4 ms·

> I would have gone with a helicopter as the system but that would require domain familiarity Would you give it a try?

by bch 4y ago

SilasX 4y ago
Well, there isn’t much to add beyond the fact them being more prone to acoustic breakage. Helicopters are a nightmare for vibrations because you have to spin the rotor really fast and forcibly, risking over-stressing critical structural components if you excite them at their resonant frequency. They’re designed to operate at only one rotor speed because that’s enough of a headache in terms of preventing it from hitting resonant modes that the structure can’t handle. So for helicopters it’s much easier to imagine a pattern of rotor movement that will break the system — though again, getting the intuition down would require having modeled vibratory systems to see when they go out of control. But at least it’s more intuitive than record players, which work with much smaller vibrations and generally operate in moderate volume limits.
- viscanti 4y ago
  I wonder why they didn't have Achilles give out a special rotor for a helicopter that would have caused the entire helicopter to break. It seems like a great analogy for people who have the required domain knowledge as well as think it would be reasonable for someone to gift someone else a helicopter rotor.
  - schoen 4y ago
    This reminds me of the Donald Duck cartoon in which for some reason some of the Duck family have acquired a steam calliope (kind of like a somewhat portable pipe organ), and are trying to figure out what to do with it. Whereupon they meet a strange hermit who lives in a cave, or something, and who says that he has absolutely everything he needs in life, and there is nothing they can offer him that would be of any value. Except for one thing. Of course, it turns out to be a steam calliope. Similarly, I suppose that, sometimes, when you really need a helicopter rotor, you really need a helicopter rotor!
  - SilasX 4y ago
    Did you miss that the analogy would have “rotor input” instead of a replacement rotor, and that I agreed it would require some domain knowledge, or is this just you adding toxic snark to look clever and discourage substantive contributions to these threads? In any case, the record player analogy is still unhelpful because it conveys no practical intuition about why a record might break its player — that doesn’t happen in practice. Unless you want to make a substantive remark by showing an everyday case where a normal record might come close to breaking a normal player.
    - viscanti 4y ago
      Giving someone a rotor input seems unrealistic. I've never heard of someone gifting one and who would swap out a rotor input with one that would cause damage to the helicopter? I think readers would find that example too farfetched.
      - SilasX 4y ago
        First of all, I already agreed in the initial post that it would require some experience with helicopters. Second, in this case, "giving it a new input" could be as simple as "changing the standing rotor speed -- 5500 RPM instead of 6500 RPM". They're so finicky, you don't need to specify a complex time history to hit a dangerous resonant mode-- though it certainly helps! Third, the fact that it's a gift is not at all required for an analogy. Of course you don't have to keep that part, and would have to reframe it so that the details of how the helicopter is provided a new input are different. You're not even trying to be charitable at this point, but make it sound as stupid as you possibly can. Please work on your curiosity.

> I would have gone with a helicopter as the system but that would require domain familiarity Would you give it a try?

by bch 4y ago

> I would have gone with a helicopter as the system but that would require domain familiarity Would you give it a try?

Well, there isn’t much to add beyond the fact them being more prone to acoustic breakage. Helicopters are a nightmare for vibrations because you have to spin the rotor really fast and forcibly, risking over-stressing critical structural components if you excite them at their resonant frequency. They’re designed to operate at only one rotor speed because that’s enough of a headache in terms of preventing it from hitting resonant modes that the structure can’t handle. So for helicopters it’s much easier to imagine a pattern of rotor movement that will break the system — though again, getting the intuition down would require having modeled vibratory systems to see when they go out of control. But at least it’s more intuitive than record players, which work with much smaller vibrations and generally operate in moderate volume limits.

viscanti 4y ago
I wonder why they didn't have Achilles give out a special rotor for a helicopter that would have caused the entire helicopter to break. It seems like a great analogy for people who have the required domain knowledge as well as think it would be reasonable for someone to gift someone else a helicopter rotor.
- schoen 4y ago
  This reminds me of the Donald Duck cartoon in which for some reason some of the Duck family have acquired a steam calliope (kind of like a somewhat portable pipe organ), and are trying to figure out what to do with it. Whereupon they meet a strange hermit who lives in a cave, or something, and who says that he has absolutely everything he needs in life, and there is nothing they can offer him that would be of any value. Except for one thing. Of course, it turns out to be a steam calliope. Similarly, I suppose that, sometimes, when you really need a helicopter rotor, you really need a helicopter rotor!
- SilasX 4y ago
  Did you miss that the analogy would have “rotor input” instead of a replacement rotor, and that I agreed it would require some domain knowledge, or is this just you adding toxic snark to look clever and discourage substantive contributions to these threads? In any case, the record player analogy is still unhelpful because it conveys no practical intuition about why a record might break its player — that doesn’t happen in practice. Unless you want to make a substantive remark by showing an everyday case where a normal record might come close to breaking a normal player.
  - viscanti 4y ago
    Giving someone a rotor input seems unrealistic. I've never heard of someone gifting one and who would swap out a rotor input with one that would cause damage to the helicopter? I think readers would find that example too farfetched.
    - SilasX 4y ago
      First of all, I already agreed in the initial post that it would require some experience with helicopters. Second, in this case, "giving it a new input" could be as simple as "changing the standing rotor speed -- 5500 RPM instead of 6500 RPM". They're so finicky, you don't need to specify a complex time history to hit a dangerous resonant mode-- though it certainly helps! Third, the fact that it's a gift is not at all required for an analogy. Of course you don't have to keep that part, and would have to reframe it so that the details of how the helicopter is provided a new input are different. You're not even trying to be charitable at this point, but make it sound as stupid as you possibly can. Please work on your curiosity.