper I read or skim through, so if you want the full paper just gimme a yell.

 

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So yesterday when I was checking papers for the sandbag topic I was also looking at shaped charge penetration in concrete, and I stumbled upon this:

9fee19e40e.png

If you ever wondered why anti-bunker shaped charges use aluminium liners, compare Test #1 with #2 and #3. While the aluminium liner has quite a bit less penetration than a steel or copper liner, it makes a much bigger hole. Which is handy if you want to drop a secondary charge through the hole you just punched. The after armour effect on tanks might be enough to disable it completely, but with a bunker you most likely need a secondary charge to effectively neutralise everyone inside the bunker. And bigger hole = bigger secondary charge.

 

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While thinking about @roguetechie's question about a focal point in shaped charges I remembered a paper which had some simulations about the penetration capabilities of a segmented HEAT jet. Sadly I can't find the paper anymore, but the advantages of segmented penetrators are fairly well known. So I was wondering whether you can control the breaking up of a HEAT jet, which should be possible by making weaker points in the jet on purpose. And when looking for a good introduction to shaped charges I found this:

7affaeb768.pngabbc1ccca4.png

Turns out you can totally make a jet that breaks up at predetermined points, and you can probably also engineer it in such a way it breaks up at predetermined times. Looking at this, it's totally possible to make a segmented HEAT jet, but it's probably very expensive to make.

 

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A while ago we were having a discussion about whether or not a long rod can ricochet. Today I went looking for data on it and lo and behold I found a whole bunch of data on it. I haven't found a formula to use (that I can understand), but as it turns out the minimum ricochet angle is about 3-4 degrees for steel penetrators with an L/D of 10.7 (modern long rods have an L/D of over 35), depending on target strength:

672da625d8.png

 

 

If you look at different L/D numbers, the ricochet angle should change, according to Tate:

0affe31b0f.png

 

However Tate's formula seems to be inaccurate when you compare it with real data:

56f0303664.png

 

Rosenberg's formula is more accurate, but it doesn't include neither L/D ratio nor target thickness, which is probably why Rosenberg's model is shifted up compared to real life data. What the relation between the real life data and Rosenberg's formula is, is unknown to me at the moment.

 

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...speaking of L/D and segmented long rods...

 

This is why segmented long rods work:

ee4d2a403f.png56edd79b56.png

 

The higher the L/D ratio, the lower the penetration efficiency. When you check the actual penetration values of different constant diameter (0.3 cm) L/D ratios, you'll see this:

c69e31bcc7.png

 

The L/D 6 has a penetration of about 1.8 cm, which is exactly right for a 1.8 cm long rod. Remember, an L/D ratio of 6 has an efficiency of close to 1.

If the L/D effect wasn't a thing, the L/D 30 should have a penetration of 1.8 cm * 5 = 9 cm. But it only has a penetration of ~6.2 cm. Which is due to it's lower efficiency of only 0.69 (9 cm * 0.69 = 6.21 cm).

 

So the point of segmented long rods is to create multiple shorter penetrators instead of one long one. This means you're basically stacking multiple high efficiency penetrators instead of using one long inefficient penetrator. With the above numbers, a long rod with 5 L/D 6 ratio rods will have 9 cm penetration while a single L/D 30 rod (which is the same length) has only 6.2 cm of penetration.

 

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More to come.

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TIL that high strength penetrators reach their max P/L ratio a lot quicker than low strength penetrators:

d92b012de7.png

(Also visible: L/D effect)

 

But depending on the materials of both the penetrator and target, high strength penetrators can reach a higher P/L ratio at lower speeds than at high speeds!

cded35aba3.png

 

@Collimatrix any idea on why, maybe?

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19 minutes ago, Bronezhilet said:

I've seen the use of gold penetrators before actually. Don't know why, maybe to not give an indication of the performance of actual long rod penetrators?

I'd guess because of the density, but it may also just be that grant money is a lot looser for this field than others.

