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Collimatrix

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Everything posted by Collimatrix

  1. Collimatrix
    ... They're making some bizarre assumptions. Why is the probability of casualty due to rocket hits mainly a function of the hydraulics catching on fire? Sure, this issue got a lot of attention in 1973, mainly because they hadn't thought about it before, but another one of the driving causes of crew loss and catastrophic tank loss is ammunition fire. Ammunition compartmentalization is one of the areas where the abrams is clearly superior to peer designs. Likewise, I'm not sure the person writing this report (is this another one of those military reform hatchet jobs? It kinda smells like it) knows how infra-red imaging works. Infra-red imagers are coated with magical, uber-expensive materials that only let through the wavelength of IR that the imager is sensitive to. The range of frequencies of "IR" (which is a largely arbitrary designation based on the wavelength where our eyesight stops working particularly well to the approximate wavelength where things start acting more like radio waves) goes from 430 THz to 300 GHz, whereas visible light goes from 430 to 790 GHz. You can make meaningful generalizations about the behavior of visible light, since all those wonderful, diverse colors we can see are very, very close to each other in wavelength. IR is much harder to make generalizations about. So, the fact that the abrams' turbine rejects more waste heat and rejects it at a higher temperature does not mean that it will have a higher infra-red signature to ground-based IR sensors. Most tank thermal imagers make images like this: Where the people are bright white. You don't need to do too much figuring with Wien's displacement law and black-body peak radiation intensity calculations to figure that a sensor that can pick up the wavelength that a 37C human body is not necessarily going to be too sensitive to 500C AGT-1500 exhaust.
  2. Collimatrix
    It's hard to make any definitive statements about what IS-7 was fitted with based on Kubinka's example; it's clearly been picked over. According to The_Warhawk, some asshole actually snuck in Kubinka and stole a bunch of the stuff from it, in addition to whatever test components were shuffled around during the development of the tank. EE's translation of the instruction placard on the loading device states that the mechanism can be turned on and off, so presumably it was powered. I guess The_Chieftain was using it manual backup mode. The placard also clearly mentions a button for the rammer, so there either was a rammer at some point or they were planning to add one. As I mentioned in Compendium, a quick look at DAV suggests that the Kubinka IS-7 is not the final model IS-7.
  3. Collimatrix
    The inverted case head is clever, and has a lot going for it at first glance. It's the primer I'm worried about. I'm really doubtful that the propellant grain would make a suitable anvil. Speaking of the propellant grain, in the HK G11, which has a similar consolidated propellant structure, there was a booster charge just ahead of the primer that busted up the consolidated grain to increase its internal surface area so it would burn in a timely fashion. This didn't always work correctly. Jim Schatz mentions it in his presentation on caseless ammo. I don't know much about those muzzleloader propellant blobs.
  4. Collimatrix
    The M2030 primer configuration looks flat unworkable, and I'm not too sure about the consolidated powder grain either. They're interesting ideas though.
  5. Collimatrix
    The M2030 round. Some intriguing ideas in this article. The author was clearly an attentive student of arms design.
  6. Collimatrix
    I'm not sure why, but I suspect that survivability was a major concern. Sukhoi's S-37 delta wasn't popular with the brass for the same reason: That NK-32/NK-321 is a hell of an engine, BTW. I'm assuming they would have reduced the bypass ratio for a fighter version, but the bomber version delivers an outstanding 55,000 lbs of thrust in afterburner. That Yakovlev MFI would have had about as much thrust as a rafale or EF-2000, just on one engine.
  7. Collimatrix
    Single engine, which I have read was not in favor at the time. After Afghanistan, Frontal Aviation was completely sold on twin engines, cost and aerodynamics be damned. Engine was going to be NK-321 derivative (blackjack's engine).
  8. Collimatrix
    Memo Kosemen has bizarre sex dreams.
  9. Collimatrix
    I found this interesting picture of the Yakovlev MFI design: Obviously, it was never built. The MiG submission was the 1.44 and the Sukhoi submission was the SU-47.
  10. Collimatrix
    What the everliving fuck?
