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Mechanically jet engines are pretty simple devices, though - basically just a bunch of connected fans. But when covered with wires and pipes and such, they may

Mechanically jet engines are pretty simple devices, though - basically just a bunch of connected fans. But when covered with wires and pipes and such, they may look quite complicated at first glance. What line of business are you in that your team was considered inefficient in comparison?

greglindahl 8y ago
It's worth noticing that China has been unable to figure out to build high-performance jet engines, to the point that most of their military and civilian engines are imported. The metallurgy is apparently quite difficult, commercial product volumes are high, and customer expectations are even higher.
- southern_cross 8y ago
  Yes, the materials issue is usually the root of the problem - weight vs. strength vs. durability. (I expect that manufacturing to the needed tolerances is pretty hard, too.) Modern jet engines are so optimized for these factors, and also for fuel efficiency, that the same general designs are now used for power generation on the ground, where things like weight don't really matter.
- ubernostrum 8y ago
  This is why AICC bought the An-225. They don't just get the planes, they get the tooling and training to build their own, including the engines. And at this point, even a multiple-generations-old high-bypass turbofan is a big jump for China's domestic industry. They are not "easy" or "simple" to make and understand once you get down to the metallurgy and the fabrication techniques for stuff like the fan and compressor blades.
  - southern_cross 8y ago
    Designs for the basic jet engine date back to at least the 1920s, and basic operating principles date back much, much further. Jet aircraft were actually flying by the 1940s, and those engines were built using the relatively primitive metallurgical and manufacturing techniques of the day. So, as I said, _mechanically_ jet engines are relatively simple devices. Materials, manufacturing, control systems, fuel efficiency, noise abatement and all that may be a very different story.
    - ubernostrum 8y ago
      I didn't say otherwise. Jet engines have always been held back not by their mechanical complexity (they're mechanically pretty simple, as you point out), but by the difficulty of obtaining/fabricating materials that can withstand the temperatures and pressures of operation at the desired weight. Reciprocating engines were far more complex mechanically, but lasted as long as they did before being supplanted by jet (gas turbine) engines precisely because of how much easier it was to build and maintain them.
      - perilunar 8y ago
        Funny you should say that. I always thought that jet engines rapidly replaced piston engines because they were easier and cheaper to build. For example, the Wikipedia article on the BMW003 says: "The BMW 003 proved cheaper in materials than the company's own 801 radial, RM12,000 to RM40,000, and cheaper than the Junkers Jumo 213 inverted V12 piston engine at RM35,000, but slightly more costly than the competing Junkers Jumo 004's RM10000.[10] Moreover, the 004 needed only 375 hours to complete (including manufacture, assembly, and shipping), compared to 1,400 for the 801." https://en.wikipedia.org/wiki/BMW_003 https://en.wikipedia.org/wiki/BMW_003 i.e. the first two german production jet engines were a third of the cost and took less than a third of the man-hours to build compared to piston engines of the same era.
        ubernostrum 8y ago
        Again, doesn't contradict anything I said. An iPhone is cheaper to build today than a typical computer of the 1960s. Does that mean it would have been cheap or easy to build a current-model iPhone in the 1960s? Because that's the argument you're making here, essentially. Once you have the necessary tech under your belt, yes, you get a bunch of benefits from switching. But until you have that tech, you're probably not going to say "oh well, won't build any planes for the next few decades, because the engines we'd use today are way more complex and less useful than the ones we'll have eventually". Jet engines are simpler than reciprocating engines. I'll happily write that on the blackboard 1000 times, if you'll write "But until you have the fundamental technology for it, you can't build any jet engines" 1000 times. Also, read your own link: Completed engines earned a reputation for unreliability; the time between major overhauls (not technically a TBO) was about 50 hours. Even those early engines, despite being cheaper, and quicker to assemble, still weren't up to the point of being usefully reliable. Jet engines are hard.
mannykannot 8y ago
At anything more than a superficial glance,they are extremely complicated. You don't get the raw power, power-to weight ratio, fuel efficiency and reliability - and yes, they are extremely reliable in general, despite these recent troubles - by just connecting a bunch of fans. In fact, you would not get anything at all from trying it, except maybe set your garage on fire, if your 'just a bunch of connected fans' comment is an indicator of the depth of your understanding.
