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This is constantly repeated, but it's not true. I work in the field of electric motors for electric aircraft, and the amount of nonsense constantly repeated on

This is constantly repeated, but it's not true. I work in the field of electric motors for electric aircraft, and the amount of nonsense constantly repeated on the Internet about how electric flight cannot be done without a breakthrough is breathtaking. Electric motors can achieve FAR greater than 1kW/kg. Here's one used sometimes on electric aircraft capable of 10kW/kg, same as a jet engine: https://emrax.com/products/emrax-268/ https://emrax.com/products/emrax-268/ The specific energy of lithium-ion is poor, but jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. There's also some efficiency improvement possible, i.e. from airliner lift-to-drag of 16-20 (and like 8-10 for a Cessna) to a more glider-like L/D of 25-35 (the best gliders can do 70). Additionally, improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy (general aviation craft are only like 10-15% fuel, but 777s can be almost 50% fuel, and electric aircraft could be 60% battery). So if you combine efficiency improvements and high battery mass, sure, electric planes still may have a tenth the range of jet liners. But jets like the 777 have a range of 10,000 to 15,000km. A tenth of that is still over 1000km! Quite doable for a very large portion of domestic flights. Since domestic flights often involve multiple hops anyway (due to hub and spoke model), you could fly basically anywhere up and down the eastern seaboard in just the typical two hops. And faster than high speed rail. But of course, there are already better lithium batteries that are available in small quantities, like lithium-sulfur, metal electrode lithium batteries, solid-state batteries, or batteries that combine those various features. ~1.5MJ/kg cells are already demonstrated and you can buy them on an evaluation basis. ~2MJ/kg is feasible as well, enabling single-hop flights all over the eastern seaboard and enabling multi-hop transatlantic flights (as low as 1200km is the minimum range needed for transatlantic flights if you really wanted to do it).