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Turns out the Javelin doesn't give a shit if a mid-wing* is damaged:

 

ba08136710.png

(The percentages after the CEP are seeker failures)

 

 

But if a mid-wing is missing or not deployed, its largely screwed, except if the missing wing is a vertical one:

 

fd98170891.png

 

Quote

Results for a missing wing show a similar trend with respect to mid-body wing orientation. Failure for a missing horizontal wing is the most severe with 100% seeker failure in most cases. Missing mid-body wings next to horizontal wings (8, 2, 4, and 6) have smaller CEP values when compared to horizontal wings but still result in significant failure percentages. Results show missing a vertical mid-body wing, either 3 or 7, results in no seeker failure and CEP values only slightly larger when than an undamaged case.

Quote

It was shown that asymmetries from damage cause large rolling motion. The rolling motion resulted in high risk of saturation of the control fins and swerving near the end of terminal guidance

I thought ATGMs could deal fairly well with wing failures, but this research suggests otherwise.

 

* Wing numbers:

2d3db97df2.png

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That has interesting implications for lasers and APS effectiveness against ATGMs.

 

I always kinda thought you had to hit an ATGM pretty hard and disrupt/detonate the warhead.  IE you want solid flak proximity, a really solid laser energy dump etc. to ensure a kill.  If it's just a matter of getting enough energy in it to melt a fin, then I become more convinced that heavy ATGMs may have a limited service lifespan, and long rod penetrators may be kinda important in the long run.

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18 minutes ago, Belesarius said:

That has interesting implications for lasers and APS effectiveness against ATGMs.

 

I always kinda thought you had to hit an ATGM pretty hard and disrupt/detonate the warhead.  IE you want solid flak proximity, a really solid laser energy dump etc. to ensure a kill.  If it's just a matter of getting enough energy in it to melt a fin, then I become more convinced that heavy ATGMs may have a limited service lifespan, and long rod penetrators may be kinda important in the long run.

Strange - the article Brone found sort of convinced me of the opposite.

 

Javelin is in no way designed for robustness, so the fact that you can bust up a wing a bit and still hit the target means that a specially-designed missile (the "IL-2-sile") might be able to take a lot more punishment and still knock down a target.

 

For kinetic APS, this might mean making your warhead casing armoured (including all-or-nothing schemes around the flight control unit and warhead), adding redundancy to your flight control system and making sure that your algorithms can handle the changes in control input.

 

For lasers, it would depend on whether battlefield pulse lasers ever become feasible. If you're dealing with beams, then the laser has to dwell on a spot for quite a while to heat it up enough for a failure to occur. This means that simply coating the exterior in carbon and getting the missile to spin quickly could be enough to defeat any reasonably mobile battlefield laser.

 

A pulsed laser, on the other hand, can rapidly get up into the 10+cm steel penetration range with fairly low power energy requirements (but very high power requirements), making armour useless. These lasers would also deliver the pulse very quickly, making spinning less effective as a strategy. My understanding is that nobody is talking about them at this point because of just how difficult it is to deliver a bunch of pulses to the same spot quickly enough to cause drilling over long distances. 

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12 minutes ago, Toxn said:

Strange - the article Brone found sort of convinced me of the opposite.

 

Javelin is in no way designed for robustness, so the fact that you can bust up a wing a bit and still hit the target means that a specially-designed missile (the "IL-2-sile") might be able to take a lot more punishment and still knock down a target.

 

For kinetic APS, this might mean making your warhead casing armoured (including all-or-nothing schemes around the flight control unit and warhead), adding redundancy to your flight control system and making sure that your algorithms can handle the changes in control input.

 

For lasers, it would depend on whether battlefield pulse lasers ever become feasible. If you're dealing with beams, then the laser has to dwell on a spot for quite a while to heat it up enough for a failure to occur. This means that simply coating the exterior in carbon and getting the missile to spin quickly could be enough to defeat any reasonably mobile battlefield laser.

 

A pulsed laser, on the other hand, can rapidly get up into the 10+cm steel penetration range with fairly low power energy requirements (but very high power requirements), making armour useless. These lasers would also deliver the pulse very quickly, making spinning less effective as a strategy. My understanding is that nobody is talking about them at this point because of just how difficult it is to deliver a bunch of pulses to the same spot quickly enough to cause drilling over long distances. 

FYI: We already have laser weapons (LaWS and MTHEL) that can destroy artillery shells and rockets, although I have no idea what progress on them is.

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7 minutes ago, Bronezhilet said:

FYI: We already have laser weapons (LaWS and MTHEL) that can destroy artillery shells and rockets, although I have no idea what progress on them is.

