7 ms·

Come on, we all know so they can go faster.

chrisseaton 6y ago
They could go faster with a single larger engine. Why do you think they went with two engines instead of a single larger engine? Redundancy.
- ghaff 6y ago
  Not clear to me that you'd design a commercial turbofan aircraft with one engine if you eliminated reliability requirements. You need to feed air to the engine and, to the degree you have wings, might as well have 2 engines.
  - chrisseaton 6y ago
    The idea that the engines need to sit on the wings like they do is something seems important, because it's so often done, but is actually not necessary. You can put a single engine in the tail, or on top of the cabin, or on the top of the cockpit, or underneath. They go on the wings because when you need two (for redundancy) it's a good place to put them for balance, and because it makes them nicely accessible for maintenance.
    - ghaff 6y ago
      Of course military aircraft have different requirements (and many have just one engine in the tail). Certainly I'm not enough of an aero/astro engineer to know if, positing a perfectly reliable engine, you'd mount just one somewhere on the fuselage.
    - TazeTSchnitzel 6y ago
      Trijets are cool!
    - dehrmann 6y ago
      > it's so often done The MD-80 had two rear engines and was a fairly popular plane. A lot of smaller jets still have rear engines, too.
      - chrisseaton 6y ago
        Not sure what you mean? I didn't say it was always done. In fact the point I was making was that it wasn't always done. I gave my own counter-examples. It's just when people look at modern planes they always see two engines and think that's the way it has to be. It clearly isn't.
      - ghaff 6y ago
        The MD-80 (and 727) were old turbojets though. Probably a lot harder to come up with a practical tailmounted design with a turbofan although I'm open to it being possible to mount one turbofan above the fuselage.
- andrewflnr 6y ago
  Citation needed. It's not at all obvious that a single huge engine is in any way better than two for a given speed.
  - chrisseaton 6y ago
    > Citation needed. Look up 'ETOPS'.
  - NikolaeVarius 6y ago
    This is basic aeronautical engineering. Barring the need for redundancy, turbofans are most efficient and quieter with larger intake sizes, the main limiting factor being fan tip speed. This is the reason that the 737 had the MCAS stuff. They increased the size of the engine that caused ground clearance problems, which required shifting them.
  - Sn0wCoder 6y ago
    Note sure this is reliable source but “ In general, twin engine aircraft allow for faster speeds, and faster pickup...”[1] 1 - https://www.vikingair.com/twin-otter-information/twin-otter-answers/what-are-advantages-twin-engine-versus-single-engine-turbo https://www.vikingair.com/twin-otter-information/twin-otter-...
- mannykannot 6y ago
  While redundancy makes it a moot issue, if I am not mistaken, 777s already use some of the most powerful engines available. As for how fast they fly, I believe it is mostly set by the speed of sound.
  - chrisseaton 6y ago
    Yes they use two of the most powerful engines... and just one of those is more than enough to fly the plane just fine almost as fast as they are allowed to... so why else would they have two of them if not redundancy? Fundamentally people can look it up themselves - 'ETOPS' - the redundancy requirement is a written regulation.
    - mannykannot 6y ago
      I think it should be obvious that I am responding to the claim "they could go faster with a single larger engine." no-one is arguing against redundancy (in which matter, ETOPS is just one aspect.)
      - deleted 6y ago
        [deleted]
      - chrisseaton 6y ago
        If they needed to go faster, they could do that with a single larger engine if they wanted to (which they may have to develop.) But they don't, because they're limited as you've explained. > no-one is arguing against redundancy Sn0wCoder said they reason they had two engines was to go faster and not redundancy, and m00dy thinks they can't fly without two engines.
        mannykannot 6y ago
        Point taken that some people had mistaken ideas about twin-engine airplanes, but those mistakes are most straightforwardly resolved by the redundancy consideration alone, which dominates other issues. > If they needed to go faster, they could do that with a single larger engine if they wanted to (which they may have to develop.) Plus a significantly different airframe and perhaps engine intakes to deal with the transonic issue that I also mentioned. It is an idea that bubbles up perennially [1], but so far, the economics have ensured that it doesn't go much beyond the concept stage. This has become rather silly, but it seques into a related issue: It seems to me that fan-blade failure incidents (or at least uncontained fan-blade failure incidents) have increased in frequency in the last few years. If so, maybe this is a sign that we are already pushing a bit too hard on the limits of current technology? [1] https://www.boeing.com/features/2019/01/spreading-our-wings-01-19.page https://www.boeing.com/features/2019/01/spreading-our-wings-...
msla 6y ago
If that was the reason, they'd paint it red!

