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>The first patent for using a gas turbine to power an aircraft was filed in 1921 by Maxime Guillaume. https://en.wikipedia.org/wiki/Jet_engine https://en.wikip

>The first patent for using a gas turbine to power an aircraft was filed in 1921 by Maxime Guillaume. https://en.wikipedia.org/wiki/Jet_engine https://en.wikipedia.org/wiki/Jet_engine After close to a century of development, one would think it would be near its technical limits. Fuel efficiency trends for new commercial jet aircraft: 1960 to 2014 https://theicct.org/publications/fuel-efficiency-trends-new-commercial-jet-aircraft-1960-2014 https://theicct.org/publications/fuel-efficiency-trends-new-... https://theicct.org/sites/default/files/publications/ICCT_Aircraft-FE-Trends_20150902.pdf https://theicct.org/sites/default/files/publications/ICCT_Ai... Current airliners appear to burn half the fuel per passenger mile as did early '70s airliners. This reflects both propulsion and aerodynamic improvements.

seanmcdirmid 7y ago
Materials probably pays a similar role in the reduction compared to aerodynamics. Just eliminating weight has been very important.
- Retric 7y ago
  Smaller seat spacing is another, as putting more people in the same aircraft increases fuel economy per passenger mile.
  - apocalyptic0n3 7y ago
    But also inversely affects the weight of the aircraft, negatively affecting the fuel economy.
    - Retric 7y ago
      While true, parasitic drag is generally a significantly larger factor at airliner speeds. Airbus A320 during Cruise: “The 7,900lbf of drag is composed of 4,700lbf of Parasitic drag or drag independent of lift and 3,200lbf of Induced drag or drag caused by lift.” https://leehamnews.com/2018/03/09/bjorns-corner-aircraft-drag-reduction-part-20/ https://leehamnews.com/2018/03/09/bjorns-corner-aircraft-dra... On top of this slightly increasing passengers, their luggage, and a few extra seats has fairly minimal impact on aircraft weight. The aircraft’s maximum fuel/range is impacted, but that’s rarely an issue.
      - cameldrv 7y ago
        Yes, but parasite drag is indirectly affected by weight. A lot of the parasite drag comes from the wings and engines, and they scale up with weight, as long as you want to keep the same takeoff/landing distances.
        Retric 7y ago
        This is a comparison of the impact of seating arrangements for otherwise identical aircraft. The maximum takeoff weight stays the same, the difference is how much fuel they can add before they hit it. Which is why ultra long haul flights tend to have more leg room. This can be as much as 5 inches for the same airlines.
        cameldrv 7y ago
        Fair enough, but my point was that for a given set of capabilities (landing speed/distance, range), if you want to add more payload, you need more wing. The additional payload costs you drag from induced drag, but it also costs you parasite drag from the bigger wing you need to generate that lift at landing speed. You even see this with some stretched versions of airliners, they enlarge the wings or make changes to the high lift devices.
    - usrusr 7y ago
      It improves the payload fraction of total mass. That is generally better. But you might have to factor the expected total mass into the design. If you want to transport the payload mass of a 747 in lead bars, the smallest plane that can fit the volume will certainly not work. But a plane designed for that lead load would be far more efficient than a 747 (or modern equivalent) that is flying almost empty by volume.
freehunter 7y ago
> After close to a century of development, one would think it would be near its technical limits. Internal combustion engines in cars have been around longer and we’re still pushing record amounts of power and record amounts of efficiency.
- deleted 7y ago
  [deleted]
- Merrill 7y ago
  This is partly due to the application of computer controls and partly due to the application of things like direct fuel injection, turbocharging, etc. that were previously available only on racing or aircraft engines. For example, the Cosworth DFV normally aspirated Formula 1 engine with 182 cubic inches was making over 520 horsepower (2.9 / cubic inch) by the end of its career in 1983.
  - fhood 7y ago
    Combustion engine development was oddly stunted though. We have known the basic formula for power for a very long time (forced induction + high compression + high octane fuel). Superchargers are ancient, turbos aren't new either, although I guess fuel injection had to wait for computers to be reliable and cost effective. Even then I don't fully understand why it took 30 years for automakers to figure out how to produce high power engines that met emissions standards.
    - abakker 7y ago
      It didn't take long to know how to do it. It took a long time to make cost effective parts that were reliable in doing it for the service life of a car. the bearings in a modern vw turbocharger are incredible. Imagine getting 100K Miles out of a turbocharger which can regularly spool to 200K RPMs. those bearings need to be made to incredible tolerances, which were not previously cost effective.
      - Merrill 7y ago
hoorayimhelping 7y ago
>After close to a century of development, one would think it would be near its technical limits. Why would one think that? It seems kind of arbitrary. Guns have been developed and iterated on for half a millennia and there are still technological advancements coming out regularly.
- tomatotomato37 7y ago
  Gunpowder-based gun technology has kinda plateued too. We pretty much hit the practical limits of size during WWII with Schwerer Gustav and battleship cannons, and the fastest firing guns still use the basic design of Richard Gatling from 1861. Most recent innovations have been in the work of pointing the gun in the right direction moreso than the gun itself. Then again, I guess caseless could be the next big innovation if they figure out the heat problem...
  - catalogia 7y ago
    Caseless ammunition, or telescoping ammunition (or both at the same time.) Either could conceivably increase how much ammunition soldiers can carry, but I'm not holding my breath for either. The status quo seems firmly in "good enough" territory and I'm pretty sure some of the other supposed benefits of caseless will fail to manifest. In particular, advocates of caseless ammunition have on occasion claimed that guns would be simplified by not having to eject brass, but I don't think that's true since said guns would still need a reasonable way to eject chambered but unfired ammunition (even if it was open-bolt.)
- Merrill 7y ago
  The Winchester '94 rifle has been in production for 125 years now, and is still available for the 30-30 brass case, centerfire, smokeless powder cartridge. There was a rapid evolution of rifles from the flintlock, black-powder, muzzle-loader to the repeating, brass cartridge, smokeless powder rifle. Since then, rifles, machine guns and pistols have evolved through successive refinements.
- dlgeek 7y ago
  Not really in firearm design since the 1950s/60s or so. There are small improvements, but the basic operating mechanisms everyone's using haven't changed since then. (Compared to the previous 60-70 years which saw the introduction of smokeless powder, box magazines, self-loading, automatic fire, etc.). (Optics are seeing this kind of development though).
notJim 7y ago
Airliners also fly more slowly than they used to https://alum.mit.edu/slice/why-hasnt-commercial-air-travel-gotten-any-faster-1960s https://alum.mit.edu/slice/why-hasnt-commercial-air-travel-g...

