7 ms·

> "what if a meteorite hit my plane while it was in flight - maybe I should add three inches of high-tension armored steel around the plane, so that my passenge

• DiabloD3 10y ago
  The A-10 isn't a plane, it's a gun with a plane wrapped around it. And it hunts tanks.
  • jessaustin 10y ago
    We took a couple of minutes off this afternoon to watch some Warthogs pulling some tight maneuvers... to think, USAF wants to sell them all to Poland...
  • protomyth 10y ago
    I am told the gun is also quite good at shooting ground troops. A relative of mine had an A-10 stay with his group most of the night. Every time the enemy decided to go after them the A-10 came back and made them rethink their actions.
    • astrodust 10y ago
      That zipper noise: To think that those are 30mm rounds being fired at that speed is just plain scary. http://www.xdtalk.com/attachments/img_7014-jpg.34438/ http://www.xdtalk.com/attachments/img_7014-jpg.34438/ If one of those is lingering, I wouldn't even fight if I was the enemy. It might not be able to kill a modern main battle tank, but I bet spraying it with rounds like that would fuck it up pretty seriously.
    • hermitdev 10y ago
      The A-10 delivers rounds at a rate that the individual shots are indistinguishable to the the human ear. Another story that I've heard is that a B-1 flying at operational altitude (200 ft above ground level, mach 2) was often as effective as dropping munitions.
      • dotancohen 10y ago
        > Another story that I've heard is that a B-1 flying at operational altitude (200 ft above ground level, mach 2) was often as effective as dropping munitions. That very topic is being discussed right now on the Aviation Stack Exchange: http://aviation.stackexchange.com/questions/35771/is-it-correct-that-a-jet-fighter-can-be-used-as-a-non-lethal-sonic-weapon/ http://aviation.stackexchange.com/questions/35771/is-it-corr...
      • ravingraven 10y ago
        The B-1 can not even reach Mach 1 at such a lot altitude. It's maximal operating velocity (at any altitude) is Mach 1.25. People tend to really underestimate how much harder it is to go faster once you reach 0.90 or so, especially at low altitudes.
  • astrodust 10y ago
    It's also going to present zero obstacle to a meteorite travelling at six times the speed of sound. It'll rip through that armor like it's not even there.
    • paulddraper 10y ago
      Mach 6 is a heck of a slow meteorite. But the if a small meteorite (only a few grams) were traveling that slow, 1.5 inches of titanium would do quite a bit.
      • astrodust 10y ago
        I'm not sure how fast these go once they hit the atmosphere. I've seen numbers in the 15 to 25km/hr range, which is pretty damned fast, but how much do they slow down in the thicker atmosphere closer to the ground?
        • kbart 10y ago
          15 to 25km/hr is a running speed of human, probably you meant 15 to 25 km/s here (actually, some meteorites hit atmosphere >70km/s). Seems like they decelerate pretty fast after that[0]: "At some point, usually between 15 to 20 km (9-12 miles or 48,000-63,000 feet) altitude, the meteoroid remnants will decelerate to the point that the ablation process stops, and visible light is no longer generated. This occurs at a speed of about 2-4 km/sec (4500-9000 mph). From that point onward, the stones will rapidly decelerate further until they are falling at their terminal velocity, which will generally be somewhere between 0.1 and 0.2 km/sec (200 mph to 400 mph). Moving at these rapid speeds, the meteorite(s) will be essentially invisible during this final “dark flight” portion of their fall." 0. http://www.amsmeteors.org/fireballs/faqf/ http://www.amsmeteors.org/fireballs/faqf/
          • throwayguestman 10y ago
            > 15 to 25km/hr just btw, 25 km/s is almost 100.000 km/h.
        • 10y ago
  • hermitdev 10y ago
    I'm sad that the AF wants to retire this plane. This plane was defined with one purpose: build a plane around this gun, that being a 30mm autocannon firing depleted uranium shells (not radioactive) that fires at such a rate that it retards the velocity of the plane carrying the gun, and would melt the gun if it fired from full to empty continuously. The plane was built for survivability. It can withstand an engine being shot off (why the engines are external on "pods"). The cockpit is (I think) surrounded by a 2 inch titanium tub. I'm not sure the JSF, i.e. F-35 will be capable of taking over this role, as is intended.
    • deleted 10y ago
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    • MereInterest 10y ago
      As a side note, depleted uranium is certainly still radioactive. "Depleted" refers to the percentage of U-235, the isotope used for making nuclear weapons. Only about 0.7% of naturally occurring uranium is U-235, with the rest being mainly U-238. U-238 emits alpha particles, with a half life of about 4 billion years. The radioactivity is unrelated to its use as bullets, which relies on its high density, but it is radioactive.
• jessaustin 10y ago
  Haha you reminded me of the old riddle about how British engineers decided where to place armor on their bombers, because, "if they put it everywhere the plane wouldn't get off the ground!"
  • tanderson92 10y ago
    Specifically, during the war the engineers took a Bayesian approach and put armor on the bombers in locations where bombers which came back did not have damage. Reason being that hits in those sections of the planes were more likely than not resulting in fatalities. Smart thinking.
    • edanm 10y ago
      Definitely smart thinning, but not sure what makes it Bayesian.
      • tanderson92 10y ago
        anti-aircraft fire is random so doesn't specifically target any section of the plane. Therefore, the planes that return to base are a biased sample of the planes that took on damage. See: http://www4.ncsu.edu/~swu6/documents/A_Reprint_Plane_Vulnerability.pdf http://www4.ncsu.edu/~swu6/documents/A_Reprint_Plane_Vulnera...