Robotbeat 7y ago
Transatlantic electric flights wouldn't be too hard. 1200km minimum hops could be done with next-gen battery tech and plenty of margin. ...Transpacific (i.e. reaching Asia from North America) wouldn't be too hard as you can hop along Alaska and the Aleutians, but reaching Hawaii is a major challenge. To get to Hawaii from LA takes 3800km (at the edge of what you can do with L/D of ~40-50 and 500Wh/kg batteries). Taking the long way from the Aleutians to Midway cuts that down to 2600km for the minimum hop distance, which is perhaps feasible with a sailplane-like L/D and the next-generation lithium-metal and/or lithium-sulfur batteries (that are already demonstrated at the lab scale). Lithium-air is the breakthrough in battery tech people want, which will enable much easier transpacific flights at transonic speeds (rather than the ~Mach 0.50 speeds you'd be limited to for the most extreme high performance airfoils), like what people are used to already. Lithium-air would also potentially enable long distance supersonic electric passenger aircraft.
godelski 7y ago
I haven't seen the 1.5MJ/kg batteries but that is still pretty far from 10MJ/kg. Your first paragraph seems pretty hostile considering this fact. Look, we all want electric aircraft. I can't wait for them. But to say that it doesn't require a major (honestly several major) breakthrough (s) is an extreme understatement and does not requisite the hostility you are giving.
- Robotbeat 7y ago
  The key thing often missed is that jet fuel is much better than it needs to be, particularly for domestic flights. Batteries don't need to equal jet fuel in order for electric air travel to be viable. We have airplanes capable of 15,000km trips. But we were making transatlantic flights back when our aircraft could only do about 2000km range reliably. Going from from Labrador, Canada to Greenland to Iceland to England, the minimum hop distance is about 1200km. https://en.wikipedia.org/wiki/Transatlantic_flight#/media/File:Aaffc-routes-jun-1942.jpg https://en.wikipedia.org/wiki/Transatlantic_flight#/media/Fi... I don't expect electric air travel to operate Transatlantic flights with 1.5MJ/kg batteries as major competitor to jet travel unless there's a very hard clampdown on greenhouse gas emissions. The logistics of adding major stops in Greenland and northern Canada to enable transAtlantic electric flight just likely won't be worth it. But for domestic flights (which are the majority of flights), electric air travel will be common. Source for ~1.5MJ/kg batteries: https://sionpower.com https://sionpower.com https://oxisenergy.com https://oxisenergy.com
  - godelski 7y ago
    Most of these discussions I see, at least on HN, seem to understand efficiency. Yeah, a lot of fuel goes into heat and not into power for the engine. People understand that. But another thing that many people don't, is that heating isn't wasted energy. It is reclaimed for heating the cabin and deicing. Which icing is a HUGE problem on aircraft. Heating is also fairly power intensive. But still, until we get into that efficiency range of batteries vs direct power of jet fuel, it is far from solved. But like you mention with greenhouse gasses, it does have to be solved. I have yet to see anyone here that is doubtful that electric aircraft will exist. I just see people (at least on HN) that are either bearish or bullish. But don't be hostile to people that are being bearish. We need both camps.
namirez 7y ago
Your numbers are not quite right. > jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg. Also, you need to take into account the prop efficiency for electric planes. Beyond Mach 0.5, the efficiency degrades very rapidly. So it's not just electric motor vs jet engine. > more glider-like L/D of 25-35 (the best gliders can do 70). This is not limited to electric planes. The reason no one has done it so far is the aeroelastic divergence. > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy Again, this can be done for any aircraft, not just the electric ones. > as low as 1200km is the minimum range needed for transatlantic flights Do you really believe there is a market for 1200km hops at Mach 0.5. We already have ATR 72 and Bombardier Q400. Why no one is using them for long haul flight?
- FabHK 7y ago
  > > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy > Again, this can be done for any aircraft, not just the electric ones. Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.
  - namirez 7y ago
    True! Actually airplanes are loaded with just enough fuel to finish their mission safely. It's not like a 777 always taking off with maximum fuel.
  - waterhouse 7y ago
    Dumb idea: If the weight of the batteries is significant, then dump out the empty ones with parachutes partway through the flight?
    - namirez 7y ago
      Like this? https://www.youtube.com/watch?v=KoGIPk8Vrl0 https://www.youtube.com/watch?v=KoGIPk8Vrl0
dmitrygr 7y ago
That engine may have good power density, but it is quite weak in general. Site quoth: "Continuous power: up to 110 kW" That is basically a negligible amount of power
- Robotbeat 7y ago
  "Quite weak in general." It's not negligible for its weight. You can always scale up an electric motor. The largest machines in the world (such as bucket wheel excavators) are driven by electric motors. Additionally, electric motors are much simpler to cluster into a distributed propulsion configuration than jet turbines are. That's why NASA's building the X-57 electric aircraft.
  - dmitrygr 7y ago
    > "scale up" yep, BUT cube-square law applies

Robotbeat 7y ago

Transatlantic electric flights wouldn't be too hard. 1200km minimum hops could be done with next-gen battery tech and plenty of margin. ...Transpacific (i.e. reaching Asia from North America) wouldn't be too hard as you can hop along Alaska and the Aleutians, but reaching Hawaii is a major challenge. To get to Hawaii from LA takes 3800km (at the edge of what you can do with L/D of ~40-50 and 500Wh/kg batteries). Taking the long way from the Aleutians to Midway cuts that down to 2600km for the minimum hop distance, which is perhaps feasible with a sailplane-like L/D and the next-generation lithium-metal and/or lithium-sulfur batteries (that are already demonstrated at the lab scale). Lithium-air is the breakthrough in battery tech people want, which will enable much easier transpacific flights at transonic speeds (rather than the ~Mach 0.50 speeds you'd be limited to for the most extreme high performance airfoils), like what people are used to already. Lithium-air would also potentially enable long distance supersonic electric passenger aircraft.

godelski 7y ago

I haven't seen the 1.5MJ/kg batteries but that is still pretty far from 10MJ/kg. Your first paragraph seems pretty hostile considering this fact. Look, we all want electric aircraft. I can't wait for them. But to say that it doesn't require a major (honestly several major) breakthrough (s) is an extreme understatement and does not requisite the hostility you are giving.

