Update: USAF seeks information maritime strike weapon [F-35]

F-35 Armament, fuel tanks, internal and external hardpoints, loadouts, and other stores.
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madrat

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Unread post08 Sep 2020, 17:07

In what world does a grain of sand cause a penetrator to tumble but the nose section of an LGB has no impact on penetration?
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wolfpak

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Unread post08 Sep 2020, 21:47

I've never heard of the grain of sand thing. The laser seeker is axisymmetric about the bomb axis so any forces generated will be consequently be the same. When looking at a 2000 lb. penetrating mass versus a 20 or 30 lb. seeker assembly the seeker just disintegrates as the penetrator plows thru it. It's a matter of the difference in mass and momentum. An analogy you can try at home is pushing with force a ogival shaped magic marker thru a paper straw. The other experiment would be to push a ogival shaped marker at a surface inclined and different angles until you get it to ricochet. Try it again with a1/8 inch cylindrical wooden dowel. You'll see the blunt dowel has a greater range of angles before it ricochets.
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madrat

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Unread post08 Sep 2020, 22:20

I guess you skimmed over that part where penetration through sand caused them to tumble.

Physics disagrees with your reckless theory. Nothing simply disintegrates into nothing. It either was nothing to start with or it wasn't. The seeker takes force to crush and for every action there is an effect.
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marauder2048

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Unread post08 Sep 2020, 22:48

madrat wrote:I guess you skimmed over that part where penetration through sand caused them to tumble.

Physics disagrees with your reckless theory. Nothing simply disintegrates into nothing. It either was nothing to start with or it wasn't. The seeker takes force to crush and for every action there is an effect.


Yeah. He's treating it like the rather sturdy seeker front-end vaporizes into nothing with no energy
expended by the penetrator and no complications with media interface whatsoever.

And I'd point out that even the legacy penetrators improved their penetration performance through...modified nose shapes!

In this case, the BLU-122 triconic nose improved penetration perf by 20% over the blunter BLU-113.
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wolfpak

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Unread post10 Sep 2020, 16:38

Gentlemen if you disagree with my analysis prove yours. Mathematics is the language of science including physics, technology and engineering. Please provide us by citing the appropriate physical laws, formulae and equations to support your claims. For starters tell use all how a particle of sand weighing less than a gram can cause a penetrator that weighs over 2000 pounds to alter course? I'd personally like to know how a lightweight sensor assembly that is designed such that it is axisymmetric about the long axis of the bomb creates a lateral force? It should not take long for you to draw up a free body diagram and provide us with the magnitude of the vectors that will support your views. Anyone with the intimate knowledge of these things should be able to do it on a back on an envelope in a minute or two.
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sprstdlyscottsmn

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Unread post10 Sep 2020, 17:12

sensor lateral force: Most GBU impact do not occur at 90 degrees, thus a lateral force.

grain of sand: Maybe I missed something, but I saw "sand" causes tumbling, nothing about "a grain of sand". When talking about a penetrator we may be talking about going through several feet of sand/dirt/rocks.
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madrat

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Unread post10 Sep 2020, 19:43

Going through sand is definitely going to be an explanation beyond a simple math formula. But like most forces placed on sand there is going to be results unlike hitting liquids. whether one or a billion grains of sand, its all relative to the impact surface.

Wolfpak is hung up on my allegory. It is what it is.
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marauder2048

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Unread post10 Sep 2020, 20:10

wolfpak wrote:Gentlemen if you disagree with my analysis prove yours.


Proof by contradiction is pretty compelling. Even the legacy penetrators switched from blunt noses to pointier
noses (triconic above) to improve penetration depth. That was the only mechanism they employed. It was
worth a 20% (!) improvement in penetration depth.

Practically all modern penetrators have eschewed nose-mounted sensors and gone for ogives which
provide the best balance between penetrator stability, heating, setback forces, aero and penetration depth.
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garrya

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Unread post10 Sep 2020, 20:33

marauder2048 wrote:In this case, the BLU-122 triconic nose improved penetration perf by 20% over the blunter BLU-113.

While now I tend to agree sharp nose is better, I don't think the improvement in BLU-122 over BLU-113 is only due to the nose shape, case was made from stronger material, and the case is thicker as well, especially at the head where it look about twice as thick. Besides, aren't they both have a blunt laser seeker on top?, is there any equivalent of GBU-28 but with GPS guidance?
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P/S: I have just realized that the nose of WW II battle ship shell is blunt even though they are meant to penetrate very strong armor. Making a sharp nose so that the shell can penetrate better should be common sense, so why they didn't do that?. I have come up with a theory: if the weapon is meant to penetrate surface made from very hard material such as steel then the chance of ricochet will be higher, in that case a blunt nose is better. That why WW II battleship AP rounds have blunt nose. By contrast, if the weapon is meant to penetrate soft or brittle surface such as soil, concrete then the chance of ricochet will be very low, in that case, a sharp nose probably more preferable.
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marauder2048

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Unread post10 Sep 2020, 21:00

garrya wrote:
marauder2048 wrote:In this case, the BLU-122 triconic nose improved penetration perf by 20% over the blunter BLU-113.

While now I tend to agree sharp nose is better, I don't think the improvement in BLU-122 over BLU-113 is only due to the nose shape


It's explicit in that presentation: improvement in penetration depth was due to the nose and the nose alone.
Improved case strength enabled the penetrator to penetrate *and* survive in harder media.

A5K is the successor to GBU-28; it has no laser seeker in the nose.

I have just realized that the nose of WW II battle ship shell is blunt even though they are meant to penetrate very strong armor.

The capping is based on the higher angle of obliquity that battleship AP shells obtained. Guided penetrators
are much tighter in their angle of obliquities.

I should also be clear on what constitutes a blunt nose. This image from the above reference is useful.
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madrat

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Unread post10 Sep 2020, 22:58

I watched a video of a new B&K 7.5mm cartridge that has about 50% better penetration using soft points versus 9mm standard rounds. The hollow point rounds were 40% less mass and didn't have near the jacketing on them yet penetrated steel plates better. The hollow point travelled significantly faster and was accurate out to 125 yards from a semiautomatic handgun. The penetration improvement had zero to do with shape or materials and everything to do with velocities. The slimmer front has obvious advantages with drag.

A penetrator rod is going to improve penetration simply because a thin rod penetrates better than either a flat nose or a simple pointed nose. Think of needles. Push the needle at an angle it breaks easily. But push it straight in and it punches through easily. So I don't think the evolution to rod tips is surprising.

The reason they don't put too much point on the tips probably has to do with aerodynamic heating. Pointy tips lose form faster than less aggressive points. You need that nose to hold it's form and retain its rigid nature. A hot tip that weakens the rigidity may flatten at impact.
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