      • smallnamespace 10y ago
        We're interested in the quantity: (1) P(crash | section hit) and adding armour to those sections where that quantity is maximized (maybe with some thought to the relative weight of armour needed for each section, but I digress). Let's directly apply Bayes' rule: (2) P(crash | section hit) = P(section hit | crash) * P(crash) / P(section hit) The denominator can be further expanded: (3) P(section hit) = P(section hit | crash) * P(crash) + P(section hit | no crash) * P(no crash) So we can see from the 2nd term that if aircraft regularly comes back with a section that's been hit and yet it hasn't crashed, then that directly reduces (1), meaning that section needs less relatively less protection, all else being equal. Another point in this method's favor is if crashed aircraft frames are too damaged to permit us to identify which sections were damaged. In that case, we can still estimate (1) just by replacing all the P(section hit | crash) terms with a uniform term. This analysis can be further expanded to the actual amount of damage each section took in a as well. The more damage a section took on surviving aircraft, the less protection it needs.
• aisofteng 10y ago
  It was recently pointed out to me by a friend with a hobby for cryptography and mathematics that "secure" doesn't mean anything - something can only be secure with respect to a specific threat model. It seems like a straightforward, almost painfully obvious definition in retrospect now, after having it articulated to me. I think education on security manners is poor and should be a standard topic.
  • sigil 10y ago
    When possible, measure security in attacker dollars. What's interesting here is that, just 5 years ago, the 2017 cost of this very attack (the Stevens attack) was estimated at 2^18.4 = $350k [0]. The collision announced today cost about $100k. Perhaps even less. [1] Cloud computing is cheaper today than many expected it to be, and it seems like we're only now entering the era of fierce competition. Who knows what the next decade will bring. If your modeled attacker cost is within an order of magnitude or two of the danger zone, beware. Better to have many orders of magnitude of headroom. Along these lines, I really like what cperciva did with attacker cost modeling in his scrypt paper. See the table on page 14 [2]. I wish more security choices were presented this way, with estimated attacker costs. Taking that even further, I wish the numbers were updated dynamically against present day hardware & compute costs. Maybe even with trendline projections. It's difficult to make good security choices without knowing costs. [0] https://www.schneier.com/blog/archives/2012/10/when_will_we_se.html https://www.schneier.com/blog/archives/2012/10/when_will_we_... [1] https://sites.google.com/site/itstheshappening/ https://sites.google.com/site/itstheshappening/ [2] https://www.tarsnap.com/scrypt/scrypt.pdf https://www.tarsnap.com/scrypt/scrypt.pdf
• slavik81 10y ago
  I would interpret it more charitably than that. He was responding to a claim that malicious collisions could be passed off as being pure chance: > it could be incredible bad luck that caused that good-looking patch to be mistakenly matching a dangerous object
• braveo 10y ago
  What's shocking is how badly people understand the purpose of an analogy. It's to communicate an idea to another person in a way that can also convey subtleties, and not just the literal words being conveyed. In this case, he was trying to convey the idea that the risk is so small and so remote that it really isn't worth spending a lot of time on. You understood the point, I understood the point, and everyone else understood the point. Which means the analogy was successful. So please, stop trying to pull the conversation on some tangent so you expound on why smart people should spend more time on the perfect analogy that you approve of.
  • M_Grey 10y ago
    Well you said it... it's not a misunderstanding, it's a podium.
    • deleted 10y ago
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  • xkxx 10y ago
    > What's shocking is how badly people understand the purpose of an analogy. The purpose of an analogy is to simplify something that's too hard to understand for the person you try to convey your idea to. Sometimes analogies are appropriate, e.g. when you teach something. When you want to convince somebody whose opinion is very different from yours, analogies aren't appropriate. They sound condescending: "because you are not smart enough to understand the real rationale behind my opinion, here is an oversimplified argument based on analogies I made just for you". The question is, did Torvalds have any real argument back then? Maybe he fell back to using analogies for the lack of any real argument. > In this case, he was trying to convey the idea that the risk is so small and so remote that it really isn't worth spending a lot of time on. To convey the idea that the risk is very small, one needs to have a proof. Real proofs shouldn't involve analogies. They should use facts and logic.
    • hulahoof 10y ago
      Sometimes facts and logic can be extremely verbose - I feel many analogies are in place not to be condescending, but because the author has faith in the reader that they can make the connection between the analogy and the problem. And to be quite honest abstracting ideas is core to problem solving, and I think it's a bit disingenuous to say that anyone misunderstood what Linus was getting at there.
• xkxx 10y ago
  A better counterargument to his argument would be: hashes are not "my plane", potential adversaries are not "a meteorite". Using analogies is okay when you try to explain a difficult idea to somebody who wants to learn about your subject. Using analogies is not okay when you want to make a solid argument, when you want to convince somebody whose stance is very different from yours.
• oceanswave 10y ago
  Here's another example of a person getting the scenario completely wrong. The adversary here is aliens and they're lobbing meteorites to take down planes. Get your head out of the groupthink people! just because it's difficult to conceptualize the foe, doesn't mean that the foe Isn't targeting you! Collanders on!
• squeaky-clean 10y ago
  This was also in response to the original sender's claim that plain ol' non-malicious bad luck could cause sha1 collisions in git commits. So this is a shockingly good example of how quotes taken out of context are pretty useless in a discussion.