5 ms·

The latest and greatest engines are not that far from the theoretical thermodynamic efficiency limit. So future designs are running into the hard part of the as

The latest and greatest engines are not that far from the theoretical thermodynamic efficiency limit. So future designs are running into the hard part of the asymptote. I doubt airlines are actually interested in committing tens of billions of capital, today, to get a dozen % improvement in fuel efficiency a decade from now. And why would a private investor take such a huge risk without guarantees of making it back several fold? So it doesn't happen.

credit_guy 4y ago
> The latest and greatest engines are not that far from the theoretical thermodynamic efficiency limit. So future designs are running into the hard part of the asymptote. No. Even if an engine got to the Carnot efficiency, you can still improve it. Massively. You can push a certain quantity of air with a velocity v or 4 times that quantity with half the velocity. The second option produces twice the thrust, for the same fuel consumption. That's the reason engines are getting larger and larger, and going for higher and higher bypass ratios. Separately, the maximum theoretical (Carnot) efficiency depends on how hot the engine runs. GE has introduced turbines made of silicon carbide, which can withstand absurdly high temperatures. Silicon carbide melts at more than 2800 Celsius, but they don't push it to such limits. But they push it to more than 1300 Celsius [1]. Military jet engines run much hotter though. Exact numbers are classified, but according to [2] the temperature inside F35's engine might reach 2000 Celsius (the actual number is obviously classified). Of course, military jet engines are many times more expensive than civilian ones, with higher maintenance costs, and lifespan about 2 orders of magnitude shorter. Still the fact that they can run this hot means improvements for the civilian jet engines are possible. And they will happen. [1] https://www.ornl.gov/news/ceramic-matrix-composites-take-flight-leap-jet-engine https://www.ornl.gov/news/ceramic-matrix-composites-take-fli... [2] https://www.researchgate.net/publication/285727346_Fahrenheit_3600 https://www.researchgate.net/publication/285727346_Fahrenhei...
wahern 4y ago
Sure, it's obviously a matter of diminishing returns and opportunity cost. But the re-engine for the A380 was basically a rote, low-risk, B-team exercise for Rolls Royce. All they had to do was tweak their existing generation stuff. The program was already well underway, and they still dropped it; they all but explicitly said the reason was, "meh, we lost interest". Something seems to have changed. Putting my cynical cap on, my hot take is this: Everybody now realizes that Emirates and Clark are exactly right. As was Airbus.[1] Demand will blow past supply (i.e. runways and gates). Ticket prices will sky rocket. But from the perspective of the plane and engine manufacturers this translates to, "if everybody sits on their hands and does nothing, we're going to enjoy a windfall of profits". Clearly, IMO, Boeing, all the engine manufacturers, and now (somewhat despite themselves) Airbus, are going to passively collude[2] to bring about this windfall. All they need to do is sit tight and wait things out. The threat of competition isn't significant enough to break the collusion; there are too few players, the barriers to entry--regulation, technical and logistical expertise, etc--too steep, and like with housing little prospect that political reforms will make it easier to build enough new runways and airports to change the capacity trajectory. Similar calculus applies to most of the established carriers. There's much more competition among them, but if the manufacturers are expected to continue to coast there's no angle to exploit in that regard and thus little incentive to agitate for disruption along this dimension, and so the carriers also get to look forward to windfall profits, notwithstanding that they'll be forking over much of it to the manufacturers. Clark just isn't cold-blooded enough to want to play that game; he's got too much of a fighting spirit. (Or perhaps more realistically it's also because if Emirates doesn't keep growing it won't be viable in this prospective future reality?) [1] Boeing wasn't wrong, either, but point-to-point only bought a couple of decades of supply expansion. [2] I think there's an economics term for this, but I don't remember it.
- rippercushions 4y ago
  Boeing, Airbus, and Rolls-Royce are going to be in for a rude awakening if/when the Chinese aircraft industry ever gets their shit together, and/or if batteries ever become light/dense enough to support electric passenger flight. That said, watching the Comac C919 shitshow (14 years and still not in revenue service, and this is for a 737/A320 clone), I'm not holding my breath. The twin-aisle C929 is still a decade away at best, and it'll take a good long time until any Western airline trusts it; even Chinese turboprops (Xian MA-60/600/700) have so far only managed to find buyers in Africa and the poorer bits of Asia. https://en.wikipedia.org/wiki/Comac_C919 https://en.wikipedia.org/wiki/Comac_C919 https://en.wikipedia.org/wiki/CRAIC_CR929 https://en.wikipedia.org/wiki/CRAIC_CR929
  - seanmcdirmid 4y ago
    The C919 and C929 both fly with western avionics and jet engines, so they aren’t really that far off from airbus and Boeing, and don’t really bring anything new to the table beyond more competition from China in putting everything together.
    - elzbardico 4y ago
      Probably the Chinese will have to rely on some derivative of the Russian PD-14 engine. It is very probable that the chinese will lose access to western engines due to sanctions in the not so remote future, and their indigenous projects are still very far behind the state of art in jet engines.
    - rippercushions 4y ago
      They're building their own engine as well: https://en.wikipedia.org/wiki/ACAE_CJ-1000A https://en.wikipedia.org/wiki/ACAE_CJ-1000A I agree that the C919/929 pose no threat as is, but the Chinese are clearly playing the long game here and their massive domestic market coupled with government arm-twisting lets them scale: the C919 has already racked up over 1000 orders.
      - 4y ago
throwaway2037 4y ago
not that far from the theoretical thermodynamic efficiency limit This is an interesting comment. It is not my field of expertise, but I am interested to learn more. Can you share more info or maybe a paper/blog? Thanks.