  11. Collimatrix
    My suspicion is that if anyone ever gets power-producing fusion reactors to work, D-D will be the reaction of choice, at least initially. D-D is only a little bit harder than D-T; ignition temperature is 15% higher or so IIRC. Energy yield is lower, but the energy is in a form that's far easier to recover so it may be about the same. Neutron flux is halved, which is very nice indeed. Deuterium is .0156% of all naturally occurring hydrogen by mole, or .0312% by mass. One liter of water contains about 3.33 x 1025 molecules, or 6.66 x 1025 atoms of hydrogen. So that's 1.04 x 1022 atoms of deuterium per liter of water. Each nuclear fusion requires two atoms of deuterium and produces 3.7 MeV, or 2.86 x 10-13 joules per atom. So, that's 3 x 109 joules of energy from fusing all the deuterium in a liter of water. Coal has an energy density of 24 MJ/kg, so the energy provided by fusing all the deuterium in one liter of water is equivalent to the energy of burning 125,000 tonnes of coal. US energy consumption for 2011 was 9.17 x 1019 joules, so 3 x 1010 liters of water would suffice. The US uses that much water in about three weeks for agriculture, showers, mud wrestling and suchlike. Someone had better double-check that math before they go quoting it; I have been known to err.
  12. Collimatrix
    McDonnell Douglas JAST concept:
  13. Collimatrix
    It's not exactly a coax, but no discussion of tank secondary firepower is complete without the STRV-2000:
  14. Collimatrix
    A few musings: -We know that the sherman was able to hold its own when faced with the big cats in Normandy and after. The German forces were still mainly equipped with Pz. III and Pz. IV based vehicles, but the panther and variants were at least occasionally locally numerous. On most of those occasions (e.g. Arracourt) the sherman proved at least equal to the task of taking on the panther. Do we have any good sources for what the Germans thought when the sherman first showed up in North Africa? I would think that an early model sherman would be vastly better than anything the Germans had at the time. -Is there any evidence that the panther is a response to the sherman?
  15. Collimatrix
    Robert Heinlein is listening from beyond the grave.
  16. Collimatrix
    Someone arguing for women in the infantry. This fellow was on the pointy end, so his opinion counts.
  17. Collimatrix
    That sounds trippy. I found a cross-section:
  18. Collimatrix
    Counting pixels to estimate size in grainy satellite photos! It's like the '80s all over again! J-20 is huuueegg.
  19. Collimatrix
    ...Right, I realized that was written largely in jargon. Since I am still working on my nuclear energy mega-effort-post, I shall quickly summarize the issues here: -With nuclear fission you have basically three fuels of any interest; U-235 (which is naturally occurring, but a bit of a PITA to get), U-233 (which is made from Th-232), and Pu-239 (which is made from U-238). Once you've got the fuels though, their performance is broadly similar and not the topic of much discussion unless you're making high-performance bombs. Commercial reactors will happily gobble up plutonium from recycled warheads (e.g. MOX fuel), for example, with only modest changes to their operating parameters compared to using their normal fuel. -With nuclear fusion, there are a lot of potential fuels to consider, and they make a big difference in performance. At this point in our species' engineering acumen, "performance" with regards to fusion reactors means "whether or not the goddamn thing will work." -The biggest problem in fusion is actually getting the damn atoms to fuse with each other. For reasons explained in the hyperlink above, it's easiest to get elements with a low atomic number to fuse. For this reason, fusion bombs work by fusing deuterium and tritium (abbreviated to D-T), which are two isotopes of hydrogen (they should be called H-2 and H-3 respectively, but everyone likes using the fancy names instead). This is why fusion bombs are sometimes called "hydrogen bombs." D-T fusion is also the easiest fusion reaction to use in power-producing fusion reactors. However, there are problems. -Unlike fission reactions, D-T fusion does not leave any radioactive byproducts from the reaction itself. However, D-T fusion produces an insanely high neutron flux (the same neutron flux from D-T fusion is what makes neutron bombs work), and this insanely high neutron flux could potentially turn the fusion reactor itself radioactive. The extent of this problem would depend on what the neutron reactor is made out of, and how that material responds to neutron bombardment. Additionally, since a high percentage of the energy from D-T fusion is in the neutrons, it's harder to use the energy from D-T fusion for anything useful, since it is difficult to harness the energy of neutrons. -There are various fusion reactions which don't have the neutron problem, or at least have it to a much smaller extent, but they are harder to achieve.