- southern_cross 8y ago
  You seem to be confusing materials and design issues with mechanical issues. I expect that I have more understanding of the situation than you do - decades' worth, in fact. I've even laid hands on - and spun, as best I could - military jet engines that had been partially dismantled. (I've also seen open civilian jet engines up close but have never laid hands on one.) Once you stripped away all of the external paraphernalia their relative mechanical simplicity was obvious, as was the reason why those particular engines had been grounded.
na85 8y ago
They're simple conceptually but are highly intricate, complex implementations in reality. Also, these are not jet engines: they're turbofans and are more than "a series of connected fans".
- theoh 8y ago
  "a series of fans within a nesting of tubes"
- southern_cross 8y ago
  A "high-bypass" design, where a large fan is driven by a relatively small jet engine. Still pretty simple mechanically, though.
  - na85 8y ago
    Simple concept, yes. But to say that it's simple to make a turbofan engine would be like saying it's simple to make your own crypto. After all, it's just multiplying some prime numbers together.
    - southern_cross 8y ago
      Actually crypto _is_ pretty simple; all you really need is an XOR function. It's in things like key management and such where it gets complicated. BTW, if I ever _really_ wanted to hide something, I would in fact roll my own crypto, using techniques that no sane crypto expert would probably even consider. Then I would wrap that in at least one layer of "official" crypto, knowing full well that this layer was possibly fundamentally flawed (even crypto experts often don't get things right), or that it might even contain a backdoor.
      - ericpauley 8y ago
        https://en.wikipedia.org/wiki/Snake_oil_(cryptography) https://en.wikipedia.org/wiki/Snake_oil_(cryptography) Specifically that your post is essentially security through obscurity. If your implementation is found then the fact that you use some bogus scheme will not help you.
throwaway5752 8y ago
Do you have any idea how complicated a single turbine blade is? It's a monocrystal of a superalloy that retains strength at over 1.5k degrees F, and it has channels for coolant because it operates beyond that temperature. You're like saying a computer is a bunch of wire and some melted sand between some copper.
- honestoHeminway 8y ago
  https://en.wikipedia.org/wiki/Turbine_blade https://en.wikipedia.org/wiki/Turbine_blade Its a shame that so much of humanity is so clueless about the technology surrounding it by now. Its all magic and fairy dust. If you stop believing into your computer, the machine will die.
- ben_w 8y ago
  Huh, interesting. I thought monocrystal blades were only for military engines and civilian engines made do with cheaper stuff which required a slightly lower maximum engine temperature. Then again, I did get my information from a friend in the pub (he’s a Cambridge PhD, but still).
- southern_cross 8y ago
  Once again, you're confusing materials and manufacturing complexity for actual mechanical complexity. I remember when I first got a close look at a jet turbine fan blade, and being puzzled by some aspects of it, like the channels that ran all the way through it. (I remember thinking that those channels must have been pretty tricky to make.) But then I realized that these were probably for cooling, like you said. I was most impressed by its relatively complex shape, and by no doubt the exotic material that it was made of and the tight tolerances it held. But in the end it's nothing more than a simple fan blade. BTW, I had some similar impressions about the close-up look I once got of a large rocket engine nozzle. Then I realized that it was really nothing more than a big coiled cooling tube surrounded by an external shell - pretty simple stuff, actually. And the "de Laval" part of that nozzle, which is what makes it work to begin with, is as simple as can be and is a design which dates back to over a century ago.
  - 8y ago
vladTheInhaler 8y ago
"In theory there is no difference between theory and practice. In practice there is."
gaius 8y ago
But when covered with wires and pipes and such, they may look quite complicated at first glance. This is like saying programming is just a bunch of 1’s and 0’s and it only look complicated because of the random curly brackets and semicolons.
- southern_cross 8y ago
  Early computers were indeed programmed using toggle switches and such to input a bunch of 1’s and 0’s, which is all the computer hardware itself understands. Additional layers were added later so that we humans could work with something that we understand, but ultimately all of that still gets translated down to individual bits. So in the end we're still programming with 1’s and 0’s, only we usually just don't realize it.

