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I work at NASA primarily supporting our aeronautics programs, and I'm excited about all-electric and hybrid-electric civil aircraft conceptual design analysis a

by thearn4 10y ago

I work at NASA primarily supporting our aeronautics programs, and I'm excited about all-electric and hybrid-electric civil aircraft conceptual design analysis and optimization (for both fixed-wing and rotary-wing). It's one of the big "what-if" areas that is being looked at by NASA aeronautics in the next decade, and an area that has a surprising diversity of intuitive reactions within the industry at large. Meaning, there is a camp if industry experts that feels that it is a dead end, and another that sees it as a practical way forward. My opinion is that there are gains to be made there, but practical systems will have to be designed and optimized in a far more integrated manner than how most civil aviation systems have been in the past (integrating, for instance, the design optimization of the propulsion, airframe, and mission profiles together at mid to high fidelity early in the conceptual design process).

termain 10y ago
And as far as I can tell, organizations struggle with doing multilevel and multidisciplinary optimization.
- paulsutter 10y ago
  (I meant to upvote this, but somehow hit down. Could someone please fix that? It's actually a really good point relating to the development of new types of systems)
  - kbenson 10y ago
    Fixed. I imagine a few other people might have as well, so you probably more than made up for it. ;)
walrus01 10y ago
> feels that it is a dead end, and another that sees it as a practical way forward Until the Wh/kg ratio of batteries improves significantly, it will be a huge problem to have electric planes. Look at the energy contents of 1 litre of Jet-A or avgas compared to the same weight in batteries. Hydrogen + fuel cell systems to achieve the same energy density require very costly extremely high pressure tanks and fueling systems, and that is before you get into the argument of whether hydrogen is a terrible use of energy. If your hydrogen supply is coming from an electrolysis process an IMMENSE amount of kWh has been consumed to fill your hydrogen tank, which should be considered for the total environmental cost. So unless your electrolysis plant is hooked up to a massive PV array or a 4GW nuclear power plant, the economics are questionable. for comparison: lithium ion batteries 0.36–0.875 MJ/kg Jet-A: 42.80 MJ/kg
- kbenson 10y ago
  What efficiency is the engine converting those 42.80 MJ/kg into power at? I know it's still far above batteries, but what's the actual level batteries have to reach to be competitive in the power to weight ratio? Even that's not the full picture though, as for a system like this you would presumably include the engine weight for an engine that could produce comparable output, but that makes it more complicated.
- glaberficken 10y ago
  >"Hydrogen + fuel cell systems to achieve the same energy density require very costly extremely high pressure tanks and fueling systems, and that is before you get into the argument of whether hydrogen is a terrible use of energy." The main problem here is you are comparing it to a fuel source which took million of years to form naturally. Think of the energy expenditure behind that!
- thearn4 10y ago
  Battery technology will definitely need to improve before any system is practical enough to build and add to a fleet. I think there are power system assumptions being made regarding mid to far term viability of metal air batteries. Currently, they are expected in operation to be much closer to the 40 MJ/kg figure than existing battery technology: https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemical_cell https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemi... That said, what becomes really interesting (and tricky) is that these types of batteries actually get heavier as they discharge, which throws off intuition for optimal trajectory analysis. We're used to thinking in terms of planes getting lighter as they consume their fuel...

by thearn4 10y ago

termain 10y ago

And as far as I can tell, organizations struggle with doing multilevel and multidisciplinary optimization.

paulsutter 10y ago
(I meant to upvote this, but somehow hit down. Could someone please fix that? It's actually a really good point relating to the development of new types of systems)
- kbenson 10y ago
  Fixed. I imagine a few other people might have as well, so you probably more than made up for it. ;)

walrus01 10y ago

> feels that it is a dead end, and another that sees it as a practical way forward Until the Wh/kg ratio of batteries improves significantly, it will be a huge problem to have electric planes. Look at the energy contents of 1 litre of Jet-A or avgas compared to the same weight in batteries. Hydrogen + fuel cell systems to achieve the same energy density require very costly extremely high pressure tanks and fueling systems, and that is before you get into the argument of whether hydrogen is a terrible use of energy. If your hydrogen supply is coming from an electrolysis process an IMMENSE amount of kWh has been consumed to fill your hydrogen tank, which should be considered for the total environmental cost. So unless your electrolysis plant is hooked up to a massive PV array or a 4GW nuclear power plant, the economics are questionable. for comparison: lithium ion batteries 0.36–0.875 MJ/kg Jet-A: 42.80 MJ/kg

kbenson 10y ago
What efficiency is the engine converting those 42.80 MJ/kg into power at? I know it's still far above batteries, but what's the actual level batteries have to reach to be competitive in the power to weight ratio? Even that's not the full picture though, as for a system like this you would presumably include the engine weight for an engine that could produce comparable output, but that makes it more complicated.
glaberficken 10y ago
>"Hydrogen + fuel cell systems to achieve the same energy density require very costly extremely high pressure tanks and fueling systems, and that is before you get into the argument of whether hydrogen is a terrible use of energy." The main problem here is you are comparing it to a fuel source which took million of years to form naturally. Think of the energy expenditure behind that!
thearn4 10y ago
Battery technology will definitely need to improve before any system is practical enough to build and add to a fleet. I think there are power system assumptions being made regarding mid to far term viability of metal air batteries. Currently, they are expected in operation to be much closer to the 40 MJ/kg figure than existing battery technology: https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemical_cell https://en.wikipedia.org/wiki/Metal%E2%80%93air_electrochemi... That said, what becomes really interesting (and tricky) is that these types of batteries actually get heavier as they discharge, which throws off intuition for optimal trajectory analysis. We're used to thinking in terms of planes getting lighter as they consume their fuel...