They could go faster with a single larger engine. Why do you think they went with two engines instead of a single larger engine? Redundancy.

ghaff 6y ago
Not clear to me that you'd design a commercial turbofan aircraft with one engine if you eliminated reliability requirements. You need to feed air to the engine and, to the degree you have wings, might as well have 2 engines.
- chrisseaton 6y ago
  The idea that the engines need to sit on the wings like they do is something seems important, because it's so often done, but is actually not necessary. You can put a single engine in the tail, or on top of the cabin, or on the top of the cockpit, or underneath. They go on the wings because when you need two (for redundancy) it's a good place to put them for balance, and because it makes them nicely accessible for maintenance.
  - ghaff 6y ago
    Of course military aircraft have different requirements (and many have just one engine in the tail). Certainly I'm not enough of an aero/astro engineer to know if, positing a perfectly reliable engine, you'd mount just one somewhere on the fuselage.
  - TazeTSchnitzel 6y ago
    Trijets are cool!
  - dehrmann 6y ago
    > it's so often done The MD-80 had two rear engines and was a fairly popular plane. A lot of smaller jets still have rear engines, too.
    - chrisseaton 6y ago
      Not sure what you mean? I didn't say it was always done. In fact the point I was making was that it wasn't always done. I gave my own counter-examples. It's just when people look at modern planes they always see two engines and think that's the way it has to be. It clearly isn't.
    - ghaff 6y ago
      The MD-80 (and 727) were old turbojets though. Probably a lot harder to come up with a practical tailmounted design with a turbofan although I'm open to it being possible to mount one turbofan above the fuselage.
andrewflnr 6y ago
Citation needed. It's not at all obvious that a single huge engine is in any way better than two for a given speed.
- chrisseaton 6y ago
  > Citation needed. Look up 'ETOPS'.
- NikolaeVarius 6y ago
  This is basic aeronautical engineering. Barring the need for redundancy, turbofans are most efficient and quieter with larger intake sizes, the main limiting factor being fan tip speed. This is the reason that the 737 had the MCAS stuff. They increased the size of the engine that caused ground clearance problems, which required shifting them.
- Sn0wCoder 6y ago
  Note sure this is reliable source but “ In general, twin engine aircraft allow for faster speeds, and faster pickup...”[1] 1 - https://www.vikingair.com/twin-otter-information/twin-otter-answers/what-are-advantages-twin-engine-versus-single-engine-turbo https://www.vikingair.com/twin-otter-information/twin-otter-...
mannykannot 6y ago
While redundancy makes it a moot issue, if I am not mistaken, 777s already use some of the most powerful engines available. As for how fast they fly, I believe it is mostly set by the speed of sound.
- chrisseaton 6y ago
  Yes they use two of the most powerful engines... and just one of those is more than enough to fly the plane just fine almost as fast as they are allowed to... so why else would they have two of them if not redundancy? Fundamentally people can look it up themselves - 'ETOPS' - the redundancy requirement is a written regulation.
  - mannykannot 6y ago
    I think it should be obvious that I am responding to the claim "they could go faster with a single larger engine." no-one is arguing against redundancy (in which matter, ETOPS is just one aspect.)
    - deleted 6y ago
      [deleted]
    - chrisseaton 6y ago
      If they needed to go faster, they could do that with a single larger engine if they wanted to (which they may have to develop.) But they don't, because they're limited as you've explained. > no-one is arguing against redundancy Sn0wCoder said they reason they had two engines was to go faster and not redundancy, and m00dy thinks they can't fly without two engines.
      - mannykannot 6y ago
        Point taken that some people had mistaken ideas about twin-engine airplanes, but those mistakes are most straightforwardly resolved by the redundancy consideration alone, which dominates other issues. > If they needed to go faster, they could do that with a single larger engine if they wanted to (which they may have to develop.) Plus a significantly different airframe and perhaps engine intakes to deal with the transonic issue that I also mentioned. It is an idea that bubbles up perennially [1], but so far, the economics have ensured that it doesn't go much beyond the concept stage. This has become rather silly, but it seques into a related issue: It seems to me that fan-blade failure incidents (or at least uncontained fan-blade failure incidents) have increased in frequency in the last few years. If so, maybe this is a sign that we are already pushing a bit too hard on the limits of current technology? [1] https://www.boeing.com/features/2019/01/spreading-our-wings-01-19.page https://www.boeing.com/features/2019/01/spreading-our-wings-...

msla 6y ago

If that was the reason, they'd paint it red!