4 ms·

We 100% cannot do those things with current technology. I'm 'commenting too fast' to reply, but show me any of your examples in flight please.

by RC_ITR 5y ago

Robotbeat 5y ago
We absolutely can. https://twitter.com/GovInslee/status/1440442441920774146 https://twitter.com/GovInslee/status/1440442441920774146 500+ miles range. Building it right now. Plus Wright Electric, Bye Aerospace’s eflyer 800, etc. Why do people so easily and confidently claim something can’t be done?
- burkaman 5y ago
  That carries 9 passengers, at ~half the speed of a standard airliner. It's exciting and I want to fly in one, but I don't think it will be faster and cheaper than trains in most cases, yet. But we're almost there.
  - Robotbeat 5y ago
    The technology is independent of scale. If it works for a nine Seater it also works for a 100 Seater. EDIT: and YES this is true. Battery specific energy is 200-400Wh/kg. That is PER kilogram. And larger planes are NOT less efficient per passenger than smaller ones. Small and large jets or propeller aircraft have a out the same life to drag ratio. If anything, larger tend to be better due to Reynolds Number effects. There is maybe not one misconception about electric flight that I’ve seen repeated most often by Internet skeptics than this false idea that “bigger is disproportionately harder for electric planes.” It is simply. Not. True.
    - burkaman 5y ago
      That's not true unfortunately, batteries are too heavy to make bigger planes workable right now. We need denser batteries and more powerful electric motors, and there are companies working on both those problems, but they aren't solved yet. Look at the specific energy of jet fuel compared to batteries on this page: https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density
      - Robotbeat 5y ago
        Specific energy is independent of scale! It’s right in the units: energy divided by mass. Watt-hours per kg. Where are you getting the claim from that larger planes can’t technically be made electric even if smaller ones can? And no, don’t switch topic to range. That is a known constraint. Focus on SCALE. It is scale-independent to zeroth and first order at least! This comes up every single time, and I feel like I’m taking crazy pills. :D
        burkaman 5y ago
        I mean I'm not really qualified to have this debate, but I'll do my best. Intuitively, if you double the weight of the plane, now you need twice as much battery to fly it. But now you've added a bunch of battery weight, so you need even more batteries to lift those batteries. You also will need more or bigger motors, which adds even more weight. At some point, your plane isn't gonna get off the ground. I am only a lowly software engineer so I don't know that much about planes or batteries. If I'm wrong then I'm wrong, and I hope I am.
        Robotbeat 5y ago
        No, that IS how it scales for range to some extent (where if you just add fuel/battery, you now need to add more power, etc), but it’s NOT how it scales for size. To first order, everything scales linearly. If you doubled the size of the aircraft, you already increased everything to compensate. This works for everything with two caveats: 1) Reynolds number means you get more efficient as you scale up in size. The effect is slight and there is nuance with respect to laminar vs turbulent flow, but it is true. 2) larger size means at some point you need truss braced wings. But this is only at pretty large sizes and only usually if you’re also shooting for high aspect ratio wings. NASA/Boeing/etc have researched truss braced wings, and it is most certainly doable. But both of these are second order effects. And they mostly cancel out. I am a materials scientist with a background in physics and I have also developed electric motors for electric aircraft. I have a good understanding of how the systems scale. You were mixing up the exponential range equation with simple size scaling. if it were true, then large aircraft of any type would be much less efficient than smaller aircraft of the same type. This is most certainly not true. In fact, usually the efficiency increases with scale. A 777x is much more efficient than a Gulfstream or some smaller regional jet per passenger mile.
    - peterdn 5y ago
      This doesn't seem right to me as it goes against my intuitive sense of how other factors generally scale with size/weight/volume (e.g. rocket equation), but I admit I'm definitely not an expert. However Wikipedia claims [1] that 250-300 Wh/kg is sufficient for small aircraft but something the size of an Airbus 320 would need 2 kWh/kg. A random recent paper about scaling electric aircraft [2] seems to imply that there are challenges to scaling size as well: > All-electric designs have been demonstrated for small air vehicles. However, such prototypes have not been scaled up to more than ten passengers due to the specific energy (E*) limitations of current battery technology. [...] A significant proportion of the energy expenditure would be used to transport the mass of the batteries; this mass would not decrease during a flight as would that of conventional fuel. Are these sources wrong, or too simplistic in their analysis, or am I misinterpreting what they're saying? [1]: https://en.wikipedia.org/wiki/Electric_aircraft#Batteries https://en.wikipedia.org/wiki/Electric_aircraft#Batteries [2]: Structural Power Performance Targets for Future Electric Aircraft - https://www.mdpi.com/1996-1073/14/19/6006 https://www.mdpi.com/1996-1073/14/19/6006
      - deepnotderp 5y ago
        The rocket equation, or its airplane cousin the Breguet range equation talk about ratios of mass, not absolute mass. These larger airplanes (eg an A320) often fly much faster and longer distances
- Nitrolo 5y ago
  Not to diminish the accomplishments shown there, but that plane seats maybe a dozen people? Most airliners can seat 100+, and their range is sometimes an order of magnitude higher than that. The problem is that batteries are significantly less energy dense than jet fuel, both by weight and by volume. To reach capacities and ranges of modern airliners you'd need batteries that are much more dense, compact, and light, and afaik there's nothing even close to the improvements needed right now.
  - Robotbeat 5y ago
    Wrong about capacity but correct about range. I have no idea why people keep thinking that batteries would work worse for 100 seats rather than nine seats. The technology is independent of scale except in the trivial sense that you need proportionally more battery and cost since you’re 10 times larger. True the range is less, but we have built jets that can go 40,000km. We don’t need that much range to do short flights, comparable in length to the California HSR project. Existing battery technology is more than sufficient for that.
golemiprague 5y ago
I agree regarding battery based aircraft, but what about hydrogen?