credit_guy 4y ago

> The latest and greatest engines are not that far from the theoretical thermodynamic efficiency limit. So future designs are running into the hard part of the asymptote. No. Even if an engine got to the Carnot efficiency, you can still improve it. Massively. You can push a certain quantity of air with a velocity v or 4 times that quantity with half the velocity. The second option produces twice the thrust, for the same fuel consumption. That's the reason engines are getting larger and larger, and going for higher and higher bypass ratios. Separately, the maximum theoretical (Carnot) efficiency depends on how hot the engine runs. GE has introduced turbines made of silicon carbide, which can withstand absurdly high temperatures. Silicon carbide melts at more than 2800 Celsius, but they don't push it to such limits. But they push it to more than 1300 Celsius [1]. Military jet engines run much hotter though. Exact numbers are classified, but according to [2] the temperature inside F35's engine might reach 2000 Celsius (the actual number is obviously classified). Of course, military jet engines are many times more expensive than civilian ones, with higher maintenance costs, and lifespan about 2 orders of magnitude shorter. Still the fact that they can run this hot means improvements for the civilian jet engines are possible. And they will happen. [1] https://www.ornl.gov/news/ceramic-matrix-composites-take-flight-leap-jet-engine https://www.ornl.gov/news/ceramic-matrix-composites-take-fli... [2] https://www.researchgate.net/publication/285727346_Fahrenheit_3600 https://www.researchgate.net/publication/285727346_Fahrenhei...

wahern 4y ago

Sure, it's obviously a matter of diminishing returns and opportunity cost. But the re-engine for the A380 was basically a rote, low-risk, B-team exercise for Rolls Royce. All they had to do was tweak their existing generation stuff. The program was already well underway, and they still dropped it; they all but explicitly said the reason was, "meh, we lost interest". Something seems to have changed. Putting my cynical cap on, my hot take is this: Everybody now realizes that Emirates and Clark are exactly right. As was Airbus.[1] Demand will blow past supply (i.e. runways and gates). Ticket prices will sky rocket. But from the perspective of the plane and engine manufacturers this translates to, "if everybody sits on their hands and does nothing, we're going to enjoy a windfall of profits". Clearly, IMO, Boeing, all the engine manufacturers, and now (somewhat despite themselves) Airbus, are going to passively collude[2] to bring about this windfall. All they need to do is sit tight and wait things out. The threat of competition isn't significant enough to break the collusion; there are too few players, the barriers to entry--regulation, technical and logistical expertise, etc--too steep, and like with housing little prospect that political reforms will make it easier to build enough new runways and airports to change the capacity trajectory. Similar calculus applies to most of the established carriers. There's much more competition among them, but if the manufacturers are expected to continue to coast there's no angle to exploit in that regard and thus little incentive to agitate for disruption along this dimension, and so the carriers also get to look forward to windfall profits, notwithstanding that they'll be forking over much of it to the manufacturers. Clark just isn't cold-blooded enough to want to play that game; he's got too much of a fighting spirit. (Or perhaps more realistically it's also because if Emirates doesn't keep growing it won't be viable in this prospective future reality?) [1] Boeing wasn't wrong, either, but point-to-point only bought a couple of decades of supply expansion. [2] I think there's an economics term for this, but I don't remember it.

rippercushions 4y ago
Boeing, Airbus, and Rolls-Royce are going to be in for a rude awakening if/when the Chinese aircraft industry ever gets their shit together, and/or if batteries ever become light/dense enough to support electric passenger flight. That said, watching the Comac C919 shitshow (14 years and still not in revenue service, and this is for a 737/A320 clone), I'm not holding my breath. The twin-aisle C929 is still a decade away at best, and it'll take a good long time until any Western airline trusts it; even Chinese turboprops (Xian MA-60/600/700) have so far only managed to find buyers in Africa and the poorer bits of Asia. https://en.wikipedia.org/wiki/Comac_C919 https://en.wikipedia.org/wiki/Comac_C919 https://en.wikipedia.org/wiki/CRAIC_CR929 https://en.wikipedia.org/wiki/CRAIC_CR929
- seanmcdirmid 4y ago
  The C919 and C929 both fly with western avionics and jet engines, so they aren’t really that far off from airbus and Boeing, and don’t really bring anything new to the table beyond more competition from China in putting everything together.
  - elzbardico 4y ago
    Probably the Chinese will have to rely on some derivative of the Russian PD-14 engine. It is very probable that the chinese will lose access to western engines due to sanctions in the not so remote future, and their indigenous projects are still very far behind the state of art in jet engines.
  - rippercushions 4y ago
    They're building their own engine as well: https://en.wikipedia.org/wiki/ACAE_CJ-1000A https://en.wikipedia.org/wiki/ACAE_CJ-1000A I agree that the C919/929 pose no threat as is, but the Chinese are clearly playing the long game here and their massive domestic market coupled with government arm-twisting lets them scale: the C919 has already racked up over 1000 orders.
    - 4y ago

throwaway2037 4y ago

not that far from the theoretical thermodynamic efficiency limit This is an interesting comment. It is not my field of expertise, but I am interested to learn more. Can you share more info or maybe a paper/blog? Thanks.