Yup, but only by staring at them for a good long while, and only where the shell/rocket is pretty soft-skinned.

 

Slap a carbon coating on it and make the casing thicker and suddenly your truck-sized laser setup will struggle to shoot it down in time.

 

My guess is that improvements in power storage et al will mean that 200kW becomes doable much sooner than anyone expects, and a proper (ie: solid-state or fibre rather than chemical or gas) 1MW beam might be possible in the near future with some serious money and effort.

 

For reference, the LaWS takes about 2 seconds to shoot down a baby drone (scaneagle) with its 30kW beam and what I'm assuming is a near-infrared frequency. According to the calculator I keep referencing; the difference between a 30kW laser zapping a drone for 2 seconds and a 200kW laser zapping it for one is that the former manages to get a 10cm spot up to melt temperature, and the latter melts through its casing entirely (to a depth of about 3mm). A 1MW beam doing the same will burn a relatively neat hole right through the drone.

 

When faced with a graphite body, however, the 30kW beam doesn't do much more than leave a smoking scorch mark on the outside. The 200kW beam, meanwhile, cooks off the outside to a depth of a fraction of a millimetre. Even the 1MW beam doesn't get you too much love: about 1mm of graphite gets blasted off. The 1MW beam can, however, widen its focus and just set the whole drone alight.

 

So a bit of suitable protection goes a long way.

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For comparison: by taking the same 30kW beam and pulsing it (1ms pulse followed by 4ms rest, 100 pulses, spot size of 5mm) you can drill a neat hole about 2cm deep into a solid block of aluminium. This would work quite nicely to punch a hole in a drone or similar, but would also need a fairly big mirror and advanced optics to pull off.

 

The 200kW beam would drill through 12cm of solid aluminium, while the 1MW beam would do the same but with a 1cm spot size. Graphite is still effective as armour, but will only completely stop the 30kW beam (~1mm hole depth). The 200kW beam will still manage about 7mm of drilling, while the 1MW beam can do about 1cm with a 1cm spot size, and 4cm with a 5mm spot size.

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Fiber lasers also get a lot of love from industry too!

 

This, in effect to my way of thinking, equates to a bunch more people circling the problem looking for a way to take a bite out of it.

 

Since you need both people working on a problem and money to fund the work, this should give fiber lasers an advantage over some other types. At least it will, if more people = more advances holds.

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1 hour ago, Ramlaen said:

Assuming the targeting system is precise enough I don't see why you couldn't target the control surfaces with a laser.

Precise targeting systems might be one of the big issues for pulsed systems. I know that power supplies seem to be a perennial concern.

 

I'd actually love someone with more real knowledge to weigh in here on the various laser systems being considered and their issues.

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3 hours ago, roguetechie said:

Fiber lasers also get a lot of love from industry too!

 

This, in effect to my way of thinking, equates to a bunch more people circling the problem looking for a way to take a bite out of it.

 

Since you need both people working on a problem and money to fund the work, this should give fiber lasers an advantage over some other types. At least it will, if more people = more advances holds.

My understanding is that lasers in general have been growing in capability more rapidly than expected. It's always a good sign when the new hot technology (solid state, in this case) is rapidly replaced by something even newer and hotter.

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35 minutes ago, roguetechie said:

Yes, I like lasers and very much want them to get cheap enough so I can put together a laser cutter that can do 1mm mild steel and such.

Cheaper commercial laser cutters suitable for steel cutting go for about R50000 now.

 

I'm sure you could hack together a cheaper rig using a laser engraver or 3-D printer and a CO2 or YaG laser bought seperately.

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Yeah I was going to put it on a 3d printer, no need for the extra grunt of a mill or etc provided I do it right...

 

I've tentatively scheduled it to get built as an attachment for my 2.0 version of the MIT multifab.

 

I'm gathering parts and etc for my 1.0 build now, which will be pretty close to a straight clone of the MIT machine whose plans, BOM, & etc I have gathered up in anticipation of this build. It's by far going to be my most expensive and ambitious DIY tool build yet though, so it's taken me quite awhile to gather the parts and cash to do it. 

 

At the end I'll probably be into the machine almost a solid $10,000 but I'm OK with this.

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