We 100% cannot do those things with current technology. I'm 'commenting too fast' to reply, but show me any of your examples in flight please.

by RC_ITR 5y ago

We 100% cannot do those things with current technology. I'm 'commenting too fast' to reply, but show me any of your examples in flight please.

Robotbeat 5y ago

We absolutely can. https://twitter.com/GovInslee/status/1440442441920774146 https://twitter.com/GovInslee/status/1440442441920774146 500+ miles range. Building it right now. Plus Wright Electric, Bye Aerospace’s eflyer 800, etc. Why do people so easily and confidently claim something can’t be done?

burkaman 5y ago
That carries 9 passengers, at ~half the speed of a standard airliner. It's exciting and I want to fly in one, but I don't think it will be faster and cheaper than trains in most cases, yet. But we're almost there.
- Robotbeat 5y ago
  The technology is independent of scale. If it works for a nine Seater it also works for a 100 Seater. EDIT: and YES this is true. Battery specific energy is 200-400Wh/kg. That is PER kilogram. And larger planes are NOT less efficient per passenger than smaller ones. Small and large jets or propeller aircraft have a out the same life to drag ratio. If anything, larger tend to be better due to Reynolds Number effects. There is maybe not one misconception about electric flight that I’ve seen repeated most often by Internet skeptics than this false idea that “bigger is disproportionately harder for electric planes.” It is simply. Not. True.
  - burkaman 5y ago
    That's not true unfortunately, batteries are too heavy to make bigger planes workable right now. We need denser batteries and more powerful electric motors, and there are companies working on both those problems, but they aren't solved yet. Look at the specific energy of jet fuel compared to batteries on this page: https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density
    - Robotbeat 5y ago
      Specific energy is independent of scale! It’s right in the units: energy divided by mass. Watt-hours per kg. Where are you getting the claim from that larger planes can’t technically be made electric even if smaller ones can? And no, don’t switch topic to range. That is a known constraint. Focus on SCALE. It is scale-independent to zeroth and first order at least! This comes up every single time, and I feel like I’m taking crazy pills. :D
      - burkaman 5y ago
        I mean I'm not really qualified to have this debate, but I'll do my best. Intuitively, if you double the weight of the plane, now you need twice as much battery to fly it. But now you've added a bunch of battery weight, so you need even more batteries to lift those batteries. You also will need more or bigger motors, which adds even more weight. At some point, your plane isn't gonna get off the ground. I am only a lowly software engineer so I don't know that much about planes or batteries. If I'm wrong then I'm wrong, and I hope I am.
        Robotbeat 5y ago
        No, that IS how it scales for range to some extent (where if you just add fuel/battery, you now need to add more power, etc), but it’s NOT how it scales for size. To first order, everything scales linearly. If you doubled the size of the aircraft, you already increased everything to compensate. This works for everything with two caveats: 1) Reynolds number means you get more efficient as you scale up in size. The effect is slight and there is nuance with respect to laminar vs turbulent flow, but it is true. 2) larger size