seanmcdirmid 7y ago

Materials probably pays a similar role in the reduction compared to aerodynamics. Just eliminating weight has been very important.

Retric 7y ago
Smaller seat spacing is another, as putting more people in the same aircraft increases fuel economy per passenger mile.
- apocalyptic0n3 7y ago
  But also inversely affects the weight of the aircraft, negatively affecting the fuel economy.
  - Retric 7y ago
    While true, parasitic drag is generally a significantly larger factor at airliner speeds. Airbus A320 during Cruise: “The 7,900lbf of drag is composed of 4,700lbf of Parasitic drag or drag independent of lift and 3,200lbf of Induced drag or drag caused by lift.” https://leehamnews.com/2018/03/09/bjorns-corner-aircraft-drag-reduction-part-20/ https://leehamnews.com/2018/03/09/bjorns-corner-aircraft-dra... On top of this slightly increasing passengers, their luggage, and a few extra seats has fairly minimal impact on aircraft weight. The aircraft’s maximum fuel/range is impacted, but that’s rarely an issue.
    - cameldrv 7y ago
      Yes, but parasite drag is indirectly affected by weight. A lot of the parasite drag comes from the wings and engines, and they scale up with weight, as long as you want to keep the same takeoff/landing distances.
      - Retric 7y ago
        This is a comparison of the impact of seating arrangements for otherwise identical aircraft. The maximum takeoff weight stays the same, the difference is how much fuel they can add before they hit it. Which is why ultra long haul flights tend to have more leg room. This can be as much as 5 inches for the same airlines.
        cameldrv 7y ago
        Fair enough, but my point was that for a given set of capabilities (landing speed/distance, range), if you want to add more payload, you need more wing. The additional payload costs you drag from induced drag, but it also costs you parasite drag from the bigger wing you need to generate that lift at landing speed. You even see this with some stretched versions of airliners, they enlarge the wings or make changes to the high lift devices.
  - usrusr 7y ago
    It improves the payload fraction of total mass. That is generally better. But you might have to factor the expected total mass into the design. If you want to transport the payload mass of a 747 in lead bars, the smallest plane that can fit the volume will certainly not work. But a plane designed for that lead load would be far more efficient than a 747 (or modern equivalent) that is flying almost empty by volume.