greglindahl 8y ago

It's worth noticing that China has been unable to figure out to build high-performance jet engines, to the point that most of their military and civilian engines are imported. The metallurgy is apparently quite difficult, commercial product volumes are high, and customer expectations are even higher.

southern_cross 8y ago
Yes, the materials issue is usually the root of the problem - weight vs. strength vs. durability. (I expect that manufacturing to the needed tolerances is pretty hard, too.) Modern jet engines are so optimized for these factors, and also for fuel efficiency, that the same general designs are now used for power generation on the ground, where things like weight don't really matter.
ubernostrum 8y ago
This is why AICC bought the An-225. They don't just get the planes, they get the tooling and training to build their own, including the engines. And at this point, even a multiple-generations-old high-bypass turbofan is a big jump for China's domestic industry. They are not "easy" or "simple" to make and understand once you get down to the metallurgy and the fabrication techniques for stuff like the fan and compressor blades.
- southern_cross 8y ago
  Designs for the basic jet engine date back to at least the 1920s, and basic operating principles date back much, much further. Jet aircraft were actually flying by the 1940s, and those engines were built using the relatively primitive metallurgical and manufacturing techniques of the day. So, as I said, _mechanically_ jet engines are relatively simple devices. Materials, manufacturing, control systems, fuel efficiency, noise abatement and all that may be a very different story.
  - ubernostrum 8y ago
    I didn't say otherwise. Jet engines have always been held back not by their mechanical complexity (they're mechanically pretty simple, as you point out), but by the difficulty of obtaining/fabricating materials that can withstand the temperatures and pressures of operation at the desired weight. Reciprocating engines were far more complex mechanically, but lasted as long as they did before being supplanted by jet (gas turbine) engines precisely because of how much easier it was to build and maintain them.
    - perilunar 8y ago
      Funny you should say that. I always thought that jet engines rapidly replaced piston engines because they were easier and cheaper to build. For example, the Wikipedia article on the BMW003 says: "The BMW 003 proved cheaper in materials than the company's own 801 radial, RM12,000 to RM40,000, and cheaper than the Junkers Jumo 213 inverted V12 piston engine at RM35,000, but slightly more costly than the competing Junkers Jumo 004's RM10000.[10] Moreover, the 004 needed only 375 hours to complete (including manufacture, assembly, and shipping), compared to 1,400 for the 801." https://en.wikipedia.org/wiki/BMW_003 https://en.wikipedia.org/wiki/BMW_003 i.e. the first two german production jet engines were a third of the cost and took less than a third of the man-hours to build compared to piston engines of the same era.
      - ubernostrum 8y ago
        Again, doesn't contradict anything I said. An iPhone is cheaper to build today than a typical computer of the 1960s. Does that mean it would have been cheap or easy to build a current-model iPhone in the 1960s? Because that's the argument you're making here, essentially. Once you have the necessary tech under your belt, yes, you get a bunch of benefits from switching. But until you have that tech, you're probably not going to say "oh well, won't build any planes for the next few decades, because the engines we'd use today are way more complex and less useful than the ones we'll have eventually". Jet engines are simpler than reciprocating engines. I'll happily write that on the blackboard 1000 times, if you'll write "But until you have the fundamental technology for it, you can't build any jet engines" 1000 times. Also, read your own link: Completed engines earned a reputation for unreliability; the time between major overhauls (not technically a TBO) was about 50 hours. Even those early engines, despite being cheaper, and quicker to assemble, still weren't up to the point of being usefully reliable. Jet engines are hard.

mannykannot 8y ago

At anything more than a superficial glance,they are extremely complicated. You don't get the raw power, power-to weight ratio, fuel efficiency and reliability - and yes, they are extremely reliable in general, despite these recent troubles - by just connecting a bunch of fans. In fact, you would not get anything at all from trying it, except maybe set your garage on fire, if your 'just a bunch of connected fans' comment is an indicator of the depth of your understanding.