means at some point you need truss braced wings. But this is only at pretty large sizes and only usually if you’re also shooting for high aspect ratio wings. NASA/Boeing/etc have researched truss braced wings, and it is most certainly doable. But both of these are second order effects. And they mostly cancel out. I am a materials scientist with a background in physics and I have also developed electric motors for electric aircraft. I have a good understanding of how the systems scale. You were mixing up the exponential range equation with simple size scaling. if it were true, then large aircraft of any type would be much less efficient than smaller aircraft of the same type. This is most certainly not true. In fact, usually the efficiency increases with scale. A 777x is much more efficient than a Gulfstream or some smaller regional jet per passenger mile.
  - peterdn 5y ago
    This doesn't seem right to me as it goes against my intuitive sense of how other factors generally scale with size/weight/volume (e.g. rocket equation), but I admit I'm definitely not an expert. However Wikipedia claims [1] that 250-300 Wh/kg is sufficient for small aircraft but something the size of an Airbus 320 would need 2 kWh/kg. A random recent paper about scaling electric aircraft [2] seems to imply that there are challenges to scaling size as well: > All-electric designs have been demonstrated for small air vehicles. However, such prototypes have not been scaled up to more than ten passengers due to the specific energy (E*) limitations of current battery technology. [...] A significant proportion of the energy expenditure would be used to transport the mass of the batteries; this mass would not decrease during a flight as would that of conventional fuel. Are these sources wrong, or too simplistic in their analysis, or am I misinterpreting what they're saying? [1]: https://en.wikipedia.org/wiki/Electric_aircraft#Batteries https://en.wikipedia.org/wiki/Electric_aircraft#Batteries [2]: Structural Power Performance Targets for Future Electric Aircraft - https://www.mdpi.com/1996-1073/14/19/6006 https://www.mdpi.com/1996-1073/14/19/6006
    - deepnotderp 5y ago
      The rocket equation, or its airplane cousin the Breguet range equation talk about ratios of mass, not absolute mass. These larger airplanes (eg an A320) often fly much faster and longer distances
Nitrolo 5y ago
Not to diminish the accomplishments shown there, but that plane seats maybe a dozen people? Most airliners can seat 100+, and their range is sometimes an order of magnitude higher than that. The problem is that batteries are significantly less energy dense than jet fuel, both by weight and by volume. To reach capacities and ranges of modern airliners you'd need batteries that are much more dense, compact, and light, and afaik there's nothing even close to the improvements needed right now.
- Robotbeat 5y ago
  Wrong about capacity but correct about range. I have no idea why people keep thinking that batteries would work worse for 100 seats rather than nine seats. The technology is independent of scale except in the trivial sense that you need proportionally more battery and cost since you’re 10 times larger. True the range is less, but we have built jets that can go 40,000km. We don’t need that much range to do short flights, comparable in length to the California HSR project. Existing battery technology is more than sufficient for that.

golemiprague 5y ago

I agree regarding battery based aircraft, but what about hydrogen?