Robotbeat 7y ago
The key thing often missed is that jet fuel is much better than it needs to be, particularly for domestic flights. Batteries don't need to equal jet fuel in order for electric air travel to be viable. We have airplanes capable of 15,000km trips. But we were making transatlantic flights back when our aircraft could only do about 2000km range reliably. Going from from Labrador, Canada to Greenland to Iceland to England, the minimum hop distance is about 1200km. https://en.wikipedia.org/wiki/Transatlantic_flight#/media/File:Aaffc-routes-jun-1942.jpg https://en.wikipedia.org/wiki/Transatlantic_flight#/media/Fi... I don't expect electric air travel to operate Transatlantic flights with 1.5MJ/kg batteries as major competitor to jet travel unless there's a very hard clampdown on greenhouse gas emissions. The logistics of adding major stops in Greenland and northern Canada to enable transAtlantic electric flight just likely won't be worth it. But for domestic flights (which are the majority of flights), electric air travel will be common. Source for ~1.5MJ/kg batteries: https://sionpower.com https://sionpower.com https://oxisenergy.com https://oxisenergy.com
- godelski 7y ago
  Most of these discussions I see, at least on HN, seem to understand efficiency. Yeah, a lot of fuel goes into heat and not into power for the engine. People understand that. But another thing that many people don't, is that heating isn't wasted energy. It is reclaimed for heating the cabin and deicing. Which icing is a HUGE problem on aircraft. Heating is also fairly power intensive. But still, until we get into that efficiency range of batteries vs direct power of jet fuel, it is far from solved. But like you mention with greenhouse gasses, it does have to be solved. I have yet to see anyone here that is doubtful that electric aircraft will exist. I just see people (at least on HN) that are either bearish or bullish. But don't be hostile to people that are being bearish. We need both camps.

namirez 7y ago

Your numbers are not quite right. > jet fuel's USEFUL specific energy is more like 10-15MJ/kg due to needing to be burned. New turbofans have efficiencies close to 50%, so it's more like 20 MJ/kg. Also, you need to take into account the prop efficiency for electric planes. Beyond Mach 0.5, the efficiency degrades very rapidly. So it's not just electric motor vs jet engine. > more glider-like L/D of 25-35 (the best gliders can do 70). This is not limited to electric planes. The reason no one has done it so far is the aeroelastic divergence. > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy Again, this can be done for any aircraft, not just the electric ones. > as low as 1200km is the minimum range needed for transatlantic flights Do you really believe there is a market for 1200km hops at Mach 0.5. We already have ATR 72 and Bombardier Q400. Why no one is using them for long haul flight?

FabHK 7y ago
> > improved modern materials means you can just have most of your take-off mass be battery, compensating for the poorer specific energy > Again, this can be done for any aircraft, not just the electric ones. Not only that: you burn the fuel, so for the second half of the flight you only need to carry half the fuel. But you have to carry the full battery mass (modulo E=mc^2) all the way.
- namirez 7y ago
  True! Actually airplanes are loaded with just enough fuel to finish their mission safely. It's not like a 777 always taking off with maximum fuel.
- waterhouse 7y ago
  Dumb idea: If the weight of the batteries is significant, then dump out the empty ones with parachutes partway through the flight?
  - namirez 7y ago
    Like this? https://www.youtube.com/watch?v=KoGIPk8Vrl0 https://www.youtube.com/watch?v=KoGIPk8Vrl0

dmitrygr 7y ago

That engine may have good power density, but it is quite weak in general. Site quoth: "Continuous power: up to 110 kW" That is basically a negligible amount of power

Robotbeat 7y ago
"Quite weak in general." It's not negligible for its weight. You can always scale up an electric motor. The largest machines in the world (such as bucket wheel excavators) are driven by electric motors. Additionally, electric motors are much simpler to cluster into a distributed propulsion configuration than jet turbines are. That's why NASA's building the X-57 electric aircraft.
- dmitrygr 7y ago
  > "scale up" yep, BUT cube-square law applies