southern_cross 8y ago
You seem to be confusing materials and design issues with mechanical issues. I expect that I have more understanding of the situation than you do - decades' worth, in fact. I've even laid hands on - and spun, as best I could - military jet engines that had been partially dismantled. (I've also seen open civilian jet engines up close but have never laid hands on one.) Once you stripped away all of the external paraphernalia their relative mechanical simplicity was obvious, as was the reason why those particular engines had been grounded.

na85 8y ago

They're simple conceptually but are highly intricate, complex implementations in reality. Also, these are not jet engines: they're turbofans and are more than "a series of connected fans".

theoh 8y ago
"a series of fans within a nesting of tubes"
southern_cross 8y ago
A "high-bypass" design, where a large fan is driven by a relatively small jet engine. Still pretty simple mechanically, though.
- na85 8y ago
  Simple concept, yes. But to say that it's simple to make a turbofan engine would be like saying it's simple to make your own crypto. After all, it's just multiplying some prime numbers together.
  - southern_cross 8y ago
    Actually crypto _is_ pretty simple; all you really need is an XOR function. It's in things like key management and such where it gets complicated. BTW, if I ever _really_ wanted to hide something, I would in fact roll my own crypto, using techniques that no sane crypto expert would probably even consider. Then I would wrap that in at least one layer of "official" crypto, knowing full well that this layer was possibly fundamentally flawed (even crypto experts often don't get things right), or that it might even contain a backdoor.
    - ericpauley 8y ago
      https://en.wikipedia.org/wiki/Snake_oil_(cryptography) https://en.wikipedia.org/wiki/Snake_oil_(cryptography) Specifically that your post is essentially security through obscurity. If your implementation is found then the fact that you use some bogus scheme will not help you.

throwaway5752 8y ago

Do you have any idea how complicated a single turbine blade is? It's a monocrystal of a superalloy that retains strength at over 1.5k degrees F, and it has channels for coolant because it operates beyond that temperature. You're like saying a computer is a bunch of wire and some melted sand between some copper.

honestoHeminway 8y ago
https://en.wikipedia.org/wiki/Turbine_blade https://en.wikipedia.org/wiki/Turbine_blade Its a shame that so much of humanity is so clueless about the technology surrounding it by now. Its all magic and fairy dust. If you stop believing into your computer, the machine will die.
ben_w 8y ago
Huh, interesting. I thought monocrystal blades were only for military engines and civilian engines made do with cheaper stuff which required a slightly lower maximum engine temperature. Then again, I did get my information from a friend in the pub (he’s a Cambridge PhD, but still).
southern_cross 8y ago
Once again, you're confusing materials and manufacturing complexity for actual mechanical complexity. I remember when I first got a close look at a jet turbine fan blade, and being puzzled by some aspects of it, like the channels that ran all the way through it. (I remember thinking that those channels must have been pretty tricky to make.) But then I realized that these were probably for cooling, like you said. I was most impressed by its relatively complex shape, and by no doubt the exotic material that it was made of and the tight tolerances it held. But in the end it's nothing more than a simple fan blade. BTW, I had some similar impressions about the close-up look I once got of a large rocket engine nozzle. Then I realized that it was really nothing more than a big coiled cooling tube surrounded by an external shell - pretty simple stuff, actually. And the "de Laval" part of that nozzle, which is what makes it work to begin with, is as simple as can be and is a design which dates back to over a century ago.
- 8y ago

vladTheInhaler 8y ago

"In theory there is no difference between theory and practice. In practice there is."

gaius 8y ago

But when covered with wires and pipes and such, they may look quite complicated at first glance. This is like saying programming is just a bunch of 1’s and 0’s and it only look complicated because of the random curly brackets and semicolons.

southern_cross 8y ago
Early computers were indeed programmed using toggle switches and such to input a bunch of 1’s and 0’s, which is all the computer hardware itself understands. Additional layers were added later so that we humans could work with something that we understand, but ultimately all of that still gets translated down to individual bits. So in the end we're still programming with 1’s and 0’s, only we usually just don't realize it.