freehunter 7y ago

> After close to a century of development, one would think it would be near its technical limits. Internal combustion engines in cars have been around longer and we’re still pushing record amounts of power and record amounts of efficiency.

deleted 7y ago
[deleted]
Merrill 7y ago
This is partly due to the application of computer controls and partly due to the application of things like direct fuel injection, turbocharging, etc. that were previously available only on racing or aircraft engines. For example, the Cosworth DFV normally aspirated Formula 1 engine with 182 cubic inches was making over 520 horsepower (2.9 / cubic inch) by the end of its career in 1983.
- fhood 7y ago
  Combustion engine development was oddly stunted though. We have known the basic formula for power for a very long time (forced induction + high compression + high octane fuel). Superchargers are ancient, turbos aren't new either, although I guess fuel injection had to wait for computers to be reliable and cost effective. Even then I don't fully understand why it took 30 years for automakers to figure out how to produce high power engines that met emissions standards.
  - abakker 7y ago
    It didn't take long to know how to do it. It took a long time to make cost effective parts that were reliable in doing it for the service life of a car. the bearings in a modern vw turbocharger are incredible. Imagine getting 100K Miles out of a turbocharger which can regularly spool to 200K RPMs. those bearings need to be made to incredible tolerances, which were not previously cost effective.
    - Merrill 7y ago

hoorayimhelping 7y ago

>After close to a century of development, one would think it would be near its technical limits. Why would one think that? It seems kind of arbitrary. Guns have been developed and iterated on for half a millennia and there are still technological advancements coming out regularly.

tomatotomato37 7y ago
Gunpowder-based gun technology has kinda plateued too. We pretty much hit the practical limits of size during WWII with Schwerer Gustav and battleship cannons, and the fastest firing guns still use the basic design of Richard Gatling from 1861. Most recent innovations have been in the work of pointing the gun in the right direction moreso than the gun itself. Then again, I guess caseless could be the next big innovation if they figure out the heat problem...
- catalogia 7y ago
  Caseless ammunition, or telescoping ammunition (or both at the same time.) Either could conceivably increase how much ammunition soldiers can carry, but I'm not holding my breath for either. The status quo seems firmly in "good enough" territory and I'm pretty sure some of the other supposed benefits of caseless will fail to manifest. In particular, advocates of caseless ammunition have on occasion claimed that guns would be simplified by not having to eject brass, but I don't think that's true since said guns would still need a reasonable way to eject chambered but unfired ammunition (even if it was open-bolt.)
Merrill 7y ago
The Winchester '94 rifle has been in production for 125 years now, and is still available for the 30-30 brass case, centerfire, smokeless powder cartridge. There was a rapid evolution of rifles from the flintlock, black-powder, muzzle-loader to the repeating, brass cartridge, smokeless powder rifle. Since then, rifles, machine guns and pistols have evolved through successive refinements.
dlgeek 7y ago
Not really in firearm design since the 1950s/60s or so. There are small improvements, but the basic operating mechanisms everyone's using haven't changed since then. (Compared to the previous 60-70 years which saw the introduction of smokeless powder, box magazines, self-loading, automatic fire, etc.). (Optics are seeing this kind of development though).

notJim 7y ago

Airliners also fly more slowly than they used to https://alum.mit.edu/slice/why-hasnt-commercial-air-travel-gotten-any-faster-1960s https://alum.mit.edu/slice/why-hasnt-commercial-air-travel-g...