  20. Collimatrix
    This is not something I've looked into extensively, but my understanding is that D-T fusion is the easiet type of fusion to achieve by a retarded margin. If I'm understanding this equation correctly, the energy that the nuclei have to overcome in order to fuse is a function of the product of their atomic numbers. Add to this that D-T fusion is four times punchier than D-D fusion, and I've read that it has far lower bremsstrahlung losses than other fusion plasmas. Come to think of it, I'm not sure if that was "far lower bremsstrahlung losses than other plasmas" or "far lower bremsstrahlung losses relative to energy density than other plasmas." D-D fusion seems like less of a pain in the ass than D-T fusion for commercial power production (you know, assuming you can ever get that to work) because less of the energy is released as insanely fast moving neutrons. About 80% of the energy from D-T fusion is released as neutron kinetic energy, and the neutrons from D-T fusion are about seven times more energetic than those released by nuclear fission. This strikes me as a large practical barrier to practical commercial fusion power. In D-D fusion neutrons are only carrying about 33% of the energy, and they're about as energetic as the neutrons released by fission. D-D fusion also produces half as many neutrons per mol compared to D-T fusion. If you want to go the other direction, and make lots of neutrons, T-T fusion sounds absolutely hilarious for bombs, since it will produce a 65% increase in neutrons per gram of fusion fuel over D-T (possibly more in practice, due to the elimination of D-D reactions in the D-T fuel). That'll learn ya!
  21. Collimatrix
    What exactly is that stuff? The Soviets had two or three composite armor fill materials during that period if memory serves.
  22. Collimatrix
    Yeah, there is a version of the T-72 that has an all-steel turret (but, bizarrely enough, a composite glacis), but I don't think that's it. Of the dozens of armor package variations of the T-72 I couldn't tell you which one that is, but I don't think it's the all-cast one. It occurs to me that when people compare the armor of the T-72 and abrams, they're asking one of the most maddeningly complicated questions in tank armor. Which version of the abrams? Thing has been up-armored like, four times now. Which version of the T-72? There are a gazillion variations.
  23. Collimatrix
    Having re-read the relevant passage in Design for Air Combat, part of the reason Dassault ditched pure deltas on the mirage F1 is that pure, stable deltas have rather poor runway performance, and high takeoff and landing speeds. Deltas have low aspect ratios and high leading edge sweep, so they're not so great at generating lift. This means they have to be flown either at high AoA or high speed to generate sufficient lift for takeoff. Also, using flaps is out on tailless deltas because there's no way to trim out the nose-down moment the flaps would generate. Super high AoA is out; the pilot can't see anything and the tail will bonk into the tarmac, so pure stable deltas usually had high takeoff and landing speeds, and lengthy takeoff and landing lengths. There is also a reduction in lift during rotation, since the elevons have to push the tail down to bring the nose up. In addition to providing torque, this action is also providing downforce. Instability goes a long way to curing this, naturally. Mirage 2000 has a landing speed of 260 KMH vs 330 KMH for the mirage III.
  24. Collimatrix
    Alright, we've got documents threads in aerospace and tanks, we need some for small arms now too. Small arms technology lags other fields by decades, by here at Sturgeon's House, it only lags by months! General Design Theory Treatises: First up is a link to George M Chinn's The Machine Gun. This is the premier English-language book on automatic weapon design theory. Also, because it was a US Government publication, it is legally available for free. The book is mainly focused on the design of autocannons, but the theory is applicable to smaller systems as well. If you read this book and understand it, you are ahead of 90% of the people in the industry. Next is this US Army document on small arms design hosted at Forgotten Weapons. The theoretical information in this is largely taken from Chinn, but it adds a lot of notes from experience on what does and does not work. It also has an excellent quantitative discussion of recoil, and some notes on various concepts the US Army was playing with at the time. More Specific Documents: Extractor Lift in the AR-15 series. This interesting series of tests disproves the rationale behind "improved" "lobstertail" AR-15 extractors. In addition, it shows just how much residual blowback pressure there is in the M4 (it's more than you'd think). Why Telescoped Ammunition Sucks. It really sucks. Jim Schatz on caseless ammunition. Very interesting read from a guy who was there when it happened.
  25. Collimatrix
    Brutality and intimidation go a long way in making people accept shitty governance. When Mugabe sent his North Korean-trained thugs to murder thousands of Ndebele, where the hell was the Western press? Where the hell was the wrath of NATO? Mugabe was still a Western Media Darling. If you are a Western Media Darling there is precious little you cannot get away with, at least in the short term. Perhaps some day I'll write a piece on the final days of Rhodesia and the early days of Zimbabwe. I think I'll call it "Georgia Peanut Farmers Suck Big Shona Dicks Volume One."
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